Tectonic Evolution And Paleoposition Of The Baoshan And Lincang Blocks Of West Yunnan During The Paleozoic

Detrital zircon U-Pb dating and Hf isotope analysis have been evidenced to be effective for reconstructing paleography and tectonic evolution of different continental blocks/terranes. Our new detrital zircon U-Pb and Hf isotopic results combined with literature data for the Paleozoic (meta) sedimentary rocks in the Baoshan and Lincang Blocks provide crucial constraints on the paleogeographic position and tectonic affinity of these blocks during Paleozoic times. The Lincang and Baoshan Blocks were linked with each other during Early Paleozoic times, located on the northern margins of Australia and India in Gondwana, respectively. But a rift-related ocean basin could likely have existed between these two blocks although they were still attached to East Gondwana during Middle Devonian-Early Permian times. In contrast, the Simao-Indochina Block had rifted from East Gondwana at least before the Late Ordovician as reflected by their young age cluster at similar to 450 Ma that is distinct from the characteristic Pan-African event (600-520 Ma) in Gondwana. Therefore, the Lincang Block did not represent a continental arc of the Simao Block before the Early Permian, but rather it rifted from the northern margin of Australia Gondwana in the Early Permian and subsequently as an independent block drifted northward to the west side of the Simao Block. Taken together, we propose that the Changning-Menglian Tethys Ocean was a long-lived ocean developing successively at least from the Late Ordovician to the Permian and that the southern continuation of the Lincang Block is the Inthanon zone rather than the Sukhothai zone.