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Yunshuai Li - One of the best experts on this subject based on the ideXlab platform.
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Grenvillian Orogeny in the oulongbuluke block nw china constraints from an 1 1 ga andean type arc magmatism and metamorphism
Precambrian Research, 2019Co-Authors: Shengyao Yu, Sanzhong Li, Jianxin Zhang, Yinbiao Peng, Yunshuai LiAbstract:Abstract A systematic petrologic, geochemical, and zircon U-Pb and Lu-Hf isotopic investigation of an ∼1.1 Ga arc magmatism and metamorphism was studied to evaluate the Grenvillian Orogeny and assembly of Rodinia in the Oulongbuluke Block in NW China. The peak metamorphic P-T conditions of the paragneiss were restricted to 4.8–5.8 kbar and 652–700 °C based on P-T pseudosection and conventional geothermobarometry. Zircon U-Pb ages of 1132 ± 33 Ma, 1118 ± 9 Ma, and 1124 ± 12 Ma were determined for the metabasite, augen granitic gneiss, and paragneiss, respectively, indicating magmatic intrusion and a metamorphism event in the late Mesoproterozoic. The metabasites exhibited enrichment of light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) and depletion of heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs), resembling the geochemical characteristics of Andean arc magmatism. The whole-rock geochemistry and in-situ zircon eHf(t) values of 4.3 and 11.2 suggested that the protolithic mafic magma originated from a subduction-modified lithospheric mantle. The low zircon eHf(t) values of −5.2 and −0.5 also suggested that the calc-alkaline augen granitic gneisses were derived from the partial melting of a late Paleoproterozoic crustal source. The ∼1.1 Ga arc-related magmatism and metamorphism in the Oulongbuluke Block indicated the occurence of a tectonic-thermal event in an Andean-type active continental margin in the late Mesoproterozoic. In this regard, the Oulongbuluke Block was likely temporarily connected to the Qilian Block and Tarim Craton, forming a single continuous block with similar Grenville age during the late Mesoproterozoic to early Neoproterozoic (1.1–0.9 Ga).
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the Grenvillian Orogeny in the altun qilian north qaidam mountain belts of northern tibet plateau constraints from geochemical and zircon u pb age and hf isotopic study of magmatic rocks
Journal of Asian Earth Sciences, 2013Co-Authors: Shengyao Yu, Jianxin Zhang, Pablo Garcia Del Real, Xilin Zhao, Jianghua Gong, Yunshuai LiAbstract:Abstract Numerous Neoproterozoic magmatic and metamorphic events in the Altun–Qilian–North Qaidam (AQNQ) region record Grenvillian orogenesis and amalgamation of the supercontinent Rodinia. However, the tectonothermal regimes responsible for these Neoproterozoic events and the assumed position of the AQNQ in Rodinia remain controversial. Zircon U–Pb age data show that the orthogneiss and paragneiss/schist of the AQNQ experienced concurrent magmatism and metamorphism at 895–925 Ma. Zircon Lu–Hf isotopic data indicate that the gneisses in the AQNQ have eHf (0.9 Ga) values and tDM2 (Hf) model ages ranging from −5.6 to +3.9 and 1.4 to 1.9 Ga. These data suggest that the early Neoproterozoic magma in the AQNQ was predominately derived from a late Paleoproterozoic–early Mesoproterozoic crustal source between 1.4 and 1.9 Ga, marking an important episode of crustal growth in the AQNQ. The Neoproterozoic magmatism is geochemically characterized by (1) high SiO2, K2O, and low P2O5; (2) A/CNK ratios >1.0, ranging from 1.03 to 1.09; (3) enrichment in Rb, Th and U, and depletion in Ba, Nb, Ta, Sr, Ti, and Eu. Based on the geochemical resemblance to high-K calc-alkaline I-type granite and zircon Lu–Hf isotope signatures, the Neoproterozoic magmatism in the AQNQ was probably derived from ancient mafic-intermediate igneous rocks in an active continental margin. The Neoproterozoic tectono-magmatic–metamorphic history of the AQNQ, directly associated with the South China block (SCB) and the Tarim block (TB), indicates that the AQNQ and the TB coexisted as a single block in the early Neoproterozoic, which was temporarily connected to the SCB to the north or west in Rodinia during the late stages of the Grenvillian Orogeny (950–900 Ma).
