福建省温屋盆地火山岩地球化学特征及构造环境分析

Analysis on Geochemical Characteristics and Tectonic Environment of Volcanic Rocks in Wenwu Basin,Fujian Province

本文以福建省温屋盆地火山岩为研究对象,开展锆石U-Pb年代学与岩石地球化学研究。结果表明,岩石富集Rb、Ba、K,中度富集Th、U、Zr、Hf,亏损Nb、Ta、Ti等元素,Sr异常不明显,Zr/Hf值为38.0~39.8,Nb/Ta值为10.4~11.0,Sr/Y为39.7~50.8,它表现出典型岛弧火山岩的微量元素特征。锆石U-Pb定年表明,温屋盆地晚白垩世寨下组流纹质晶屑凝灰岩和斜长流纹岩^(206)Pb/^(238)U加权平均年龄为101.8 Ma±1.6 Ma和99.9 Ma±1.1 Ma。结合区域研究成果,晚白垩世岩浆活动以普遍发育双峰式火山岩为特征,这表明俯冲板块开始向东回撤,从而导致当时的构造环境为弧后环境。

Taking the volcanic rocks in the Wenwu Basin of Fujian Province as the research object,this paper conducts zircon U-Pb geochronology and rock geochemistry research.The results show that the rocks are enriched in Rb,Ba,K,moderately enriched in Th,U,Zr,Hf,and depleted in Nb,Ta,Ti and other elements,and the Sr anomaly is not significant,Zr/Hf value is 38.0~39.8,Nb/Ta value is 10.4~11.0,and Sr/Y value is 39.7~50.8,it exhibits the trace element characteristics of typical island arc volcanic rocks.Zircon U-Pb dating indicates that the weighted average ages of ^(206)pb/^(238)U for the Late Cretaceous Zhaixia Formation rhyolite crystalline tuff and plagioclase rhyolite in the Wenwu Basin are 101.8 Ma±1.6 Ma and 99.9 Ma±1.1 Ma,respectively.Based on regional research results,the Late Cretaceous magmatic activity was characterized by the widespread development of bimodal volcanic rocks,indicating that the subducting plate began to retreat eastward,resulting in a backarc tectonic environment at that time.