摘要: 扬子陆块北缘大洪山地区莲沱组是华南新元古代中期重要的地层单元，其形成时期和Rodinia超大陆裂解具有耦合性，与第一次雪球地球Sturtian冰期启动时间具有先后性，但其沉积时限和物源仍需深入研究确定，从而为解剖这些重大地质历史事件提供基础性支撑。本文对该区域莲沱组砂岩的碎屑锆石进行了U-Pb年代学分析，莲沱组沉积时限为ca. 800–714 Ma；碎屑锆石年龄显著峰值为ca. 2500 Ma、ca. 2000 Ma、ca. 880 Ma和ca. 820 Ma，次要峰值为ca. 780 Ma；结合古流向、砾石成分和沉积相展布特征分析，研究区莲沱组物源来自下伏地层打鼓石群和花山群沉积的再旋回以及扬子陆块北缘的太古代至新元古代岩浆岩，物源主体来自研究区北东方向。同时，鄂西地区、鄂东南至赣西北地区、鄂西南至湘北地区和鄂北大洪山地区主体具有相似的太古代、古元古代和新元古代碎屑锆石年龄峰值，根据扬子陆块北缘-东南缘岩浆岩分布特征，指示扬子陆块区域上莲沱组物源主体具有北-北东向供给。
Provenance analysis of the Liantuo Formation in Dahongshan area, the notrhern Yangtze Block: evidence from sedimentology and detrital zircon U-Pb chronology
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Abstract: The Liantuo Formation is a key mid-Neoproterozoic stratigraphic unit in the Dahongshan area of Yangtze Block, South China. Its deposition time is coupled with the breakup of the Rodinia supercontinent, and it is the last sedimentary layer before the Sturtian ice Age of the first snowball Earth. However, its deposition time and provenance need to be further studied and to provide fundamental support for dissecting these major geological historical events. Here, we analyzed detrital zircons U-Pb chronology from Liantuo Formation sandstone in this area, which shows sedimentary time is ca. 800-714 Ma and major peaks of detrital zircons are ca. 2500 Ma, ca. 2000 Ma, ca. 880 Ma, and ca. 820 Ma, and the secondary peaks are ca.780 Ma. Combined with the characteristics of paleo-flow direction, gravel composition, and sedimentary facies distribution analysis, the provenance of the Liantuo Formation in the study area is from the depositional recycle of the Dagushi Group and Huashan Group in the lower strata and the Archean to Neoproterozoic magmatic rocks in the northern Yangtze Block, and it is mainly from the northeast direction of the study area. Meanwhile, the western Hubei, southeastern Hubei to northwestern Jiangxi, southwest Hubei to northern Hunan, and Dahongshan of the northern Hubei areas have similar detrital zircon age peaks of Archean, Paleoproterozoic, and Neoproterozoic. And according to the distribution characteristics of magmatic rocks in the north and southeast margin of the Yangtze Block, which suggests that the provenance of the Liantuo Formation in the northern Yangtze Block has a north-northeast supply.