东天山卡瓦布拉克地区片麻状花岗岩形成时代及地质意义

The Formation Age and Their Geological Significance of Gneissose Granites Neighbouring Kawabulake Area in East Tianshan Mountain

东天山卡瓦布拉克地区发育大量片麻状花岗岩,据野外特征分为含斑片麻状花岗岩和不含斑片麻状花岗岩,片麻理属后期韧性剪切叠加改造结果.本文获得含斑片麻状花岗岩LA-ICP-MS锆石U-Pb年龄为(942.1±7.2)Ma和(941.9±4.9)Ma;不含斑晶的片麻状花岗岩年龄为(424.2±3.4)Ma,这些年龄数据表明片麻状花岗岩分别形成于新元古代和中志留世.野外调查表明,片麻状花岗岩侵入于长城系星星峡群和卡瓦布拉克群中,被块状石炭纪花岗岩侵入.研究区西侧上覆泥盆纪地层未发生明显韧性变形.据此限定区内韧性剪切变形发生于晚志留世(约424 Ma)之后至泥盆纪之前.

The gneissose granites developed very much neighbouring kawabulake area in East Tianshan Mountain. According to the fielded characteristics, these granites can be divided into two types, namely bearing-porphyritic and non-bearing-porphyritic gneissose granites, their gneissosities formed due to reconstruction of ductile shearing.This article obtained two IA-ICP-MS zircon U-Pb ages of （942.1±7.2） Ma and （941.9±4.9） Ma from bearing-porphyritic gneissose granites and a LA-ICP-MS zircon U-Pb ages of （424.2±3.4） Ma from non-bearing-porphyritic gneissose granites, which showed that the two typical gneissose granites fromed in neo-proterozoic and Mid-Silurian. The fielded investigations showed that gneissose granites intruded into obviously XingXingXia Group and/or Kawabulake Group, and were intruded into by the carboniferous granites. At the same time, the upper devonian strata had hardly ductile deformations in the west of the study area. So that, the time of the ductile shearing deformation can be limited between mid-silurian （about 424 Ma） to before devonian period.