The late Paleozoic tectonic framework of the southeastern Central Asian Orogenic Belt is key to restricting the accretion orogeny between the Siberia Craton and the North China Craton. To clarify the framework, petrog...The late Paleozoic tectonic framework of the southeastern Central Asian Orogenic Belt is key to restricting the accretion orogeny between the Siberia Craton and the North China Craton. To clarify the framework, petrogenesis of early Permian intrusive rocks from southeastern Inner Mongolia was studied. Zircon U-Pb dating for bojite and syenogranite from Ar-Horqin indicate that they were emplaced at 288–285 Ma. Geochemical data reveal that the bojite is highly magnesian and low-K to middle-K calc-alkaline, with E-MORB-type REE and IAB-like trace element patterns. The syenogranite is a middle-K calc-alkaline fractionated A-type granite and shows oceanic-arc-like trace element patterns, with depleted Sr-Nd-Hf isotopes,(~(87)Sr/~(86)Sr)I = 0.7032–0.7042, ε_(Nd)(t) = +4.0 to +6.6 and zircon ε_(Hf)(t) = +11.14 to +14.99. This suggests that the bojite was derived from lithospheric mantle metasomatized by subducted slab melt, while the syenogranite originated from very juvenile arc-related lower crust. Usng data from coeval magmatic rocks from Linxi-Ar-Horqin, the Ar-Horqin intra-oceanic arc was reconstructed, i.e., initial transition in 290–280 Ma and mature after 278 Ma. Combined with regional geological and geophysical materials in southeastern Inner Mongolia, an early Permian tectonic framework as ‘one narrow ocean basin of the PAO', ‘two continental marginal arcs on its northern and southern' and ‘one intra-oceanic arc in its southern' is proposed.展开更多
We performed geochronological and geochemical analyses of the A-type granite in the Hongol area, central Inner Mongolia, to determine its age, petrogenesis and tectonic setting, which are significant for clarifying th...We performed geochronological and geochemical analyses of the A-type granite in the Hongol area, central Inner Mongolia, to determine its age, petrogenesis and tectonic setting, which are significant for clarifying the Late Paleozoic tectonic evolution of the Xing’an Mongolian Orogenic Belt(XMOB). The rock type of the A-type granite in the Hongol area is alkali-feldspar granite, and it constitutes a western part of the Baiyinwula-Dongujimqin A-type granite belt. Zircon U-Pb geochronology yieldsPb/U ages ranging from 293 to 286 Ma for the alkali-feldspar granite, indicating this granitic pluton formed in the Early Permian. The alkali-feldspar granite is high in silica(SiO=75.13 wt%-80.17 wt%), aluminum(AlO=10.59 wt%-13.17 wt%) and alkali(NaO+KO=7.33 wt%-9.11 wt%), and low in MgO(0.08 wt%-0.39 wt%) and CaO(0.19 wt%-0.70 wt%). It is obviously enriched in LILEs such as Rb, Th and K,depleted in HFSEs such as Nb, Ti, La and Ce, with pronounced negative anomalies of Nb, Ti, P, Eu, Sr and Ba. Its Sr-Nd-Pb isotopic compositions show positive ε(t)(+0.72-+3.08), low T(805-997 Ma),and high radioactive Pb with(Pb/Pb)of 18.710-19.304,(Pb/Pb)of 15.557-15.604 and(Pb/Pb)of 37.887-38.330. Petrological characteristics and geochemical data suggest that the alkalifeldspar granite in the Hongol area belongs to aluminous A-type granite. This A-type granite formed in a post-collisional extensional setting and was generated by the partial melting of felsic rocks in the middlelower crust resulting from post-collisional slab breakoff. It is suggested that the Paleo-Asian Ocean was closed before the Permian in central Inner Mongolia.展开更多
