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

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外文摘要：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,whole-rock 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 K2O+Na2O=3.11-4.04 wt％,K2O/Na2O=0.50-0.72,and Mg#=62.24-65.13.They are enriched in LILE but depleted in HFSE with higher initial 87Sr/86Sr ratio(0.706896-0.714743)and lower εNd(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 asthenosphere-derived 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 might be associated with the initial slab rollback and corresponding lithospheric extension occurred potentially at ca.145 Ma.

外文关键词：

Early Cretaceous mafic dikemetasomatized lithospheric mantleTuanshanbei doleriteJiangnan OrogenSouth China

作者：

WANG Cheng、WEI Hantao、LIU Qingquan、YANG Zhao

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作者单位：

Guangdong Provincial Key Laboratory of Geodynamics and Geohazards,School of Earth Sciences and Engineering,Sun Yat-sen University,Guangzhou 510275,China

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

Development and Research Centre,China Geological Survey,Beijing 100037,China

School of Environmental Studies,China University of Geosciences,Wuhan 430074,China

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基金：

国家自然科学基金国家自然科学基金国家自然科学基金Fundamental Research Funds for the Central Universities,Sun Yatsen University

项目编号：

42302235418302114227210023ptpy143

出版年：

2024

DOI：

10.1111/1755-6724.15129

地质学报(英文版)