摘要
西藏南部的拉萨地体记录了新特提斯洋俯冲和随后的陆陆碰撞造山作用,然而对于新特提斯洋俯冲消亡到印度-欧亚大陆初始碰撞这一构造转换时期的深部动力学演化过程却未有较好的约束。本文对西藏中部拉萨地体南缘的罗扎花岗斑岩开展了岩相学、锆石年代学、锆石原位Hf同位素和全岩地球化学研究。结果表明,罗扎花岗斑岩的锆石U-Pb年龄为66.4 Ma和67.3 Ma,为晚白垩世末期产物。岩石中未见角闪石及富铝矿物,具有高SiO_(2)(77.93%~83.24%)、高碱(K_(2)O+Na_(2)O=3.95%~6.69%)、低磷(P2O5=0.01%~0.02%),轻重稀土元素分馏强烈、负Eu异常显著,富集大离子亲石元素(Rb、Sr、Ba等)、亏损高场强元素(Nb、Ta、Ti等)等特征,为典型的高分异Ⅰ型花岗岩。另外,锆石的Hf同位素组成不均一,变化范围较大[εHf(t)值为-4.9~+4.33]。综合研究表明,罗扎花岗斑岩是在新特提斯洋俯冲的晚阶段,由新特提斯洋板片回转导致软流圈上涌,使中拉萨地体古老下地壳发生部分熔融,并与少量幔源岩浆混合之后,经高程度结晶分异作用而形成的。
There are records of the northward subduction of the Neo-Tethyan oceanic slab and the subsequent continental-continental collision in the Lhasa terrane of the southern Tibet,however,the deep dynamic evolution process of the tectonic transition from the closure of the subducted Neo-Tethys oceanic plate to the initial collision of Indian continent-Asian continent has not been well constrained yet.Here we have presented petrographic,zircon U-Pb dating,zircon Hf isotopic,and whole-rock major and trace elements data of the Luozha granite porphyry samples from the southern margin of the central part of the Lhasa terrane.Zircon U-Pb dating of two samples of the Luozha granite porphyry yielded consistent ages of 66.4 Ma and 67.3 Ma,indicating that it was formed in Late Cretaceous.Hornblende and aluminum-rich minerals are not found in the rocks which are characterized with high SiO_(2)(77.93%~83.24%),high alkaline(K_(2)O+Na_(2)O contents of 3.95%~6.69%),low P2O5(0.01%~0.02%),strong fractionation between LREE and HREE,significant negative Eu anomlies,enriched large-ion lithophile elements(Rb,Sr,and Ba),and depleted high-field-strength elements(Nb,Ta,and Ti).These characteristics of the Luozha granite porphyry suggested that it belongs to the highly fractionatedⅠ-type granite.In addition,the Luozha granite porphyry has various zircon Hf isotopic compositions withεHf(t)values varying from-4.9 to+4.3.According to the comprehensive study,it is believed that the Luozha granite porphyry was formed in the late stage of the subduction of the Neo-Tethys oceanic plate by the magma which was mainly derived from the partial melting of the ancient lower crust of the Lhasa terrane resulted from the hot asthenospheric mantle ascending due to the roll-back of the Neo-Tethys oceanic slab and partly from the mantle magma through the high degree crystallization differentiation.
作者
刘洲基
邓煜霖
郎兴海
成德健
王旭辉
何青
董咪
梁海辉
吕娜
杨同山
LIU Zhou-ji;DENG Yu-lin;LANG Xing-hai;CHENG De-jian;WANG Xu-hui;HE Qing;DONG Mi;LIANG Hai-hui;LYU Na;YANG Tong-shan(Tianyuan Mineral Resources Development Co.Ltd of Tibet,Xigaze,Tibet 857000,China;College of Earth Science,Chengdu University of Technology,Chengdu 610059,China)
出处
《矿物岩石地球化学通报》
CAS
CSCD
北大核心
2022年第6期1178-1192,共15页
Bulletin of Mineralogy, Petrology and Geochemistry
基金
四川省科技计划项目(2020JDJQ0042)
国家自然科学基金项目(41502079,41972084)
国家重点研发计划课题(2018YFC0604105)
成都理工大学珠峰科学研究计划(2020ZF11407)
西北大学大陆动力学国家重点实验室开放基金(18LCD04)
自然资源部深地资源成矿作用与矿产预测重点实验室开放基金(ZS1911)
中国地质调查局项目(DD20190167,DD20160346)。
