PALEOMAGNETISM, AGE, AND GEOCHEMISTRY OF THE DENCHAI BASALT, NORTHERN THAILAND

The Denchai Basalt of northern Thailand is part of a large continental alkalic basaltic province extending through Thailand into Laos, Kampuchea, and Vietnam. It covers an area of about 70 km2 and consists of seven flows, all with reversed magnetic polarity. The uppermost flow has yielded an age of 5.64 ± 0.28 Ma by the K-Ar method. During the igneous activity, magmas were apparently erupted from only one vent area, but changed in chemical composition from hawaiite" (transitional to continental tholeiite) to true hawaiite and then to basanite. The basanite is the probable source of gem-quality zircon and sapphire mined from placer deposits associated with the basalts. © 1979."