Paleomagnetic study on the Mesozoic tectonic evolution of the Indochina Block

We report a combined paleomagnetic and U-Pb geochronologic study on sedimentary rocks from the Nam Phong, Phu Kradung, Phra Wihan and Sao Khua formations in the Nakhon Thai Basin, NW Thailand in order to provide independent constraints on the tectonic movement of the Indochina Block during the Mesozoic era. The detrital zircon U-Pb geochronologic analyses indicate the maximum allowable depositional age of the three formations to be similar to 208, similar to 154 and similar to 140 Ma, respectively. This constrains that the Phra Wihan Formation as well as the overlying Sao Khua Formation should have a deposition age of the Early Cretaceous. Our detrital zircon U-Pb age spectra for the three formations further ascertain the view that the Indochina Block experienced a sediment provenance transition during the Middle to Late Jurassic times. Combined with previous reliable paleomagnetic data from the Khorat Basin of Indochina, paleomagnetic analyses on the three sampling formations from the Nakhon Thai Basin yield three paleomagnetic poles, at 55. 9 degrees N/172.2 degrees E (A(95) =4. 6 degrees) for Late Triassic Nam Phong Formation, 61. 0 degrees N/182. 3 degrees E (A(95) = 6. 3 degrees) for Late Jurassic Phu Kradung Formation, and 67. 0 degrees N/192. 1 degrees E (A(95) = 3. 6 degrees) for Early Cretaceous Phra Wihan Formation, respectively. The site-mean directions of the characteristic remanence for the former two paleopoles passed the fold test at 95% confidence level and show a well regional consistency between the Khorat and Nakhon Thai basins, suggesting that they are very likely primary remanences, and consequently their corresponding paleomagnetic poles could be used as key poles for the construction of Mesozoic apparent polar wander path (APWP) for the Indochina Block. Thus, we construct a new Mesozoic APWP for the Indochina Block in the light of our new paleomagnetic results from the Nakhon Thai Basin of NW Thailand and reliable Mesozoic paleomagnetic results from the Khorat Basin in central Indochina. The new Mesozoic APWP of Indochina indicates that the significant southward movement of similar to 1200-1400 km since the Late Triassic of the Indochina Block was mainly occurred in the Mesozoic times. However, for the post-Late Triassic vertical-axis clockwise rotation of the Indochina Block, although the Cenozoic India-Asia collision and the continuous indentation of India into the Asian continent could result in a significant vertical-axis clockwise rotation of the Indochina Block, the significant southward movement of the Indochina Block during the Jurassic to Cretaceous times was also accompanied by a clockwise rotation of 18. 8 degrees +/- 17. 8 degrees.