Rodinia超大陆裂解、Sturtian冰期事件和扬子地块东南缘大规模锰成矿作用

扬子地块东南缘是我国南华纪“大塘坡式”沉积型锰矿的重要富集区,南华纪大规模锰矿成矿作用与Rodinia超大陆裂解形成的裂谷盆地、Sturtian冰期-间冰期的气候事件具有密切关系。南华纪裂谷盆地呈北东东向展布,可分为地垒、地堑和次级地垒、地堑,锰矿主要形成于裂谷盆地的地堑区的次级地堑中。Sturtian冰期之后,冰后期经历了小冰期和小间冰期的气候波动,锰矿受这种气候波动影响,推测小冰期的富氧的寒冷海水受温度-密度环流影响进入海底,促使原生氧化锰矿的形成,之后准同生交代形成菱锰矿。冰期(或小冰期)海底的天然气水合物在冰后期(小间冰期)的泄漏促使了菱锰矿的形成。因此华南扬子地块东南缘大规模锰矿成矿作用受原型裂谷盆地和冰期-冰后期气候波动的双重影响。 

Linking the Cryogenian Manganese Metallogenic Process in the Southeast Margin of Yangtze Block to Break-up of Rodinia Supercontinent and Sturtian Glaciation

The metallogenic process of Cryogenian Datangpo-type manganese deposit in the southeast margin of Yangtze Block is closely related to the development of Nanhua Rift Basin and Sturtian glaciations interglaciation.Accompanying with the break-up of Rodinia supercontinent,the Nanhua Rift Basin distributed in NEE trend,it can be divided into graben and horst and each graben can be further divided into subgraben and subhorst.The manganese deposit formed in the subgrabens within the graben area.After the Sturtian glaciation,cold events disturbed the warming process and both cold and oxidized freshwater came from the melted glacier.Cold and oxidized seawater generated from cold events could lead to the oxidation of the bottom water in the basin.Dissolved Mn2+ in the bottom water was then oxidized to Mn oxides and hydroxides and precipitated into the sediments.In early diagenesis stage,the organic materials reacted with Mn oxides and hydroxides and formed rhodochrosite.We suggest that methane leaking in post-glaciation accelerated this metallogenic process.The Mn metallogenic process in the Southeast margin of Yangtze Block is controlled by the original rift basin structure and paleoclimatic fluctuations in Sturtian glaciation and post-glaciation.