The Mesoarchean to Neoarchean period (ca. 3.0−2.5 Ga) is the most important stage during the emergence and evolution of plate tectonics. However, plate subduction at this time may have been less stable and perhaps more susceptible to the lubrication effect of sediments than the modern counterpart. Such predictions have not yet been verified by field-based investigations. In this work, we identified two types of rock units (i.e., sanukitoids and associated adakitic suites, exposed in the Eastern Hebei Complex of the North China Craton) and illustrated their petrogenesis and tectonic context through field, geochronologic, geochemical, and isotopic investigations. Laser ablation−inductively coupled plasma−mass spectrometry zircon U-Pb analyses suggest that the two magmatic suites formed within a relatively short time span of ca. 2596−2544 Ma and ca. 2559−2533 Ma, respectively. The sanukitoids are composed of meta-andesites and diorite porphyrites and characterized by relatively high MgO (3.94−5.62 wt%), Mg# (50−61), Cr (73−343 ppm), and Ni (37−111 ppm) values. The adakitic rocks are composed of granodiorite-granite gneisses and have relatively high Sr (316−1001 ppm) and low Y (7−13 ppm) and Yb (0.83−1.37 ppm) contents, and relatively high Sr/Y (36−89) and La/Yb (16−45) ratios. Rocks from both suites exhibit depletions of Nb, Ta, and Ti and have similar Sr-Nd-Hf-Zn isotopes: variable (87Sr/86Sr)i (0.7002−0.7053), weakly positive εNd(t) (+0.3 to +1.7) and εHf(t) (+1.8 to +6.8), and slightly heavy δ66Zn (0.30‰−0.36‰). These geochemical characteristics indicate that the sanukitoids were derived from the melting of subducted sediments followed by melt-mantle interaction, whereas the adakitic rocks were produced by direct partial melting of subducted plate (including tonalite-trondjhemite-granodiorite melts) under a garnet stability field with minor sediments. Such distinct magmatic rock associations, together with the coeval charnockites and tholeiites with diverse compositions in the adjacent area, can be best explained by a slab breakoff model. Further, events associated with slab breakoff are likely to represent a transition of a quasi-plate tectonic regime, characterized by multiple, continuous, and stagnant attempts to start the modern-style subduction on Earth. In addition, the emergence of sanukitoids and associated magmas symbolized the onset of supracrustal recycling into the mantle. Combined with the Nd-Hf-Zn isotopes of diverse magmatic rocks in the North China Craton that are comparable to other Precambrian magmatic rock suites worldwide, we suggest that supracrustal recycling symbolized the onset of plate tectonics since ca. 3.0 Ga, and by inference played a key role in the development of subduction-driven plate tectonics in addition to Earth’s secular cooling.
{"title":"Pervasive Neoarchean melting of subducted sediments generating sanukitoid and associated magmatism in the North China Craton, with implications for the operation of plate tectonics","authors":"Jialiang Li, Shengwen Liu, Haibo Ma, Chen Wu, Di‐Cheng Zhu, Jingao Liu","doi":"10.1130/b37279.1","DOIUrl":"https://doi.org/10.1130/b37279.1","url":null,"abstract":"The Mesoarchean to Neoarchean period (ca. 3.0−2.5 Ga) is the most important stage during the emergence and evolution of plate tectonics. However, plate subduction at this time may have been less stable and perhaps more susceptible to the lubrication effect of sediments than the modern counterpart. Such predictions have not yet been verified by field-based investigations. In this work, we identified two types of rock units (i.e., sanukitoids and associated adakitic suites, exposed in the Eastern Hebei Complex of the North China Craton) and illustrated their petrogenesis and tectonic context through field, geochronologic, geochemical, and isotopic investigations. Laser ablation−inductively coupled plasma−mass spectrometry zircon U-Pb analyses suggest that the two magmatic suites formed within a relatively short time span of ca. 2596−2544 Ma and ca. 2559−2533 Ma, respectively. The sanukitoids are composed of meta-andesites and diorite porphyrites and characterized by relatively high MgO (3.94−5.62 wt%), Mg# (50−61), Cr (73−343 ppm), and Ni (37−111 ppm) values. The adakitic rocks are composed of granodiorite-granite gneisses and have relatively high Sr (316−1001 ppm) and low Y (7−13 ppm) and Yb (0.83−1.37 ppm) contents, and relatively high Sr/Y (36−89) and La/Yb (16−45) ratios. Rocks from both suites exhibit depletions of Nb, Ta, and Ti and have similar Sr-Nd-Hf-Zn isotopes: variable (87Sr/86Sr)i (0.7002−0.7053), weakly positive εNd(t) (+0.3 to +1.7) and εHf(t) (+1.8 to +6.8), and slightly heavy δ66Zn (0.30‰−0.36‰). These geochemical characteristics indicate that the sanukitoids were derived from the melting of subducted sediments followed by melt-mantle interaction, whereas the adakitic rocks were produced by direct partial melting of subducted plate (including tonalite-trondjhemite-granodiorite melts) under a garnet stability field with minor sediments. Such distinct magmatic rock associations, together with the coeval charnockites and tholeiites with diverse compositions in the adjacent area, can be best explained by a slab breakoff model. Further, events associated with slab breakoff are likely to represent a transition of a quasi-plate tectonic regime, characterized by multiple, continuous, and stagnant attempts to start the modern-style subduction on Earth. In addition, the emergence of sanukitoids and associated magmas symbolized the onset of supracrustal recycling into the mantle. Combined with the Nd-Hf-Zn isotopes of diverse magmatic rocks in the North China Craton that are comparable to other Precambrian magmatic rock suites worldwide, we suggest that supracrustal recycling symbolized the onset of plate tectonics since ca. 3.0 Ga, and by inference played a key role in the development of subduction-driven plate tectonics in addition to Earth’s secular cooling.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"52 8","pages":""},"PeriodicalIF":4.9,"publicationDate":"2024-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139447887","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lei Zou, Jing-Hui Guo, Li-Fei Zhang, Guangyu Huang, Shu‐Juan Jiao, Zhong-Hua Tian, Ping-Hua Liu
