New understanding and achievements in regional geological survey of 1∶250 000 Huaihua sheet, Hunan province

In this regional geological survey project, 1∶250 000 Huaihua sheet is located in the southeastern margin of the Yangtze block, and it is divided into four tectonic units from west to east: Wuling fault-bend fold belt, Yuanma basin, Xuefeng thrust belt and Shaoyang depression fold belt. Through investigation, the sedimentary relationship and its boundary between Banxi Group and Gaojian Group are found out in the study area. It is proposed that a depression formed in Chang’an stage of Nanhuan Period lies at the junction of Lianshao Basin and Xuefeng Mountain. The intrusive stages are divided, and the sequence of magmatic evolution is established. Combined with isotopic dating data, the intrusive ages and erupted ages of Baimashan-Longshan complex and its surrounding granites are ascertained. The tectonic deformation characteristics and tectonic patterns of Xuefeng orogenic belt are identified; the formation and evolution process of Yuanma basin are established.