豫西五丈山花岗岩地球化学特征及形成时代研究

Geochemical characteristics and zircon U-Pb age of the Wuzhangshan granite in western Henan Province

豫西五丈山岩体位于华北板块南缘,西邻秦岭造山带,属华熊台隆,熊耳山断隆。通过野外实际调查,确定岩体具有4个主要的成岩期次:第1期为斑状黑云母二长花岗岩;第2期为中粗粒斑状含角闪石二长花岗岩;第3期为中细粒含角闪石二长花岗岩;第4期为中细粒斑状含角闪石二长花岗岩,这4期花岗岩具有不规则套环式的分布特征。岩石学研究表明:4期花岗岩岩性一致,仅在岩石颜色、结构和矿物含量、粒度存在差异。地球化学研究表明:岩石具有高碱、富铝;Eu略显正异常,Ce异常不明显,富集La、Sr、Zr、Sm等大离子亲石元素,亏损Nd、Nb、Ce等高场强元素,为过铝质高钙碱性/钾玄岩岩石系列,属于I型到S型过渡类型花岗岩,形成于碰撞造山带中。

The wuzhangshan rock mass in western henan is located at the southern margin of the north China plate and adjacent to the qinling orogenic belt in the west.According to the field investigation,the rock mass has four main diagenetic stages.Phase 1 is porphyritic quartz difeldite.Phase 2 is medium coarse porphyritic monzogranite.Phase 3 is meso-fine-grained contain porphyritic monzogranite.Phase 4 is meso-fine-grained porphyritic monzogranite,which is characterized by irregular annulus type distribution.The petrological study shows that the lithology of the 4 phase granites is the same,only the color,structure,mineral content and particle size of the rocks are different.The chronology shows that the age of the granitic rocks in the 2 nd to 4 th stage is( 160.46±0.96) Ma,( 158.5±0.51) Ma,( 158.4±1.2) Ma,respectively.Geochemical studies show that rocks are high in alkali and rich in aluminum.Eu shows a slight positive anomaly,while Ce anomaly is not obvious,with the enrichment of large ionic lithophile elements such as La,Sr,Zr and Sm,and the loss of high field strength elements such as Nd,Nb and Ce.This is a series of peraluminous high-calc-alkaline/potassium basalt,belonging to the transition type I to s-type granite,formed in the collision orogenic belt.