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1
T, Aga, and Haruna A. I. "The field geology and petrography of the kofayi younger granite complex, central Nigeria." International Journal of Advanced Geosciences 7, no. 2 (2019): 95. http://dx.doi.org/10.14419/ijag.v7i2.29055.
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The Kofayi Younger Granite Complex is one of the several anorogenic alkaline Younger Granite Complexes that is located approximately 45 kilometres north east of Jos, Nigeria. The complex is found to comprise of felsic rocks like; biotite-granites, biotite microgranites and granodiorites. They are also found to be associated with mafic rocks like diorites which, at some portions have formed hybrid rocks. Quartz- feldspar- granites are the porphyritic rocks that found in the ring complex. The complex intrude the basement rocks of central Nigeria. Structural trends on these rocks suggest that they were controlled by some deep seated structures of the basement. Mineral suite identified include; fayalite, pyroxene, amphibole, k-feldspar, biotite, quartz, iron- oxide and accessory minerals like zircon, apatite, and allanite. Generally, the petrography of these rock samples reveal the presence of a mafic magma which has two pulses (a mafic and felsic pulse) of injection.
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Wolska, Anna. "Petrology and geochemistry of granitoids and their mafic micogranular enclaves (MME) in marginal part of the Małopolska Block (S Poland)." Mineralogia Polonica 43, no. 1-2 (2012): 3–127. http://dx.doi.org/10.2478/v10002-012-0003-5.
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AbstractGranitic plutons (the Dolina Będkowska valley and Pilica area) were found in a few boreholes in the Małopolska Block (MB). These granitic rocks may represent apical parts (apophyses) of a great magmatic bodies (batholiths) located in deeper level of the Ediacaran/Paleozoic basement. They are described as ‘stitching intrusions’, generated during/after collision in Carboniferous/Permian period (~300 Ma) between the Upper Silesian Block (USB) and the Małopolska Block (MB).These rocks are fresh, unaltered granodiorites that are pale grey in colour. They have holocrystalline, medium- to coarse-grained structure and massive texture. For the first time, several mafic microgranular enclaves (MME), varying in size and colour, were found in the granodioritic host (HG). The occurrence of MME in the host granodioritic rocks is evidence of a mingling process between mafic and felsic magmas.The MME are pale/dark grey in colour, fine-grained rocks with ‘porphyritic’ textures. They consist of large megacrysts/xenocrysts of plagioclase, quartz, alkali feldspars and the fine-grained groundmass of pseudo-doleritic textures (lath-shaped plagioclases, blade-shaped amphiboles/biotites). According to their modal/mineral composition, they represent Q-diorites and tonalites.The MME, similar to the host granodiorites (HG), are I-type rocks, exhibit high Na2O content >3.2 wt%; normative diopside or normative corundum occurs (mainly <1%). They are metaluminous to slightly peraluminous (ASI <1.1) and have calc-alkaline, medium-K to high-K character. They generally belong to magnesian series (#Mg=0.20-0.40) and have low agpaitic index (<0.87). They are low evolved magmatic rocks. The rocks studied are enriched in LREEs (La, Ce, Sm) compared to HREEs. The Eu* negative anomaly and high Sr contents point to varying degrees of plagioclase fractionation connected to the mixing process rather than simple fractional crystallization. Both rocks studied (HG and MME) are characterized by a high content of LILEs (K, Ba, Rb) in normalized patterns and a low HFS/LIL elements ratio (Ta, Nb)/(K, Rb, La). The projection points of the rocks studied plot in different fields of various petrochemical diagrams: mainly in the arc granites that are rare in the pre-collisional granites as well as the syn-subductional to post-collisional granites fields.For the first time, inner textures in rock-forming minerals related to mixing processes are described both in the granodioritic host (HG) and in the MME. Mantled boxy cellular plagioclase megacrysts with ‘old cores’ of labradorite composition, and amphibole aggregates with titanite and opaque minerals, represent peritectic rather than primary residual minerals. The plagioclase, quartz and alkali feldspar megacrysts/xenocrysts were mechanically transferred from the granodioritic host (HG) to MME. The presence of lath-shaped plagioclases, blade-shaped amphiboles/biotites and acicular-shaped apatites in the groundmass of the MME is evidence of undercooling of hot mafic blobs in a relatively cold granodioritic magma chamber. The MME were hybridized by leucocratic melt squeezed from the granodioritic magma in a later stage of the mixing process (quartz and alkali crystals in the interstices in the MME groundmass). In the granodiorites (HG), the spike and spongy cellular zones as well as biotite/amphibole zones in plagioclase megacrysts are connected to the mixing process.Both of the rocks studied are characterized by different amounts of major elements (SiO2, Na2O and K2O), trace elements (Ni, Cr, V, Ti and P), #Mg and modified alkali-lime index (MALI) that is related to their origins from different sources. On the other hand, they have similar chondrite-normalized patterns (for trace elements and REE), LILEs contents (Sr, Ba, Rb), aluminum saturation index (ASI) and isotopic signatures (high 86Sr/87Sr (0.079-0.713) and low 143Nd/144Nd (0.512) values but lower than in continental crust), which are evidence of the strong hybridisation of mafic enclaves by the granodioritic host magma. The parental rocks of both rocks studied have a similar mafic signature but were generated in different sources: the host granodiorites (HG) magma in lower continental crust rocks, and the MME magma in enriched upper mantle. The MME crystallized from strongly hybridized magma of intermediate compositions (Q-diorite, tonalite) rather than from primary mafic magma. The host granodiorites (HG) originated from completely homogenized crustal granodioritic magma which inherited its geochemical signature from ancient arc-rocks in a subduction-related setting
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FEELY, MARTIN, DAVID SELBY, JON HUNT, and JAMES CONLIFFE. "Long-lived granite-related molybdenite mineralization at Connemara, western Irish Caledonides." Geological Magazine 147, no. 6 (2010): 886–94. http://dx.doi.org/10.1017/s0016756810000324.
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AbstractNew Re–Os age determinations from the Galway Granite (samples: KMG = 402.2 ± 1.1 Ma, LLG = 399.5 ± 1.7 Ma and GBM = 383.3 ± 1.1 Ma) show that in south Connemara, late Caledonian granite-related molybdenite mineralization extended from c. 423 Ma to c. 380 Ma. These events overlap and are in excellent agreement with the published granite emplacement history determined by U–Pb zircon geochronology. The spatial distribution of the late-Caledonian Connemara granites indicates that initial emplacement and molybdenite mineralization occurred at c. 420 Ma (that is, the Omey Granite and probably the Inish, Leterfrack and Roundstone granites) to the N and NW of the Skird Rocks Fault, an extension of the orogen-parallel Southern Uplands Fault in western Ireland. A generally southern and eastward progression of granite emplacement (and molybdenite mineralization) sited along the Skird Rocks Fault then followed, at c. 410 Ma (Roundstone Murvey and Carna granites), at c. 400 Ma (Errisbeg Townland Granite, Megacrystic Granite, Mingling Mixing Zone Granodiorite, Lough Lurgan Granite and Kilkieran Murvey Granite) and at c. 380 Ma (Costelloe Murvey Granite, Shannapheasteen and Knock granites). The duration of granite magmatism and mineralization in Connemara is similar to other sectors of the Appalachian–Caledonian orogeny and several tectonic processes (e.g. slab-breakoff, asthenospheric flow, transtension and decompression) may account for the duration and variety of granite magmatism of the western Irish Caledonides.
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Broska, Igor, and Igor Petrík. "Variscan thrusting in I- and S-type granitic rocks of the Tribeč Mountains, Western Carpathians (Slovakia): evidence from mineral compositions and monazite dating." Geologica Carpathica 66, no. 6 (2015): 455–71. http://dx.doi.org/10.1515/geoca-2015-0038.
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AbstractThe Tribeč granitic core (Tatric Superunit, Western Carpathians, Slovakia) is formed by Devonian/Lower Carboniferous, calc-alkaline I- and S-type granitic rocks and their altered equivalents, which provide a rare opportunity to study the Variscan magmatic, post-magmatic and tectonic evolution. The calculatedP-T-Xpath of I-type granitic rocks, based on Fe-Ti oxides, hornblende, titanite and mica-bearing equilibria, illustrates changes in redox evolution. There is a transition from magmatic stage atTca. 800–850 °C and moderate oxygen fugacity (FMQ buffer) to an oxidation event at 600 °C between HM and NNO up to the oxidation peak at 480 °C and HM buffer, to the final reduction at ca. 470 °C at ΔNN= 3.3. Thus, the post-magmatic Variscan history recorded in I-type tonalites shows at early stage pronounced oxidation and low temperature shift back to reduction. The S-type granites originated at temperature 700–750 °C at lower water activity and temperature. TheP-Tconditions of mineral reactions in altered granitoids at Variscan time (both I and S-types) correspond to greenschist facies involving formation of secondary biotite. The Tribeč granite pluton recently shows horizontal and vertical zoning: from the west side toward the east S-type granodiorites replace I-type tonalites and these medium/coarse-grained granitoids are vertically overlain by their altered equivalents in greenschist facies. Along the Tribeč mountain ridge, younger undeformed leucocratic granite dykes in age 342±4.4 Ma cut these metasomatically altered granitic rocks and thus post-date the alteration process. The overlaying sheet of the altered granites is in a low-angle superposition on undeformed granitoids and forms “a granite duplex” within Alpine Tatric Superunit, which resulted from a syn-collisional Variscan thrusting event and melt formation ~340 Ma. The process of alteration may have been responsible for shifting the oxidation trend to the observed partial reduction.
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ESSAIFI, ABDERRAHIM, SCOTT SAMSON, and KATHRYN GOODENOUGH. "Geochemical and Sr–Nd isotopic constraints on the petrogenesis and geodynamic significance of the Jebilet magmatism (Variscan Belt, Morocco)." Geological Magazine 151, no. 4 (2013): 666–91. http://dx.doi.org/10.1017/s0016756813000654.
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AbstractIn the Variscan fold belt of Morocco, the Jebilet massif is characterized by Palaeozoic metasedimentary rocks intruded by syntectonic magmatism that includes an ultramafic–granitoid bimodal association and peraluminous granodiorites emplacedc. 330 Ma, intruded by younger leucogranitesc. 300 Ma. The mafic–ultramafic rocks belong to a tholeiitic series, and display chemical and isotopic signatures consistent with mixing between mantle-derived and crust-derived magmas or assimilation and fractional crystallization. The granites within the bimodal association are mainly metaluminous to weakly peraluminous microgranites that show characteristics of A2-type granites. The peraluminous, calc-alkaline series consists mainly of cordierite-bearing granodiorites enclosing magmatic microgranular enclaves and pelitic xenoliths. Detailed element and isotope data suggest that the alkaline and the peraluminous granitoids were formed in the shallow crust (<30 km) by partial melting of tonalitic sources at high temperatures (up to 900°C) and by partial melting of metasedimentary protoliths at relatively low temperatures (c. 750°C), respectively. Mixing between the coeval mantle-derived and crust-derived magmas contributed to the large variation of initial εNdvalues and initial Sr isotopic ratios observed in the granitoids. Further contamination occurred by wall-rock assimilation during ascent of the granodioritic plutons to the upper crust. The ultramafic–granitoid association has been intruded by leucogranites that have high initial Sr isotopic ratios and low initial εNdvalues, indicating a purely crustal origin. The heating events that caused emplacement of the Jebilet magmatism are related to cessation of continental subduction and convective erosion/thinning of the lithospheric mantle during plate convergence.
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Dunning, G. R., D. H. C. Wilton, and R. K. Herd. "Geology, geochemistry and geochronology of a taconic batholith, southwestern Newfoundland." Transactions of the Royal Society of Edinburgh: Earth Sciences 80, no. 2 (1989): 159–68. http://dx.doi.org/10.1017/s0263593300014449.
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ABSTRACTFoliated to massive hornblende and biotite-bearing tonalite, trondhjemite and granodiorite comprise a terrane of batholithic dimensions in southwestern to central Newfoundland. These rocks intrude and include Ordovician ophiolite fragments and metasedimentary rocks of Fleur de Lys type, and are cut by a suite of Silurian gabbro-diorite and norite and Siluro-Devonian (?) granite intrusions.A U/Pb (zircon, sphene) age of 456 ± 3 Ma (2σ) and a K/Ar (hornblende) age of 455 ± 14 Ma (previously reported) for a representative least-deformed tonalite of the Southwest Brook Complex indicate that it crystallised and cooled in Caradoc time. A less precise U/Pb (zircon) age of 428 ± 41 Ma (2σ) is measured for tonalitic Cape Ray Granite in southern Newfoundland. On discrimination diagrams which use Rb, Nb and Y contents to infer tectonic setting, these rocks fall in the field of volcanic arc granites. The occurrence of zircon cores with average ages of 1430 + 18/–17 and 1541 ± 173 Ma (2σ) also indicate that the magmas formed in part by partial melting of Proterozoic crust, or sediments derived from such crust. It is suggested that the tonalitic magmas were generated during the Taconic Orogeny in an arc: continent collision zone at the ancient margin of eastern North America.Tonalitic rocks in western Newfoundland broadly correlative in age and chemistry with the batholith include the Burlington Granodiorite and Hungry Mountain Complex, as well as allochthonous slices of foliated tonalite emplaced over Ordovician platform carbonates W of Grand Lake.
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Boerboom, Terrence J., and Robert E. Zartman. "Geology, geochemistry, and geochronology of the central Giants Range batholith, northeastern Minnesota." Canadian Journal of Earth Sciences 30, no. 12 (1993): 2510–22. http://dx.doi.org/10.1139/e93-217.
