北天山东段石英滩地区早二叠世火山岩岩石组合与岩浆生成动力学机制

The Early Permian Volcanic Rock Associations and the Dynamics Mechanism for the Magma Generation in the Shiyingtan Area,Eastern Tianshan

北天山东段早石炭世雅满苏岛弧带位于中天山北缘的阿其克库都克断裂和康古尔断裂之间。哈尔加乌组为二叠纪的火山岩地层。在区域上,哈尔加乌组火山岩与下伏地层上石炭统吐古吐布拉克组呈角度不整合接触。上覆地层为中—上二叠统阿其克布拉克组,二者呈微角度不整合接触。哈尔加乌组火山岩属于典型双峰式火山岩组合,流纹岩、英安岩占主体地位,而玄武安山岩、玄武岩较少。该组火山熔岩锆石U-Pb SHRIMP年龄为(280.6±1.8)Ma,鉴于区域内在该时段内属于后碰撞伸展环境。因此,认为该组火山岩形成于后碰撞伸展环境。岩石地球化学特征表明,该组玄武岩属碱性玄武岩系列,其他样品均属钙碱性火山岩系列。玄武安山岩具有轻稀土含量较高,重稀土含量较低、低Ti高Al的典型岛弧岩浆地化特征,这表明该组火山岩主体部分的形成是先期岛弧环境的物质在后碰撞伸展环境下再熔融所致。玄武安山岩及玄武岩的4个样品全部落在尖晶石稳定域,为软流圈物质上涌到达岩石圈的深度部分熔融的产物,玄武安山岩源自于被消减板片交代改造的岩石圈地幔;英安岩、流纹岩是不同深度的地壳物质重熔的产物。

The Early Carboniferous Yamansu arc belt of North Tianshan is situated between the Aqikekuduk fault and Kanggur fault, in the northern margin of Middle Tianshan. The Haer- jiawu Formation is Permian volcanic strata. Regionally, the Haerjiawu Formation shows angular unconformity with the underlying Upper Carboniferous Tugutubulake Formation. The Haerjiawu Formation is the typical bimodal volcanic rocks, which are basically consisted by rhyolites and da- cites, with minor basaltic andesites and basalts. The age of the Haerjiawu Formation has been obtained by zircon SHRIMP U-Pb dating, which is （280. 6 ± 1. 8） Ma, with a tectonic environment of post-collision extension. The geochemistry characteristics of the formation indicate that the basalts belong to the alkali basalt series, while the others are calc-alkaline volcanic rocks. The basaltic andesites have a high content of LREE and low content of HREE, together with a low value of Ti and high value of Al, indicating an origin of typical island arc. Besides, all the samples fall into the area of VA in all kinds of tectonic plotting. It＇s concluded that the main bodies of volcanic rocks were formed by the remelting of previous island arc substances in the post-collison- al environment. All the basaltic andesites and basalts fall into the stable domain of spinel, indicating that they were formed by the partial melting of the asthenophere substances at the depth of lithosphere. The basaltic andesites were originally from the Subcontinental Lithospheric Mantle substances modified and replaced by the reduction slab. Rhyolites and dacites are the products of the remelting of the crust.