Accretion Processes of Oceanic Crust in Slow-spreading Ridges:Plagiogranite Perspective of the Xigaze Ophiolite,South Tibet  

作　　者：LI Yuan LI Ruibao YANG Shengbiao ZHANG Jian YANG Jingsui 

机构地区：[1]Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China [2]School of Earth Sciences and Resources,Chang’an University,Xi’an 710054,China [3]Tianjin Institute of Geology and Mineral Resources,Tianjing 300170,China [4]School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China

出　　处：《Acta Geologica Sinica(English Edition)》2022年第6期1945-1959,共15页地质学报（英文版）

基　　金：supported by grants from the National Natural Science Foundation of China(Grant Nos.41720104009 and 41772231);the China Geological Survey Project(Grant No.DD20190060).

摘　　要：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 midocean 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.

关 键 词：Xigaze ophiolite PLAGIOGRANITE fractional crystallization multiple magma injection ocean-continent transition zone 

分 类 号：P736[天文地球—海洋地质] P588.121[天文地球—海洋科学]