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The Grenvillian Orogeny in the Altun–Qilian–North Qaidam mountain belts of northern Tibet Plateau: Constraints from geochemical and zircon U–Pb age and Hf isotopic study of magmatic rocks
Journal of Asian Earth Sciences, 2013Co-Authors: Shengyao Yu, Jianxin Zhang, Pablo Garcia Del Real, Xilin Zhao, Jianghua Gong, Yunshuai LiAbstract:Abstract Numerous Neoproterozoic magmatic and metamorphic events in the Altun–Qilian–North Qaidam (AQNQ) region record Grenvillian orogenesis and amalgamation of the supercontinent Rodinia. However, the tectonothermal regimes responsible for these Neoproterozoic events and the assumed position of the AQNQ in Rodinia remain controversial. Zircon U–Pb age data show that the orthogneiss and paragneiss/schist of the AQNQ experienced concurrent magmatism and metamorphism at 895–925 Ma. Zircon Lu–Hf isotopic data indicate that the gneisses in the AQNQ have eHf (0.9 Ga) values and tDM2 (Hf) model ages ranging from −5.6 to +3.9 and 1.4 to 1.9 Ga. These data suggest that the early Neoproterozoic magma in the AQNQ was predominately derived from a late Paleoproterozoic–early Mesoproterozoic crustal source between 1.4 and 1.9 Ga, marking an important episode of crustal growth in the AQNQ. The Neoproterozoic magmatism is geochemically characterized by (1) high SiO2, K2O, and low P2O5; (2) A/CNK ratios >1.0, ranging from 1.03 to 1.09; (3) enrichment in Rb, Th and U, and depletion in Ba, Nb, Ta, Sr, Ti, and Eu. Based on the geochemical resemblance to high-K calc-alkaline I-type granite and zircon Lu–Hf isotope signatures, the Neoproterozoic magmatism in the AQNQ was probably derived from ancient mafic-intermediate igneous rocks in an active continental margin. The Neoproterozoic tectono-magmatic–metamorphic history of the AQNQ, directly associated with the South China block (SCB) and the Tarim block (TB), indicates that the AQNQ and the TB coexisted as a single block in the early Neoproterozoic, which was temporarily connected to the SCB to the north or west in Rodinia during the late stages of the Grenvillian Orogeny (950–900 Ma).
Aphrodite Indares - One of the best experts on this subject based on the ideXlab platform.
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Abstract: Transformation of Fe–Ti gabbro to coronite, eclogite, and amphibolite in the Baie du Nord segment, Manicouagan Imbricate zone, eastern Grenville province: evidence for high heat flow in the lower crust during orogenesis
2020Co-Authors: Aphrodite IndaresAbstract:Fe-Ti gabbro from the Baie du Nord Segment of the Manicouagan lmbricate zone, metamorphosed under high-P-T conditions during the Grenvillian Orogeny, has been the focus of a detailed micropetrological study. Textures and mineral chemistry suggest that the mineral assemblages represent progressive stages of metamorphic transformation resulting in the formation of coronas, pseudomorphs after igneous phases (transitional), and true granoblastic eclogite. The transitional and eclogitic samples also have coronas developed locally around igneous xenocrysts of plagioclase and olivine. Coronitic Fe-Ti gabbro is transformed to amphibolite at deformed margins and contains clinopyroxene-bearing leucosomes with garnet poikiloblasts that are indicative of high-PT dehydration melting. Interpretation of garnet zoning and thermobarometry suggest that the highest-P-T conditions are recorded by coronas around xenocrysts (ca. 720-800°C at 14-17 kbar) and gamet-clinopyroxene cores in granoblastic assemblages (ca. 740-820°C at 13-17 kbar) in the eclogitic samples. Re-equilibration during the early stages of exhumation at high-T conditions (>700°C) affected all samples, and is indicated by the widespread development of pargasite-bearing plagioclase collars in the coronitic and transitional metagabbro and by widespread re-equilibration of the eclogite giving lower P-T estimates at grain boundaries. However, the difference in calculated P conditions between coronite and eclogite samples is consistent with increasing pressure (depth) from the coronite (11-13 kbar) to the eclogite ( 13-17 kbar). The P-T conditions recorded by these rocks define an apparent isothermal P-T path. In fact, this is a steep metamorphic field gradient, indicating that all the samples experienced temperatures in excess of 800°C both during and shortly after peak metamorphism over a range of depths (ca. 65-35 km). This is tum suggests high heat flow through this segment of the lower crust during the Grenvillian Orogeny.
