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1
Ibe, Chinedu Uduma. "Geochemical characterization of the gneisses and schists in Ekumtak area: further evidence for a metasedimentary protolith and moderate weathering intensity for the Precambrian Basement complex of Nigeria." Serie Correlación Geológica 35, no. 2 (2020): 17–36. https://doi.org/10.5281/zenodo.5046024.
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The study area is characterized by migmatitic banded gneisses and garnet mica schists. These rocks are associated with amphibolite and granitic intrusions. These migmatitic gneisses and schists are characterized by paragenetic mineral assemblages that reflect an evolutionary history that involved processes of sedimentation and upper amphibolite facies metamorphism. Geochemical data show that the rocks are silica rich with moderate to elevated concentrations of Al2 O3 which is consistent with pelitic rocks. The gneisses show positive anomalies in Rb, K, Th, La, Sm and strong negative anomalies in Ta, Nb, Sr, Ti, Tm, Yb, Zr and Y, with an overall enrichment of the large ion lithophile elements (LILE: K, Ba and Rb) and depletion of the high field strength elements (HFSE: Zr, Ti and Y). Specifically, the Eu-anomalies, expressed as (Eu/Eu*) range from 0.03 to 1.4 in the gneisses and from 0.09 to 1.1 in the schists. LaN/YbN ratios are from 7 to 93 for the gneisses and 1.9 to 46.4 for the schist. These values suggest that the protoliths of these metasedimentary rocks are predominantly shales, greywackes and arkosic sandstones with surbodinate basic to intermediate volcanic components. Their chemical index of alteration values ranges from 57.7-71.7 in the gneisses and 66.6-74.9 in the schists with mean of 68% and standard deviation of ±3.4 suggesting a recycle process and relatively moderate chemical weathering of the protoliths. The metasedimentary origin for the rocks is consistent with results from other parts of the Nigerian Precambrian Basement complex.
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Sadegh, Hadiseh Rahimi, Hesam Moeinzadeh, and Kazu Nakashima. "Geochemistry, mineral chemistry and P-T evaluation of metasediments of Bahram-Gur complex, ES Sanandaj-Sirjan zone, Iran." Mineralogia 50, no. 1-4 (2019): 34–68. http://dx.doi.org/10.2478/mipo-2019-0003.
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AbstractThe Bahram-Gur area in the southeastern part of the Sanandaj – Sirjan metamorphic zone, contains metabasites and metasediments. The metasedimentary rocks are mainly garnet schists and garnet-staurolite schists that were metamorphosed under amphibolite facies conditions. The rocks consist of garnet ± staurolite, biotite, muscovite, chlorite and quartz. The geochemistry of the Bahram-Gur metasediments classifies them as quartziferous sedimentary rocks. The protoliths of the metasedimentary rocks were close to greywackes from an ensialic arc basin depositional setting, with a source comprising mostly mixture of acid and intermediate magmatic rocks in the upper continental crust. The metamorphic conditions of formation of the Bahram-Gur metasedimentary are investigated by geothermobarometric methods. The results show that the metasedimentary rocks formed at temperatures of 600-750°C and pressures of 5-7.5 kbar.
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Hanson, Ann E. H., Stacia M. Gordon, Kyle T. Ashley, Robert B. Miller, and Elizabeth Langdon-Lassagne. "Multiple sediment incorporation events in a continental magmatic arc: Insight from the metasedimentary rocks of the northern North Cascades, Washington (USA)." Geosphere 18, no. 1 (2021): 298–326. http://dx.doi.org/10.1130/ges02425.1.
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Abstract The rheology and composition of arc crust and the overall evolution of continental magmatic arcs can be affected by sediment incorporation events. The exhumed Cretaceous–Eocene North Cascades arc exposes abundant metasedimentary rocks that were incorporated into the arc during multiple events. This study uses field relationships, detrital zircon geochronology, bulk rock geochemistry, geothermometry, and quartz-in-garnet geobarometry to distinguish approximate contacts and emplacement depths for different metasedimentary units to better understand their protolith incorporation history and impact on the arc. The Skagit Gneiss Complex is one of the main deep crustal units of the North Cascades arc. It includes metasedimentary rocks with distinct detrital zircon signatures: Proterozoic–Cretaceous (Group 1) or Triassic–Cretaceous (Group 2) zircon populations. Both metasedimentary groups achieved near-peak metamorphic conditions of 640–800 °C and 5.5–7.9 kbar; several Group 2 samples reveal the higher pressures. A third group of metasedimentary rocks, which was previously interpreted as metamorphosed equivalents of backarc sediments (Group 3), exhibited unimodal Triassic or bimodal Late Jurassic–Early Cretaceous detrital zircon signatures and achieved near-peak conditions of 570–700 °C and 8.7–10.5 kbar. The combined field and analytical data indicate that protoliths of Group 1 and Group 2 metasedimentary rocks were successively deposited in a forearc basin and underthrusted into the arc as a relatively coherent body. Group 3 backarc sediments were incorporated into the arc along a transpressional step-over zone. The incorporation of both forearc and backarc sediments was likely facilitated by arc magmatism that weakened arc crust in combination with regional transpression.
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RÉGNIER, JEAN-LUC, JOCHEN E. MEZGER, and CEES W. PASSCHIER. "Metamorphism of Precambrian–Palaeozoic schists of the Menderes core series and contact relationships with Proterozoic orthogneisses of the western Çine Massif, Anatolide belt, western Turkey." Geological Magazine 144, no. 1 (2006): 67–104. http://dx.doi.org/10.1017/s0016756806002640.
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The tectonic setting of the southern Menderes Massif, part of the western Anatolide belt in western Turkey, is characterized by the exhumation of deeper crustal levels onto the upper crust during the Eocene. The lowermost tectonic units of the Menderes Massif are exposed in the Çine Massif, where Proterozoic basement orthogneisses of the Çine nappe are in tectonic contact with Palaeozoic metasedimentary rocks of the Selimiye nappe. In the southern Çine Massif, orthogneiss and metasedimentary rocks are separated by the southerly dipping Selimiye shear zone, preserving top-to-the-S shearing under greenschist facies conditions. In contrast, in the western Çine Massif, the orthogneiss is deformed and mylonitic near the contact with the metasedimentary rocks. The geometry of the mylonite zone and the observed shear directions change from north to southwest. In the north, the mylonite zone dips shallowly to the north, with top-to-the-N shear sense indicators showing northward thrusting of the orthogneiss over the metasedimentary rocks. In the southwest, the mylonite zone resembles a steep N–S striking strike-slip shear zone associated with top-to-the-SSW sense of shear. Overall, the geometry of the mylonite shear zone is consistent with northward movement of the orthogneiss relative to the metasedimentary rocks. Different shear senses are attributed to strain partitioning.AFM diagrams and P–T pseudosections with mineral parageneses of metasedimentary rocks of the Selimiye nappe and metasedimentary enclaves within the orthogneiss of the Çine nappe indicate a single Barrovian-type metamorphism. An earlier higher pressure phase is evident from staurolite–chloritoid inclusions in garnets of the Çine nappe, suggesting a clockwise P–T path. A similar path is inferred for the Selimiye nappe. Index minerals and the sequence of mineral parageneses point to a single amphibolite facies metamorphic event affecting metasedimentary rocks of both nappes, which predates Eocene emplacement of the high pressure–low temperature Lycian and Cycladic blueschist nappes. Northward thrusting of the orthogneiss onto the metasedimentary rocks of the Selimiye nappe is coeval with amphibolite facies metamorphism. Recently postulated polymetamorphism cannot be supported by this study. Petrological data provide no evidence for burial of the lower units of the Menderes Massif to depth greater than 30 km during closure of the Neo-Tethys. A major pre-Eocene tectonic event associated with top-to-the-N thrusting and Barrovian-type metamorphism could lend support to the idea of a Neo-Tethys (sensu stricto) suture south of the Menderes Massif and below the Lycian nappes.
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Zelt, C. A., D. A. Forsyth, B. Milkereit, D. J. White, I. Asudeh, and R. M. Easton. "Seismic structure of the Central Metasedimentary Belt, southern Grenville Province." Canadian Journal of Earth Sciences 31, no. 2 (1994): 243–54. http://dx.doi.org/10.1139/e94-024.
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Crust and upper-mantle structure interpreted from wide-angle seismic data along a 260 km profile across the Central Metasedimentary Belt of the southern Grenville Province in Ontario and New York State shows (i) relatively high average crustal and uppermost mantle velocities of 6.8 and 8.3 km/s, respectively; (ii) east-dipping reflectors extending to 24 km depth in the Central Metasedimentary Belt; (iii) weak lateral velocity variations beneath 5 km; (iv) a mid-crustal boundary at 27 km depth; and (v) a depth to Moho of 43–46 km. The wide-angle model is generally consistent with the vertical-incidence reflectivity of an intersecting Lithoprobe reflection line. The mid-crustal boundary correlates with a crustal detachment zone in the Lithoprobe data and the depth extent of east-dipping wide-angle reflectors. Regional structure and aeromagnetic anomaly trends support the southwest continuity of Grenville terranes and their boundaries from the wide-angle profile to two reflection lines in Lake Ontario. A zone of wide-angle reflectors with an average apparent eastward dip of 13° has a surface projection that correlates spatially with the boundary between the Elzevir and Frontenac terranes of the Central Metasedimentary Belt and resembles reflection images of a crustal-scale shear zone beneath Lake Ontario. A high-velocity upper-crustal anomaly beneath the Elzevir–Frontenac boundary zone is positioned in the hanging wall associated with the concentrated zone of wide-angle reflectors. The high-velocity anomaly is coincident with a gravity high and increased metamorphic grade, suggesting northwest transport of mid-crustal rocks by thrust faulting consistent with the mapped geology. The seismic data suggest (i) a reflective, crustal-scale structure has accommodated northwest-directed tectonic transport within the Central Metasedimentary Belt; (ii) this structure continues southwest from the exposed Central Metasedimentary Belt to at least southern Lake Ontario; and (iii) crustal reflectivity and complexity within the eastern Central Metasedimentary Belt is similar to that observed at the Grenville Front and the western Central Metasedimentary Belt boundary.