High-pressure (HP) and ultrahigh-temperature (UHT) granulites with a high geothermal gradient (greater than 500 °C/GPa) are prominent features of Paleoproterozoic orogenic belts and may represent paired metamorphic belts present during the early stages of plate tectonics. Understanding their pressure−temperature−time (P-T-t) paths and metamorphic evolutionary relationships could provide valuable constraints on the tectonic processes of Paleoproterozoic orogenic belts. Here, we describe garnet mafic and clinopyroxene-orthopyroxene (Cpx-Opx) granulites from the Diebusige area of the Alxa Block in the western part of the Khondalite Belt, North China Craton. Through detailed petrographic, phase equilibrium modeling, and Ti-in-amphibole thermometric studies, we obtained the preserved peak mineral assemblages of two types of mafic granulites: garnet + clinopyroxene + amphibole + plagioclase + quartz + ilmenite, and clinopyroxene + orthopyroxene + plagioclase + amphibole + garnet (rare) + ilmenite. The preserved peak P-T conditions were determined to be 850−890 °C/11.4−13.2 kbar (HP granulite-facies) and 950−970 °C/8.2−9.2 kbar (UHT conditions), with thermal gradients of ∼70 °C/kbar (moderate differential temperature/differential pressure, dT/dP) and ∼110 °C/kbar (high dT/dP), respectively. Using sensitive high-resolution ion microprobe U-Pb dating and rare earth element analysis of zircons, we found that the garnet mafic granulite recorded an HP granulite-facies metamorphic age of ca. 1.95 Ga and a retrograde cooling age of ca. 1.8 Ga, while the Cpx-Opx granulite recorded a consistent retrograde cooling age of ca. 1.8 Ga. By combining these results with the metamorphic evolution and timing (ca. 1.92−1.91 Ga) of UHT rocks from the Khondalite Belt, we suggest that the garnet (HP) mafic and Cpx-Opx (UHT) granulites may represent different stages of the same metamorphic event, shedding light on the processes involved in the collision and subsequent exhumation of Paleoproterozoic orogenic belts.
{"title":"Metamorphic evolution of high-pressure and ultrahigh-temperature granulites from the Alxa Block, North China Craton: Implications for the collision and exhumation of Paleoproterozoic orogenic belts","authors":"Lei Zou, Jing-Hui Guo, Li-Fei Zhang, Guangyu Huang, Shu‐Juan Jiao, Zhong-Hua Tian, Ping-Hua Liu","doi":"10.1130/b37120.1","DOIUrl":"https://doi.org/10.1130/b37120.1","url":null,"abstract":"High-pressure (HP) and ultrahigh-temperature (UHT) granulites with a high geothermal gradient (greater than 500 °C/GPa) are prominent features of Paleoproterozoic orogenic belts and may represent paired metamorphic belts present during the early stages of plate tectonics. Understanding their pressure−temperature−time (P-T-t) paths and metamorphic evolutionary relationships could provide valuable constraints on the tectonic processes of Paleoproterozoic orogenic belts. Here, we describe garnet mafic and clinopyroxene-orthopyroxene (Cpx-Opx) granulites from the Diebusige area of the Alxa Block in the western part of the Khondalite Belt, North China Craton. Through detailed petrographic, phase equilibrium modeling, and Ti-in-amphibole thermometric studies, we obtained the preserved peak mineral assemblages of two types of mafic granulites: garnet + clinopyroxene + amphibole + plagioclase + quartz + ilmenite, and clinopyroxene + orthopyroxene + plagioclase + amphibole + garnet (rare) + ilmenite. The preserved peak P-T conditions were determined to be 850−890 °C/11.4−13.2 kbar (HP granulite-facies) and 950−970 °C/8.2−9.2 kbar (UHT conditions), with thermal gradients of ∼70 °C/kbar (moderate differential temperature/differential pressure, dT/dP) and ∼110 °C/kbar (high dT/dP), respectively. Using sensitive high-resolution ion microprobe U-Pb dating and rare earth element analysis of zircons, we found that the garnet mafic granulite recorded an HP granulite-facies metamorphic age of ca. 1.95 Ga and a retrograde cooling age of ca. 1.8 Ga, while the Cpx-Opx granulite recorded a consistent retrograde cooling age of ca. 1.8 Ga. By combining these results with the metamorphic evolution and timing (ca. 1.92−1.91 Ga) of UHT rocks from the Khondalite Belt, we suggest that the garnet (HP) mafic and Cpx-Opx (UHT) granulites may represent different stages of the same metamorphic event, shedding light on the processes involved in the collision and subsequent exhumation of Paleoproterozoic orogenic belts.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"8 3","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138951928","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jianzhou Tang, Zhicheng Zhang, Mark B. Allen, Shuguang Song, Cong Ding, Ke Li, Yan Chen
Early Cretaceous intraplate volcanic rocks are widespread in NE Asia, but their origin remains controversial. This work presents zircon U-Pb ages, whole-rock element and Sr-Nd isotope data for mafic volcanic rocks from the Erlian Basin, a wide rift basin in NE Asia. There were two episodes of Early Cretaceous mafic volcanism in the Erlian Basin, and the eruptions show contrasting geochemical compositions. The early mafic volcanic rocks, with U-Pb ages of ca. 140−135 Ma, show slightly depleted Sr-Nd isotope compositions (ISr(t) = 0.7042−0.7052; εNd(t) = +0.82 to +3.0) and arc-like trace-element compositions, which are derived from subduction-related fluid/melt metasomatized lithosphere mantle. The late mafic volcanic rocks (dated at ca. 125 Ma) have enriched Sr-Nd isotopes (ISr(t) = 0.7055−0.7077; εNd(t) = −0.50 to −2.67) and oceanic-island basalt (OIB)-like trace-element compositions, revealing the metasomatism of melts from crustal materials and asthenosphere mantle. The two types of mafic volcanic rocks may record the interactions of the mantle and melts from the subducted paleo-Pacific oceanic slab at different depths. The landward-then-oceanward migration pattern of the Mesozoic volcanism from NE Asia can be explained by the flat subduction and subsequent slab roll-back of the Paleo-Pacific Ocean, consistent with migration patterns from the North China Craton and South China Block, implying similar Jurassic−Cretaceous subduction evolution along the entire East Asia margin. Some Late Jurassic to Early Cretaceous dates from east Mongolia and the southern margin of the Erlian Basin diverge from this trajectory. In combination with previous studies, we suggest that the Early Cretaceous pervasive intraplate volcanism in the Erlian Basin and adjacent areas of NE Asia mainly resulted from the slab roll-back of the Paleo-Pacific Ocean with a combined effect from the post-collision extension of the Mongol-Okhotsk orogen.
