Crustal Contamination of the Mantle-Derived Liuyuan Basalts:Implications for the Permian Evolution of the Southern Central Asian Orogenic Belt  

作　　者：Yuanyang Yu Keqing Zong Yu Yuan Reiner Klemd Xin-Shui Wang Jingliang Guo Rong Xu Zhaochu Hu Yongsheng Liu 

机构地区：[1]State Key Laboratory of Geological Processes and Mineral Resources,School of Earth Sciences,China University of Geosciences,Wuhan 430074,China [2]GeoZentrum Nordbayern,Universität Erlangen-Nürnberg,Schlossgarten 5a,Erlangen,D-91054,Germany [3]State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang,550081,China

出　　处：《Journal of Earth Science》2022年第5期1081-1094,共14页地球科学学刊（英文版）

基　　金：co-supported by the National Natural Science Foundation of China(No.41922021);the MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(No.MSFGPMR01-03)。

摘　　要：The Permian basalts in the Central Asian Orogenic Belt(CAOB)are crucial for constraining the closure of the Paleo-Asian Ocean.However,the origin of these basalts is still under discussion.Here,we present comprehensive bulk-rock geochemical,Sr-Nd-Pb-Hf isotopic,and zircon U-Pb-Lu-Hf isotopic data of the Liuyuan basalts and coexisting gabbros,which are located in the Beishan Orogen in the southern CAOB,to constrain their emplacement setting and tectonic implications.Our new gabbro ages of ca.288–294 Ma are interpreted to represent the formation time of the Liuyuan basaltic belt.The Liuyuan basalts show MORB-like rare earth element(REE)patterns and bulk-rockε_(Hf)(t)andε_(Nd)(t)values of 11.0–15.4 and 4.6–9.2,respectively,suggesting an origination mainly from a depleted mantle source.However,positive Pb anomalies,Nb-Ta depletions,and high Th/Yb ratios as well as evolved Sr-Nd-Pb-Hf isotopic compositions of some samples indicate variable continental crustal contribution.According to the covariation of Pb anomalies(Pb^(*)=2×Pb_(N)/(Ce_(N)+Pr_(N)))with Sr-Nd-Pb-Hf isotopic compositions,we speculate that parent magma of the Liuyuan basalt was contaminated by continental crustal materials during the eruption rather than having been generated from an enriched mantle source.As revealed by mixing modelling,the Liuyuan basaltic magmas would require a minor(<10%)upper continental crustal assimilation to explain the enriched trace elemental and radiogenic Sr-Nd-Pb-Hf isotopic signatures.Consequently,the Liuyuan basaltic belt is believed to have been generated in a continental extensional environment instead of an oceanic setting and does not constitute a Permian ophiolitic suture zone as previously suggested,since the Paleo-Asian Ocean was already closed in the southern Beishan Orogen in the Early Permian.

关 键 词：crustal contamination Liuyuan basaltic belt Central Asian Orogenic Belt Beishan Orogen Pb anomaly TECTONICS 

分 类 号：P534.46[天文地球—古生物学与地层学] P542[天文地球—地质学]