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The Giants Range batholith is a large composite granitoid body that intrudes deformed supracrustal rocks in the western part of the Wawa Subprovince of the Archean Superior Province. Peak fabric development in the supracrustal rocks coincides with D2 deformation, the product of regional transpression across the southern Superior Province. U–Pb zircon ages on two phases of the Giants Range batholith bracket D2 deformation to an interval between 2685 and 2669 Ma. Two well-exposed components of the central part of the Giants Range batholith are the pre- to syn-D2 Britt granodiorite, which contains a linear D2 metamorphic fabric, and the syn- to post-D2 Shannon Lake granite, which cuts deformation fabrics in the Britt granodiorite and the supracrustal rocks. Geochemical discrimination plots imply emplacement of the Britt granodiorite in an arc environment and the Shannon Lake granite in a collision setting. Zircons yield U–Pb ages of 2681 ± 4 and 2685 ± 4 Ma for the Britt granodiorite and 2674 ± 5 and 2674 ± 27 Ma for the Shannon Lake granite. Timing of D2 deformation near the Giants Range batholith corresponds well with similar rocks exposed along strike 170 km to the east near Shebandowan Lake, Ontario, where the end of D2 deformation has been bracketed between 2692 and 2681 Ma. The slightly younger ages for D2 deformation in Minnesota reflect later volcanic-arc development and associated plutonism than at Shebandowan Lake, possibly due to oblique convergence along a westward-migrating tectonic front.
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Mao, Qigui, Jingbin Wang, Wenjiao Xiao, et al. "From Ordovician nascent to early Permian mature arc in the southern Altaids: Insights from the Kalatage inlier in the Eastern Tianshan, NW China." Geosphere 17, no. 2 (2021): 647–83. http://dx.doi.org/10.1130/ges02232.1.
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Abstract The Kalatage inlier in the Dananhu-Haerlik arc is one of the most important arcs in the Eastern Tianshan, southern Altaids (or Central Asian orogenic belt). Based on outcrop maps and core logs, we report 16 new U-Pb dates in order to reconstruct the stratigraphic framework of the Dananhu-Haerlik arc. The new U-Pb ages reveal that the volcanic and intrusive rocks formed in the interval from the Ordovician to early Permian (445–299 Ma), with the oldest diorite dike at 445 ± 3 Ma and the youngest rhyolite at 299 ± 2 Ma. These results constrain the ages of the oldest basaltic and volcaniclastic rocks of the Ordovician Huangchaopo Group, which were intruded by granite-granodiorite-diorite plutons in the Late Ordovician to middle Silurian (445–426 Ma). The second oldest components are intermediate volcanic and volcaniclastic rocks of the early Silurian Hongliuxia Formation (S1h), which lies unconformably on the Huangchaopo Group and is unconformably overlain by Early Devonian volcanic rocks (416 Ma). From the mid- to late Silurian (S2-3), all the rocks were exhumed, eroded, and overlain by polymictic pyroclastic deposits. Following subaerial to shallow subaqueous burial at 416–300 Ma by intermediate to felsic volcanic and volcaniclastics rocks, the succession was intruded by diorites, granodiorites, and granites (390–314 Ma). The arc volcanic and intrusive rocks are characterized by potassium enrichment, when they evolved from mafic to felsic and from tholeiitic via transitional and calc-alkaline to final high-K calc-alkaline compositions with relatively low initial Sr values, (87Sr/86Sr)i = 0.70391–0.70567, and positive εNd(t) values, +4.1 to +9.2. These new data suggest that the Dananhu-Haerlik arc is a long-lived arc that consequently requires a new evolutionary model. It began as a nascent (immature) intra-oceanic arc in the Ordovician to early Silurian, and it evolved into a mature island arc in the middle Silurian to early Permian. The results suggest that the construction of a juvenile-to-mature arc, in combination with its lateral attachment to an incoming arc or continent, was an important crustal growth mechanism in the southern Altaids.
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GRENNE, T., R. B. PEDERSEN, T. BJERKGÅRD, A. BRAATHEN, M. G. SELASSIE, and T. WORKU. "Neoproterozoic evolution of Western Ethiopia: igneous geochemistry, isotope systematics and U–Pb ages." Geological Magazine 140, no. 4 (2003): 373–95. http://dx.doi.org/10.1017/s001675680300801x.
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New geochemical, isotopic and age data from igneous rocks complement earlier models of a long-lived and complex accretionary history for East African Orogen lithologies north of the Blue Nile in western Ethiopia, but throw doubt on the paradigm that ultramafic complexes of the region represent ophiolites and suture zones. Early magmatism is represented by a metavolcanic sequence dominated by pyroclastic deposits of predominantly basaltic andesite composition, which give a Rb–Sr whole-rock errorchron of 873±82 Ma. Steep REE patterns and strong enrichments of highly incompatible trace elements are similar to Andean-type, high-K to medium-K calc-alkaline rocks; εNd values between 4.0 and 6.8 reflect a young, thin continental edge. Interlayered basaltic flows are transitional to MORB and compare with mafic rocks formed in extensional, back-arc or inter-arc regimes. The data point to the significance of continental margin magmatism already at the earliest stages of plate convergence, in contrast with previous models for the East African Orogen. The metavolcanites overlap compositionally with the Kilaj intrusive complex dated at 866±20 Ma (U–Pb zircon) and a related suite of dykes that intrude thick carbonate-psammite sequences of supposedly pre-arc, continental shelf origin. Ultramafic complexes are akin to the Kilaj intrusion and the sediment-hosted dykes, and probably represent solitary intrusions formed in response to arc extension. Synkinematic composite plutons give crystallization ages of 699±2 Ma (Duksi, U–Pb zircon) and 651±5 Ma (Dogi, U–Pb titanite) and testify to a prolonged period of major (D1) contractional deformation during continental collision and closure of the ‘Mozambique Ocean’. The plutons are characterized by moderately peraluminous granodiorites and granites with εNd values of 1.0–2.0. They were coeval with shoshonitic, latitic, trachytic and rare trachybasaltic intrusions with very strong enrichments of highly incompatible trace elements and εNd of 0.4–8.0. The mafic end-member is ascribed to partial melting of enriched sub-continental mantle that carried a subduction component inherited from pre-collision subduction. Contemporaneous granodiorite and granite formation was related to crustal underplating of the mafic magmas and consequent melting of lower crustal material derived from the previously accreted, juvenile arc terranes of the East African Orogen.
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Li, Dapeng, Yuelong Chen, Guoliang Xue, et al. "Initiation of modern-style subduction in the Neoarchean: From plume to subduction with frequent slab break-off." GSA Bulletin 132, no. 9-10 (2020): 2119–34. http://dx.doi.org/10.1130/b35522.1.
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Abstract Fundamental geodynamic changes from vertical tectonics to lateral subduction occurred during the Neoarchean, yet detailed processes related to this transition and initiation of modern-style subduction remain enigmatic. Successive Neoarchean magmatic rocks including both plume-derived komatiites and subduction-related supracrustal and intrusive rocks appeared and preserved key information on the late Archean geodynamic changes in the Western Shandong Province granite-greenstone belt (WSP), North China Craton. In this study, whole-rock geochemical and Sm-Nd isotopic data and zircon U-Pb and Lu-Hf isotopes are reported for early Neoarchean supracrustal and intrusive rocks for the WSP. Temporally, the early Neoarchean magmatic movements in the WSP can be subdivided into two stages, including the early stage (2.77–2.69 Ga) and the late stage (2.69–2.60 Ga). Spatially, from southwest to northeast, intrusive rocks with similar ages define three belts (A, B, and C). Early stage tholeiitic and enriched meta-basalts were plume-related, representing oceanic crust opening from a pre-early Neoarchean continent. Slab subduction at least initiated at ca. 2.74 Ga and generated various Neoarchean tonalite-trondhjemite-granodiorites, quartz diorites, and arc-related volcanic rocks and mafic intrusions. Episodic emergence of meta-basaltic rocks and/or mafic intrusions with depleted εHf(t) values and low (La/Yb)N ratios indicates frequent slab break-offs during ca. 2.70–2.68 Ga, 2.66–2.64 Ga, and 2.62–2.60 Ga due to a relatively hotter mantle and regional heating by mantle plume. Secular geochemical changes of mafic and felsic rocks in this study outline roles of slab subduction in contributions of cooling the mantle, secular mantle refertilization, and crustal growth.
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SKARPELIS, NIKOS, BASILIOS TSIKOURAS, and GEORGIA PE-PIPER. "The Miocene igneous rocks in the Basal Unit of Lavrion (SE Attica, Greece): petrology and geodynamic implications." Geological Magazine 145, no. 1 (2007): 1–15. http://dx.doi.org/10.1017/s0016756807003949.
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AbstractThe Miocene igneous rocks in the Basal Unit of the Lavrion area form part of the granitoid province of the central Aegean. Undeformed, subvertical dykes of quartz-syenite to granodiorite and granite porphyries, and a little deformed but variably altered granodiorite stock intrude metamorphic rocks of the Basal Unit. A 9.4 ± 0.3 Ma K–Ar age on feldspar for a dyke rock provides a minimum age for the igneous activity in the Basal Unit. East–west orientation of porphyry dykes is indicative of a regional extensional stress field with roughly north–south direction. Substantial extension in the Basal Unit after granodiorite emplacement is evident from widespread quartz veining associated with hydrothermal alteration of the granodiorite and the occurrence of mineralized tension gashes cutting the hydrothermally altered hornfelses. Final emplacement of the Blueschist Unit over the Basal Unit by extensional detachment post-dates contact metamorphism of the rocks surrounding the granodiorite. Geochemical diagrams show a continuous range of compositions from the dykes to the granodiorite. Radiogenic isotope compositions are compatible with a common magmatic source for the two lithologies. Elemental variations, as well as the considerable geochemical similarity of the dyke rocks to the Hercynian paragneiss of the central Cyclades, indicate that crustal melts were significant components during the evolution of the igneous rocks with fractional crystallization as an important process during later stages of evolution. The granodiorite displays geochemical signatures indicative of a significant mafic mantle-derived magma component.
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Macey, P. H., R. J. Thomas, H. P. Smith, D. Frei, and P. J. le Roux. "Lithostratigraphy of the Naros Granite (Komsberg Suite), South Africa and Namibia." South African Journal of Geology 124, no. 3 (2021): 795–804. http://dx.doi.org/10.25131/sajg.124.0040.
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Abstract The Naros Granite occurs as a large, northwest-trending ovoid batholith roughly 30 km long and 15 km wide straddling the Orange River border between South Africa and Namibia, 25 km northeast of Onseepkans. It consists mainly of a leucocratic to mesocratic grey, coarse-grained equigranular hornblende-biotite granite-granodiorite that is locally mildly feldspar porphyritic. Small, ovoid mafic autoliths are common and characteristic of the Naros Granite. The composition of the unit varies from granite to granodiorite with a minor leucogranitic phase observed along the southern margin of the batholith. Hornblende and biotite are ubiquitous mafic minerals but small amounts of orthopyroxene occur locally. The Naros Granite has yielded tightly-constrained U-Pb zircon ages between 1 114 Ma and 1 101 Ma. The Naros Granite is generally unfoliated to weakly deformed with only localised shearing along contacts with the surrounding country rocks giving rise to orthogneissic fabrics. It has an intermediate to felsic composition (mean SiO2: 63.9 ± 2.2 wt.%) and is strongly metaluminous. This, together with its biotite-hornblende ± orthopyroxene mineral assemblage and the abundance of mafic autoliths, suggests it is an I-type granitoid, with the source magma produced by partial melting of older igneous rocks that had not undergone any significant chemical weathering. The Naros Granite is the youngest and most evolved member of the ~1.11 Ga Komsberg Suite, a collection of late- to post-tectonic I-type metaluminous, intermediate to felsic, biotite ± hornblende granitoids and their charnockitic equivalents that have intruded the older pre-tectonic gneisses of the Kakamas Domain of the Namaqua Metamorphic Sector.
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m ABU EL-LEIL ALI, Ibrahim, Abdellah Sadek TOLBA, Hamdy Ahmed Mohamed AWAD, Aleksey Valer’evich NASTAVKIN, Sayed Ahmed OMAR, and Mohamed Galal EL-FEKY. "Geological and geochemical studies on El-Missikat granites, Central Eastern Desert, Egypt." NEWS of the Ural State Mining University, no. 4 (December 20, 2020): 7–18. http://dx.doi.org/10.21440/2307-2091-2020-4-7-18.
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Objective. The present work deals with the detailed investigations of the geology, geochemistry, and tectonic setting of the studied granitic rocks. Research methods. This work involves both field work (Collection samples and drawing of a new geological map) and laboratory work (preparation of thin sections for petrographic studies by polarizing microscope), Atomic absorption, X-ray Fluorescence analysis (XRF) in the Central Laboratories of the Acme in Canada and Mass-Spectrometer with Inductively Coupled Plasma (ICPMS). Result. The study area restricted in the Central Eastern Desert of Egypt between the Red sea and the Nile Valley. ElMissikat pluton is covered by island arc related rock (as xenolith), older granites, and younger granites, in addition to different types of dikes and veins swarms. Petrographically older granites are classified into quartz diorite, tonalite and granodiorite, whereas the younger granites are divided into monzogranite, syenogranite and altered granites. The geochemical studies suggest the granitic rocks are calc-alkaline affinity. The quartz diorite, tonalite and granodiorite are related to volcanic arc granites, while the monzogranite and syenogranite are similar to the infinity of the within plate granites behavior. The quartz diorite, tonalite, granodiorite and monzogranite are belonging to I-type granite, otherwise the syenogranite has A-type granites. Conclusion. According to geological and petrographical studies the investigated granites are represented by quartz diorite, tonalite and granodiorite, whereas the younger granites are divided into monzogranite, syenogranite and altered granites that are traversed by different types of dikes and veins swarms . Generally, the older granites have low content of LILE, most probably due to the relatively low content of K-feldspars and HFSE. The younger granites exhibit a fractionated pattern from LREE to HREE with negative Eu anomaly.
