华夏地块西北缘南华系泗洲山组杂砾岩层成因、物源及区域对比

PROVENANCE AND SEDIMENT ARY FEATURES OF THE DIAMICTITE UNIT IN THE NANHUAN SIZHOUSHAN FORMATION IN THE NORTHWESTERN MARGIN OF THE CATHAYSIA BLOCK AND ITS CORRELATION

华夏地块西北缘与扬子地块东南缘南华纪地层对比影响到对大地构造背景的认识。本文以华夏地块西北缘湘东南地区南华系泗洲山组下部含砾板岩层位为突破口,开展宏观及微观沉积结构、构造和碎屑物源研究,讨论该组含砾层位成因及物源特征并进行区域对比。结果表明,泗洲山组下部含砾板岩的宏观、微观沉积特征均指示其形成与冰川活动相关,最大沉积年龄为730—740 Ma,其成因和沉积年龄均与扬子地块东南缘长安组一致。综合前人的研究成果,利用标志层位,华夏地块西北缘与扬子地块东南缘南华系可以很好地对比。碎屑锆石物源研究结果表明,研究剖面泗洲山组底部石英砂岩物源为亲扬子型,而含砾层位物源有亲华夏型的混入。结合区域上其他相关研究成果,从南华纪至早古生代,亲华夏型物源在华南有一个持续向北西推进的过程。湘东南地区可以作为研究华夏地块与扬子地块南华纪地层对比的桥梁,为华南板块南华纪大地构造格局研究提供新的切入点。

Correlation of the Nanhuan System between the northwestern margin of the Cathaysia Block and the southeastern margin of the Yangtze Block affects our understanding of the regional tectonic background.In this work,the macro-and micro-sedimentary textures/structures of the lower diamictite unit of the early Nanhuan Sizhoushan Formation distributing in the northwestern margin of the Cathaysia Block,detrital zircon U-Pb ages of the basal quartz sandstone and the above-mentioned diamictite unit,and the origin of the diamictite unit and its provenance,were studied comprehensively.It could be concluded that the lower diamictite unit was resulted from glaciation and its maximum deposition age is 730-740 Ma,which is consistent to the Chang'an Formation in the southeastern part of the Yangtze Block.The provenance of the bottom layer of the Sizhoushan Formation is characteristic of pro-Yangtze type,and the provenance of upper diamictite unit is the mixture of pro-Cathaysia and pro-Yangtze types.A northwestwards progradation of the pro-Cathaysia type provenance during the late Neoproterozoic to early Paleozoic could be demonstrated based on the results of this study and other published data.The southeastern area of Hunan Province could be the transitional area for sedimentary correlation between the Yangtze and Cathaysia blocks.The results provide new insights for tectonic research of South China Block during the Nahuan.