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Salminen, Paula, and Matti Kurhila. "New age constraints for metasedimentary rocks in southern Finland." Bulletin of the Geological Society of Finland 95, no. 2 (2024): 83–106. http://dx.doi.org/10.17741/bgsf/95.2.001.
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Metasedimentary rocks from nine sampling sites in southern Finland and an intermediate dyke in one of these sites were sampled for analysis of U–Pb zircon age and geochemical composition. The zircons of the metasedimentary rock samples yield 207Pb/206Pb dates ranging from 3281 to 1810 Ma. The nearly concordant dates from apparent detrital zircon cores indicate a prominent source with age around 2.1–2.0 Ga. The maximum depositional ages estimated for six of the metasedimentary rock samples span from 1.96 to 1.89 Ga. The data from zircon rims and overgrowths and metamorphic zircons in the metasedimentary rock samples indicate regional metamorphic events in the study area at least at ca. 1.89 and 1.84 Ga, and possibly also at ca. 1.87 Ga. The minimum age of the deposition (≤1.89 Ga) was estimated based on the ages of the regional metamorphism and the intrusive rocks. Some zircon rims and overgrowths yield ≥1.91 Ga 207Pb/206Pb dates, which are considered to possibly represent metamorphic events in the source areas.
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García-Ramírez, Carlos Alberto, and Vanessa Rey-León. "Petrología y geoquímica de los Ortoneises aflorantes en los sectores central y este en el Macizo de Santander, Andes Colombianos." Revista Mexicana de Ciencias Geológicas 39, no. 1 (2022): 27–42. http://dx.doi.org/10.22201/cgeo.20072902e.2022.1.1652.
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Los Ortoneises aflorantes en los sectores central y este en el Macizo de Santander, consisten en intercalaciones de neis hornbléndico, neis biotítico y neis cuarzo–feldespático, predominando las dos primeras variedades. En estos ortoneises aparecen lentes esporádicos de anfibolita. Los ortoneises son el resultado del emplazamiento sintectónico de granitoides en rocas de los Esquistos del Silgará, durante el pico metamórfico de esta unidad metasedimentaria. Se observan algunas diferencias estructurales y composicionales en los ortoneises de los sectores central y este; la foliación más desarrollada, se observa en el sector central y la presencia de moscovita, al parecer se restringe solo al sector este. Las características geoquímicas evidencian que los ortoneises del sector central son de composición granítica, mientras que, para los ubicados en el sector este, su composición varía entre granito y granodiorita. Estos ortoneises fueron formados en una margen continental activa. El contenido de Tierras raras (REE) en los ortoneises evidencian tres patrones diferentes de comportamiento: 1) Los ortoneises félsicos muestran un paulatino empobrecimiento en las REE ligeras (La–Sm) y un empobrecimiento en REE pesadas (Eu–Lu); 2) ortoneises con clara anomalía negativa en Eu* y 3) La anfibolita está muy empobrecida en REE ligeras y va incrementando el contenido de REE pesadas con ausencia de anomalía en Eu*. Las condiciones P–T de metamorfismo para los ortoneises del sector central fueron: T = 690–770 °C y P = 0.53–0.85 GPa, mientras que, en el este, la temperatura obtenida varía entre 680 y 693 °C. La ocurrencia, relaciones de campo entre los ortoneises estudiados con unidades metasedimentarias y las edades, son muy similares a la de los ortoneises aflorantes a lo largo de los Andes y el sureste de México, evidenciando un arco magmático desarrollado a lo largo del protomargen de Gondwana Occidental.
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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 (1998): 649–56. http://dx.doi.org/10.1139/e98-010.
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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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Thrane, Kristine, and James N. Connelly. "Zircon geochronology from the Kangaatsiaq– Qasigiannguit region, the northern part of the 1.9–1.8 Ga Nagssugtoqidian orogen, West Greenland." Geological Survey of Denmark and Greenland (GEUS) Bulletin 11 (December 5, 2006): 87–100. http://dx.doi.org/10.34194/geusb.v11.4918.
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The Kangaatsiaq–Qasigiannguit region in the northern part of the Palaeoproterozoic Nagssugtoqidian orogen of West Greenland consists of poly-deformed orthogneisses and minor occurrences of interleaved, discontinuous supracrustal belts. Laser ablation ICP-MS 207Pb/206Pb analyses of detrital zircons from four metasedimentary rocks (supplemented by ion probe analysis of one sample) and igneous zircons from six granitoid rocks cutting metasedimentary units indicate that the supracrustal rocks in the Kangaatsiaq–Qasigiannguit (Christianshåb) region are predominantly Archaean in age. Four occurrences of metasedimentary rocks are clearly Archaean, two have equivocal ages, and only one metasedimentary unit, from within the Naternaq (Lersletten) supracrustal belt, is demonstrably Palaeoproterozoic and readily defines a large fold complex of this age at Naternaq. The 2.9–2.8 Ga ages of detrital Archaean grains are compatible with derivation from the local basement orthogneisses within the Nagssugtoqidian orogen. The detrital age patterns are similar to those of metasediments within the central Nagssugtoqidian orogen but distinct from age patterns in metasediments of the Rinkian belt to the north, where there is an additional component of pre-2.9 Ga zircons. Synkinematic intrusive granitoid rocks constrain the ages of some Archaean deformation at 2748 ± 19 Ma and some Palaeoproterozoic deformation at 1837 ± 12 Ma.
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Zaika, V. A., A. A. Sorokin та A. P. Sorokin. "Age and sources of the metasedimrntary rocks of the Tokur terrane in the Mongol-Okhotsk fold belt: results of the U–Pb geoсhronological and Lu–Hf isotope studies". Доклады Академии наук 486, № 4 (2019): 446–50. http://dx.doi.org/10.31857/s0869-56524864446-450.
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This paper presents the results of U–Pb (LA–ICP–MS) and Lu–Hf isotope studies of detrital zircons from metasedimentary rocks of the Tokur Terrane. It has been shown that metasedimentary rocks of the Tokur and Ekimchan formations are characterized by similar age peaks of detrital zircons, which indicates a close (or same) age of these formations. The lower age of the sedimentation is determined by the age of the youngest zircons of 326–323 Ma. The upper age boundary is determined of 254–251 Ma, based on the intruded of the Late Permian granitoids. The main sources of zircons in the metasedimentary rocks of the Tokur Terrane are the igneous and metamorphic complexes of the southeast framing of the North Asia Craton. The Tokur Terrane can be considered as a fragment of the Paleozoic accretionary complex, the formation in front of the southeastern margin of the North Asia Craton.
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Borradaile, G., and H. Brown. "The Shebandowan group: "Timiskaming-like" Archean rocks in northwestern Ontario." Canadian Journal of Earth Sciences 24, no. 1 (1987): 185–88. http://dx.doi.org/10.1139/e87-016.
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This group of Archean volcanic and metasedimentary rocks is generally considered to be younger than the Keewatin metavolcanic rocks. The metasedimentary rocks are disposed in tight to isoclinal folds with strong plunge variations that are mainly due to a primary tectonic event. The folds are accompanied by a single, penetrative tectonic microfabric and a coplanar magnetic fabric. The contacts of the group with the adjacent Keewatin rocks are unexposed but are inferred to be faulted, at least in part.
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Pehrsson, Sally, Simon Hanmer, and Otto van Breemen. "U–Pb geochronology of the Raglan gabbro belt, Central Metasedimentary Belt, Ontario: implications for an ensialic marginal basin in the Grenville Orogen." Canadian Journal of Earth Sciences 33, no. 5 (1996): 691–702. http://dx.doi.org/10.1139/e96-052.
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The Raglan gabbro belt of the Ontario Grenville Orogen is coincident with the top of the Central Metasedimentary Belt boundary thrust zone, a major mid-crustal shear zone separating the Central Gneiss Belt in the footwall from the Central Metasedimentary Belt in the hanging wall. It has been suggested that the gabbros making up the belt are coeval, that they formed in a marginal basin within the Central Metasedimentary Belt, and that they formed a horizon of Theologically stiff material that controlled the localization of the top of the boundary thrust zone during its initiation as the marginal basin closed at ca. 1190 Ma. U–Pb zircon dating of plutons within the Raglan gabbro belt was undertaken to test the coeval nature of intrusions in the belt. Magmatic crystallization ages for three of the gabbros fall in the range 1246–1227 Ma, and a fourth yields a minimum age of ca. 1175 Ma. The results are permissive of a common origin for the gabbros and allow that the Raglan gabbro belt may have been related to the marginal basin, at least with respect to the later stages of its evolution. Inherited 1440–1301 Ma zircons in the gabbros suggest interaction with underlying Central Gneiss Belt crust during magmatism and support an ensialic marginal-basin model, as opposed to an island-arc model, for the evolution of the northwestern part of the Central Metasedimentary Belt.
