Triassic Neo-Tethys Ocean opening with development of continental extensional basin in Sibumasu block: Insight from the Kalaw-Pinlaung basin in Shan Plateau, Myanmar

The Kalaw-Pinlaung Basin is a narrow, elongated, NNW-SSE-trending trough, approximately 170 km long and 60 km wide. This Basin is mainly composed of Mesozoic rocks, which overlie the Permo-Triassic limestones. It is situated in the Eastern Highlands (Shan Plateau), bounded to the west by the Sagaing Fault and the Inthanon suture zone to the east. The Shan Plateau (Sibumasu Block) developed as regional-scale en-echelon folding, which is conceptually dragged along by the extensive movement of Gondwana during the Upper Carboniferous, regarding the polar wander path from Ordovician to Permian, particularly the Variscan Orogeny. Leading to the Variscan Orogen in Europe, the Sibumasu Block (Cimmerian Superterrane) was a peri-Gondwana block that was dragged by Gondwana. The Sibumasu Block developed continental extension when the Neo-Tethys Ocean likely began to open around 265 Ma by movement of the Cimmerian Superterrane, while the Paleo-Tethys Oceanic crust has been subducted beneath Eurasia. The Sibumasu block detached from Gondwana in the post-Permian period, so that the Sibumasu Block remained attached to Gondwana until the end of the Permian. A passive continental margin develops through extensional basins towards the ocean, characterized by synthetic half-graben basins that form listric normal faults. These faults are geomorphologically expressed as fault scarps and tilted terrain, indicating the presence of half-grabens. The Kalaw-Pinlaung Basin is characterized as a synthetic half-graben basin by listric normal faults, in which the pre-rift sediments of the Thitsipin Limestone Formation are recognized as fault-bounded blocks, trending parallel with basin alignment. The Kalaw-Pinlaung Basin is divided into five half-grabens from west to east: Half-Graben I, Half-Graben II, Half-Graben III, Half-Graben IV, and Half-Graben V. The Half-graben basins are filled by the Upper Triassic to Cretaceous rocks, turbidite to continental sediments, as well as deep marine to fluviatile environments. The Kalaw-Pinlaung Basin opened an outlet of the extensional basin in the Kyaukse-Lungyaw area south of Mandalay city. During the Mesozoic period, the tectonic development of the present Myanmar Region included the West Myanmar Block (Indo-Myanmar Range and Central Myanmar Basin), the Sibumasu Block (Shan Plateau), and the Sukhothai Block (Inthanon zone).