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Syn-orogenic magmatism over 100 m.y. in high crustal levels of the central Grenville Province: Characteristics, age and tectonic significance
Lithos, 2018Co-Authors: Pierre-arthur Groulier, Aphrodite Indares, G. R. Dunning, Abdelali Moukhsil, George A. JennerAbstract:Abstract The Escoumins Supracrustal Belt (ESB) represents higher levels of the infrastructure of a large hot orogen, exposed in a broadly dome and basin pattern. It consists of remnants of a Pinwarian-age (1.52–1.46 Ga) oceanic arc and arc-rift sequence, preserved in the low-P Belt of the central Grenville Province, and was intruded by diverse Grenvillian-age plutons. The plutonic rocks range from quartz monzodiorite to granite and have intrusion ages covering a time interval of ~100 My, that represents the entire range of the Grenvillian Orogeny. Moreover, the ages, field relations and geochemical signatures of the different intrusions can be matched with different documented stages of the Orogeny. The oldest pluton, the magnesian, biotite-bearing Bon-Desir granite (1086 ± 2 Ma), has positive eNd (+0.6), TDM = 1.52 Ga, and is attributed to melting of a juvenile Pinwarian crust as a result of slab break-off, at the onset of continental collision. The ferroan and Ba–Sr enriched, biotite-, amphibole- and clinopyroxene-bearing Michaud plutonic suite (1063 ± 3 Ma) and biotite-rich felsic sill (1045 ± 3 Ma) have eNd (−0.01 − +0.8) and TDM = 1.45–1.48 Ga. Their geochemistry is consistent with fractionation of a mafic magma derived from melting of a Geon 14 subduction-modified subcontinental lithospheric mantle. This magmatism is consistent with convective thinning of subcontinental lithosphere, potentially linked to tectonic extrusion and orogenic collapse. This collapse ultimately led to the juxtaposition of the low-P Belt with the high-T mid-P Belt in the hinterland of the Grenville Province and to amphibolite-facies metamorphism in the former, producing metamorphic zircon overgrowths at 1037 ± 10 Ma. Finally, 988 ± 5 Ma to 983 ± 5 Ma syn-kinematic peraluminous two-mica garnetiferous leucogranite bodies and pegmatites with inherited 1055 ± 2 Ma metamorphic monazite were derived from melting of previously metamorphosed deeper levels of the low-P Belt. This is consistent with a high geothermal gradient linked to thinning of the crust in a Basin and Range setting. The geochemical and age pattern of Grenvillian-age magmatism in the ESB, in conjunction with the overall architecture of the Province, suggests that Laurentia was the upper plate during the Grenvillian Orogeny.
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Pinwarian to Grenvillian magmatic evolution in the central Grenville Province: new constraints from ID–TIMS U–Pb ages and coupled Lu–Hf S–MC–ICP–MS data
Canadian Journal of Earth Sciences, 2015Co-Authors: Lars Eivind Augland, Abdelali Moukhsil, Fabien Solgadi, Aphrodite IndaresAbstract:Understanding the magmatic evolution of the rocks once comprising the hinterland of the Grenville Orogen through their Mesoproterozoic formation is a key to understanding the Grenvillian Orogeny as a whole. In this contribution, we present high-precision isotope dilution thermal ionization mass spectrometry (ID–TIMS) U–Pb and coupled solution multicollector inductively coupled plasma mass spectrometry (S–MC–ICP–MS) Lu–Hf zircon data from magmatic rocks occurring in the allochthonous belt of the Grenville Orogen in the central part of the Grenville Province. We document the presence of a large tract of Pinwarian crust represented by a 1497 ± 5 Ma granitic gneiss, as well as large late Geon 14 to early Geon 13 (1434 +7/−11, 1413 ± 12, 1393 ± 8, 1383 ± 1 Ma) magmatic complexes. One Grenvillian plutonic suite of 1015 ± 2 Ma that cross-cuts the host-rock metamorphic fabric has also been dated. This age provides a minimum age of Ottawan metamorphism in the region. The Hf-isotopic data show that the magmatic roc...
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Mafic and ultrapotassic rocks from the Canyon domain (central Grenville Province): geochemistry and tectonic implications
Canadian Journal of Earth Sciences, 2012Co-Authors: Carolina Valverde Cardenas, Aphrodite Indares, George A. JennerAbstract:The Canyon domain and the Banded complex in the Manicouagan area of the Grenville Province preserve a re- cord of magmatic activity from ∼1.4 to 1 Ga. This study focuses on 1.4-1.2 Ga mafic rocks and 1 Ga ultrapotassic dykes. Geochemistry and Sm-Nd isotopic signatures were used to constrain the origin of these rocks and evaluate the changing role of the mantle with time and tectonic setting from the late evolution of the Laurentian margin to the Grenvillian Orogeny, in the Manicouagan area. The mafic rocks include layers inferred to represent flows, homogeneous bodies in mafic migma- tite, and deformed dykes, all of which were recrystallized under granulite-facies conditions during the Grenvillian Orogeny. In spite of the complexities inherent in these deformed and metamorphosed mafic rocks, we were able to recognize suites with distinctive geochemical and isotopic signatures. Integration of this data along with available ages is consistent with a 1.4 Ga continental arc cut by 1.2 Ga non-arc basalts derived from depleted asthenospheric mantle, with varied degrees of crustal contamination and inferred to represent magmatism in an extensional environment. The 1 Ga ultrapotassic dykes postdate the Grenvillian metamorphism. They are extremely enriched in incompatible elements, have negative Nb anomalies, relatively unradiogenic Sr-isotopic compositions (initial 87 Sr/ 86 Sr ~ 0.7040) and ɛNd - 3t o-15. Some dykes have composi- tional characteristics consistent with derivation from the mantle, ruling out crustal contamination as a major process in their petrogenesis. The most likely source region for the ultrapotassic dykes is a metasomatized subcontinental lithospheric man- tle, with thermal input from the asthenosphere in association with post-orogenic delamination.
