赣南地区密坑山早白垩世A型花岗岩的锆石U-Pb年代学、地球化学及岩石成因  

Zircon U-Pb Geochronology, Geochemistry and Petrogenesis of Early Cretaceous A-type Granites in the Mikengshan Area, Southern Jiangxi Province

作　　者：梁鹤 郭海峰 王强[1,2,3] 熊小林 欧权[1] 曾纪鹏[1] 苟国宁 郝露露 LIANG He;GUO Haifeng;WANG Qiang;XIONG Xiaolin;OU Quan;ZENG Jipeng;GOU Guoning;HAO Lulu(State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China;CAS Center for Excellence in Tibetan Plateau Earth Sciences(CETES),Beijing 100101,China)

机构地区：[1]中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640 [2]中国科学院大学,北京100049 [3]中国科学院青藏高原地球科学卓越创新中心,北京100101

出　　处：《大地构造与成矿学》2018年第4期746-758,共13页Geotectonica et Metallogenia

基　　金：国家重点研发计划项目(2016YFC0600407)、国家自然科学基金重点项目(41630208)、广州市重要科技项目(201707020032)和广东人才项目(2014TX01Z079)联合资助。

摘　　要：密坑山-岩背地区为华南典型的锡成矿区,区内发育燕山期的花岗岩、斑岩和斑岩锡矿(如岩背锡矿)。尽管该区锡矿与花岗质岩浆作用的关系密切,但区内花岗岩的时代与成因仍然存在争议。密坑山花岗岩体为密坑山-岩背地区最大的花岗岩体,侵入于上侏罗统鸡笼嶂组流纹质凝灰熔岩及火山碎屑岩中,主体岩性为钾长花岗岩。本文报道了密坑山钾长花岗岩的时代、地球化学特征。LA-ICP-MS锆石U-Pb定年结果显示,该岩体形成于早白垩世(~138 Ma)。岩石具有高SiO_2(74.42%～76.69%),富钾(K_2O/Na_2O=1.37～1.94),低Al_2O_3(12.39%～13.49%)和Mg~#(11～19),弱过铝质(A/CNK=1.03～1.1),负Eu、Sr、Ba异常,富集高场强元素,以及高10000×Ga/Al比值(3.46～4.96)和略微高的锆石饱和温度(807～817℃),显示了铝质A型花岗岩的特点。同时,岩石也具有高Rb含量(842～1295)×10^(-6)、Rb/Sr比值(90～255)以及稀土元素四分组效应,显示了高分异花岗岩的特点。因此,作者认为密坑山钾长花岗岩为高分异铝质A型花岗岩。花岗岩略微偏高的ε_(Nd)(t)值(-3.4～-4.6),反映成岩过程中或其源区有地幔组分的参与。综合区域岩浆岩和构造资料,认为密坑山钾长花岗岩形成于伸展背景中,很可能与俯冲古太平洋板块的后撤所导致的岩石伸展过程有关。In the Mikengshan-Yanbei area,a special region for the tin mineralization in South China,there are some Yanshanian granites and porphyries and associated porphyry tin deposits(e.g.,Yanbei).Although the tin mineralization is closely associated with the granitoids magmatism,the age and petrogenesis of the granites remain controversial.The Mikengshan pluton,which intrudes into the rhyolitic tuff and pyroclastic rocks of the Upper Jurassic Jilongzhang Formation,is the largest one in Mikengshan-Yanbei area and mainly consists of K-feldspar bearing granites.In this study,we report new age and geochemical data for the Mikengshan K-feldspar bearing granites.LA-ICP-MS zircon U-Pb age dating shows that they were generated in the Early Cretaceous(~138 Ma).They have high SiO2(74.42%to 76.69%),low Al2O3(12.39%to 13.49%)and Mg#(11 to 19),and negative Eu,Sr and Ba anomalies,and are rich in potassium(most K2O/Na2O=1.37 to 1.94)and high field strength elements(HFSEs),and are weakly peraluminous(A/CNK=1.03 to 1.1)with high 10000×Ga/Al ratios(3.46 to 4.96)and slightly high zircon saturation temperatures(807℃to 817℃),showing the characteristics of the typical A-type granites.Moreover,they have high Rb contents 842×10?6 to 1295×10?6,Rb/Sr(90 to 255)ratios and show rare earth elements(REE)tetrad effect,which are similar to those of high fractionated granites.Thus,we suggested that the Mikengshan K-feldspar bearing granites are high fractionated and aluminous A-type granite.Their slightly highεNd(t)values(-3.4 to-4.6)indicate that the mantle components should have played a role during their formation.Taking into account regional igneous rocks and tectonic setting data,we suggest that the Mikengshan K-bearing granites were formed in an extensional setting,which was probably related to the roll-back of the subducted Paleo-Pacific plate.

关 键 词：铝质A型花岗岩 高分异花岗岩 锡矿化 白垩纪 密坑山 华南 

分 类 号：P597[天文地球—地球化学] P595[天文地球—地质学]