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湘东南骑田岭岩体A型花岗岩的地球化学特征及其构造环境
Geochemical characteristics and tectonic setting of Qitianling A-type granitic pluton in southeast Hunan
  
中文关键词:A型花岗岩,地球化学特征,后造山构造环境,燕山早期,骑田岭,湘东南,华南
英文关键词:A_type granites,geochemical characteristics,post_orogenic tectonic setting,early Yanshanian,Qitianling,southeast Hunan,South China,
基金项目:中国地质调查局区域地质调查资助项目(200213000035)
柏道远  陈建超  马铁球  王先辉
湖南地质调查院 湖南湘潭411100 (柏道远,陈建超,马铁球)
,湖南地质调查院 湖南湘潭411100(王先辉)
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中文摘要:
      骑田岭复式花岗岩体地处湘东南矿集区的中南部。本文研究讨论了骑田岭岩体的主体,即中侏罗世骑田岭序列花岗岩。其岩石类型为角闪石黑云母花岗闪长岩角闪石黑云母二长花岗岩黑云母二长花岗岩。各岩石单元从早至晚,SiO2含量总体由低变高,变化范围在65.92%~75.68%之间。岩石高钾、富碱,K2O含量为4.10%~5.27%,平均4.86%;Na2O K2O为7.12%~8.24%,平均7.85%;K2O/Na2O值平均为1.63;ACNK值在0.90~1.05之间,平均为0.96;KN/A在0.71~0.89之间,平均为0.78,属钾玄岩系列与高钾钙碱性系列准铝质弱过铝质花岗岩类。ΣREE平均达375.6μg/g,在原始地幔标准化图解上显示出Ba、Nb、Sr、P、Ti、Eu负异常和U、Th、Nd、Zr、Sm、Y的正异常,具明显的分异结晶作用特征。ISr值为0.70854~0.71281,εNd(t)值为-5.05~-7.57,tDM为1.35~1.56Ga,明显低于湘桂内陆带花岗岩的背景值(1.8~2.4Ga)和区域基底的时代(1.7~2.7Ga),反映出有幔源物质加入。经多种相关图解判别均显示其为A型花岗岩,骑田岭序列应形成于后造山拉张构造环境。讨论认为湘东南及华南地区燕山早期构造环境为后造山而不是陆内裂谷环境。
英文摘要:
      Qitianling composite granitic pluton is in the middle south of the southeastern Hunan ore concentration area. The Middle Jurassic Qitianling granite, the main intrusive body of Qitianling pluton, is studied in this paper. The Qitianling granite is composed of hornblende biotite granodiorite, hornblende biotite monzonitic granite and biotite monzonitic granite. SiO2 content increases from early to late granitic units, varying in the range of 65.92%~75.68%. The rocks are potassium-high (K2O=4.10%~5.27%, 4.86% on average) and alkali-rich (Na2O+K2O=7.12%~8.24%, 7.85% on average) ones, and have an average K2O/Na2O value of 1.63, ACNK values of 0.90~1.05 (0.96 on average) and KN/A values of 0.71~0.89 (0.78 on average), thus belonging to metaluminous to weakly peraluminous granitoids of shoshonite series and K_high calc_alkaline series. The rocks have an average ΣREE of 375.6 μg/g and show evident negative Ba,Nb, Sr, P, Ti and Eu anomalies as well as positive U, Th, Nd, Zr, Sm and Y anomalies, suggesting evident fractional crystallization. They have ISrvalues of 0.708?54~0.712?81, εNd (t) values of -5.05~-7.57 and tDM ages of 1.35~1.56 Ga, which is lower than the background age of granitoids in Hunan and Guangxi (1.8~2.4 Ga) and the region_al basement's age (1.7~2.7 Ga), implying participation of mantle materials. Various oxide and trace element diagrams for discrimination of structural environment reveal that the Qitianling granite was formed in a post_orogenic extensionalstructural environment. The authors consider that the early Yanshanian tectonicsetting in southeast Hunan and South China is a post_orogenic one instead of an intracontinental rift.
柏道远,陈建超,马铁球,王先辉,2005,湘东南骑田岭岩体A型花岗岩的地球化学特征及其构造环境[J].岩石矿物学杂志,24(4):255~272.
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