Terrestrial heat flow in areas of dynamic influence of faults in the Baikal rift zone

Abstract

Terrestrial heat flow in the Baikal rift zone is irreg- ularly distributed. Its high values are associated with active faults and areas of dynamic influence of faults. Stress pat- terns in these regions have been studied across and along major faults. Measurement sites under consideration are those located not farther than 30 km from the given fault axis. Across the fault strike, heat flow values are revealed to decrease with distance from the fault axis. Along the fault strike, variations of heat flow values are within measurement errors, with the exception of thermal spring sites. It is estab- lished that heat flow values are regularly changeable. Similar relationships are obtained for heat flow patterns in other con- tinental rift zones. ducted in exploratory drillholes ranging from 0.3 to 3-5 km in depth (0.3 to 1 km in ridges, 1 to 2.5 km in intermountain depressions, and 2.5 to 5 km on the Siberian microplate) and from 0.5 to 2 km (mostly<1 km) at altitudes above sea level. Precise heat flow measurements were carried out for several weeks or several months (occasionally up to 5 years) after drilling had been complete. Results of hydrogeological and cryological studies were also used in constructing the map (Lysak, 1978; 1984; 1995). Marine studies at transversal profiles across Lake Baikal were carried out by oceanographic techniques from aboard of a scientific vessel. Either a thermal gradiometer (Duchkov et al., 1987) or a cable thermistor probe penetrating through 1 m to 3 m thickness of bottom sediments were used (Golubev, 1982; Golubev et al., 1993). An average heat flow value of Lake Baikal basin is 78±36 mW/m 2 . In other rift depressions (Tunka, Barguzin), it is 62±13 mW/m 2 . Thermal waters of these intermoun- tain artesian basins are distinguished in the thermal field as regional anomalies. Their local high values exceed 80- 100 mW/m 2 in the fault zones bordering these depressions. At the north-eastern flank of the BRZ, heat flow drops down to 50 mW/m 2 and below; it can reach 70-80 mW/m 2 only at