雅鲁藏布江缝合带白朗县白岗尖晶石-石榴子石相二辉橄榄岩的相界反应及其意义  

A Study on Mineralogical Phase Confines Reaction from Spinel to Garnet in Baigang lherzolite of the Yarlung Zangbo Suture Zone,and Its Geological Implication

作　　者：夏斌[1,2] 周国庆[3] 李建峰[1] 陈根文[1] 刘维亮[2] 王冉 董冰华[1] 

机构地区：[1]中国科学院广州地球化学研究,广州510640 [2]中山大学海洋学院,广州510006 [3]南京大学地球科学与工程学院,南京210093 [4]深圳中广核工程设计有限公司,广东深圳518029

出　　处：《地质论评》2012年第3期453-470,共18页Geological Review

基　　金：国家自然科学基金重点项目(编号40534019)的成果

摘　　要：西藏白朗县白岗村蛇绿混杂岩中有一罕见的尖晶石石榴子石二辉橄榄岩小岩块,被松软的蛇纹岩化尖晶石二辉橄榄岩包裹其中。岩块中发育有碎基单斜辉石、斜方辉石中出溶单斜辉石、切过出溶单斜辉石的贯入单斜辉石和外来碎粒单斜辉石及钙质辉石+铬尖晶石→钙铁石榴子石相界反应。同时,在岩块和包壳岩石的橄榄石中出现针状硅镁石出溶物。计算这些矿物的温度压力表明,它们的温度压力都处于>800℃,>1.8GPa以上的地幔石榴子石域超高压环境,而且,经历过一个上升→俯冲→上升的"N"字形历程。In Baigang ophiolitic m6lange of the Yarlung Zangbo Suture Zone exposes an unusual spinel - garnet lherzolite block, which is surrounded by soft crust of serpentinized lherzolite. In this block, there are four kinds of clino-pyroxene. They are earliest recrystallized matrix clino-pyroxene, exsolution elino-pyroxene, inserting elino-pyroxene, and exotic clastic elino-pyroxene. It can also be seen the metamorphic reaction that is calcarous pyroxene ＋ spinel→andradite. We also find there are some needle-like humite exsolution in olivine in both core and crustal lherzolites. Geo-thermobarometers are applied to these lherzolites, which give a result of higher than 900℃ temperature and more than 1.8GPa pressure, and also implies that the spinel -garnet lherzolite block have experienced aletter N-like tectonic route composed of ascending, subdction and re - ascending three stages.

关 键 词：蛇绿混杂岩块 尖晶石-石榴子石相界反应 橄榄石中硅镁石出溶物 深俯冲-折返 西藏白岗 

分 类 号：P588.125[天文地球—岩石学]