内蒙古东乌珠穆沁旗阿木古楞复式花岗岩体时代、成因及地质意义  

Ages,Origin and Geological Implications of the Amuguleng Composite Granite in East Ujimqin Banner,Inner Mongolia

作　　者：何付兵[1] 徐吉祥[1] 谷晓丹[2] 程新彬[1] 魏波[1] 李昭[1] 梁亚南[1] 王泽龙[1] 黄淇[1] 

机构地区：[1]北京市地质调查研究院,北京100195 [2]中国石油大学(北京),北京102200

出　　处：《地质论评》2013年第6期1150-1164,共15页Geological Review

基　　金：内蒙古1:5万巴彦敖包等四幅区域地质调查项目(基[2010]矿评01-09-04)的成果

摘　　要：阿木古楞岩体位于内蒙古东乌珠穆沁旗旗行政中心正北。路线地质调查可分解为两期岩石单元:灰黄色中细粒、粗中粒含巨斑二长花岗岩和灰白色细粒二长花岗岩。前者锆石U-Pb加权平均年龄为314.2±2.2Ma,为晚石炭世岩浆活动的产物,后者锆石U-Pb加权平均年龄为167.1±1.3Ma,为中—晚侏罗世岩浆活动的产物。这两期花岗岩副矿物均富含磁铁矿、独居石、磷灰石和榍石,中—晚侏罗世花岗岩还发育萤石矿物。在地球化学特征上,两期花岗岩也表现出相似性:主量元素表现为总体富Si,且有较高的分异指数(DI)及碱/铝(NK/A)、Fe2O/FeO比值,较低的总Fe、Ti、Mg、Ca和P含量;微量元素蛛网图则表现为富集大离子亲石元素Rb、Th、U、Pb,弱富集轻稀土元素La、Ce,明显亏损高场强元素Nb、Ba和Sr、Ti;而稀土元素配分图表现出相对富集轻稀土元素、亏损重稀土元素,轻重稀土元素分异较大、重稀土曲线却较为平坦的右倾型特征。综合分析认为:两期花岗岩单元均属于高分异准铝质—弱过铝质高钾钙碱性系列的I型花岗岩,其源区物质均可能为来自亏损地幔物质经过改造形成的年轻的陆壳高K、正常水含量的长英质陆壳岩石物质,且晚石炭世花岗岩单元长英质陆壳岩石物质来源中还混合有幔源的玄武质组分。而其中—晚侏罗世花岗岩单元岩浆来源更有可能源于早期的晚石炭世花岗岩的重熔或部分重熔,至少具有类似的岩浆源区。阿木古楞岩体中晚石炭世花岗岩单元形成于中亚造山挤压造山大地构造背景下的同碰撞晚期构造—岩浆事件,中—晚侏罗世花岗岩单元形成于蒙古—鄂霍次克洋和古太平洋构造域转换、大地构造背景以伸展拉张为主的后碰撞造山构造—岩浆事件。Amuguleng granite is located at the north of East Ujimqin Banner （Dong Ujimqin Qi ） Administration Center in Inner Mongolia. Geological investigation indicates that the granite composing of 2 intrusive rocks： gray-yellow medium-fine, medium-coarse grained adamellite containing huge phenocryst and gray-white fine adamellite. Zircon U-Pb age of the granite dated as 314.2±2.2Ma and 167.1±1.3Ma, suggesting that they were products of magmatic evolution during Late Carboniferous and Middle Late Jurassic respectively. Accessory minerals of both the two granites are rich in magnetite, monazite, and sphene, and there is fluorite in the Mid - Late Jurassic granite. Compositon of the rocks indicates that these two kinds of granites have similar geochemical characteristics： major element are characterized by enrichment of Si, higher DI and NK/A , FezO/FeO ratios. The race element spider diagram indicates that granites are relatively rich in Rb, Th, U, Pb, slightly enriched in the light rare earth elements La, Ce, and depleted in high field strength elements such as Nb, Ba and Sr, Ti; While the distribution model of REE is right oblique, which is relatively LREE-enriched and HREE-depleted, and the HREE curve is flat. Based on the results, these two kinds of granites are attributed to high differentiated metaluminous-weakly peraluminous high-K calc-alkaline series, which are the typical I-type granites. The source materials might come from younger crustal felsic rocks with high K and normal water content, And the source material of felsic continental rocks of late Carboniferous granite unit is mixed with mantle-derived basaltic components. The Middle Late Jurassic granitic magma maybe originated from the remelting or the partial remelting of Late Carboniferous granite, at least, it has similar magma source with that of the Late Carboniferous granite. The Late Carboniferous granite unit was formed in compression setting at the late syn-collision stage of Central Asian Orogeny. The Middle Late Jurassic granite unit was

关 键 词：阿木古楞 花岗岩 锆石U-PB年龄 岩石地球化学 构造背景 东乌珠穆沁旗 

分 类 号：P588.121[天文地球—岩石学]