Evidence for a Crustal Heat Source for Low-Temperature Geothermal Systems in the Central Alaskan Hot Springs Belt

摘要

~(3)He/~(4)He isotopic data suggests that low-temperature geothermal systems in the Central Alaskan Hot Springs Belt (CAHSB) are heated by a crustal heat source. The overall rate of circulation in CAHSB systems appears to be low, with minimum fluid residence ages of 170,000 years. Heat production from nearby Cretaceous to Tertiary age plutons is anomalously high due to significant concentrations of radioactive elements U, Th and K. High heat production in granites may be responsiblehfor local elevation of the geothermal gradient in hot springs areas. Small-scale fractures and faults provide the permeable pathways for fluid circulation. Shear strain in a backarc fault-block-rotation setting is likely keeping those pathways open. Hence, CAHSB geothermal fluids have acquired their heat by descending to relatively shallow crustal depths under conditions of high geothermal gradient.