思茅地块西缘龙洞河组放射虫动物群及其地质意义

Radiolarian Fauna from the Longdonghe Formation at the Western Margin of the Simao Massif and its Geologoical Significance

思茅地块西缘的龙洞河组为一套火山—沉积岩系 ,原定时代为晚石炭世 ,被认为属南澜沧江洋弧后盆地沉积。现在龙洞河组层状硅质岩断片中发现了晚泥盆世放射虫化石 ,在细碧角斑岩之硅质岩夹层中发现了早石炭世放射虫动物群 ,表明龙洞河组不全是晚石炭世地层 ,而是由晚古生代的一些地层断片组成。思茅地块西缘深水沉积盆地的演化始于泥盆纪 ,应为滇西南古特提斯多岛洋的一个分支 ,向南可能与泰国难河带对比。

The Longdonghe Formation,at the western margin of the Simao massif is made up of volcanic, volcaniclastic and sedimentary rocks and was assigned to Late Carboniferous—Early Permian and thought to be sediments in the back arc basin. Two radiolarian faunas have been recently obtained from the bedded siliceous rocks in the Dawazi section and from the bedded chert intercalations of spilite keratophyre sequence in the Dapingzhang section. These radiolarian faunas are assigned to the Late Devonian and Early Carboniferous respectively, which indicate that the Longdonghe Formation is composed of some Late Devonian to Early Permian thrust slices, not continuous Late Carboniferous to Early Permian lithostratigraphy. In tectonic palaeogeography, the western margin of the Simao massif is characterized by deep water rift basin during Late Devonian to Early Carboniferous and possibly is a branch of the Palaeotethyan Archipelagoes ocean in West Yunnan.The branch may be the northern extension of the Nan River belt in Northeast Thailand.