Bulletin of the Geological Society of Malaysia, Volume 52, June 2006, pp. 67 - 73
Dept of Geology, University of Malaya, 50603 Kuala Lumpur
Abstract: The basalts exposed near Bukit Mersing, Sarawak are early Eocene in age, and lie conformably over the highly folded, imbricated metasediments of the Rajang Group. Initially thought to be ophiolite, it lies close to the "Tatau-Bukit Mersing Line", which was thought to be a major thrust fault or terrane suture, containing obducted ocean floor material. The one analysis published in 1957 showed a K2O value of 2.82%, too high for ocean floor basalt produced at a spreading center. New analyses confirm that K contents in these rocks are high. The K is hosted in K-feldspar rims around plagioclase phenocrysts. Based on the chemistry, and on field relationships, the Tau Range basalt is not ophiolite, but is likely to be Oceanic Island basalt, developed over oceanic crust, caused by short-lived hot spot magmatism.