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Structural controls of hot-spring systems on southwestern Montana

January 1, 1979

Thermal waters that issue as hot (more than 38C) springs in southwestern Montana appear to circulate to depth along Cenozoic block faults, deep fractures penetrating the dominantly crystalline rock crust, or major structural lineaments. At individual hot springs, rising thermal waters are transmitted along conduits formed by the intersection of a major fault with other faults, fracture zones, anticlinal axes (which may be faulted or fractures), or sedimentary aquifers. Step faults and other intra-valley faults may influence circulation at some springs. At others, fracture zones alone may provide the necessary vertical permeability. Normal regional heat apparently is sufficient to maintain the hydrothermal systems without enhancement from cooling igneous bodies. The thermal gradient normally is higher in low thermal conductivity sediments of the block-fault valleys than the 30C per kilometer average for crystalline rock. To attain reservoir temperatures of 60 to 120C indicated by chemical geothermometers, waters would have to circulate to depths of about 2 to 4 kilometers in crystalline rock and about 1 to 2 kilometers in valley sediments. (Kosco-USGS)

Publication Year 1979
Title Structural controls of hot-spring systems on southwestern Montana
DOI 10.3133/ofr791333
Authors Robert A. Chadwick, Robert Benjamin Leonard
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Open-File Report
Series Number 79-1333
Index ID ofr791333
Record Source USGS Publications Warehouse