Structural and petrological data suggest that the Xigaze ophiolite from the Yarlung Zangbo Suture Zone(YZSZ)in south Tibet was a typical slow-spreading ridge.A new field,geochemical,mineral,and U-Pb zircon dataset of plagiogranite intrusions were used to constrain the dynamic processes of oceanic accretion in this slow-spreading ridge.Plagiogranites mainly occur as dykes or intrusions intruded into the whole sequence of the ophiolite and have a similar orientation to the dolerite dykes developed in the late stage of detachment faulting.U-Pb zircon ages of 122-123 Ma were obtained for two types of plagiogranites and associated dolerite dykes.Detailed geochemical and mineralogical examinations suggest that the plagiogranites are the product of low-pressure(2-3 kbar)fractional crystallization of mid-ocean ridge basalt-like magma and unlikely to have been derived from the partial melting of hydrous gabbroic rocks.The complex cross-cut relationship between the plagiogranites and ophiolite sequence reflects that they are controlled by small discontinued melt lenses rather than a big magma chamber under the ridge axis and reveals multiple injections during the oceanic crust accretion.The formation of plagiogranites possibly reflects the complex characteristic of oceanic accretion at slow-spreading ridges,time-dependent on structural(external)and magmatic(internal)processes.

LI Yuan;LI Ruibao;YANG Shengbiao;ZHANG Jian;YANG Jingsui

Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Sciences and Resources,Chang'an University,Xi'an 710054,China;Tianjin Institute of Geology and Mineral Resources,Tianjing 300170,China;School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China

地质学报（英文版）

[1]LI Yuan;LI Ruibao;YANG Shengbiao;ZHANG Jian;YANG Jingsui-.Accretion Processes of Oceanic Crust in Slow-spreading Ridges:Plagiogranite Perspective of the Xigaze Ophiolite,South Tibet)[J].地质学报（英文版）,2022(06):1945-1959

Ridges,Plagiogranite,Xigaze,Ophiolite,YZSZ,plagiogranite,Plagiogranites,dolerite,plagiogranites

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