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Friderichsen, J. D., R. E. Holdsworth, H. F. Jepsen, and R. A. Strachan. "Caledonian and pre-Caledonian geology of Dronning Louise Land, North-East Greenland." Rapport Grønlands Geologiske Undersøgelse 148 (January 1, 1990): 133–41. http://dx.doi.org/10.34194/rapggu.v148.8133.
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The western border of the East Greenland Caledonides is exposed in Dronning Louise Land, where it is marked by a N–S trending thrust Imbricate Zone. The autochthonous crystalline basement to the west of the Imbricate Zone is dominated by orthogneisses, and unconformably overlain by two metasedimentary sequences (Zebra Series and Trekant Series). These metasedimentary units can be recognised in the Caledonian thrust slices of the Imbricate Zone and also as folded inliers in the gneiss complexes to the east, and witness to a progressive increase in Caledonian deformation and metamorphism.
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Subba Rao, D. V., and S. M. Naqvi. "Archaean Komatiites from the Older Schist Belt of Kalyadi in Western Dharwar Craton, Karnataka." Journal Geological Society of India 53, no. 3 (1999): 347–54. http://dx.doi.org/10.17491/jgsi/1999/530307.
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Abstract The cluster of enclaves at Kalyadi, Hassan district includes ultramafic-mafic metavolcanic rocks and minor metasedimentary rocks such as chert, cherty quartzite and pelite. Occurrence of pillow and vesicular structures in the ultramafic rocks is being reported for the first time from this area. The average composition of the ultramafic rocks is : SiO2 46.05%, TiO2 0.18%, MgO 31.81%, K2O 0.15%. Cr 3409 ppm and Ni 1610 ppm with a CaO/Al2O3) ratio close tol. The composition, relict igneous structures and metasedimentary rock association are suggestive of a komatiitic affinity for these rocks, which possibly accumulated under subaqueous conditions.
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Dafov, Michelle N., Anahi Carrera, George E. Gehrels, et al. "U-Th-Pb Geochronology and Lu-Hf Isotope Geochemistry of Detrital Zircons in Metasedimentary Rocks of the Southern Coast Mountains Batholith." Lithosphere 2020, no. 1 (2020): 1–21. http://dx.doi.org/10.2113/2020/8854686.
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Abstract Most metasedimentary rocks in the southern Coast Mountains batholith are of uncertain tectonic affinity because they occur in discontinuous pendants surrounded by large intrusive bodies, and many protolith features are obscured by regional deformation and metamorphism. This study uses U-Th-Pb ages and Lu-Hf isotope signatures of detrital zircons in metasedimentary rocks in Bute, Loughborough, and Knight Inlets in an effort to test possible correlations with the adjacent Wrangellia, Alexander, Taku, Yukon-Tanana, and Stikine terranes. Detrital zircons from metasedimentary samples yield ages that belong to age groups of 590-528 Ma (peak age of 560 Ma), 485-432 Ma (peak age of 452 Ma), 356-286 Ma (peak age of 307 Ma), and 228-185 Ma (peak ages of 215 and 198 Ma). A small number of ~1.1-1.9 Ga grains are also present. εHft values of the 590-185 Ma grains yield a progression from intermediate (0 to +5) values to more juvenile (mostly +4 to +15) values from Neoproterozoic through early Mesozoic time. The Comparison of these results with similar data sets from adjacent terranes demonstrates that primary connections with the Yukon-Tanana and Taku terranes are unlikely but are consistent with primary connections with the Wrangellia, Stikine, and/or Alexander terranes. Unfortunately, the available constraints are not sufficient to eliminate any of these options or the possibility that the pendants are a unique tectonic fragment. Zircons from the metasedimentary samples also yield U-Th-Pb ages of 165-128 Ma (peak age of 152 Ma) and 114-88 Ma (peak age of 102 Ma). εHft values of these zircon domains are mostly juvenile (+7 to +13). Comparison of U concentrations, U/Th values, and CL textures of zircons from the metasedimentary samples, leucocratic sills that intrude the pendants, and surrounding plutonic bodies suggests that most of the young grains, as well as widespread younger rims on older grains, grew during metamorphism associated with emplacement of the adjacent plutonic bodies. Some young grains were derived from thin felsic sills or veins that were unintentionally included in the sampled material.
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Ramacciotti, C. D., C. Casquet, E. G. Baldo, et al. "The Maz Metasedimentary Series (Western Sierras Pampeanas, Argentina). A relict basin of the Columbia supercontinent?" Geological Magazine 159, no. 3 (2021): 309–21. http://dx.doi.org/10.1017/s0016756821000935.
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AbstractThe Maz Metasedimentary Series is part of the Maz Complex that crops out in the sierras of Maz and Espinal (Western Sierras Pampeanas) and in the Sierra de Umango (Andean Frontal Cordillera), northwestern Argentina. The Maz Complex is found within a thrust stack of Silurian age, which later underwent open folding. The Maz Metasedimentary Series mainly consists of medium-grade garnet–staurolite–kyanite–sillimanite schists and quartzites, with minor amounts of marble and calc-silicate rocks. Transposed metadacite dykes have been recognized along with amphibolites, metagabbros, metadiorites and orthogneisses. Schist, quartzite and metadacite samples were analysed for SHRIMP U–Pb zircon dating. The Maz Metasedimentary Series is polymetamorphic and records probably three metamorphic events during the Grenvillian orogeny, at c. 1235, 1155 and 1035 Ma, and a younger metamorphism at c. 440–420 Ma resulting from reactivation during the Famatinian orogeny. The sedimentary protoliths were deposited between 1.86 and 1.33–1.26 Ga (the age of the Andean-type Grenvillian magmatism recorded in the Maz Complex), and probably before 1.75 Ga. The main source areas correspond to Palaeoproterozoic and, to a lesser magnitude, Meso-Neoarchaean rocks. The probable depositional age and the detrital zircon age pattern suggest that the Maz Metasedimentary Series was laid down in a basin of the Columbia supercontinent, mainly accreted between 2.1 and 1.8 Ga. The sedimentary sources were diverse, and we hypothesize that deposition took place before Columbia broke up. The Rio Apa block, and the Río de la Plata, Amazonia and proto-Kalahari cratons, which have nearby locations in the palaeogeographic reconstructions, were probably the main blocks that supplied sediments to this basin.
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Michailidis, Kleopas, Anna Kassoli-Fournaraki, and Richard V. Dietrich. "Origin of zoned tourmalines in graphite-rich metasedimentary rocks from Macedonia, northern Greece." European Journal of Mineralogy 8, no. 2 (1996): 393–404. http://dx.doi.org/10.1127/ejm/8/2/0393.
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Percival, John A. "A regional perspective of the Quetico metasedimentary belt, Superior Province, Canada." Canadian Journal of Earth Sciences 26, no. 4 (1989): 677–93. http://dx.doi.org/10.1139/e89-058.
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Alternating greenstone–granite and metasedimentary gneiss belts are a first-order tectonic feature of the southern Superior Province. The tectonic development of the Quetico metasedimentary belt is reviewed with regard to depositional, structural, and metamorphic–plutonic history. Over its 1200 km length, the belt consists of marginal metasedimentary schists of turbiditic origin and interior metasedimentary migmatite and peraluminous leucogranite. Polyphase deformation has resulted in a steep easterly-striking foliation and regional, gently east-plunging stretching lineation. Metamorphic grade varies in a low-P facies series from greenschist at the belt margins to upper amphibolite and local granulite in the central migmatite – intrusive granite zone. Mineral assemblages in the central zone yield estimates of metamorphic pressure that increase systematically eastward over 800 km from about 250 MPa (2.5 kbar) near the Canada – United States border to 600 MPa (6 kbar) in granulites adjacent to the Kapuskasing structural zone.Geochronology suggests that sediments were deposited at approximately the same time as active volcanism in adjacent volcanic belts, although evidence of volcanic–sedimentary stratigraphic contiguity is weak as a result of later transcurrent movement parallel to major lithological boundaries. Adjacent belts are inferred to have been contiguous since common D2 deformation, 2689–2684 Ma ago. Major plutonism and associated metamorphism occurred in the Quetico Belt approximately 2670–2650 Ma ago, significantly later than major plutonism in the adjacent volcanic belts.The linear disposition of greywacke-rich sediments over 1200 km invites an analogy with modern accretionary prisms. However, the high-temperature, low-pressure metamorphism of the Quetico Belt is inconsistent with such a low-heat-flow environment, and a change in tectonic regime would be required to account for the metamorphism and intracrustal plutonism. Simple cessation of subduction beneath the thick sedimentary prism could have led to restoration of isotherms, with possible attendant crustal melting and isostatic recovery.
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URMANTSEVA, Lena, and Olga TURKINA. "Paleoproterozoic, High-Metamorphic, Metasedimentary Units of Siberian Craton." Acta Geologica Sinica - English Edition 83, no. 5 (2009): 875–83. http://dx.doi.org/10.1111/j.1755-6724.2009.00116.x.
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FERRERO, S., O. BARTOLI, B. CESARE, et al. "Microstructures of melt inclusions in anatectic metasedimentary rocks." Journal of Metamorphic Geology 30, no. 3 (2012): 303–22. http://dx.doi.org/10.1111/j.1525-1314.2011.00968.x.
