On the Banxi Group and its related tectonic problems in south China

Abstract

In south China, the Banxi Group is a stratigraphic unit. It has attracted wide attention since Hsu (1980, 1987) and Hsu et al. (1987, 1988) interpreted it as a Banxi Melange in their tectonic model of ‘Huanan Alps’ in the 1980s. Our geological studies lead us to believe that it is reasonable to redefine the Banxi Group as a lithostratigraphic unit composed of the Madiyi and Wuqiangxi Formations in the Xuefeng-Wuling mountain area. The Banxi Group in Hsu's Banxi Melange refers to the larger ‘Banxi Group’ as adopted in the 1960s and 1970s. The stratigraphic, tectonic, isotopic and paleontologic data clearly indicate that: (1) the Banxi Group has a normal sedimentary sequence; (2) the lower subgroup of the former larger ‘Banxi Group’ is a set of metamorphic rocks with ophiolite blocks and was formed before Sinian and not in the Mesozoic collision orogeny in south China (‘Huanan Alps’); (3) there is no structural window or klippe that can be taken as evidence for a ‘Huanan Alps’ as in Hsu's concept of a Banxi Melange. As a result, Hsu's concept is untenable, and there is no ‘Huanan Alps’ or Mesozoic collision orogeny between the Yangtze and Huanan blocks.