Heat flow and geothermal field of the Baikal region

Data on the geotemperature field of the central part of the Baikal Rift Zon e (BRZ) and adjacent regions of the Siberian Platform and Transbaikalia are summarized. About 800 measurements of heat flow were made here, 700 of the m were carried out in the Baikal basin (shallow-depth measurements in the u pper layer of sediments). The average heat flow through the Baikal bottom i s 71+/-21 mW/m(2). At some sites of the bottom extremely high Plows (up to 6000-8000 mW/m(2)) confined to the local centers of discharge of underwater sources have been revealed. In the montane framing of the rift troughs hea t now is much less intense - no more than 15-40 mW/m(2). In the south of th e Siberian Platform and in Transbaikalia average heat flow is 40+/-9 and 52 +/-11 mW/m(2), respectively. This differentiated heat flow distribution in the BRZ is, probably, the result of active water exchange in intermount art esian basins, which leads to cooling of feeding zones (mountain ridges) by meteogenic waters and further warming-up of the sedimentary cover of these basins (discharge areas). Special studies in the North-Muya tunnel supporte d this hypothesis. The validity of numerous shallow-depth measurements of h eat flow in Lake Baikal is corroborated by the temperatures measured in the First underwater boreholes BDP-93 and BDP-96. By the location of the lower boundary of the gas hydrate layer of the Baikal sediments, 500 estimates o f heat flow in the Southern and Central basins were made. In accordance roi th these estimates, average heat flow is 76+/-10 mW/m(2), which also corrob orates the above average heat flow value. Heat now data were used to foreca st deep temperatures by the geothermal method. The paper analyzes the forec ast temperature distributions at depths of 10, 20, 30, and 40 km. The valid ity of a geothermal forecast for the rift troughs is corroborated by the re sults of thermobarometric study of mineral inclusions from deep-seated volc anites of East Sayan and the Vitim Plateau. These data also evidence that h eat flow and deep temperatures within the BRZ are underestimated.