皖南太平岩体锆石LA-ICP-MS U-Pb年龄和地球化学特征——对华南中生代岩石圈伸展减薄的启示  

Zircon LA-ICP-MS U-Pb Ages and Geochemical Features of Taiping Pluton in South Anhui——Enlightment of Mesozoic Lithospheric Thinning for South China

作　　者：周术召 徐生发[2] 余心起[1] 邱骏挺[1,3] 杨鑫朋 陈子微 刘秀[1] 

机构地区：[1]中国地质大学地球科学与资源学院,北京100083 [2]安徽省地质矿产勘查局332地质队,安徽黄山245000 [3]核工业北京地质研究院,北京100029

出　　处：《地质论评》2016年第6期1549-1564,共16页Geological Review

基　　金：国家自然科学基金资助项目(编号:41272232)的成果~~

摘　　要：太平岩体位于黄山市,岩性以花岗闪长岩为主,岩体中发育数条近南北走向的二长花岗斑岩脉体。LA-ICP-MS锆石U-Pb测年结果显示,太平甘棠镇附近的花岗闪长岩和二长花岗斑岩脉的加权平均年龄为146.8±1.2Ma和131.0±1.2Ma。花岗闪长岩的A/CNK值为1.3,CaO和Na_2O含量高,稀土配分曲线呈右倾型,Eu无明显异常;相对亏损Nb、Ta、Ti元素,属过铝质I型花岗岩。二长花岗斑岩脉具有高的SiO_2、K_2O+Na_2O含量和K_2O/Na_2O值;Eu明显负异常,亏损Ba、Sr、P、Ti,形成4个明显的凹槽,A/CNK值为1.54,属强过铝质A型花岗岩。结合前人研究成果,本文认为黄山复式岩体的岩性经历了从花岗闪长岩到二长花岗斑岩再到花岗岩的转变,在此过程中,岩石的地球化学特征、成岩压力等都是渐变的。通过综合分析,认为皖浙赣地区早侏罗世构造动力体制经历了由挤压向拉伸的转换,逐渐变小的岩浆成岩压力,暗示华南地区晚中生代岩石圈伸展减薄的机制更倾向于热侵蚀模式。Objetives： The Taiping pluton is located in Huangshan city, Anhui province. It is mainly composed of granodiorite, and a crossed by several nearly NS direction monzogranite porphyry dikes in its west. Methods：Countersigned the age of granite by zircon U-Pb dating and their petrology characteristics by whole rock analysis. Results：The LA-ICP-MS zircon U-Pb dating yield out a weighted average 146.8 ± 1.2 Ma for granodiorite and 131.0 ± 1.2 Ma for monzogranite porphyry from Taiping Gantang town. For granodiorite, the A/CNK is less than 1, the content of CaO and Na2O is high, and the REE pattern is in right dip form with weakly negative Eu anomalies or no Eu anomalies. It is relative depletion in Nb, Ta, Ti, and belong to metaluminous I-type granites. The monzonitic granite porphyry is riched in SiO2, K2O ＋ Na2O, K2O/Na2O, and obvious depletion in Eu. In the spider diagram, there have been appearance four grooves as a result of depleted in Ba, Sr, P, and Ti. It can be concluded that the monzonitic granite porphyry belongs to peraluminous A-type granites. ConcLusions：Combining the previous results, this paper believes that the lithology of Huangshan composite body had underwent the comagmatic evolution from granodiorite to monzogranite porphyry, then to granite, and the geochemical characteristics and diagenetic pressure are gradually changing during the process. It is also believed that the tectonic dynamic mechanism had experienced a transition from extension to compression in Anhui-- Zhejiang--Jiangxi adjacent area during the early Jurassic. While the decreasing diagenetic pressure suggests that the mechanism of Mesozoic lithospheric thinning in south China are more inclined thermal erosion model.

关 键 词：锆石U-PB定年 太平岩体 中生代 岩石圈减薄 皖浙赣地区 华南 

分 类 号：P597.3[天文地球—地球化学] P583[天文地球—地质学]