摘要
贺兰山孔兹岩系作为华北克拉通西部孔兹岩带的重要组成部分,其成因问题一直存在争议。近来,在对贺兰山富铝岩系研究过程中,发现了具有"蓝晶石+条纹长石+石榴石"特征组合的高压泥质麻粒岩。通过岩相观测与相平衡定量模拟,确定其曾经历四个阶段的变质演化过程,即早期进变质阶段(M1)、变质峰期阶段(M2)、峰期后降压阶段(M3)和晚期退变阶段(M4)。早期进变质阶段,以石榴石中包裹黑云母和白云母为特征。变质峰期阶段,以出现"蓝晶石+条纹长石+石榴石"组合为特征,变质温、压条件为850～870℃、1.4～1.5GPa。峰期后降压阶段以峰期石榴石和蓝晶石转变为堇青石和夕线石为特征,温压条件大致为840～860℃、0.6～0.8GPa。晚期退变阶段以出现新生黑云母为标志,温、压条件为780～810℃、0.45～0.55GPa。PT轨迹具有顺时针演化样式,峰期后表现为先发生近等温降压(ITD)、后发生近等压冷却(IBC)的退变过程,反映陆-陆碰撞发生高压麻粒岩相变质作用,后又快速折返到正常地壳深度的变质动力学过程,进而从岩石学角度证明华北克拉通西部孔兹岩带是由北部的阴山陆块与南部的鄂尔多斯陆块发生碰撞所致。
The khondalite series in Helanshan region is a main part of the khondalite belt in the western block of the North China Craton,the metamorphic evolution of which is still ambiguous.Recently,high pressure pelitic granulite with typical mineral assemblage of garnet+kyanite+perthite were discovered in the Helanshan khondalite series.Petrographic observation and phase modeling indicate that the pelitic granulite experienced four stages of metamorphism.An early prograde metamorphic stage(M1)was recognized from inclusions of biotite and muscovite in garnet.The peak metamorphic stage(M2)is characterized by the presence of garnet+kyanite+perthite,with a probable PT condition of 1.4~1.5GPa at ca.850~870℃.The post-peak decompression(M3)is indicative of an isothermally overprinting of sillimanite and cordierite from kyanite and garnet with pressures of 0.6~0.8 GPa at ca.840~860℃.Development of most biotite suggested a late-stage retrogression(M4)under PT conditions of 780~810℃,0.45~0.55GPa.This clock-wise P-T path,characteristic of a post-peak isothermal decompression(ITD)and followed by cooling,is consistent with a thinning process of thickened continental crust which may be a result of the collision between the Yinshan block and Ordos block.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2010年第7期2113-2121,共9页
Acta Petrologica Sinica
基金
国家自然科学基金(40872123)
国土资源部百名优秀青年科技人才奖励计划
科技部基本科研业务费和地质大调查项目(1212010611702)联合资助
