桐柏北部宽坪群变泥质岩的变质作用研究  

A study of metamorphism of metapelites from the Kuanping Group,Northern Tongbai

作　　者：胡娟[1] 刘晓春[1] 曲玮[1] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081

出　　处：《地学前缘》2010年第1期104-113,共10页Earth Science Frontiers

基　　金：国家重点基础研究发展计划"973"项目(2009CB825006);国家自然科学基金项目(40672047);国土资源大调查项目(1212010711812)

摘　　要：桐柏北部宽坪群发育一套由斜长角闪岩、变泥质岩、大理岩以及石英岩夹层组成的中级变质岩石。本文选取4个含石榴变泥质岩样品进行了详细的岩石学研究,其中回龙寺组的一个样品含有特征的十字石+蓝晶石组合,而左老庄组的一个样品则含有夕线石。回龙寺组样品中的石榴石均具有明显的进变质成分环带,而左老庄组样品中的石榴石均遭受到晚期低温扩散的影响,所以在计算其形成条件时选取了生长于峰期变质阶段的特定部位。运用传统的石榴石-黑云母-白云母-斜长石-石英地质温压计估算回龙寺组的变质p-T区间为590～610℃、0.95～1.14GPa,左老庄组为630～650℃、0.65～0.89GPa,分别相当于低角闪岩相和高角闪岩相。这一结果与变质反应曲线所限定的温压范围基本一致,并且后者中还存在由蓝晶石区域向相对高温低压的夕线石区域转变的过程。低-高角闪岩相的宽坪群与低角闪岩相的二郎坪群和麻粒岩相的秦岭群紧密伴生,且变质时代近于一致(440～400Ma),说明华北南缘在志留纪—早泥盆世发生了岛弧、微陆块与华北板块大陆边缘的碰撞造山作用。A suite of medium-pressure metamorphic rocks composed of amphibolites,metapelites,marbles and intercalated quartzites occur in the Kuanping Group,Northern Tongbai. In this paper we report petrological results on four garnet-bearing metapelites from this group,including a staurolite-kyanite-bearing sample collected from the Huilongsi Formation,and a sillimanite-bearing sample taken from the Zuolaozhuang Formation. Garnet from samples in the Huilongsi Formation exhibits a pronounced compositional zoning that resulted from progressive metamorphism,whereas that from samples in the Zuolaozhuang Formation is weakly affected by late low-temperature diffusion. In such a case,the garnet domains that grow at peak metamorphic stage were chosen to calculate its formation temperatures. Using conventional garnet-biotite-muscovite-plagioclase-quartz geothermobarometry,p-T conditions were estimated to be 590-610 ℃ and 0.95-1.14 GPa for the Huilongsi Formation,and 630-650 ℃ and 0.65-0.89 GPa for the Zuolaozhuang Formation,in agreement with lower and upper amphibolite facies,respectively. These p-T estimates are in accordance with p-T regions limited by metamorphic reaction curves. A transformation from kyanite to sillimanite is also indicated in the Zuolaozhuang Formation. The close association of lower-upper amphibolite facies Kuanping Group,lower amphibolite facies Erlangping Group and granulite facies Qinling Group with similar metamorphic ages （440-400 Ma） suggests that collisional orogenesis occurred between arc,microcontinent and southern margin of the North China craton during the Silurian to the Early Devonian.

关 键 词：变泥质岩 中级变质作用 宽坪群 桐柏北部 

分 类 号：P588.3[天文地球—岩石学]