Kinematic effect of the Andaman Sea opening on the Tanintharyi coastal strip bending with the formation of the Mergui Archipelago, Myanmar

The structural, bathymetric, and temporal complexities of the Mergui-Andaman Basin cannot be explained by a single, steady-state post-middle Miocene spreading phase. During the late Miocene (∼11 Ma), the Sagaing Fault’s kinematics shifted from transtension in a pull-apart basin of the Andaman Sea Opening to transpression in the Central Myanmar Basin (CMB). This transition resulted in a northward compression in the CMB while a pull-apart basin developed south of the Sagaing Fault. The northward movement of the West Myanmar Block (Myanmar Plate) caused ∼460 km of Andaman Sea Opening along the N-S transform fault, while an additional 150 km of eastward movement occurred along the ENE-WSW fault. The Sagaing Fault connects to the active backarc spreading center in the Andaman Sea through short transfer faults. Tectonic evolution was influenced by the Indian Plate’s movement relative to the Eurasian Plate following the Gondwana breakup during the Cretaceous, leading to forced subduction along the IMR at the proto-West Myanmar and proto-West Sumatra margins. The West Myanmar and West Sumatra Blocks, originally part of an oceanic plateau, were juxtaposed with the Sibumasu Block in the present Mergui Archipelago during the Triassic. Isotopic evidence from Andaman Flysch (Oligocene) suggests the West Myanmar Block as a primary sediment source. The Sagaing Fault and its associated faults (Mae-Ping, Three Pagodas, Ranong, and Khlong-Marui) have been reactivated, displaying dextral-to-sinistral and sinistral-to-dextral movements. Geochronological correlations indicate a link between the Sagaing Fault movement and Mogok Belt magmatism. The Andaman Sea Opening has also influenced the bending of the Tanintharyi Coastal Strip, providing evidence of fault reactivation and the formation of the Mergui Archipelago through a Backarc Simple Shear Extension Model. • The Andaman Sea Opening’s N-S transform fault has shifted ∼460 km northward since • the late Miocene, while the study measures the ENE-WSW transform fault at ∼150 km. • The backarc simple shear extension influenced the bending of the Tanintharyi Coastal • Strip, forming the Mergui Archipelago. • The Mergui Archipelago consists of four tectonic lines, with island chains forming • ridges and valleys. • Ductile deformation in northern Thailand (Mae Ping and Three Pagodas Faults) shares • structural similarities with the Ranong and Khlong Marui Faults.