湖南白马山龙潭超单元、瓦屋塘花岗岩锆石SHRIMP U-Pb年龄及其地质意义  

SHRIMP U-Pb Dating of Zircons from the Baimashan Longtan Super-Unit and Wawutang Granites in Hunan Province and Its Geological Implication

作　　者：李建华[1] 张岳桥[1] 徐先兵[2] 李海龙[1] 董树文[3] 李廷栋[3] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]中国地质大学地球科学学院,武汉430074 [3]中国地质科学院,北京100037

出　　处：《吉林大学学报（地球科学版）》2014年第1期158-175,共18页Journal of Jilin University：Earth Science Edition

基　　金：财政部"深部探测技术与实验研究"专项之子课题(Sinoprobe-08-01);国家自然科学基金项目(41172184)

摘　　要：运用阴极发光技术，对湖南白马山龙潭超单元2个样品和瓦屋塘花岗岩1个样品的锆石进行了内部结构分析，在此基础上利用锆石SHRIMPU-Pb定年方法进行了同位素年代学测定。其中，白马山龙潭超单元2个黑云母二长花岗岩样品分别给出了（215．9＆#177;1．9）Ma和（212．2＆#177;2．1）Ma的主体谐和年龄。同时还测得了一组较年轻的谐和年龄（（201．0＆#177;2．8）Ma）和一组较老的锆石核部年龄（230．3～227．0Ma），表明研究区印支晚期存在多期花岗质岩浆的侵入活动。瓦屋塘岩体黑云母二长花岗岩1个样品给出了（217．7＆#177;1．8）Ma的谐和年龄。这2个岩体的形成进一步佐证了华南大陆印支晚期岩浆活动于210～225Ma，达到岩浆活动的峰期。地球化学测试结果显示，白马山和瓦屋塘岩体均为弱过铝强过铝质花岗岩，具壳源型花岗岩的特征，形成于后碰撞期或碰撞晚期的构造环境，源于早元古代变质杂砂岩的部分熔融。结合区域大地构造背景认为，这2个岩体形成于秦岭大别和松马2条印支期缝合带碰撞结束后的印支晚期伸展构造背景下，为热应力松弛阶段，板内挤压加厚的地壳减压熔融作用的产物。In this study ,internal structures of zircons from the Baimashan and Waw utang biotite monzogranite plutons are analyzed by the CL technology ,and reliable ages of zircons are dated by the＆amp;nbsp;SHRIMP U Pb method .Two samples from the Baimashan Longtan super-unit yield weighted mean 206 Pb/238 U ages of （215 .9 ＆#177; 1 .9） Ma and （212 .2 ＆#177; 2 .1） Ma ,respectively .Moreover ,several zircons exhibit core-rim textures ,in which the zircon cores yield older ages of 230 .3 227 .0 Ma ,and the zircon rims yield younger mean 206 Pb/238 U age of （201 .0 ＆#177; 2 .8）Ma .These data suggest that the Baibashan biotite monzogranite was generated by multi-phase magmatic intrusions . One biotite monzogranite sample from the Wawutang granite yields a weighted mean 206 Pb/238 U age of （217 .7 ＆#177; 1 .8） Ma .These geochronological data provide new evidences for the conclusion that there occurred a peak magmatism （210 225 Ma） in South China during the late stage of the Indosinian orogeny .Geochemical studies indicate that the Baimashan and Waw utang plutons are typical post-orogenic crust-sourced peraluminous granites ,resulted from partial melting of the Paleoproterozic metamorphic greywacke .These data allow us to infer that the two plutons were formed after the Early Triassic collision along the Songma and Qingling Dabie sutures ,associated with the parting melting of the thickened crust in the post orogenic extensional setting .

关 键 词：白马山 瓦屋塘 锆石SHRIMPU-PB定年 印支期花岗岩 地壳伸展 湖南 

分 类 号：P597.1[天文地球—地球化学]