额尔古纳地块基底地质构造

THE BASEMENT TECTONICS OF ERGUN MASSIF

额尔古纳地块是额尔古纳-马门-加格达奇拼合地块中的典型代表.研究表明,其基底由前中元古代绿岩及与之伴生的花岗质杂岩组成,它们具有地壳早期演化的地质构造特征.绿岩带为典型的变质基性-酸性火山岩及部分变质沉积岩系构成的火山-沉积建造,火山岩以拉斑玄武岩为主,向上过渡为钙碱性火山岩系列,表现为双峰态型特点.花岗岩类为TTG岩系及石英二长岩-花岗岩组合.花岗岩-绿岩地体内各岩石类型的岩石地球化学特征与国外太古宙及我国华北陆台花岗岩-绿岩带内同类岩石极为相似.双峰态型火山岩及绿岩建造组合,以及类似于TH2、FII型的变质基性火山岩和长英质火山岩特征,结合高铝型英云闪长岩-奥长花岗岩组合,指示了研究区绿岩带的形成环境类似于大陆边缘弧后裂谷型火山-沉积盆地.

Ergun massif is a typical representative of the Ergun Mamyn Jiagedaqi matching massifs.Its basement is composed of Mesoproterozoic greenstone and associated complex,with the tectonic characteristics of earlier crustal evolution.The greenstone belt is a typical volcanic sedimentary formation formed by metabasic acid volcanic rocks and partly metasedimentary rocks.The bimodal volcanic rocks are mainly tholeiite,which transforms upward into calc alkali volcanic rock series.The granitoids are of TTG rock series and adamellite granite assemblage.The lithogeochemical features of all types of rocks in the granite greenstone massif are very much similar to those of the same types in the Archean granite greenstone belts abroad and in North China platform.All the characteristics of the greenstone basin in the studied area suggest a likely forming environment of back arc rift type of volcanic sedimentary basin in continental margin.