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

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 (2 sigma), which provides the first robust evidence for the Cambrian crust in Upper Peninsula of Thailand. The zircon epsilon Hf-(T) values range from +3.7 to -6.1 with model ages (T-DM(C)) 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. (C) 2013 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.