内蒙古标山一带石英闪长岩地质特征及构造意义

A Discussion on the Geological Characteristics and Tectonic Significance of Quartz-tonalite in Biaoshan Area,Inner Mongolia

研究区位于甘新蒙交汇的北山地区,地质构造较复杂。前人对该区侵入岩时代、成因及形成环境等研究较少,大地构造格局和归属一直存在诸多不同认识。通过对标山一带石英闪长岩的研究,可为北山地区大地构造单元划分提供基础资料。该期石英闪长岩呈断续环带状分布于加里东晚期侵入岩外围,侵入体呈不规则带状NWW向展布,规模较大,呈岩基状产出。该岩体为高钾钙碱性岩系,准铝质岩石。轻重稀土之比LREE/HREE=6.34～17.42,轻重稀土分异程度较高。标准化蛛网图中,高场强元素Nb,Ta,P,Ti亏损较明显,具典型岛弧岩浆岩地球化学特征。利用LA-ICP-MS测定石英闪长岩锆石U-Pb年龄为(453±12)Ma。结合前人研究成果认为,标山一带石英闪长岩就位于岛弧构造环境,为红柳河-洗肠井俯冲带自南向北俯冲产物。

The study area located at Beishan area,which is the intersection of Gansu,Xinjiang and Inner Mongolia,the geologic structure are complicated.There are few researches on the intrusive rocks,the genesis and the formation environment of this area,and there are also many different understandings of the tectonic pattern and attribution.Based on the study of quartz diorite in the area of Biaoshan,it can provide basic information for the division of tectonic elements in Beishan area.The quartz-diorite of the Biaoshan present intermittent ring outside of the late Caledonian intrusive rocks.This NWW-trending intrusive rocks spread irregular strip with huge area.The rocks are high potassium calc-alkalic rock series and quasi aluminum rock.Light rare earth elements are more than the heavy that explains high degree of differentiation.High field strength elements(Nb,Ta,P,Ti)are characterized by obviously depleted in the standardized spider diagram,suggesting typical tectonic setting of arc magmatic rocks.Zircons LA-ICP MS U-Pb dating of the quartz-diorite yields an age of(453±12)Ma.On the basis of the published and our new data,we documented that the quartz-diorite located in the Biaoshan area intrudes into the island-arc,which can be considered as the product of the Hongliuhe-Xichangjing S-N trending subduction.