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1
Cox, Simon C. "Inter-related plutonism and deformation in South Victoria Land, Antarctica." Geological Magazine 130, no. 1 (January 1993): 1–14. http://dx.doi.org/10.1017/s0016756800023682.
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AbstractThe Lower Palaeozoic Bonney Pluton is a regionally extensive coarse-grained, variably megacrystic, monzodioritic to granitic body that crops out over 1000 km2 in South Victoria Land. It intruded upper amphibolite facies Koettlitz Group metasediments and interlayered orthogneisses. Magmatic fabrics are developed in the centre of the pluton by flow alignment of K-feldspars before the majority of phases had crystallized, whereas solid-state fabrics developed in the pluton margins by ductile–plastic deformation. Structures developed in the host-rocks vary around this elongate northwest–southeast-trending pluton. Upright, tight northwest–southeast-trending macroscopic folds are developed at the sides of the pluton, with axis-parallel stretching lineations and boudinage indicating strong northwest–southeast extension. Broad warps of tight macroscopic folds, and mesoscopic refolded folds, sheath folds and complicated interference patterns characterize areas at the ends of the pluton. Emplacement of the pluton involved radial expansion in a regional northeast–southwest compression, and growth predominantly in the northwest–southeast direction. Superposition of the radial expansion and regional compression resulted in an inhomogeneous strain field at a regional scale, with coaxial strain at the sides of the pluton and non-coaxial strain at the ends. Upright folds developed at the pluton's sides, and became tighter with continued coaxial deformation. Non-coaxial structures developed at the ends of the pluton and were pushed aside by the growing pluton into areas of coaxial deformation, resulting in complex folding, re-folding and sheath folds. Metamorphism of the host-rocks and migmatite development was more intense at the sides of the pluton than near the ends, possibly due to different P-T-t paths of host-rocks around syntectonic plutons.
2
Irzon, Ronaldo, Ildrem Syafri, Irfani Agustiany, Arief Prabowo, and Purnama Sendjaja. "Petrology and Geochemistry of The Volcanic Arc Tarusan Pluton in Comparison to Lolo Pluton, West Sumatra." Jurnal Geologi dan Sumberdaya Mineral 20, no. 4 (November 5, 2019): 199. http://dx.doi.org/10.33332/jgsm.geologi.20.4.199-210.
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The Volcanic Arc Suite is the group of batholiths in the range of the Barisan Mountains and mostly denotes I-type affinity. Previous investigations of the intrusions in West Sumatra emphasized the crystallization age without completing geochemistry characteristics. No former study discussed a pluton which mapped in the Kota XI Tarusan District. This study explains the geochemistry and petrology of the Tarusan Pluton using polarized microscope, XRF, and ICP-MS at the Center for Geology Survey of Indonesia. The microscopic analysis confirms the granite character of the samples. Although both plutons are identified as I-type calc-alkaline series, the Tarusan Pluton is peraluminous granite whilst the Lolo Pluton denotes wider range from metaluminous to peraluminous of granodiorite to granite. Both the plutons are clearly classified as volcanic arc granitoid in the correlation to Volcanic Arc Suite of Sumatra. Negative Ba, Nb, and P anomalies together with positive K, Nd, and Y anomalies are pronounced on the two felsic intrusions. Negative Eu anomaly on the Tarusan Pluton but the positive one at the Lolo Pluton might explain different magma evolution process.Keywords: volcanic arc granite, geochemistry, Tarusan Pluton, Lolo Pluton.
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Irzon, Ronaldo, Ildrem Syafri, Irfani Agustiany, Arief Prabowo, and Purnama Sendjaja. "Petrology and Geochemistry of The Volcanic Arc Tarusan Pluton in Comparison to Lolo Pluton, West Sumatra." Jurnal Geologi dan Sumberdaya Mineral 20, no. 4 (November 5, 2019): 199. http://dx.doi.org/10.33332/jgsm.geologi.v20i4.471.
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The Volcanic Arc Suite is the group of batholiths in the range of the Barisan Mountains and mostly denotes I-type affinity. Previous investigations of the intrusions in West Sumatra emphasized the crystallization age without completing geochemistry characteristics. No former study discussed a pluton which mapped in the Kota XI Tarusan District. This study explains the geochemistry and petrology of the Tarusan Pluton using polarized microscope, XRF, and ICP-MS at the Center for Geology Survey of Indonesia. The microscopic analysis confirms the granite character of the samples. Although both plutons are identified as I-type calc-alkaline series, the Tarusan Pluton is peraluminous granite whilst the Lolo Pluton denotes wider range from metaluminous to peraluminous of granodiorite to granite. Both the plutons are clearly classified as volcanic arc granitoid in the correlation to Volcanic Arc Suite of Sumatra. Negative Ba, Nb, and P anomalies together with positive K, Nd, and Y anomalies are pronounced on the two felsic intrusions. Negative Eu anomaly on the Tarusan Pluton but the positive one at the Lolo Pluton might explain different magma evolution process.Keywords: volcanic arc granite, geochemistry, Tarusan Pluton, Lolo Pluton.
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Grammatikopoulos, T. A., A. H. Clark, and D. A. Archibald. "Petrogenesis of the Leo Lake and Lyndhurst plutons, Frontenac terrane, Central Metasedimentary Belt, southeastern Ontario, Canada." Canadian Journal of Earth Sciences 44, no. 1 (January 1, 2007): 107–26. http://dx.doi.org/10.1139/e06-072.
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The 1167 ± 2 Ma Leo Lake pluton, located at the southern part of the Frontenac terrane in Central Metasedimentary Belt of southeastern Ontario, is a bimodal pluton that is dominated by olivine gabbro, gabbro, syenite, and lesser monzonite. The adjoining 1166 ± 3 Ma Lyndhurst pluton is composed of syenite and granite, and exhibits magma mingling. Even though geochemical data from both plutons suggest fractional crystallization as the main crystallization process, magma mingling is evident in the Lyndhurst pluton. Hornblende from the Leo Lake syenite yields a 40Ar–39Ar age of 1120 ± 6 Ma and titanite from the adjacent St. Lawrence skarn yields a U–Pb age of 1147 ± 8 Ma. The 40Ar–39Ar age indicates that the pluton cooled to 550 °C at a rate of ca. <2 °C/Ma following emplacement. The two plutons are similar in petrology to several other granitic, syenitic, and monzonitic intrusions of the Frontenac suite in the Frontenac terrane. Moreover, the spatial distribution, textural features, and geochemistry indicate that the plutons are coeval. The present data indicate that the two plutons may have been produced from evolved mantle-derived melts, and may have assimilated varying proportions of crustal melts.
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Bauer, Robert L. "Multiple folding and pluton emplacement in Archean migmatites of the southern Vermilion granitic complex, northeastern Minnesota." Canadian Journal of Earth Sciences 23, no. 11 (November 1, 1986): 1753–64. http://dx.doi.org/10.1139/e86-161.
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Analysis of folding in the southwestern Vermilion granitic complex suggests that F2 folds, which formed in a regional north–south compressional regime, were locally reoriented during pluton emplacement and were subsequently refolded by F3 folds generated by continuing north–south compression. An east–west-trending F2 antiform, crossing the boundary between the southern Vermilion granitic complex and the adjacent Vermilion district, was intruded by a tonalite pluton during the later stages of F2 folding. Either emplacement of the pluton or emplacement of the nearby Lac La Croix batholith is believed to have reoriented the F2 fold so that, subsequently, the pluton and the F2 antiform were refolded by a doubly plunging east–west-trending F3 fold, now cored by the pluton.A similar relationship occurs between F2 and F3 folds north of the Vermilion fault in the main portion of the complex. Here, F3 conical folds, not cored by plutons, refold F2 folds about northwest-trending vertex axes. Analysis of the refolding of minor F2 folds and L2 lineations in this area suggests they were nearly coaxial with the F3 folds prior to the F3 folding.
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Gualda, Guilherme A. R., and Silvio R. F. Vlach. "The Serra da Graciosa A-type granites and syenites, southern Brazil. Part 1: regional setting and geological characterization." Anais da Academia Brasileira de Ciências 79, no. 3 (September 2007): 405–30. http://dx.doi.org/10.1590/s0001-37652007000300006.
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The Serra da Graciosa region includes important occurrences of granites and syenites of the Graciosa A-type Province (formerly Serra do Mar Suite), southern Brazil. Using fieldwork, petrography, and remote sensing imagery, we characterize the geology of the plutons in the region. Five individual plutons were recognized. Two correspond to the previously defined Marumbi and Anhangava Plutons. We divide the former "Graciosa Pluton" into three new plutons: Capivari, Órgãos, and Farinha Seca. The plutons are elliptical with northeast-southwest orientation. Two petrographic associations can be recognized: an alkaline association that includes peralkaline and metaluminous hypersolvus alkalifeldspar granites and syenites (Anhangava, Farinha Seca, Órgãos), and an aluminous association composed of metaluminous and weakly peraluminous subsolvus granites (Capivari, Órgãos, Anhangava, Marumbi). Occurrences of each association are limited to one individual pluton or to portions of a pluton, and the age relationships are not well established. Monzodioritic rocks are found marginal to the Órgãos and Farinha Seca Plutons, and interaction with silicic magmas locally produced hybrid quartz syenites (Farinha Seca Pluton). Geothermobarometry indicates emplacement at shallow crustal levels (P = 2 ± 0.6 kbar), and crystallization temperatures within the interval 900-700ºC for the granitic and syenitic rocks, and 1000-750ºC for the monzodioritic rocks.
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KOUKOUVELAS, IOANNIS K., and SOTIRIOS KOKKALAS. "Emplacement of the Miocene west Naxos pluton (Aegean Sea, Greece): a structural study." Geological Magazine 140, no. 1 (January 2003): 45–61. http://dx.doi.org/10.1017/s0016756802007094.
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Synmagmatic and solid-state structures within the Naxos pluton and its rim may provide insight into the interplay between plutonism and regional deformation at upper-crustal level. Within the hornblende–biotite granite of western Naxos, synmagmatic foliations display two distinct patterns, onion-skin in the north and tangential to the rim in the south. The two areas are separated by the NE-trending Glinadon fault. Deformed mafic enclaves in the pluton are prolate, with their long axes parallel to the synmagmatic lineation. In contrast, phenocryst distribution analysis, using the Fry method, defines an apparent oblate strain with a horizontal stretching lineation. Planar markers within the pluton progressively steepen through the vertical at the east pluton border. Several lines of evidence, such as dykes intruding axial areas of rim-parallel folds, foliated or folded aplite veins, folds and spaced cleavage in the mollase, and inverted stratigraphy, suggest pluton emplacement and deformation during transpressional deformation. A northward divergent flow regime with magma spreading out mainly from the Naxos fault, and the deflection of both the synmagmatic foliation pattern and the flow lines at the Glinadon fault, suggest that the NE–SW- and N–S-trending faults were active during pluton formation. In the south the pluton has grown by the expansion of dykes occupying P-shear positions with respect with the Naxos fault; in the north a piecemeal block down-drop complements this process and favours voluminous magma concentration. During the late evolutionary stages of pluton construction, the magma chamber was compartmentalized into NE-trending sectors affected by block rotation in an anticlockwise manner. Understanding the role of faults in the emplacement of the Naxos pluton is important for understanding emplacement of other plutons in the Aegean Sea region, since most of them are controlled by N–S- (Ikaria pluton) or NE- (Tinos, Serifos and Delos plutons) trending faults.
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Davis, W. J., S. Lacroix, C. Gariépy, and N. Machado. "Geochronology and radiogenic isotope geochemistry of plutonic rocks from the central Abitibi subprovince: significance to the internal subdivision and plutono-tectonic evolution of the Abitibi belt." Canadian Journal of Earth Sciences 37, no. 2-3 (April 2, 2000): 117–33. http://dx.doi.org/10.1139/e99-093.
