北秦岭二郎坪群抱树坪组碎屑锆石LA-MC-ICP-MS U-Pb定年及物源特征  

LA-MC-ICP-MS Zircon U-Pb Dating and Provenance Characteristic from Baoshuping Formation of Erlangping Group of the North Qinling

作　　者：欧伟程 李承东[3] 张永清 赵利刚 许腾 许雅雯 孙烜烨 OU Weicheng;LI Chengdong;ZHANG Yongqing;ZHAO Ligang;XU Teng;XU Yawen;SUN Xuanye(Chinese Academy of Geological Sciences,Beijing 100037,China;China University of Geosciences,Beijing 100083,China;Tianjin Center of Geological Survey,China Geological Survey,Tianjin 300170,China;Sinosteel Tianjin Geology Co.,Ltd.,Tianjin 300061,China)

机构地区：[1]中国地质科学院,北京100037 [2]中国地质大学(北京),北京100083 [3]中国地质调查局天津地质调查中心,天津300170 [4]中钢集团天津地质研究院有限公司,天津300061

出　　处：《现代地质》2022年第1期347-361,共15页Geoscience

基　　金：中国地质调查局项目“全国陆域及海区地质图件更新与共享”(DD20190371);国家自然科学青年基金项目“锐钛矿U-Pb同位素定年方法及其在桂西那豆铝土矿矿床中的应用”(41803047)。

摘　　要：北秦岭造山带中二郎坪群构造属性及形成时代一直存在争议,其中的抱树坪组更是缺少年代学数据报道。为了进一步厘定抱树坪组时代及形成的构造环境,对其碎屑锆石开展LA-MC-ICP-MS定年及物源研究。结果表明,取自原划分为抱树坪组中的斜长黑云石英岩(18P_(3)TW2)和含透辉黑云阳起斜长变粒岩(18P_(3)TW3)具有完全不同的锆石年龄谱特征,揭示它们属于不同时代的地层。18P_(3)TW2碎屑锆石年龄谱为多峰,锆石来源于北秦岭微陆块及华北地块,缺乏早古生代岩浆弧锆石,最年轻的一组锆石年龄为493~972Ma。18P_(3)TW3碎屑锆石年龄谱为单峰,其中最年轻一组锆石年龄为420~440Ma,主体来源于二郎坪岛弧岩浆岩。通过野外特征、锆石年龄组成和物源特征综合分析,18P_(3)TW2所代表的地层形成于盆地初期,没有大规模火山活动,不应归属于抱树坪组。18P_(3)TW3所代表的抱树坪组地层形成于盆地晚期,主体沉积时代为奥陶纪—志留纪,最晚地层可能延续到早泥盆世。结合区域地质背景,抱树坪组形成于早古生代商丹洋向北俯冲所产生的弧后伸展盆地构造环境。The tectonic attributes and age of Erlangping Group in the North Qinling orogenic belt have been controversial,and Baoshuping Formation lacks chronological data.In order to further determine the age and tectonic setting of Baoshuping Formation,detrital zircon dating and provenance studies by LA-MC-ICP-MS were carried out.The results show that the plagioclase biotite quartzite(18P_(3)TW2)and the diopside-bearing biotite actinolite plagioclase granulite(18 P_(3)TW3)from Baoshuping Formation have completely different zircon age spectrum characteristics,indicate that they belong to the strata of different ages.The detrital zircons age spectrum of 18P_(3)TW2,which originates from the North Qinling micro-continental block and North China block,is multi-peaked but short of the data about Early Paleozoic magmatic arc.The youngest group of zircons range from 493 Ma to 972 Ma.The detrital zircons age spectrum of the 18 P_(3)TW3 is unimodal,and the main source of zircons is the Erlangping arc magmatic rocks,of while the youngest group of zircons is 420-440 Ma.With comprehensive analysis of field characteristics,age spectrum of zircons and provenance characteristics,the strata represented by 18P_(3)TW2 was formed in the early stage of the basin without large-scale volcanic action,so it should not be attributed to Baoshuping Formation.Baoshuping Formation,represented by the 18 P_(3)TW3,was formed in the late period of the basin,the main sedimentary age is Ordovician-Silurian,and the latest strata may extend to Early Devonian.Combined with the regional geological background,Baoshuping Formation was formed in the tectonic environment of the back-arc extensional basin caused by the northward subduction of Shangdan Ocean in Early Paleozoic.

关 键 词：北秦岭 二郎坪群 抱树坪组 碎屑锆石 LA-MC-ICP-MS锆石U-Pb定年 

分 类 号：P597[天文地球—地球化学]