EARLY PALEOZOIC TECTONIC EVOLUTION AND PROCESSES IN THE WEST SEGEMENT OF THE NORTHERN PROTO-TETHYS TECTONIC DOMAIN, EAST ASIA

The Proto-Tethys Ocean is a complex ocean that rifted from Rodinia. Its closure resulted in the Proto-Tethys Tectonic Domain, which is located between north of the Burma Thailand/Baoshan microblocks and south of the Tarim-North China Block in the late Early Paleozoic. The Proto-Tethys Tectonic Domain contains many other blocks/microblocks.However, there are arguments on the boundaries of the Proto-Tethys Tectonic Domain, attributes and affinities of different continents and micro-blocks, and the assembly processes of the blocks. This is a key to plate reconstruction in East Asia for understanding the pre-Pangea tectonic background in the Early Palaeozoic. This study reached four conclusions:

1．The Early Paleozoic Proto-Tethys Ocean in China is characterized by an archipelagic ocean with assembly of multi-micro-continental blocks. The opening and closing are characterized by siccior-like refiting from east to west and subduction from west to east, respecitively.

2． According to exhumation time of the eclogites, the South Qilian Ocean subducted southward (460 ~ 420 Ma). After the closure of the South Qilian Ocean, the Kunlun Ocean closed at 428 Ma, the last closure one is the North Qilian Ocean (420 ~ 410 Ma). The northern boundary of the Proto-Tethys Ocean has always been in the North Qilian Ocean.

3．The evolution of the Tethys Ocean can be summarized as the processes of numerous blocks rifting away from the northern Gondwana margin. These blocks had affinities with the Yangtze Block from Sinian to Early-middle Cambrian. The Alxa Block had affinities with the North China Block from Neoproterozoic to Early Paleozoic.

4．Structural geological data, combined with geochronological data and others, revealed that the North Qilian Ocean had a polarity of southward subduction while the South Qilian Ocean was opened as a back-arc basin under this southward subduction. The South Kunlun Ocean with a northward subduction then subducted later than the southward subduction of the North Qilian Ocean, developing the Middle Kunlun Ocean as a back-arc basin which devoloped into one ocean in late Paleozoic. Then the Middle Kunlun Ocean, due to its northward subduction, resulted in the Qimantage back-arc basin.

Acknowledgement: This research was financially supported by NSFC grants (41190072, 41325009 and 41190070).