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Nine new U-Pb ages are reported for plutons of the central granite-gneiss zone of the Abitibi belt in Quebec. The large plutonic complex along Lithoprobe seismic reflection line 28 formed by multiple intrusion over at least 40 million years, synchronous with and postdating formation of adjacent volcanic sequences. Ages for the four principal plutons within the complex are: Mistaouac at 2726 ± 2 Ma, Boivin at 2713 ± 2 Ma, Rousseau at 2703 ± 2 Ma, and Paradis at 2686 ± 2 Ma. The latter also constrains deformation within the Laberge deformation zone to be at least in part younger than 2686 Ma. Inherited zircons in the Mistaouac pluton indicate that the oldest pluton formed in significantly older crust (>2.75 Ga), not presently exposed in the area. The La Reine and Waswanapi plutons have ages of ca. 2695 Ma similar to other tonalitic plutons in the area and elsewhere in the Abitibi belt. A syenite pluton deformed within the Douay fault zone, a late fault associated with the Casa Berardi zone, has an age of 2676+6-5 Ma, similar to alkalic plutons associated with the Destor-Porcupine and Cadillac-Larder Lake deformation zones of the southern Abitibi belt. Two samples from the Lac Case pluton yielded monazite ages of 2676 ± 3 and 2660 ± 3 Ma. Nd, Pb, and Sr isotopic compositions for central Abitibi belt plutons show dominantly juvenile sources with minor contributions of older crust in the Lac Case pluton. Although geochronological data for volcanic rocks has been used to suggest that the northern zone is older and magmatic activity youngs to the south, consideration of the ages for plutonic and volcanic rocks does not support such hypothesis. The available data indicate that magmatism occurred throughout the Abitibi subprovince from 2730 to 2685 Ma, permissive of a linked tectono-magmatic evolution for the northern and southern zones.
9
Suarez, M., M. Herve, and A. Puig. "Cretaceous diapiric plutonism in the southern cordillera, Chile." Geological Magazine 124, no. 6 (November 1987): 569–75. http://dx.doi.org/10.1017/s0016756800017398.
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AbstractThe Castores and probably the Santa Rosa plutons of north-west Isla Navarino, southern Chile, have been emplaced by in situ diapirism into metasedimentary rocks of the Upper Jurassic (?)–Lower Cretaceous Yaghan Formation. For the former, this model is consistent with the concentric foliation paralleling the margin of the pluton and the foliation and stratification planes in the metamorphic aureole. Only the southern part of the Santa Rosa Pluton is preserved, and it has some structures similar to those of the Castores Pluton, which can also be interpreted as produced by an inflating diapir. The main intrusive rocks of these plutons are quartz-monzodiorites and quartz-diorites with synmagmatic foliation. They were preceded by minor bodies of hornblende gabbros, and followed by dykes and small bodies of non-foliated granodiorites. Non-foliated to weakly foliated granodiorites, forming the centre of the Castores Pluton, probably represent a younger intrusive pulse.Twelve K–Ar mineral dates from 10 specimens of plutonic rocks, interpreted as near crystallization ages, span the period 80–90 Ma. These dates do not show the sequence of intrusion of the different rock-types, which may suggest that all of them were intruded and cooled in a short period of time. The timing of emplacement of these plutons in relation to tectonism is difficult to determine; however, a post-tectonic emplacement for at least the Castores Pluton, is proposed.
10
Cruz, C., H. Sant'Ovaia, and F. Noronha. "Magnetic mineralogy of Variscan granites from northern Portugal: an approach to their petrogenesis and metallogenic potential." Geologica Acta 18 (March 9, 2020): 1–20. http://dx.doi.org/10.1344/geologicaacta2020.18.5.
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Northern Portugal is characterized by the occurrence of numerous W hydrothermal deposits spatially associated with granites. The primary goal of this work is to establish a relationship between the magnetic behavior of thegranites and the redox conditions during magma genesis, as this can influence the occurrence of mineralizations, namely of W (Mo). To this end, the magnetic mineralogy of the granites of the Lamas de Olo Pluton, a posttectonic pluton in northern Portugal, with associated W (Mo) occurrences was characterized and compared with the magnetic mineralogy of other post-tectonic Variscan plutons. This pluton is composed of different biotite granites: Lamas de Olo, Alto dos Cabeços and Barragem. To better characterize its magnetic behavior, differentanalytical techniques that complement previous magnetic susceptibility studies were performed. The magnetic mineralogy of Lamas de Olo Pluton was then compared with other post-tectonic Variscan plutons such as the Vila Pouca de Aguiar, Peneda-Gerês and Lavadores-Madalena plutons. The presence of magnetite in some of these granites is important because it points to melt-oxidized conditions not commonly found in Iberian Variscan granites. Our study shows that granite areas where magnetite and/or magnetite/ilmenite coexist are important targets for W (Mo) mineralizations. The results indicate that a few plutons have granites with a complex redox history which leads to the formation of magnetite and ilmenite.
11
Denyszyn, Steven W., Roland Mundil, Sarah J. Brownlee, and Paul R. Renne. "High-precision U–Pb geochronology of the Butedale pluton, British ColumbiaThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh." Canadian Journal of Earth Sciences 48, no. 2 (February 2011): 557–65. http://dx.doi.org/10.1139/e10-044.
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The Butedale pluton, a ca. 100 km long compositionally zoned batholith, is part of the Coast Plutonic Complex that extends the length of the Canadian Pacific coast. Its age and thermal history are relevant to the Butedale pluton’s role as a test case of the Baja–BC hypothesis, as paleomagnetic evidence suggests that it may have formed thousands of kilometres to the south and moved northward along what is now the Coast Shear Zone. High-resolution U–Pb (chemical abrasion – thermal ionization mass spectrometry (CA–TIMS), zircon) analysis of rocks across the width of the Butedale pluton indicates that it is actually made up of at least two distinct magmatic events that formed the West Butedale pluton (ca. 95 Ma) and the East Butedale pluton (ca. 85 Ma). The East Butedale pluton was reheated by the emplacement of a younger adjacent pluton, which may have caused partial Pb loss and resulting excess scatter of 206Pb/238U zircon ages within individual samples. The West Butedale pluton may be the same age as, and part of, the nearby Ecstall pluton, thereby doubling the length of the Ecstall pluton to ca. 200 km. Single-grain, high-precision U–Pb analysis of zircon reveals previously unknown complexity and detail of emplacement and thermal history in the Butedale plutons.
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Law, R. D., S. S. Morgan, M. Casey, A. G. Sylvester, and M. Nyman. "The Papoose Flat Pluton of eastern California: a reassessment of its emplacement history in the light of new microstructural and crystallographic fabric observations." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 83, no. 1-2 (1992): 361–75. http://dx.doi.org/10.1017/s0263593300008026.
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ABSTRACTOne of the most outstanding apparent examples in N America of a forcibly emplaced pluton is the Papoose Flat Pluton of eastern California. Sideways expansion of this granitic pluton, during emplacement into a series of Cambrian shelf strata, has been regarded by early workers as resulting in the observed intense crystal plastic deformation of the pluton's mylonitic border facies and surrounding country rocks. This deformation is evidenced by up to 90% thinning of individual stratigraphic layers within the pluton's metamorphic aureole, although such intense penetrative deformation of the country rocks is not observed outside the aureole.Previously published quartz c-axis fabrics associated with this deformation (and presented on projection planes oriented perpendicular to lineation) were interpreted as being symmetrical with respect to foliation and lineation, implying almost coaxial deformation histories. Such fabrics could be interpreted as indicating that the pluton evolved by “ballooning” as a result of new magma being intruded into its core during emplacement. However, a major problem with applying the strict ballooning model to the Papoose Flat Pluton is that while oblate strains would be expected to develop in association with a ballooning mechanism, the mylonitic rocks of this elongate WNW-ESE-trending pluton and its aureole are characterised by both a strongly developed foliation, which is concordant with the pluton's margin, and an intense, NW-SE trending, shallow plunging stretching lineation.Previously published fabrics from the Papoose Flat Pluton and its metamorphic aureole have been rotated on to a projection plane oriented parallel to lineation and perpendicular to foliation. Examination of the fabrics in this projection plane has revealed that they are in fact dominantly asymmetric, and that a constant sense of asymmetry is detected across the pluton, suggesting a consistent (top-to-the-SE) shear-sense. This new interpretation is strongly supported by microstructural and petrofabric analysis of additional L-S tectonites collected, during recent fieldwork, from both the aureole and quartz veins within the pluton's gneissic border facies. Thus mylonite formation around the Papoose Flat Pluton could have involved large-scale consistently oriented translation and associated shearing, rather than passive “blister-like” coaxial deformation associated with pluton ballooning. It should be noted that mylonitic deformation is restricted to the western half of the pluton, features indicative of a more “permitted” emplacement mechanism being found in the eastern portion of the pluton.The detected top-to-the-SE shear-sense could be interpreted as indicating that the granitic material forming the western part of the pluton was forcibly intruded in a northwestward direction from the pluton source as a nearly solidified wedge beneath a static cover of sedimentary rocks. Alternatively, the detected shear sense could also be interpreted as indicating SE-directed thrusting of the cover rocks over the underlying pluton, the western margin of the pluton suffering intense mylonitic deformation, while the eastern margin was located in a “stress-shadow” region. If this alternative interpretation is correct, then the deformation temperatures indicated by the pattern of quartz c-axis fabrics dictate that thrusting must either be synchronous with pluton emplacement, or at least have commenced during the early stages of pluton cooling.
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Andreichev, V. L., A. A. Soboleva, O. V. Udoratina, and Yu L. Ronkin. "Zirconology of syenites of the Northern Timan." Vestnik of Geosciences 6 (2021): 16–27. http://dx.doi.org/10.19110/geov.2021.6.2.
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Northern Timan is an uplifted block of the Upper Precambrian basement of the Timan Ridge, where intrusive rocks of various compositions cut Neoproterozoic metaterrigenous rocks of the Barmin Group and are overlain by Lower Silurian limestone. Syenites are widespread in the Cape Bolshoy Rumyanichny pluton and compose the Krayny Kameshek and Malyi Kameshek plutons. To determine the age of the syenites, U—Pb dating of zircons was carried out using secondary ion mass spectrometry (SIMS). The age of zircons from syenite of the Cape Bolshoy Rumyanichny pluton is 613 ± 7 Ma, Krayny Kameshek pluton — 602 ± 5 Ma, and Malyi Kameshek pluton — 598 ± 17 Ma. Similar zircon ages are known for other alkaline igneous rocks that occur within the Cape Bolshoy Rumyanichny pluton: olivine-kersutite gabbro — 614 ± 2 Ma, granites — 614 ± 11 Ma. Zircons from subalkaline granites of the Bolshoy Kameshek pluton are of the same age — 613 ± 6 Ma. The location of the plutons in the area of the Late Riphean passive margin of Baltica, the close association of subalkaline and alkaline granites, syenites, and alkaline gabbros indicate the anorogenic nature of these magmatic rocks and possible relationship with mantle plume activity. Ediacaran magmatic rocks of 614—600 Ma located in the Northern Timan could be associated with the final stages of Rodinia breakup, accompanied by plume-related magmatism, the products of which are also known in the eastern part of Laurentia and in the Scandinavia.
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Benn, Keith. "Anisotropy of magnetic susceptibility fabrics in syntectonic plutons as tectonic strain markers: the example of the Canso pluton, Meguma Terrane, Nova Scotia." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 100, no. 1-2 (March 2009): 147–58. http://dx.doi.org/10.1017/s1755691009016028.