{"title":"Origin of Early Cretaceous mafic volcanic rocks from the Erlian Basin west of the Great Xing’an Range of North China: Implications for the tectono-magmatic evolution of East Asia","authors":"Jianzhou Tang, Zhicheng Zhang, Mark B. Allen, Shuguang Song, Cong Ding, Ke Li, Yan Chen","doi":"10.1130/b37068.1","DOIUrl":"https://doi.org/10.1130/b37068.1","url":null,"abstract":"Early Cretaceous intraplate volcanic rocks are widespread in NE Asia, but their origin remains controversial. This work presents zircon U-Pb ages, whole-rock element and Sr-Nd isotope data for mafic volcanic rocks from the Erlian Basin, a wide rift basin in NE Asia. There were two episodes of Early Cretaceous mafic volcanism in the Erlian Basin, and the eruptions show contrasting geochemical compositions. The early mafic volcanic rocks, with U-Pb ages of ca. 140−135 Ma, show slightly depleted Sr-Nd isotope compositions (ISr(t) = 0.7042−0.7052; εNd(t) = +0.82 to +3.0) and arc-like trace-element compositions, which are derived from subduction-related fluid/melt metasomatized lithosphere mantle. The late mafic volcanic rocks (dated at ca. 125 Ma) have enriched Sr-Nd isotopes (ISr(t) = 0.7055−0.7077; εNd(t) = −0.50 to −2.67) and oceanic-island basalt (OIB)-like trace-element compositions, revealing the metasomatism of melts from crustal materials and asthenosphere mantle. The two types of mafic volcanic rocks may record the interactions of the mantle and melts from the subducted paleo-Pacific oceanic slab at different depths. The landward-then-oceanward migration pattern of the Mesozoic volcanism from NE Asia can be explained by the flat subduction and subsequent slab roll-back of the Paleo-Pacific Ocean, consistent with migration patterns from the North China Craton and South China Block, implying similar Jurassic−Cretaceous subduction evolution along the entire East Asia margin. Some Late Jurassic to Early Cretaceous dates from east Mongolia and the southern margin of the Erlian Basin diverge from this trajectory. In combination with previous studies, we suggest that the Early Cretaceous pervasive intraplate volcanism in the Erlian Basin and adjacent areas of NE Asia mainly resulted from the slab roll-back of the Paleo-Pacific Ocean with a combined effect from the post-collision extension of the Mongol-Okhotsk orogen.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"76 17","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138957899","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The early Paleozoic tectono-magmatic activity within the South China block, which is well illustrated by Ordovician−Devonian granites in the western Qinhang belt, was the response to closure of the Proto-Tethys Ocean and convergence of continental blocks. The spatiotemporal distribution and source characteristics of the granites provide us the opportunity to understand the processes and driving mechanisms of intracontinental orogeny. As an example, the Miaoershan-Yuechengling granite batholith in northern Guangxi, located along the western margin of the Qinhang orogenic belt, is mainly composed of quartz monzonite and monzogranite. All the granitic rocks from Miaoershan-Yuechengling batholith are composed of K-feldspar, quartz, plagioclase, biotite, and hornblende. Geochronologic dating indicates that the Miaoershan-Yuechengling batholith was emplaced during the late Silurian and Early Devonian, respectively. The rocks have high SiO2, with an average value of 73.29 wt%, and total alkalis (Na2O + K2O = 7.21−10.03 wt%), but low Al2O3 (12.96−15.51 wt%), showing characteristics of the high-potassium calc-alkaline series of S-type peraluminous granites (Al2O3/[CaO + Na2O + K2O] = 1.03−1.22). Trace elements in the Miaoershan-Yuechengling granitic rocks are characterized by enrichment of large ion lithophile elements and depletion of high field strength elements. Their rare earth element (REE) trends are characterized by relatively flat distribution patterns with weak light REE enrichment, weak heavy REE fractionation, and negative Eu anomalies. Zircons from the rocks have negative εHf(t) values ranging from −13.24 to −5.1, with crustal model ages (THf2) of 2.2−1.7 Ga. These features indicate that they are S-type granites with parental magmas originating from partial melting of sandy argillaceous sources of Paleoproterozoic lower continental crust. The thermal budget for Ordovician to Early Devonian magmatism is attributed either to crustal thickening in relation to intracontinental orogenic compression or to crustal thinning due to postorogenic tectonic extension during assembly and breakup of Greater Gondwana. This study reveals that the change in mantle convection systems during plate interactions acted as a major driving force for the early orogenic processes, late collapse of the orogenic belt, and massive syncollisional to postorogenic magmatism.
