“阿尔金山岩群”的组成及其构造意义

Composing of the Altyn Tagh Formation-complex and its tectonic significa tion

以往文献所谓的“古元古代阿尔金山岩群”主要由3种岩石组合组成。第一种为英云闪长质—花岗闪长质片麻岩,占出露面积的70%左右;第二种为副变质岩系,占出露面积的25%左右,包括以夕线石榴片麻岩为代表的高温低压变质岩和以蓝晶石榴片麻岩为代表的高压变质岩;第三种为呈透镜体状分布在前二者中的榴辉岩、石榴斜长角闪岩和基性超基性岩石,占出露面积的5%以下。这种组成表明“古元古代阿尔金山岩群”不具有“岩群“的意义,而是碰撞杂岩带。“阿尔金山岩群”在岩石组合特征、含有榴辉岩、超基性岩石透镜体和榴辉岩的变质年代方面都与柴达木盆地北缘具有可比性,分析“阿尔金山岩群”是柴达木盆地北缘碰撞杂岩带的西延部分。

The so-called'Paleoproterozoic Altyn Tagh Group-complex'in the literature consists dominantly of three rock associations.The first one is tonalitic-granodioritic gneiss,which accounts for ～70%of the outcrop area;the second one is the parametamorphic series,which makes up～25%of the outcrop area,including high-temperature and low -pressure metamorphic rocks represented by sillimanite-garnet gneiss and high-pressure metamorphic rocks represented by kyanite-garnet gneiss;the third one is eclogite,gar-net-plagioclase amphibolite and basic-ultrabasic rocks,which occur as lenses in the above-mentioned two associations and take up>5%.Such a composition indicates that the'Paleoproterozoic Altyn Tagh Group-complex'has no implication of a'group-complex'but a collision complex zone.The'Altyn Tagh Group-complex'may be correlated with the rocks on the north margin of the Qaidam basin in respect to the characteristics of rock associations ,intercalation of eclogite and ultrabasic rock lenses and metamorphic chronology of eclogite.So the authors conclude that the'Altyn Tagh Group-complex'is the westward extension of the collision complex zone of the north margin of Qaidam basin.