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ABSTRACTThe anisotropy of magnetic susceptibility (AMS) is widely and routinely used to measure the preferred orientations of Fe-rich minerals in undeformed and weakly deformed granite plutons. The interpretation of the mapped AMS fabrics depends on rock-textural observations, on the map patterns of the fabrics in plutons, and on comparisons of the pluton fabrics to tectonic structures in the country rocks. The AMS may document emplacement-flow related fabrics, but the emplacement fabrics may be reworked or completely overprinted by rather weak tectonic strains of the magma mush or the cooling pluton, especially in syntectonic intrusions. The Late Devonian Canso granite pluton is an excellent example of overprinting of emplacement fabrics by weak tectonic strains. The Canso pluton was emplaced ca. 370 Ma along the boundary between the Meguma and Avalon tectonic terranes, in the northern Appalachian orogen. The AMS was mapped along two traverses that cross the pluton and that are perpendicular to the terrane boundary. Textural evidence suggests the rocks underwent very modest post-full crystallisation strains. The AMS records the dextral transcurrent shearing that occurred on the terrane boundary during emplacement and cooling of the Canso pluton, supporting interpretations that weakly deformed syntectonic granites can be used as indicators of regional bulk kinematics. AMS fabrics in Late Devonian granites of the Meguma Terrane suggest partitioning of the non-coaxial shearing into the terrane bounding fault, with pure-shear dominated deformation further from the fault. Numerical simulations suggest that the kinematics recorded by the fabrics in the Canso pluton was simple-shear, or transpression or transpression with small components of pure shear oriented perpendicular to the bounding shear zone.
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Paterson, Scott R., and David W. Farris. "Downward host rock transport and the formation of rim monoclines during the emplacement of Cordilleran batholiths." Transactions of the Royal Society of Edinburgh: Earth Sciences 97, no. 4 (2008): 397–413. http://dx.doi.org/10.1017/s026359330000153x.
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AbstractThe mechanisms by which Cordilleran plutons are emplaced vary widely. However, the present authors have examined a series of plutons ranging from 2-35 km emplacement depth that have many common features, which suggest that downward transport of host rock is the most important mechanism during magma ascent and pluton emplacement. Many of these Cordilleran plutons preserve gently dipping, unfaulted roofs attached to steep walls bordered by narrow ductile aureoles. Flat lying roof strata commonly roll over into steeply dipping rim monoclines and anticlines that young towards and follow the pluton margin. Field observations suggest that such rim monoclines and anticlines formed due to gravitationally driven roof collapse and channel flow along margins. In the examples in this paper, pluton walls are often comprised of narrow steeply dipping ductile aureoles in which the intensity of strain increases downward. Aureole ductile strains are insufficient to account for the volume of magma emplaced, and are typically <40% of pluton volume. However, when aureole strain is combined with minimum estimates of stoping and host rock rotation during rim monoclines formation, sufficient space can be created. The examples suggest that gravitationally driven downward host rock transport by stoping and rigid rotations along roofs and walls and by focused channel flow by ductile strain along walls are common processes during the rise of Cordilleran plutons, and is one process that contributes to crustal thickening and the growth of crustal roots.
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Shellnutt, J. Gregory, and Jaroslav Dostal. "Derivation of the Early Carboniferous Wedgeport pluton by crystal fractionation of a mafic parental magma: a rare case of an A-type granite within the Meguma terrane (Nova Scotia, Canada)." Geological Magazine 157, no. 2 (August 13, 2019): 248–62. http://dx.doi.org/10.1017/s0016756819000694.
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AbstractThe Cambrian–Ordovician metasedimentary rocks of the Meguma terrane (Canadian Appalachians) were extensively intruded by silicic plutons during Middle Devonian to Early Carboniferous times. Syn-plutonic but volumetrically minor mafic-ultramafic intrusions were also emplaced. In most localities, the silicic plutons and mafic-ultramafic intrusions do not appear to be petrogenetically related and are likely derived from different sources. The Attwoods Brook gabbronorite of SW Nova Scotia yielded an in situ zircon weighted-mean 206Pb–238U age of 357.9 ± 3.3 Ma that is within the uncertainty of the age of the neighbouring Wedgeport pluton (357 ± 1 Ma). The Wedgeport pluton is a rare example of a mantle-derived, peraluminous A-type granite within the Meguma terrane. The similar ages and Nd isotopes of the Attwoods Brook gabbronorite (εNd(t) = +1.1 to +4.0) and Wedgeport pluton (εNd(t) = +2.1 to +3.3) suggest the two intrusions are petrogenetically related. Fractional crystallization modelling demonstrates that a parental magma similar to the Attwoods Brook gabbronorite can produce residual silicic liquids that resemble the granites of the Wedgeport pluton, indicating that they could be members of the same intrusive complex. The emplacement of the gabbronorite and Wedgeport pluton occurred during a period of tensional plate stress that was contemporaneous with rifting of the Maritimes Basin that produced the Fountain Lake continental flood basalts and A-type granites of the Cobequid Highlands within the Avalon terrane. It is possible that the Early Carboniferous rocks of SW Nova Scotia are related to the rifted-related magmatism within the Maritimes Basin.
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Himmelberg, Glen R., Peter J. Haeussler, and David A. Brew. "Emplacement, rapid burial, and exhumation of 90-Ma plutons in southeastern Alaska." Canadian Journal of Earth Sciences 41, no. 1 (January 1, 2004): 87–102. http://dx.doi.org/10.1139/e03-087.
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In southeastern Alaska, granodioritetonalite plutons of the AdmiraltyRevillagigedo belt intruded the JurassicCretaceous Gravina belt along the eastern side of the Alexander terrane around 90 Ma. These plutons postdate some deformation related to a major contractional event between the previously amalgamated Wrangellia and Alexander terranes and the previously accreted terranes of the North American margin. We studied the aureole mineral assemblages of these plutons near Petersburg, Alaska, determined pressure and temperature of equilibration, and examined structures that developed within and adjacent to these plutons. Parallelism of magmatic and submagmatic fabrics with fabrics in the country rock indicates synchroneity of pluton emplacement with regional deformation and suggests that magma transport to higher crustal levels was assisted by regional deformation. Replacement of andalusite by kyanite or sillimanite indicates crustal thickening soon after pluton emplacement. Regional structural analysis indicates the crustal thickening was accomplished by thrust burial. Thermobarometric analyses indicate the aureoles reached near-peak temperatures of 525 to 635 °C at pressures of 570 to 630 MPa. Consideration of the rate of thermal decay of the aureoles suggests that burial was rapid and occurred at rates around 5 to 8 mm/year. Structural observations indicate there was contractional deformation before, during, and after emplacement of the 90-Ma plutons. Initial exhumation of the AdmiraltyRevillagigedo belt in the Petersburg area may have occurred along a thrust west of the pluton belt within the Gravina belt.
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Lü, Zhao-Ying, Chang-Qian Ma, Yuan-Yuan Liu, Fu-Hao Xiong, Chang-Xin Wei, Mu-Long Chen, Gui-Cheng Xue, and Yu-Sheng He. "Petrogenesis of the Jurassic Guiping Complex in the Southwestern South China Block: Insights into the Subduction Processes of the Paleo-Pacific Slab." Minerals 11, no. 8 (July 26, 2021): 807. http://dx.doi.org/10.3390/min11080807.
Full textAbstract:
Late Jurassic NE-trending A-type granitoids are widespread in the Shihang belt, South China, though their petrogenesis and geodynamic settings remain controversial. The Guiping complex is located on the southwest margin of the Shihang belt. In this study, the petrography, major and trace element geochemistry, whole-rock Sr-Nd isotopes, and zircon U-Pb geochronology of the Guiping complex were investigated. The Guiping complex is composed of the Fenghuangling and Xishan plutons; both plutons yielded zircon U-Pb ages of ca. 160 Ma. The Fenghuangling pluton has low SiO2 content of 54.26% to 60.31%, whereas the Xishan pluton exhibits high SiO2 content of 65.19% to 71.18%. Both of them are metaluminous and belong to the high-K calc-alkaline series and are enriched in large-ion lithophile elements (LILEs) such as Rb, Th, U, and Pb. The Fenghuangling and Xishan plutons showed enrichment in light rare earth elements (LREEs) and high-field strength elements (Nb, Ta, Zr, and Hf) and depletion in heavy rare earth elements (HREEs). Marked Nb and Ta negative anomalies were not observed. Due to the high contents of Zr + Ce + Nb + Y and high Ga/Al ratios, all the samples belonged to the group of A-type granites. The Fenghuangling and Xishan plutons had low ISr (mainly in the range of 0.7046–0.7058) and high εNd(t) (−0.60 to 1.94) values, though obviously different from those of the Precambrian basement in South China. Furthermore, they lie between the ocean island basalt (OIB) of the asthenosphere and the arc basaltic rocks of the enriched lithospheric mantle. Therefore, we proposed that the basaltic parental magma of the Guiping complex originated from partial melting of the enriched lithospheric mantle, which was metasomatized by asthenosphere-related OIB-type basaltic magma. Mafic microgranular enclaves in the Xishan pluton displayed positive Nb and Ta anomalies, which is consistent with OIB-type basalts. The enclaves also had similar Sr-Nd isotopic compositions to the Xishan pluton. That indicated that the enclaves were probably formed by mixing of the OIB-type basaltic magma and the Xishan pluton. In conclusion, the formation of the Late Jurassic NE-trending A-type granite belt was attributed to back-arc extension as a result of the rollback of the Paleo-Pacific Plate.
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Barr, Sandra M., Alan S. Macdonald, and John Blenkinsop. "The Cheticamp pluton: a Cambrian granodioritic intrusion in the western Cape Breton Highlands, Nova Scotia." Canadian Journal of Earth Sciences 23, no. 11 (November 1, 1986): 1686–99. http://dx.doi.org/10.1139/e86-156.
Full textAbstract:
The Cheticamp pluton consists of biotite granodiorite (locally megacrystic) in the north and museovite–biotite granodiorite in the south, in probable faulted contact. These two rock types, especially the biotite granodiorite, show a broad range in modal and chemical compositions. They are interpreted to be cogenetic, with the museovite–biotite grandiorite derived from the biotite granodiorite by crystal fractionation involving mafic minerals, plagioclase, and sphene. The overall peraluminous composition of the suite resulted from the fractionation process, probably enhanced by alteration, rather than from derivation from peraluminous source rocks.A seven-point, whole-rock, Rb–Sr isochron indicates an age of 525 ± 40 Ma. The pluton intruded dioritic rocks and quartzo-feldspathic gneisses, thus indicating Precambrian ages for these units. It probably also postdates the Western Highlands volcanic–sedimentary complex, a major undated stratigraphic unit in the Cape Breton Highlands. Although the age overlaps the range of Rb–Sr ages from plutons of the Avalon Terrane of the Appalachian orogen, the geological setting of the Cheticamp pluton differs from that of true Avalonian plutons, such as those in southeastern Cape Breton Island.
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Olivier, Philippe, and Laurent Améglio. "Structure and emplacement in a transcurrent regime and late magmatic rotation of the Variscan granite plutons of Veinazès and Marcolès (Châtaigneraie, French Massif Central)." Bulletin de la Société Géologique de France 173, no. 3 (May 1, 2002): 207–18. http://dx.doi.org/10.2113/173.3.207.