{"title":"Ordovician−Early Devonian granitic magmatism as the consequence of intracontinental orogenic activity along the Qinhang belt in South China","authors":"Xinchen Yuan, Junlai Liu, Qijun Yang, Baojun Zhou, Yong Lv, Jiwen Wu","doi":"10.1130/b36992.1","DOIUrl":"https://doi.org/10.1130/b36992.1","url":null,"abstract":"The early Paleozoic tectono-magmatic activity within the South China block, which is well illustrated by Ordovician−Devonian granites in the western Qinhang belt, was the response to closure of the Proto-Tethys Ocean and convergence of continental blocks. The spatiotemporal distribution and source characteristics of the granites provide us the opportunity to understand the processes and driving mechanisms of intracontinental orogeny. As an example, the Miaoershan-Yuechengling granite batholith in northern Guangxi, located along the western margin of the Qinhang orogenic belt, is mainly composed of quartz monzonite and monzogranite. All the granitic rocks from Miaoershan-Yuechengling batholith are composed of K-feldspar, quartz, plagioclase, biotite, and hornblende. Geochronologic dating indicates that the Miaoershan-Yuechengling batholith was emplaced during the late Silurian and Early Devonian, respectively. The rocks have high SiO2, with an average value of 73.29 wt%, and total alkalis (Na2O + K2O = 7.21−10.03 wt%), but low Al2O3 (12.96−15.51 wt%), showing characteristics of the high-potassium calc-alkaline series of S-type peraluminous granites (Al2O3/[CaO + Na2O + K2O] = 1.03−1.22). Trace elements in the Miaoershan-Yuechengling granitic rocks are characterized by enrichment of large ion lithophile elements and depletion of high field strength elements. Their rare earth element (REE) trends are characterized by relatively flat distribution patterns with weak light REE enrichment, weak heavy REE fractionation, and negative Eu anomalies. Zircons from the rocks have negative εHf(t) values ranging from −13.24 to −5.1, with crustal model ages (THf2) of 2.2−1.7 Ga. These features indicate that they are S-type granites with parental magmas originating from partial melting of sandy argillaceous sources of Paleoproterozoic lower continental crust. The thermal budget for Ordovician to Early Devonian magmatism is attributed either to crustal thickening in relation to intracontinental orogenic compression or to crustal thinning due to postorogenic tectonic extension during assembly and breakup of Greater Gondwana. This study reveals that the change in mantle convection systems during plate interactions acted as a major driving force for the early orogenic processes, late collapse of the orogenic belt, and massive syncollisional to postorogenic magmatism.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"34 4","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138957230","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Muhtar, Wenjiao Xiao, M. Brzozowski, Q. Mao, He Yang, Changzhi Wu
Permian−Triassic metaluminous−peraluminous granitoids, mafic−ultramafic plutons, and Ni-Cu and Au deposits are prominent features in the Eastern Tianshan of the southern Altaids. However, the genetic relationship between coeval granitoids and mafic−ultramafic intrusions, and the geodynamics of magmatism and related mineralization, remain ambiguous. To address these ambiguities, we present petrological, geochemical, and bulk-rock Sr-Nd-Fe and zircon U-Pb-Hf isotope analyses of granitoids from the Shuangchagou Complex and gabbros from the Huangshandong Complex in the Eastern Tianshan. Zircon U-Pb ages demonstrate that the Huangshandong gabbro was emplaced at ca. 277.8 ± 1.4 Ma. In contrast, U-Pb ages determined from zircons in the granitic rocks of the Shuangchagou Complex suggest that the complex crystallized from three stages of magmatism: (1) strongly peraluminous S-type granitic magma represented by early-stage gneiss and granitic veins (ca. 289 Ma), (2) metaluminous to weakly peraluminous I-type granitic magmas represented by the intermediate-stage granitoids (ca. 283−261 Ma), and (3) late-stage granitoids (ca. 250−241 Ma). The intermediate- and late-stage granitoids (ca. 283−241 Ma) show clear enrichments in the light rare earth elements and large ion lithophile elements (e.g., Rb, Th, and U), and depletions in high field strength elements (e.g., Nb, Ta, and Ti), similar to arc magmas, which indicates that the North Tianshan oceanic plate was still subducting during the Middle Triassic. Considering the diversity of magmatic rocks (e.g., mid-oceanic-ridge−type mafic rocks, and I-, S- and A-type igneous rocks), mineralization styles (e.g., Alaskan-type Ni-Cu sulfide deposits and orogenic gold deposits), and the dextral strike-slip faults (e.g., Kanggur Fault) that occurred concurrently in the Eastern Tianshan during the Early Permian to Middle Triassic, we suggest that splitting of the subducted portion of the North Tianshan oceanic plate created a slab window that allowed the upwelling and partial melting of asthenospheric mantle to form the mafic−ultramafic intrusions and related Ni-Cu sulfide deposits. Sustained migration of magma provided the heat necessary to induce partial melting, devolatilization, and desulfurization of crustal materials, producing the Permian−Triassic, high-K to calc-alkaline I- and S-type granitoids, and associated orogenic gold deposits. By integrating the results of this study with published work regarding the Kanggur Accretionary Complex, we suggest that the subduction of the North Tianshan Ocean may have lasted until the Late Triassic.
