缅甸硬玉岩中的流体包裹体  

Fluid inclusions in the Myanmar jadeitites

作　　者：祁敏[1] 沈昆 向华[1] 

机构地区：[1]大陆构造与动力学国家重点实验室,中国地质科学院地质研究所,北京100037 [2]山东省地质科学研究院,山东济南250013

出　　处：《岩石矿物学杂志》2015年第3期405-417,共13页Acta Petrologica et Mineralogica

基　　金：中国地质科学院地质研究所所长基金项目(J1325);大陆构造与动力学国家重点实验室自主基金(Z1301-a5)

摘　　要：缅甸硬玉岩是世界上最大和最重要的玉石矿床之一,位于印度板块和欧亚板块之间的新特提斯洋缝合带中。研究表明,缅甸硬玉岩是新特提斯洋壳俯冲过程中橄榄岩经高压变质、交代作用形成的。对不同变质程度缅甸硬玉岩样品中的流体包裹体的研究表明,缅甸硬玉岩中含有4种类型的流体包裹体:1不含或含少量甲烷的低盐度水溶液包裹体(Ⅰ型),呈孤立状或小群(簇状)产于硬玉晶体核部,或沿着硬玉晶体的生长环带分布,具有原生生长结构;2含石盐子晶的H2O+Na Cl±CH4三相包裹体(Ⅱ型);3纯甲烷(CH4)包裹体(Ⅲ型),可以细分为高密度(Ⅲa)和低密度(Ⅲb)两种;4气相或空包裹体(Ⅳ型)。研究表明,缅甸硬玉岩及其相关岩石在形成和演化过程中发生了多期次流体交代事件。硬玉形成过程中,交代橄榄岩的流体相可能来自海水。首次在缅甸硬玉岩中识别出高盐度的含水包裹体和高密度的含CH4包裹体。高盐度的含水包裹体可能与硬玉岩重结晶过程相关,而高密度的CH4流体可能为俯冲板片的上地幔楔中超基性岩蛇纹石化过程的副产物。计算的流体包裹体等容线表明,硬玉岩演化过程中这些流体包裹体发生了不同程度的再平衡。Lying in a distinctive tectonic locality within the collisional belt between the India and Eurasian plates, the Myanmar jadeitites deposit is one of the largest and most important jadeite deposits in the world. It has been shown that the Myanmar jadeitites formed during the subduction of the Neo-Tethys oceanic crust when peridotites experienced highpressure metamorphism and metasomatism. In this paper, a fluid inclusion study of the Myanmar jadeitite samples with variable deformation degrees was carried out and, as a result, four types of fluid inclusions were identified： 1 low-salinity aqueous inclusions with or without minor CH4（ typeⅠ）, the primary typeⅠ inclusions occur either as isolated ones or in clusters in the core or along the growth zones of jadeite crystals with primary growth textures; 2 three-phase H2 O ± CH4 inclusions with halite daughter crystals（ typeⅡ）; 3 pure CH4 inclusions which can be subdivided into high-density ones（ type Ⅲa） and low-density ones（ Ⅲb）; 4 gaseous or empty inclusions（ type Ⅳ）. This investigation revealed that several fluid events occurred during the formation and evolution of Myanmar jadeitites and related rocks. A fluid phase that originated probably from sea water should have been present during the formation of jadeitite in the high-pressure metamorphic-metasomatic process of peridotite; the high-salinity aqueous inclusions and high-density CH4 inclusions were recognized for the first time in the Myanmar jadeitites, the high-salinity aqueous fluid was probably related to the recrystallization process of the jadeidite, and the preserved high-density CH4 in the jadeitite was probably generated as a by-product of serpentinization of ultramafic rocks in the mantle wedge above the subducting slab,coupled with the complete consumption of water during hydration of serpentine. The calculated fluid inclusion isochores suggest that various degrees of reequlibration of these fluid inclusion occurred during the evoluition of the jadeitites.

关 键 词：硬玉岩 流体-岩石相互作用 流体包裹体 缅甸 

分 类 号：P578.954[天文地球—矿物学] P588[天文地球—地质学]