The central part of South Mongolia,located to the north of the Solonker Suture,is a key region for studying the late Paleozoic tectonic evolution of the Central Asian Orogenic Belt(CAOB).Voluminous late Paleozoic gran...The central part of South Mongolia,located to the north of the Solonker Suture,is a key region for studying the late Paleozoic tectonic evolution of the Central Asian Orogenic Belt(CAOB).Voluminous late Paleozoic granitic rocks,especially of Carboniferous age,were intruded in this area.However,these granitoids have not been well studied and there is a lack of precise ages and isotopic data.This has hampered our understanding of the tectonic evolution of southeastern Mongolia,and even the entire CAOB.In this paper,we provide new U-Pb isotopic ages and geochemical analyses for these Carboniferous granites.One granite from the Ulaanbadrakh pluton yielded a zircon U-Pb age of 326 Ma,which indicates emplacement in the Early Carboniferous,and three other granites from the Khatanbulag region gave zircon U-Pb ages of 316 Ma,315 Ma,and 311 Ma,which indicate emplacement in the Late Carboniferous.The Early Carboniferous granite has SiO2 contents of 70.04–70.39 wt%and K_(2)O+Na_(2)O contents of 6.48–6.63 wt%,whereas the Late Carboniferous granites have more variable compositions(SiO2=65.29–77.91 wt%and K2O+Na2O=5.30–7.27 wt%).All the granites are weakly-peraluminous I-types that are relatively enriched in U,Th,K,Zr,Hf,and LREEs.The whole rock Sr-Nd and zircon in situ Lu-Hf isotope analyses for the Early Carboniferous granite gave positive values ofεNd(t)(2.87)andεHf(t)(4.31–12.37)with young Nd(TDM=860 Ma)and Hf(TDMc=1367–637 Ma)two-stage model ages,indicating derivation from juvenile crustal material.In contrast,the Late Carboniferous granites had more diverse values ofεNd(t)(–4.03 to 2.18)andεHf(t)(–12.69 to 5.04)with old Nd(TDM=1358–1225 Ma)and Hf(TDMc=2881–1294 Ma)depleted mantle two-stage model ages,suggesting derivation from remelting of Precambrian basement.Based on the existing results,the tectonic setting of the Late Carboniferous granites in the central part of South Mongolia is known for its diversity,and this paper believes that the tectonic background of the carboniferous granite records the tectonic transition from a continental-margin-arc to a postcollisional extensional setting during the Late Carboniferous–Permian.展开更多
Swarms of orthopyroxenite and websterite veins are found within Egiingol residual SSZ peridotite massif of Dzhida terrain(Central Asian Orogenic Belt,Northern Mongolia).The process of Egiingol pyroxenite veins formati...Swarms of orthopyroxenite and websterite veins are found within Egiingol residual SSZ peridotite massif of Dzhida terrain(Central Asian Orogenic Belt,Northern Mongolia).The process of Egiingol pyroxenite veins formation is investigated using new major and trace element analyses of pyroxenite minerals,calculations of closure temperatures and composition of equilibrium melt.The pyroxenites show abundant petrographic and geochemical evidence for replacement of the residual peridotite minerals by ortho-and clinopyroxene due to melt-rock interaction.Relics of peridotite olivines are found in pyroxenites,Cr#of spinel increases from peridotites to pyroxenites,and compositions of ortho-and clinopyroxene change from peridotite to pyroxenite.The authors show that calculated equilibrium melts for investigated pyroxenites are very similar to compositions of boninite lavas from the Dzhida terrain.Therefore,formation of pyroxenite veins most likely resulted from percolation of boninite melts through the Egiingol peridotites.Orthopyroxenite veins formed at first,followed by websterite veins.Thus,the authors assume that pyroxenite veins represent the channels for boninitic melts migration in supra-subduction environment.展开更多
