浙东地区晚中生代火山岩地球化学特征、岩石成因及构造环境

中国东部中生代发生的大规模岩浆活动是地学界长期以来关注的课题之一。本文通过对浙东地区晚中生代火山岩锆石U-Pb年代学、主量、稀土及微量元素地球化学的研究,讨论其岩石成因及形成的构造环境。研究表明,大爽组底部火山岩年龄为155.2±1.4 Ma(MSWD=0.83),显示浙东地区晚中生代火山岩的形成时代并不限于白垩纪,火山喷发至少于晚侏罗世就已经开始;岩石总体属高钾钙碱性系列,少量属钾玄岩系列;基性岩石、中性岩石与中酸性(酸性)岩之间不具有同源演化关系,基性岩石来源于富集地幔,并受到了不同程度的地壳混染,中性岩石可能来源于先存于下地壳深部的新元古代岛弧岩石,中酸性(酸性)岩石来源于地壳,中酸性岩浆与酸性岩浆之间存在演化关系;岩石总体形成于地壳幕式减薄环境,而其弧岩浆岩特征主要反映源岩属性。

Geochemical characteristics,petrogenesis and tectonic environment of the Late Mesozoic volcanic rocks in eastern Zhejiang area

Large scale magmatism of Mesozoic in eastern China is one of the subjects what are abiding preoccupations in geo-academic circles. In this paper, we discuss the petrogenesis and tectonic environment of the Late Mesozoic volcano rocks in eastern Zhejiang area, through the study of zircon U-Pb chronology, major element and REE, trace elements geochemistry. Research shows that, the formation age of the Late Mesozoic volcano rocks in eastern Zhejiang area is not limited to the Cretaceous, it had at least begun from the Late Jurassic because the age of the volcano rocks from the bottom of Dashuang Formation is 155.2±1.4 Ma （MSWD = 0.83）; the volcanic rocks belongs to high-K calc-alkaline series, and a few belong to shoshonite series; the basic rocks, the intermediate rocks and the intermediate-acid rocks （the acid rocks） don’t have the homologous evolution relationship, the basic rocks was derived from the enriched mantle and had suffered different degrees of crustal contamination, the intermediate rocks was derived from Neoproterozoic island arc rock existed in lower crust, the intermediate-acid rocks （the acid rocks） was derived from the crust. There is the evolutionary relationship between intermediate-acid magma and acid magma. The rocks overall formed in crust episodic thinning environment, and the arc magmatite features mainly reflects the source rock properties.