摘要
方柱石是一种含挥发分的架状铝硅酸盐矿物,其成因一直有争议。对喜马拉雅造山带定结地区基性麻粒岩中方柱石及其出溶物的矿物化学和纳米结构分析表明:(1)方柱石为富S类型;(2)内部出溶矿物为陨硫铁,晶胞参数为a=b=0.5968nm,c=1.174nm,α=β=90°,γ=120°;(3)陨硫铁的(001)面平行于方柱石的(100)面。出溶前的方柱石在榴辉岩相条件下形成,其稳定压力上限与Fe含量呈正相关关系。在麻粒岩相作用时,无水条件下方柱石内的SO^(2-)_(4)发生自氧化还原反应而产生出溶矿物和O_(2),反应方程式为:Fe ^(2+)+SO_(2)-4=FeS+2O_(2)。类似反应可能导致下地壳氧逸度高于中上地壳。方柱石的形成与分解记录了喜马拉雅造山带的形成过程,在大陆俯冲与折返过程中扮演重要角色,对地壳深部挥发分的调节起到了重要作用,并对地球深部氧逸度调节机制的研究开拓了新的思路。
Scapolite-group minerals are widespread volatile-bearing aluminosilicates in granulite facies metamorphic rocks,but the formation mechanism and the behavior of scapolite is poorly understood.EPMA and TEM analyses of the scapolite and its exsolution lamellae from a mafic granulite in Dinggye area show that:(1)the scapolite is rich in SO_(2)-4;(2)the lamellae are troilite with(001)parallel to the host crystal(100);and(3)its unit cell of the lamellae is:a=b=0.5968nm,c=1.174nm,α=β=90°,γ=120°.The scapolite before exsolution formed in eclogite facies conditions and its upper limit of pressure is strongly controlled by Fe content.During later granulite facies metamorphism,SO_(2)-4 with these scapolites experienced a self-redox reaction to produce the lamellae plus O_(2)in a H _(2)O-free condition,the reaction equation is described as follows:Fe^(2+)+SO_(2)-4=FeS+2O_(2).Similar reactions could lead to an elevated oxygen fugacity in the lower crust than in the middle and upper crust.The formation and breakdown of scapolite provide a valuable record on the deep processes during the tectonic evolution of the Himalayan orogen.In addition,these processes might play an important role controlling the geochemical behaviors of volatile components during the subduction and exhumation of continental orogenic belts.This exploits a new tool for the investigation of deep-Earth oxygen fugacity adjustment.
作者
邸英龙
曾令森
陈晶
高利娥
张立飞
DI YingLong;ZENG LingSen;CHEN Jing;GAO LiE;ZHANG LiFei(Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;Electron Microscopy Laboratory,School of Physics,Peking University,Beijing 100871,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2021年第11期3435-3444,共10页
Acta Petrologica Sinica
基金
国家自然科学基金项目(92055202)
第二次青藏高原科学考察项目(2019QZKK0702)
中国地质调查局地质调查项目(DD20190057)联合资助.
