摘要
胶北地块发育一套早元古代变质杂岩,主要由浅变质到中高级变质的滨海相至浅海相的沉积岩系列组成,属于胶-辽-吉构造活动带的一部分。其中具有顺时针变质作用PT轨迹的高压基性麻粒岩和高压泥质麻粒岩指示了造成该带闭合的碰撞构造过程。本文研究与高压基性麻粒岩密切共生的钙硅酸盐岩。首先根据矿物反应关系研究,确定钙硅酸盐岩是由含石榴石的基性麻粒岩经钙质交代形成的。进一步采用残留单斜辉石-石榴石组合、退变矿物组合,并根据SACMF体系矿物组合演化的PT视剖面图,计算得出钙硅酸盐岩经历了早期温压条件为780～850℃、1.0～1.1GPa的变质作用和晚期温压条件为400～650℃、0.6～0.75GPa的退变质作用和交代作用,从而得出顺时针的P-T轨迹。这一结果表明,钙硅酸盐岩形成于陆-陆碰撞过程的晚期阶段,是高压基性麻粒岩在折返过程中经历退变质和Ca质交代联合作用的结果。钙硅酸盐岩的形成机制及其与石榴石基性麻粒岩原岩的成因联系的确立,丰富了对于碰撞变质地块抬升过程及其岩石学效应的认识。
Jiaobei terrane contains low to high grade Paleoproterozoic metamorphosed sedimentary sequence deposited under littoral to neritic environments,belonging to part of the Jiao-Liao-Ji belt of the Eastern Block in the North China Craton.The clock wise P-T paths concluded from HP mafic and pelitic granulites indicate the closing and collisional process of the belt.This study focuses on the formation of calc-silicate that is closely associated with HP mafic granulite.On the basis of mineral assemblage evolution of the PT peudosention in SACFM system,critical metamorphic reactions,combined with calculation of Grt-Cpx thermometer,the precursor granulite is estimated having experienced at least 780~850℃ and 1.0~1.1GPa metamorphic conditions,and retrograde to 400~650℃ and 0.6~0.75GPa.Accordingly,a clock wise P-T path is concluded.Results show that the calc-silicate develops on the late stage of continent-continent collision during the exhumation process of the HP granulite,combined with Ca metasomatism at the same time.Establishment of the genetic relationship of calc-silicate and the mafic garnet granulite present the importance of petrological paragenetic association during the exhumation of collisional metamorphic terrane.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2011年第4期961-968,共8页
Acta Petrologica Sinica
基金
国家自然科学基金重点项目(40730315)
国家自然科学基金项目(40872122)
科技部973项目(2009CB825007)联合资助
