辽北晚太古宙含镁钠闪石的片麻岩包体:古老蓝闪片岩残留  

The Upper Archean Enclavement of Magnesioriebeckites-Bearing Gneiss in Liaoning Province: Old Glaucophane-Schist Relict

作　　者：刘永祥[1] 孙德育[1] 刘鹏举 

机构地区：[1]长春地质学院地质系

出　　处：《岩石学报》1995年第1期83-92,共10页Acta Petrologica Sinica

基　　金：国家自然科学基金

摘　　要：辽宁省抚顺市东部华北板块中含镁钠闪石的角闪黑云斜长片麻岩形成于２．４８４Ｇａ之前，有可能是陆内碰撞或构造推覆作用产生的蓝闪片岩遭受了后期角闪岩相－麻粒岩相变质作用改造的残留体。镁钠闪石由于在其周围形成同轴向的普通角闪石保护壳，早晚变质作用在压力条件上的相似性、连续性以及后期地质作用的快速性而保留下来。The Eastern region of Fushun City, Liaoning province, consists of various granitic gneisses and metamorphic gneisses and amphibolites. The results of the study of the geological attitude,petrology and geochemistry of the granitic gneiss indicate that it is resulted from the ana-migmatization occurring at the later period of the regional amphibolite factes metamorphism, thus the enclavements of the metamorphic rocks are the relicts of the migmatization. The magnesioriebeckites were only formed in hornblendebiotite-plagioclase gneiss. The various characteristics of the rocks indicate that the original rocks of the gneiss correspond to tuffaceous sandstone; the magnesioriebeckites being columnar crystal (long/width ≤2) were included by hornblendes; its M= [Mg/ (Fe2+ +Fe3+ +AlⅥ )] is 0. 9325-1. 1708, A(Al/Si) is 0. 0415～0.0433. For these reasons, the magnesioriebeckites are thought to be the metamorphic minerals. The magnesioriebeckites are protected due to the protecting shell of the coaxial hornblende that formed around them.The magnesioriebeckites were formed under the conditions: P is0. 7～1. 0GPa, T is 460～510℃. But, the P and T regional metamorphic conditions of later amphibolite factes to granulite factes are 0. 9～1. 1GPa and 680℃～875℃, respectively. Therefore, the high pressure state of later metamorphism is the key factor that the magnesioriebeckites can be protected. The Rb-Sr isotopic age of the regional amphibolite factes is 2.484Ga,and the U-Pb isotopic age of the granitic geniss that included the magnesioriebeckites-bearing gneiss is 2. 469Ga. Therefore, the magnesioriebeckites-bearing hornblende-biotite-plagioclase gneiss was formed before 2. 484Ga being possibly a partial relict of the upper archean glaucophane-schist zone.

关 键 词：片麻岩 蓝闪片岩 含镁钠闪石 

分 类 号：P588.345[天文地球—岩石学]