Detrital zircon U–Pb and Hf analyses of Silurian–Devonian sediments in the Sukhothai Terrane, northern Thailand: Implications for the middle Paleozoic arc belt

The Sukhothai Terrane in northern Thailand comprises a continental basement and a Permo-Triassic magmatic arc related to the subduction of the main Paleo-Tethys Ocean. The Donchai Group represents the oldest sedimentary sequence of the Sukhothai Terrane and consists mainly of meta-sandstone, quartzo-feldspathic schist, phyllite and silty slate. This paper presents new detrital zircon U–Pb geochronology and Lu–Hf isotope data, and geochemical results for the sedimentary rocks of the Donchai Group to elucidate the depositional age, provenance and nature of the group. The youngest detrital zircon ages (433–403 Ma) suggest that the Donchai Group was accumulated between 433 Ma and 368 Ma, revealing Silurian–Devonian arc magmatic rocks on the western margin of the Sukhothai Terrane. Sediments of the Donchai Group were sourced from both the continental basement and a Silurian–Early Devonian magmatic arc, suggesting a depositional setting on the continental slope of a back-arc basin along the western flank of the Sukhothai Terrane. The Silurian–Devonian arc belt in SW China likely extend to the Chiang Rai region, to the west of the Sukhothai Terrane, northern Thailand, revealing the northward subduction of the Proto-Tethys Ocean along the western Simao and Sukhothai margin during the middle Paleozoic. The inferred arc and back-arc configuration of the Proto-Tethys in northern Thailand is comparable with that recently established in Yunnan, SW China. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6858373