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Barr, S. M., C. E. White, N. G. Culshaw, and J. WF Ketchum. "Geology and tectonic setting of Paleoproterozoic granitoid suites in the Island Harbour Bay area, Makkovik Province, Labrador." Canadian Journal of Earth Sciences 38, no. 3 (2001): 441–63. http://dx.doi.org/10.1139/e00-086.
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Paleoproterozoic granitoid rocks in the Island Harbour Bay area (Kaipokok domain, Makkovik Province, Labrador) are divided into four separate suites on the basis of field relations, petrology, and age. The redefined Island Harbour Bay plutonic suite consists of ca. 18951870 Ma dioritic to granitic (mainly granodioritic and granitic) units. The rocks are variably foliated as a result of emplacement under amphibolite-facies conditions in a dextral transpressive regime during Andean-type subduction. The dominant mafic mineral is biotite, and accessory epidote, allanite, and titanite are abundant. The suite is calc-alkalic, but with rare-earth element patterns similar to those of Archean tonalitictrondhjemiticgranodioritic suites. It is interpreted to have formed deep in an Andean-type magmatic arc at the margin of the Nain continent. In contrast, the younger Hares Islands and Drunken Harbour granites (emplaced at ca. 1805 and 1790 Ma, respectively) were part of widespread late-orogenic magmatic activity in the Makkovik Province. In contrast to the Island Harbour Bay plutonic suite, these units retain igneous textures and are either unfoliated or display magmatic foliation, locally modified by emplacement in active shear zones. The ca. 1716 Ma Blacklers Bight granite varies from porphyritic to equigranular, is fluorite-bearing, and has chemical features approaching those of continental A-type granites. Similar granite occurs farther south in the Makkovik Province, reflecting widespread anorogenic magmatic activity at that time, perhaps related to mafic magma underplating. Variable interaction with Archean (Nain Province) crust by granitic magmas of all three ages is evidenced by εNd values ranging from 7.2 to 2.5.
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He, Xiaohu, Zheng Liu, Guochang Wang, Nicole Leonard, Wang Tao, and Shucheng Tan. "Petrogenesis and tectonic setting of the Early Cretaceous granitoids in the eastern Tengchong terrane, SW China: Constraint on the evolution of Meso-Tethys." Lithosphere 12, no. 1 (2020): 150–65. http://dx.doi.org/10.1130/l1149.1.
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Abstract As a result of the evolution of Meso-Tethys, Early Cretaceous granitoids are widespread in the eastern Tengchong terrane, SW China, which is considered as the southern extension of the Tibetan Plateau. These igneous rocks are therefore very important for understanding the tectonic setting of Meso-Tethys and the formation of the Tibetan Plateau. In this paper, we present new zircon U-Pb dating, whole-rock elemental, and Nd isotopic data of granitoids obtained from the eastern Tengchong terrane. Our results show that these granitoids are composed of monzogranites and granodiorites and formed at ca. 124 Ma in the Early Cretaceous. Mineralogically and geochemically, these granitoids display metaluminous nature and affinity to I-type granites, which are derived from preexisting intracrustal igneous source rocks. The predominantly negative whole-rock εNd(t) values (−10.86 to −8.64) for all samples indicate that they are derived mainly from the partial melting of the Mesoproterozoic metabasic rocks in the lower crust. Integrating previous studies with the data presented in this contribution, we propose that the Early Cretaceous granitic rocks (135–110 Ma) also belong to I-type granites with minor high fractionation. Furthermore, in discriminant diagrams for source, granitoids are mainly derived from the partial melting of metaigneous rocks with minor sediments in the lower crust. The new identification of the Myitkyina Meso-Tethys ophiolitic suite in eastern Myanmar and mafic enclaves indicate that these Cretaceous igneous rocks were the products of the tectonic evolution of the Myitkyina Tethys Ocean, which was related to post-collisional slab rollback. Moreover, the Tengchong terrane is probably the southern extension of the South Qiangtang terrane.
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Zhao, Yan, Wenhao Ao, Hong Zhang, Qian Wang, Mingguo Zhai, and Yong Sun. "Latest Paleoproterozoic (ca. 1.8–1.6 Ga) extensional tectonic setting in the Dunhuang terrane, NW China: Evidence from geochronological and geochemical investigations on A-type granite and metamafic rock." Lithosphere 11, no. 6 (2019): 834–54. http://dx.doi.org/10.1130/l1114.1.
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Abstract Latest Paleoproterozoic (ca. 1.8–1.6 Ga) magmatic rocks outcrop in the Dunhuang terrane, represented by A-type granites and mafic (basaltic) rocks that have metamorphosed into amphibolites. The A-type granites, emplaced at ca. 1.79–1.77 Ga, are geochemically characterized by high Na2O + K2O, Fe2O3T, Zr, Nb, and Ce contents, as well as high Fe2O3T/(Fe2O3T + MgO) and Ga/Al ratios. Furthermore, they have Nb/Ta, Y/Nb, Rb/Nb, and Sc/Nb ratios of 12.10–15.56, 1.45–1.79, 3.52–6.51, and 0.11–0.19, respectively, showing affinity to A2-type granite. The A-type granites have negative εNd(t) values (−5.4 to −4.8) with Neoarchean depleted mantle (TDM2) ages (2591–2494 Ma), corresponding to coupling between εHf(t) values (−4.85 to -0.92) and TDM2 ages (2817–2556 Ma) of zircons. Therefore, the A-type granite pluton was mostly generated by partial melting of Neoarchean tonalitic to granodioritic basement rocks of the Dunhuang Complex in a postcollisional tectonic setting following a late Paleoproterozoic continent-continent collisional event. The metamafic rocks have a protolith age of 1605 ± 45 Ma and metamorphic age of 317 ± 20 Ma, indicating a Paleozoic tectonic event. The metamafic rock samples are geochemically characterized by relatively high alkali (Na2O + K2O = 4.39–4.81 wt%) contents and low Nb/Y (0.63–0.66) ratios, and they show steep rare earth element (REE) patterns with light REE enrichment and insignificant Eu anomalies and Nb-Ta, Zr-Hf, and Ti anomalies, resembling subalkaline oceanic-island basalt affinity. They have positive εNd(t) values (+0.8 to +1.8) close to the chondrite evolutionary line and variable εHf(t) values (-1.09 to +9.06) of zircons. Hence, the protolith of the metamafic rocks may have been produced by magma mixing processes between a depleted mantle source and a metasomatized lithospheric mantle source during the initial rifting stage in an extensional setting, completing the formation of the Precambrian Dunhuang Complex. Considering the ca. 1.85–1.80 Ga regional metamorphism in the Dunhuang terrane, the latest Paleoproterozoic (ca. 1.8–1.6 Ga) A2-type granitic magmatism and mafic magmatism documented the postorogenic to initial rifting processes following the global-scale late Paleoproterozoic collisional event, which is comparable with ca. 1.80–1.67 Ga postcollisional and ca. 1.60–1.53 Ga anorogenic magmatism in the North China craton, but different from that of the Tarim craton.
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Doggart, S., P. H. Macey, and D. Frei. "Lithostratigraphy of the Mesoproterozoic Twakputs Gneiss." South African Journal of Geology 124, no. 3 (2021): 783–94. http://dx.doi.org/10.25131/sajg.124.0041.
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Abstract The Twakputs Gneiss is a garnetiferous, K-feldspar megacrystic, biotite granite-granodiorite orthogneiss. It represents a major unit in the Kakamas Domain of the Mesoproterozoic Namaqua-Natal Metamorphic Province extending about 250 km between Riemvasmaak in South Africa and Grünau in southern Namibia. The Twakputs Gneiss occurs as foliation-parallel, sheet-like bodies tightly infolded together with granulite-facies paragneisses into which it intrudes along with a variety of other pre-tectonic granite and leucogranite orthogneisses. These rocks were subsequently intruded by late-tectonic garnet-leucogranites, granites and charnockites. The Twakputs Gneiss is a distinctive unit characterised by large ovoid to elongate megacrysts of twinned perthitic K-feldspar, set in a coarse-grained matrix of garnet, biotite, quartz and feldspar. It contains a penetrative foliation defined by the alignment of K-feldspars and streaks of biotite that developed during the main phase D2 of the Namaqua Orogeny (~1.2 to 1.1 Ga). The foliation and an accompanying elongation lineation are more intensely developed along lithological contacts, especially at the margins of the mega-scale F3 domes and basins that refold the regional fabrics. U-Pb zircon dating of the Twakputs Gneiss has yielded concordia ages of between ~1192 and 1208 Ma. Whole-rock geochemistry shows consistent major, trace and REE elemental trends, and thus reflect chemical variability from a single fractionating magma. The Twakputs Gneiss has a granitic to granodiorite composition and is strongly peraluminous. The geochemistry and the ubiquitous presence of garnet and pelitic xenoliths indicate an S-type granite protolith. The Twakputs Gneiss is the most voluminous and widespread member of the Eendoorn Suite which comprises seven textural variants of garnetiferous, K-feldspar-megacrystic granitoid orthogneiss of the same age.
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Wilkin, Richard T., and Theodore J. Bornhorst. "Geology and geochemistry of granitoid rocks in the Archean Northern complex, Michigan, U.S.A." Canadian Journal of Earth Sciences 29, no. 8 (1992): 1674–85. http://dx.doi.org/10.1139/e92-132.
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The Northern complex, located in the Upper Peninsula of Michigan, is an Archean greenstone–granite terrane that lies at the southern margin of the Superior Province. The origin of the plutonic suites in the Northern complex can be interpreted within a plate tectonic model proposed for the Superior Province and related to northward-directed subduction and subsequent collision along the Great Lakes tectonic zone. The following plutonic suites are recognized based on intrusive relationships, as well as textural and compositional differences: (i) gneissic tonalite suite; (ii) foliated tonalite suite; (iii) trondhjemite–granite suite; (iv) hornblendite–syenite suite; and (v) late granite dike suite. Rocks in the gneissic and foliated tonalite suites have lithologic and geochemical characteristics typical of Archean trondhjemite–tonalite–granodiorite assemblages exposed elsewhere in the Superior Province. They were emplaced during a primary deformation event and are interpreted to represent partial melts that formed during north-directed subduction of oceanic crust just prior to collision along the Great Lakes tectonic zone. During a second deformation event, stocks and plugs of the trondhjemite–granite suite, derived by intracrustal melting of amphibolite associated with collision and tectonic thickening, intruded both interior and exterior to a preexisting volcanic portion of the Northern complex. The hornblendite–syenite suite, composed of hornblende-rich syenites to monzodiorites with geochemical features that include high Mg numbers, and elevated Cr and Ni content, was derived from partial melting of the mantle during collision along the Great Lakes tectonic zone. The late granite dike suite, comprising late-stage, muscovite- and biotite-bearing quartz – alkali feldspar pegmatite and finer grained granitic lithologies, represents the last magmatic event in the Northern complex emplaced after collision.
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Emon, K. A., V. A. Jackson, and G. R. Dunning. "Geology and U-Pb geochronology of rocks of the Eokuk Uplift: a pre-2.8 Ga basement inlier in the northwestern Slave Province, Nunavut, Canada." Canadian Journal of Earth Sciences 36, no. 7 (1999): 1061–82. http://dx.doi.org/10.1139/e98-094.
Full textAbstract:
Rocks of the Eokuk Uplift have been mapped in detail along the coast of Coronation Gulf and 10 key units have been dated by U-Pb analysis of zircon, monazite, and titanite. The combined data indicate that this inlier of the Slave Province has a >3.2 Ga crustal component, evidence of a granulite-grade orogenic event predating 2.8 Ga and a lack of evidence for any significant orogenic activity corresponding to the 2.7-2.6 Ga events common in the rest of the Slave Province. The oldest rocks in the study area are a succession of granitoid and supracrustal gneisses that have been metamorphosed to amphibolite to granulite facies. From field relationships, the oldest rock is a granodiorite to tonalite orthogneiss, with a zircon crystallization age of 3254+13-6 Ma. A granite gneiss, which may be a small felsic intrusion or an anatectic melt of the tonalite gneiss, yields a zircon age of 3216+14-13 Ma. A K-feldspar megacrystic monzogranite gneiss contains old, discordant, possibly inherited zircons with 207Pb/206Pb ages ranging from 3103 to 3039 Ma, together with coexisting 2879 ± 3 Ma zircon and monazite. These high-grade gneisses are intruded by two megacrystic granite plutons, dated at 2887 ± 2 and 2881+4-3 Ma. The absence of extensive recrystallization and complex structures in these plutons indicates that this igneous event postdated the high-grade metamorphism. An amphibolite-grade synplutonic metamorphic event is dated at ~2880 Ma by new monazite in the older gneiss units. A series of variably deformed mafic to felsic dykes and pegmatites intrude both the granites and gneisses and constrain the end of penetrative deformation in the area. Of these, a boudinaged diorite dyke, with a strong internal foliation parallel to the regional fabric, is dated at 2877 ± 3 Ma. A younger granodiorite dyke that crosscuts the regional fabric at a high angle and has only a weak internal foliation yields an age of 2864+3-9 Ma. An undeformed syenogranite pegmatite, which represents a suite that intrudes all other units in the study area, has a combined zircon-monazite age of 2852 ± 3 Ma. The varying degrees of deformation in these minor intrusive rocks constrains the end of deformation in the study area to ca. 2850 Ma. This contrasts with data from the rest of the Slave Province, where the main phases of deformation, metamorphism, and synmetamorphic plutonism have been dated at ca. 2.62-2.59 Ga. Metamorphic titanite ages from the diorite and granodiorite dykes indicate two lower amphibolite to greenschist facies metamorphic events: one at ca. 2705 Ma and one at ca. 2646 Ma. The youngest Archean magmatic event in the area is represented by granite intrusions at 2594+3-2 Ma, coeval with crystallization of titanite at greenschist-grade conditions in some of the older gneissic and intrusive rocks.