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Wolf, Mathias, Rolf L. Romer, and Johannes Glodny. "Isotope disequilibrium during partial melting of metasedimentary rocks." Geochimica et Cosmochimica Acta 257 (July 2019): 163–83. http://dx.doi.org/10.1016/j.gca.2019.05.008.
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Rodgers, John. "Is the West Karmøy complex igneous or metasedimentary?" Tectonophysics 231, no. 1-3 (1994): 113–22. http://dx.doi.org/10.1016/0040-1951(94)90124-4.
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Forsyth, D. A., B. Milkereit, A. Davidson, et al. "Seismic images of a tectonic subdivision of the Grenville Orogen beneath lakes Ontario and Erie." Canadian Journal of Earth Sciences 31, no. 2 (1994): 229–42. http://dx.doi.org/10.1139/e94-023.
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New seismic data from marine air-gun and Vibroseis profiles in Lake Ontario and Lake Erie provide images of subhorizontal Phanerozoic sediments underlain by a remarkable series of easterly dipping reflections that extends from the crystalline basement to the lower crust. These reflections are interpreted as structural features of crustal-scale subdivisions within the Grenville Orogen. Broadly deformed, imbricated, and overlapping thrust sheets within the western Central Metasedimentary Belt are succeeded to the west by a complex zone of easterly dipping, apparent thrust faults that are interpreted as a southwest subsurface extension of the boundary zone between the Central Metasedimentary Belt and the Central Gneiss Belt. The interpreted Central Metasedimentary Belt boundary zone has a characteristic magnetic anomaly that provides a link from the adjacent ends of lakes Ontario and Erie to structures exposed 150 km to the north. Less reflective, west-dipping events are interpreted as structures within the eastern Central Gneiss Belt. The seismic interpretation augments current tectonic models that suggest the exposed ductile structures formed at depth as a result of crustal shortening along northwest-verging thrust faults. Relatively shallow reflections across the boundary region suggest local, Late Proterozoic extensional troughs containing post-Grenville sediments, preserved possibly as a result of pre-Paleozoic reactivation of basement structures.
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Ague, Jay J., Santiago Tassara, Megan E. Holycross, et al. "Slab-derived devolatilization fluids oxidized by subducted metasedimentary rocks." Nature Geoscience 15, no. 4 (2022): 320–26. http://dx.doi.org/10.1038/s41561-022-00904-7.
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AbstractMetamorphic devolatilization of subducted slabs generates aqueous fluids that ascend into the mantle wedge, driving the partial melting that produces arc magmas. These magmas have oxygen fugacities some 10–1,000 times higher than magmas generated at mid-ocean ridges. Whether this oxidized magmatic character is imparted by slab fluids or is acquired during ascent and interaction with the surrounding mantle or crust is debated. Here we study the petrology of metasedimentary rocks from two Tertiary Aegean subduction complexes in combination with reactive transport modelling to investigate the oxidative potential of the sedimentary rocks that cover slabs. We find that the metasedimentary rocks preserve evidence for fluid-mediated redox reactions and could be highly oxidized. Furthermore, the modelling demonstrates that layers of these oxidized rocks less than about 200 m thick have the capacity to oxidize the ascending slab dehydration flux via redox reactions that remove H2, CH4 and/or H2S from the fluids. These fluids can then oxidize the overlying mantle wedge at rates comparable to arc magma generation rates, primarily via reactions involving sulfur species. Oxidized metasedimentary rocks need not generate large amounts of fluid themselves but could instead oxidize slab dehydration fluids ascending through them. Proposed Phanerozoic increases in arc magma oxygen fugacity may reflect the recycling of oxidative weathering products following Neoproterozoic–Palaeozoic marine and atmospheric oxygenation.
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Mueller, P. A., and C. D. Frost. "The Wyoming Province: a distinctive Archean craton in Laurentian North America." Canadian Journal of Earth Sciences 43, no. 10 (2006): 1391–97. http://dx.doi.org/10.1139/e06-075.
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The Wyoming Province is a distinctive Archean craton in the northwestern United States that can be subdivided into three subprovinces, namely, from oldest to youngest, the Montana metasedimentary province, the Beartooth–Bighorn magmatic zone, and the Southern accreted terranes. Archean rocks of the Montana metasedimentary province and the Beartooth–Bighorn magmatic zone are characterized by (1) their antiquity (rock ages to 3.5 Ga, detrital zircon ages up to 4.0 Ga, and Nd model ages exceeding 4.0 Ga); (2) a distinctly enriched 207Pb/204Pb isotopic signature, which suggests that this part of the province was not produced by the amalgamation of exotic terranes; and (3) a distinctively thick (15–20 km), mafic lower crust. The Montana metasedimentary province and Beartooth–Bighorn magmatic zone were cratonized by about 3.0–2.8 Ga. Crustal growth occurred via continental-arc magmatism and terrane accretion in the Southern accreted terranes along the southern margin of the province at 2.68–2.50 Ga. By the end of the Archean, the three subprovinces were joined as part of what is now the Wyoming Province. Subsequent to amalgamation of the Wyoming crust to Laurentia at ca. 1.8–1.9 Ga, Paleoproterozoic crust (1.7–2.4 Ga) was juxtaposed along the southern and western boundaries of the province. Subsequent tectonism and magmatism in the Wyoming region are concentrated in the areas underlain by these Proterozoic mobile belts.
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McEachern, Sally J., and Otto van Breemen. "Age of deformation within the Central Metasedimentary Belt boundary thrust zone, southwest Grenville Orogen: constraints on the collision of the Mid-Proterozoic Elzevir terrane." Canadian Journal of Earth Sciences 30, no. 6 (1993): 1155–65. http://dx.doi.org/10.1139/e93-098.
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U–Pb zircon and titanite geochronology on syntectonic intrusions from the Ontario Central Metasedimentary Belt boundary thrust zone has constrained the timing of two major periods of northwest-directed ductile thrusting on this crustal-scale shear zone. Initiation of deep-seated uppermost amphibolite facies deformation is constrained to a period before 1190 Ma, over 100 Ma earlier than previous estimates. Major reimbrication of the shear zone took place ca. 1080 – 1060 Ma and was more pronounced in the southwestern segment. The initiation of deformation within the boundary thrust zone coincides with the emplacement of the hanging wall Elzevir terrane of the Central Metasedimentary Belt onto the Mid-Proterozoic Laurentian margin. The structural nature and temporal and kinematic consistency of the reimbrication phase along the 200 km exposed length of the shear zone is thought to be due to within-plate reactivation of the existing, rheologically weak structure, a result of continent–continent collision ca. 1080–1060 Ma during the later stage of the Grenville orogenic cycle.Collision of the Elzevir terrane, interpreted to be an ensialic marginal basin, with the Laurentian margin along the Central Metasedimentary Belt boundary thrust zone is thought to potentially record closure of the marginal basin ca. 1190 Ma. A distinctive tonalitic suite of rocks preserved in the boundary thrust zone may be composed of fragments of the remnant arc to the marginal basin.
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Yang, Haiming, Kurt Kyser, and Kevin Ansdell. "Metamorphism of the MacLean Lake and Central Metavolcanic belts, La Ronge domain, Trans-Hudson Orogen: pressure-temperature variations and tectonic implications." Canadian Journal of Earth Sciences 35, no. 8 (1998): 905–22. http://dx.doi.org/10.1139/e98-039.
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Metamorphic assemblages differ between the metasedimentary MacLean Lake belt and the adjacent Central Metavolcanic belt in the La Ronge domain, Trans-Hudson Orogen. The former consists of meta-arkoses, psammitic gneisses, metaconglomerates, and calc-silicate gneisses of upper amphibolite facies (600-740°C, 440-660 MPa) with local migmatization, whereas the latter is comprised mainly of metavolcanic and plutonic rocks, with minor metasedimentary schists of greenschist to lower amphibolite facies (480-630°C, 520-560 MPa). Petrographic evidence indicates that peak metamorphic conditions were reached towards the end of D1 deformation during which the Central Metavolcanic belt was thrust onto the MacLean Lake belt along the McLennan Lake tectonic zone, which separates the two belts. Peak metamorphic assemblages did not undergo retrograde alteration during D2 deformation, indicating that high temperature was maintained during D2 deformation. Differences in pressure (P) and temperature (T) between the northeastern and southwestern parts of the Central Metavolcanic belt may have resulted from tilting along strike after peak metamorphism. Peak temperatures increase gradually from the Central Metavolcanic belt to MacLean Lake belt across the McLennan Lake tectonic zone. Peak pressures in the two belts are similar, implying that the Central Metavolcanic belt thrust sheet was probably thin. The P-T data for the MacLean Lake belt indicate a relatively high thermal gradient (40-50°C/km), similar to that in the metasedimentary Kisseynew domain in the orogen.
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Rahman, Z. A., U. Hamzah, and N. Ahmad. "Geotechnical Characteristics of Oil-Contaminated Granitic and Metasedimentary Soils." Asian Journal of Applied Sciences 3, no. 4 (2010): 237–49. http://dx.doi.org/10.3923/ajaps.2010.237.249.
