北淮阳晚侏罗世金刚台组火山岩岩石化学和地球化学特征及构造环境

PETROCHEMISTY, GEOCHEMISTRY AND TECTONIC SETTING OF LATE JURASSIC VOLCANIC ROCKS OF JINGANGTAI FORMATION IN BEIHUAIYANG AREA

晚侏罗世金刚台组火山岩分布在北淮阳中生代火山岩带的中部，主要岩石类型为火山碎屑岩类。据岩石化学成分，金刚台组火山岩可划分为安山质、英安质、粗面英安质和流纹质几种类型，并属于高钾钙碱性系列。其岩石化学和地球化学显示岩浆起源于下地壳，并经历了正常的分离结晶作用，有轻微的混染，岩浆开始结晶温度为９３６～１１２２℃，压力约为０２４ＧＰａ。据岩石地球化学方法判别，其构造环境具有类似于火山弧的特点，结合区域构造动力学背景分析。

The volcanic rocks of Jingangtai Formation are distributed over the middle part of the Beihuaiyang volcanic rock belt. The volcanic activity occured in the Late Jurrassic period and mainly formed pyroclastic rocks. The volcanic rocks belong to high kalium calc alkalic series and can be divided into andesite, dacite, trachydacite and rhyolite by petrochemical composition. According to the features of petrochemisty and geochemistry of the volcanic rocks, the authors calculated out that the volcanic magma originated in the lower crust and underwent fractional crystallization with light hybridization. Its crystallization temperature is about 936～1122℃, pressure is about 0 24GPa. The tectonic setting of the volcanic rocks was like volcanic arc on the basis of the methods of petrochemistry and geochemistry. It is related to the crustal thicking induced by late intracontinental subduction of Dabieshan orogenic belt.