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Kholodnov, V. V., E. S. Shagalov, G. A. Kallistov, G. Yu Shardakova, D. N. Salikhov, and E. V. Konovalova. "The Akhunovo–Petropavlovsk Granitoid Area as a Continental-Margin Center of the Long-Term Mantle–Crust Interaction: The Role of Subductional and Rift–Plume Sources." Russian Geology and Geophysics 62, no. 6 (2021): 648–65. http://dx.doi.org/10.2113/rgg20194121.
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Abstract —The Akhunovo–Petropavlovsk area of the late Paleozoic granite magmatism is located in the northeast of the Magnitogorsk megazone (MMZ) in the South Urals. It is a series of successively intruded rocks (Petropavlovsk, Akhunovo, Karagai, and Uiskii Bor intrusions) differing not only in composition, the depth of formation, and ore content but also in the relationship with magmatic and fluid sources and in magma generation mechanisms. This area differs significantly in the number and composition of intrusive complexes from the igneous rocks and ore associations in the central and western parts of the MMZ. The granite magmatism pulses alternated with the collisional shearing/spreading and rifting stages. The Petropavlovsk mesoabyssal granite intrusion (347.0 ± 8.6 Ma) formed at the early stage of the area evolution. Its rocks are similar in composition to a suprasubductional series (melting products of a mantle source enriched not only in water fluid but also in Cl). Later (310–306 Ma), at the collision–compression stage, crustal intrusion of the Akhunovo–Karagai granodiorite–granite complex took place. The intruded rocks are similar to the Middle Urals continental-margin gabbro-tonalite–grano-diorite–granite plutons (320–290 Ma) bearing large gold–sulfide–quartz deposits (Berezovskoe etc.). At the final stage of the area evolution, during the transition from continental-margin regime to hard collision between the East European and Kazakhstan continents (late Carboniferous) and the intense shearing/spreading deformations, the Uiskii Bor granosyenite–granite intrusion (304.0 ± 4.8 Ma) rich in K and HFSE formed. Granite intrusions of this type have been revealed in the MMZ for the first time. Thus, the granitoid complexes of the Akhunovo–Petropavlovsk area formed under changes in geodynamic settings and are characterized by different compositions, depths of occurrence, and genesis. This permits us to consider the area a typical continental-margin center of the long-term mantle–crust interaction, where magma generation proceeded at different mantle and crust levels, with the participation of both suprasubductional and enriched plume-related rift sources.
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Scarrow, Jane H., R. J. Pankhurst, P. T. Leat, and A. P. M. Vaughan. "Antarctic Peninsula granitoid petrogenesis: a case study from Mount Charity, north-eastern Palmer Land." Antarctic Science 8, no. 2 (1996): 193–206. http://dx.doi.org/10.1017/s0954102096000260.
Full textAbstract:
At Mount Charity, north-eastern Palmer Land, Rb–Sr whole-rock dating has identified three successive phases of granitoid emplacement in Triassic (232 ± 4 Ma), Jurassic (168 ± 1 Ma), and Cretaceous (120 ± 4 Ma) times. The Triassic suite comprises tonalites, granodiorites (including one two-mica granodiorite), monzogranite and a granite having either I-type or S-like mineralogies. The Jurassic suite includes only S-like granites, and the Cretaceous biotite tonalites and biotite granodiorite are all I-type. The three suites have negative ∈Nd and positive ∈Sr, and have subtly different Nd and Sr isotope characteristics: Suite A, ∈Srt =+30 to +53 and ∈Ndt =−0.9 to −3.1, Suite B, ∈Srt =+43 to +64 and ∈Ndt =−2 to −5.3, Suite C, ∈Srt =+22 to +23 and ∈Ndt =−2.5 to −2.6. Mineralogical and compositional differences between the three suites suggest that different sources were tapped. All the granitoids are isotopically intermediate in composition between Palmer Land crust and depleted asthenosphere. We suggest that the I-type granitoids were produced by melting of meta-igneous crust; by contrast, the S-like granitoids represent partial melts of garnet-bearing sedimentary crust. Syn-magmatic structures in Suite A are compared with known structural events in western Palmer Land and suggest that extension controlled Triassic pluton emplacement. The Jurassic magmas were also emplaced during an episode of arc extension, and intrusion of the Cretaceous magmas was probably controlled by regional extension and dextral transtension. Successive phases of magmatism focussed at Mount Charity are consistent with reactivated faults acting as magma conduits.
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ZHU, JIE, QIUGEN LI, XU CHEN, et al. "Geochemistry and petrogenesis of the early Palaeozoic appinite-granite complex in the Western Kunlun Orogenic Belt, NW China: implications for Palaeozoic tectonic evolution." Geological Magazine 155, no. 8 (2017): 1641–66. http://dx.doi.org/10.1017/s0016756817000450.
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AbstractThe Datong pluton, the largest early Palaeozoic granitoid in the Western Kunlun Orogenic Belt (WKOB) in NW China, is a typical appinite-granite complex. It consists of diorites, quartz diorites, monzodiorites, quartz monzodiorites, monzonites, quartz monzonites, syenites, granodiorites and monzogranites. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating yielded crystallization ages of 459 ± 3 Ma for the quartz monzonites and 452 ± 5 Ma for the monzogranites (Late Ordovician). The rocks possess a wide range of SiO2 (56.0–73.4 wt %), MgO (0.17–4.55 wt %) and Mg no. (25–60), with high K2O (2.83–5.29 wt %) contents, exhibiting high-K calc-alkaline to shoshonitic traits. They are characterized by enrichments in large-ion lithophile elements (LILEs) and light rare Earth elements (LREEs), as well as depletions in high-field-strength elements (HFSEs). The rocks have initial 87Sr/86Sr ratios of 0.7086–0.7185, negative εNd(t) values of –3.72 to –1.79 and εHf(t) values vary from –1.6 to +4.7. These features are modelled to show that they were most likely derived from an enriched lithospheric mantle source and that fractional crystallization with minor crustal contamination was involved in their petrogenetic process. Considering the distribution and chronology of the Palaeozoic intrusions – such as Kegang, Bulong, Qiukesu, Yierba, North Kudi, Dongbake, Buya, Ayilixi and Warengzilafu granitoid plutons with ages of c. 420–530 Ma – in conjunction with the Palaeozoic metamorphic overprinting in the WKOB, we propose a divergent double-subduction model to explain the destruction of the Proto-Tethys Ocean and suggest that the Datong pluton was likely emplaced in a post-collisional setting following the termination of subduction in response to slab break-off.
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Wiszniewska, Janina, Ewa Krzemińska, Olga Polechońska, Zdzisław Petecki, Michał Ruszkowski, and Sylwester Salwa. "NEW RESULTS OF POLYMETALLIC, PGE AND REE MINERALIZATION RESEARCH IN THE SUWAŁKI ANORTHOSITE MASSIF (NE POLAND)." Biuletyn Państwowego Instytutu Geologicznego 472, no. 472 (2018): 271–84. http://dx.doi.org/10.5604/01.3001.0012.6933.
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Suwałki Anortosite Massif (SAM) occurs in the crystalline basement of NE Poland within 200 km of the magmatic, Mesoproterozoic AMCG (anorthosite–mangerite–charnockite–granite) rock suite terrane called the Mazury Complex. SAM was discovered as a result of the drilling research of the prominent negative magnetic and gravimetric anomalies. There is an extensive negative anomaly of both potential fields related to the anorthosite massif. Gravimetric anomaly is surrounded by the bands of positive anomalies caused by rocks with elevated densities, such as granitoids, monzondiorites and granodiorites. A negative magnetic anomaly is surrounded by the bands of positive anomalies with significant amplitudes, particularly strongly marked from the south, west and north. Positive magnetic anomalies are associated with the presence of rocks with proven strong magnetic susceptibility due to the content of ferrolites (ilmenite-magnetite rocks) with accompanying Fe-Cu-Ni-Co sulphide mineralization. Fe-Ti-(V) ore deposits in the SAM were discovered in the early 1960s, in the region of Krzemianka and Udryn, but also Jeleniewo and Jezioro Okrągłe, under a thick overburden of Phanerozoic sedimentary rocks within small positive magnetic anomalies. These deposits were documented in about 100 deep boreholes to a depth of 2300 m, and the resources in C1 + C2 category were estimated for about 1.5 billion tons of titanium-magnetite ores with vanadium, mainly in the Krzemianka and Udryn ore fields. The model age obtained by the Re-Os NTIMS method for Fe-Ti-V ores and sulphides from the Krzemianka and Jezioro Okrągłe ore deposits was 1559 ±37 Ma with an initial ratio of 187Os/188Os = 1.16 ±0.06. This age was recognized as the age of the entire Suwałki Massif. Despite many years of research, the deep structure and the form of the massif has not been fully recognized. At present, geophysical and geological 3D modelling of borehole data is carried out using the OasisMontaj (Geosoft) software package. The 3D model is generated in the GeoModeller 3D application (Intrepid Geophysics) in order to recognize the geological correctness and interpretation of magnetic-gravity anomalies of the whole massif and its cover.
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Fontana, Fernando F., Steven Tassios, Jessica Stromberg, Caroline Tiddy, Ben van der Hoek, and Yulia A. Uvarova. "Integrated Laser-Induced Breakdown Spectroscopy (LIBS) and Multivariate Wavelet Tessellation: A New, Rapid Approach for Lithogeochemical Analysis and Interpretation." Minerals 11, no. 3 (2021): 312. http://dx.doi.org/10.3390/min11030312.
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This paper demonstrates a novel approach that uses wavelet tessellation in rapid analysis of raw geochemical data produced by laser-induced breakdown spectroscopy (LIBS) to produce pseudologs that are representative of stratigraphy. Single-line LIBS spectral data for seven major rock-forming elements (Al, Ca, Fe, Mg, Si, Na and K) were collected from a synthetic 22-sample rock-block comprising two distinct lithological groups based on mineralogy, chemistry and texture: plutonic rocks and marble. Seven sublithologies are identified within the rock-block from traditional laboratory whole-rock geochemical analysis: marble, Mg-marble, granite, quartz monzonite, foidolite, granodiorite and gabbroic diorite. Two-domain clustering (k = 2) on raw spectral LIBS data combined with wavelet tessellation was applied to generate a simplified lithological stratigraphy of marble and plutonic rocks and generate a pseudolog identical to the rock-block stratigraphy. A pseudolog generated from seven-domain clustering (k = 7) and wavelet tessellation successfully discriminated most sublithologies within the rock-block slabs, especially marble slabs. Small-scale units were identified within the more mineralogically and geochemically complex plutonic slabs. The spatial resolution of the LIBS analysis, with a measurement spacing of ~0.35 mm, allowed for assessment of individual mineral compositions and rock textures, and small-scale units within the plutonic rocks can be correlated to specific coarse-grained minerals or mineralogical associations. The application of the wavelet tessellation method to raw LIBS geochemical data offers the possibility of rapid and objective lithogeochemical analysis and interpretations which can predate further analysis (quantitative) and supplement geological logging.
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Abrahams, Y., and P. H. Macey. "Lithostratigraphy of the Mesoproterozoic Donkieboud Granodiorite (Komsberg Suite), South Africa and Namibia." South African Journal of Geology 123, no. 3 (2020): 421–30. http://dx.doi.org/10.25131/sajg.123.0028.
