HR: 09:45h
AN: V31B-08    [PDF]
TI: On the Trail of Missing Heat: Forward Gravity Modeling of the San Francisco Volcanic Field, Northern Arizona
AU: * Fry, B N
EM: Bill.Fry@nau.edu
AF: Northern Arizona University, PO Box 4099, Flagstaff, AZ 86011 United States
AU: Morgan, P
EM: Paul.Morgan@nau.edu
AF: Northern Arizona University, PO Box 4099, Flagstaff, AZ 86011 United States
AB: The San Francisco volcanic field is a Quaternary field in northern Arizona, the age and size of which suggests there is a high possibility for an associated exploitable high temperature geothermal resource. Sunset Crater, the youngest dated feature in the field, erupted less than 1000 years ago. The youngest felsic volcanism in the area, located near Strawberry Crater, has been dated at about 51,000 years b.p. Felsic magmas are viscous, and therefore felsic magmatism is generally associated with upper crustal plutons, whereas mafic magmas commonly form surface flows. Heat from felsic magmatism tends to remain near subsurface ponds of the magma. Felsic magmatic systems can sustain substantial geothermal heat for tens to hundreds of thousands of years after emplacement. Knowledge of the quantity and distribution of felsic magmatism is therefore paramount to understanding the geothermal potential of the field. Surface heat flow in the study area ranges from $\sim$20 to $\sim$50 mW/m$^{2}$, anomalously low for the region. Hydrological characteristics of the San Francisco volcanic field are thought to mask increased surface heat flow from the magmatic system. The deep water table ($>$300m) and a 2-level hydraulic system prevent characteristic surface manifestations of hydrothermal potential, such as hot springs and elevated surface heat flow. Lack of these thermal features at the surface precludes analysis of the resource based solely on surficial mapping and measurements. Forward modeling of the gravity field of a 50 km x 45 km area covering the eastern San Francisco volcanic field has been completed. Results suggest that a large felsic body ($\sim$-0.15 g/cc contrast) trends northeastward under the Sugarloaf Mountain-O'Leary Peak-Strawberry Crater magmatic trend. This trend parallels a regional basement fabric, likely of early- to middle-Proterozoic origin. These results are being correlated with new surface geologic mapping and radiometric dating of young felsic volcanic rocks to guide an exploratory drilling program.
DE: 0903 Computational methods, potential fields
DE: 0920 Gravity methods
DE: 1219 Local gravity anomalies and crustal structure
DE: 8135 Hydrothermal systems (8424)
DE: 9350 North America
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting