内蒙古京格斯台晚石炭世碱性花岗岩年代学及地球化学特征——岩石成因及对构造演化的约束  

Geochronology and Geochemistry of Late Carboniferous Jinggesitai Alkaline Granites,Inner Mongolia:Petrogenesis and Implications for Tectonic Evolution

作　　者：王树庆[1] 胡晓佳[1] 赵华雷[1] 辛后田[1] 杨泽黎 刘文刚[1] 何丽[2] WANG Shuqinga HU Xiaojia ZHAO Hualei XIN Houtian YANG Zeli LIU Wengang HE Li(Tianjin institute of Geology and Mineral resources, Tianjin, 300170 Regional Geology and Mineral Resources Survey Institute of Hebei Province, Langfang, 065000)

机构地区：[1]天津地质矿产研究所,天津300170 [2]河北省区域地质矿产调查研究所,河北廊坊065000

出　　处：《地质学报》2017年第7期1467-1482,共16页Acta Geologica Sinica

基　　金：中国地质调查项目(编号:1212014121079;1212011121079)资助的成果

摘　　要：京格斯台碱性花岗岩出露于内蒙古东乌旗西北部的中蒙边境一带,是准噶尔-南蒙古-内蒙古碱性花岗岩带的一部分,为一套含钠铁闪石碱性花岗岩类。锆石LA-MC-ICPMS U-Pb测年获得了301.3±1.5Ma(n=21,MSWD=1.3)的年龄,表明侵位时代为晚石炭世。全岩地球化学分析显示样品具有高SiO2(75.16%~76.96%)、高碱(K2O=4.61%~5.04%,Na2O=3.98%~4.24%)、贫CaO(0.08%~0.25%)、MgO(0.07%~0.1%),低FeOt(1.05%~2.05%),高的FeOt/MgO比值(12.85~29.66),属于弱过铝质系列;富集Rb、Th、U、K等大离子亲石元素及Zr、Hf等高场强元素,弱亏损Nb、Ta,强烈亏损Ba、Sr、P、Ti等;稀土元素总量较低[ΣREE范围为(70.19~193.93)×10^(-6),平均值为126.82×10^(-6)],轻稀土略富集,具有明显的Eu负异常(δEu=0.03~0.07),呈类似"海鸥"型稀土配分模式。岩石学及地球化学特征表明京格斯台碱性花岗岩属于碱质A型花岗岩。锆石原位Hf同位素和全岩Nd同位素分析显示其具有亏损的Hf-Nd同位素组成εHf(t)和εNd(t)均为正值,Hf地壳存留模式年龄范围为385~1605Ma,并且多数集中于600~900Ma,二阶段Nd模式年龄范围为582~650Ma,这表明源岩为幔源新生地壳物质,代表了新元古代一次地壳增生。综合岩石学、岩石地球化学和同位素地球化学数据,我们认为京格斯台碱性花岗岩是由新生地壳,在晚石炭世贺根山洋闭合后的后造山伸展阶段,在上涌软流圈的加热及减压作用下部分熔融形成的,形成于后造山构造环境。In this paper, we present zircon U-Pb dating, in-situ Hf isotopic analysis, whole rock Nd isotopic and geochemical data of the late Carboniferous alkaline granites from Jinggesitai region, central part of the Xingmeng Orogenic Belt. Zircon U-Pb dating give weighted average age of 301.3±1.5Ma （n=21, MSWD =1.3）, indicating that this intrusion was formed in late carboniferous. These rocks show the characterics of high silica （75.16~76.96%）, alkali（K20=4.61~5. 04% ,Na2O=3.98~4. 24%） contents,low CaO （0.08~0.25%）, MgO （0.07~0.1%）, FeOt（1.05~2.05%） contents, respectively, but with high FeOt/ MgO ratios （12.85~29.66）, which are similar with typical A-type granite. Trace elemental data of these rocks show enrichment of Rb, Th, U, K, Zr, Hf, but strong depletion of Sr, Ba, P, Ti. Total REE contents are moderate （EREE = 70. 19 ~ 193. 93× 10^ 6 ） with obvious fractionation between LREE and HREE（（La/Yb）N range from 3.85 to 11.55） and strong negative Eu abnormity （δEu range from 0.03~ 0.07）. Furthermore, these rocks have positive zircon εHf（t） and whole rock εNd（t） values, with two stage Hf and Nd model ages of Neoproterozoic, indicating the source of Jinggesitai alkaline granites of juvenile crust from mantle in Neoproterozoic. These geochemical and Nd-Hf isotopic signatures argue for derivation from partial melting of juvenile crust by depression and heating of upwelling asthenosphere in a extensional setting, demonstrating late Post-Orogenic tectonic regime of Erlian-Dongwuqi region in 301Ma.

关 键 词：碱性花岗岩 京格斯台 晚石炭世 兴蒙造山带 后造山 

分 类 号：P534.45[天文地球—古生物学与地层学] P588.15[天文地球—地质学]