Tectono-structural framework of the Indo-Myanmar Ranges: Implications for the structural development on the geology of the Rakhine Coastal Region, Myanmar

Abstract

The Indo-Myanmar Ranges (IMR), known as an accretionary prism, lies between the Kaladan Fault (subduction suture) in the west and Kabaw Fault (the boundary between flysch units and molasse units) in the east is very important to interpret the paleogeographic evolution of the major continents, restoring the paleogeography and plate boundary evolution between the India Plate and West Myanmar Block. The present study explained compression along the Shillong Massif into the IMR with a conceptual model that involves 6-stages of deformation processes. The Kabaw Fault along the eastern rim of Kabaw Valley or the western border of the Kabaw Formation occurs as both an east-dipping thrust and a dextral strike-slip fault. The tectonic model proposed for the IMR is a double-wedge system, in which retro-wedge and east-dipping Kabaw Fault are interrelated to form Nappe of Triassic unit (Thanbaya Formation) with double plunging synclines of Chindwin and Minbu-Salin sub-basins. The Jurassic unit (Kyauksitchaung Formation) is newly found along the eastern base of the IMR as a lithostratigraphic unit and a window structure under the Nappe of the Triassic unit. The alignment of the Kaladan Fault is newly proposed as a suture zone revealed by the window structures of the Oligocene flysch unit under the Nappe of Neogene units on the onshore area, and localities of the mud volcanoes and structural trend of small islands at the offshore area. The formation of circular structures on the Ramree Archipelago is explained by superimposed folding with heterogenous simple shear deformation of the dome and basin structures due to the NW movement of the Broken-Block of IMR colliding with foreland basins including Chittagong-Tripura Fold Belt (CTFB) and Baronga (Boronga) Islands.