缅甸含硬玉的蛇纹石化橄榄岩及其围岩的岩石学研究

Petrology of jadeite-bearing serpentinized peridotite and its country rocks from Northwestern Myanmar (Burma).

以缅甸帕敢地区含硬玉岩的蛇纹石化橄榄岩及其围岩 -未细分的变质岩为研究对象 ,较详细地研究了各类岩石的岩相学、岩石化学及主要矿物的组成 ,认为该区超基性岩为含铬铁矿的蛇纹石化纯橄岩 ,它的围岩由含多硅白母蓝闪石片岩、石榴斜长角闪岩、大理岩及透辉石大理岩、石英岩等构成。通过其中典型的变质反应分析与计算 ,认为围岩的变质程度分别为蓝闪石片岩相和的高角闪岩相 ,其中蓝闪石片岩相的压力大于 0 .8～ 1.0 GPa,斜长角闪岩相的温度为 5 82℃。通过对比分析世界上不同产地硬玉岩的特征 ,认为硬玉岩 ,尤其是优质者 ,产出环境如下 :(1)容矿岩体属超基性岩 ,以含铬铁矿的纯橄岩为最佳 ;(2 )围岩中存在低温高压变质岩 ,即蓝闪石片岩 -榴辉岩类 ;(3)

Jadeite-bearing serpentinized peridotite is chromite-bearing dunite, its values of Mg/(Mg+Fe) in either residual olivines or whole rocks are higher than 90mol%. Metamorphic rocks outer the dunite are phengite-bearing blueschist, garnet amphibolite, marble or diopside-bearing marble, quartzite etc. The mineral assemblages in blueschist are glaucophane + barroisite + phengite and glaucophane + barroisite; in amphibolite, garnet + tschermakite; in marble, diopside + calcite; in quartzite, quartz + stilonmelane. The major, rare and trace elements in each rock were displayed and studied. The metamorphic degree of the Northern Burma schists is much higher than that of greenschist face by the former study. The metamorphic pressure of blueschist was suggested to be higher than 0.8 similar to1.0GPa, and the temperature of amphibolite, to be about 582 degreesC. In addition, the discoveries of three-phase fluid inclusions in jadeite and high to ultrahigh pressure metamorphic amphiboles also show that jadeite area in western Myanmar is a high or ultrahigh pressure metamorphic belt. The constraints on the occurrence of pure jadeitite, especially the better quality jadeitite, could be summarized as follows. First, their host rocks are ultra-mafic rocks, the best is chromite-bearing dunite. Second, metamorphic rocks outer dunite are high-pressure metamorphic rocks as glaucophane schist or eclogite. Third, almost all jadeitites occur in the subduction or collision zone.