| Abstract |
Data on 94 hot springs in Thailand indicate that they are mostly dominated by Na-HCO3 (-S04) type water with minor CI and occur mostly in granitic terrains. Bariation in geochemical composition is relatively nonsignificant although in the south the thermal springs contain less abundant TDS and other alkaline values. In general, hot springs in the north have strongest mineral constituents with the amounts of TDS varying from 315 to 700, Ma 80-176 mg/l, S04 16-65 mg/l and CI 1.7-31.0 mg/l. In the south, although data are rather scarce, chemistry of springs in general is similar to the north, heatflow data of Thailand indicate that northern Thailand can be divided into 2 regions-the western region with heatflow over 1.5 HF and the eastern region with heatflow less than 1.5 HF. The occurrence of geothermal resources suggests that geothermal fields are controlled by tensional and strike-0slip tectonics in association with seismically active faults and shallow to deep igneous bodies. In Vietnam, most of the reported thermal springs (up to 60 locations) are of Na-C03 (-CI)- type water. Geochemical characteristics of hot springs in northern Vietnam are HCO3-dominated, in the central they are CI-and HCO3-dominated. More significant is that in the deltaic plain of the Red River, the thermal springs are characterized by the presence of CH4. It is notably important that the marked geochemical contrast of thermal springs may indicate the difference in geotectonic units occurring as a result of heterogeneous mantle melting with mixing crustal materials in central and southern Vietnam and of extensional and strike-slip tectonics in the south. In Myanmar, thermal springs are quite abundant and widespread. Up to a total of 92 thermal springs are reported. They are much more concentrated in granited region in eastern Myanmar in the N-S trend. Most of the hot springs occurs in magmatic regions, particularly along the N-trending fault and fracture zones. In the northeastern part near China border, the hot springs are distributed in the northeast trend following major fault zones, immediately close to the metamorphic igneous terrains. Exploratory drilling from reports on petroleum activities in central region advocated the existence of high geothermal gradients in proximity to shallow-depth magma bodies and active fault zone. |