In continental subduction complexes minor volumes of high-pressure mafic rocks(eclogites)often co-exist with much more abundant felsic(granitic)and metasedimentary rocks,which are vital for resolving the origin and me...In continental subduction complexes minor volumes of high-pressure mafic rocks(eclogites)often co-exist with much more abundant felsic(granitic)and metasedimentary rocks,which are vital for resolving the origin and metamorphic evolution of subducted continental crust.In SW Mongolia,the Alag Khadny eclogite-bearing accretionary complex(AKC)is assumed to represent either a remnant of oceanic slab,or a continental margin,subducted in the Early Cambrian.Here we present geochronological,geochemical and petrological evidence of subduction records for the three major types of lithologies that host mafic eclogites,including Mesoproterozoic and Neoproterozoic granitic basement and overlying Neoproterozoic continental-margin sediments.Variably deformed,ferroan and peraluminous metagranitoids compose a major part of AKC and are interlayered with eclogites in its southern and eastern margins.They have geochemical features of post-collisional/intraplate high-K calc-alkaline granites.LA-ICP-MS U-Pb zircon geochronology of three distinct metagranite samples show uniform protolith crystallization ages of ca.0.96 Ga and uncertain re-crystallization in the Late Neoproterozoic or Early Paleozoic metamorphic event,whereas abundant zircon inheritance indicates older,Mesoproterozoic to Paleoproterozoic crustal substrate during granite generation.The existence of Mesoproterozoic crust is highlighted by finding of distinct metagranitoids with the U-Pb zircon crystallization age of ca.1.6 Ga.Hafnium isotope signatures(T_(DM)^(C)2.88-1.85 Ga)of zircons from all lithologies preserved the evidence of reworked Neoarchean to Paleoproterozoic crust,similar to that of the Baidrag block(southern Mongolia),for both Mesoproterozoic and Neoproterozoic rocks.Regardless of the specific lithology,the rocks display indicators of high-pressure metamorphic re-equilibration,including garnet(X_(Ca)up to 0.65)+epidote+phengite(Si p.f.u.up to 3.56)±rutile assemblage in metagranitoids,garnet+phengite(Si p.f.u.up to 3.42)in quartz-rich semi-pelites and garnet+phengite(Si p.f.u.up to 3.39)+medium-Mg chloritoid(X_(Mg)up to 0.25)+kyanite+rutile in metapelites.Corresponding P-T conditions recovered from different lithologies reveal incoherent subduction of rocks,which could be shallow for granitic basement(1.1-1.4 GPa and 600-670℃)and clastic metasediments(1.4-1.6 GPa,570-620℃),but deeper for metapelites(2.1-2.3 GPa,500-570℃).consistent with that of eclogites,The combined data show that the Alag Khadny complex represents a remnant of a rifted Mesoproterozoic to Neoproterozoic(ca.1.6-0.96 Ga)continental margin consequently metamorphosed under HP conditions during Late Neoproterozoic-Early Cambrian evolution of the southern Central Asian Orogenic Belt.Acquired P-T estimates imply that high-pressure metagranitoids and metasedimentary rocks equilibrated at different depths,but most likely shared a common subduction-related metamorphic evolution.展开更多
We report paleomagnetic results for Early Cretaceous lava flows collected from the Suhongtu area of Inner Mongolia, the middle part of the Tianshan-Mongolia Fold Belt (TMFB). Rock-magnetic experiments for different la...We report paleomagnetic results for Early Cretaceous lava flows collected from the Suhongtu area of Inner Mongolia, the middle part of the Tianshan-Mongolia Fold Belt (TMFB). Rock-magnetic experiments for different lava flows indicate that the main magnetic mineral is pseudo-single-domain (PSD) magnetite. The characteristic high-temperature remanence com- ponent is isolated by thermal demagnetization temperature steps between 300°C and 585"C, which yields a mean direction of D = 23.6°, I=56.0° with α 95 = 2.3°. We interpret this high-temperature remanence component as primary magnetization based mainly upon the petrographic analysis, which shows that the shape of magnetite crystal is relatively rounded square or polygon without internal reflection and deuterogenous phenomenon. The correspond- ing pole of the high-temperature remanence component is at 71.1°N, 200.5°E with A 95 = 2.7°. This Early Cretaceous pole is in good agreement with those for Siberia, North China, and Inner Mongolia, suggesting that these continental blocks had already sutured together in the Early Cretaceous, which would further provide constraints on better understanding of the formation and evolution of the TMFB.展开更多
