滇西盈江地区上新世双峰式火山岩的地球化学特征及其构造意义
Geochemical evidence of the Pliocene bimodel volcanic rocks in Yingjiang area of western Yunnan Province and its tectonic significance
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摘要: 盈江地区上新世火山岩是腾冲火山岩的重要组成部分，但以往研究极少涉及。通过对该火山岩进行岩石地球化学和KAr年代学研究，同时与腾冲火山岩东侧的龙江河谷地区的上新世火山岩对比，认为盈江和腾冲地区上新世火山岩是大陆构造背景下造山带造山后伸展作用下形成的火山岩，具有高Al2O3（15.54%~17.44%）、高K2O（0.94%~3.50%）的岩石化学特点，为高钾钙碱性系列火山岩，形成于拉张环境，为双峰式火山岩（玄武岩DI=33~50，英安岩DI=62~76）。造山带裂谷火山岩常具弧火山岩的岩石化学特点，但其形成于造山带造山后的拉张环境，与板块俯冲作用没有直接关系。造山带裂谷火山岩发育在早期造山带，是造山带发展过程中一定阶段的岩浆作用的产物。Abstract: The Pliocene volcanic rocks in Yingjiang area constitute an important part of Tengchong volcanic rocks, but they are rarely involved in previous studies. In this paper, through the study of petrochemistry and K-Ar geochronology of the volcanic rocks and a comparison with the eastern Tengchong Pliocene volcanic rocks in the Longjiang River Valley area, the authors consider that the Pliocene volcanic rocks in Yingjiang and Tengchong areas seem to be a kind of rift volcanic rocks of the post-tectonic orogenic belt formed under the effect of extension that appeared in the continental tectonic background. With high Al2O3 (15.54%~17.44%) and high K2O (0.94%~3.50%) petrochemical characteristics, the rocks should belong to high potassium calc-alkaline volcanic rock series. They formed in an extensional environment and belong to bimodel volcanic rocks (basalt DI=33~50, dacite DI=62~76). The rocks have the geochemical characteristics of arc volcanic rocks, but they formed in a tensional environment in post-tectonic orogenic belt and had nothing to do with the plate subduction. The rift volcanic rocks of orogenic belts formed in the early orogenic belt and hence were magmatic products in the process of the development of the orogenic belt at a certain stage.
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