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湖北大洪山地区花山群六房咀组之上不整合覆盖了一套紫红色砂-砾岩。这套岩石的沉积时代存在争议,一种观点认为是南华纪早期;另一种观点认为是晚侏罗世。利用LA-ICP-MS分析技术,对这套碎屑沉积岩进行了碎屑锆石U-Pb测年,获得有效年龄数据125组,年龄值变化范围较大(3223~771Ma),主要集中于新太古代末—古元古代早期(约2500Ma)、古元古代(约2000Ma)和新元古代(约800Ma)3个时间段。对比鄂东南地区和三峡地区莲沱组岩石学特征和碎屑锆石年龄分布特征,认为其具有相似的物源,这套岩系沉积时代应该为南华纪早期而非晚侏罗世。综合分析扬子地块的前寒武纪年龄,认为扬子地块可能存在大量未岀露的新太古代末—古元古代早期(约2500Ma)基底,约2500Ma的岩石应该是扬子地块深部基底的重要组成部分。扬子地块存在广泛的古元古代(约2000Ma)岩浆活动,这期岩浆活动可能是Columbia超大陆聚合在扬子地块的响应。新元古代(约800Ma)扬子地块北缘存在Rodinia超大陆裂解同期裂谷,裂谷内基性岩可能为大洪山地区南华纪地层中基性岩砾石的物源。
The unconformity above the Huafang Group Liuhuzui Formation in the Dahongshan area of Hubei Province covers a set of fuchsia sand-conglomerate. The depositional age of this rock is controversial, one view is that of the South China Era; the other view is that of the Late Jurassic. U-Pb detrital zircon dating of this clastic sedimentary rock was performed using LA-ICP-MS analysis technique, and 125 sets of effective age data were obtained, ranging in age from 3223 to 771Ma, mainly focusing on new Late Paleozoic - Early Paleoproterozoic (about 2500 Ma), Paleoproterozoic (about 2000 Ma) and Neoproterozoic (about 800 Ma) three time periods. Comparing the petrological characteristics and age distribution of detrital zircons of the Lintuo Formation in the southeastern area of Hubei Province and the Three Gorges area, it is considered that they have similar provenance. The sedimentary age of this series of rocks should be the early Nanhua, not the Late Jurassic. Based on a comprehensive analysis of the Precambrian age of the Yangtze block, it is concluded that there may be a large amount of undisclosed Neo-Archean-Early Paleoproterozoic (about 2500 Ma) basement in the Yangtze block, and that the approximately 2500 Ma rock should be important for the deep basement of the Yangtze block component. There is a wide range of Paleoproterozoic (about 2000 Ma) magmatism in the Yangtze block. The magmatic activity may be the response of the Columbia supercontinent in the Yangtze block. In the northern margin of the Yangtze block of the Neoproterozoic (about 800 Ma), the Rodinia supercontinent rift exists in the northern margin of the Yangtze block. The basic rocks in the rift may be the source of the basic rock gravels in the Nanhuaji formation in the Dahongshan area.