张家口地区张家口组火山岩元素地球化学特征及成因
首发时间:2010-01-06
摘要:张家口地区出露的早白垩世张家口组主要由流纹岩和粗面岩组成。本文首次报道了该地区张家口组火山岩主量元素和微量元素高精度分析测试结果。该套流纹岩和粗面岩具有富铁,高钾和全碱,富集REE、Rb、Th、U、Zr、Ga等不相容元素,Nb、Ta相对LREE亏损的特点;低分异样品不具有明显负Eu异常。张家口地区张家口组长英质火山岩的元素地球化学特征与还原型A型花岗岩相似,是华北克拉通拉斑质基性下地壳在高温、低氧逸度和低水逸度条件下的部分熔融产物,形成于碰撞后构造背景。
关键词: 火山岩 地球化学 岩石成因 张家口组 燕山 张家口地区
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ELEMENT GEOCHEMISTRY AND PETROGENESIS OF THE ZHANGJIAKOU FORMATION VOLCANIC ROCKS IN ZHANGJIAKOU AREA, NORTH CHINA
Abstract:The Early Creataceous Zhangjiakou Formation exposed in Zhangjiakou area, North China, is mainly composed of rhyolite and trachyte. The high-precise analysis of main and trace elements for these volcanic rocks is firstly reported in this study. The results show that, these felsic volcanic rocks are iron enriched and reduced, and have high contents of potassium, total alkali, and incompatible elements such as rare earth elements (REE), Rb, Th, U, Zr, and Ga etc.; but they also exhibit Nb, Ta depelation relative to the light rare earth elements (LREE), and there are no significant negative anomaly of Eu for those less-fractionated samples. The element geochemistry of Zhangjiakou volcanic rocks in Zhangjiakou area is similar to that of reduced A-type granitoid. It is deduced that these felsic volcanic rocks are originated by partial melting of the tholeiitic lower crust of North China craton under the high temperature, low H2O fugacity, and low O2 fugacity condition. The tectonic setting of these rocks is post-collisional environment.
Keywords: Volcanic rock Geochemistry Petrogenesis Zhangjiakou Formation Yanshan Zhangjiakou Area
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