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Valli, Franck, Stephane Guillot, and Kéiko H. Hattori. "Source and tectono-metamorphic evolution of mafic and pelitic metasedimentary rocks from the central Quetico metasedimentary belt, Archean Superior Province of Canada." Precambrian Research 132, no. 1-2 (2004): 155–77. http://dx.doi.org/10.1016/j.precamres.2004.03.002.
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Timmermann, H., R. A. Jamieson, N. G. Culshaw, and R. R. Parrish. "Time of metamorphism beneath the Central Metasedimentary Belt boundary thrust zone, Grenville Orogen, Ontario: accretion at 1080 Ma?" Canadian Journal of Earth Sciences 34, no. 7 (1997): 1023–29. http://dx.doi.org/10.1139/e17-084.
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New U–Pb zircon and titanite data from the Muskoka domain, Grenville Province, Ontario, provide protolith and metamorphic ages for the southwestern Central Gneiss Belt. Discordant analyses from a migmatitic orthogneiss and its leucosome form a linear array with an upper intercept age of 1457 ± 6 Ma and a lower intercept age of 1064 ±18 Ma. U–Pb analyses on metamorphic zircon from an amphibolite yield a set of concordant analyses with an average 207Pb/206Pb age of 1079 ± 3 Ma. A weakly migmatitic granitoid rock and a transecting charnockitic vein in the immediate footwall of the Central Metasedimentary Belt boundary thrust zone yielded a discordant array of analyses wth an upper intercept age of 1394 ± 13 Ma and a lower intercept age of 1066 ± 8 Ma. The charnockitic vein yielded concordant zircon ages of 1077 ± 2 Ma. The upper intercept ages are interpreted in terms of protolith crystallization, and the concordant and lower intercept ages as Grenviilian high-grade metamorphism and associated anatexis. We have found no evidence for a ca. 1190–1160 Ma metamorphic event in these rocks, as required by some regional tectonic interpretations. We conclude that emplacement of the Central Metasedimentary Belt over the Central Gneiss Belt, which caused high-grade metamorphism in the Muskoka domain, occurred at or shortly before ca. 1080 Ma, and that this marks the time of accretion of the Central Metasedimentary Belt to the southeast margin of Laurentia.
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Hanmer, Simon, and Sally McEachern. "Kinematical and rheological evolution of a crustal-scale ductile thrust zone, Central Metasedimentary Belt, Grenville orogen, Ontario." Canadian Journal of Earth Sciences 29, no. 8 (1992): 1779–90. http://dx.doi.org/10.1139/e92-140.
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The Central Metasedimentary Belt boundary thrust zone is a 10 km thick, 200+ km long, stack of crystalline thrust sheets, enclosed by an anastomosing network of ductile thrust zones, formed at mid- to deep-crustal depths in the southwest Grenville orogen, Ontario. It has behaved as a coherent upper amphibolite facies thrust zone, accommodating northwestward transport of the Central Metasedimentary Belt, the largest lithotectonic entity in this part of the orogen, by coherent and contemporaneous displacements. The earliest thrusting was well under way by ca. 1.19–1.18 Ga and the boundary thrust zone was reactivated at ca. 1.08–1.05 Ga. The early thrusting records the closure of a back-arc basin within the Central Metasedimentary Belt, which closed at ca. 1.19–1.18 Ga. The younger thrusting may reflect continental collision to the southeast of the exposed Grenville and represent intraplate reactivation of the boundary thrust zone, which acted as an older, crustal-scale zone of weakness. Transverse mid- to deep-crustal thrusting was apparently contemporaneous with longitudinal (orogen-parallel) shearing at higher structural levels. The rheological behaviour of the deforming media may have influenced the localization of both the upper and lower limits of the boundary thrust zone at the time of its initiation. The upper limit coincides with a chain of relatively stiff metagabbro bodies, which may have acted as a barrier to the upward migration of fluids responsible for syntectonic nephelinization at the top of the thrust zone.
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CARPENTER, R. L., and N. A. DUKE. "Geological Setting of the West Meliadine Gold Deposits, Western Churchill Province, Nunavut, Canada." Exploration and Mining Geology 13, no. 1-4 (2004): 49–65. http://dx.doi.org/10.2113/gsemg.13.1-4.49.
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Abstract The West Meliadine area is underlain by structurally interleaved panels of mafic and minor ultramafic metavolcanic rocks and metasedimentary rocks that occur along the northern margin of the Neoarchean Rankin Inlet greenstone belt. Three structural and metamorphic domains are recognized: (1) the easterly Wesmeg domain; (2) the central Barracuda-Ridge domain; and (3) the westerly Peter Lake domain. The Wesmeg domain is characterized by a series of southeast-trending, north-dipping, foliation-parallel panels of greenschist facies mafic metavolcanic and metasedimentary rocks. The Barracuda-Ridge domain is comprised of greenschist to amphibolite facies mafic metavolcanic rocks that define an east-northeast-trending structural grain. The Peter Lake domain consists of amphibolite facies mafic metavolcanic rocks and minor metasedimentary rocks intruded by a monzonite pluton. West Meliadine hosts the economically significant Wesmeg gold deposits, as well as other important gold showings across the Barracuda-Ridge and Peter Lake domains. The geological setting of the Wesmeg gold deposits resembles that of a break or fault zone. The Pyke Break is a major geophysical discontinuity (>65-km strike length) and is the first-order structural control on gold mineralization at West Meliadine. It is several kilometers wide and characterized by polyphase deformation and shear zone development accompanied by lode-gold mineralization. In general, gold concentration is related to quartz and iron-carbonate veining, iron sulfides (mainly arsenopyrite and pyrrhotite), and accompanying silicate alteration minerals that overprint favorable chemical and structural traps late in the history of deformation.
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Wasteneys, Hardolph, James McLelland, and Sydney Lumbers. "Precise zircon geochronology in the Adirondack Lowlands and implications for revising plate-tectonic models of the Central Metasedimentary Belt and Adirondack Mountains, Grenville Province, Ontario and New York." Canadian Journal of Earth Sciences 36, no. 6 (1999): 967–84. http://dx.doi.org/10.1139/e99-020.
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New high-precision, single-grain dating of leucogranites from the Adirondack Lowlands, dated previously by multigrain zircon methods at ca. 1416 Ma (Wellesley Island) and ca. 1285-1230 Ma (Hyde School Gneiss), has yielded U-Pb zircon ages of ca. 1172 Ma, identical to that of Rockport granite of the Frontenac terrane. In addition, sensitive high resolution ion microprobe (SHRIMP) zircon dating of the intrusive Antwerp-Rossie suite in the Adirondack Lowlands indicates a maximum emplacement age of ca. 1207+26-11 Ma which fixes a minimum age for deposition of regional metasedimentary rocks that it crosscuts. These results remove apparent chronological discrepancies across the St. Lawrence River, thus expanding the significance of the Rockport granite and Hyde School Gneiss and requiring modification of plate-tectonic models for the Central Metasedimentary Belt and Adirondack Mountains in the interval ca. 1350-1125 Ma.
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Macera, Patrizia, Anselmo D. I. Pisa, and Daniela Gasperini. "Geochemical and Sr-Nd isotope disequilibria during multi-stage anatexis in a metasedimentary Hercynian crust." European Journal of Mineralogy 23, no. 2 (2011): 207–22. http://dx.doi.org/10.1127/0935-1221/2011/0023-2091.
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Clarke, D. Barrie, Andrew S. Henry, and Mike A. Hamilton. "Composition, age, and origin of granitoid rocks in the Davin Lake area, Rottenstone Domain, Trans-Hudson Orogen, northern Saskatchewan." Canadian Journal of Earth Sciences 42, no. 4 (2005): 599–633. http://dx.doi.org/10.1139/e04-067.
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The Rottenstone Domain of the Trans-Hudson orogen is a 25-km-wide graniticmigmatitic belt lying between the La Ronge volcanicplutonic island arc (18901830 Ma) to the southeast and the ensialic Wathaman Batholith (1855 Ma) to the northwest. The Rottenstone Domain consists of three lithotectonic belts parallel to the orogen: (i) southeast gently folded migmatized quartzo-feldspathic metasedimentary and mafic metavolcanic rocks intruded by small concordant and discordant white tonalitemonzogranite bodies; (ii) central intensely folded and migmatized metasedimentary rocks and minor metavolcanic rocks intruded by largely discordant, xenolith-rich, pink aplite-pegmatite monzogranite bodies; and (iii) northwest steeply folded migmatized metasedimentary rocks cut by subvertical white tonalitemonzogranite sheets. Emplacement of granitoid rocks consists predominantly of contiguous, orogen-parallel, steeply dipping, syntectonic and post-tectonic sheets with prominent magmatic schlieren bands, overprinted by parallel solid-state deformation features. The white granitoid rocks have A/CNK (mol Al2O3/(mol CaO + Na2O + K2O)) = 1.141.22, K/Rb ≈ 500, ΣREE (sum of rare-earth elements) < 70 ppm, Eu/Eu* > 1, 87Sr/86Sri ≈ 0.7032, and εNdi ≈ 2. The pink monzogranites have A/CNK = 1.111.16, K/Rb ≈ 500, ΣREE > 90 ppm, Eu/Eu* < 1, 87Sr/86Sri ≈ 0.7031, and εNdi ≈ 2. The white granitoid rocks show a wider compositional range and more compositional scatter than the pink monzogranites, reflecting some combination of smaller volume melts, less homogenization, and less control by crystalmelt equilibria. All metavolcanic, metasedimentary, and granitic rocks in the Rottenstone Domain have the distinctive geochemical signatures of an arc environment. New sensitive high-resolution ion microprobe (SHRIMP) UPb geochronology on the Rottenstone granitoid rocks reveals complex growth histories for monazite and zircon, variably controlled by inheritance, magmatism, and high-grade metamorphism. Monazite ages for the granitoid bodies and migmatites cluster at ~1834 and ~1814 Ma, whereas zircon ages range from ~2480 Ma (rare cores) to ~19001830 Ma (cores and mantles), but also ~18181814 Ma for low Th/U recrystallized rims, overgrowths, and rare discrete euhedral prisms. These results demonstrate that at least some source material for the granitic magmas included earliest Paleoproterozoic crust (Sask Craton?), or its derived sediments, and that Rottenstone granitic magmatism postdated plutonism in the bounding La Ronge Arc and Wathaman Batholith. We estimate the age of terminal metamorphism in the Davin Lake area to be ~1815 Ma. Petrogenetically, the Rottenstone migmatites and granitoid rocks appear, for the most part, locally derived from their metasedimentary and metavolcanic host rocks, shed from the La Ronge Arc, Sask Craton, and possibly the Hearne Craton. The Rottenstone Domain was the least competent member in the overthrust stack and probably underwent a combination of fluid-present melting and fluid-absent decompression melting, resulting in largely syntectonic granitoid magmatism ~18351815 Ma, analogous to granite production in the High Himalayan gneiss belt.