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Abstract Introduction. – The Variscan basement of the French Massif Central is considered [Faure, 1995] to have suffered (i) a southwestward nappe stacking during the early Carboniferous ; (ii) a NW-SE trending extension during the late Visean and granite emplacement during Namurian and Westphalian time ; (iii) a NE-SW trending extension during late Carboniferous-early Permian. The structure of the Veinazès and Marcolès monzogranitic plutons, located in the Châtaigneraie (southern French Massif Central), is studied in this paper through the anisotropy of magnetic susceptibility technique (AMS) to better understand the effects of the Namurian-Westphalian phase which is poorly documented in this region. Magnetic and structural study. – The long axis K1 of the AMS ellipsoid represents the magnetic lineation and the short axis K3 is normal to the magnetic foliation. This magnetic fabric may be equated with the mineral fabric. Km, the mean magnetic susceptibility, corresponds to the arithmetic mean (K1+K2+K3)/3. Pp %, the magnetic anisotropy ratio, corresponds to ((K1 – D/K3 – D) – 1) × 100, D being the diamagnetic component. Magnetic susceptibility (K) values (fig. 3 ; table I) range from 3.5 to 18.9 × 10−5 SI (mean 12.3 × 10−5 SI) for Veinazès, and from 0.7 to 13.1 x 10−5 SI (mean 8.1 × 10−5 SI) for Marcolès. Such values are typical of dominantly paramagnetic rocks. This is confirmed by the very good correspondence between these measured values and the magnetic susceptibilities calculated from sites for which chemical analyses are available (table II). For Veinazès the highest K values are mainly located in the western part of the pluton, whereas the weakest are in the northeastern part (fig. 3). This corresponds roughly to the distribution of the main petrographic facies determined by Joubert [1978] and Bogdanoff et al. [1989a]. The anisotropy of the magnetic susceptibility ratio (Pp %) (fig. 4 ; table I) ranges from 0.9 % to 5.3 % (mean 2.2 %) for Veinazès and from 0.8 % to 4 % (mean 2.2 %) for Marcolès. The part of the Veinazès pluton located to the south-west of the Sansac-Montsalvy line displays a mean anisotropy (2.7 %) clearly higher than the northeastern part of the pluton (1.6 %). For Marcolès, the map of Pp % does not display significant distribution heterogeneities. Three types of microstructures were determined in thin-sections in the Veinazès and Marcolès granites (fig. 5) : 1–undeformed magmatic textures ; 2– late magmatic weakly deformed textures ; 3– late magmatic deformed textures. There is a good correspondence between the mapped distribution of these microstructures (fig. 6) and the Pp % values (fig. 4). Magnetic foliations (fig. 7 & 8 ; table I). Veinazès : to the north-east of the Sansac-Montsalvy line, the foliations are roughly organized in a dome. To the south-west of this line, the foliations are mainly WNW-ESE trending with a medium to steep northward dip. Near the borders of the pluton the foliations become WSW-ENE. Marcolès : the foliations are concentrated around a NW-SE trending mean direction, with generally steep (≥ 60o) and northeast dips. Near the extremities of the pluton the foliations are closer to an E-W trend. In both plutons the pattern of foliations tends to form Z-sigmoids. Magnetic lineations (fig. 7 & 9 ; table I). Veinazès : to the north-east of the pluton, the lineations display generally shallow plunges and N-S trending directions. In the central part of the pluton they display very shallow plunges and are mainly E-W trending. To the west, the lineations display shallow to steep plunges mainly trending either E-W or NW-SE. Marcolès : most lineations are NW-SE to E-W trending, with middle SE or eastward plunges. These lineations form a Z-sigmoid pattern in plan view. Discussion and interpretation. – The shallow plunging lineations carried by rather steep foliations and the sigmoidal features observed in plan view, show that most magmatic fabrics of both plutons may correspond to strike-slip movements. Moreover, the organization of the main cleavage in the country rocks around the Veinazès pluton could correspond to an E-W-trending left-lateral transcurrent zone (fig. 1). In the western part of the Châtaigneraie, the mean direction of the cleavage becomes N150oE-165oE, with eastward middle to steep dips, indicating a clockwise rotation with respect to the regional trend. Dextral shearings are linked to this NNW-SSE band. Gravimetric data indicate that the Veinazès pluton is characterized by a rather flat floor and a single zone of relative deepening (2.5 km) between Ladinhac and Sansac-Veinazès (fig. 10), interpreted as a possible root. For the Marcolès pluton the maximum depth (1.25 km) is located beneath the village of Marcolès. We propose the following model (fig. 11) for the emplacement of the Veinazès and Marcolès plutons during the late Namurian-early Stephanian time-span: initial opening of the crust corresponding to the present deepest parts of the plutons floor, led by ENE-WSW-trending left-lateral strike-slip faults (fig. 11a) ; magmatic ascent and accretion of the plutons (fig. 11b) ; about 40o clockwise rotation of the Marcolès pluton, the SW end of the Veinazès pluton and their country rocks, linked to a NNW-SSE right-lateral strike-slip band (fig. 11c). We consider that these events predate the low temperature sinistral movements along the NNE-SSW-trending Sillon Houiller during the Stephanian time. Conclusion. – The magmatic fabrics measured in the Veinazès and Marcolès plutons, combined with previous data from the country rocks, show the probable importance of transcurrent movements for the emplacement of these plutons. The rotation suffered by the western part of this region after granites were emplaced would need to be better contrained by palaeomagnetic measurements on the Marcolès pluton.
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Cox, Simon C., and Andrew H. Allibone. "Petrogenesis of orthogneisses in the Dry Valleys region, South Victoria Land." Antarctic Science 3, no. 4 (December 1991): 405–17. http://dx.doi.org/10.1017/s0954102091000500.
Full textAbstract:
Granitoid gneisses intercalated with Koettlitz Group metasediments in the upper Ferrar, Taylor and Wright valleys of South Victoria Land comprise various hornblende+biotite orthogneisses and biotite orthogneisses, including the km-scale Dun and Calkin plutons. K-feldspar megacryst inclusion textures and discordant cross-cutting relationships with enclosing metasediments are interpreted as firm evidence of an intrusive origin for hornblende+biotite and biotite orthogneiss. The scale of several concordant orthogneiss bodies (including the Dun and Calkin plutons), the presence of mafic enclaves, and relict flow differentiation in hornblende+biotite orthogneiss are also compatible with a plutonic origin. Orthogneisses were emplaced prior to deformation that produced macroscopic upright, tight, folds about NW-trending axes. Petrography and geochemistry indicate I-type affinities for hornblende+biotite orthogneisses and the Dun Pluton. Hornblende+biotite and biotite orthogneisses (with the exception of the Dun Pluton) are part of a single petrogenetic suite, together with younger Bonney, Valhalla, and Hedley plutons. Emplacement of a continuum of I-type intrusives is envisaged which spanned Koettlitz Group deformation, and possibly caused much of the deformation. Hornblende+biotite and biotite orthogneisses are deformed precursors to the younger Bonney, Valhalla, and Hedley plutons. The Dun Pluton contains Fe-rich salitic clinopyroxene relicts and exhibits a unique geochemistry. It is rich in Sr, Al2O3, Na2O, and poor in FeO, K2O, Rb, Y, V. Chemical and petrographic features indicate an evolved body, possibly derived from a primitive source distinct from other orthogneisses and granitoids.
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Govan, V. A., V. Br�zel, M. H. Allsopp, and S. Davison. "A PCR Detection Method for Rapid Identification ofMelissococcus pluton in Honeybee Larvae." Applied and Environmental Microbiology 64, no. 5 (May 1, 1998): 1983–85. http://dx.doi.org/10.1128/aem.64.5.1983-1985.1998.
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ABSTRACT Melissococcus pluton is the causative agent of European foulbrood, a disease of honeybee larvae. This bacterium is particularly difficult to isolate because of its stringent growth requirements and competition from other bacteria. PCR was used selectively to amplify specific rRNA gene sequences of M. pluton from pure culture, from crude cell lysates, and directly from infected bee larvae. The PCR primers were designed from M. pluton 16S rRNA sequence data. The PCR products were visualized by agarose gel electrophoresis and confirmed as originating from M. plutonby sequencing in both directions. Detection was highly specific, and the probes did not hybridize with DNA from other bacterial species tested. This method enabled the rapid and specific detection and identification of M. pluton from pure cultures and infected bee larvae.
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Dunphy, J. M., J. N. Ludden, and R. R. Parrish. "Stitching together the Ungava Orogen, northern Quebec: geochronological (TIMS and ICP–MS) and geochemical constraints on late magmatic events." Canadian Journal of Earth Sciences 32, no. 12 (December 1, 1995): 2115–27. http://dx.doi.org/10.1139/e95-165.
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Late magmatic activity in the Ungava Orogen of northern Quebec is manifest as granitic dykes and small, rare plutons that crosscut all tectono-stratigraphic elements of the orogen. Conventional U–Pb geochronology (thermal ionization mass spectrometry (TIMS)) on one particularly important pluton that cuts all these domains (the Lac Duquet monzogranite) indicates its age of emplacement at 1742.2 ± 1.3 Ma. This undeformed and nonmetamorphosed pluton postdates the youngest structures in the orogen (D4 folds), thereby constraining the timing of the latest deformation to >1742 Ma. Laser ablation inductively coupled plasma–mass spectrometry (ICP–MS) on zircons from the same sample identified a large range in 207Pb/206Pb ages of inherited grains from 1.7 to 3.2 Ga, corresponding to the ages of the host rocks for the pluton. This high-K peraluminous monzogranite pluton contains moderate to high concentrations of large ion lithophile elements and fractionated and enriched light rare earth elements, similar in composition to the surrounding continental crust and to other crustally derived granites. Initial 87Sr/86Sr values of 0.7040–0.7051 and εNd ranging from −4.4 to −9.7 indicate incorporation of a significant amount of older material in the petrogenesis of the pluton. It is proposed that anatexis of the surrounding continental crust due to structural thickening during the waning stages of the Ungava orogeny resulted in the generation of the Lac Duquet pluton and was the source for its inherited zircons.
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Grammatikopoulos, A. L., Sandra M. Barr, P. H. Reynolds, and R. Doig. "Petrology and age of the Mechanic Settlement Pluton, Avalon terrane, southern New Brunswick." Canadian Journal of Earth Sciences 32, no. 12 (December 1, 1995): 2147–58. http://dx.doi.org/10.1139/e95-167.
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The Mechanic Settlement Pluton, located at the northern margin of the Caledonian Highlands in southern New Brunswick, is composed of rocks ranging from ultramafic (lherzolite, plagioclase-bearing lherzolite) through mafic (mainly olivine gabbronorite and gabbro) to intermediate (quartz diorite and monzodiorite). Spatial distribution of these lithologies, textural features, and geochemistry are consistent with evolution of a tholeiitic mafic parent magma by crystal fractionation processes, with some evidence for magma mingling between evolved gabbroic and quartz dioritic magmas. The dioritic rocks form most of the southwestern (upper?) part of the pluton, whereas the varied gabbroic rocks with ultramafic layers form the northeastern part. U–Pb (zircon) dating of a quartz diorite sample from the southwestern part of the pluton indicates crystallization at 557 ± 3 Ma. Amphibole and phlogopite in two lherzolite samples from the northeastern part of the pluton gave 40Ar/39Ar dates of 550 ± 5 and 539 ± 5 Ma, respectively, indicating that the pluton cooled rapidly through the closure temperature for amphibole, with subsequent slower cooling to the time of phlogopite closure. The pluton is interpreted to be the intrusive equivalent of basaltic units in the host Coldbrook Group, analogous to granitic plutons elsewhere in the Caledonian Highlands which appear to be the intrusive equivalents of felsic volcanic rocks in the group. These plutonic and volcanic rocks represent a major, short-lived (ca. 560–550 Ma), dominantly bimodal igneous event, apparently related to late Precambrian extension within the Avalon terrane of southern New Brunswick.
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Zamanian, Hassan, and Behrooz Asadollahi. "Geochemistry and ore potential of the Almoughlagh batholith, western Iran." Geologos 19, no. 3 (September 1, 2013): 229–42. http://dx.doi.org/10.2478/logos-2013-0014.
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Abstract The Almoughlagh batholith intruded the dioritic Baba Ali pluton during the Oligo-Miocene; the pluton and is now exposed as a big enclave within the batholith. The pluton intruded the Songhor Series during the Late Kimmeridgian (~136 Ma) orogeny. The intrusion by the batholith transformed the diorite to metadiorite and the impure carbonate units of the Songhor Series. The batholith consists of rock types such as quartz syenite and syenogranite, which have a low average quartz content, and which are metaluminous to peraluminous and calc-alkaline in composition. Comparison of the compositions of the Almoughlagh batholith and the pluton with its Cu, Mo, Fe, Sn, W, Au, and Zn skarn deposits, indicates that the Baba Ali diorite geochemically shows much resemblance with those which could bring about Fe-Cu skarn mineralization, whereas the compositions of the Almoughlagh granitoids resembles those of the plutons associated with Mo and Zn skarn deposits. The associated hydrothermal activity related to the Almoughlagh batholith culminated in magnetite mineralisation in the Baba Ali and the Chenar mines in which copper mineralisation also is considerable.
