Chapter 5 - Paung Laung–Mawchi Zone

Abstract

The Paung Laung–Mawchi zone is a well-defined topographic feature that runs south–southeast for 250 km from near Kyaukse to east of the Mawchi tin-tungsten mine. The zone is up to a few kilometers wide and is important because it lies between the Shan Plateau to the east and Slate belt to the west; because it forms part of a longer zone that extends northeastward into Yunnan and southward southern Thailand; and because it has been interpreted as a major dextral strike-slip fault, the suture zone of a closed Meso-Tethyan ocean, or a suture zone on which a strike-slip fault is superimposed. The zone forms a linear valley with a minor offset near Lebyin and Ye-bu and is occupied by rivers of which the largest is the south-flowing Paung Laung. The best-known part of the zone is north of 20°30′N, where a folded succession with the mid-Jurassic to early Cretaceous Kyaukhsu Taung Formation at the base overlies the late Paleozoic Mergui Group to the west. The Formation is overlain by marine formations, which include early Cretaceous turbidites, and the Patchaung Volcanics, which have some similarities to forearc basin deposits. The Kyaukhsu Taung Formation correlates with the Loi-an Formation on the Plateau, meaning that any ocean basin between the Slate belt and Plateau had closed before the late Jurassic. The zone is bounded in the east by the Pan Laung Fault, which is at least locally an east-dipping thrust, but in the south the eastern boundary may be an extensional fault. The distinctive Paleozoic and Triassic carbonates of the Shan Plateau stop abruptly at the west-facing Shan Scarp, which lies immediately east of the Paung Laung–Mawchi zone.