基金funded by project grants from the Chinese Geological Survey (Grants Nos. DD20190039, DD20160048–01, DD20160345–17, DD20190372, DD20190360 and 1212011220435)the Liaoning Education Department (Grant No. LQN201915)。
文摘The late Paleozoic tectonic framework of the southeastern Central Asian Orogenic Belt is key to restricting the accretion orogeny between the Siberia Craton and the North China Craton. To clarify the framework, petrogenesis of early Permian intrusive rocks from southeastern Inner Mongolia was studied. Zircon U-Pb dating for bojite and syenogranite from Ar-Horqin indicate that they were emplaced at 288–285 Ma. Geochemical data reveal that the bojite is highly magnesian and low-K to middle-K calc-alkaline, with E-MORB-type REE and IAB-like trace element patterns. The syenogranite is a middle-K calc-alkaline fractionated A-type granite and shows oceanic-arc-like trace element patterns, with depleted Sr-Nd-Hf isotopes,(~(87)Sr/~(86)Sr)I = 0.7032–0.7042, ε_(Nd)(t) = +4.0 to +6.6 and zircon ε_(Hf)(t) = +11.14 to +14.99. This suggests that the bojite was derived from lithospheric mantle metasomatized by subducted slab melt, while the syenogranite originated from very juvenile arc-related lower crust. Usng data from coeval magmatic rocks from Linxi-Ar-Horqin, the Ar-Horqin intra-oceanic arc was reconstructed, i.e., initial transition in 290–280 Ma and mature after 278 Ma. Combined with regional geological and geophysical materials in southeastern Inner Mongolia, an early Permian tectonic framework as ‘one narrow ocean basin of the PAO', ‘two continental marginal arcs on its northern and southern' and ‘one intra-oceanic arc in its southern' is proposed.
基金国家自然科学基金(42102260、41730213、41890831、42072267、41972229)长安大学中央高校基本科研业务专项资金-高新技术研究支持计划培养项目(300102272204)+1 种基金裘搓基金会Croucher Chinese Visitorships(2022-2023)陕西高校青年创新团队The Youth Innovation Team of Shaanxi Universities联合资助。
基金financially supported by projects of the China Geological Survey (Grant Nos. 1212011220458, 1212011220492)
文摘We performed geochronological and geochemical analyses of the A-type granite in the Hongol area, central Inner Mongolia, to determine its age, petrogenesis and tectonic setting, which are significant for clarifying the Late Paleozoic tectonic evolution of the Xing’an Mongolian Orogenic Belt(XMOB). The rock type of the A-type granite in the Hongol area is alkali-feldspar granite, and it constitutes a western part of the Baiyinwula-Dongujimqin A-type granite belt. Zircon U-Pb geochronology yieldsPb/U ages ranging from 293 to 286 Ma for the alkali-feldspar granite, indicating this granitic pluton formed in the Early Permian. The alkali-feldspar granite is high in silica(SiO=75.13 wt%-80.17 wt%), aluminum(AlO=10.59 wt%-13.17 wt%) and alkali(NaO+KO=7.33 wt%-9.11 wt%), and low in MgO(0.08 wt%-0.39 wt%) and CaO(0.19 wt%-0.70 wt%). It is obviously enriched in LILEs such as Rb, Th and K,depleted in HFSEs such as Nb, Ti, La and Ce, with pronounced negative anomalies of Nb, Ti, P, Eu, Sr and Ba. Its Sr-Nd-Pb isotopic compositions show positive ε(t)(+0.72-+3.08), low T(805-997 Ma),and high radioactive Pb with(Pb/Pb)of 18.710-19.304,(Pb/Pb)of 15.557-15.604 and(Pb/Pb)of 37.887-38.330. Petrological characteristics and geochemical data suggest that the alkalifeldspar granite in the Hongol area belongs to aluminous A-type granite. This A-type granite formed in a post-collisional extensional setting and was generated by the partial melting of felsic rocks in the middlelower crust resulting from post-collisional slab breakoff. It is suggested that the Paleo-Asian Ocean was closed before the Permian in central Inner Mongolia.
