New Permo-Carboniferous geochemical data from central Thailand: implication for a volcanic arc model

Current ideas and models of geotectonic reconstructions of Southeast Asia are reviewed and new data on Late Carboniferous through Middle Permian tuffites and sills from central Thailand are presented in the light of the problems of Southeast Asian palaeogeography. The volcanic rocks of quartz-keratophyric to spilitic composition are associated with platform carbonates and deep basin sediments. Their geochemistry and the character of the accompanying sediments suggest the existence of a Late Palaeozoic volcanic arc separating a subduction zone in the west from a back arc basin to the east. The geotectonic frame of Southeast Asia is explained in terms of repeated accretion of volcanic arcs by the Late Palaeozoic subduction zone along the northern Tethys margin

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

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 40Ar/39Ar, 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

Flood deposits penecontemporaneous with ∼0.8 Ma tektite fall in NE Thailand: impact-induced environmental effects?

Although a crater is not yet identified, the Australasian tektite strewn field provides evidence that a major impact cratering event took place in the Southeast Asian region at ∼0.8 Ma, just prior to the Brunhes/Matuyama geomagnetic polarity reversal. Paleomagnetic evidence including reversed polarity in mud lens closely associated with in situ tektites suggests that tektite-bearing flood deposits near Ban Ta Chang and Chum Phuang in northeast Thailand are penecontemporaneous with the impact event. The deposits include abundant organic debris, including whole tree trunks and mammal bones, that preserved due to reducing conditions, which are also responsible for the presence of abundant iron sulphides. Sedimentological observations suggest a series of major flood events that are out of character with the modern meandering river system to which they are related. The deposits are consistent with the effects of regional deforestation, increased run off and erosion, and other environmental disruptions expected in the aftermath of a major impact event. © 2004 Elsevier B.V. All rights reserved.link_to_subscribed_fulltex