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New insights on the 1.7-1.0 Ga crustal evolution of the central Grenville Province from the Manicouagan - Baie Comeau transect
Precambrian Research, 2010Co-Authors: G. R. Dunning, Aphrodite IndaresAbstract:Abstract Integrated field relationships and U–Pb geochronology of rocks exposed along the southern part of the Manicouagan reservoir (central Grenville Province, Quebec) provide insights into protolith formation and thermal events that range in age from ca. 1.7 to 0.9 Ga and share common features with the rest of the Grenville Province and beyond. From presently lower to higher structural levels, main findings include the recognition of: (a) ca. 1.70–1.75 Ga granitic magmatism and metamorphism in the southern part of the parautochthonous Gagnon terrane, correlative in age with late stages of magmatism in the Makkovik Orogen to the northeast; (b) a ca. 1.69 gabbro-anorthosite suite (Island domain) which is inferred to represent the southwesternmost exposure of Labradorian crust in the central Grenville Province; (c) a 1.4 Ga volcaniclastic sequence and associated plutonic rocks (Canyon domain), which based on lithological association and age, is inferred to represent the NNE extension of the Montauban island arc; and (d) a ca. 1.2 Ga bimodal felsic-mafic volcanic to intermediate volcaniclastic sequence (Banded complex), inferred to have originated in an intra-continental rift system, contemporaneously with the Composite Arc Belt (southwestern Grenville Province) and with widespread extensional magmatism elsewhere in the Canadian Shield. In addition, 1.3 Ga granitoid plutons are documented to intrude Labradorian units at the NW boundary of Canyon domain. The significance of these plutons is ambiguous, as they may represent either stitching plutons, marking the accretion of the 1.4 Ga Canyon domain to the Laurentian margin, or the first stage in the development of the ca. 1.2 Ga continental rift system. The hinterland units (Island domain, Canyon domain and Banded complex) were metamorphosed under medium-pressure granulite facies conditions during the culmination of the Grenvillian Orogeny between 1.08 and 1.04 Ga. This metamorphism was accompanied by ca. 1.07 Ga A-type granitic magmatism in Canyon domain. In addition, locally abundant ca. 0.98 Ga late-tectonic felsic pegmatite and ultrapotassic dykes occur in Canyon domain. This event is coeval with titanite ages documented in a wide range of units. The data on the Grenvillian evolution suggest mantle-derived magmatism and associated metamorphism in the hinterland during both the culmination and the waning stages of the Grenvillian Orogeny.
Saurabh Singhal - One of the best experts on this subject based on the ideXlab platform.
