西大别造山带红安高压榴辉岩的变质演化:岩相学与Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-O(Fe2O3)体系中相平衡关系  

Metamorphic evolution of high-pressure eclogite from Hong'an.Western Dabie Orogen,central China:Evidence from petrography and calculated phase equilibria in system Na_2O-CaO-K_2O-FeO-MgO-Al_2O_3-SiO_2-H_2O-O(Fe_2O_3)

作　　者：娄玉行[1] 魏春景[1] 初航[1] 王伟[1] 张景森[1,2] 

机构地区：[1]北京大学地球与空间科学学院,造山带与地壳演化教育部重点实验室,北京100871 [2]河北工程大学资源学院,邯郸056038

出　　处：《岩石学报》2009年第1期124-138,共15页Acta Petrologica Sinica

基　　金：国家自然科学基金资助项目(40525006).

摘　　要：西大别造山带红安高压榴辉岩主要矿物为石榴石、绿辉石、冻蓝闪石、石英和绿帘石,有时可见蓝闪石、多硅白云母和钠云母。石榴石具有生长环带且边缘成分变化大,可分为代表峰期的Ⅰ型边(X_(Mg)高、Grs低)和受退变质改造的Ⅱ型边(X_(Mg)低、Grs高)。石榴石内蓝闪石包体发育冻蓝闪石退变边,说明包体不能完全反映进变质条件。基质绿辉石比包体绿辉石Jd含量低,在一个晶体内成分有明显变化和沿解理缝发育冻蓝闪石,显示峰后绿辉石有成分变化和退变质改造。基质中冻蓝闪石晶体较大,核部见有蓝闪石残留,说明二者有成因联系。冻蓝闪石和绿辉石都发育后成合晶结构,石榴石有韭闪石的反应冠状体。在THERMOCALC程序计算的P-T视剖面图中,石榴石Ⅰ型边反映的峰期P.T条件为2.4～2.6GPa、570～585℃,和基质中多硅白云母Si含量等值线限定范围一致,对应硬柱石蓝闪石榴辉岩组合。石榴石Ⅱ型边P-T范围为1.9～2.4GPa、530～570℃,低于峰期条件。在可能的峰后降压过程中,岩石先后主要经历了硬柱石脱水生成绿帘石和蓝闪石、绿辉石退变为冻蓝闪石的反应阶段。绿辉石、冻蓝闪石发育的后成合晶说明晚期退变过程缺乏流体,石榴石的韭闪石冠状体也可能在该阶段产生,都受局部成分域控制。红安高压榴辉岩中各矿物与成分代表不同变质阶段,称其为冻蓝闪石榴辉岩只是对现有主要组成矿物的描述,不是基于共生关系的严格岩石学命名。The high-pressure eclogites in Western Dabie Orogen have a similar assemblage involving garnet,omphacite,barroisite, quartz and epidote with glaucophane,phengite and paragonite occasionally present.Garnet in the eclogite generally has growth zonations with compositional variation in rims which can be divided into two types.The type I rim reflecting peak metamorphic stage is relatively poor in Grs and rich in X_(Mg),and the typeⅡrim is rich in Grs and poor in X_(Mg),representing retrograde stage.Glaucophane enveloped in garnet was overgrown with a barroisite rim,indicating that inclusions in garnet could not always reflect the prograde process as garnet grows.Omphacite shows that jadeite decreases from the inclusions in garnet to the grains in matrix,and also obviously varies within a particular grain in matrix.The growth of many narrow barroisite rods are found along omphacite's cleavages.These changes in omphacites probably reflect retrograde stages.Barroisite in matrix commonly is large in grain size and occasionally has a few glaucophanes survived in the core,indicating that the barroisite may be derived from earlier glaucophane.Omphacite and barroisite are generally transformed into symplectites at their rims and fissures,and garnet commonly develops with pargasite corona.Using contours of composition isopleths for type I garnet rim on P-T pseudosections,the peak P-T range has been estimated as 570～585℃C at 2.4～2.6GPa in lawsonite-stable field,consistent with the condition estimated from the Si content of phengite in matrix.However,the typeⅡgarnet rim reflects a P-T condition of 530～570℃C at 1.9～2.4GPa,lower than that estimated from type I garnet rim.During the probable post-peak decompression stages,the most distinctive changes are firstly lawsonite decomposition to epidote,releasing considerable amount of water in the rock,and then barriosite overprinting on glaucophane and omphacite duo to some fluid infiltration. The subsequent appearance of symplectites around barroisite and omphacite ref

关 键 词：石榴石环带 榴辉岩 相平衡 P-T轨迹 西大别造山带 

分 类 号：P588.348[天文地球—岩石学]