地质学报2018，Vol.92Issue(4)：665-686,22.
内蒙古西乌旗罕乌拉地区双峰式侵入体年代学、地球化学特征及其对古亚洲洋闭合时限的制约
Geochronological and Geochemical Features of Bimodal Intrusive Rocks in the Hanwula Area of Xiwu Banner, Inner Mongolia: Constraints on Closure of the Paleo-Asian Ocean
摘要
Abstract
There remains controversy about petrogenesis and tectonic environments of the Permian magmatic rocks in the southern margin of the Central Asia Orogenic Belt (CAOB).This study carried out analyses of petrology,zircon U-Pb isotopic geochronology and geochemistry of the Yiheshaorong complex massif in the Hanwula area of Xiwu Banner,Inner Mongolia.The results show that the Yiheshaorong complex massif comprises gabbro,pyroxene diorite and alkali-feldspar granite.Their geochemical features show SiOe content of 44.01％～77.60％,which exhibits a gap between 55.91％ and 75.97％,displaying a good bimodal geochemical distribution.LA-ICP-MS U-Pb dating yielded the ages of 280.1-±-1.3 Ma and 279.8 ± 1.2 Ma for gabbro and alkali-feldspar granite,respectively,suggesting they are early Permian intrusive rocks.The gabbros are a suite of low-K tholeiitic-calc alkaline rocks,with SiO2 =44.01％～52.63％,Na2O +K2O=2.78％～5.33％ (Na2O＞K2O),Al2O3=15.11％～24.43％,TiO2 =0.55％～3.59％ and Mg# =23～ 60.Low total REEs and flat REE distribution pattern,positive Eu anomalies,enrichment of LILE (such as Ba,K,Sr,and Eu),and depletion of HFSE (like Nb,Zr,and Hf) imply that this gabbros were formed in a subduction setting.The alkali-feldspar granites are characterized by high SiO2,K2 O+Na2O,FeOT/MgO,low Al2 O3,CaO and MgO;relatively low total REEs and seagull-type distribution pattern;high total amount of trace elements,characterized evidently by enrichment of LILE (such as K,Th,U and Rb,and depletion of Ba,Nb,Ta,Sr,P and Ti).All these features are consistent with features of A-type granite.Therefore,the granites should be the product of partial melting of felsic crust in low pressure,high temperature condition.Together with their petrological and geological features,it can be concluded that the Yiheshaorong complex massif was most probably formed in a back-arc spreading basin triggered by oceanic crust subduction before closure of the Paleoasian Ocean in the Early Permian.关键词
中亚造山带/西乌旗/早二叠世/双峰式侵入岩/A型/弧后扩张环境Key words
Central Asia Orogenic Belt (CAOB)/Xiwu Banner/Early Permian/bimodal intrusive rocks/A-type/back-arc spreading引用本文复制引用
张晓飞,周毅,曹军,滕超,王必任,张华川,冯俊岭,刘俊来..内蒙古西乌旗罕乌拉地区双峰式侵入体年代学、地球化学特征及其对古亚洲洋闭合时限的制约[J].地质学报,2018,92(4):665-686,22.基金项目
本文为中国地质调查局项目“内蒙古1∶5万呼格吉勒图、巴彦华、巴彦布拉格、彦吉嘎庙幅区域地质调查”(1212011220453)项目资助的成果. （1212011220453）