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U–Pb (zircon) geochronologic constraint on tectono-magmatic evolution of Chaur granitoid complex (CGC) of Himachal Himalaya, NW India: implications for the Neoproterozoic magmatism related to Grenvillian Orogeny and assembly of the Rodinia superconti
International Journal of Earth Sciences, 2020Co-Authors: Paramjeet Singh, Saurabh SinghalAbstract:Many elongated, lenticular intrusive granitoids of various ages are scattered within the Lesser Himalayan metamorphic belt, all along the ~ 2500 km length of the Himalaya. The Neoproterozoic Chaur granitoid complex (CGC) of Chaur area is characterized by foliated and non-foliated peraluminous granites occurring as an isolated granitoid body within the Jutogh group. In this work, we present the whole-rock geochemical data of six samples and U–Pb (zircon) geochronology of two different granites of the CGC and one granitic gneiss sample of Jutogh group from Himachal Pradesh of NW Himalaya. Our newly obtained results of U–Pb (zircon) geochronological age populations from all granitoid sample yield age between 766 and 1080 Ma with few younger phases and older inherited ages. We obtained U–Pb (zircon) ages from two sample of the CGC, out of which one gives the two prominent age spectra for ^206Pb/^238U with weighted mean age of 826 ± 4.97/9.74 Ma, MSWD = 0.65, n = 8) and 868 ± 6.21/12.17 Ma, MSWD = 1.28, n = 7). Similarly, another granite of CGC gives the weight mean age of 929 ± 6.48/12.70 Ma (MSWD = 1.28, n = 11). The granitic gneiss of the Jutogh group also gives two prominent age spectra for ^206Pb/^238U, with weighted mean age of 861 ± 8.27/16.21 Ma (MSWD = 0.31, n = 10) and 932 ± 10.0/19.6 Ma (MSWD = 1.57, n = 8). The whole-rock geochemical data show calc-alkaline composition of all six samples and suggest a subduction-related accretion setup. The depletion in the Nb, Sr, P and Ti in CGC indicates a magmatic arc type magma. U–Pb (zircon) ages of all three samples have a similar phase of crystallization and we defined as ~ 930 Ma age of crystallization of CGC. The whole-rock geochemical data suggest that all the three samples possibly came from the same magma source during the Neoproterozoic magmatic events in the northern marginal part of the Indian plate. It is envisaged that the unknown microcontinents present in the northern margin collide with the Indian plate and the subduction process coincides with the onset of the Grenvillian Orogeny during the Neoproterozoic. The extension of these minor collision orogen may have been connected with Lhasa, Trim as well as Greater India blocks. In this collisional process, the crustal melt was generated and intruded in the form of CGC within the pre-existing Paleoproterozoic crust of Indian plate. The whole process indicates that the subduction of unknown microcontinent under the Indian plate may be correlated with the Grenvillian Orogeny and formation of the Rodinia supercontinent during Neoproterozoic.
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u pb zircon geochronologic constraint on tectono magmatic evolution of chaur granitoid complex cgc of himachal himalaya nw india implications for the neoproterozoic magmatism related to Grenvillian Orogeny and assembly of the rodinia supercontinent
International Journal of Earth Sciences, 2020Co-Authors: Paramjeet Singh, Saurabh SinghalAbstract:Many elongated, lenticular intrusive granitoids of various ages are scattered within the Lesser Himalayan metamorphic belt, all along the ~ 2500 km length of the Himalaya. The Neoproterozoic Chaur granitoid complex (CGC) of Chaur area is characterized by foliated and non-foliated peraluminous granites occurring as an isolated granitoid body within the Jutogh group. In this work, we present the whole-rock geochemical data of six samples and U–Pb (zircon) geochronology of two different granites of the CGC and one granitic gneiss sample of Jutogh group from Himachal Pradesh of NW Himalaya. Our newly obtained results of U–Pb (zircon) geochronological age populations from all granitoid sample yield age between 766 and 1080 Ma with few younger phases and older inherited ages. We obtained U–Pb (zircon) ages from two sample of the CGC, out of which one gives the two prominent age spectra for 206Pb/238U with weighted mean age of 826 ± 4.97/9.74 Ma, MSWD = 0.65, n = 8) and 868 ± 6.21/12.17 Ma, MSWD = 1.28, n = 7). Similarly, another granite of CGC gives the weight mean age of 929 ± 6.48/12.70 Ma (MSWD = 1.28, n = 11). The granitic gneiss of the Jutogh group also gives two prominent age spectra for 206Pb/238U, with weighted mean age of 861 ± 8.27/16.21 Ma (MSWD = 0.31, n = 10) and 932 ± 10.0/19.6 Ma (MSWD = 1.57, n = 8). The whole-rock geochemical data show calc-alkaline composition of all six samples and suggest a subduction-related accretion setup. The depletion in the Nb, Sr, P and Ti in CGC indicates a magmatic arc type magma. U–Pb (zircon) ages of all three samples have a similar phase of crystallization and we defined as ~ 930 Ma age of crystallization of CGC. The whole-rock geochemical data suggest that all the three samples possibly came from the same magma source during the Neoproterozoic magmatic events in the northern marginal part of the Indian plate. It is envisaged that the unknown microcontinents present in the northern margin collide with the Indian plate and the subduction process coincides with the onset of the Grenvillian Orogeny during the Neoproterozoic. The extension of these minor collision orogen may have been connected with Lhasa, Trim as well as Greater India blocks. In this collisional process, the crustal melt was generated and intruded in the form of CGC within the pre-existing Paleoproterozoic crust of Indian plate. The whole process indicates that the subduction of unknown microcontinent under the Indian plate may be correlated with the Grenvillian Orogeny and formation of the Rodinia supercontinent during Neoproterozoic.
Shengyao Yu - One of the best experts on this subject based on the ideXlab platform.
