内蒙古扎鲁特旗香山镇地区大石寨组火山岩年代学、地球化学特征及其地质意义  

GEOCHRONOLOGY AND GEOCHEMISTRY OF DASHIZHAI FORMATION VOLCANIC ROCKS IN XIANGSHAN TOWN,JARUD BANNER,INNER MONGOLIA AND ITS GEOLOGICAL SIGNIFICANCE

作　　者：王亚东 姜山[1] 王之晟 王晓奇[1] 王洪志[1] 卢天军[1] 于兵 Wang Yadong;Jiang Shan;Wang Zhisheng;Wang Xiaoqi;Wang Hongzhi;Lu Tianjun;Yu Bing(The No.243 Team of Nuclear Industry,Chifeng 024000,China)

机构地区：[1]核工业二四三大队,内蒙古赤峰024000

出　　处：《矿物岩石》2021年第2期13-23,共11页Mineralogy and Petrology

基　　金：中国地质调查局项目“内蒙古1∶5万工农屯(L51E021003)等六幅区域地质矿产调查”(DD20160201-12)

摘　　要：内蒙古地区的二叠统大石寨组火山岩的成因及形成环境说法不一,众说纷纭。内蒙古扎鲁特旗香山镇地区大石寨组火山岩为一套中酸性火山熔岩-碎屑岩组合。锆石U-Pb测年结果显示大石寨组火山岩的年龄为264.0±1.2 Ma(MSWD=0.80),为中二叠世早期。岩石地球化学数据表明:扎鲁特旗香山镇地区大石寨组火山岩属于过铝质高钾钙碱性岩石(Al_(2)O_(3))均值16.90%;全碱(K_(2)O+Na_(2)O)平均值为7.45%;A/CNK平均值1.10)。轻重稀土分馏明显((La/Sm)_(N)为1.43~1.45),((La/Yb)_(N)为10.14~12.6);稀土元素总量偏低(ΣREE为137.36~158.45×10^(-6));δEu位0.90~1.07,均值0.97。没有显示明显的负铕异常(δEu=0.90~1.07);稀土元素分配模式为右倾型。富集大离子亲石元素Rb,Ba,Th,K和Sr;而高场强元素Ti,P,Ta,Nb较为亏损。其形成机制可能由地幔楔部分的熔融,同时在俯冲过程有洋壳沉积物和俯冲流体的混入。该组火山岩形成于活动大陆边缘弧的环境下,构造背景为古亚洲洋板块向北俯冲作用,且古亚洲洋在中二叠世早期未曾闭合。Different opinions have been discussed on the origin and forming environment of volcanic rocks in the Permian Dashizhai Formation in Inner Mongolia. The Dashizhai Formation volcanic rocks in Xiangshanzhen area, Jarud Banner, Inner Mongolia are a set of intermediate-acid volcanic lava-clastic rock assemblages. Zircon U-Pb dating shows that the age of the Dashizhai Formation volcanic rocks is 264.0±1.2 Ma(MSWD=0.80), formed in the early Middle Permian. Petrogeochemical analysis data shows that the volcanic rocks of Dashizhai Formation in Xiangshan Town area belong to peraluminous high-K calc-alkaline rocks w(Al2O3) average 16.90%, with the average value of total alkali w(K2O+Na2O) of 7.45% and with the average value of A/CNK equal to 1.10). The fractionation of heavy and heavy rare earths is obvious(La/Sm)N=1.43-1.45 and(La/Yb)N=10.14-12.60. The total amount of REE is low(ΣREE is 137.36-158.45×10-6);δEu ranges from 0.90 to 1.07, with an average value of 0.97. There is no obvious negative Eu anomaly(δEu=0.90-1.07) and shows right-incline distribution pattern of rare earth elements. The volcanic rocks enrich in large ion lithophile elements Rb, Ba, Th, K and Sr, and deplete in high field strength elements Ti, P, Ta and Nb. According to the above listed data, it is considered that the formation mechanism of the volcanic rocks may be caused by the melting of mantle wedge, the mixing of oceanic crust sediments and subduction fluids during subduction. The Paleo-Asian Ocean did not closed in the early Middle Permian and the Dashizhai Formation volcanic rocks were formed in the environment of active continental margin arc with a tectonic background of northward subduction of the Paleo-Asian Ocean plate.

关 键 词：大石寨组 U-PB测年 火山岩﹔岩石地球化学 扎鲁特旗 

分 类 号：P579[天文地球—矿物学]