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Abstract The Donkieboud Granodiorite pluton forms an extensive intrusion across the border region between South Africa and southeast Namibia. The mesocratic grey, weakly to moderately K-feldspar porphyritic biotite ± hornblende ± orthopyroxene granodiorite represents the most extensive member of the late- to post-tectonic Komsberg Suite (~1 125 to 1 105 Ma) which intruded as sheet-like bodies into the older high grade paragneisses and orthogneisses (~1 230 to 1 140 Ma) of the Kakamas Domain of the Mesoproterozoic Namaqua-Natal Province. The Donkieboud Granodiorite comprises three main textural variations namely:a porphyritic to weakly porphyritic, relatively undeformed rock with randomly orientated ovoid and twinned feldspar phenocrysts;a weakly- to well-foliated gneiss with between 3 to 10% feldspar phenocrysts set in a medium-grained matrix anda patchy metamorphic charnockite variety. Large inclusions of the strongly foliated Twakputs (~1 210 Ma) and the Witwater (~1 140 Ma) garnetiferous granite gneisses occur within the Donkieboud Granodiorite and mafic xenoliths are common. The Donkieboud Granodiorite is variably deformed ranging from unfoliated to being gneissic. The foliation developed during its intrusion into an existing but waning regional stress field with the strain increasing towards the contacts with the surrounding country rocks. Subsequent km-scale open folding resulted in the reorientation of the gneissic foliation and locally, intense reworking of the fabrics along the margins of the folds. In places, the Donkieboud unit is crosscut by discrete mylonitic shears with a west to northwest trend. U-Pb zircon dating of the Donkieboud Granodiorite samples yielded concordia ages of between 1 118 and 1 107 Ma. Overall the Donkieboud Granodiorite has an intermediate to felsic composition (mean SiO2: 63.9 ± 2.2 wt.%) and is strongly metaluminous. This, together with its biotite-hornblende ± orthopyroxene mineral assemblage and the abundance of mafic xenoliths, suggests it is an I-type granitoid, with the source magma produced by partial melting of older igneous rocks that had not undergone any significant amount of chemical weathering. The εNd values of -1.15 and -0.11 and TDM values of 1 615 and 1 505 Ma are typical of the Komsberg Suite and indicate a significant contribution of older crustal material to the magma of the Donkieboud pluton.
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Uher, Pavel, Igor Broska, Ewa Krzemińska, Martin Ondrejka, Tomáš Mikuš, and Tomáš Vaculovič. "Titanite composition and SHRIMP U–Pb dating as indicators of post-magmatic tectono-thermal activity: Variscan I-type tonalites to granodiorites, the Western Carpathians." Geologica Carpathica 70, no. 6 (2019): 449–70. http://dx.doi.org/10.2478/geoca-2019-0026.
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Abstract Titanite belongs to the common accessory minerals in Variscan (~360–350 Ma) metaluminous to slightly peraluminous tonalites to granodiorites of I-type affinity in the Tatric and Veporic Units, the Western Carpathians, Slovakia. It forms brown tabular prismatic-dipyramidal crystals (~0.5 to 10 mm in size) in association with quartz, plagioclase, and biotite. Titanite crystals commonly shows oscillatory, sector and convolute irregular zonal textures, reflecting mainly variations in Ca and Ti versus Al (1–2 wt. % Al2O3, 0.04–0.08 Al apfu), Fe (0.6–1.6 wt. % Fe2O3, 0.02–0.04 Fe apfu), REE (La to Lu + Y; ≤4.8 wt. % REE2O3, ≤ 0.06 REE apfu), and Nb (up to 0.5 wt. % Nb2O5, ≤0.01 Nb apfu). Fluorine content is up to 0.5 wt. % (0.06 F apfu). The compositional variations indicate the following principal substitutions in titanite: REE3+ + Fe3+ = Ca2+ + Ti4+, 2REE3+ + Fe2+ = 2Ca2+ + Ti4+, and (Al, Fe)3+ + (OH, F)− = Ti4+ + O2−. The U–Pb SHRIMP dating of titanite reveal their Variscan ages in an interval of 351.0 ± 6.5 to 337.9 ± 6.1 Ma (Tournaisian to Visean); titanite U–Pb ages are thus ~5 to 19 Ma younger than the primary magmatic zircon of the host rocks. The Zr-in-titanite thermometry indicates a relatively high temperature range of titanite precipitation (~650–750 °C), calculated for assumed pressures of 0.2 to 0.4 GPa and a(TiO2) = 0.6–1.0. Consequently, the textural, geochronological and compositional data indicate relatively high-temperature, most probably early post-magmatic (subsolidus) precipitation of titanite. Such titanite origin could be connected with a subsequent Variscan tectono-thermal event (~340 ± 10 Ma), probably related with younger small granite intrusions and/or increased fluid activity. Moreover, some titanite crystals show partial alteration and formation of secondary titanite (depleted in Fe and REE) + allanite-(Ce) veinlets (Sihla tonalite, Veporic Unit), which probably reflects younger Alpine (Cretaceous) tectono-thermal overprint of the Variscan basement of the Western Carpathians.
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Zhao, Chuntao, Jinggui Sun, Yang Liu, et al. "Constraints of magmatism on the Ergu Fe–Zn polymetallic metallogenic system in the central Lesser Xing’an Range, NE China: evidence from geochronology, geochemistry and Sr–Nd–Pb–Hf isotopes." Geological Magazine 158, no. 10 (2021): 1862–90. http://dx.doi.org/10.1017/s0016756821000479.
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AbstractThe medium-sized Ergu Fe–Zn polymetallic skarn deposit is located in the central Lesser Xing’an Range, NE China. The ore bodies are mainly hosted in the contact zone between granodiorite intrusions and lower Cambrian dolomitic crystalline limestones or skarns. To reveal the magmatic influence on the mineralization, resource potential and metallogenic geodynamic process of this deposit, a systematic study of the geology, petrology, zircon U–Pb dating, element geochemistry, amphibole geochemistry and Sr–Nd–Pb–Hf isotopes of the Ergu deposit intrusives was conducted. The results show the following: (1) The major rock types in the mine area are medium-grained granodiorite and porphyritic granite, and the rock related to mineralization is medium-grained granodiorite. Zircon U–Pb dating suggests that the granodiorite and porphyritic granite formed at 181.9–183.8 Ma and 182.7 Ma, respectively. Thus, an Early Jurassic magmatic event led to the formation of the Ergu deposit. (2) The granodiorite and porphyritic granite are high-K calc-alkaline I-type granites that formed by comagmatic evolution with varying degrees of fractional crystallization and were likely derived from partial melting of the lower crust. The Ergu deposit occurred in an active continental-margin tectonic setting. (3) The high water content (5.69 wt % H2O), high oxygen fugacity (ΔFMQ = +1.75 to +1.82) and intermediate-plutonic emplacement (3.13 km) of the granodioritic magma are key factors in the formation of the Ergu deposit. The porphyry granite is characterized by high water content (>4 wt % H2O), reduced oxygen fugacity (ΔFMQ = −0.47) and shallow emplacement (<3 km).
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Li, Yilong, Jianping Zheng, Wenjiao Xiao, Guoqing Wang, and Fraukje M. Brouwer. "Circa 2.5 Ga granitoids in the eastern North China craton: Melting from ca. 2.7 Ga accretionary crust." GSA Bulletin 132, no. 3-4 (2019): 817–34. http://dx.doi.org/10.1130/b35091.1.
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Abstract The Neoarchean crust-mantle interaction and crustal evolution of the North China craton are controversial and are instructive of the processes of continental crust growth and cratonic evolution. We present here a systematic study of the petrology, geochemistry, and geochronology of Neoarchean granitoids from the eastern North China craton to elucidate their petrogenesis and tectonic setting. The rocks were collected from the Jielingkou, Anziling, and Qinhuangdao plutons, and an amphibole-monzoporphyry dike in the Qinhuangdao pluton. Samples from the Jielingkou pluton, consisting dominantly of monzodiorite and diorite with minor monzonite and granodiorite, contain 52.2–64.4 wt% SiO2, 2.46–4.52 wt% MgO (Mg# = 0.41–0.54), 3.76–5.77 wt% Na2O, and K2O/Na2O ratios of 0.29–0.71. The Anziling pluton samples, comprising syenite and monzonite, display slightly higher SiO2 (60.9–66.7 wt%) and K2O/Na2O ratios (0.70–1.11), but lower MgO (1.54–2.33 wt%) and Mg# (0.40–0.47) values, compared to the Jielingkou rocks. The Qinhuangdao pluton samples, consisting mainly of granite and minor syenite and granodiorite, with some diorite and monzoporphyry dikes, are characterized by the highest SiO2 values (75.7–76.9 wt%) and K2O/Na2O ratios (0.73–1.41) and lowest MgO content (0.14–0.32 wt%) among the studied samples. The amphibole-monzoporphyry dike has intermediate SiO2 (56.3 wt%), high MgO (3.79 wt%), Na2O (5.55 wt%), and Mg# (0.45), and low K2O/Na2O ratio (0.66). Zircon U-Pb laser-ablation–inductively coupled plasma–mass spectrometry dating showed that all plutons have a ca. 2.5 Ga crystallization age. Zircon crystals have mildly positive εHf(t) values (+0.24 to +5.45) and a depleted mantle model age (TDM1) of ca. 2.7 Ga. We interpret the granitoid rocks as sanukitoid-related, Closepet-type granites, potassium-rich adakites, and potassium-rich granitoid rocks that crystallized in the late Neoarchean (2.5 Ga) and were derived from partial melting of mantle peridotite that was metasomatized with the addition of slab melt, thickened alkali-rich juvenile lower crust and juvenile metamorphosed tonalitic rocks. Mantle plume activity ca. 2.7 Ga is thought to have been responsible for the early Neoarchean tectono-thermal event in the eastern North China craton. This activity resulted in a major crustal accretion period in the craton, with subordinate crustal reworking at its margins. A steep subduction regime between ca. 2.55 Ga and ca. 2.48 Ga led to the remelting of older crustal material, with subordinate crustal accretion by magma upwelling from a depleted mantle source resulting in late Neoarchean underplating. This crustal reworking and underplating resulted in the widespread ca. 2.5 Ga plutons in the eastern North China craton. Continental crust growth in the North China craton thus occurred in multiple stages, in response to mantle plume activity, as well as protracted subduction-related granitoid magmatism during the Neoarchean.
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Högdahl, Karin, and Stefan Bergman. "Chapter 5 Paleoproterozoic (1.9–1.8 Ga), syn-orogenic magmatism and sedimentation in the Ljusdal lithotectonic unit, Svecokarelian orogen." Geological Society, London, Memoirs 50, no. 1 (2020): 131–53. http://dx.doi.org/10.1144/m50-2016-30.
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AbstractDuctile shear zones with dextral transpressive deformation separate the Ljusdal lithotectonic unit from the neighbouring units (Bothnia–Skellefteå and Bergslagen) in the 2.0–1.8 Ga Svecokarelian orogen. Sedimentation steered by regional crustal extension at c. 1.86–1.83 Ga was sandwiched between two separate phases of ductile strain with crustal shortening and predominantly high-grade metamorphism with plutonic activity. Metamorphism occurred under low-pressure, medium- to high-temperature conditions that locally reached granulite facies. The earlier shortening event resulted in the accretion of outboard sedimentary and c. 1.89 Ga volcanic rocks (formed in back- or inter-arc basin and volcanic arc settings, respectively) to a continental margin. Fabric development (D1), the earlier phase of low-pressure and variable temperature metamorphism (M1) and the intrusion of a predominantly granitic to granodioritic batholith with rather high εNd values (the Ljusdal batholith) occurred along this active margin at 1.87–1.84 Ga. Thrusting with westerly vergence, regional folding and ductile shearing (D2–3), the later phase of low-pressure and variable temperature metamorphism (M2), and the subsequent minor shear-related intrusion of granite, again with relatively high εNd values, prevailed at 1.83–1.80 Ga. Mineral deposits include epithermal Au–Cu deposits hosted by supracrustal rocks, V–Fe–Ti mineralization in subordinate gabbro and norite bodies inside the Ljusdal batholith, and graphite in metasedimentary rocks.
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Breemen, O. van, and K. L. Currie. "Geology and UPb geochronology of the Kipawa Syenite Complex a thrust related alkaline pluton and adjacent rocks in the Grenville Province of western Quebec." Canadian Journal of Earth Sciences 41, no. 4 (2004): 431–55. http://dx.doi.org/10.1139/e04-010.
Full textAbstract:
The Kipawa Syenite Complex, a thin, folded sheet of amphibole syenite, quartz syenite and minor nepheline syenite, lies along a west-vergent thrust separating a lower slice comprising the Kikwissi granodiorite and biotite tonalite dated at 2717 +1511 Ma, and unconformably overlying metasedimentary rocks from an overlying slice containing the Red Pine Chute orthogneiss, an alkali granite gneiss, and the Mattawa Quartzite. The syenite complex, dated at 1033 ± 3 Ma, lies within the lower slice but has metasomatically altered the overlying slice. Texturally guided UPb spot analyses on partially metasomatised zircons from the alkali granite gneiss yield a cluster of 207Pb/206Pb ages at 1389 ± 8 Ma, interpreted as the time of igneous crystallization and four ages overlapping the time of syenite emplacement, interpreted as in situ, metasomatic growth. The highest structural slice comprises garnet amphibolite separated from lower slices by the Allochthon Boundary Thrust. Metamorphic grade increases upward from greenschist grade in the biotite tonalite to amphibolite grade (690 °C, 9 kbar (1 kbar = 100 MPa)) at the lower boundary of the alkali granite. Emplacement of the Kipawa Syenite Complex took place after assembly of the thrust stack had begun and after emplacement of the allochthon or hot slab responsible for the inverted metamorphic gradient. Origin of the syenite is tentatively ascribed to anatexis of material metasomatized by flow of alkaline solutions along a major shear surface. Crystallization of new zircon in the margins of the syenite shows that metasomatism continued from ca. 1035 to 990 Ma, redistributing alkalies, fluorine, rare-earth elements and zirconium.
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Sheraton, John W., Robert J. Tingey, Lance P. Black, and Robin L. Oliver. "Geology of the Bunger Hills area, Antarctica: implications for Gondwana correlations." Antarctic Science 5, no. 1 (1993): 85–102. http://dx.doi.org/10.1017/s0954102093000112.
