LAUSR

Abstract The widespread granitic rocks of the Sibumasu terrane were emplaced during the collision of the Sibumasu and Indochina in the Triassic. Previous studies have suggested that each granite had a simple, single-step magmatic evolution. In situ LA-MC-ICP-MS U-Pb zircon dating of granites and gneiss from Thailand revealed the evolution of these rocks: Inherited zircon core ages (515 ± 130 Ma) from a granite of the Chonburi pluton in the Central-Granitoid Belt are coeval with an orthogneiss protolith age (513.6 ± 9.2 Ma) from Hua Hin area. Similar Cambrian ages were also reported from the Khao Tao area in southern Thailand. Moreover, there are a series of inherited zircon core ages from Neo-Proterozoic (1017 ± 43 and 984 ± 56 Ma), Ordovician (449 ± 26 Ma), Devonian (385 ± 15 Ma), Carboniferous (316 ± 12 Ma) to Permian (276 ± 31 and 266 ± 12 Ma). Taken together, these Neo-Proterozoic to Permian protolith ages are interpreted to represent the basement of the Sibumasu terrane in Thailand. Two magmatic zircon growth events can be distinguished at approximately (a) 241.8 ± 8.2 to 235 ± 12 Ma and (b) 230.6 ± 3.4 to 213.4 ± 3.0 Ma. We concluded that the Sibumasu and Indochina collision during the Triassic caused a two-step magmatic evolution of the granites of the Sibumasu terrane. The first magmatic crystallization during the Middle Triassic corresponded to the Sibumasu and Indochina collision, and the second magmatic crystallization during the Late Triassic was related to the late-collisional stage.