青海南部治多县莫云一带上三叠统那底岗日组火山岩特征及其构造环境

Geochemical signatures and tectonic setting of the volcanic rocks from the Upper Triassic Nadigangri Formation in the Mugxung region,Zhidoi,southern Qinghai

摘要: 青海南部治多县莫云一带的那底岗日组火山岩主要为碱性玄武岩和玄武安山岩。低Ti、高A l,轻稀土元素富集,轻重稀土呈现较强的分馏并具有轻微的负铕异常;富集大离子亲石元素,亏损高场强元素;(⁸⁷Sr/⁸⁶Sr) i值为0.70774~0.70801,εNd (t)值为-3.3~-4.5,反映了岛弧构造环境。那底岗日组火山岩为拉竹龙-金沙江洋(或甘孜-理塘洋)洋壳向南消减形成的岩浆弧。

Abstract: The volcanic rocks from the Upper Triassic Nadigangri Formation in the Mugxung region,Zhidoi,southern Qinghai consist of intermediate to basic rocks assembled by alkaline basalt and basaltic andesite.Petrochemically,the volcanic rocks are characterized by low Ti,high Al,enrichment of LREE,high fractionation of LREE and HREE,slightly negative Eu anomaly,enrichment of macro-ion lithophile elements,and depletion of high field strength elements.The(⁸⁷Sr/⁸⁶Sr) i values between 0.70774 and 0.70801 and the εNd(t) values between-3.3 and-4.5 suggest an island-arc environment.Tectonically,the volcanic rocks from the Late Triassic Nadigangri Formation constitute a magmatic arc originated during the southward subduction of the Lazhuglung-Jinshajiang(or Garze-Litang) oceanic crust.