Early Cretaceous Metasomatized Lithospheric Mantle beneath the Central Jiangnan Orogen in South China:Geochemical and Sr-Nd Isotope Evidence from the Tuanshanbei Dolerite  

作　　者：WANG Cheng WEI Hantao LIU Qingquan YANG Zhao 

机构地区：[1]Guangdong Provincial Key Laboratory of Geodynamics and Geohazards,School of Earth Sciences and Engineering,Sun Yat-sen University,Guangzhou 510275,China [2]Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring,Ministry of Education,School of Geosciences and Info-Physics,Central South University,Changsha 410083,China [3]Development and Research Centre,China Geological Survey,Beijing 100037,China [4]School of Environmental Studies,China University of Geosciences,Wuhan 430074,China

出　　处：《Acta Geologica Sinica(English Edition)》2024年第3期602-616,共15页地质学报（英文版）

基　　金：financially supported by the National Natural Science Foundation of China(Grant Nos.42302235,41830211,42272100);Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.23ptpy143)。

摘　　要：It is well established that Cretaceous magmatism in the South China Block(SCB)is related to the Paleo-Pacific subduction.However,the starting time and the associated deep crust-mantle processes are still debatable.Mafic dike swarms carry important information on the deep earth(including mantle)geodynamics and geochemical evolution.In the Jiangnan Orogen(South China).there is no information on whether the Mesozoic magmatic activities in this region are also directly related to the Pacific subduction or not.In this study,we present detailed zircon U-Pb geochronological,wholerock element and Sr-Nd isotope data for Early Cretaceous Tuanshanbei dolerite dikes,and provide new constraints on the condition of the lithospheric mantle and mantle dynamics of the SCB during that time.LA-ICP-MS zircon U-Pb dating suggests that this dolerite erupted in the Early Cretaceous(~145 Ma).All samples have alkaline geochemical affinities with K_(2)O+Na_(2)O=3.11-4.04 wt%,K_(2)O/Na_(2)O=0.50-0.72,and Mg^(#)=62.24-65.13.They are enriched in LILE but depleted in HFSE with higher initial^(87)Sr/^(86)Sr ratio(0.706896-0.714743)and lower ε_(Nd)(t)(-2.61 to-1.67).They have high Nb/U,Nb/La,La/Sm and Rb/Sr,and low La/Nb,La/Ta,Ce/Pb,Ba/Rb,Tb/Yb and Gd/Yb ratios.Such geochemical signatures suggest that the fractional crystallization is obvious but crustal contamination play a negligible role during magmatic evolution.Tuanshanbei dolerite were most likely derived from low-degree(2%-5%)partial melting of a phlogopite-bearing mantle material consisted of~85% spinel peridotite and~15% garnet peridotite previously metasomatized by asthenospherederived fluids/melts with minor subduction-derived fluids/melts.Slab-rollback generally lead to the upwelling of the hot asthenosphere.The upwelling of asthenosphere consuming the lithospheric mantle by thermo-mechanical-chemical erosion.The lithospheric mantle may have partially melted due to the heating by the upwelling asthenosphere and lithospheric extension.It is inferred that the Tuanshanbei dolerite mig

关 键 词：Early Cretaceous mafic dike metasomatized lithospheric mantle Tuanshanbei dolerite Jiangnan Orogen South China 

分 类 号：P534.53[天文地球—古生物学与地层学] P31[天文地球—地质学] P597.3