基金supported financially by the National Key Research and Development Program of China(Grant Nos 2018YFC0603702 and 2017YFC0601301)NSFC projects(Grant Nos 41372077 and U1403291)+1 种基金projects of the China Geological Survey(Grant Nos DD20190685,DD20160024,DD20160123,and DD20160345)This publication is a contribution to IGCP Project 662。
文摘The central part of South Mongolia,located to the north of the Solonker Suture,is a key region for studying the late Paleozoic tectonic evolution of the Central Asian Orogenic Belt(CAOB).Voluminous late Paleozoic granitic rocks,especially of Carboniferous age,were intruded in this area.However,these granitoids have not been well studied and there is a lack of precise ages and isotopic data.This has hampered our understanding of the tectonic evolution of southeastern Mongolia,and even the entire CAOB.In this paper,we provide new U-Pb isotopic ages and geochemical analyses for these Carboniferous granites.One granite from the Ulaanbadrakh pluton yielded a zircon U-Pb age of 326 Ma,which indicates emplacement in the Early Carboniferous,and three other granites from the Khatanbulag region gave zircon U-Pb ages of 316 Ma,315 Ma,and 311 Ma,which indicate emplacement in the Late Carboniferous.The Early Carboniferous granite has SiO2 contents of 70.04–70.39 wt%and K_(2)O+Na_(2)O contents of 6.48–6.63 wt%,whereas the Late Carboniferous granites have more variable compositions(SiO2=65.29–77.91 wt%and K2O+Na2O=5.30–7.27 wt%).All the granites are weakly-peraluminous I-types that are relatively enriched in U,Th,K,Zr,Hf,and LREEs.The whole rock Sr-Nd and zircon in situ Lu-Hf isotope analyses for the Early Carboniferous granite gave positive values ofεNd(t)(2.87)andεHf(t)(4.31–12.37)with young Nd(TDM=860 Ma)and Hf(TDMc=1367–637 Ma)two-stage model ages,indicating derivation from juvenile crustal material.In contrast,the Late Carboniferous granites had more diverse values ofεNd(t)(–4.03 to 2.18)andεHf(t)(–12.69 to 5.04)with old Nd(TDM=1358–1225 Ma)and Hf(TDMc=2881–1294 Ma)depleted mantle two-stage model ages,suggesting derivation from remelting of Precambrian basement.Based on the existing results,the tectonic setting of the Late Carboniferous granites in the central part of South Mongolia is known for its diversity,and this paper believes that the tectonic background of the carboniferous granite records the tectonic transition from a continental-margin-arc to a postcollisional extensional setting during the Late Carboniferous–Permian.
基金The reported study was funded by RFBR according to the research project(18-35-00535)IGC State Assignment Project(0350-2019-0008).
文摘Swarms of orthopyroxenite and websterite veins are found within Egiingol residual SSZ peridotite massif of Dzhida terrain(Central Asian Orogenic Belt,Northern Mongolia).The process of Egiingol pyroxenite veins formation is investigated using new major and trace element analyses of pyroxenite minerals,calculations of closure temperatures and composition of equilibrium melt.The pyroxenites show abundant petrographic and geochemical evidence for replacement of the residual peridotite minerals by ortho-and clinopyroxene due to melt-rock interaction.Relics of peridotite olivines are found in pyroxenites,Cr#of spinel increases from peridotites to pyroxenites,and compositions of ortho-and clinopyroxene change from peridotite to pyroxenite.The authors show that calculated equilibrium melts for investigated pyroxenites are very similar to compositions of boninite lavas from the Dzhida terrain.Therefore,formation of pyroxenite veins most likely resulted from percolation of boninite melts through the Egiingol peridotites.Orthopyroxenite veins formed at first,followed by websterite veins.Thus,the authors assume that pyroxenite veins represent the channels for boninitic melts migration in supra-subduction environment.
