CCSD(0～5158m)HP-UHP变质岩中石英脉流体包裹体研究

Fluid inclusions in quartz veins in HP-UHP metamorphic rocks from Chinese Continental Scientific Drilling Project.

本文对中国大陆科学钻探(CCSD)0～5158m HP-UHP变质岩石英脉中流体包裹体进行了研究,通过冷热台与拉曼光谱测定发现其中含有4种流体包裹体:(Ⅰ型)盐水溶液包裹体,并进一步分为高盐度盐水溶液包裹体(Ⅰa型)、中高盐度盐水溶液包裹体(Ⅰb型)、中等盐度盐水溶液包裹体(Ⅰc型)和低盐度盐水溶液包裹体;(Ⅱ型)N_2-CH_4纯气相包裹体;(Ⅲ型)含方解石子矿物的流体包裹体;(Ⅳ型)CO_2-NaCl-H_2O包裹体及纯CO_2包裹体。其中Ⅲ和Ⅳ型流体包裹体是CCSD石英脉中首次发现。Ⅰa、Ⅰb型流体包裹体主要以原生的形式赋存在榴辉岩及片麻岩的石英脉或石英颗粒当中,它们主要是被捕获于折返早期高压变质重结晶阶段;Ⅰc和Ⅰd两类包裹体则主要以次生的形式赋存于榴辉岩及片麻岩的石英脉或石英颗粒当中,说明它们是在超高压变质岩折返过程的较晚阶段捕获的。以原生形式出现的含方解石子晶及CO_2包裹体,指示部分石英脉及其围岩可能经历过超高压变质作用甚至麻粒岩相阶段。CCSD中的石英脉可能主要形成于折返早期高压变质重结晶阶段,其中的HP-UHP岩石在板块折返及其以后退变质过程中释放出的变质流体活动范围有限,没有经历大规模的流动或迁移。

By microthermometric measurement and Raman analysis, four types of fluid inclusions are found in quartz veins in CCSD HP-UHP metamorphic rocks of 0 similar to 5158m. They are: (I) brine (NaCl-H2O) inclusions (type I), which can be subdivided into high salinity (type Ia), medium-high salinity (type Ib), medium salinity (type Ic) and low salinity (type Id) brine inclusions; (2) N-2-CH4 pure gaseous inclusions (type II); (3) Calcite daughter mineral-bearing inclusions (type III); (4) CO2-NaCl-H2O and pure CO2 inclusions(type IV). The type III and IV ones are first discovered in the CCSD. Type Ia, Ib, II, III and IV inclusions mainly occur as primary ones in quartz veins in eclogites and gneisses, indicating that they were probably captured in decompression-recrystallization stage of the HP-UHP metamorphic rocks. Type le and Id inclusions occur mostly as secondary ones in matrix quartz in eclogites and gneisses, implying that they were captured in the later retrograde stage. The H2O-carbonate inclusions and CO2 inclusions occurring as primary ones, suggest that a part of the quartz veins and their host rocks might have undergone UHP metamorphism. The quartz veins in the CCSD were probably formed in the stage of decompression-recrystallization, while the metamorphic fluid expelled from exhumation of the HP-UHP rocks in CCSD chiefly flowed at grain scale.