First evidence of the Cambrian basement in Upper Peninsula of Thailand and its implication for crustal and tectonic evolution of the Sibumasu terrane

• U/Pb age of 502 Ma evidences the Cambrian basement in Thailand.
• Disperse Hf(T) in zircons suggests a mixed Proterozoic crust-mantle source.
• Isotopic similarity of Cimmerian granites implies a close paleogeographic association.
• This close paleogeographic association is along the Gondwana margin.

Although the Sibumasu terrane in Asia was previously considered to be composed of Phanerozoic rocks with Cambrian crystalline basement, no reliable or direct radiometric dating evidences of such crystalline basement was ever reported. Our new in-situ zircon U/Pb dating of the Khao Tao orthogneiss yields a concordant age of 501.5 ± 7.5 Ma (2σ), which provides the first robust evidence for the Cambrian crust in Upper Peninsula of Thailand. The zircon εHf(T) values range from + 3.7 to − 6.1 with model ages (TCDM) of 1244–1827 Ma, suggests a mixed crust-mantle source. The chemical similarity and spatial continuity of the Khao Tao orthogneiss with other pre-Neotethys marginal Eurasian and Sibumasu granitoids indicate the linear paleogeographic association under a similar magmatic arc-related regime along the Gondwana India–Australia margin as part of the Pan-African Orogeny system.

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