Heavy minerals in modern river sediments of the Malay Peninsular
Inga Sevastjanova, completed MRes project
The Malay Peninsula is surrounded by several offshore petroleum producing basins that contain large volumes of Cenozoic sediments. Many authors have suggested that the deposition of clastic material into these basins occurred simultaneously, and in response to the India-Asia collision and prefer a Himalayan provenance for the sediments. However, a number of provenance studies carried out in the region by the SE Asia Research Group do not support this hypothesis, arguing instead for the importance of local sources.
It is unclear when exactly the Malay Peninsula became elevated although it appears to have acted as an important source for sediments during the Cenozoic, and is likely to have supplied clastic material to the North Sumatra Basin, the Crocker Fan of western Sabah, and West Java. Despite this, little is known about the detrital heavy minerals coming from the Malay Peninsula. As there are almost no Cenozoic sediments in the Malay Peninsula, the project focuses on the heavy mineral suites in modern rivers.
The main aims of the project are to identify detrital heavy minerals of the Malay Peninsula, to study their geographical variation, to relate particular heavy mineral assemblages to specific source rocks, and to aid future studies involving the distribution of sediments in the SE Asia region. The main source rocks for the modern stream sediments are granitoids. The granitoids are traditionally grouped into two north-south trending provinces: the Main Range province in the west, and the Eastern province on the coast of the South China Sea. Granitoids of the Main Range province are predominantly S-type, whereas the granitoids of the Eastern Province are I-type. The Bentong-Raub suture zone separates the two provinces from each other and includes an accretionary complex with oceanic ribbon-bedded cherts, serpentinites, melange, schists, clastic metasedimentary rocks, and limestones. Sedimentary rocks in the western part of the Malay Peninsula are mainly metapelitic; carbonates are also common. In the eastern part, sedimentary sequences comprise mainly carbonates, clastic and volcaniclastic rocks.
Heavy mineral assemblages are composed predominantly of zircon, tourmaline, amphibole and andalusite, varying in their proportions across the area. Sphene is common in the northern part of the peninsula. Monazite concentrations are present locally and are associated with S-type granitoids. Cassiterite was found only in minor amounts. Rutile and garnet are uncommon. Zircons are euhedral or subhedral with a few rounded grains, suggesting predominantly a first cycle provenance. Large numbers of brown zircons are typical of the Malay Peninsula. Typology studies of garnet, rutile, and zircon are underway and U-Pb dating of zircons is also in progress.