{"title":"Permian−Triassic magmatism above a slab window in the Eastern Tianshan: Implications for the evolution of the southern Altaids","authors":"M. Muhtar, Wenjiao Xiao, M. Brzozowski, Q. Mao, He Yang, Changzhi Wu","doi":"10.1130/b37133.1","DOIUrl":"https://doi.org/10.1130/b37133.1","url":null,"abstract":"Permian−Triassic metaluminous−peraluminous granitoids, mafic−ultramafic plutons, and Ni-Cu and Au deposits are prominent features in the Eastern Tianshan of the southern Altaids. However, the genetic relationship between coeval granitoids and mafic−ultramafic intrusions, and the geodynamics of magmatism and related mineralization, remain ambiguous. To address these ambiguities, we present petrological, geochemical, and bulk-rock Sr-Nd-Fe and zircon U-Pb-Hf isotope analyses of granitoids from the Shuangchagou Complex and gabbros from the Huangshandong Complex in the Eastern Tianshan. Zircon U-Pb ages demonstrate that the Huangshandong gabbro was emplaced at ca. 277.8 ± 1.4 Ma. In contrast, U-Pb ages determined from zircons in the granitic rocks of the Shuangchagou Complex suggest that the complex crystallized from three stages of magmatism: (1) strongly peraluminous S-type granitic magma represented by early-stage gneiss and granitic veins (ca. 289 Ma), (2) metaluminous to weakly peraluminous I-type granitic magmas represented by the intermediate-stage granitoids (ca. 283−261 Ma), and (3) late-stage granitoids (ca. 250−241 Ma). The intermediate- and late-stage granitoids (ca. 283−241 Ma) show clear enrichments in the light rare earth elements and large ion lithophile elements (e.g., Rb, Th, and U), and depletions in high field strength elements (e.g., Nb, Ta, and Ti), similar to arc magmas, which indicates that the North Tianshan oceanic plate was still subducting during the Middle Triassic. Considering the diversity of magmatic rocks (e.g., mid-oceanic-ridge−type mafic rocks, and I-, S- and A-type igneous rocks), mineralization styles (e.g., Alaskan-type Ni-Cu sulfide deposits and orogenic gold deposits), and the dextral strike-slip faults (e.g., Kanggur Fault) that occurred concurrently in the Eastern Tianshan during the Early Permian to Middle Triassic, we suggest that splitting of the subducted portion of the North Tianshan oceanic plate created a slab window that allowed the upwelling and partial melting of asthenospheric mantle to form the mafic−ultramafic intrusions and related Ni-Cu sulfide deposits. Sustained migration of magma provided the heat necessary to induce partial melting, devolatilization, and desulfurization of crustal materials, producing the Permian−Triassic, high-K to calc-alkaline I- and S-type granitoids, and associated orogenic gold deposits. By integrating the results of this study with published work regarding the Kanggur Accretionary Complex, we suggest that the subduction of the North Tianshan Ocean may have lasted until the Late Triassic.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"102 52","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138958653","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cataclastic bands in high-porosity sandstones significantly influence fluid flow, thus impacting the exploration and development of oil and gas. However, little experimental research has been conducted on the main factors controlling the formation, evolution, and physical properties of cataclastic bands. Moreover, it is difficult to use field surveys to discern variations and trends in the structural and physical properties of cataclastic bands formed during different deformation processes. In this study, we used a high-pressure and low-velocity ring-shear apparatus to analyze high-porosity, pure sandstone. Multiple sets of ring-shear experiments were carried out using the effective normal stress or shear displacement as a single variable. The experimental samples were analyzed based on physical property tests and thin sections. Our results indicate that the particles in the cataclastic bands generally have better roundness and are smaller (by at least two to three orders of magnitude) than the host rock. The porosity and permeability of the cataclastic bands are ∼70% lower and two to three orders of magnitude lower than those of the host rock, respectively. The characteristics of the cataclastic bands are controlled by two main factors, namely, the effective normal stress and shear displacement. The effective normal stress controls the intensity of the cataclasis, and the shear displacement controls the physical properties of the grains and indirectly controls the evolutionary stage, which corresponds to the intensity of cataclasis. As the effective normal stress or shear displacement increases, the cataclasis in the cataclastic bands intensifies, and the grain size decreases; then, the decrease in the porosity gradually declines, and the permeability decrease and thickness increase and then plateau. The results of this study reveal the evolutionary mechanisms of the structural and physical properties of cataclastic bands in high-porosity sandstones and lay a theoretical foundation for determining the effect of these bands on fluid flow in oil and gas reservoirs.
{"title":"An experimental investigation of the characteristics of cataclastic bands in high-porosity sandstones","authors":"Mingming Jiang, Xiaofei Fu, Zicheng Wang","doi":"10.1130/b36801.1","DOIUrl":"https://doi.org/10.1130/b36801.1","url":null,"abstract":"Cataclastic bands in high-porosity sandstones significantly influence fluid flow, thus impacting the exploration and development of oil and gas. However, little experimental research has been conducted on the main factors controlling the formation, evolution, and physical properties of cataclastic bands. Moreover, it is difficult to use field surveys to discern variations and trends in the structural and physical properties of cataclastic bands formed during different deformation processes. In this study, we used a high-pressure and low-velocity ring-shear apparatus to analyze high-porosity, pure sandstone. Multiple sets of ring-shear experiments were carried out using the effective normal stress or shear displacement as a single variable. The experimental samples were analyzed based on physical property tests and thin sections. Our results indicate that the particles in the cataclastic bands generally have better roundness and are smaller (by at least two to three orders of magnitude) than the host rock. The porosity and permeability of the cataclastic bands are ∼70% lower and two to three orders of magnitude lower than those of the host rock, respectively. The characteristics of the cataclastic bands are controlled by two main factors, namely, the effective normal stress and shear displacement. The effective normal stress controls the intensity of the cataclasis, and the shear displacement controls the physical properties of the grains and indirectly controls the evolutionary stage, which corresponds to the intensity of cataclasis. As the effective normal stress or shear displacement increases, the cataclasis in the cataclastic bands intensifies, and the grain size decreases; then, the decrease in the porosity gradually declines, and the permeability decrease and thickness increase and then plateau. The results of this study reveal the evolutionary mechanisms of the structural and physical properties of cataclastic bands in high-porosity sandstones and lay a theoretical foundation for determining the effect of these bands on fluid flow in oil and gas reservoirs.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"114 25","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138959619","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The post-collisional evolution of the Tibetan lithosphere is of paramount significance to our understanding of collisional orogeny. It is generally postulated that the Lhasa lithospheric mantle was horizontally shortened and thickened coherently with the overlying crust to form a physical barrier, preventing Indian subduction beneath Tibet until the thickened mantle root was foundered during the Miocene. This study first identifies post-collisional oceanic-island basalt (OIB)-type magmatism in the Lhasa Block (LB), as attested by zircon U-Pb age (ca. 58 Ma) and geochemistry—positive Nb-Ta anomalies, high La/Yb, and depleted bulk-rock Sr-Nd and zircon Hf isotopes, of diabase in the northern (inboard relative to Indus Suture) part of this block. Coupled with extensive early Paleogene arc-type magmatism in the southern-central LB and thermodynamic modeling, we suggest that these diabases were formed by partially molten upwelling asthenosphere near the base of continental crust, where much of the underlying lithospheric mantle had been removed due to Neo-Tethyan slab rollback and lithospheric delamination. Compared to OIB-type magmatism worldwide, the diabases investigated here were emplaced peculiarly in a region where the continental crust was under horizontal compression and shortening by coeval thrusting. Our study thus implies a decoupled deformation between the crust and mantle of the LB during the early Indian-Asian collision.
