Structural evolution of the Li Basin, northern Thailand

Exposures in the Oligocene to Miocene section of coal mines in the Li Basin of northern Thailand show a complex structural evolution. The basins forme d under approximately east-west extension. NW to north-south-striking norma l faults are dominant with some east-west normal faults also being],resent, but much less frequently. Episodically compressional and/or strike-slip ev ents affected the basin creating new east-west to NE-SW-striking thrusts an d folds and inverting some normal faults. The latest episode of compression formed NW-SE to north-south striking thrusts and folds. Cross-cutting stru ctures, reactivation of structures, syn-sedimentary deformation and unconfo rmites help to constrain the relative timing of structural events. At least five episodes of predominantly NNW-SSE to NE-SW oriented compression inter rupted the extensional development of the basin. The compression was probab ly related to the escape tectonics of the Himalayan orogeny. The episodic n ature of the compression and extension is inconsistent with either simple s trike-slip related opening of the rift basins or simple extension. The data from the Li Basin indicate a reappraisal of current tectonic models for th e region is necessary.