Geological maps of Southeast Asia (Asia, 1971; Vietnam, 1971; Thailand, 1969) show numerous occurrences of basalt, which are considered to be late Cenozoic in age. Occurrences in Thailand and western Kampuchea are generally small and scattered; those in eastern Kampuchea, southern Laos, and Vietnam are larger and more extensive (Fig. 1). Basalt bodies of similar age also occur in Malaysia and southern China (Fig. 1). These basalts form a late Cenozoic continental volcanic province comparable to those in eastern Australia (Irving and Green, 1976) and the western United States (Christiansen and Lipman, 1972; Leeman and Rogers, 1970). Basalts in Southeast Asia are especially intriguing as they are a major source of gem-quality ruby, sapphire, and zircon (Fontaine and Workman, 1978; Berrange and Jobbins, 1976).
The purpose of this paper is to describe the distribution, geochemistry, and age of basalts in Southeast Asia. Available geochemical and age data are compiled and combined with new data from previously unstudied areas. This is the first known regional synthesis that has been attempted for this large but relatively undocumented basaltic province.