{"title":"Paleocene oceanic-island basalt−type magmatism in the Lhasa Block attests to decoupled mantle-crust deformation during Indian-Asian collision","authors":"Yun-Chuan Zeng, Ji-feng Xu, Jian‐Lin Chen, Bao-di Wang, F. Huang, Hongxia Yu","doi":"10.1130/b37289.1","DOIUrl":"https://doi.org/10.1130/b37289.1","url":null,"abstract":"The post-collisional evolution of the Tibetan lithosphere is of paramount significance to our understanding of collisional orogeny. It is generally postulated that the Lhasa lithospheric mantle was horizontally shortened and thickened coherently with the overlying crust to form a physical barrier, preventing Indian subduction beneath Tibet until the thickened mantle root was foundered during the Miocene. This study first identifies post-collisional oceanic-island basalt (OIB)-type magmatism in the Lhasa Block (LB), as attested by zircon U-Pb age (ca. 58 Ma) and geochemistry—positive Nb-Ta anomalies, high La/Yb, and depleted bulk-rock Sr-Nd and zircon Hf isotopes, of diabase in the northern (inboard relative to Indus Suture) part of this block. Coupled with extensive early Paleogene arc-type magmatism in the southern-central LB and thermodynamic modeling, we suggest that these diabases were formed by partially molten upwelling asthenosphere near the base of continental crust, where much of the underlying lithospheric mantle had been removed due to Neo-Tethyan slab rollback and lithospheric delamination. Compared to OIB-type magmatism worldwide, the diabases investigated here were emplaced peculiarly in a region where the continental crust was under horizontal compression and shortening by coeval thrusting. Our study thus implies a decoupled deformation between the crust and mantle of the LB during the early Indian-Asian collision.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"82 4","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138995359","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
As the typical products of collisional orogeny, gneiss domes are important geological units with which to decipher the crustal deformation and evolutionary history of continental collision. However, their formation mechanisms remain poorly understood. This issue is well illustrated by the debate surrounding the origin of the North Himalaya gneiss dome zone, which has been attributed to middle-crustal channel flow, thrust-duplex development, extensional detachment faulting, or diapiric flow related to partial crustal melting. These models predict different internal structures within individual domes that can be tested by high-resolution seismic imaging. Here, we present newly acquired seismic-reflection data collected along an ∼120-km-long north-south traverse across the central segment of the North Himalaya gneiss dome zone. Analysis and interpretation of the seismic data constrained by surface geology observations imply that (1) the subducting Indian lower crust is decoupled from the deformed middle and upper crust in the North Himalaya, (2) a crustal-scale stack of antiformal duplexes with a structural thickness of ∼35 km defines the cores of the gneiss domes imaged by the seismic survey, and (3) highly reflective, sheetlike bodies imaged in our seismic profile are best interpreted as leucocratic intrusions developed synchronously during gneiss dome development. As a whole, our work suggests that the North Himalaya gneiss dome zone was created by coeval crustal shortening and partial melting of orogenic crust.