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The Bunger Hills area of the East Antarctic Shield consists of granulite-facies felsic orthogneiss, with subordinate paragneiss and mafic granulite. The igneous precursors of granodioritic orthogneiss were emplaced 1500-1700 Ma ago, and late Archaean (2640 Ma) tonalitic orthogneiss occurs in the nearby Obruchev Hills. Peak metamorphism (M1) (at about 750-800°C and 5-6kb) occurred 1190 ±15 Ma ago (U-Pb zircon age), and was accompanied by the first of three ductile deformations (D1). Emplacement of voluminous, mainly mantle-derived plutonic rocks, ranging from gabbro, through quartz monzogabbro and quartz monzodiorite, to granite, followed between 1170 (during D3) and 1150 Ma. Intrusion of abundant dolerite dykes of four chemically distinct suites at about 1140 Ma was associated with shear zone formation, indicating at least limited uplift; all subsequent deformation was of brittle-ductile type. Alkaline mafic dykes were emplaced 500 Ma ago. Marked geochronological similarities with the Albany Mobile Belt of Western Australia suggest that high-grade metamorphism occurred during collision between the Archaean Yilgarn Craton of Australia and the East Antarctic Shield about 1200 Ma ago.
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Gardiner, N. J., J. A. Mulder, C. L. Kirkland, T. E. Johnson, and O. Nebel. "Palaeoarchaean TTGs of the Pilbara and Kaapvaal cratons compared; an early Vaalbara supercraton evaluated." South African Journal of Geology 124, no. 1 (2021): 37–52. http://dx.doi.org/10.25131/sajg.124.0010.
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Abstract The continental crust that dominates Earth’s oldest cratons comprises Eoarchaean to Palaeoarchaean (4.0 to 3.2 Ga) felsic intrusive rocks of the tonalite-trondhjemite-granodiorite (TTG) series. These are found either within high-grade gneiss terranes, which represent Archaean mid-continental crust, or low-grade granite-greenstone belts, which represent relic Archaean upper continental crust. The Palaeoarchaean East Pilbara Terrane (EPT), Pilbara Craton, Western Australia, and the Barberton Granite-Greenstone Belt (BGGB), Kaapvaal Craton, southern Africa, are two of the best exposed granite-greenstone belts. Their striking geological similarities has led to the postulated existence of Vaalbara, a Neoarchaean-Palaeoproterozoic supercraton. Although their respective TTG domes have been compared in terms of a common petrogenetic origin reflecting a volcanic plateau setting, there are important differences in their age, geochemistry, and isotopic profiles. We present new zircon Hf isotope data from five granite domes of the EPT and compare the geochemical and isotopic record of the Palaeoarchaean TTGs from both cratons. Rare &gt;3.5 Ga EPT evolved rocks have juvenile εHf(t) requiring a chondritic source. In contrast, younger TTG domes developed via 3.5 to 3.4 and 3.3 to 3.2 Ga magmatic supersuites with a greater range of εHf(t) towards more depleted and enriched values, trace element signatures requiring an enriched source, and xenocrystic zircons that reflects a mixed source to the TTGs, which variously assimilates packages of older felsic crust and a more juvenile mafic source. EPT TTG domes are composite and record multiple pulses of magmatism. In comparison, BGGB TTGs are less geochemically enriched than those of the EPT and have different age profiles, hosting coeval magmatic units. Hafnium isotopes suggest a predominantly juvenile source to 3.2 Ga northern Barberton TTGs, limited assimilation of older evolved crust in 3.4 Ga southern Barberton TTGs, but significant assimilation of older (Hadean-Eoarchaean) crust in the ca. 3.6 Ga TTGs of the Ancient Gneiss Complex. The foundation of the EPT is younger than that for the oldest components of the Eastern Kaapvaal. Although the broader prevailing Palaeoarchaean geologic framework in which these two cratons formed may reflect similar a geodynamic regime, the superficial similarities in dome structures and stratigraphy of both cratonic terranes is not reflected in their geochemical and age profiles. Both the similarities and the differences between the crustal histories of the two cratons highlights that they are formed from distinct terranes with different ages and individual evolutionary histories. Vaalbara sensu lato represents typical Palaeoarchaean cratonic crust, not in the sense of a single homogeneous craton, but one as diverse as the continents are today.
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Garde, A. A., C. R. L. Friend, A. P. Nutman, and M. Marker. "Rapid maturation and stabilisation of middle Archaean continental crust: the Akia terrane, southern West Greenland." Bulletin of the Geological Society of Denmark 47 (December 31, 2000): 1–27. http://dx.doi.org/10.37570/bgsd-2000-47-01.
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from the Akia terrane, southern West Greenland, supported by Sm-Nd isotope geochemistry, document its middle Archaean accretional history and provide new evidence about the location of its northern boundary. Zircon populations in grey gneiss and inherited zircons in granite show that magmatic accretion of new continental crust, dominated by intrusion of tonalite sheets in a convergent island arc setting, occurred between c. 3050 and 3000 Ma, around and within a c. 3220 Ma continental core. In the central part of the terrane, tonalite sheets were intercalated with older supracrustal rocks of oceanic affinity by intrusion, thrusting and folding during the Midterhøj and Smalledal deformation phases of Berthelsen (1960). Continued tonalite injection led to a thermal maximum with granulite facies conditions at c. 2980 Ma, dated by metamorphic zircons in grey gneiss. The metamorphic maximum was contemporaneous with upright, angular folds of the Pâkitsoq deformation phase. Within a few million years followed high-grade retrogression and intrusion of two large dome-shaped tonalite-granodiorite complexes, granites s.l. derived from remobilisation of grey gneiss, and post-kinematic diorite plugs. Whereas the relative chronology of these events is firmly established from field observations, zircons from the post-granulite facies intrusions all yielded statistically indistinguishable emplacement ages of c. 2975 Ma. These results show that crustal growth occurred in several short-lived events starting at c. 3220 Ma, and that final maturation and stabilisation of new, thick continental crust took place rapidly (within c. 20 Ma) at c. 2975 Ma.
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Manby, G. M. "The petrology of the Harkerbreen Group, Ny Friesland, Svalbard: protoliths and tectonic significance." Geological Magazine 127, no. 2 (1990): 129–46. http://dx.doi.org/10.1017/s0016756800013820.
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AbstractThe late Precambrian–early Palaeozoic rocks of Ny Friesland, which have been subjected to Caledonian deformation and metamorphism, constitute part of the Eastern Province or Terrane of Svalbard. The Harkerbreen group and other divisions of the Stubendorffbreen supergroup form a high-grade and intensely deformed core complex to this terrane which is bounded to the west by the Billefjorden Fault Zone and to the east by a major north–south shear zone. The Stubendorffbreen rocks exhibit two gneissic foliations, one axial planar to a large scale, F1 fold nappe closing to the east and the other axial planar to kilometre-scale upright F2 folds subsidiary to the Atomfjella Arch. Metamorphism in the mid-amphibolite facies range coincided with generation of these folds, and F3.crenulation folding was accompanied by waning P–T conditions. A significant proportion of the gneisses within the Harkerbreen group display silica–major element covariation patterns consistent with their position in the granodiorite field on the AFM plot. Incompatible, immobile element ratios Zr/Ti v. Nb/Y indicate affinities with rhyolites to rhyodacites which is also suggested by their REE profiles. Normalized multi-element plots of the gneisses are similar to those of granites from attenuated within-plate settings such as Mull and Skaergaard. The amphibolites which were intruded in the D1–D2 interval appear to be derivatives of fractionated basalts. They plot across the calk-alkaline tholeiite boundary on the AFM diagram, and the calc-alkaline character of some of the amphibolites is further suggested by their Yb-normalized Ce-Ta abundances. Zr-Ti-Y and REE abundances would support their derivation from a related suite of fractionated basalt liquids. On the Zr/Y v. Zr discrimination diagram the amphibolites appear to have compositions transitional between Mid Ocean Ridge and Within-Plate basalts whilst the Zr-Nb-Ta plot indicates Volcanic Arc Basalt affinities. Th-Hf-Ta and multi-element plots, however, indicate a marginal to back-arc basin setting possibly above a mature subduction zone. The late Caledonian Chydenius granite is an adamellite with mixed within-plate and syn-orogenic characteristics typical of post-collisional granites.
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Serra-Varela, Samanta, Pablo D. González, Raúl E. Giacosa, et al. "Evolution of the Palaeozoic basement of the North Patagonian Andes in the San Martín de los Andes area (Neuquén, Argentina): petrology, age and correlations." Andean Geology 46, no. 1 (2018): 102. http://dx.doi.org/10.5027/andgeov46n1-3124.
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In San Martín de los Andes area (Argentinian Patagonia) the Palaeozoic basement consists of metamorphic and plutonic rocks. The metamorphic rocks include strongly deformed schists, gneisses and migmatites. Their geochemical and petrographic characteristics suggest that the protholith could have been a sequence of pelites and greywackes. Detrital zircon analysis (U-Pb Q-ICP-LA-MS) yielded a maximum depositional age of 501±14 Ma (Series 3 Cambrian) for this sedimentary protolith. Metasedimentary rocks are affected by a regional foliation defined by the minerals of the metamorphic peak. This is a S2 foliation, since relics of a former foliation are present in some samples. This regional foliation is locally affected by open folds that develop an incipient crenulation cleavage (S3). The high-grade metamorphism includes partial melting processes, where the incipient segregates intrude parallel to the regional foliation and also cut it in presence of abundant melt. Zircons from anatectic granites formed during this partial melting process yielded a U-Pb Concordia age of 434.1±4.5 Ma (Llandovery-Wenlock, Silurian). The age of maximum sedimentation and the anatectic age constrain the metamorphic evolution of the basement into the lower Palaeozoic (between upper Cambrian and lower Silurian). The igneous rocks of the basement are granodiorites, tonalities, and some gabbros that cut the metamorphic basement and contain xenoliths and roof pendants from the country rocks. These plutonic rocks are affected by low-grade metamorphism, with the development of discrete, centimetric to hectometric, brittle-ductile shear zones. The age of these igneous rocks has been constrained through U-Pb zircons analysis, carried out by several authors between ca. 370 and 400 Ma (Devonian). The maximum sedimentation age for the protolith and its metamorphic evolution seems to be related to an early Palaeozoic orogenic event, probably the Patagonian Famatinian orogeny. In contrast, the Devonian igneous rocks of San Martín de los Andes could represent a Devonian magmatic arc, related to subduction processes developed at the beginning of the Gondwanan orogenic cycle, which culminates with the Gondwanan orogeny.
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Malone, John, David Malone, Jennifer Gifford, John Craddock, Jeanette Arkle, and Michael Wolf. "Geochronology of the southern margin of the Bighorn Batholith, Wyoming." Mountain Geologist 56, no. 3 (2019): 267–94. http://dx.doi.org/10.31582/rmag.mg.56.3.267.
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The Bighorn Mountains in north-central Wyoming reveal one of the largest exposures of 2800 Ma to 3000 Ma rocks in Laurentia. The northern part of the crystalline core is composed of the composite Bighorn batholith, whereas the central and southern areas of the range expose older gneiss complexes as well as minor supracrustal rocks. We provide new high-resolution LA-ICPMS U-Pb data on zircons sampled from eleven samples of tonalite, granodiorite, mylonite, and migmatite from the southern margin of the Bighorn batholith in the headwaters of the north fork of Paint Rock Creek. These rocks range from strongly foliated to massive and are difficult to subdivide into mappable units in the field because of their lithologic and structural similarities. Several cross-cutting mylonite zones (<10-meter-wide) that trend ~N70°E-N80E and dip steeply are present in the study area. Three distinct age populations are evident: ~2930-2940 Ma, 2905-2915 Ma, and 2880-2890 Ma. Several samples contain xenocrystic zircons >3000 Ma, ranging to 3500 Ma, which indicates assimilation of older crust. Each of the three age populations reported here are older than the previously reported age of ~2850 Ma age for the northern Bighorn Batholith but within the 2890 Ma, 2940 Ma, and 2950 Ma age groupings previously reported for the southern gneiss terrane. Three conclusions can be drawn from these data. First, the Bighorn batholith, at least along the southern margin, contains phases at least 80 million years older than the northern phase of the body, and emplacement was protracted and occurred over a ~100 Ma period. Second, episodes of both intrusion and shearing took place in this area as the various phases of the Bighorn batholith were emplaced. Finally, the existence of inherited zircons within the Bighorn batholith in the age range of ~3.0 Ga to 3.5 Ga indicates that the Bighorn batholith intruded through older crust. This older crust is perhaps a northern extension of Sacawee block in the northern Granite Mountains of central Wyoming, which may underlie the Bighorn Mountains.
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Wasström, Annika. "Petrology of a 1.95 Ga granite-granodiorite-tonalite-trondhjemite complex and associated extrusive rocks in the Knaften area, northern Sweden." GFF 127, no. 2 (2005): 67–82. http://dx.doi.org/10.1080/11035890501272067.
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ZHAO, GUOCHUN, ALFRED KRÖNER, SIMON A. WILDE, et al. "Lithotectonic elements and geological events in the Hengshan–Wutai–Fuping belt: a synthesis and implications for the evolution of the Trans-North China Orogen." Geological Magazine 144, no. 5 (2007): 753–75. http://dx.doi.org/10.1017/s0016756807003561.
