准噶尔盆地腹部早二叠纪—晚石炭纪火山岩的构造背景分析

Tectonic settings of the Late Carboniferous-Early Permian volcanic rocks,central Junggar Basin

从中生代到新生代,准噶尔盆地腹部地区连续沉积,缺少腹部地区的样品,因此准噶尔地区晚古生代构造演化的研究常集中于盆地周围的褶皱造山带。本文通过对早二叠纪—晚石炭纪钻井岩心样品的地球化学、岩石学特征进行研究。结果表明:1)许多钻井的不同层位中,都发育着表明水上喷发环境的褐色凝灰岩;2)准噶尔盆地腹部早二叠纪—晚石炭纪火山岩主要是碱性玄武岩、安山岩及少量的流纹岩,样品的大部分以高碱为特征,反映了喷发于陆上增厚地壳的构造背景;3)岩心观察、薄片鉴定及主量和微量元素的分析结果表明,晚古生代准噶尔盆地腹部属于大陆构造背景。石炭系火山岩的底部也许存在许多的古老陆块基底。

Studies on the tectonic settings of the Late Paleozoic Junggar region are traditionally focused on the folded mountain belts around Junggar Basin, due to lack of samples gained in the central region where it is covered with continuous sediments from Mesozoic to Cenozoic. This paper concentrates on petro-geochemistry and lithology of the holebore specimens,which occur in Upper Carboniferous-Lower Permian in central Junggar Basin. Then, it is proposed that ： 1 ） The brown stuff specimens which suggest an eruption above continent are found in various holebore from many layers; 2）Upper Carboniferous-Lower Permian volcanic rocks obtained from central Junggar Basin are mainly alkali basahs and andesites, as well as a little dacites; the major parts of the samples are characterized with high alkali, which are probably erupted from thickened crust with suggesting continental tectonic settings; and 3）in Late Paleozoic the central Junggar Basin was probably continental tectonic settings as suggested by the observation of cores, microscopic sections and combined the analysis of the major and trace elemental data. Further conclusion arrives at that there may be more ancient continental basement below the Carboniferous volcanic rocks.