Teruhiko Watanabe

Heat flow in the Philippine Sea

Abstract The distribution of heat flow in the Philippine Sea is very complicated. Unlike other marginal seas behind island arcs and the Pacific Basin proper in front of arcs, the Philippine Sea has neither uniformly high nor low heat flow but shows numerous adjacent areas of high and low heat flow. Contouring is difficult but the pattern of heat flow distribution is fairly well established in the northwestern Philippine Sea, i. e. the area of the western Shikoku Basin and the Ryukyu Trench and Island Arc. The basin and trench southeast of the Ryukyu (Nansei-Shoto) Arc are characterized by low heat flow, and the area behind the arc by high heat flow. This distribution is consistent with the pattern over other trench and island arc systems. There is a well-defined area of high heat flow in the northern Shikoku Basin. Scattered measurements in the eastern part of the Philippine Sea behind the Izu-Bonin (Ogasawara) Arc are also predominantly high, suggesting, that the area of high heat flow in the Shikoku Basin may be part of a broad region of above average heat flow behind this arc. Several measurements west of the Mariana Arc indicate low heat flow in the trough between the outer and inner arcs and above average heat flow west of the inner ridge. Scattered measurements in the Philippine and Parece Vela basins south of latitude 22°N give highly variable results. High values predominate, however, more measurements are required before it can be established that these basins on the whole have significantly above normal heat flow.

Terrestrial heat flow in western South America

Abstract Twenty heat-flow measurements were made in western South America (nine in Chile, one in Argentine, five in Peru, one in Ecuador, and five in Bolivia), using available holes. From the values obtained, combined with several others published previously, it may be concluded that the heat flow in this subduction plate boundary area resembles that of other trench-arc systems, with low heat flow prevailing closer to the trench and high heat flow prevailing on the volcanic arc. Due to the limited distribution of sites, the regional heat flow in the area landward of the volcanic zone cannot be assessed with confidence, although high heat flow, somewhat analogous to that observed in young back-arc basins of island arcs, might exist in Bolivia, but not in Argentine.

Preliminary report of terrestrial heat flow study in the South American continent; distribution of geothermal gradients

Abstract Measurements of terrestrial heat flow have been made in twenty mines in western South America. In addition to these mines, underground temperature data at thirty-five oil fields over the whole South American continent have been examined. Since thermal conductivity values for these sites have not been determined yet, only geothermal gradient values are reported here. The thermal gradient features may be summarized as follows 1. (1) most of the values are normal or subnormal over the whole area of the continent; 2. (2) high values are concentrated in the Andes area, and often seem to be associated with geothermal activities 3. (3) lower values are observed in the Pacific coast area and in the area along the Amazon River 4. (4) normal values (2.5–3.5°C/100 m) are observed in the eastern part of the Brazilian Shield, while the values appear slightly depressed in its southern part.