中国东北地区中生代火山岩岩石学特征与盆地形成

中国东部广泛分布中生代火山岩，它是环太平洋火山作用的重要组成部分。东北地区是中生代火山岩分布最广泛的地区之一，其形成时代从晚三叠世到晚白垩世，其中晚侏罗世—早白垩世是火山作用最强烈的时期。中生代火山岩主要有高钾钙碱性火山岩系列和钾玄岩系列，并以高钾钙碱性火山岩为主。岩石类型主要有钾玄岩、安粗岩、粗面岩、橄榄粗安岩、英安岩和流纹岩。从东向西火山岩表现出了一个化学组成上的极性。岩石的Ｔｉ、Ｔａ含量低和富Ｋ、Ｒｂ等，以及构造判别图解表明该区火山岩属造山带火山岩。上述特征表明，东北地区中生代火山活动属于与伊佐奈崎（Ｉｚａｎａｇｉ）板块俯冲作用有关的挤压造山。与火山岩共存的早白垩世的Ａ型花岗岩表明，早白垩世东北地区处于拉伸构造环境。因此，松辽、海拉尔以及二连等盆地的形成与早白垩世造山带的崩塌有关。

PETROLOGY OF THE MESOZOIC VOLCANIC ROCKS AND THE BASIN FORMATION IN THE NORTHEAST CHINA

Mesozoic volcanic rocks are widely distributed in the East of China, which is an important part of the Circum Pacific volcanic zone. The Northeast China is one of the areas with the widest development of the Mesozoic volcanic rocks. The volcanism was generated from Later Triassic to Later Cretaceous in this area. There are mainly two rock series: high K calc alkaline and shoshonitic series, and high K calc alkaline series is predominant over shoshonitic one. The rocks include shoshonite, latite, trachyte, mugearite, dacite and rhyolite. There is a compositional polarity for the volcanic rocks from the east to west of this area. The characteristics of low contents of Ti and Ta and an enrichment in K, Rb etc. and the log σ -log τ diagram show the rocks′ orogenic nature. This suggests that the Mesozoic volcanic activities in this area are closely related to the subduction of the Izanagi plate. However, post orogenic A type granites in the Early Cretaceous indicate the tensional environment. Therefore, the formation of Songliao basin, Hailaer basin and Erlian basin are related to the orogenic belt collapse in the Early Cretaceous.