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Goel, O. P., G. C. Kandpal, and S. S. Garhia. "Multiple Deformation in the Almora Group of Rocks Around Paharpani, District Nainital (U.P.)." Journal Geological Society of India 26, no. 12 (1985): 873–79. http://dx.doi.org/10.17491/jgsi/1985/261202.
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Abstract The medium grade metasedimentary rocks of Precambrian age around Paharpani, occurring in association with magmatites, gneisses, granites and/or granodiorites constitute a part of the Almora Group. The rocks show complex structures resulting from multipe deformations. Mesoscopic and macroscopic struc1ures indicate that the intense first deformation produced tight to isoclinal reclined folds (F1), leading to thrusting of the Almora Group of rocks over the low grade metasedimentary rocks of the Ramgarh Group along the South Almora Thrust. The effect of less severe deformation on these F1 folds was the formation of warps, crenulations and upright to inclined folds (F2), which show a variation in trend from NW/WNW to SE/ESE and plunge from 12° to 40°, The last phase of deformation produced NNE-ENE trending asymmetrical, open folds (F3) and crenulations. Superposition of F2 folds has resulted in type 1 interference patterns of Ramsay.
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Clarke, D. Barrie. "The Origins of Strongly Peraluminous Granitoid Rocks." Canadian Mineralogist 57, no. 4 (2019): 529–50. http://dx.doi.org/10.3749/canmin.1800075.
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Abstract Strongly peraluminous granites (SPAGs), with 1.20 < A/CNK < 1.30, are relatively rare rocks. They contain significant modal abundances of AFM minerals such as Bt-Ms-Crd-Grt-And-Toz-Tur-Spl-Crn of potentially magmatic, peritectic, restitic, and xenocrystic origin. Determining the origin of a SPAG depends to a large extent on establishing the correct origin of these AFM minerals. Strongly peraluminous granitic rocks can form in eight distinctly different ways: (1) as the melt fraction resulting from dehydration partial melting of peraluminous metasedimentary rocks; (2) as the bulk composition of diatexitic migmatite resulting from extensive partial melting of peraluminous metasedimentary rock; (3) as a diatexite modified by incomplete restite unmixing; (4) by bulk contamination of a less strongly peraluminous granite magma with highly peraluminous metasedimentary rocks; (5) by selective acquisition or concentration of AFM minerals by a less strongly peraluminous granite magma; (6) by fractional crystallization of quartz and feldspar from a less strongly peraluminous granite magma; (7) by removal of alkalies (Ca, Na, K) by release of a suprasolidus aqueous fluid from a less strongly peraluminous granite magma; and (8) by subsolidus hydrothermal alteration of a less strongly peraluminous granite rock. Contamination by pelitic material is the most effective process for creating SPAG plutons. A detailed case study of the South Mountain Batholith shows that its early SPAGs contain high modal abundances of Bt-Crd-Grt, largely of external origin, whereas its later SPAGs contain high modal abundances of Ms-And-Toz, largely the products of fluido-magmatic processes.
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Puchalski, Raya C., Sandra M. Barr, and Chris E. White. "Field relations and petrology of the Trafalgar Plutonic Suite and comparisons with other Devonian granitoid plutons in the Meguma terrane, Nova Scotia, Canada." Atlantic Geology 56 (April 18, 2020): 001–17. http://dx.doi.org/10.4138/atlgeol.2020.001.
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The Trafalgar Plutonic Suite intruded metasedimentary rocks of the Goldenville and Halifax groups in the northeastern part of the Meguma terrane of southern Nova Scotia at about 374 Ma, based on previously published U–Pb and 40Ar/39Ar mineral ages. Using field and petrographic observations, the suite is divided into 20 different plutons on the combined basis of variations in grain size (fine, medium, or coarse), texture (equigranular or porphyritic) and modal mineralogy (quartz diorite/tonalite, granodiorite, monzogranite, and syenogranite). The granodiorite, monzogranite, and syenogranite plutons are relatively uniform in composition with little variation in mineralogy or chemistry within each pluton or between plutons of the same lithology. In contrast the quartz diorite/tonalite plutons show mineralogical and chemical variation, both within and between plutons. The granodiorite, monzogranite, and syenogranite plutons closely resemble other peraluminous granitoid plutons characteristic of the Meguma terrane. The quartz diorite/tonalite plutons are varied but chemically resemble minor Devonian mafic intrusions elsewhere in the Meguma terrane. Like other plutons of the Meguma terrane, the Trafalgar Plutonic Suite has chemical characteristics of volcanic-arc to syn-collisional granitoid rocks and likely has experienced extensive contamination by metasedimentary material as documented by previous studies of plutons in the Meguma terrane. The minor quartz diorite/tonalite plutons are additional examples of the mafic rocks that have been proposed in tectonic models of the Meguma terrane to have facilitated melting of the lower crust to generate granodioritic parent magmas, followed by crystal fractionation and extensive contamination by metasedimentary material.
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Biševac, Vanja, Erwin Krenn, Fritz Finger, Borna Lužar-Oberiter, and Dražen Balen. "Provenance of Paleozoic very low- to low-grade metasedimentary rocks of South Tisia (Slavonian Mountains, Radlovac Complex, Croatia)." Geologica Carpathica 64, no. 1 (2013): 3–22. http://dx.doi.org/10.2478/geoca-2013-0001.
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Abstract Monazite age dating, detrital heavy mineral content and whole-rock geochemistry provided insight into the provenance, depositional history and paleogeological setting of the Radlovac Complex very low- to low-grade metasedimentary rocks (South Tisia, Slavonian Mountains, Croatia). Electron microprobe based Th-U-Pb dating of detrital monazite indicates a Variscan age of the protolith (330 ± 10 Ma). The detrital heavy mineral assemblages of representative metasedimentary rocks are dominated by apatite, zircon, tourmaline and rutile accompanied by minor quantity of epidote/zoisite, monazite and titanite. Judging from the heavy mineral assemblage, felsic igneous rocks served as the source material. This is consistent with the major and trace element spectrum of studied metasedimentary rocks characterized by high concentration of Th, high L + MREEs and high ratios of La/Sc, Th/Sc, La/Co, Th/Co and Th/Cr. The occurrence of magmatic monazite, zircon and xenotime and the absence of metamorphic heavy minerals suggest that granitoids, migmatites and migmatitic gneisses served as one major source for the metapsammites. Such rock types are commonly exposed in the Papuk Complex of the older surrounding complexes, while the Psunj Complex also contains metamorphic rocks. This is in good correlation with the monazite ages presented here which fits better with ages of Papuk Complex representative rocks than with those of the Psunj Complex known from the literature. Overall, data show that the Radlovac Complex represents the detritus of the local Variscan crust characterized by granitoid bodies, migmatites and migmatitic gneisses typical for the Papuk Complex.
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Zeng, Fafu, and Andrew J. Calvert. "Imaging the upper part of the Red Lake greenstone belt, northwestern Ontario, with 3-D traveltime tomography." Canadian Journal of Earth Sciences 43, no. 7 (2006): 849–63. http://dx.doi.org/10.1139/e06-027.
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Seismic reflection line 2B was shot across the Archean Red Lake greenstone belt and Sydney Lake fault zone that marks the northern boundary of the English River metasedimentary belt, as part of the Western Superior Lithoprobe transect. Three-dimensional tomographic inversion of first arrival traveltimes recorded in this survey delineate the subsurface to depths as great as 1.5 km around this crooked two-dimensional seismic line. Within the Red Lake greenstone belt, P-wave velocities of 6.2–7.0 km s–1 occur at 500 m depth in the Mesoarchean Balmer assemblage, clearly distinguishable from the lower velocities of 5.1–6.1 km s–1 of the Neoarchean Confederation assemblage. Although the overall range of velocities in the metasedimentary rocks of the English River subprovince is similar to that found in the Confederation assemblage, lower velocities of 5.1–5.4 km s–1 are found in the upper 300 m of the metasedimentary rocks. In particular, two 2–3 km wide, east-northeast-striking zones of low velocity are associated with the Sydney Lake fault zone and the Pakwash Lake fault zone. Correlation of the velocities with the coincident reflection section suggests that these two faults delineate a fault-bounded block in the hanging wall of a more northerly fault zone that crops out within the Uchi subprovince. Anomalous regions of low velocity, which occur at the boundary between the Confederation and Balmer assemblages, and within the Balmer assemblage, may also be related to shear zones that have minimal near-surface expression, felsic lithologies, or hydrothermal alteration of the basalts.