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Grenvillian Orogeny in the oulongbuluke block nw china constraints from an 1 1 ga andean type arc magmatism and metamorphism
Precambrian Research, 2019Co-Authors: Shengyao Yu, Sanzhong Li, Jianxin Zhang, Yinbiao Peng, Yunshuai LiAbstract:Abstract A systematic petrologic, geochemical, and zircon U-Pb and Lu-Hf isotopic investigation of an ∼1.1 Ga arc magmatism and metamorphism was studied to evaluate the Grenvillian Orogeny and assembly of Rodinia in the Oulongbuluke Block in NW China. The peak metamorphic P-T conditions of the paragneiss were restricted to 4.8–5.8 kbar and 652–700 °C based on P-T pseudosection and conventional geothermobarometry. Zircon U-Pb ages of 1132 ± 33 Ma, 1118 ± 9 Ma, and 1124 ± 12 Ma were determined for the metabasite, augen granitic gneiss, and paragneiss, respectively, indicating magmatic intrusion and a metamorphism event in the late Mesoproterozoic. The metabasites exhibited enrichment of light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) and depletion of heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs), resembling the geochemical characteristics of Andean arc magmatism. The whole-rock geochemistry and in-situ zircon eHf(t) values of 4.3 and 11.2 suggested that the protolithic mafic magma originated from a subduction-modified lithospheric mantle. The low zircon eHf(t) values of −5.2 and −0.5 also suggested that the calc-alkaline augen granitic gneisses were derived from the partial melting of a late Paleoproterozoic crustal source. The ∼1.1 Ga arc-related magmatism and metamorphism in the Oulongbuluke Block indicated the occurence of a tectonic-thermal event in an Andean-type active continental margin in the late Mesoproterozoic. In this regard, the Oulongbuluke Block was likely temporarily connected to the Qilian Block and Tarim Craton, forming a single continuous block with similar Grenville age during the late Mesoproterozoic to early Neoproterozoic (1.1–0.9 Ga).
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the Grenvillian Orogeny in the altun qilian north qaidam mountain belts of northern tibet plateau constraints from geochemical and zircon u pb age and hf isotopic study of magmatic rocks
Journal of Asian Earth Sciences, 2013Co-Authors: Shengyao Yu, Jianxin Zhang, Pablo Garcia Del Real, Xilin Zhao, Jianghua Gong, Yunshuai LiAbstract:Abstract Numerous Neoproterozoic magmatic and metamorphic events in the Altun–Qilian–North Qaidam (AQNQ) region record Grenvillian orogenesis and amalgamation of the supercontinent Rodinia. However, the tectonothermal regimes responsible for these Neoproterozoic events and the assumed position of the AQNQ in Rodinia remain controversial. Zircon U–Pb age data show that the orthogneiss and paragneiss/schist of the AQNQ experienced concurrent magmatism and metamorphism at 895–925 Ma. Zircon Lu–Hf isotopic data indicate that the gneisses in the AQNQ have eHf (0.9 Ga) values and tDM2 (Hf) model ages ranging from −5.6 to +3.9 and 1.4 to 1.9 Ga. These data suggest that the early Neoproterozoic magma in the AQNQ was predominately derived from a late Paleoproterozoic–early Mesoproterozoic crustal source between 1.4 and 1.9 Ga, marking an important episode of crustal growth in the AQNQ. The Neoproterozoic magmatism is geochemically characterized by (1) high SiO2, K2O, and low P2O5; (2) A/CNK ratios >1.0, ranging from 1.03 to 1.09; (3) enrichment in Rb, Th and U, and depletion in Ba, Nb, Ta, Sr, Ti, and Eu. Based on the geochemical resemblance to high-K calc-alkaline I-type granite and zircon Lu–Hf isotope signatures, the Neoproterozoic magmatism in the AQNQ was probably derived from ancient mafic-intermediate igneous rocks in an active continental margin. The Neoproterozoic tectono-magmatic–metamorphic history of the AQNQ, directly associated with the South China block (SCB) and the Tarim block (TB), indicates that the AQNQ and the TB coexisted as a single block in the early Neoproterozoic, which was temporarily connected to the SCB to the north or west in Rodinia during the late stages of the Grenvillian Orogeny (950–900 Ma).
