Bulletin of the Geological Society of Malaysia, Volume 29, July 1991, pp. 1–100
Laboratory for Isotope Geology, University of Berne, Switzerland
Abstract: The Malaysian Peninsula belongs to the Southeast Asian tin belt. It is divided by a suture into two different magmatic provinces of S- and I-type characteristics. Three areas within the S-type granitoid province of the Main Range have been studied. New K-Ar mica and fission track zircon and apatite ages were established, and Rb-Sr whole-rock data from literature have been reinterpreted in the light of these new data. The results were compared with existing Rb-Sr isochrons of the I-type granitoid province and with the one reported from the northern extension of the belt stretching into Thailand. This integrated study led to the better understanding of: a) the behavior of the different isotopic systems in different geological environments, and b) the complex magmatic, tectonic and cooling history of Southeast Asian granitoids.
Applying the intrusion extrapolation method, based on the evolutionary trend of decreasing Rb-Sr ages and increasing initial (87/86)Sr (Kwan et al., paper submitted), periods of 300, 250, 210, and 90 Ma for the Main Range and of 260, 240, 210 and 90 Ma for the I-type granite province became evident. The best evaluated initial (87/86)Sr for the source regions of the granitoids are 0.708 to 0.709 and 0.704 respectively. The major magmatic event in the Main Range dates of the late-Permian.
The close time range of individual magmatic periods and their spatial distribution can best be explained in the context of plate tectonics by northward motion of compositionally different arcs; by their collision to one another and to the East Asian Continent; subsequent deformation; subduction reversal; following the model of Hamilton (1988).
The most crucial event for the Main Range granitoids was the intrusion of the highly evolved, late-Triassic post-collision granites. They induced a regional hydrothermal convection system, which is considered to have lasted for a maximum of 40 Ma dependent upon the crustal level. This hydrothermal system was responsible for the major tin mineralization processes and the entire granite alteration. Biotite of the crystallized granitoids is considered to be the main Sn supplier.
The K-Ar and fission track ages indicate a slow post-orogenic cooling in the range of 1-5°C/Ma. With FT zircon ages different crustal levels can be distinguished within the Main Range, and the discordant K-Ar mica and the differently reset Rb-Sr whole-rock ages can be correlated with depth.
After the early-Cretaceous the Main Range has been dominated by tectonic activities, such as differential vertical uplift of the Main Rage combined with the juxtapositioning of blocks, thrust faulting close to the Bentong-Raub suture and Tertiary left-lateral displacement, which is inferred from isotopic and petrological evidences.