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首页> 外文期刊>Contributions to Mineralogy and Petrology >Fluid history of UHP metamorphism in Dabie Shan, China: a fluid inclusion and oxygen isotope study on the coesite-bearing eclogite from Bixiling
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Fluid history of UHP metamorphism in Dabie Shan, China: a fluid inclusion and oxygen isotope study on the coesite-bearing eclogite from Bixiling

机译：中国大别山超高压变质的流体历史：碧西岭含铅云母榴辉岩的流体包裹体和氧同位素研究

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摘要

The coesite-bearing eclogites and associated ultramafic rocks of Bixiling form the largest metamorphic complex in the Dabie-Sulu ultrahigh-pressure (UHP) metamorphic belt. They mainly consist of "fresh" eclogite, kyanite-rich eclogite, retrograded eclogite and garnet peridotite. Fluid inclusion and oxygen isotope studies have been carried out on the different types of eclogite and peridotite in order to identify the role of fluids during the metamorphic evolution culminating in UHP metamorphism. Five types of fluid inclusions were distinguished based on textural criteria and fluid compositions: (1) primary Ca-rich brines in quartz blebs in kyanite; (2) primary NaCl-dominated high-salinity inclusions in omphacite and kyanite; (3) primary NaCl-dominated medium- to high-salinity inclusions in matrix quartz; (4) carbonic inclusions in omphacite and matrix quartz; (5) secondary low-salinity aqueous (or pure water) inclusions in matrix quartz. The Ca-rich fluid inclusions in quartz blebs in kyanite represent the earliest recognizable fluids (prograde metamorphism) as they largely escaped late re-equilibration. Fluid inclusions in omphacite and kyanite may have been trapped during peak metamorphic conditions, whereas low-salinity aqueous inclusions in matrix quartz were trapped during the latest stage of uplift. NV-laser oxygen isotope measurements show that garnet and clinopyroxene from the "fresh" eclogite, kyanite-rich eclogite and garnet peridotite have narrow #delta#~(18)O values ranging from 3.0 to 3.9 per thousand. In contrast, garnet and omphacite in retrograded eclogite have #delta#~(18)O values of -1.8 to -1.2 and of -1.1 to -0.6 per thousand, respectively. The difference in oxygen isotope composition is interpreted to result from partial oxygen isotope exchange between the UHP complex and retrograde fluids during late exhumation. Fluids derived from the surrounding gneiss were probably responsible for the low-salinity solutions found in secondary fluid inclusions and the lowering of the #delta#~(18)O values of the retrograded eclogite.
机译：碧星岭含岩的榴辉岩和相关的超镁铁质岩石形成了大别苏鲁超高压（UHP）变质带中最大的变质复合体。它们主要由“新鲜”榴辉岩，富含蓝晶石的榴辉岩，回生榴辉岩和石榴石橄榄岩组成。已经对不同类型的榴辉岩和橄榄岩进行了流体包裹体和氧同位素研究，以便确定流体在超高压变质作用最终达到的变质演化过程中的作用。根据质地标准和流体成分，可分为五种类型的流体包裹体：（1）蓝晶石石英泡中富含钙的初级盐水; （2）辉绿岩和蓝晶石中以NaCl为主的高盐夹杂物; （3）基体石英中以NaCl为主的中至高盐度夹杂物; （4）绿辉石和基质石英中的碳夹杂物; （5）基质石英中的次低盐度水（或纯水）夹杂物。蓝晶石石英泡中富含Ca的流体包裹体是最早可识别的流体（渐进变质），因为它们很大程度上逃避了后期的重新平衡。辉石和蓝晶石中的流体包裹体可能在峰变质条件下被捕集，而基质石英中低盐度的含水包裹体在隆升的最新阶段被捕集。 NV激光氧同位素测量表明，“新鲜”榴辉岩，富蓝晶石榴辉岩和石榴石橄榄橄榄岩的石榴石和斜辉石具有狭窄的δδ〜（18）O值，范围为千分之3.0至3.9。相反，凝结榴辉岩中的石榴石和绿辉石的＃delta＃〜（18）O值分别为-1.8至-1.2和-1.1至-0.6 /千。氧同位素组成的差异被解释为是由于末次发掘期间UHP配合物与逆行流体之间发生了部分氧同位素交换而导致的。来自周围片麻岩的流体可能是造成次生流体包裹体中低盐度溶液的原因，并且降低了返凝榴辉岩的δ-（18）O值。

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