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The Grenvillian Orogeny in the Altun–Qilian–North Qaidam mountain belts of northern Tibet Plateau: Constraints from geochemical and zircon U–Pb age and Hf isotopic study of magmatic rocks
Journal of Asian Earth Sciences, 2013Co-Authors: Shengyao Yu, Jianxin Zhang, Pablo Garcia Del Real, Xilin Zhao, Jianghua Gong, Yunshuai LiAbstract:Abstract Numerous Neoproterozoic magmatic and metamorphic events in the Altun–Qilian–North Qaidam (AQNQ) region record Grenvillian orogenesis and amalgamation of the supercontinent Rodinia. However, the tectonothermal regimes responsible for these Neoproterozoic events and the assumed position of the AQNQ in Rodinia remain controversial. Zircon U–Pb age data show that the orthogneiss and paragneiss/schist of the AQNQ experienced concurrent magmatism and metamorphism at 895–925 Ma. Zircon Lu–Hf isotopic data indicate that the gneisses in the AQNQ have eHf (0.9 Ga) values and tDM2 (Hf) model ages ranging from −5.6 to +3.9 and 1.4 to 1.9 Ga. These data suggest that the early Neoproterozoic magma in the AQNQ was predominately derived from a late Paleoproterozoic–early Mesoproterozoic crustal source between 1.4 and 1.9 Ga, marking an important episode of crustal growth in the AQNQ. The Neoproterozoic magmatism is geochemically characterized by (1) high SiO2, K2O, and low P2O5; (2) A/CNK ratios >1.0, ranging from 1.03 to 1.09; (3) enrichment in Rb, Th and U, and depletion in Ba, Nb, Ta, Sr, Ti, and Eu. Based on the geochemical resemblance to high-K calc-alkaline I-type granite and zircon Lu–Hf isotope signatures, the Neoproterozoic magmatism in the AQNQ was probably derived from ancient mafic-intermediate igneous rocks in an active continental margin. The Neoproterozoic tectono-magmatic–metamorphic history of the AQNQ, directly associated with the South China block (SCB) and the Tarim block (TB), indicates that the AQNQ and the TB coexisted as a single block in the early Neoproterozoic, which was temporarily connected to the SCB to the north or west in Rodinia during the late stages of the Grenvillian Orogeny (950–900 Ma).
Toby Rivers - One of the best experts on this subject based on the ideXlab platform.
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Protracted late- to post-Ottawan cooling and exhumation of the mid crust in a Grenvillian inlier, central Appalachians, USA – New data and a new hypothesis
Precambrian Research, 2019Co-Authors: Richard A. Volkert, Toby RiversAbstract:Abstract New 40Ar/39Ar hornblende and biotite data from granulite-facies gneisses across the Grenvillian New Jersey Highlands inlier in the central Appalachians permit estimates of the rates of regional cooling and exhumation following the Ottawan phase of the Grenvillian Orogeny. 40Ar/39Ar hornblende and biotite results yielded plateau ages of ca. 947–914 Ma and ca. 887–819 Ma, respectively, constraining post-Ottawan cooling from the peak metamorphic temperature of ∼770 °C to ∼300 °C at a slow rate of 1.9–3.5 °C/Myr. Following assumptions about the physical properties of these mid-crustal rocks, we calculate they were exhumed from a peak burial depth of ∼22 km, and passed through the 500 °C and 300 °C isotherms at depths of ∼14 km and ∼7.5 km, respectively, indicating a slow exhumation rate of 0.06–0.11 km/Myr. The dual signal of slow cooling and exhumation is interpreted to be due to an extended period of elevated mantle heat flow triggered by delamination or convective removal of the lower mantle lithosphere beneath the orogen. Together with lower crustal intrusion and (or) crustal underplating by asthenospheric magmas, this is interpreted to have resulted in extensional collapse of the overthickened crust, juxtaposition of crustal levels, and the formation of large metamorphic core complexes. Mafic intrusions and (or) underplating not only provided an important heat source in the lower crust, but also increased the average crustal density, thereby slowing the rates of uplift, erosion and exhumation. We interpret the dual signal as a cryptic signature of pervasive extensional orogenic collapse after the Ottawan phase of the Grenvillian Orogeny.
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Protracted continental collision — evidence from the Grenville OrogenThis article is one of a series of papers published in this Special Issue on the theme Lithoprobe — parameters, processes, and the evolution of a continent.
Canadian Journal of Earth Sciences, 2010Co-Authors: Andrew Hynesa. Hynes, Toby RiversAbstract:The Grenville Orogen in North America is interpreted to have resulted from collision between Laurentia and another continent, probably Amazonia, at ca. 1100 Ma. The exposed segment of the orogen was derived largely from reworked Archean to Paleoproterozoic Laurentian crust, products of a long-lived Mesoproterozoic continental-margin arc and associated back arc, and remnants of one or more accreted mid-Mesoproterozoic island-arc terranes. A potential suture, preserved in Grenvillian inliers of the southeastern USA, may separate rocks of Laurentian and Amazonian affinities. The Grenvillian Orogeny lasted more than 100 million years. Much of the interior Grenville Province, with peak metamorphism at ca. 1090–1020 Ma, consists of uppermost amphibolite- to granulite-facies rocks metamorphosed at depths of ca. 30 km, but areas of lower crustal, eclogite-facies nappes metamorphosed at 50–60 km depth also occur and an orogenic lid that largely escaped Grenvillian metamorphism is preserved locally. Overall, deform...