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Devine, Fionnuala, Donald C. Murphy, and Sharon D. Carr. "Yukon–Tanana terrane in the southern Campbell Range, Finlayson Lake belt, southeastern Yukon: the geological setting of retrogressed eclogite of the Klatsa metamorphic complex." Canadian Journal of Earth Sciences 44, no. 3 (2007): 317–36. http://dx.doi.org/10.1139/e06-110.
Full textAbstract:
Yukon–Tanana terrane in the southern Campbell Range is composed of rocks that have different metamorphic, exhumation, and structural histories, and that have formed in disparate parts of the Paleozoic Yukon–Tanana volcanic arc. The geological relationships in the southern Campbell Range reveal the tectonic and structural history of the Klatsa metamorphic complex, which represents the remnants of an Early Mississippian subduction zone beneath the Yukon–Tanana arc. The Klatsa metamorphic complex is composed of foliated to massive serpentinite, leucogabbro, amphibolite, and retrogressed eclogitic quartz–muscovite schist with lenses of metabasite. It was structurally juxtaposed on Upper Mississippian to Lower Permian metasedimentary rocks of the White Lake, King Arctic, and Money Creek formations. Regional and local structural and stratigraphic relationships suggest that the Klatsa metamorphic complex is part of the Cleaver Lake thrust sheet, the structurally highest thrust sheet in a north- to northeast-vergent thrust belt that deformed the Yukon–Tanana terrane during the Early Permian. Restoration of the displacement on the Cleaver Lake and underlying thrust faults places the Klatsa metamorphic complex on the western margin of Yukon–Tanana terrane. Late Devonian to Early Mississippian subduction is thought to have occurred along this margin based on previous paleogeographic reconstructions. Generally north- to northeast-vergent D1 to D3 folds deformed the Klatsa metamorphic complex and adjacent metasedimentary rocks. Jurassic(?) D4 imbricate thrust faulting has, in part, reactivated the Cleaver Lake thrust fault contacts and imbricated the Klatsa metamorphic complex with metasedimentary rocks in fault panels that are repeated at a scale of 10 to hundreds of metres.
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Crowley, James L. "U–Pb geochronologic constraints on the cover sequence of the Monashee complex, Canadian Cordillera: Paleoproterozoic deposition on basement." Canadian Journal of Earth Sciences 34, no. 7 (1997): 1008–22. http://dx.doi.org/10.1139/e17-083.
Full textAbstract:
The cover sequence in the Monashee complex is a platformal metasedimentary succession that occupies a nearly unique position in the Canadian Cordillera due to its unconformable contact with exposed crystalline basement. Zircon U–Pb data and field observations show that the lower part of the sequence contains Paleoproterozoic rocks, the oldest known metasedimentary rocks in the Cordilleran miogeocline, and the upper part of the sequence is Mesoproterozoic or younger. Maximum age constraints on the lower part are provided by 1.99 Ga detrital zircons from the basal unit and a 1862 ± 1 Ma orthogneiss upon which it was presumably deposited. Minimum age constraints are provided by rocks that intruded into the lower part: 1852 ± 4 Ma pegmatite, 1762 ± 6 Ma leucogranite, and 724 ± 5 Ma syenitic gneiss. The upper part of the sequence must be considerably younger than the lower part because it contains a detrital zircon dated at ~1.21 Ga. Other detrital zircons, dated at Neoarchean (2.95–2.86 Ga) and Paleoproterozoic (1.85–1.81, 1.75 Ga), suggest a source in the western Canadian Shield. These ages constrain the thickness of Mesoproterozoic and Neoproterozoic metasedimentary rocks in the cover sequence to be < 2 km. Combining these ages with previously interpreted Paleozoic deposition ages for the middle and upper parts of the sequence constrains the thickness to be <0.2 km, considerably less than that of coeval rocks above the Monashee complex in the hanging wall of the Monashee décollement. Such a contrast suggests that deposition above and below the décollement occurred in different parts of the Cordilleran miogeocline.
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White, Chris E., Sandra M. Barr, and Ulf Linnemann. "U–Pb (zircon) ages and provenance of the White Rock Formation of the Rockville Notch Group, Meguma terrane, Nova Scotia, Canada: evidence for the “Sardian gap” and West African origin." Canadian Journal of Earth Sciences 55, no. 6 (2018): 589–603. http://dx.doi.org/10.1139/cjes-2017-0196.
Full textAbstract:
The White Rock Formation is the lowermost formation of the Rockville Notch Group, an assemblage of Silurian–Devonian rocks preserved in five areas along the northwestern margin of the Meguma terrane of Nova Scotia. The formation consists mainly of mafic and felsic metavolcanic rocks, interlayered with and overlain by marine metasedimentary rocks. Felsic metatuff has now been dated from four locations near both the bottom and top of the volcanic pile and yielded a narrow age range (with errors) of about 446–434 Ma. These dates confirm a 30 Ma hiatus after deposition of the Early Ordovician Hellgate Formation in the underlying Halifax Group. This hiatus is coeval with the “Sardian gap” in the Lower Palaeozoic of peri-Gondwanan Europe. The metavolcanic–metasedimentary assemblage is overlain by mainly metasiltstone with abundant quartzite and metaconglomerate lenses; some of the latter were previously interpreted to be Ordovician tillite, an interpretation no longer viable. New detrital zircon data from metasedimentary samples indicate that the major sediment sources for the White Rock Formation have ages of ca. 670–550 and ca. 2050 Ma, similar to ages from the underlying Goldenville and Halifax groups. A smaller population of Mesoproterozoic zircon grains indicates that the Meguma terrane interacted with a terrane composed mainly of Mesoproterozoic crust during the Silurian and Devonian. The occurrence of the “Sardian gap” and the detrital zircon record constrain the palaeoposition of the Meguma terrane to have been close to Cadomia and West Africa in the Early Cambrian to Early Silurian.
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MENG, EN, CHAO-YANG WANG, ZHUANG LI, et al. "Palaeoproterozoic metasedimentary rocks of the Ji'an Group and their significance for the tectonic evolution of the northern segment of the Jiao–Liao–Ji Belt, North China Craton." Geological Magazine 155, no. 1 (2017): 149–73. http://dx.doi.org/10.1017/s0016756817000632.
Full textAbstract:
AbstractIn this paper we present new petrological and whole-rock geochemical data for the Palaeoproterozoic metasedimentary rocks in the upper part of the Ji'an Group within the Jiao–Liao–Ji Belt, China, as well as zircon U–Pb age dates andin situLu–Hf isotope data. The new data improve our understanding of the original nature of the metasedimentary rocks, further providing insights into their tectonic setting and the evolutionary history of the northern segment of the Jiao–Liao–Ji Belt. The zircons can be divided into two groups, viz., one of magmatic origin and the other of metamorphic origin. Zircon U–Pb dating gave mean or statistical peak ages for the magmatic zircons at 2035, 2082, 2178, 2343–2421, 2451–2545, 2643–2814 and 2923–3446 Ma, and mean peak ages for the metamorphic zircons at 1855 and 1912 Ma, which indicate a maximum depositional age of 2.03 Ga and two-stage metamorphic events atc. 1.91 and 1.85 Ga for the metasedimentary rocks. Geochemical data show that (1) the protoliths of these rocks were mainly sandstones, greywackes and claystones, together with some shales; (2) the main sources of the sedimentary material were Palaeoproterozoic granites and acid volcanic rocks, with minor contributions from Archaean granitic rocks; and (3) the sediments were deposited in an active continental margin setting. Moreover, along the northeastern margin of the Eastern Block of the North China Craton there is evidence of ancient crustal materials as old as 3.76 Ga, and multiple crustal growth events at 3.23–3.05, 2.80–2.65, 2.54–2.45 and 2.28–2.08 Ga.
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Kerr, Andrew, George A. Jenner, and Brian J. Fryer. "Sm–Nd isotopic geochemistry of Precambrian to Paleozoic granitoid suites and the deep-crustal structure of the southeast margin of the Newfoundland Appalachians." Canadian Journal of Earth Sciences 32, no. 2 (1995): 224–45. http://dx.doi.org/10.1139/e95-019.
