Abstract

The Late Cretaceous–Palaeogene structural and tectonic events in the northern region of Sundaland represent a poorly known, but potentially important orogenic development in SE Asia. Extensive Late Cretaceous S-type granites extending from Malaysia through Thailand to Myanmar have long been used to infer an episode of crustal thickening, an inference supported by the presence of late Cretaceous–Eocene ophiolites in Myanmar. However, structural evidence for a well-developed associated fold and thrust belt has been lacking. Apatite and zircon fission-track studies of Thailand indicate a broad regional uplift from about 80 Ma to 40 Ma, suggesting an episode of crustal thickening, but the uplift amount is modest, and not that expected for a major fold and thrust belt. Left lateral motion on major NW–SE-trending strike-slip fault zones (Mae Ping and Three Pagodas faults) in Myanmar and Thailand has been attributed to Himalayan–Tibetan escape tectonics. This paper demonstrates that the fault zones are considerably more complicated than just NW–SE trends. They are a network of branching faults with important north–south trends as well as NW–SE trends, they form large-scale, nested strike-slip duplex structures and affect a region over 1000 km long and up to 250 km wide. This diffuse, branching network of strike-slip fault trends may represent a substantial Late Cretaceous–Palaeogene transpressional belt. Himalayan escape tectonics represent later increments of deformation with both Oligocene sinistral and late Oligocene–Recent dextral reactivation.

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