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Assembly and preservation of lower, mid, and upper orogenic crust in the Grenville Province—Implications for the evolution of large hot long-duration orogens
Precambrian Research, 2008Co-Authors: Toby RiversAbstract:Abstract It is argued that the Grenville Province is a large hot long-duration orogen with a plateau in the hinterland, remnants of which are preserved in the hangingwall of the Allochthon Boundary Thrust and characterised by metamorphism from ca. 1090 to 1020 Ma (Ottawan phase of the Grenvillian Orogeny). Hinterland rocks are grouped into three tectonic units on the basis of their Ottawan metamorphic signatures, the allochthonous High Pressure Belt, the allochthonous Medium–Low Pressure Belt, and an orogenic lid lacking evidence for penetrative metamorphism. P–T and geochronological data indicate Ottawan metamorphism developed under a relatively high geothermal gradient and was followed by slow cooling, compatible with some form of channel flow. Metamorphic rocks in the Parautochthonous Belt in the footwall of the Allochthon Boundary Thrust, also divided into medium and high-pressure units, were metamorphosed from ca. 1000 to 980 Ma (Rigolet phase) under a lower geothermal gradient and underwent rapid cooling. Their evolution is interpreted to record advance of the orogen into its former foreland after channel flow had ceased. The Allochthon Boundary Thrust is thus a material focal plane separating high-grade rocks derived from opposite sides of the orogen metamorphosed at different times under different P–T–t gradients. Preservation of the Orogenic Lid and low pressure segments of the allochthonous Medium–Low Pressure Belt is a result of gravitational collapse of the orogenic plateau, initiated in late Ottawan time, and the formation of a crustal-scale horst-and-graben architecture. This study emphasises the importance of gravitational collapse during the prolonged compressional phase, a feature not presently accommodated in numerical models of large hot long-duration orogens.
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Grenville Front zone, Gagnon terrane, southwestern Labrador: Configuration of a midcrustal foreland fold‐thrust belt
Tectonics, 2008Co-Authors: J. A. M. Van Gool, Toby Rivers, Tom CalonAbstract:[1] Evolution of a metamorphic fold-thrust belt in Archean and Proterozoic rocks in the Gagnon terrane, northwestern Grenville province, involved underthrusting beneath a crustal-scale, orogenic wedge and metamorphism ranging from upper greenschist facies (∼600 ± 100 MPa/450 ± 50°C) to upper amphibolite facies (∼1100 ± 100 MPa/750 ± 50°C) during the terminal stages of the Grenvillian Orogeny. Structural and metamorphic data indicate that D1 structures formed at peak pressures during basal accretion to the overriding orogenic wedge, whereas D2 structures developed within the wedge during its displacement toward the foreland in a sinistral transpressive setting. The fold-thrust belt developed sequentially on two levels: a thin-skinned, cover-dominated thrust system preceded and overlies a thick-skinned, basement-dominated system. The D3 cross-folds postdated normal faulting at the top of the wedge and formed during gravitational collapse. On the basis of this study, characteristic features of midcrustal, metamorphic, thrust wedges include growth by basal accretion, polyphase ductile deformation and noncoaxial strain, dual-level development, extensive basement involvement, and terminal gravitational collapse associated with cross-folding.
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Lithoprobe line 55: integration of out-of-plane seismic results with surface structure, metamorphism, and geochronology, and the tectonic evolution of the eastern Grenville Province
Canadian Journal of Earth Sciences, 2000Co-Authors: Andrew Hynes, Aphrodite Indares, Toby Rivers, André GobeilAbstract:Lithoprobe line 55, in the Grenville Province of eastern Quebec, provides unusually good control on the three-dimensional (3-D) geometry and structural relationships among the major lithological units there. Archean basement underlies the exposed Proterozoic rocks, along the entire seismic line, and there is a lateral ramp in this basement immediately behind a lobate stack of thrust slices of high-pressure metamorphic rocks comprising the Manicouagan Imbricate Zone (MIZ). Integration of the 3-D geometry with P-T and geochronological data allows derivation of a tectonic model for the region. The MIZ was buried to depths >60 km at 1050 Ma. Preservation of its high-pressure assemblages, and the absence of metamorphism at 990 Ma, which is characteristic of lower pressure metamorphic rocks that tectonically overlie them, indicates the MIZ rocks were rapidly unroofed, early in the tectonic history. There were two discrete pulses of crustal thickening during the Grenvillian Orogeny in this region. The first, inv...
