摘要
敦煌地块南缘小红山花岗岩体侵位于敦煌岩群中,岩性主要为黑云二长花岗岩和黑云花岗闪长岩。通过LA-ICP-MS锆石U-Pb同位素定年,获得小红山黑云母二长花岗岩的206 Pb/238 U的加权平均年龄为289.6±3.9Ma,表明侵位时代为早二叠世。岩石地球化学分析显示其具有高硅、高铝、富碱和低镁的特征,稀土元素在球粒陨石标准化稀土配分模式图上呈轻稀土富集的右倾型稀土配分模式,弱负Eu异常,富集大离子亲石元素(如Rb、Cs、Th、K、Pb),亏损Nb、Ta、P、Ti等高场强元素,岩石强烈富集Sr、亏损Yb和Y,具有较高的Sr/Y比值,岩石具有与埃达克岩石一致的地球化学特征,是加厚下地壳部分熔融的产物。小红山花岗岩全岩Sr-Nd同位素的87Sr/86Sr值介于0.706622～0.707778之间,143 Nd/144 Nd介于0.51212～0.512264之间,εNd(t)=-4.093～-6.887,显示出壳源特征;Nd模式年龄TDM2=1.39～1.62Ga,平均为1.49Ga,表明其源区可能与敦煌岩群相关。结合成岩年龄和区域构造演化特征,推测敦煌地块南缘在石炭纪到早二叠世处于碰撞造山作用向陆内伸展环境转换的构造背景,可能强烈卷入了一系列与古亚洲洋闭合相关的古生代造山活动中。
The Xiaohongshan granite on the southern margin of the Dunhuang block intrudes the Dunhuang rocks,and consists mainly of e biotite monzonitic granite and biotite granodiorite.LA-ICP-MS zircon U-Pb isotopic dating yielded a weighted 206Pb/238U average age of 289.6±3.9 Ma for the Xiaohongshan biotite monzonite,indicating that the emplacement age was Early Permian.The geochemical analyses show that the granite is characterized by high silicon,high aluminum,alkali-rich and low magnesium.The rare earth elements show a LREE-enriched right-dipping pattern and weak negative Eu anomaly in the chondritenormalized REE distribution patterns.Enrichment of large ion lithophile elements(such as Rb,Cs,Th,K,Pb),depletion of high field-strength elements(such as Nb,Ta,P,Ti,etc),especially enriched Sr and depleted Yb and Y,as well as relatively high Sr/Y raito,suggest that the rock has the same geochemical characteristics as that of Adakite was should be the product of partial melting of the thickened lower crust.The 87 Sr/86 Sr values of whole rock of the Xiaohongshan granite range from 0.706622 to 0.707778,143 Nd/144 Nd values range from 0.51212 to 0.512264 withεNd(t)=-4.093 to -6.887,indicating characteristic of the crust source.The Nd model age TDM2 of 1.39~1.62 Ga(ave.1.49 Ga)indicates that its source area may be related to the Proterozoic Dunhuang rocks.Combined with the diagenetic age and regional tectonic evolution characteristics,it can be concluded that the southern margin of the Dunhuang block might have involved into in a series of Paleozoic orogenic events related to closure of the paleo-Asian ocean in a tectonic setting from the collisional orogeny to the intracontinental extensional environment during the Carboniferous to Early Permian.
作者
黄万堂
王玉玺
李通国
杨婧
张翔
王怀涛
王晓伟
朱永新
HUANG Wantang;WANG Yuxi;LI Tongguo;YANG Jing;ZHANG Xiang;WANG Huaitao;WANG Xiaowei;ZHU Yongxin(Gansu Provincial Bureau of Geology and Mineral Exploration and Development,Lanzhou,730000;Geological Survey of Gansu Province,Lanzhou ,730000;School of Earth Sciences of Lanzhou University,Key Laboratory of Mineral Resources in Western China,Lanzhou,730000)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2018年第12期2437-2452,共16页
Acta Geologica Sinica
基金
甘肃省基础地质调查项目"甘肃省多坝沟地区1:5万矿产远景调查"(20151616)
甘肃省地质勘查基金项目(201701-D18)
中国地质调查局地质调查项目"中国矿产地质与成矿规律综合集成和服务(矿产地质志)"(DD20160346)联合资助成果
