On Geodynamic Evolution of Simao Region (Southwestern Yunnan, China) during Late Paleozoic and Triassic

Over the last years, the Simao region, southwestern Yunnan, China, turned out to be a very promising target to elucidate plate tectonic processes around the Permian Triassic boundary within the Tethyan domain of Asia. New data from this area reveal that Upper Paleozoic compressional deformations occurred along the Lancangjiang and in areas to the east. Along Lancangjiang, an angular unconformity is exposed, which separates quartz phyllites—formed during a Carboniferous tectono metamorphic event—from Triassic red beds to roofing rhyolites. The acidic volcanics were often said to be remnants of a volcanic arc that was active during the Triassic subduction and closure of an oceanic realm along the Lancangjiang zone. According to our new data, however, these volcanics indicate most probably an Upper Triassic stage of rifting. In the Yunxian anticline (NW of Simao), an angular unconformity of intra Permian age is exposed where Carboniferous to lower Middle Permian strata, which were deposited in a rather deep basin, are unconformably overlain by a shallow marine sequence of upper Middle to Upper Permian sediments. The angular unconformity is of the same age as the syn orogenous sediments first described and dated from the Phetchabun region in Thailand and hence a convincing argument for a Late Variscan orogeny forming an extensive zone of mountain building that can be traced through the central parts of mainland Southeast Asia.