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Perpétuo, Marcela Paschoal, Wagner da Silva Amaral, Felipe Grandjean da Costa, Evilarde Carvalho Uchôa Filho, and Daniel Francisco Martins de Sousa. "Geochemistry of the Serra das Melancias Pluton in the Serra da Aldeia Suite: a classic post-collisional high Ba-Sr granite in The Riacho do Pontal Fold Belt, NE Brazil." Brazilian Journal of Geology 46, no. 2 (June 2016): 221–37. http://dx.doi.org/10.1590/2317-4889201620160002.
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ABSTRACT: The Serra da Aldeia Suite is composed by circular or oval-shaped plutons, intrusive in meta-sedimentary and meta-volcanosedimentary rocks in the Riacho do Pontal Fold Belt, NE Brazil. The Serra das Melancias Pluton, belonging to Serra da Aldeia Suite, is located southeastern of Piaui state, near Paulistana city. These plutons represent a major magmatic expression in this area and contain important information about the late magmatic/collisional geologic evolution of the Brasiliano Orogeny. Based on petrographic and geochemical data, three facies were defined in the Serra das Melancias Pluton: granites, syenites and quartz monzonites. The rocks display high-K and alkaline to shoshonitic affinities, are metaluminous and show ferrous character. They are enriched in Light Rare Earth Elements and Large Ion Lithophile Elements, with negative anomalies in Nb, Ta and Ti. Their high Ba, Sr, K/Rb, low Rb, relatively low U, Th, Nb to very low Heavy Rare Earth Elements and Y resemble those of typical high Ba-Sr granitoids. The geochemical data suggest the emplacement of Serra das Melancias Pluton in a transitional, late to post-orogenic setting in the Riacho do Pontal Fold Belt during the late Brasiliano-Pan African Orogeny.
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Moran, Patrick C., Sandra M. Barr, Chris E. White, and Michael A. Hamilton. "Petrology, age, and tectonic setting of the Seal Island Pluton, offshore southwestern Nova Scotia." Canadian Journal of Earth Sciences 44, no. 10 (October 1, 2007): 1467–78. http://dx.doi.org/10.1139/e07-023.
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The Seal Island Pluton outcrops only on small islands located on the continental shelf 45 km south of Nova Scotia, although geophysical data indicate that the pluton is part of large granitoid units that cover thousands of square kilometres farther offshore. Based on the island outcrops, the Seal Island Pluton consists of biotite monzogranite and muscovite–biotite monzogranite of uncertain relative age. Metasedimentary xenoliths combined with characteristic magnetic patterns indicate that the pluton intruded the Cambrian–Ordovician Meguma Group. Compared with the biotite monzogranite, the muscovite–biotite monzogranite is higher in SiO2, more peraluminous, and more depleted in heavy rare-earth elements, and also has lower εNd (–1.39 versus +0.82), possibly the result of more contamination by Meguma Group sedimentary rocks. The biotite monzogranite yielded a Late Devonian U–Pb (zircon) age of 362.8 ± 0.7 Ma. Although the relatively minor petrological differences between the two units do not preclude a co-magmatic relationship, the muscovite–biotite monzogranite could be 10–15 Ma older than the biotite monzogranite, based on its petrological similarities to parts of the onshore ca. 376–372 Ma Shelburne and Port Mouton plutons. Comparison with granite samples in offshore drill core indicates that granitoid rocks similar to those exposed on Seal and surrounding islands form part of large plutons farther offshore in the Meguma terrane. The age and petrochemical data from both onshore and offshore plutons indicate that peraluminous granitoid rocks in the Meguma terrane were derived from similar sources over a span of at least 20 million years. Magma genesis may have been related to mantle upwelling and stepping back of the subduction zone to the southeast subsequent to docking of Meguma terrane with adjacent Avalonia.
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Mathieu, Lucie, and Denis Racicot. "Petrogenetic Study of the Multiphase Chibougamau Pluton: Archaean Magmas Associated with Cu–Au Magmato-Hydrothermal Systems." Minerals 9, no. 3 (March 12, 2019): 174. http://dx.doi.org/10.3390/min9030174.
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The Chibougamau pluton is a Neoarchean multiphase intrusion that is related to Cu–Au porphyry-style deposits. In Archean greenstone belts, porphyries are marginal and poorly documented mineralizations. Such deposits are, however, important in the Chibougamau area, where the main historical mining camp (Central Camp) is a magmato-hydrothermal system. Understanding such systems requires documenting the related magmatic rocks. This contribution focuses on the petrogenesis of the Chibougamau pluton to elucidate how the intrusion participated in Cu and Au mineralized systems. Using field descriptions, whole-rock analyses, and petrographic observations, we describe the source, emplacement mechanism, and chemical evolution of the Chibougamau pluton. The Chibougamau pluton is a TTD (tonalite-trondhjemite-diorite) suite that contains more K than most plutons of similar age. This suite was produced from a heterogeneous source; i.e., a hydrated basalt and possibly a metasomatized mantle. These are rare (and thus prospective) characteristics for an Archean intrusion. In addition, differentiation may have been sufficiently prolonged in the diorite phase to concentrate metals and fluids in the evolved magma. These magmatic constraints must now be tested against a renewed understanding of the Cu-dominated mineralized systems of the Chibougamau area.
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Dokuz, Abdurrahman, Faruk Aydin, and Orhan Karslı. "Postcollisional transition from subduction- to intraplate-type magmatism in the eastern Sakarya zone, Turkey: Indicators of northern Neotethyan slab breakoff." GSA Bulletin 131, no. 9-10 (April 11, 2019): 1623–42. http://dx.doi.org/10.1130/b31993.1.
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Abstract Postcollisional magmatism in the eastern Sakarya zone was recorded by voluminous basic volcanism and repeated plutonism during the early Cenozoic. The temporal and geochemical evolution of these magmatic rocks is important for understanding the possible geodynamic history of the Sakarya zone. Here, we investigated three representative plutons lying between the towns of Çamlıhemşin (Rize) and İspir (Erzurum), Turkey. These are largely composed of medium-K gabbroic diorites (Marselavat Pluton), shoshonitic monzonites (Güllübağ Pluton), and high-K granites (Ayder Pluton). We present whole-rock geochemistry, 40Ar/39Ar geochronology, and Sr, Nd, and Pb isotope analyses from the plutons to constrain the timing of variations in magmatism and source characteristics, and we provide a new approach to the proposed geodynamic models, which are still heavily debated. The 40Ar/39Ar geochronology reveals a cooling sequence from ca. 45 Ma for the Marselavat Pluton through ca. 41 Ma for the Güllübağ Pluton to ca. 40 Ma for the Ayder Pluton. Whole-rock geochemistry and Sr, Nd, Pb isotopes suggest that crustal contamination was not an important factor affecting magma compositions. Although there was no arc-related tectonic setting in the region during the middle Eocene, the Marselavat Pluton shows some subduction affinities, such as moderately negative Nb and Ta anomalies, and slightly positive Pb anomalies. These signatures were possibly inherited from a depleted mantle source that was modified by hydrous fluids released from the oceanic slab during Late Cretaceous subduction. Geochemical traces of the earlier subduction become uncertain in the Güllübağ samples. They display ocean-island basalt–like multi-element profiles and Nb/Ta, Ce/Pb, and La/Ba ratios. All these point to a mantle source in which earlier subduction signatures were hybridized by the addition of asthenospheric melts. Melting of calc-alkaline crustal material, probably emplaced during the first phase of middle Eocene magmatism (Marselavat), led to the formation of granitic plutonism (Ayder Pluton). Our data in conjunction with early Eocene adakite-like rocks show that melt generation, as in the given sequence, was most probably triggered by breakoff of the northern Neotethyan oceanic slab, ∼13 m.y. after the early Maastrichtian collision between the Sakarya zone and Anatolide-Tauride block, and continued until the end of the middle Eocene. A shallow-marine transgression occurred contemporaneously with the middle Eocene magmatism throughout the Sakarya zone. An extension in this magnitude seems unlikely to be the result of orogenic collapse processes only. The main cause of this extension was most probably related to the northward subduction of the southern Neotethys Ocean beneath the Anatolide-Tauride block. The result is a volumetrically larger amount of middle Eocene magmatism than that expected in response to slab breakoff.
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Brown, E. H. "Magma Loading in the Southern Coast Plutonic Complex, British Columbia and Washington." Lithosphere 2020, no. 1 (November 10, 2020): 1–17. http://dx.doi.org/10.2113/2020/8856566.
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Abstract The southen end of the 1800 km long Coast Plutonic Complex (CPC), exposed in the Harrison Lake area of British Columbia and in the North Cascades of Washington, bears a record of great crustal thickening -20 to 40 km in localized zones during Late Cretaceous times. During this period, the CPC was positioned at the continental margin during collision/subduction of the Farallon plate. Arc magmatism and regional orogenic contraction were both active as potential crustal thickening processes. Magmatism is favored in this report as the dominant factor based on the delineation of four spatially and temporally separate loading events, the close association of the loaded areas with emplacement of large plutons, and a paucity of evidence of deep regional tectonic contraction. The timing and spatial location of crustal loading events are documented by the following: zircon ages in plutons; an early event of low pressure in pluton aureoles evidenced by andalusite, now pseudomorphed by high-pressure minerals; high pressures in country rock in pluton aureoles measured by mineral compositions in the assemblages garnet-biotite-muscovite-plagioclase and garnet-aluminum silicate-plagioclase; high pressures recorded in plutons by Al-in-hornblende barometry; and uplift ages of plutons derived from K-Ar and Ar-Ar ages of micas and hornblende in plutons.
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Symons, David TA, Philippe Erdmer, and Phil JA McCausland. "New 42 Ma cratonic North American paleomagnetic pole from the Yukon underscores another Cordilleran paleomagnetism-geology conundrum." Canadian Journal of Earth Sciences 40, no. 10 (October 1, 2003): 1321–34. http://dx.doi.org/10.1139/e03-047.
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Eocene posttectonic plutons of the Beaver River alkalic complex in southeastern Yukon intruded DevonianMississippian and Triassic sandstones in the Foothills of the Canadian Cordillera. A paleomagnetic collection of 27 sites from three separate plutons produced 326 specimens that were analyzed using alternating field and thermal step demagnetization methods. The A component characteristic remanent magnetization (ChRM) resides in magnetite with normal polarity in the 42.6 ± 0.8 Ma Beaver River pluton, reversed polarity in the 42.1 ± 0.7 Ma Larson Creek East pluton, and both polarities in the 41.3 ± 0.4 Ma Larson Creek West pluton, corresponding with magnetic polarity chrons 20n, 19r, and the boundary between chron 19r and 18n, respectively. The ChRMs of the plutons are indistinguishable (2σ) with a mean for the 42.0 ± 0.5 Ma complex of D = 158.8°, I = 73.1° (N = 21 sites, α95 = 3.0°, k = 116.8). A positive paleomagnetic contact test shows the A component to be primary, and the poorly isolated B component suggests the host rocks for Larson Creek West are Early to Middle Devonian. The paleopole for the Beaver River complex at 79.2°N, 145.8°E (N = 21, dp = 4.8°, dm = 5.4°; Q = 7) is concordant with interpolated 42 Ma reference poles for the North American craton. In contrast, paleopoles from the accreted Intermontane and eastern Coast Belt terranes record clockwise rotations of 24° ± 10° (Eocene) and 13° ± 5° (OligocenePliocene), indicating that the allochthonous Intermontane terranes have been progressively driven ~240 ± 120 km eastwards up and over pericratonic and cratonic North American lower crust by Pacific plate subduction since the mid-Eocene.
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Schöpa, Anne, Catherine Annen, John H. Dilles, R. Stephen J. Sparks, and Jon D. Blundy. "Magma Emplacement Rates and Porphyry Copper Deposits: Thermal Modeling of the Yerington Batholith, Nevada." Economic Geology 112, no. 7 (November 1, 2017): 1653–72. http://dx.doi.org/10.5382/econgeo.2017.4525.
