Palaeomagnetism of the Sibumasu and Indochina blocks: implications for the extrusion tectonic model

Abstract: The Jurassic-Cretaceous Kalaw redbeds of Myanmar yield a prefolding Late Cretaceous to Early Palaeogene magnetization which records c. 25-30 ° of clockwise (CW) rotation relative to the South China block. This corresponds to 10-15 ° CW relative to the Lower Cretaceous Khorat Plateau VGP. The data also show 5 ° of northward transport relative to the 100 Ma South China VGP or 12 ° relative to the Khorat Lower Cretaceous VGP. Similar CW rotations are measured in remagnetized Palaeozoic arbonates in Peninsular Thailand and Langkawi Island, Malaysia. These block motions most likely took place between the Late Cretaceous and the Late Oligocene. These and other recently published ata have several implications for the extrusion tectonic model: (i) Sundaland has only rotated 25-30 ° CW relative to South China during the Tertiary; (ii) southeastward t anslation is only 300-500 kin; and (iii) Sundaland is composed of smaller sub-blocks, some of which have moved northward. This is interpreted toindicate that deformation ofthe Sibumasu block is dominated by the oblique subduction of the Indian Ocean Plate while deformation of the Indochina block is dominated by extrusion, in turn driven by convergence between th Indian Craton and Eurasia. SE Asia has been located at the intersection o