Detrital zircon LA-ICP-MS U-Pb isotopic ages of the Triassic Lampang Group in ChiangRai area, Thailand and their geological significance

There have long been many controversies about the correlations between Paleo-Tethyan geosutures in western Yunnan Province of China and Southeast Asia. In this paper, the petrography, geochronology, and geochemistry were studied by using four samples collected from the Triassic Lampang Group in ChiangRai area. The results suggest that the source rocks of the clastic rocks are basic-intermediate rocks, with the addition of some felsic rocks. The tectonic setting of the source area is island arc. The oldest zircon U-Pb isotopic age is 3269Ma±29Ma. Other ages show three significant peaks: 280～250Ma, 500～440Ma and 1200～1100Ma. These age peaks indicate that the main sources of the Triassic Lampang Group in the study area are ChiangRai volcanic belt and pre-Devonian metamorphic rocks in the west, with the supply of small amounts of clastic materials from the volcanic arc belts in the eastern part of the study area. The comparison between detrital zircon age spectrums shows that, before the Proto-Tethys phase, there were similar tectonic-thermal events in Lampang terrane and Western Australia. In the Proto-Tethys phase and the subsequent period, the tectonic-thermal events in Lampang terrane and Yangtze plate were similar to each other, indicating that the main Paleo-Tethys ocean basin should be in the west of Lampang terrane, which supports the viewpoint that ChiangMai tectonic zone represents the main ocean basin of Paleo-Tethys.