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Abstract Many porphyry copper deposits are associated with granitoid plutons. Porphyry copper deposit genesis is commonly attributed to degassing of pluton-forming intermediate to silicic magma chambers during slow cooling and crystallization. We use numerical simulations of thermal evolution during pluton growth to investigate the links between pluton construction, magma accumulation and solidification, volatile release, and porphyry copper deposit formation. The Jurassic Yerington batholith, Nevada, serves as a case study because of its exceptional exposure, revealing the geometry of three main intrusions. The last intrusion, the Luhr Hill granite, is associated with economic porphyry copper deposits localized over cupolas where dikes and fluid flow were focused. Our simulations for the conceptual model linking porphyry copper deposits with the presence of large, highly molten magma chambers show that the Luhr Hill granite must have been emplaced at a vertical thickening rate of several cm/yr or more. This magma emplacement rate is much higher than the time-averaged formation rates of other batholiths reported in the literature. Such low rates, although common, do not lead to magma accumulation and might be one of the reasons why many granitoid plutons are barren. Based on our results, we formulate the new testable hypothesis of a link between porphyry copper deposit formation and the emplacement time scale of the associated magma intrusion.
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Bartley, John M., Drew S. Coleman, and Allen F. Glazner. "Incremental pluton emplacement by magmatic crack-seal." Transactions of the Royal Society of Edinburgh: Earth Sciences 97, no. 4 (December 2006): 383–96. http://dx.doi.org/10.1017/s0263593300001528.
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ABSTRACTA growing body of evidence indicates that some, and perhaps most, plutons are highly composite. However, the geometrical forms of increments and the processes by which they are added are poorly known. Magmatic crack-seal probably is an important incremental assembly process, particularly in the upper crust where wall-rock fracture is important. Evidence for magmatic crack-seal is clearest where it is antitaxial, i.e., new fractures form at the contact between wall rock and a growing intrusion. Local deviation of antitaxial cracks into wall rocks isolates wall-rock bodies that therefore mark increment contacts. Wall rock isolated by this process remains in situ and thus is likely to preserve a ghost stratigraphy. Previously described plutons are identified, and interpreted to have grown by antitaxial magmatic crack-seal. In contrast, it remains unclear what observable geological record may remain in plutons formed by syntaxial crack-seal, in which new cracks form in the middle of the growing pluton. Several plutons are identified that preserve possible indirect evidence for growth by syntaxial crack seal, but conclusive identification of a direct record of the process remains elusive. However, plutons with sharp discordant contacts but few xenoliths may have been emplaced incrementally by syntaxial magmatic crack-seal.
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Clarke, D. Barrie, Raymond Fallon, and Larry M. Heaman. "Interaction among upper crustal, lower crustal, and mantle materials in the Port Mouton pluton, Meguma Lithotectonic Zone, southwest Nova Scotia." Canadian Journal of Earth Sciences 37, no. 4 (April 3, 2000): 579–600. http://dx.doi.org/10.1139/e99-124.
Full textAbstract:
The Port Mouton pluton is unique among the Late Devonian peraluminous granitoid bodies in the Meguma Lithotectonic Zone of southwestern Nova Scotia in its lithological heterogeneity, extensive physical and chemical interaction with the country rocks, clear evidence for mingling and mixing with mafic magmas, and highly abundant pegmatites. New UPb age determinations on monazite establish an intrusion age of 373 ± 1 Ma, similar to the ages of other Meguma Lithotectonic Zone granitoid plutons and mafic intrusions. Field relations, petrology, and geochemistry define three stages of intrusion of the Port Mouton pluton: (i) early stage, discontinuously exposed around the outer margin of the pluton, dominated by coarse-grained tonalite-granodiorite, and with Rb/Sr < 0.55, Eu/Eu* > 0.40, and GdN/LuN < 2; (ii) middle stage, occupying the interior of the pluton, dominated by medium-grained granodiorite-monzogranite, and with Rb/Sr > 0.55, Eu/Eu* < 0.40, and GdN/LuN > 2; and (iii) late stage, consisting of abundant minor sheets throughout the pluton, dominated by fine-grained tonalite, granodiorite, and leucogranite that are similar to rocks of the early and middle stages. The Port Mouton pluton shows a wider range of 87Sr/86Sri (0.7036-0.7154), and a wider range and generally higher εNdi (3.72 to +2.12), than other granitoid rocks in the Meguma Lithotectonic Zone, potentially reflecting a complex, partially equilibrated, interaction among mantle, lower crust, and upper crust. Field, petrological, and chemical evidence for the involvement of mantle-derived magmas and melting of upper crust permit modelling of the Port Mouton pluton granitoid compositions by three simultaneous mixing equations. These mixing model results suggest that the early stage granitoid rocks can form from simple three-component mixing relationships when the bulk distribution coefficients between residuum and melt for Sr and Nd range from 1.05 to 1.18, or two-component mixing combined with fractionation of material like the known felsic lower crust. The middle stage granitoid rocks only yield solutions involving two-component mixing and fractionation of material unlike the known felsic lower crust. We conclude that the Late Devonian mafic magmas played a major role in the formation of granitoid magmas in the Meguma Lithotectonic Zone by supplying heat and material to cause partial fusion of the Avalon lower crust.
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Auréjac, Jean-Baptiste, Gérard Gleizes, Hervé Diot, and Jean-Luc Bouchez. "The Quérigut Complex (Pyrenees, France) revisited by the AMS technique : a syntectonic pluton of the Variscan dextral transpression." Bulletin de la Société Géologique de France 175, no. 2 (March 1, 2004): 157–74. http://dx.doi.org/10.2113/175.2.157.
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Abstract The Variscan Querigut Pluton (eastern Axial Zone, Pyrenees), recently dated at 307 ± 2 Ma, is a classical example for the structural study of granitoids. We present a new structural analysis of this pluton using the powerful technique of magnetic susceptibility anisotropy (AMS). A model of pluton emplacement is proposed on the basis of complementary microstructural analyses allowing the determination of the temperatures of fabric acquisition in the magmatic units, and of the shear sense criteria in the surrounding country rocks. This pluton is constituted by two main units that have intruded metasedimentary rocks where regional metamorphic conditions decrease from southwest to northeast. A well-foliated southern granodioritic unit, rich in Devonian marble xenoliths, is bounded to the south by Cambro-Ordovician metapelites. A weakly foliated northern monzogranitic unit, bounded to the north by Devonian marbles, comprises two sub-types : an outer biotite-monzogranite and an inner biotite-muscovite leucomonzogranite. Abundant basic stocks of variable sizes and lithologies outcrop in the granodioritic unit and in the southern part of the monzogranitic unit. Mean magnetic susceptibility and magnetic foliation maps show a very good agreement with the previous compiled petrographic and structural maps, strengthening the validity of the AMS technique. The northern monzogranitic units display two unevenly distributed structural patterns : (a) a NE-SW-trending pattern of weakly to steeply dipping foliations, dominant in the outer biotite monzogranite, is associated to subhorizontal NE-SW lineations ; and (b) a NW-SE-trending pattern of steeply dipping foliations, dominant in the inner biotite-muscovite monzogranite, is concentrated in NW-SE elongated corridors, associated to subhorizontal NW-SE lineations. In the southern granodioritic unit, foliation patterns follow roughly both the main regional foliation pattern and the pluton boundary, with foliation dips increasing to the south. Subhorizontal NW-SE trending magnetic lineations in the inner parts of this unit, are progressively verticalized toward the southern pluton boundary. A progressive increase in total magnetic anisotropy is observed toward the border of the pluton, correlated with both an increase in solid-state deformation and a decrease of the final temperature of fabric acquisition. These features result from a pluri-kilometric shear zone localized in the western half of the granodioritic unit, decreasing in thickness in its eastern half and along N060oE trending contacts with the country rocks. In the northern monzogranitic unit, one can roughly correlate the magmatic microstructures to the NE-SW trending fabric, and the superimposed subsolidus microstructures to the NW-SE-trending corridors, where rather low-temperature (< 300 oC) fluid-assisted cataclastic microstructures may also appear. The country-rocks, half kilometer away from the pluton border, display the D2 regional Variscan pattern, with subvertical and N110oE-striking foliations and subhorizontal and E-W-trending stretching lineations associated to a dextral shear. Closer to the pluton, the country-rocks are subjected to the pluton influence, particularly along the southern border where a strong flattening is associated to subvertical lineations related to local thrusting of the pluton onto its country rocks. An emplacement model is proposed through the injection of three principal magma batches (granodiorite, biotite-monzogranite and biotite-muscovite monzogranite) that successively and progressively built up the pluton while the whole region was subjected to a dextral and compressive deformation regime, in agreement with AMS results obtained from several other plutons of the Pyrenees.
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Ravat, D. N., L. W. Braile, and W. J. Hinze. "Earthquakes and Plutons in the Midcontinent - Evidence From the Bloomfield Pluton, New Madrid Rift Complex." Seismological Research Letters 58, no. 2 (April 1, 1987): 41–52. http://dx.doi.org/10.1785/gssrl.58.2.41.
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Abstract A three-dimensional gravity and magnetic model of the Bloomfield Pluton near New Madrid, Missouri, has been generated that provides an excellent match to the observed gravity and magnetic anomaly maps. Although this modeling is inherently non-unique, the steep gradients on the flanks of the anomalies constrain the causative body to a relatively shallow depth (≈2 km) and define the outline of the steep-sided (near-vertical) pluton. Comparison of the configuration of the Bloomfield Pluton with concentrated microearthquake seismicity in part of the New Madrid Seismic Zone indicates that earthquakes in the northern part of the zone occur primarily on the southeastern side of the pluton at about 10 km from the edge of the body. Based on the location of hypocenters and earthquake focal mechanisms, there is no evidence that stress concentration associated with the mass excess of the pluton is the cause of earthquakes near the pluton. The seismicity may be along zones of weakness independent of the pluton. Among other explanations investigated to explain the constant distance of earthquakes from the pluton, we favor the possibility of a zone of rigidity contrast caused by the thermal metamorphism of the country rock associated with the pluton intrusion. We have estimated increased temperatures of the country rock using an instantaneous intrusion model. Maximum anomalous country rock temperatures of greater than 100°C dominated the region within 10 km of the pluton edge. This ‘thermally metamorphosed’ aureole may provide sufficient homogeneity in the upper crust to localize anomalous stresses away from the margin and along the most favorable zones of weakness, thus influencing the locations of earthquakes.
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Jamieson, R. A., O. van Breemen, R. W. Sullivan, and K. L. Currie. "The age of igneous and metamorphic events in the western Cape Breton Highlands, Nova Scotia." Canadian Journal of Earth Sciences 23, no. 12 (December 1, 1986): 1891–901. http://dx.doi.org/10.1139/e86-177.
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Plutonic rocks of four different ages have been recognized in the Cape Breton Highlands on the basis of U–Pb dating of zircons. Two plutons, the North Branch Baddeck River leucotonalite [Formula: see text] and the Chéticamp pluton (550 ± 8 Ma), give dates that fall within the range of Late Proterozoic to Cambrian ages considered characteristic of the Avalon tectonostratigraphic zone of the eastern Appalachians. Late Ordovician to Silurian tonalite (Belle Côte Road orthogneiss, 433 ± 20 Ma) was metamorphosed, deformed, and incorporated into the central Highlands gneiss complex by approximately 370–395 Ma. High-level subvolcanic plutons (Salmon Pool pluton, [Formula: see text]) postdate all metamorphic rocks in the area. The presence of the older plutons is consistent with interpretation that the Cape Breton Highlands form part of the Avalon zone, but the presence of Ordovician–Silurian plutonic rocks and Devonian amphibolite-facies metamorphism is anomalous in comparison with the Avalon zone of Newfoundland and southeastern Cape Breton Island. Terranes with similar Late Proterozoic to mid-Paleozoic plutonic and metamorphic histories form a discontinuous belt along the northwest side of the Avalon zone southwest of Cape Breton Island. These rocks probably reflect events during and after the accretion of the Avalon zone to North America.