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The Hengshan–Wutai–Fuping belt is located in the middle segment of the Trans-North China Orogen, a Palaeoproterozoic continental collisional belt along which the Eastern and Western blocks amalgamated to form the North China Craton. The belt consists of the medium- to high-grade Hengshan and Fuping gneiss complexes and the intervening low- to medium-grade Wutai granite–greenstone terrane, and most igneous rocks in the belt are calc-alkaline and have affinities to magmatic arcs. Previous tectonic models assumed that the Hengshan and Fuping gneiss assemblages were an older basement to the Wutai supracrustal rocks, but recent studies indicate that the three complexes constitute a single, long-lived Neoarchaean to Palaeoproterozoic magmatic arc where the Wutai Complex represents an upper crustal domain, whereas the Hengshan and Fuping gneisses represent the lower crustal components forming the root of the arc. The earliest arc-related magmatism in the belt occurred at 2560–2520 Ma, marked by the emplacement of the Wutai granitoids, which was followed by arc volcanism at 2530–2515 Ma, forming the Wutai greenstones. Extension driven by widespread arc volcanism led to the development of a back-arc basin or a marginal sea, which divided the belt into the Hengshan–Wutai island arc (Japan-type) and the Fuping relict arc. At 2520–2480 Ma, subduction beneath the Hengshan–Wutai island arc caused partial melting of the lower crust to form the Hengshan tonalitic–trondhjemitic–granodioritic (TTG) suites, whereas eastward-directed subduction of the marginal sea led to the reactivation of the Fuping relict arc, where the Fuping tonalitic–trondhjemitic–granodioritic suite was emplaced. In the period 2360–2000 Ma, sporadic phases of isolated granitoid magmatism occurred in the Hengshan–Wutai–Fuping region, forming 2360 Ma, c. 2250 Ma and 2000–2100 Ma granitoids in the Hengshan Complex, the c. 2100 Ma Wangjiahui and Dawaliang granites in the Wutai Complex, and the 2100–2000 Ma Nanying granitoids in the Fuping Complex. At c. 1920 Ma, the Hengshan–Wutai island arc underwent an extensional event, possibly due to the subduction of an oceanic ridge, leading to the emplacement of pre-tectonic gabbroic dykes that were subsequently metamorphosed, together with their host rocks, to form medium- to high-pressure granulites. At 1880–1820 Ma, the Hengshan–Wutai–Fuping arc system was juxtaposed, intensely deformed and metamorphosed during a major and regionally extensive orogenic event, the Lüliang Orogeny, which generated the Trans-North China Orogen through collision of the Eastern and Western blocks. The Hengshan–Wutai–Fuping belt was finally stabilized after emplacement of a mafic dyke swarm at 1780–1750 Ma.
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LI, ZHEN, JIAN-SHENG QIU, and XI-SHENG XU. "Geochronological, geochemical and Sr–Nd–Hf isotopic constraints on petrogenesis of Late Mesozoic gabbro–granite complexes on the southeast coast of Fujian, South China: insights into a depleted mantle source region and crust–mantle interactions." Geological Magazine 149, no. 3 (2011): 459–82. http://dx.doi.org/10.1017/s0016756811000793.
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AbstractThe Quanzhou (QZ) and Huacuo (HC) gabbro–granite complexes on the southeast coast of Fujian, South China, are important components of a Late Mesozoic calc-alkaline volcanic–plutonic belt in the region. The complexes provide an excellent opportunity to investigate the genetic relationships between acid and basic magmas, and their interactions within the intrusive environment. The complexes are composed mainly of monzogranite and biotite granodiorite in the QZ complex, and biotite granite in the HC complex, with lesser amounts of hornblende gabbro. Zircon U–Pb dating provides consistent crystallization ages of 109 ± 1 Ma and 108 ± 1 Ma for the QZ gabbros and monzogranites, and an age of 111 ± 1 Ma for the HC gabbro, which is contemporaneous with the spatially associated HC granites. Both the mafic and felsic intrusions in these complexes are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs), and are depleted in high-field-strength elements (HFSEs; e.g. Nb and Ta). They show similarly homogeneous Sr–Nd isotopic compositions. All these factors indicate a close genetic relationship between the gabbroic and granitic rocks in the QZ and HC complexes. Although the enriched Sr–Nd isotopic signatures of the QZ and HC gabbros seemingly point to an enriched mantle source (EM-1), they have highly variable zircon Hf isotopic compositions, with εHf(t) values ranging from negative to positive (specifically –4.6 to +6.1 for the QZ gabbros and –4.8 to +11.6 for the HC gabbros). We interpret the parental basic magmas of these gabbros to have received contributions from a depleted mantle source and crustal components. Contributions from such a depleted mantle source resulted in the growth of juvenile basaltic lower crust, the partial melting of which generated the parental felsic magmas of the QZ and HC complexes. Furthermore, based on a synthesis of petrography, geochronology, elemental and isotopic geochemistry and tectonics, we propose that break-off and rollback of the Late Mesozoic subducted Palaeo-Pacific Plate triggered the upwelling of asthenospheric mantle below the coastal area of the South China Block, which induced extension of the overlying continental lithosphere, and finally initiated the large-scale Late Yanshanian magmatism in the study area.
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PIPER, J. D. A., N. J. McARDLE, and Y. ALMASKERI. "Palaeomagnetic study of the Cairnsmoor of Fleet Granite and Criffel-Dalbeattie granodiorite contact aureoles: Caledonian tectonics of the Southern Uplands of Scotland and Devonian palaeogeography." Geological Magazine 144, no. 5 (2007): 811–35. http://dx.doi.org/10.1017/s0016756807003536.
Full textAbstract:
The plutons of Cairnsmoor of Fleet (392±2 Ma) and Criffel-Dalbeattie (397±2 Ma, both mineral isochron ages) comprise two of four major post-tectonic granitic complexes emplaced into the Southern Uplands, an Ordovician–Silurian back-arc and foreland basin complex formed at the northern margin of the Iapetus Suture. To expand the palaeomagnetic record of the Southern Uplands we have studied palaeomagnetism and magnetic fabrics in traverses spanning contacts of these intrusions with host mudrocks. A uniform anisotropy of magnetic susceptibility (AMS) fabric across the Cairnsmoor of Fleet contact has been enhanced by recrystallization into hornfels near the contact and records a late Acadian regional stress operative during, or soon after, emplacement of the pluton in Middle Devonian times. Magnetization during slow cooling recorded a dual polarity (‘A’) remanence in granite and hornfels with mean direction D/I = 92/−2° (α95 = 6.5°) yielding a palaeopole (Q = 6) at 2°N, 265°E linked to cooling at c. 392 Ma. Subsidiary magnetizations are overprints imparted during Variscan tectonism (‘B’, D/I = 194/6°) and Jurassic rifting within the adjoining Irish Sea Basin (‘C’, c. 160–140 Ma, D/I = 172/−52°). The Criffel-Dalbeattie pluton has more complex AMS fabrics recording both deformation and emplacement effects. Hematite of secondary hydrothermal origin is a significant feature of the rock magnetic record in the aureole, which is otherwise dominated by paramagnetism. The granodiorite is more strongly magnetized than the country rocks, accounting for a positive aeromagnetic anomaly. A fairly dispersed dual polarity remanence (mean D/I = 115/55°, α95 = 18°) in granodiorite and late tectonic porphyrite dykes is probably the oldest magnetization preserved in this pluton because it correlates with an excursion of Britain into southerly palaeolatitudes at c. 410 Ma and indicates an Early Devonian emplacement age. The palaeofield at c. 397 Ma, the currently accepted isotopic age, is recorded by a minority overprinted remanence (mean D/I = 272/2°, α95 = 12°) similar to the record in the Cairnsmoor of Fleet pluton and granites from the adjoining Lake District terrane. Granite complexes of the Southern Uplands Block collectively record regional rotation and excursion of Britain into southerly latitudes between c. 410 and 390 Ma. Comparable Silurian–Devonian palaeomagnetic poles identify common apparent polar wander (APW) in paratectonic and orthotectonic terranes from the Variscan Front in the south to the Laurentian foreland in the north following climactic Acadian deformation. APW between 430 and 390 Ma embracing the (post-closure) history of the Caledonian orogen is a loop executed at rates much higher than typical rates of plate motion and appears to record a component of true polar wander. The ∼110° arc length is identical to polar shift identified between mid-Silurian and Lower–Middle Devonian poles from Gondwana. The two paths superimpose to show that the western margin of Gondwana was in proximity to the SE margin of Laurentia during Acadian deformation in Early–Middle Devonian times and remote from the Caledonides; the residual Rheic Ocean subsequently closed by a combination of pivotal and left lateral strike-slip motions.
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Kanouo, Nguo Sylvestre, Arnaud Patrice Kouske, Gabriel Ngueutchoua, Akella Satya Venkatesh, Prabodha Ranjan Sahoo, and Emmanuel Archelaus Afanga Basua. "Eoarchean to Neoproterozoic Detrital Zircons from the South of Meiganga Gold-Bearing Sediments (Adamawa, Cameroon): Their Closeness with Rocks of the Pan-African Cameroon Mobile Belt and Congo Craton." Minerals 11, no. 1 (2021): 77. http://dx.doi.org/10.3390/min11010077.
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The core of detrital zircons from the southern Meiganga gold-bearing placers were analyzed by Laser Ablation Split Stream analytical techniques to determine their trace element abundances and U-Pb ages. The obtained data were used to characterize each grain, determine its formation condition, and try to trace the provenance. The Hf (5980 to 12,010 ppm), Y (27–1650 ppm), U (25–954 ppm), Th (8–674 ppm), Ti (2–256 ppm), Ta, Nb, and Sr (mainly <5 ppm), Th/U (0.06–2.35), Ti zircon temperature (617–1180 °C), ∑REE (total rare earth element) (98–1030 ppm), and Eu/Eu* (0.03 to <1.35) are predominant values for igneous crustal-derived zircons, with very few from mantle sources and of metamorphic origin. Crustal igneous zircons are mainly inherited grains crystallized in granitic magmas (with some charnockitic and tonalitic affinities) and a few from syenitic melts. Mantle zircons were crystallized in trace element depleted mantle source magmatic intrusion during crustal opening. Metamorphic zircons grown in sub-solidus solution in equilibrium with garnet “syn-metamorphic zircons” and in equilibrium with anatectic melts “anatectic zircons” during crustal tectono-metamorphic events. The U-Pb (3671 ± 23–612 ± 11 Ma) ages distinguish: Eoarchean to Neoproterozoic igneous zircons; Neoarchean to Mid Paleoproterozoic anatectic zircons; and Late Neoproterozoic syn-metamorphic grains. The Mesoarchean to Middle Paleoproterozoic igneous zircons are probably inherited from pyroxene-amphibole-bearing gneiss (TTGs composition) and amphibole-biotite gneiss, whose features are similar to those of the granites, granodiorites, TTG, and charnockites found in the Congo Craton, south Cameroon. The youngest igneous zircons could be grains eroded from Pan-African intrusion(s) found locally. Anatectic and syn-metamorphic zircons could have originated from amphibole-biotite gneiss underlying the zircon-gold bearing placers and from locally found migmatized rocks that are from the Cameroon mobile belt, which could be used as proxies for tracking gold.
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Slaman, L. R., S. M. Barr, C. E. White, and D. van Rooyen. "Age and tectonic setting of granitoid plutons in the Chéticamp belt, western Cape Breton Island, Nova Scotia, Canada." Canadian Journal of Earth Sciences 54, no. 1 (2017): 88–109. http://dx.doi.org/10.1139/cjes-2016-0073.
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Geological mapping in the Chéticamp granitoid belt in combination with petrographic and geochemical studies and U–Pb (zircon) dating by laser ablation inductively coupled plasma mass spectrometry have resulted in major reinterpretation of the geology in the western part of the Ganderian Aspy terrane of Cape Breton Island. Nine new U–Pb (zircon) ages show that the former “Chéticamp pluton” consists of 10 separate plutons of five different ages: late Neoproterozoic (ca. 567 Ma), Cambrian–Ordovician (490–482 Ma), Ordovician–Silurian (442–440 Ma), mid-Silurian (ca. 428 Ma), and late Devonian (366 Ma). The three late Neoproterozoic granodioritic to monzogranitic plutons are older than the adjacent metavolcanic and metasedimentary rocks of the Jumping Brook Metamorphic Suite, whereas the tonalitic to quartz dioritic Cambrian–Ordovician plutons intruded those metamorphic rocks. Petrographic characteristics and approximately 100 whole-rock chemical analyses show that with the exception of the mid-Silurian Grand Falaise alkali-feldspar granite, which has A-type within-plate characteristics, the plutonic units have calc-alkaline affinity and were emplaced in a volcanic-arc tectonic setting. These results are evidence that fragments of a long history of episodic subduction-related magmatism and terrane collision are preserved in this small part of Ganderia. Eight new Sm–Nd isotopic analyses are consistent with the Ganderian affinity of the Chéticamp plutonic belt. The ca. 490–482 Ma plutons are the first direct evidence in Cape Breton Island for the Penobscottian event recognized in the Exploits Subzone of central Newfoundland and in New Brunswick. However, the structural relationship of the Chéticamp plutonic belt to the rest of the Aspy and Bras d’Or terranes remains enigmatic, as is the apparent absence of effects of Devonian deformation and metamorphism in the older plutonic units.
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Castro, Antonio, Carmen Rodriguez, Carlos Fernández, Eugenio Aragón, Manuel Francisco Pereira, and José Francisco Molina. "Secular variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?" Geosphere 17, no. 3 (2021): 766–85. http://dx.doi.org/10.1130/ges02338.1.
