南盘江盆地八渡辉绿岩斜锆石和锆石U-Pb年龄及其地质意义  

Baddeleyite and Zircon U-Pb Dating of Badu Diabase in the Nanpanjiang Basin and Its Tectonic Significance

作　　者：夏文静 闫全人 向忠金[3] 夏磊 江文[1] 李晓剑 周斌 邓莉 XIA Wen-jing;YAN Quan-ren;XIANG Zhong-jin;XIA Lei;JIANG Wen;LI Xiao-jian;ZHOU Bin;DENG Li(College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049;Institut des Sciences de la Terre d’Orléans,UMR 7327-CNRS/Universitéd’Orléans,Orléans 45100;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037;Research Institute of Exploration and Development,SINOPEC Zhongyuan Oilfield Company,Puyang,Henan 457001)

机构地区：[1]中国科学院大学地球与行星科学学院,北京100049 [2]法国奥尔良大学地球科学研究所,奥尔良45100 [3]中国地质科学院地质研究所,北京100037 [4]中国石化中原油田分公司勘探开发研究院,河南濮阳457001

出　　处：《地球学报》2019年第2期265-278,共14页Acta Geoscientica Sinica

基　　金：国家自然科学基金项目(编号:40472119; 40872147);中国地质调查局项目(编号:12120113067500; DD20160201-07);中国科学院大学博士研究生国际合作培养计划(编号:UCAS[2015]37)联合资助~~

摘　　要：南盘江盆地是华南板块西南缘最大的沉积盆地之一。它的构造属性、形成时间及机制长期存在争议,影响着对华南印支造山过程的准确理解。南盘江盆地内除三叠系填充物外,断续出露着古生代碳酸盐岩。这些古生代碳酸盐岩实为三叠纪盆地下伏地层在盆地伸展张开过程中形成的断隆,在这些断隆周边发育有似层状或脉状辉绿岩,记录了南盘江盆地发育初期或早期的地质演化信息。本文用CamecaIMS1280二次离子质谱仪对南盘江盆地东南部八渡辉绿岩中的斜锆石和锆石进行了U-Pb同位素测试,分别获得206Pb/238U年龄加权平均值(269.3±4.2)Ma(95%置信度,N=15,MSWD=0.27)和(265.0±2.9)Ma(95%置信度,N=8,MSWD=0.02),表明八渡辉绿岩侵位于中二叠世沃德期(Wordian;265.1～268.8Ma),指示了南盘江盆地在此时处于伸展构造体制。这与南盘江盆地内广泛发育晚二叠世—早三叠世(258～248 Ma)基性岩浆活动,以及南盘江盆地晚二叠世—早三叠世时期沉积环境由碳酸盐岩台地相沉积快速转变为以浊积扇相为主的深水沉积等地质事实,共同表明南盘江盆地在中二叠世—早三叠世处于伸展构造体制。The Nanpanjiang basin is the biggest terrigenous clasitic basin developed on the southwest margin of the South China block.The tectonic setting of the Nanpanjiang Basin during its formation,the onset time and the mechanism of the basin’s opening have been long debated.These debates obstruct our understanding on the evolution of the Indochina orogen.Inside the Nanpanjiang basin,in addition to the Triassic deposition,some Paleozoic carbonatites were also outcropped,which developed into faulted blocks of the basement during the basin stretching.Around the Paleozoic carbonate faulted blocks,some stratoid or veined diabase were outcropped.As the initial record of the basin evolution,the diabase is a perfect research target for studying the age and geodynamics of the basin's opening.In this study,the diabase samples were acquired near to Badu Town,Tianlin County,Guangxi,which is in the southeastern part of the Nanpanjiang Basin.The U-Pb dating was conducted with Cameca IMS 1280 on the baddeleyite and zircon concentrated from the diabase samples.The results yielded the weighted mean 206Pb/238U ages of(269.3±4.2)Ma(N=15,MSWD=0.27)and(265.0±2.9)Ma(N=8,MSWD=0.02),respectively.This result demonstrates that the Badu diabase emplaced during the Wordian,Middle Permian(265.1~268.8 Ma),and indicates that the Nanpanjiang Basin was stretching during this period.Besides this magmatic event dated by this study,a later mafic magmatic event continued widely in the Nanpanjiang basin during the Late Permian to the Early Triassic(258~248 Ma).Sedimentologic study suggests that,from the Late Permian to the Early Triassic,the sedimentary environment of the Nanpanjiang basin changed from calci-clastic platform to turbidite fan.All these facts suggest that the Nanpanjiang Basin experienced extension during the Middle Permian to Early Triassic.

关 键 词：南盘江盆地 八渡辉绿岩 斜锆石 锆石 SIMS U-PB年龄 动力学背景 

分 类 号：P578.941[天文地球—矿物学] P597.1[天文地球—地质学]