Full textAbstract:
In the Eastern Central Mobile Belt of the Newfoundland Appalachians, late Precambrian basement inliers have εNd from −3 to +2, but Cambro-Ordovician metasedimentary rocks have initial εNd below −7. This region is inferred to have an "inverted" crustal residence structure, which influenced subsequent Appalachian-cycle magmatism. Ordovician and Silurian granitoid suites have εNd of −8 to −2, bracketing both basement and cover, but peraluminous, "S-type" granites have the lowest εNd. Devonian granites have initial εNd values from −5 to +1, and low εNd is associated with peraluminous character. These Paleozoic granites show geographic trends, with lowest εNd values in areas where metasedimentary rocks are abundant. They are suggested to contain anatectic material from both Precambrian basement and metasedimentary cover, but some "I-type" suites probably also include a mantle-derived component. In the adjacent Avalon Zone, Precambrian plutonic suites mostly have εNd from +1 to +6, but there are negative εNd values (−8 to −4) in the westernmost Avalon Zone. Devonian plutonic suites mostly have εNd from +2 to +5. Thus, the Precambrian crust of the Avalon Zone is largely "juvenile," except at its westernmost edge. Contrasts across the Eastern Central Mobile Belt–Avalon Zone boundary, defined by the Dover–Hermitage Bay fault system, indicate a major, crustal-scale structure, and suggest an isotopically distinct "central block" beneath the central Appalachian Orogen, rather than a simple extension of "Avalonian" crust. Similar geographic–isotopic patterns have been reported in Nova Scotia and New Brunswick, suggesting that this pattern represents a first-order deep-crustal subdivision of the northern Appalachian Orogen.
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Bucholz, Claire E., and Christopher J. Spencer. "Strongly Peraluminous Granites across the Archean–Proterozoic Transition." Journal of Petrology 60, no. 7 (2019): 1299–348. http://dx.doi.org/10.1093/petrology/egz033.
Full textAbstract:
Abstract Strongly peraluminous granites (SPGs) form through the partial melting of metasedimentary rocks and therefore represent archives of the influence of assimilation of sedimentary rocks on the petrology and chemistry of igneous rocks. With the aim of understanding how variations in sedimentary rock characteristics across the Archean–Proterozoic transition might have influenced the igneous rock record, we compiled and compared whole-rock chemistry, mineral chemistry, and isotope data from Archean and Paleo- to Mesoproterozoic SPGs. This time period was chosen as the Archean–Proterozoic transition broadly coincides with the stabilization of continents, the rise of subaerial weathering, and the Great Oxidation Event (GOE), all of which left an imprint on the sedimentary rock record. Our compilation of SPGs is founded on a detailed literature review of the regional geology, geochronology, and inferred origins of the SPGs, which suggest derivation from metasedimentary source material. Although Archean and Proterozoic SPGs are similar in terms of mineralogy or major-element composition owing to their compositions as near-minimum melts in the peraluminous haplogranite system, we discuss several features of their mineral and whole-rock chemistry. First, we review a previous analysis of Archean and Proterozoic SPGs biotite and whole-rock compositions indicating that Archean SPGs, on average, are more reduced than Proterozoic SPGs. This observation suggests that Proterozoic SPGs were derived from metasedimentary sources that on average had more oxidized bulk redox states relative to their Archean counterparts, which could reflect an increase in atmospheric O2 levels and more oxidized sedimentary source rocks after the GOE. Second, based on an analysis of Al2O3/TiO2 whole-rock ratios and zircon saturation temperatures, we conclude that Archean and Proterozoic SPGs formed through partial melting of metasedimentary rocks over a similar range of melting temperatures, with both ‘high-’ and ‘low-’temperature SPGs being observed across all ages. This observation suggests that the thermo-tectonic processes resulting in the heating and melting of metasedimentary rocks (e.g. crustal thickening or underplating of mafic magmas) occurred during generation of both the Archean and Proterozoic SPGs. Third, bulk-rock CaO/Na2O, Rb/Sr, and Rb/Ba ratios indicate that Archean and Proterozoic SPGs were derived from partial melting of both clay-rich (i.e. pelites) and clay-poor (i.e. greywackes) source regions that are locality specific, but not defined by age. This observation, although based on a relatively limited dataset, indicates that the source regions of Archean and Proterozoic SPGs were similar in terms of sediment maturity (i.e. clay component). Last, existing oxygen isotope data for quartz, zircon, and whole-rocks from Proterozoic SPGs show higher values than those of Archean SPGs, suggesting that bulk sedimentary 18O/16O ratios increased across the Archean–Proterozoic boundary. The existing geochemical datasets for Archean and Proterozoic SPGs, however, are limited in size and further work on these rocks is required. Future work must include detailed field studies, petrology, geochronology, and constraints on sedimentary source ages to fully interpret the chemistry of this uniquely useful suite of granites.
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Zaika, V. A., and A. A. Sorokin. "Age and Sources of Metasedimentary Rocks of the Galam Terrane in the Mongol–Okhotsk Fold Belt: Results of U–Pb Age and Lu–Hf Isotope Data from Detrital Zircons." Geotectonics 55, no. 6 (2021): 779–94. http://dx.doi.org/10.1134/s001685212106008x.
Full textAbstract:
Abstract The Mongol–Okhotsk fold belt is one of the major structural elements of East Asia. In this article, we present U–Pb age and Hf isotope data for detrital zircons from metasedimentary rocks of the Galam Terrane. Our new data confirm that these rocks contain a significant amount of Archean and Paleoproterozoic zircons: most grains, regardless of age, have negative εHf(t) values from –30.0 to –10.0 and model age tHf(C) > 2.2 Ga. The main sources of detrital material for the metasedimentary rocks of the Galam Terrane were igneous and metamorphic complexes of the southeastern margin of the Siberian Craton. Some of the Devonian and Carboniferous zircons have slightly negative and positive εHf(t) values of ‒7.4 to +6.9 and younger tHf(C) ages of 1.46–0.90 Ga. These zircons were derived from eroded island arcs in the Mongol–Okhotsk Paleocean. Our results suggest that the Galam Terrane is a Paleozoic accretionary complex of the Siberian Craton.
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Chugaev, A. V., I. V. Chernyshev, A. E. Budyak, G. V. Mandzhieva, A. S. Sadasyuk, and B. I. Gareev. "Variations of the 238U/235U isotope ratio in metasedimentary rocks and evidence of changes in sedimentation conditions during the Ediacaran period of the Neoproterozoic." Доклады Академии наук 484, no. 4 (2019): 472–77. http://dx.doi.org/10.31857/s0869-56524844472-477.
Full textAbstract:
The isotopic composition of uranium is a new geochemical indicator that facilitates reconstruction of the redox conditions of geological processes. In this paper the results of study of the 238U/235U isotope ratio in the Neoproterozoic metasedimentary rocks of the Baikal–Patom fold belt (Northern Transbaikalia) were obtained using the MC-ICP-MS method and 233U+236U double spike. The scale of 238U/235U ratio variations (δ238U = –0.37 to –0.11‰) is within the range of (–0.39 to +0.15‰), typical of metasedimentary terrigenous rocks of marine origin. In terms of the δ238U values, uranium of the BPB rocks studied is heavier than seawater uranium (δ238U = –0.41 ± 0.03). There is a correlation between the δ238U value in the rocks and their position in the stratigraphic section. Variations of the 238U/235U ratio in the terrigenous-carbonate sequences of BPB indicate that the sedimentation conditions changed and euxinic conditions were established in the course of evolution of the paleobasin in the Late Ediacarian Period.
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Mohanty, S., and K. Naha. "Stratigraphic Relations of the Precambrian Rocks in the Salumbar Area, Southeastern Rajasthan." Journal Geological Society of India 27, no. 6 (1986): 479–93. http://dx.doi.org/10.17491/jgsi/1986/270601.
Full textAbstract:
Abstract Around Salumbar in the Udaipur district, Rajasthan, the Banded Gneissic Complex (BGC). the Aravalli metasedimentary rocks, the Dudar Gneiss and the Lakapa Granite Gneiss have been involved in the same style and sequence of muhiple deformation. The oldest rocks are the migmatites forming the BGC, which underlie the Aravalli metasediments with an unconformity marked by a conglomerate. Rare relict pre-Aravalli structures in the BGC, and the conglomerate containing gneissic pebbles provide incontrovertible evidence for a part of the BGC being the original basement. Identical structural style and sequence of the basement gneisses wilh those of the metasedimentary cover rocks, however, point to mobilization so that they could take part in the earliest deformation affecting the metasediments in a ductile manner. The Dudar Gneiss has formed by migmatization of the Aravalli rocks synkinematically with the first deformation, whereas the Lakapa Granite Gneiss has been emplaced as a syn-to late-tectonic intrusion.
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Payne, L., L. Ross, and R. Bauer. "SEM Petrography of Hydrothermally Altered, Metamorphic Monazite in the Quetico Sub-Province of Northeastern Minnesota." Microscopy and Microanalysis 7, S2 (2001): 536–37. http://dx.doi.org/10.1017/s1431927600028750.
Full textAbstract:
Metasedimentary rocks of the Archean Quetico subprovince of the Superior province in northeastern Minnesota contain monazite that has undergone low-grade hydrothermal alteration and disseminated sulfide mineralization. The area contains multiply deformed, metasedimentary rocks with abundant granitic veins that were subjected to deep burial, deformation, and syntectonic Barrovian metamorphism ranging from kyanite-staurolite grade to sillimanite-muscovite grade. Continued deformation and concomitant granitic intrusion produced rapid decompression and a well-developed high-temperature, low-pressure thermal aureole adjacent to the granitic intrusive bodies. This second metamorphic event is characterized by mineral assemblages containing cordierite or andalusite after staurolite. Subsequent reburial of the area produced prennite/pumpellyite facies regional metamorphism that is widespread but only locally recognized.The initial aim of this study was to determine the petrographic relationships between monazite, a light rare-earth phosphate, and the surrounding minerals as a basis for absolute age dating, by electron probe microanalyzer (EPMA), of deformation and related metamorphic events.