Coupled detrital zircon U–Pb and Hf analysis of the Sibumasu Terrane: from Gondwana to northwest Thailand

Abstract

The evolution of the Sibumasu Terrane forms a principal component in the history of the Tethys Oceans with the northward movement of Gondwana-derived terranes creating the Asian continent that we recognise today. While there are various reconstructions for the palaeoposition of the Sibumasu Terrane during the Proterozoic and Paleozoic, the terrane is commonly placed outboard of the northwest Australian margin in the Gondwanan supercontinent. In this study, U–Pb and Lu–Hf isotopic information has been collected from detrital zircons of Paleozoic and Mesozoic sedimentary rocks obtained from the Sibumasu Terrane in northwest Thailand. This is the first zircon Hf analysis from these sedimentary sequences. These new data are statistically and visually compared with data from Sibumasu, Indochina, Sukhothai, West Burma and Tethyan Himalayas terranes along with the terranes of China, India and Western Australia. Our detrital data are consistent with other published data indicating consistent sources across the Sibumasu Terrane, inconsistent with composite terrane reconstructions. However, temporally, the detrital ages change from older Paleozoic sedimentary sequences (sourcing zircons from Neoproterozoic and older “Gondwanan” sources) to latest Permian-Triassic sedimentary units with Indosinian zircon sources. This change is consistently reflected in this study through both the U–Pb ages and Hf signatures with Proterozoic age peaks characteristic of Gondwana and younger Indosinian sources being consistent with granitoids emplaced through the amalgamation of Thailand. The temporal changes in the isotopic systems reflect the movement of the Sibumasu Terrane from the northwest Australian margin of Gondwana to its collision with the terranes of present-day Asia.