米仓山地区早寒武世仙女洞组沉积物源新认识:沉积学、重矿物和碎屑锆石年代学的证据
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中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室,中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室;中国地质大学(北京),中国地质科学院矿产资源研究所国土资源部成矿作用与资源评价重点实验室,中国石油集团测井有限公司长庆事业部

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New Insights into Provenance of Early Cambrian Xiannüdong Formation in the Micangshan Area: Evidence from Sedimentology,Heavy Mineral and Detrital Zircon Chronology
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MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS,MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS; China University of Geosciences, Beijing,MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS; China University of Geosciences, Beijing,Changqing Division, China Petroleum Logging CO.LTD.

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    摘要:

    长期以来,一直认为米仓山地区早寒武世地层主要由汉南古陆和/或摩天岭古陆提供沉积物,实际并非如此。米仓山地区早寒武世仙女洞组主要由鲕粒灰岩以及角砾灰岩等组成。本文根据沉积相时空展布、交错层理恢复的物源方向、重矿物以及碎屑锆石LA-ICP-MS U-Pb测年,综合探讨仙女洞组的物源方向以及物源区。沉积相时空展布和古流向表明,仙女洞组的物源主要来自西北和西南方向,非前人判断沉积物来自东北和/或西北方向。碎屑重矿物锆石、磷灰石、白钛石、铬尖晶石和磁铁矿组合表明物源主要来自于岩浆岩,部分为基性岩浆岩。对仙女洞组3件样品碎屑锆石U-Pb年龄分析,获得172组U-Pb有效年龄。碎屑锆石的谐和年龄表明,物源主要集中在744~896Ma和1755~2493Ma。综合相展布、古水流、重矿物组合以及碎屑锆石测年,仙女洞组的物源主要来自:① 西北方向,摩天岭古陆的碧口群、横丹群和鱼洞子群的火山-沉积岩以及新元古代侵入岩;② 西南方向,主要为康滇古陆的花岗岩、流纹岩、辉绿岩等。

    Abstract:

    It has long been regarded that the Lower Cambrian rocks were mainly from Hannan Oldland and/or Motianling Oldland in the Micangshan area, but this idea may be challenged. The Xiannüdong Formation in the Micangshan area consists of oolitic limestone, limestone breccias, and nodular limestone. According to sedimentary facies distribution, paleocurrent direction restored by cross bedding, heavy mineral assemblages and detrital zircon LA-ICP-MS U-Pb dating, we comprehensively analyzed the source areas of the Xiannüdong Formation. The temporal and spatial distribution of sedimentary facies and the direction of paleocurrents indicate that the provenance direction of the Xiannüdong Formation mainly came from the northwest and southwest, not from northwest and/or northeast judged by other predecessors. The assemblage of detrital heavy minerals, including zircon, apatite, leucoxene, chromium spinel and magnetite indicates that the sediments mainly derived from magmatic rocks, and partly from mafic magmatic rocks. LA-ICP-MS U-Pb dating for three samples of detrital zircons from the Xiannüdong Formation yielded 172 sets of effective ages. The concordia ages of detrital zircons indicate that the provenance was mainly from 744~896 Ma and 1755~2493 Ma rocks. Combined with facies distribution, paleocurrent directions, heavy mineral assemblages and detrital zircon dating, it can be concluded that the Xiannüdong Formation derived mainly from (1) the Motianling Oldland in northwest, which includes volcano-sedimentary rocks of the Bikou Group, Hengdan Group and Yudongzi Group, and Neoproterozoic intrusive rocks, and (2) the Kangdian Oldland in southwest, which consists of granite, rhyolite and diabase.

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张英利,贾晓彤,王宗起,陈木银.2018.米仓山地区早寒武世仙女洞组沉积物源新认识:沉积学、重矿物和碎屑锆石年代学的证据[J].地质学报,92(9):1918-1935.
ZHANG Yingli, JIA Xiaotong, WANG Zongqi, CHEN Muyin.2018. New Insights into Provenance of Early Cambrian Xiannüdong Formation in the Micangshan Area: Evidence from Sedimentology, Heavy Mineral and Detrital Zircon Chronology[J]. Acta Geologica Sinica,92(9):1918-1935.

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  • 收稿日期:2017-08-04
  • 最后修改日期:2018-07-15
  • 录用日期:2017-12-04
  • 在线发布日期: 2018-09-11
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