A palaeomagnetic study of the Middle Permian and Middle Triassic limestones from Shan State, Myanmar: Implications for collision of the Sibumasu Terrane and Indochina Terrane

摘要

We report herein a new palaeomagnetic study on the Middle Permian and Middle Triassic limestones from Shan State of eastern Myanmar, aiming to resolve the spatial location of the Sibumasu Terrane during the collision of tectonic blocks in Southeast Asia and to constrain the timing of convergence between the Sibumasu Terrane and Indochina Terrane. Based on the rock magnetic and palaeomagnetic experiments, three stable characteristic remnant magnetizations are recognized from limestone specimens of Middle Permian and Middle Triassic age. The characteristic Component C of the Middle Permian limestone passed the fold test at 95% confidence level, indicative of a pre-folding origin. The mean direction of this component is D = 10.7 degrees, I = 17.9 degrees (kappa = 130.3, alpha(95) = 10.8 degrees) before and D = 13.7 degrees, I = -25.3 degrees (kappa = 1894.9, alpha(95) = 2.8 degrees) after tilt correction, corresponding to a palaeomagnetic pole at 254.1 degrees E, 53.2 degrees N (A(95) = 1.7 degrees). This suggests that the Sibumasu Terrane was placed at a palaeolatitude of similar to 13.0 degrees S during the Middle Permian. The Component C separated from the Middle Triassic samples also passed the fold test with a mean direction of D = 207.3 degrees, I = -8.3 degrees (kappa = 12.9, alpha(95) = 6.2 degrees) before tilt correction and D = 205.6 degrees, I = -33.5 degrees (kappa = 27.1, alpha(95) = 4.2 degrees) after tilt correction, corresponding to a palaeomagnetic pole at 187.3 degrees E, 65.8 degrees N (dp/dm = 2.7 degrees/4.8 degrees). This implies that the Sibumasu Terrane was located at a palaeolatitude of similar to 18.3 degrees N during the Middle Triassic. Based upon the detailed palaeomagnetic analysis, this study supports the view that the collision of the Sibumasu Terrane and Indochina Terrance occurred during or before the Middle-Late Triassic times.