The timing of strike-slip shear along the Ranong and Khlong Marui faults, Thailand

Abstract

[1] The timing of shear along many important strike-slip faults in Southeast Asia, such as the Ailao Shan-Red River, Mae Ping and Three Pagodas faults, is poorly understood. We present 40 Ar/ 39 Ar, U-Pb SHRIMP and microstructural data from the Ranong and Khlong Marui faults of Thailand to show that they experienced a major period of ductile dextral shear during the middle Eocene (48-40 Ma, centered on 44 Ma) which followed two phases of dextral shear along the Ranong Fault, before the Late Cretaceous (>81 Ma) and between the late Paleocene and early Eocene (59-49 Ma). Many of the sheared rocks were part of a pre-kinematic crystalline basement complex, which partially melted and was intruded by Late Cretaceous (81-71 Ma) and early Eocene (48 Ma) tin-bearing granites. Middle Eocene dextral shear at temperatures of ∼300-500°C formed extensive mylonite belts through these rocks and was synchronous with granitoid vein emplacement. Dextral shear along the Ranong and Khlong Marui faults occurred at the same time as sinistral shear along the Mae Ping and Three Pagodas faults of northern Thailand, a result of India-Burma coupling in advance of India-Asia collision. In the late Eocene (<37 Ma) the Ranong and Khlong Marui faults were reactivated as curved sinistral branches of the Mae Ping and Three Pagodas faults, which were accommodating lateral extrusion during India-Asia collision and Himalayan orogenesis.

The closure of Palaeo-Tethys in Eastern Myanmar and Northern Thailand: New insights from zircon U–Pb and Hf isotope data

“…They measured Eocene crystallization ages from the Sedo granite, southeast of Mandalay, of 48.0 ± 0.9 and 53.8 ± 0.8 Ma. Further south, Watkinson et al (2011) reported Cretaceous SHRIMP U-Pb ages on zircons from both a weakly foliated tourmaline-muscovite-biotite porphyritic granite, a dominantly S-type mineralogy, and a more mylonitic granite. Both samples are sited within the Ranong Fault zone in southern Thailand (Fig.…”

Did Oligocene crustal thickening precede basin development in northern Thailand? A geochronological reassessment of Doi Inthanon and Doi Suthep

“…They measured zircon core ages of 214 ± 2 Ma and 212 ± 2 Ma, and Cretaceous zircon rim ages of 81.2 ± 2 Ma and 85-75 Ma respectively. Watkinson et al (2011) also reported Cretaceous SHRIMP U-Pb zircon ages of 81 to 70 Ma from granites exposed along the Ranong Fault zone in southern Thailand. We agree that Cretaceous ages measured at Doi Inthanon are part of a more regional magmatic and metamorphic overprint affecting Thailand and Myanmar, and further, we believe this is likely to be related to the eastwards subduction of Neo-Tethys under Sibumasu prior to the onset of the Himalayan Orogeny (e.g.…”

Quantitative finite strain analysis of high-grade metamorphic rocks within the Mae Ping shear zone, western Thailand

“…The Ranong and Khlong Marui shear zones in the southern Thailand extend from the continental margin and Mergui basin to the Gulf of Thailand from W to E (Tapponnier et al, 1986;Lacassin et al, 1997;Charusiri et al, 2002). All four major strike-slip shear zones in Thailand were probably active during the Eocene (Lacassin et al, 1997;Watkinson et al, 2011;Kanjanapayont et al, 2012b;Nantasin et al, 2012;Palin et al, 2013).…”