POLYPHASE DEFORMATION IN A FORE-ARC BACK-ARC BASIN, SALIN SUBBASIN, MYANMAR (BURMA)/

The Salin subbasin of Myanmar (part of the larger Central basin) is a fore-arc/back-arc basin coupler situated between an oblique subduction zone to the west and a major right-lateral strike-slip fault to the e ast. Surface and subsurface expressions of folds and faults suggest th at the basin experienced north-northwest-directed extensional deformat ion in the Miocene followed by east-northeast-directed Pliocene-Pleist ocene transpressional deformation, resulting in a variety of structura l styles, including thrust faults, oblique-reverse faults, strike-slip faults, and normal faults. Fault-propagation folds cored by west-dipp ing thrust faults in the basin center are located above steps in the t op-of-basement surface (most likely fault controlled). Unconformities at the base of and within the Pliocene-Pleistocene synorogenic section indicate that the thrust faults were active during the Pliocene-Pleis tocene. The southeastern region contains broad, north-northwest-trendi ng uplifts and east-northeast-striking normal faults associated with t hickened Miocene synorogenic deposits. Pliocene-Pleistocene sedimentar y rocks lie unconformably above the Miocene section and are folded abo ve the uplifts, reflecting Pliocene-Pleistocene compression. In the so uthern part of the basin, Miocene sedimentary rocks thicken dramatical ly over the 20 degrees N uplift and the Yedwet uplift, suggesting that the north-northwest-striking faults that bound them represent Pliocen e-Pleistocene inversion of Miocene normal faults. During the Miocene, the Burma plate acted as a forearc sliver coupled with the India plate , subducting obliquely underneath it, and moved northward relative to Asia along the Sagaing fault. Normal faulting and local basin formatio n took place at this time. When the northern part of the Burma plate c ollided with eastern Asia in the Pliocene, transpressional deformation predominated, creating thrust and reverse faults, positive flower str uctures, and inverted basins.