Tectonic Evolution And Processes In The West Segement Of The Northern Proto-tethys Tectonic Domain

The Proto-Tethys Ocean is a complex one that rifted from Rodinia. Its closuredeveloped the Proto-Tethys Tectonic Domain which is positioned north of the BurmaThailand/Baoshan microblocks and south of the Tarim-North China Block in the lateearly Paleozoic. The Proto-Tethys Tectonic Domain contains many otherblocks/microblocks such as the Qilian, the Qaidam, the Yangtze, the Cathaysia, theIndosinian and the Lanping-Simao and others. In the northwestern part of theProto-Tethys Tectonic Domain, a series of ophiolite belts or high-ultrahigh pressurebelts developed along the north borders of the Qilian and the Qaidam in the late earlyPaleozoic. These geological records indicate that the Proto-Tethys Ocean experienceda complicated configuration of ocean-continent distribution and processes ofdispersion and convergence during the Paleozoic. However, there are arguments onthe boundaries of the Proto-Tethys Tectonic Domain, attributes and relations ofdifferent continents and micro-continentals, and the assembly processes of the blockswith the North China Block in the late early Paleozoic.This is a key to the plate reconstruction for understanding the tectonic backgroundin the early Palaeozoic, which is the earlier time of the formation of the Pangeasupercontinent. This thesis will adopt the methods of field geological investigation,tectonics analysis, igneous petrology, sedimentology, geochemistry, deformtiongeochronology and others to study the following aspects in the northwest of theProto-Tethys Tectonic Domain, which are:(1) to define the northwest boundary ofthe Pro-Tethys Tectonic Domain;(2) to establish a affinity amongcontinents/micro-continents and ocean-land configuration in the northern Proto-Tethys Ocean;(3) to clarify the processes and the time of micro-continentsassembly in the northern Proto-Tethys Ocean.1．The early Paleozoic Proto-Tethys Ocean in China is characterized by anarchipelagic ocean with assembly of multi-micro-continental blocks. Its opening andclosing are different along some tectonic belts. Qilian Ocean westward to the northArkin ocean, the South Qilian Ocean westward to the south Arkin ocean, is marked bysiccior-like open from east to west; According to the contrast of formation times ofthe eclogites, the Proto-Tethys oceanic crust is marked by siccior-like subductionfrom west to east.2． According to exhumation time of the eclogites, the South Qilian Oceansubducted southward (460~420Ma), the northern boundary of the Proto-TethysOcean is still located in north of the North Qilian Ocean. After the closure of theSouth Qilian Ocean, the Kunlun Ocean closed at428Ma, the last closure one is theQilian Ocean (420~410Ma). The northern boundary of the Proto-Tethys Ocean hasalways been in the North Qilian Ocean.3．The evolution of the Tethy Ocean can be summarized as the processes ofnumerous blocks spliting from the northern Gondwana. Before Sinian have affinitieswith the Yangtze Block from Sinian to Early-middle Cambrian. The Alxa Block hadaffinities with the North China Block from Neoproterozoic to Early Paleozoic. Inshort, the affinities among the various micro-continental blocks, the North ChinaBlock and the Yangtze Block are changible through time.4．Structral geological data combined with deformation, geochronological data, arcmagmatism and sedimentary rock distribution, revealed that the North Qilian Oceanwith a polarity of southward subduction. While the South Qilian Ocean spreaded as aback-arc basin with a southward subduction, and the ocean exsisted for a very shorttime. The Kunlun Ocean then spreaded after the subduction of the North Qilian Ocean(later a little) with a southward subduction, and formed the Middle Kunlun Ocean as aback-arc basin which devoloped into ocean at the late Paleozoic. Then the Qimantageback-arc basin began to form with northward subduction.