东乌旗罕乌拉韧性剪切带的构造属性及其年代约束  

Chronology Constraint and Tectonic Evolution of Hanwula Early Cretaceous Ductile Shear Belt in Dong Ujimqin,Inner Mongolia

作　　者：程银行[1] 滕学建[1] 李艳锋[1] 杨俊泉[1] 刘洋[1] 彭丽娜[1] 李影[1] 李敏[1] 

机构地区：[1]天津地质矿产研究所,天津300170

出　　处：《地球科学（中国地质大学学报）》2014年第4期375-386,共12页Earth Science-Journal of China University of Geosciences

基　　金：内蒙古1:5万沙麦(No.1212011120697);奥尤特区调项目(No.1212011220446)

摘　　要：为研究东乌旗北部罕乌拉韧性剪切带的运动学性质及其时代,通过野外宏观调查和定向标本显微分析来研究花岗质糜棱岩的宏观-微观变形构造特征,并对经韧性剪切作用的花岗质糜棱岩进行LA-MC-ICPMS锆石U-Pb定年.研究表明花岗质糜棱岩的长石、石英等主要造岩矿物具塑性变形和动态生长的特征,发育典型的"σ"、"δ"和"S-C"组构,对研究区34组糜棱面理和线理数据进行赤平投影,剪切面(C面)平均面理产状为338°∠24°,线理产状为303°∠17°,显示出左行滑脱型韧性剪切带的特征;锆石U-Pb测年结果表明韧性剪切作用之前就位的花岗质岩石成岩年龄为135.9±1.2Ma^130.0±0.5Ma,属早白垩世,且该剪切带被下白垩统大磨拐河组(相当于凡兰吟期-欧特里沃期)砂砾岩覆盖.综上所述,结合最新区域研究成果认为,早白垩世(135.9±1.2Ma^130.0±0.5Ma)东乌旗地区经历了大规模左行伸展构造活动,这一成果深化了对该区早白垩世地壳构造演化的认识.Through field investigation, microscopic analyses of oriented samples and zircon LA-MC-ICPMS U-Pb dating, gra nitic mylonites of the ducticle shear belt in Hanwula area have been studied, for their kinematic characteristics and ages. In these rocks, main rockforming minerals （feldspar and quartz） all show the typical characteristics of plastic deformation and dynamic crystallization, with typical fabrics such as ＂a＂, ＂8＂ and ＂S-C＂ structures. Averages of 34 coupled attitudes of mineral lineation and shearing foliation are 338°〈24° and 303°〈17°. All the above indicate the left lateral slip in this belt. The zircon LIPb dating data suggest that these granitic mylonites are formed in Early Cretaceous with detail ages of 135.9±1.2 Ma to 130.0±0.5 Ma and the ductile shear belt is covered by glutenite of the Lower Cretaceous Damoguaihe Group （Valanginian Hauterivian）. Thus, we consider that Dong Ujimqin area had experienced regional left-lateral extensional structure movement in Early Cretaceous. This study filled the blank of petrology and geochronology study of the ductile shear belt in Hanwula and enhanced the understanding of the Early Cretaceous crust tectonic evolution in Dong Ujimqin.

关 键 词：早白垩世 韧性剪切带 花岗质糜棱岩 构造 锆石U-PB年龄 地质年代学 

分 类 号：P542[天文地球—构造地质学]