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Smith, I. E. M., A. J. R. White, B. W. Chappell, and R. A. Eggleton. "Fractionation in a zoned monzonite pluton: Mount Dromedary, southeastern Australia." Geological Magazine 125, no. 3 (May 1988): 273–84. http://dx.doi.org/10.1017/s0016756800010219.
Full textAbstract:
AbstractMount Dromedary pluton is one of several predominantly monzonite plutons and smaller intrusive bodies which constitute the Dromedary igneous complex in southeastern New South Wales. The pluton exhibits a striking arrangement of petrographically, but not always chemically, distinct zones ranging from mafic monzonite at the outside to quartz monzonite in the centre. The rocks display a mineralogical and geochemical integrity which indicates a consanguineous relationship. Minor compositional discontinuities between zones, together with observed and inferred minor intrusive zone boundaries, suggest that each zone has to some extent evolved independently. Negative Eu anomalies in REE abundance patterns show that some of the zones have been affected by fractionation of feldspar, but complementary accumulates are not found at the present levels of exposure. The pattern of zoning can be explained by a process of shallow fractional crystallization in which variations within zones are the result of lateral accretion of alkali feldspar as well as settling and/or lateral accretion of mafic phases at lower levels in the intrusion and upward displacement of fractionated magma. The parental magma of the pluton probaby originated by partial melting of an alkali basalt composition with an amphibolite mineralogy at the base of the crust.
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Peytcheva, Irena, Elena Tacheva, Albrecht von Quadt, and Rossen Nedialkov. "U-Pb zircon and titanite ages and Sr-Nd-Hf isotope constraints on the timing and evolution of the Petrohan-Mezdreya pluton (Western Balkan Mts, Bulgaria)." Geologica Balcanica 47, no. 2 (November 2018): 25–46. http://dx.doi.org/10.52321/geolbalc.47.2.25.
Full textAbstract:
A combination of methods is applied in the present study to define the exact age of the Petrohan and Mezdreya plutons and trace their magma evolution. Field, petrological, and geochemical studies of the Petrohan pluton revealed its complex evolution and emphasized the role of magma mingling and mixing, complementary to the normal assimilation and fractional crystallization (AFC) processes. Using high-precision conventional U-Pb (CA)-ID-TIMS zircon and titanite dating in combination with CA-LA-ICP-MS zircon dating and tracing, we suggest an incremental growth of a common Petrohan-Mezdreya pluton. It was assembled over minimum 4.5 Ma from 311.14±0.48 Ma to 307.54±0.54 Ma. The younger age of the gabbro (308.12±0.33 Ma), compared with the age of granodiorites (311.14±0.48 Ma), provides numerical proofs for magma replenishment during the assembling of the Petrohan pluton. Whole-rock strontium-neodymium (initial 87Sr/86Sr ratios of 0.70521–0.70527 to 0.70462 and 143Nd/144Nd of 0.51221 to 0.51210) and Hf-zircon isotope data (ε-Hf from –5.8 to +3.6) argue for interaction of mantle derived magma with crustal melts but also mixing and mingling and transfer of zircon grains between the gabbroic and granitic melts. Possible petrogenetic scenario includes melting of subcontinental mantle lithosphere and crust and evolution trough AFC, FC and mingling/mixing processes. Considering the Petrohan-Mezdreya pluton as part of the Variscan orogeny in SE Europe, our new data support the accretion/collision of both the Balkan and Sredna Gora/Getic units with Moesia in the Early Carboniferous followed by syn- and post-collisional Carboniferous and Permian magmatism.
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Poujol, M., J. Jaguin, J.-F. Moyen, P. Boulvais, and J.-L. Paquette. "Archaean S-Type granites: petrology, geochemistry and geochronology of the Lekkersmaak and Willie plutons, Kaapvaal Craton, South Africa." South African Journal of Geology 124, no. 1 (March 1, 2021): 87–110. http://dx.doi.org/10.25131/sajg.124.0004.
Full textAbstract:
Abstract S-type granites correspond to reworking of pre-existing continental material and form by partial melting of (meta)sediments. Early-to-mid Archaean S-type granites are rare and are more frequently found, usually as relatively small intrusions, during the Neoarchaean and the Archaean-Proterozoic transition. In the context of Archaean geology, their paucity is therefore significant, in that it matches the uncommon nature of processes during this period. In this study, we focus on the Late Mesoarchaean Willie pluton and Neoarchaean Lekkersmaak pluton, which crop out to the south of the Murchison Greenstone Belt in the Northern Kaapvaal Craton, South Africa. These intrusions represent the oldest S-type plutons known so far in the region. We constrain their petrogenesis by documenting their petrology, mineralogy (mineral composition), geochemistry (major and trace elements, Sr, Nd and O isotopes) and zircon U-Pb geochronology. The large Lekkersmaak and smaller Willie plutons represent two granites sharing many geochemical characteristics; they are both peraluminous, Ms-bearing S-type granites although they are more sodic and less potassic than typical S-type granites. The Willie granite was emplaced 2 816 ± 9 Ma ago while the Lekkersmaak yielded an emplacement age of 2 771 ± 2 Ma. Therefore, S-Type magmatism in the area occurred twice at 2.82 Ga and then 40 Myr later at 2.77 Ga, involving comparable immature metasedimentary sources and conditions of partial melting. Finally, a sample from the Lekkersmaak pluton devoid of S-type features as it is muscovite-free and aluminum poor was emplaced 2 734 ± 11 Ma ago. This confirms the episodic nature of magmatic activity south of the Murchison Greenstone Belt.
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Smillie, Robert W. "Suite subdivision and petrological evolution of granitoids from the Taylor Valley and Ferrar Glacier region, south Victoria Land." Antarctic Science 4, no. 1 (March 1992): 71–87. http://dx.doi.org/10.1017/s0954102092000130.
Full textAbstract:
Detailed geological mapping and geochemical analysis of early Palaeozoic granitoid plutons and dykes from the Taylor Valley and Ferrar Glacier region in south Victoria Land reveal two distinct suites. This suite subdivision-approach is a departure from previous lithology-based schemes and can be applied elsewhere in south Victoria Land. The older calc-alkaline Dry Valleys 1 suite is dominated by the compositionally variable Bonney Pluton, a flow-foliated concordant pluton with an inferred length of over 100 km. Plutons of this suite are elongate in a NW-SE direction and appear to have been subjected to major structural control during their emplacement. The younger alkali-calcic Dry Valleys 2 suite comprises discordant plutons and numerous dyke swarms with complex age relationships. Field characteristics of this suite indicate that it was passively emplaced into fractures at higher levels in the crust than the Dry Valleys 1 suite. Whole-rock geochemistry confirms this suite subdivision based on field relationships and indicates that the two suites were derived from different parent magmas by fractional crystallization. The Dry Valleys 1 suite resembles Cordilleran I-type granitoids and is inferred to be derived from partial melting of the upper mantle and/or lower crust above an ancient subduction zone. The Dry Valleys 2 suite resembles Caledonian I-type granitoids and may have resulted from a later episode of crustal extension.
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Pe-Piper, Georgia. "Mineralogy of an Appinitic Hornblende Gabbro and Its Significance for the Evolution of Rising Calc-Alkaline Magmas." Minerals 10, no. 12 (December 3, 2020): 1088. http://dx.doi.org/10.3390/min10121088.
Full textAbstract:
The magmatic and sub-solidus evolution of calcic amphiboles and Fe–Ti oxides was investigated in the Neoproterozoic Frog Lake pluton, Nova Scotia, Canada, in order to understand the relationship between the history of hydrous magma and the resulting mineralogy. The pluton occurs as sheet-like bodies of hornblende gabbro and hornblendite, with lesser tonalite dykes and granite bodies, interlayed with screens of medium-grade metamorphic country rock. Small, diffuse clots of felsic minerals are present in the gabbro. The subsolidus growth of actinolite occurs in early clinopyroxenes and amphiboles. Ilmenite is the dominant Fe–Ti oxide, as interstitial magmatic crystals. The increase of Mn towards the margin of the ilmenite crystals indicates a gradual increase in oxygen fugacity with time, leading to the precipitation of titanite and ferrohypersthene. The replacement of titanite by ilmenite and ilmenite lamellae in the amphiboles suggests subsequent reducing conditions during the sub-solidus crystallisation. The gabbros in the coeval, but apparently shallower, Jeffers Brook granodiorite laccolith have dominant magnetite and Mg-rich subsolidus amphiboles, which are indicative of high oxygen fugacity. The differences between the two plutons suggest that there was a greater flux of hydrothermal water through the sheet-like architecture of the Frog Lake pluton.
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Davis, W. J., N. Machado, C. Gariépy, E. W. Sawyer, and K. Benn. "U–Pb geochronology of the Opatica tonalite-gneiss belt and its relationship to the Abitibi greenstone belt, Superior Province, Quebec." Canadian Journal of Earth Sciences 32, no. 2 (February 1, 1995): 113–27. http://dx.doi.org/10.1139/e95-010.
Full textAbstract:
U–Pb ages for zircon, monazite, and titanite from samples collected from two transects across the Opatica tonalite-gneiss belt in the Superior Province of Quebec indicate that the belt contains rocks that are significantly older than those in the adjacent low-grade northern Abitibi belt. Tonalite and tonalite gneiss, which make up most of the belt, formed over an interval of 100 Ma, from pre-2800 to 2702 Ma. Five samples have ages of ca. 2807 ± 13, 2773 ± 23, [Formula: see text], [Formula: see text], and 2702 ± 3 Ma. Zircon growth at 2718–2721 Ma in the two oldest samples may record an early period of high-grade metamorphism in the belt. Hornblende diorite, monzodiorite, and tonalite plutons were intruded at 2693–2696 Ma, particularly along the southern boundary with the Abitibi belt. These include the Canet pluton at [Formula: see text][Formula: see text] Ma, the Lac Ouescapis pluton at 2693 ± 2 Ma, and the Barlow pluton at 2696 ± 3 Ma. Pink granite plutons and dykes are the youngest intrusive rocks in the belt; three samples have yielded zircon ages of 2690 ± 2 and 2686 ± 4 Ma and a monazite age of 2678 ± 2 Ma. The timing of D1 deformation is bracketed by the age of the youngest gneiss sample containing the D1 structures, at 2702 ± 3 Ma, and the 2690 ± 2 Ma age of a granite dyke that cuts D1 structures. The south-vergent D2 event is recorded in the 2693–2696 Ma plutons and must have occurred synchronously with or after this plutonism. D3 dextral strike-slip movement on the Nottoway River shear zone occurred after 2686 ± 4 Ma, and may be associated with post-regional metamorphic titanite growth at 2672 and 2657 Ma. Titanite ages cluster at 2678–2681 Ma along the Matagami transect and at 2665 Ma north of Chibougamau, and record the time of cooling of the belt below the titanite closure temperature.
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Papadopoulou, L., G. Christofides, Α. Koroneos, M. Bröcker, T. Soldatos, and G. Eleftheriadis. "EVOLUTION AND ORIGIN OF THE MARONIA PLUTON, THRACE, GREECE." Bulletin of the Geological Society of Greece 36, no. 1 (January 1, 2004): 568. http://dx.doi.org/10.12681/bgsg.16754.
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The Maronia pluton is the youngest of the Tertiary plutons that occurred in Thrace. Three rock groups have been distinguished: a basic, an intermediate and an acid one. Based on geochemical and isotopie characteristics, the basic group probably represents a magma that isotopically equilibrated with the intermediate group at a certain point of its evolution. The evolution of the intermediate group can be described by an assimilation-fractional crystallization process (AFC). The acid group represents crustai melts that are not genetically related to the basic and intermediate groups. The emplacement of the pluton is related to post-collisional extension resulting from the subduction of the African under the European plate. The magma source of the basic and intermediate group is considered to be a LI LE- and LREE-enriched subcontinental lithospheric mantle. The acid group has probably derived by the partial melting of crustai rocks and in particular, gneiss.
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Higgins, Michael D., Mohcine Ider, and Otto van Breemen. "U-Pb ages of plutonism, wollastonite formation, and deformation in the central part of the Lac-Saint-Jean anorthosite suite." Canadian Journal of Earth Sciences 39, no. 7 (July 1, 2002): 1093–105. http://dx.doi.org/10.1139/e02-033.
