Preliminary numerical analysis of the magma-hydrothermal history of The Geysers geothermal system, California, USA

摘要: Abstract Numerical approximations to the thermal history of a representative 2-D semi-infinite section through cooling pluton equivalent in size, configuration, and composition Quaternary-age Geysers plutonic complex (generally known as felsite) provide new insights into evolution associated, pre-vapor-dominated, magmatic-hydrothermal system. A reference state model demonstrates that 300 o C peak paleotemperatures preserved metagraywacke 1.4 km above felsite (in core from scientific drillhole SB-15-D) could not have been attained by pure conductive heat transfer. The are readily matched, however, convective-cooling which fluids igneous source can migrate within permeable (0.05 millidarcy, or 5 × 10 −17 m 2 ) reservoir size geometry modern vapor-dominated regime intermittently open surface narrow vertical conduit proxying Big Sulphur Creek strike-slip fault zone. Under these conditions, maxima achieved only 55–70 ky post-intrusion. Model temperatures thereafter cool 235°C (the value for 650 130°C 1 My. latter is close 1.2–1.1 Ma calculated crystallization age explored portions felsite. These relationships suggest felsite-heated hydrothermal system, at levels penetrated SB-15-D, should cooled currently prevailing temperature about 0.5 Ma. This clearly did happen, simplest analysis accordance with previous investigations), large temporal discrepancy points more intrusive than age-dating has thus far revealed.