Redefinition Of The Southern Border And Oceanic And Continental Framework Of The Southern Proto-tethys Ocean

The Tibetan Plateau and the western Yunnan Sanjiang region are an important research platform for studying Tethys Tectonic Domain, where record aboundant geological processes of Proto-Tethys, Paleo-Tethys and Neo-Tethys oceans. In addition, the evolution of the Proto-tethys Ocean had led to a massive transition of the east Asia and even the global ocean continental framework, being an important link and tectonic setting in the process of reconstruction pattern of the Pangea Supercontinent. As the southern branch of the Proto-tethys Ocean, the redefinition of the southern border of the Proto-tethys Ocean and the determination of the oceanic-continental framework in the southern Proto-tethys Ocean have great significance for us to understand of the evolution of the Proto-tethys Ocean and Pangea assembly in east Asia.The southern Proto-tethys Ocean had widely experienced Caledonian tectonism, but the related geologic records, such as ophiolite, island arc volcanic rocks are rare, and the related reports are also relatively few. This paper, by means of multidisplinary synthesis, discriminates further the geological records of the southern Proto-tethys Ocean reproted by previous results, finally figures out the outline of the southern boundary of the Proto-tethys Ocean and further determines its oceanic and continental framework, based on understanding and absorbing previous geological data about the southern Proto-tethys Ocean. By the comparison of the basements of the microcontinents, ophiolites, island-arc magmatic rocks, HP-UHP metamorphic rocks and detrital zircon age spectrum and lithofacies paleogeography of the southern Proto-tethys Ocean, this paper has got several conclusions as follows:(1) The basements of Southern Qiangtang Terrane, Lhasa Block and Tengchong-Baoshan Terrane belong to Gondwana Supercontinent, while the Northern Qiangtang Terrane, and others are the basements affinitive to the Yangtze Basement, illustrating that the southern bouder of Proto-tethys Ocean (the northern boundary of Gondwanaland-the northern boundary affected by pan-african events) is the Lungmu co-Shuanghu Suture Zone-Changning-Menglian Suture Zone.(2) The Lungmu co-Shuanghu Suture Zone and the Changning-Menglian Suture Zone developed at least two stage of ophiolite-early Paleozoic and late Paleozoic (ophiolites developed along the Bangong Co-Nujiang River Suture Zone are newer), therefore, during the early Paleozoic two suture zones should be the same one on behalf of the most southern boundary of the Proto-tethys Ocean.(3) The early Paleozoic (late Cambrian-early ordovician) magma activity in the Lhasa Terrane, The Tengchong-Baoshan Terrane and the Southern Qiangtang Terrane had all developed. However, there have not been records of early Paleozoic magmatic activity reported in Australia. In the Neoproterozoic, records of magma activity in the Lhasa Terrane and that of northern Australia are consistent, but there is no record in Himalayas and India during the same period. All of these suggests that during the early Paleozoic, the Southern Qiangtang Terrane, the Lhasa Terrane and the Tengchong-Baoshan Terrane had been located in a same active continental margin on the northern rim of Gondwana Supercontinent and the southern margin of the Proto-tethys Ocean as a string island arcs.(4) The metamorphic ages got from the Lungmu co-Shuanghu HP-UHP metamorphic belt in the central Qiangtang Terrane and the Sumdo HP-UHP metamorphic belt in the central Lhasa Terrane are in late paleozoic(probably Permian), representing the closure time of the Plao-tethys Ocean. Thus, it shows that the Proto-tethys Ocean and the Plao-Tethys Ocean had a continous evolution.(5) The detrital zircon spectra reveal that in early Paleozoic the Lhasa Terrane and the Tengchong-Baoshan Terrane have an affinity with Australia mainland, and so does the Southern Qiangtang Block and the Himalayan India landmass. While the Southern and Northetn Qiangtang terranes were separated during the early Paleozoic.(6) During the early Paleozoic, the lithofacies paleogeography of the Tibetan Plateau and the western Yunnan Sanjiang region displays the evolution of the Proto-tethys Ocean, revealing evolutionary inheritage of the Proto-Tethys Ocean and the Paleo-Tethys Ocean. During this period, the paleontology of the Tengchong-Baoshan Block was similar with that of Gondwana Supercontinent and different from that of the Yangtze Block. The Southern Qiangtang Terrane and the Lhasa Terrane both developed fauna of cold water that had affinity to that of Gondwana Supercontinent.