東北日本の新生代熱史
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概要
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The geothermal history was inferred from the changes of the paleotemperature which was estimated on the basis of vitrinite reflectivity values and authigenic minerals. Paleotemperature estimates show that in Northeast Japan, a large scale thermal event associated with the orogenic movement occurred in the Early Cretaceous time. After the orogeny the thermal state changed in the Pacific side region, where the crust has cooled since the Late Cretaceous time. At the Early Miocene time the volcanic activities resumed in the Japan Sea side region and extended eastward. The volcanic belt reached the maximum extent at the early Middle Miocene time, and the volcanic front has since retreated. Distribution of the paleo temperature at the late Middle Miocene time resembles that of the present state, but high gradient areas slightly diminished in extent at the present. In the Pacific side region exterior to the volcanic front, the isopleth of the geothermal gradient slants across the geologic structures of basement rocks, and geothermal gradient becomes higher toward the volcanic front. This fact indicates that the temperature distribution of the region would reflect the thermal structure of the upper mantle, independent of the geologic structure of the crust. In the Japan Sea side region behind the volcanic front, the present geothermal gradient has relation to the distribution of volcanoes and the Tertiary geologic structures. The volcanoes are located on upheaval blocks. In the sedimentary basins of the region, the geothermal gradient of structurally high areas is higher than that of adjacent subsiding areas.
- 日本地質学会の論文
- 1989-03-15