二连盆地北缘晚中生代火山岩Ar-Ar年代、地球化学及构造背景

Ar-Ar age, geochemistry and petrogenesis of Late Mesozoic volcanic rocks in the northern marginal region of Erlian basin, Inner-Mongolia.

中国东北二连盆地周缘分布有三组时代不同的晚中生代火山岩,其中早、中期为两套地球化学性质不同的流纹岩,晚期为玄武质火山岩。本文通过测定火山岩基质Ar-Ar同位素年龄,表明早期查干诺尔组流纹岩形成于142Ma,晚期不拉根哈达组基性火山岩形成于129Ma,可见二连盆地北缘晚中生代火山岩时代均为早白垩世。通过对主、微量元素地球化学特征和Sr-Nd-Pb同位素组成研究,以及与邻区同期满克头鄂博组英安岩和流纹岩、玛尼吐组英安岩、霍林河地区查干诺尔组英安岩、流纹岩对比,认为早期查干诺尔组流纹岩来源于新成下地壳,岩浆演化过程经历了强烈分异作用;中期流纹岩源区为中上地壳或下地壳岩浆经历了上地壳强烈同化混染作用;晚期不拉根哈达组基性火山岩则源于受俯冲洋壳流体交代的富集岩石圈地幔。结合早白垩世区域岩石圈减薄背景,本文认为研究区早白垩世火山岩形成于陆内伸展构造环境。

The studied area is located in the northern margin of Erlian basin, NE of China. The Late Mesozoic volcanic rocks in this area are mainly composed of rhyolite, basalt, trachy-basalt and basaltic andesite. (40)Ar-(39)Ar dating of Chagannuoer Formation rhyolite and Bulagenhada Formation basaltic andesite give a plateau age of 141.57 +/- 1.59Ma and 129.05 +/- 1.86Ma, respectively, indicating that these volcanic rocks were formed in Early Cretaceous. The geochemical characteristics of the volcanic rocks show that the earlier Chagannuoer Formation rhyolites origined from lower crustal magma, which experienced high degrees fractional crystallization or assimilation and fractional crystallization. The magma origination of Daotenuoer Formation rhyolites were middle-upper crust or lower crustal magma suffered strong asiimilation of upper crust. Bulagenhada Formation basic volcanics origined from the metasomatized lithospheric mantle modified by previous subducted ocean slabs, and Combining previous studies, we suggest that the tectonic environment of Early Cretaceous was intense lithopheric extension and thinning, related to Northern China lithopheric thinning geological event in Late Mesozoic.