Metamorphic evolution of Sumdo eclogite in Lhasa Block of the Tibetan Plateau: Phase equilibrium in NCKMnFMASHTO System
Metamorphic evolution of Sumdo eclogite in Lhasa Block of the Tibetan Plateau: Phase equilibrium in NCKMnFMASHTO System
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发表时间：
2015
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通讯作者：
H. Ji
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作者：
H. Ji
拉萨地块榴辉岩主要由石榴子石、绿辉石、多硅白云母、绿帘石和金红石组成。榴辉岩中的石榴子石没有明显的分带，核部均匀。Xpy和Xgr从核心到边缘降低。绿辉石的分带性较弱。Jd值从核心到边缘增加。绿辉石劈理中沿着生长的一些细棒状体可能反映了退变质过程。石榴子石中的多硅白云母比基质中的多硅白云母具有更高的Si值。首次将相平衡模拟方法应用于拉萨地块中常见的榴辉岩的研究。在NCKMn FMASHTO系统中对样品13 SD 43进行了P-T假切片。根据石榴子石核部的最大Xpy值和多硅白云母的最大Si值，确定其峰期变质条件为610℃，32 Kbar，峰期矿物组合为g+o + law + phn + ru。通过相平衡和岩相学研究，可以识别榴辉岩的多种变质演化过程。研究表明，拉萨地块榴辉岩可能经历了超高压变质作用并快速折返至中地壳，这可能为拉萨地块缝合带的存在提供了新的证据。
The eclogite in the Lhasa block mainly consists of garnet, omphacite, phengite, epidote and rutile. The garnet in the eclogite has no visible zonation and a homogeneous core. The Xpy and Xgr decrease from core to rim. Most of the omphacites showweak zonation. The Jd value increases from core to rim. The growth of some narrow barroisite rods along omphacite cleavage may reflect retrograde processes. The phengite included in garnet has higher Si value than that in the matrix. The authors applied for the first time the phase equilibrium simulation method to the study of this common eclogite in the Lhasa block. P- T pseudosection of sample 13SD43 was employed in the NCKMn FMASHTO system. The maximum Xpy in the core of garnet and the maximum Si value in phengite were used to determine the peak metamorphic condition of 610℃,32 Kbar, with a peak mineral assemblage of g+o + law + phn + ru. With the help of phase equilibrium and petrography research, several metamorphic evolution processes of the eclogite could be recognized. Studies show that the eclogites in the Lhasa block probably experienced UHP metamorphism and rapid exhumation to the middle crust, which might have provided new evidence for the existence of the suture zone in the Lhasa block.