引用本文:毛帆, 裴先治, 李瑞保, 李佐臣, 裴磊, 刘成军, 赵少伟, 高峰, 陈有炘, 周海.扬子板块西北缘碧口微地块南华系碎屑锆石U-Pb年龄及其物源示踪[J].沉积与特提斯地质,2021,41(1):41-57.[点击复制]
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扬子板块西北缘碧口微地块南华系碎屑锆石U-Pb年龄及其物源示踪
毛帆,裴先治,李瑞保,李佐臣,裴磊,刘成军,赵少伟,高峰,陈有炘,周海
0
(1. 长安大学地球科学与资源学院, 陕西 西安 710054;
2. 西部矿产资源与地质工程教育部重点实验室, 陕西 西安 710054)
摘要:
扬子板块西北缘碧口微地块红岩沟地区碧口群火山岩系之上发育有南华—震旦纪沉积盖层,但南华系的沉积时代尚缺乏依据,其物源及构造背景也仍无定论。本文采用LA-ICP-MS锆石U-Pb测年方法,对南华系上部含砾岩系中的长石砂岩进行了碎屑锆石测年研究,结果表明碎屑锆石的年龄可以分为两组:(1)新元古代晚期年龄组(750~800Ma),峰值年龄为795Ma;(2)新元古代早中期年龄组(820~920Ma),该组有明显峰值,峰值年龄为850Ma。碎屑锆石最小年龄组平均年龄为750Ma,即南华系上部含砾岩系沉积时代不老于750Ma,结合地层序列中的层位关系,认为该地层的沉积时代可能为晚南华世。综合研究认为,南华系上部含砾岩系物源具多源性,主要来自扬子板块西北缘碧口微地块内部和南侧后龙门山构造带、汉南-米仓山微地块的新元古代中酸性岩浆岩,北侧勉略构造带出露的岩浆岩可能也为该地层提供了少量的物源,其沉积事件对应于新元古代中晚期(~810Ma)碧口微地块及扬子板块西北缘后碰撞-裂解阶段。
关键词:  扬子板块西北缘  碧口微地块  南华系  碎屑锆石  LA-ICP-MS锆石U-Pb定年
DOI:10.19826/j.cnki.1009-3850.2020.10009
投稿时间:2020-07-23修订日期:2020-10-20
基金项目:国家自然科学基金项目(项目号:41872233、41872235);陕西省自然科学基金项目(项目号:2020JQ-353、2019JM-312);中央高校基本科研业务费资助项目(项目号:300102279108)
The LA-ICP-MS U-Pb dating of detrital zircons from the Nanhua System in Bikou Terrane, northwestern margin of Yangtze Block
Mao Fan, Pei Xianzhi, Li Ruibao, Li Zuochen, Pei Lei, Liu Chengjun, Zhao Shaowei, Gao Feng, Chen Youxin, Zhou Hai
(1. School of Earth Science and Resource, Chang'an University, Xi'an 710054, Shanxi, China;
2. Key Laboratory of Western Mineral Resource and Geological Engineering of Ministry of Education, Xi'an, 710054, Shanxi, China)
Abstract:
The Nanhua System occurs in Hongyangou area, northwestern margin of Yangtze block. Its age is unclear, and the tectonic setting under which the Nanhua System was deposited is in dispute. In this paper, detrital zircons from the feldspar sandstone in the upper Nanhua System are tested by LA-ICP-MS zircon U-Pb dating. The results show that zircons' U-Pb ages can be divided into two groups:the Late Neoproterozoic group (750~800 Ma), with a small peak at 795 Ma, and the Early and Middle Neoproterozoic group (820~920 Ma), with a main peak at 850 Ma. The weighted mean age of the youngest detrital zircons is 750 Ma, representing the maximum depositional age of the coarse-grained rocks of Upper Nanhua System. Considering the relationships of stratigraphic sequences, it is concluded that the depositional age of sedimentary strata of the Nanhua System was late Nanhua period, and it is proposed that the detrital materials of the Nanhua System are mainly from the Neoproterozoic intermediate-acid magmatic rocks in the Bikou terrane, the Hannan-Micangshan complex, and the Longmenshan tectonic belt in the northwestern margin of the Yangtze block, and less from magmatic rocks exposed in the Mianlue tectonic belt. It is suggested that The Nanhua System is the sedimentary response of the Bikou Micro-block to the late Neoproterozoic (~810 Ma) post-collision-crack event of the northwest margin of the Yangtze Block.
Key words:  northwestern margin of Yangtze block  Bikou terrane  Nanhua System  detrital zircon  zircon LA-ICP-MS U-Pb dating

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