{"title":"Structural evolution of the North Himalaya domes as revealed by crustal-scale seismic-reflection surveying","authors":"Zhuoxuan Shi, Rui Gao, Zhanwu Lu, Wenhui Li, Hongqiang Li, Hongda Liang, Rui Qi, Xiao‐Fan Deng, Xinyu Dong","doi":"10.1130/b37042.1","DOIUrl":"https://doi.org/10.1130/b37042.1","url":null,"abstract":"As the typical products of collisional orogeny, gneiss domes are important geological units with which to decipher the crustal deformation and evolutionary history of continental collision. However, their formation mechanisms remain poorly understood. This issue is well illustrated by the debate surrounding the origin of the North Himalaya gneiss dome zone, which has been attributed to middle-crustal channel flow, thrust-duplex development, extensional detachment faulting, or diapiric flow related to partial crustal melting. These models predict different internal structures within individual domes that can be tested by high-resolution seismic imaging. Here, we present newly acquired seismic-reflection data collected along an ∼120-km-long north-south traverse across the central segment of the North Himalaya gneiss dome zone. Analysis and interpretation of the seismic data constrained by surface geology observations imply that (1) the subducting Indian lower crust is decoupled from the deformed middle and upper crust in the North Himalaya, (2) a crustal-scale stack of antiformal duplexes with a structural thickness of ∼35 km defines the cores of the gneiss domes imaged by the seismic survey, and (3) highly reflective, sheetlike bodies imaged in our seismic profile are best interpreted as leucocratic intrusions developed synchronously during gneiss dome development. As a whole, our work suggests that the North Himalaya gneiss dome zone was created by coeval crustal shortening and partial melting of orogenic crust.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"11 18","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138972249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Topuz, Osman Candan, Oscar Laurent, Ali Mohammadi, C. Okuyucu, Ömer Faruk Çelik, Jia-Min Wang
The Sakarya Zone of northern Turkey contains a well-preserved Early−Middle Jurassic and Late Cretaceous submarine magmatic arc constructed over pre-Jurassic bedrocks that are considered to be the eastward extension of the Armorican Terrane Assemblage in Europe. In this study, we present U-Pb-Hf isotopic data from the detrital zircons of middle Permian and Lower Jurassic sandstones to reveal episodes of Paleozoic−early Mesozoic magmatic flare-ups. Detrital zircon ages, together with data from the literature, define three major age groups at 400−380 Ma, 326−310 Ma, and 250−230 Ma, which indicates three distinct magmatic flare-ups. In addition, there are minor age clusters at 460−430 Ma and 215−195 Ma. Initial εHf values of the detrital zircons indicate significant juvenile input during the Triassic flare-up, the involvement of significantly reworked crustal material during the late Carboniferous magmatic flare-up, and both juvenile and reworked crustal material during the Middle Devonian magmatic flare-up. Within the pre-Jurassic continental basement rocks of the Sakarya Zone, the late Carboniferous igneous rocks are well documented and most voluminous, and the Middle Devonian rocks are known locally, while the Triassic igneous rocks—apart from those in Triassic accretionary complexes—are hardly known. Because the Sakarya Zone is a Gondwana-derived continental block that was later involved in the Variscan and Alpine orogenies, these magmatic flare-ups cannot be explained by subduction-related processes along a single subduction zone. We propose that the Sakarya Zone rifted from the northern margin of Gondwana during the Late Ordovician−Silurian, the Devonian magmatic flare-up (400−380 Ma) was related to the southward subduction of the Rheic Ocean beneath the Sakarya Zone during its northward drift, the late Carboniferous magmatic flare-up (326−310 Ma) occurred following the collision of the Sakarya Zone with Laurussia, and the Triassic flare-up (250−230 Ma) resulted from northward subduction of the Tethys Ocean beneath the Sakarya Zone. Comparison with data from the literature shows that the Triassic and late Carboniferous magmatic flare-ups are also characteristic features of neighboring Armorican domains, such as the Balkans and the Caucasus; however, the Middle Devonian flare-up appears to be restricted to the Sakarya Zone. Along with the late Carboniferous flare-up, the Late Ordovician−Silurian flare-up, which is locally recorded in the Sakarya Zone, is typical of the Armorican Terrane Assemblage as a whole.
{"title":"Middle Devonian, late Carboniferous, and Triassic magmatic flare-ups in eastern Armorica (Sakarya Zone, Turkey) as revealed by detrital zircon U-Pb-Hf isotopic data","authors":"G. Topuz, Osman Candan, Oscar Laurent, Ali Mohammadi, C. Okuyucu, Ömer Faruk Çelik, Jia-Min Wang","doi":"10.1130/b36950.1","DOIUrl":"https://doi.org/10.1130/b36950.1","url":null,"abstract":"The Sakarya Zone of northern Turkey contains a well-preserved Early−Middle Jurassic and Late Cretaceous submarine magmatic arc constructed over pre-Jurassic bedrocks that are considered to be the eastward extension of the Armorican Terrane Assemblage in Europe. In this study, we present U-Pb-Hf isotopic data from the detrital zircons of middle Permian and Lower Jurassic sandstones to reveal episodes of Paleozoic−early Mesozoic magmatic flare-ups. Detrital zircon ages, together with data from the literature, define three major age groups at 400−380 Ma, 326−310 Ma, and 250−230 Ma, which indicates three distinct magmatic flare-ups. In addition, there are minor age clusters at 460−430 Ma and 215−195 Ma. Initial εHf values of the detrital zircons indicate significant juvenile input during the Triassic flare-up, the involvement of significantly reworked crustal material during the late Carboniferous magmatic flare-up, and both juvenile and reworked crustal material during the Middle Devonian magmatic flare-up. Within the pre-Jurassic continental basement rocks of the Sakarya Zone, the late Carboniferous igneous rocks are well documented and most voluminous, and the Middle Devonian rocks are known locally, while the Triassic igneous rocks—apart from those in Triassic accretionary complexes—are hardly known. Because the Sakarya Zone is a Gondwana-derived continental block that was later involved in the Variscan and Alpine orogenies, these magmatic flare-ups cannot be explained by subduction-related processes along a single subduction zone. We propose that the Sakarya Zone rifted from the northern margin of Gondwana during the Late Ordovician−Silurian, the Devonian magmatic flare-up (400−380 Ma) was related to the southward subduction of the Rheic Ocean beneath the Sakarya Zone during its northward drift, the late Carboniferous magmatic flare-up (326−310 Ma) occurred following the collision of the Sakarya Zone with Laurussia, and the Triassic flare-up (250−230 Ma) resulted from northward subduction of the Tethys Ocean beneath the Sakarya Zone. Comparison with data from the literature shows that the Triassic and late Carboniferous magmatic flare-ups