基金performed within the framework of the IGC State Assignment Project No.0350-2016-0028Ministry of Science and Technology of Taiwan(MOST 106-2811-M-001-035)during postdoctoral research of SYuS at Institute of Earth Science(Academia Sinica,Taipei,Taiwan)further supported by the Foundation of Russian Federation President(Grant No.MK-67.2020.5)。
文摘In continental subduction complexes minor volumes of high-pressure mafic rocks(eclogites)often co-exist with much more abundant felsic(granitic)and metasedimentary rocks,which are vital for resolving the origin and metamorphic evolution of subducted continental crust.In SW Mongolia,the Alag Khadny eclogite-bearing accretionary complex(AKC)is assumed to represent either a remnant of oceanic slab,or a continental margin,subducted in the Early Cambrian.Here we present geochronological,geochemical and petrological evidence of subduction records for the three major types of lithologies that host mafic eclogites,including Mesoproterozoic and Neoproterozoic granitic basement and overlying Neoproterozoic continental-margin sediments.Variably deformed,ferroan and peraluminous metagranitoids compose a major part of AKC and are interlayered with eclogites in its southern and eastern margins.They have geochemical features of post-collisional/intraplate high-K calc-alkaline granites.LA-ICP-MS U-Pb zircon geochronology of three distinct metagranite samples show uniform protolith crystallization ages of ca.0.96 Ga and uncertain re-crystallization in the Late Neoproterozoic or Early Paleozoic metamorphic event,whereas abundant zircon inheritance indicates older,Mesoproterozoic to Paleoproterozoic crustal substrate during granite generation.The existence of Mesoproterozoic crust is highlighted by finding of distinct metagranitoids with the U-Pb zircon crystallization age of ca.1.6 Ga.Hafnium isotope signatures(T_(DM)^(C)2.88-1.85 Ga)of zircons from all lithologies preserved the evidence of reworked Neoarchean to Paleoproterozoic crust,similar to that of the Baidrag block(southern Mongolia),for both Mesoproterozoic and Neoproterozoic rocks.Regardless of the specific lithology,the rocks display indicators of high-pressure metamorphic re-equilibration,including garnet(X_(Ca)up to 0.65)+epidote+phengite(Si p.f.u.up to 3.56)±rutile assemblage in metagranitoids,garnet+phengite(Si p.f.u.up to 3.42)in quartz-rich semi-pelites and garnet+phengite(Si p.f.u.up to 3.39)+medium-Mg chloritoid(X_(Mg)up to 0.25)+kyanite+rutile in metapelites.Corresponding P-T conditions recovered from different lithologies reveal incoherent subduction of rocks,which could be shallow for granitic basement(1.1-1.4 GPa and 600-670℃)and clastic metasediments(1.4-1.6 GPa,570-620℃),but deeper for metapelites(2.1-2.3 GPa,500-570℃).consistent with that of eclogites,The combined data show that the Alag Khadny complex represents a remnant of a rifted Mesoproterozoic to Neoproterozoic(ca.1.6-0.96 Ga)continental margin consequently metamorphosed under HP conditions during Late Neoproterozoic-Early Cambrian evolution of the southern Central Asian Orogenic Belt.Acquired P-T estimates imply that high-pressure metagranitoids and metasedimentary rocks equilibrated at different depths,but most likely shared a common subduction-related metamorphic evolution.
文摘We report paleomagnetic results for Early Cretaceous lava flows collected from the Suhongtu area of Inner Mongolia, the middle part of the Tianshan-Mongolia Fold Belt (TMFB). Rock-magnetic experiments for different lava flows indicate that the main magnetic mineral is pseudo-single-domain (PSD) magnetite. The characteristic high-temperature remanence com- ponent is isolated by thermal demagnetization temperature steps between 300°C and 585"C, which yields a mean direction of D = 23.6°, I=56.0° with α 95 = 2.3°. We interpret this high-temperature remanence component as primary magnetization based mainly upon the petrographic analysis, which shows that the shape of magnetite crystal is relatively rounded square or polygon without internal reflection and deuterogenous phenomenon. The correspond- ing pole of the high-temperature remanence component is at 71.1°N, 200.5°E with A 95 = 2.7°. This Early Cretaceous pole is in good agreement with those for Siberia, North China, and Inner Mongolia, suggesting that these continental blocks had already sutured together in the Early Cretaceous, which would further provide constraints on better understanding of the formation and evolution of the TMFB.