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The Lac-Saint-Jean anorthosite suite (LSJAS) is the largest ensemble of plutons in the Grenville Province. Zircons from a pluton in the central part of the LSJAS yield an age of 1140+105 Ma, which accords with existing 11571142 Ma ages determined from the southern part of the LSJAS. The Du Bras granite is a linear pluton emplaced into the dominantly dextral Pipmuacan shear zone (PSZ). The UPb zircon age of 1148 ± 2 Ma for the Du Bras granite confirms earlier proposals that it is a granophyre, formed at greater depths by partial melting of paragneiss by the heat of the crystallizing anorthosite. Parts of the pluton are strongly deformed by the shear zone, and other parts cut the shear zone. This suggests that the pluton dates one phase of movement of the PSZ. The Canton-St-Onge wollastonite deposit was developed in paragneisses preserved within the PSZ. Titanite from this deposit gives an age of 1163 ± 18 Ma, identical within error to that of the Du Bras granite, indicating that this pluton may have provided the skarn fluids. A second plutonic cycle comprises the post-tectonic Astra granite, which stitches the PSZ, and an amazonite-bearing pegmatite dyke. Zircons gave an age of 1028 ± 2 Ma for the Astra granite. The amazonite-bearing dyke only yielded monazite, one fraction of which gave an age similar to that of the Astra granite. Other fractions record the effects of a thermal event at 10201017 Ma that may be related to a widespread magmatic event. The undeformed Venus de Milot syenitic intrusion yields a UPb age of 988 ± 2 Ma. It was emplaced along the northwest-trending Lac Rioux fault, indicating that one phase of movement occurred before 988 Ma. Another strand of the same fault system also cuts the intrusion, showing later reactivation that may have been associated with the formation of the Saguenay Graben.
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Key, R. M., E. R. Phillips, and B. C. Chacksfield. "Emplacement and thermal metamorphism associated with the post-orogenic Strath Ossian Pluton, Grampian Highlands, Scotland." Geological Magazine 130, no. 3 (May 1993): 379–90. http://dx.doi.org/10.1017/s0016756800020069.
Full textAbstract:
AbstractThe multiphase Strath Ossian Pluton was intruded into metasedimentary rocks of the Neoproterozoic Grampian and Appin groups (Grampian Highlands, Scotland) during Silurian or early Devonian times. Emplacementfollowed the main ductile tectono-thermal history of the area and took place during post-orogenic regional uplift and cooling. Early emplacement of dioritic magma in the northern part of the pluton resulted in migmatization of its immediate country rocks with the generation of new ductile structures. The main granodiorite was then emplaced with magma migrating towards the southeast where wall-rock stoping took place. Elsewhere the pluton created its own space with little stoping or veining. Thermal metamorphism caused by granodiorite emplacement resulted in the progressive development of the assemblage quartz+ plagioclase + biotite+ cordierite +andalusite ± K-feldspar in the metapelitic country rocks. Six prograde mineral assemblage zones are identified in the aureole. Final emplacement of a marginal porphyritic microgranite was accompanied by the release of alkaline fluids into the thermal aureole. This produced sillimanite (fibrolite) in association with hydrous phases such as chlorite and white mica. The development of andalusite and cordierite-bearing assemblages is estimated to have occurred at temperatures of 650±50 °C at an estimated pressure of 3.2±0.5 kbars. An approximately isobaric temperature change of 300±50 °C across the width of the main aureole is deduced. The migmatization close to the plutons margins took place at temperatures of about 700 °C. An estimated depth of emplacement of about 11 km is obtained for the Strath Ossian Pluton. This implies considerable regional uplift both prior to, andimmediately after its emplacement. Thus it has been estimated that at the peak of regional metamorphism, probably during the Ordovician Period, the country rocks were at a depth of 15 to 18.5 km, whereas the early Devonian dykes of the Etive dyke swarm, which cut the Strath Ossian Pluton, were emplaced at, or near surface.
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Behn, Mark D., J. Dykstra Eusden, Jr., and John A. Notte III. "A three-dimensional gravity model of the southern contact of the Sebago pluton, Maine." Canadian Journal of Earth Sciences 35, no. 6 (June 1, 1998): 649–56. http://dx.doi.org/10.1139/e98-010.
Full textAbstract:
The Sebago pluton is a two-mica granite that intruded the metasedimentary rocks of the Central Maine Terrane around 292 Ma. In recent years, geologists have raised an increasing number of questions related to the overall thickness of the Sebago pluton and the position of its subsurface contact with the underlying metasedimentary rocks. Past studies have shown the Sebago pluton to be a thin, 1-2 km thick, subhorizontal sheet dipping 3° to the northeast. This study examines anomalies in the Earth's gravitational field related to the southern portion of the Sebago pluton, specifically to determine the thickness of the pluton and to locate the subsurface contact between the pluton and the underlying metasedimentary rocks. A three-dimensional model shows the thickest portions of the pluton (~1.8 km) to occur at the bottom of a bowl hape along the southwestern contact. Moreover, the model shows the pluton to thin toward the northern and eastern regions of the study area, where the average thickness is less than 0.5 km. The pluton appears to extend southward below the cover of the metasedimentary rocks along the southwestern contact. Thus, contrary to previous models, the Sebago pluton is not a northeasterly dipping sheet of uniform thickness, but rather an arched sheet with an irregular thickness extending beneath the metasedimentary rocks along both its northern and southern contacts. Based on this new geometry, either the relationship of the pluton to the surrounding metamorphic zones must be modified, or the possibility must be considered that the Sebago pluton is actually a composite batholith, composed of a younger (Permian) granite to the north and an older (Carboniferous) granite to the south.
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McCarthy, William, R. John Reavy, Carl T. Stevenson, and Michael S. Petronis. "Late Caledonian transpression and the structural controls on pluton construction; new insights from the Omey Pluton, western Ireland." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 106, no. 1 (March 2015): 11–28. http://dx.doi.org/10.1017/s1755691015000201.
Full textAbstract:
ABSTRACTThe Galway Granite Complex is unique among the British and Irish Caledonian granitoid terranes, as it records punctuated phases of magmatism from ∼425–380 Ma throughout the latest phase of the Caledonian Orogeny. Remapping of the Omey Pluton, the oldest member of this suite, has constrained the spatial distribution and contact relationships of the pluton's three main facies relative to the nature of the host rock structure. The external contacts of the pluton are mostly concordant to the limbs and hinge of the Connemara Antiform. New AMS data show that a subtle concentric outward dipping foliation is present, and this is interpreted to reflect pluton inflation during continued magma ingress. Combined field, petrographic and AMS data show that two sets of shear zones (NNW–SSE and ENE–WSW) cross-cut the concentric foliation, and that these structures were active during the construction of the pluton. We show that regional sinistral transpression at ∼420 Ma would have caused dilation along the intersection of these two fault sets, and suggest that this facilitated centralised magma ascent. Lateral emplacement was controlled by the symmetry of the Connemara Antiform to ultimately produce a discordant phacolith. We propose that regional sinistral transpression at ∼420 Ma influenced the siting of smaller intrusions over NNW–SSE faults, and that the later onset of regional transtension caused larger volumes of magma to intrude along the E–W Skird Rocks Fault at ∼400 Ma.
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ZHANG, SHUAN-HONG, YUE ZHAO, BIAO SONG, and DUN-YI LIU. "Petrogenesis of the Middle Devonian Gushan diorite pluton on the northern margin of the North China block and its tectonic implications." Geological Magazine 144, no. 3 (March 9, 2007): 553–68. http://dx.doi.org/10.1017/s0016756807003275.
Full textAbstract:
The Gushan diorite pluton, located at the northern margin of the North China block, was emplaced during Middle Devonian times (SHRIMP U–Pb zircon age of 390 ± 5 Ma). Rocks from the pluton are characterized by low SiO2 and high alkali contents, and they show monzodiorite compositions in a total alkali v. silica (TAS) plot. They exhibit light REE-enrichment, no to slightly positive Eu anomalies, strong depletion in Rb, Th, U, Nb, Ta, P, Zr, Hf and Ti, enrichment in Ba, K and Sr, low contents of Y and Yb, and high Sr/Y ratios. They have a relatively narrow range of isotopic compositions with initial 87Sr/86Sr ratios of ∼ 0.7050, εNd(T) values of −9.5 to −7.5 and zircon εHf(T) values from −11.8 to −5.8. These features are remarkably similar to another Middle Devonian intrusion, the Shuiquangou syenitic complex at the northern margin of the North China block. These similarities suggest that the two intrusions probably have a common origin. They were considered to be derived from a type I enriched mantle, ultimately with some involvement of ancient lower crustal components, and were likely emplaced in a back-arc extension environment related to southward subduction of the Palaeo-Asian oceanic plate or during the cessation of the subduction. Aluminium-in-hornblende barometry studies of the Middle Devonian Gushan pluton yielded emplacement depths of about 18 km. Combined with previous geobarometry results on the Carboniferous plutons within the Inner Mongolia Palaeo-uplift on the northern margin of the North China block, it is inferred that the uplift and exhumation of the plutons within the Inner Mongolia Palaeo-uplift during Middle Devonian to Late Carboniferous times were not as distinct as those during Late Carboniferous to Early Jurassic times, and the strong uplift and exhumation of the Inner Mongolia Palaeo-uplift were achieved during Late Carboniferous to Early Jurassic times.
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Dallmeyer, R. David, and R. Damian Nance. "Tectonic implications of 40Ar/39Ar mineral ages from late Precambrian – Cambrian plutons, Avalon composite terrane, southern New Brunswick, Canada." Canadian Journal of Earth Sciences 29, no. 11 (November 1, 1992): 2445–62. http://dx.doi.org/10.1139/e92-192.
Full textAbstract:
Within the Avalon composite terrane exposed in southern New Brunswick, late Precambrian, low-grade volcanic–sedimentary sequences are juxtaposed against late Precambrian gneisses (Brookville Gneiss) and older platformal metasedimentary rocks (Green Head Group) along the Caledonia Fault. Both assemblages host petrographically similar suites of calc-alkalic dioritic and granodioritic plutons. Those intruding volcanic–sedimentary sequences (Caledonia terrane) record ca. 615–625 Ma crystallization ages typical of arc-related magmatism throughout the Avalon composite terrane. However, 40Ar/39Ar age data from stocks intruding gneisses and platformal metasedimentary rocks (Brookville terrane) suggest significantly younger crystallization ages.36Ar/40Ar versus 39Ar/40Ar isotope correlation ages recorded by hornblende are interpreted to closely date postmagmatic cooling within six plutons: Fairville Granite (547 ± 1 Ma); French Village Quartz Diorite (539 ± 2 and 537 ± 1 Ma); Rockwood Park Granodiorite (529 ± 2 and 523 ± 3.5 Ma); Musquash Granite (526 ± 2 Ma); Milkish Head Granite (Red Bridge pluton, 520 ± 1.5 Ma); Lepreau Diorite (Talbot Road pluton, 519 ± 2 Ma and Hansen Stream pluton, 518 ± 1.5 Ma. A hornblende isotope correlation age of 530 ± 2 Ma from penetratively foliated amphibolite within the French Village Quartz Diorite suggests that the magmatic activity was locally accompanied by ductile shear. Muscovite within granitic pegmatite in the Brookville Gneiss records a 40Ar/39Ar plateau age of 510 ± 1 Ma interpreted to date final phases of associated magmatic activity.Arc-related magmatism extending into the Cambrian contrasts with the characteristic tectono-stratigraphic record in the Avalon composite terrane where late Precambrian igneous rocks are overstepped by Cambrian–Ordovician shallow-marine strata with only a local and minor record of rift-related volcanic activity. Although the Brookville terrane shows affinities with the Avalon composite terrane during the late Precambrian, the 40Ar/39Ar age data suggest that it was isolated as a distinct tectono-stratigraphic element by the Early Cambrian.