are also characteristic features of neighboring Armorican domains, such as the Balkans and the Caucasus; however, the Middle Devonian flare-up appears to be restricted to the Sakarya Zone. Along with the late Carboniferous flare-up, the Late Ordovician−Silurian flare-up, which is locally recorded in the Sakarya Zone, is typical of the Armorican Terrane Assemblage as a whole.","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"353 2","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138974044","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The tectonics and landscape of SE China experienced significant changes throughout the Mesozoic and early Cenozoic, largely in response to variations in the slab dynamics of the paleo-Pacific plate, which was subducting beneath continental Asia. We investigated the Mesozoic Yong’an basin in western Fujian Province of SE China in comparison to the sedimentary records of coeval basins in the region to document how its clastic sediment types and their provenance varied through time during the Mesozoic and what regional geologic processes may have controlled these variations. The average εNd value of samples from the Middle Jurassic Zhangping Formation is −16.6, and its detrital zircons are dominated by 1800 Ma and 2000 Ma grains, sourced from the northern Wuyishan Mountains. These mountains underwent significant rock and surface uplift by the Middle Jurassic and became the main source of clastic sediments in SE China. The Lower Cretaceous Bantou Formation contains pyroclastic rocks and represents fluvial-lacustrine deposits with εNd values of −14.8 to −12.4 and abundant 160−120 Ma detrital zircons, sourced from Late Jurassic granitoid rocks, which were widely exposed at the surface in SE China by this time. The upper Lower and lower Upper Cretaceous Shaxian Formation contains coarse-grained and poorly sorted sandstones-conglomerates with volcanic and granitic rock fragments, and it rests unconformably on the Bantou Formation. The Shaxian Formation represents fluvial- to alluvial-fan deposits, and its formation marks the timing of a rapid uplift of the paleo−Coastal Mountains. The Upper Cretaceous Chong’an Formation (>2000 m thick) contains abundant volcanic and granitic rock clasts and represents alluvial-fan and fluvial deposits. The average εNd values of the Shaxian and Chong’an Formations range between −9.3 and −7.5, and their most abundant detrital zircon ages are between 120 Ma and 80 Ma. By the end of the Late Cretaceous, the paleo−Coastal Mountains constituted a nearly 4-km-high magmatic belt, with much of SE China situated in its rain shadow at a lower elevation to the north. Eocene−Oligocene sedimentary basin rocks in Taiwan have an average εNd value of −10.9 and abundant Phanerozoic detrital zircons. The sediment source for these rocks was the paleo−Coastal Mountains. The Miocene basinal strata in Taiwan have more negative εNd values (−13.0) and contain Jurassic−Cretaceous as well as abundant Paleoproterozoic and Neoproterozoic zircons, indicating that the Wuyishan Mountains were again the main sediment source later in the Cenozoic. Denudation rates in the SE margin of South China were high (0.12−0.10 km/yr) during the Cretaceous (140−60 Ma), while they were very low in SW China and in the interior of South China during the same period. These differences confirm the existence of high coastal mountains in SE China until the Late Cretaceous. Denudation rates in eastern South China, particularly the coastal areas, were very low (0.06−0.02 km/
{"title":"Landscape inversion episodes in SE China during the Mesozoic−early Cenozoic: Constrained by trace-element contents, Nd isotope geochemistry, and detrital zircon U-Pb geochronology of sedimentary basins","authors":"Yi Yan, Anbei He, Y. Dilek, Zuofei Zhu, Qi Zhao","doi":"10.1130/b36739.1","DOIUrl":"https://doi.org/10.1130/b36739.1","url":null,"abstract":"The tectonics and landscape of SE China experienced significant changes throughout the Mesozoic and early Cenozoic, largely in response to variations in the slab dynamics of the paleo-Pacific plate, which was subducting beneath continental Asia. We investigated the Mesozoic Yong’an basin in western Fujian Province of SE China in comparison to the sedimentary records of coeval basins in the region to document how its clastic sediment types and their provenance varied through time during the Mesozoic and what regional geologic processes may have controlled these variations. The average εNd value of samples from the Middle Jurassic Zhangping Formation is −16.6, and its detrital zircons are dominated by 1800 Ma and 2000 Ma grains, sourced from the northern Wuyishan Mountains. These mountains underwent significant rock and surface uplift by the Middle Jurassic and became the main source of clastic sediments in SE China. The Lower Cretaceous Bantou Formation contains pyroclastic rocks and represents fluvial-lacustrine deposits with εNd values of −14.8 to −12.4 and abundant 160−120 Ma detrital zircons, sourced from Late Jurassic granitoid rocks, which were widely exposed at the surface in SE China by this time. The upper Lower and lower Upper Cretaceous Shaxian Formation contains coarse-grained and poorly sorted sandstones-conglomerates with volcanic and granitic rock fragments, and it rests unconformably on the Bantou Formation. The Shaxian Formation represents fluvial- to alluvial-fan deposits, and its formation marks the timing of a rapid uplift of the paleo−Coastal Mountains. The Upper Cretaceous Chong’an Formation (>2000 m thick) contains abundant volcanic and granitic rock clasts and represents alluvial-fan and fluvial deposits. The average εNd values of the Shaxian and Chong’an Formations range between −9.3 and −7.5, and their most abundant detrital zircon ages are between 120 Ma and 80 Ma. By the end of the Late Cretaceous, the paleo−Coastal Mountains constituted a nearly 4-km-high magmatic belt, with much of SE China situated in its rain shadow at a lower elevation to the north. Eocene−Oligocene sedimentary basin rocks in Taiwan have an average εNd value of −10.9 and abundant Phanerozoic detrital zircons. The sediment source for these rocks was the paleo−Coastal Mountains. The Miocene basinal strata in Taiwan have more negative εNd values (−13.0) and contain Jurassic−Cretaceous as well as abundant Paleoproterozoic and Neoproterozoic zircons, indicating that the Wuyishan Mountains were again the main sediment source later in the Cenozoic. Denudation rates in the SE margin of South China were high (0.12−0.10 km/yr) during the Cretaceous (140−60 Ma), while they were very low in SW China and in the interior of South China during the same period. These differences confirm the existence of high coastal mountains in SE China until the Late Cretaceous. Denudation rates in eastern South China, particularly the coastal areas, were very low (0.06−0.02 km/","PeriodicalId":55104,"journal":{"name":"Geological Society of America Bulletin","volume":"62 6","pages":""},"PeriodicalIF":4.9,"publicationDate":"2023-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138976454","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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