A preliminary Upper Triassic paleomagnetic pole for the Khorat plateau (Thailand): consequences for the accretion of Indochina against Eurasia

Abstract

We report new paleomagnetic results from the Upper Triassic (Norian) Huai Hin Lat Formation at the base of the Khorat Group in Central Thailand. Five sites of conglomerate, sandstone and limestone reveal a stable component of magnetization ( D = 43°, I = 43°; α 95 = 7.5°). We argue that this component is of primary origin on the basis of a positive fold test, observation of both normal and reversed directions and a reported magnetostratigraphy from Middle Triassic to Cretaceous. The new Triassic pole yields, together with published younger poles, a Mesozoic apparent polar wander path for Indochina. This unit is found to have remained at tropical northern latitudes since the Upper Triassic. Comparison with Eurasian poles reveals 1650 ± 850 km of SW-NE convergence and 15° ± 10° of counterclockwise rotation between 205 and 160 Ma. Two mechanisms are discussed to account for this motion. The first one implies the closure of an oceanic basin to the north of the South China block. The second one involves post-welding intracontinental deformation.