新疆博格达造山带西段石炭纪双峰式火山岩地球化学特征及成因

新疆博格达造山带博格达峰南侧柳树沟组出露大量双峰式火山岩组合。本文对博格达造山带西段石炭纪双峰式火山岩地球化学特征研究结果表明:①玄武岩具有贫K富Na、富Ti富Al和富Mg的特征,w(K₂O)/w(TiO₂)、w(K₂O)/w(P₂O₅)值较低且范围较小,总体上玄武岩有轻度的地壳物质混染作用;HREE相对富集,轻重稀土无明显的分馏,玄武质岩浆可能源于亏损地幔部分熔融。②流纹岩富K贫Na,低Ti、Mg;与其共生的玄武岩不同,流纹岩稀土元素含量高于玄武岩,轻重稀土分馏较为明显,为右倾斜率稀土配分模式,Eu的负异常较强(δEu=0.17~0.20),流纹岩可能为地壳物质重熔形成。③博格达造山带西段在晚石炭世时期处于大陆裂谷环境,其形成与古亚洲洋顺着克拉麦里碰撞带斜向对准格尔吐哈地块发生俯冲紧密相关。

Geochemical characteristics and genesis of the Carboniferous bimodal volcanic rocks in the west Bogda orogenic belt, Xinjiang Autonomous Region

A large number of bimodal volcanic assemblages occur in the Liushugou Formation on the southern side of the Bogda Peak of the Bogda Orogenic Belt.Basalt is depleted in K and rich in Na,Ti,Al and Mg with lower values of w(K₂O)/w(TiO₂)and w(K₂O)/w(P₂O₅)and limited range.Generally the basalt is slightly contaminated by crustal materials with relative HREE enrichment and without HREE and LREE fractionation.The basaltic magma may originate from partial melting of the depleted mantle.Rhyolite is rich in K,but poor in Na,low in Ti,Mg.Differing from the basalt the rhyolite is higher in REE with obvious HREE and LREEE fractionation and a right slope distribution model and stronger negative Eu anomaly(δEu=0.170.20).The rhyolite may be formed by the remelting of crustal material.Comprehensive analysis shows that the Bogda area was under continental rift environment in Late Carboniferous Epoch and the rock assemblage is closely related to the subduction of the Paleo-Asian Ocean beneath the Junggar-Taha block along the Clamary collision zone.