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
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financially supported by the National Natural Science Foundation of China(42102260,42172236,42072264,41902229,and 42072267)Hong Kong Research Grants Council General Research Fund(17307918)+1 种基金the Fundamental Research Funds for the Central Universities,Chang’an University,China(300102272204)Opening Foundation of State Key Laboratory of Continental Dynamics,Northwest University,China(21LCD09)。
