The Khlong Marui Fault (KMF) and Ranong Fault (RF) are major NNE-trending strike-slip faults which
dissect peninsular Thailand. They have been assumed to be conjugate to the NW-trending Three Pagodas
Fault (TPF) and Mae Ping Fault (MPF) in Northern Thailand, which experienced a diachronous reversal in
shear sense during India–Eurasia collision. It follows that the KMF and RF are expected to show the
opposite shear sense and a slip sense reversal at a similar time to the TPF and MPF. New field data from
the KMF and RF reveal two phases of ductile dextral shear separated by Campanian magmatism.
Paleocene to Eocene post-kinematic granites date the end of this phase, while a brittle sinistral phase
deforms the granites, and has exhumed the ductile fault rocks. The timing of these movements precludes
formation of the faults in response to Himalayan extrusion tectonics. Instead, they formed near the
southern margin of a Late Cretaceous–Paleocene orogen, and may have been influenced by variations in
the rate of subduction ahead of India and Australia. North-south compression prior to reactivation of the
subduction zone around southern Sundaland in the Eocene caused widespread deformation in the overriding plate, including sinistral transpression on the KMF and RF