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Abstract This study of Sr-Nd initial isotopic ratios of plutons from the North Patagonian batholith (Argentina and Chile) revealed that a secular evolution spanning 180 m.y., from the Jurassic to Neogene, can be established in terms of magma sources, which in turn are correlated with changes in the tectonic regime. The provenance and composition of end-member components in the source of magmas are represented by the Sr-Nd initial isotopic ratios (87Sr/86Sr and 143Nd/144Nd) of the plutonic rocks. Our results support the interpretation that source composition was determined by incorporation of varied crustal materials and trench sediments via subduction erosion and sediment subduction into a subduction channel mélange. Subsequent melting of subducted mélanges at mantle depths and eventual reaction with the ultramafic mantle are proposed as the main causes of batholith magma generation, which was favored during periods of fast convergence and high obliquity between the involved plates. We propose that a parental diorite (= andesite) precursor arrived at the lower arc crust, where it underwent fractionation to yield the silicic melts (granodiorites and granites) that formed the batholiths. The diorite precursor could have been in turn fractionated from a more mafic melt of basaltic andesite composition, which was formed within the mantle by complete reaction of the bulk mélanges and the peridotite. Our proposal follows model predictions on the formation of mélange diapirs that carry fertile subducted materials into hot regions of the suprasubduction mantle wedge, where mafic parental magmas of batholiths originate. This model not only accounts for the secular geochemical variations of Andean batholiths, but it also avoids a fundamental paradox of the classical basalt model: the absence of ultramafic cumulates in the lower arc crust and in the continental crust in general.
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Bennett, Venessa, Valerie A. Jackson, Toby Rivers, Carolyn Relf, Pat Horan, and Mike Tubrett. "Geology and UPb geochronology of the Neoarchean Snare River terrane: tracking evolving tectonic regimes and crustal growth mechanisms." Canadian Journal of Earth Sciences 42, no. 6 (2005): 895–934. http://dx.doi.org/10.1139/e04-065.
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UPb zircon crystallization ages determined by isotope dilution thermal ionization mass spectrometry (IDTIMS) and laser ablation microprobe inductively coupled plasma mass spectrometry (LAMICPMS) for 13 intrusive units in the Neoarchean Snare River terrane (SRT) provide tight constraints on the timing of crust formation and orogenic evolution. Seven metaluminous plutons were emplaced over ~80 Ma from ca. 2674 to 2589 Ma, whereas six peraluminous bodies were emplaced in a ~15 Ma interval from ca. 2598 to 2585 Ma. A detrital zircon study yielded an age spectrum with peaks correlative with known magmatic events in the Slave Province, with the ca. 2635 Ma age of the youngest detrital zircon population providing a maximum estimate for the onset of sedimentation. This age contrasts with evidence for pre-2635 Ma sedimentation elsewhere in the SRT, indicating that sedimentation was protracted and diachronous. Evolution of the SRT can be subdivided into four stages: (i) 26742635 Ma formation of a metaluminous protoarc in a tonalitetrondhjemitegranodiorite (TTG) granitegreenstone tectonic regime (TR1) and coeval with early turbidite sedimentation; (ii) 26352608 Ma continued turbidite sedimentation, D1/M1 juxtaposition of turbidites and protoarc lithologies prior to ~2608 Ma, and metaluminous granitoid plutonism; (iii) 26082597 Ma onset of TR2, collision of Snare protoarc with Central Slave Basement Complex, D2/M2 crustal thickening and mid-crustal granulite-facies metamorphism, sychronous with metaluminous and peraluminous plutonism; and (iv) 25972586 Ma orogenic collapse, D3/M3 mid-crustal uplift, granulite-facies metamorphism, and waning metaluminous and peraluminous plutonism. The distribution of igneous rocks yields an "orogenic stratigraphy" with an older upper crust underlain by a younger synorogenic mid-crust. These data can be used to provide constraints for the interpretation of the Slave Northern Cordillera Lithospheric Evolution (SNORCLE) Lithoprobe transect.
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de Wit, M. J., S. Bowring, R. Buchwaldt, et al. "Geochemical reconnaissance of the Guéra and Ouaddaï Massifs in Chad: evolution of Proterozoic crust in the Central Sahara Shield." South African Journal of Geology 124, no. 2 (2021): 353–82. http://dx.doi.org/10.25131/sajg.124.0048.
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Abstract In 1964, W.Q. Kennedy suggested that the crust of Saharan Africa is different from the rest of Africa. To date, the geologic evolution of this region remains obscure because the age and composition of crystalline basement are unknown across large sectors of the Sahara. Most of Africa comprises Archaean cratons surrounded by Palaeo- to Mesoproterozoic orogenic belts, which together constitute Africa’s three major shields (the Southern, Central and West African Shields), finally assembled along belts of Pan-African rocks. By contrast, central Saharan Africa (5.3x106 km2), an area just over half the size of Europe, is considered either as a Neoproterozoic region constructed of relatively juvenile crust (0.5 to 1.0 Ga), or as an older (North African) shield that was reactivated and re-stabilized during that time, a period commonly referred to as “Pan African”. Here, using U-Pb zircon age determinations and Nd isotopic data, we show that remote areas in Chad, part of the undated Darfur Plateau stretching across ¾ million km2 of the central Sahara, comprise an extensive Neoproterozoic crystalline basement of pre-tectonic gabbro-tonalite-granodiorite and predominantly post-tectonic alkali feldspar granites and syenites that intruded between ca. 550 to 1050 Ma. This basement is flanked along its western margin by a Neoproterozoic continental calc-alkaline magmatic arc coupled to a cryptic suture zone that can be traced for ~2400 km from Tibesti through western Darfur into Cameroon. We refer to this as the Central Saharan Belt. This, in a Gondwana framework, is part of a greater arc structure, which we here term the Great Central Gondwana Arc (GCGA). Inherited zircons and Nd isotopic ratios indicate the Neoproterozoic magmas in the central Sahara were predominantly derived from Mesoproterozoic continental lithosphere. Regional deformation between 613 to 623 Ma marks the onset of late alkaline granite magmatism that was widespread across a much larger area of North Africa until about 550 Ma. During this magmatism, the region was exhumed and eroded, leaving a regional peneplain on which early Palaeozoic (Lower-Middle Cambrian) siliciclastic sediments were subsequently deposited, as part of a thick and widespread cover that stretched across much of North Africa and the Arabian Peninsula. Detrital zircons in these cover sequences provide evidence that a substantial volume of detritus was derived from the central Sahara region, because these sequences include ‘Kibaran-age’ zircons (ca. 1000 Ma) for which a source terrain has hitherto been lacking. We propose that, in preference to calling the central Sahara a “ghost” or “meta” craton, it should be called the Central Sahara Shield.
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Zhang, Xuebing, Fengmei Chai, Chuan Chen, Hongyan Quan, and Xiaoping Gong. "Geochronology, geochemistry and tectonic implications of late Carboniferous Daheyan intrusions from the Bogda Mountains, eastern Tianshan." Geological Magazine 157, no. 2 (2019): 289–306. http://dx.doi.org/10.1017/s001675681900075x.
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AbstractThe Daheyan region, situated in the SW of the Bogda Mountains in eastern Tianshan, is important for understanding the accretionary history of the Central Asian Orogenic Belt. We investigated Carboniferous intrusions from the Daheyan area, SW Bogda Mountains, obtaining new zircon U–Pb ages, whole-rock geochemical data and Hf isotope data for these intrusions. Zircon U–Pb dating indicates that syenogranite, diorite, granodiorite and monzonite of the Daheyan intrusions were all formed during late Carboniferous (311–303 Ma) magmatism. The syenogranite has geochemical characteristics of A-type granites that were mainly sourced from melting of juvenile crust. In comparison, the low-Mg-number diorite intrusion, with tholeiite and metaluminous features, was derived from young crust and mixed some mantle materials. The granodiorite and monzonite are both I-type granites, and are both sourced from the melting of juvenile crust. Based on a comprehensive analysis of previous geochronological, geochemical and isotopic data of magmatic and sedimentary rocks in the Bogda–Harlik belt, we consider that late Carboniferous intrusive rocks of the Bogda Mountains formed in an intra-arc extension related to a continent-based arc setting.
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Koga, Kazuhiro, and Motohiro Tsuboi. "Petrogenesis of Granitic Rocks in the Hisakajima Island, Goto Archipelago, Southwestern Japan: A Geochemical Study." Minerals 11, no. 3 (2021): 248. http://dx.doi.org/10.3390/min11030248.
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Whole-rock chemical compositions including rare earth elements for the granitic rocks from the Hisakajima Island, Goto Archipelago, southwestern Japan were measured in order to constrain their origin and petrogenesis. The granites were divided into two types—a granodioritic group (GD) and a high Fe/Mg ratio granitic group (HFG). The granitic magma was formed by the upwelling of high-temperature mantle material, which might be related to the extension of the Japan Sea around the Middle Miocene. The origin of the GD magma was attributed to the mantle material, while the origin of the HFG magma was attributed to partial melting of the crust by upwelling of the high-temperature mantle. The amount of rare earth elements revealed the secondary addition of light rare earth elements through hydrothermal processes for the granites. Chondrite normalized rare earth element patterns revealed that the HFG rocks were not well differentiated.
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Kohút, Milan, Pavel Uher, Marián Putiš, et al. "SHRIMP U-Th-Pb zircon dating of the granitoid massifs in the Malé Karpaty Mountains (Western Carpathians): evidence of Meso-Hercynian successive S- to I-type granitic magmatism." Geologica Carpathica 60, no. 5 (2009): 345–50. http://dx.doi.org/10.2478/v10096-009-0026-z.
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SHRIMP U-Th-Pb zircon dating of the granitoid massifs in the Malé Karpaty Mountains (Western Carpathians): evidence of Meso-Hercynian successive S- to I-type granitic magmatismRepresentative granitic rock samples from the Malé Karpaty Mountains of the Western Carpathians (Slovakia) were dated by the SHRIMP U-Th-Pb isotope method on zircons. Oscillatory zoned zircons revealed concordant Mississippian magmatic ages: 355±5 Ma in Bratislava granodiorite, and 347±4 Ma in Modra tonalite. The results document nearly synchronous, successive Meso-Hercynian plutonic events from S-type to I-type granites. The Neo-Proterozoic inherited zircon cores (590±13 Ma) were identified in the Bratislava S-type granitic rocks whereas scarce Paleo-Proterozoic inherited zircons (1984±36 Ma) were detected within the Modra I-type tonalites.
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Zandomeni, Priscila S., Juan A. Moreno, Sebastián O. Verdecchia, et al. "Crystallization Conditions and Petrogenetic Characterization of Metaluminous to Peraluminous Calc-Alkaline Orogenic Granitoids from Mineralogical Systematics: The Case of the Cambrian Magmatism from the Sierra de Guasayán (Argentina)." Minerals 11, no. 2 (2021): 166. http://dx.doi.org/10.3390/min11020166.
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The Sierra de Guasayán (Eastern Sierras Pampeanas, Argentina) is formed by low to medium grade metamorphic rocks intruded by Cambrian metaluminous (La Soledad quartz-diorite), slightly peraluminous (Guasayán, El Escondido and El Martirizado granodiorite plutons), and strongly peraluminous (Alto Bello granodiorite) granitoids of the Pampean magmatic arc. Chemical compositions of amphibole, plagioclase, biotite, and titanite indicate that these granitoids were emplaced at low pressure (mostly <3 kbar) and temperature (<770 °C) under oxidizing conditions (QFM + 1 and QFM + 2), which are similar to the emplacement conditions reported for other granites of the Pampean magmatic arc. Mineral assemblages and whole-rock and mineral chemistry of the granitoids from the Sierra de Guasayán indicate an I-type affinity for the La Soledad quartz-diorite (amphibole, biotite, and titanite), S-type affinity for the Alto Bello granodiorite (biotite, muscovite, cordierite, and sillimanite), and a hybrid nature for the main Guasayán and El Escondido plutons (biotite, monazite, and magnetite). This hybrid nature is supported by the presence of abundant mafic microgranular enclaves and rapakivi texture and by published zircon Hf-isotope data (εHfi ranging from −4.76 to −0.12). This suggests, in turn, the involvement of hybridization in the genesis of these granitoids, which seems to be a common mechanism operating in the Pampean magmatic arc.
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Castro, Antonio. "The dual origin of I-type granites: the contribution from experiments." Geological Society, London, Special Publications 491, no. 1 (2019): 101–45. http://dx.doi.org/10.1144/sp491-2018-110.
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AbstractNew laboratory experiments using granulite xenoliths support a dual origin for I-type granites as primary and secondary. Primary I-type granites represent fractionated liquids from intermediate magma systems of broadly andesitic composition. Fluid-fluxed melting of igneous rocks that resided in the continental crust generates secondary I-type granites. The former are directly related to subduction, with Cordilleran batholiths as the most characteristic examples. Experiments with lower crust granulite sources, in the presence of water, show that amphibole is formed by a water-fluxed peritectic rehydration melting reaction. Entrainment of only 10% of restites composed of amphibole, pyroxene, plagioclase and magnetite, is sufficient to account for discrepancies in aluminium saturation index and maficity in secondary I-type granites. Lower crust granulite xenoliths, attached to a sanukitoid containing 6 wt% water, have been used in two-layer capsules to test fluid-fluxed melting reactions as the origin of secondary I-type granites. It is proposed that sanukitoid magmas act as water donors that trigger extensive melting of the lower crust, giving rise to granodioritic liquids. Because primary granites are related to coeval subduction, and secondary ones are crustal melts from older subduction-related rocks, the distinction between both I-types is essential in tectonic reconstructions of ancient orogenic belts.