HR: 11:35h
AN: S41G-05    [PDF]
TI: Heat Generation and Strength of Seismogenic Faults Constrained by Fission-Track Data
AU: * Kirschner, D L
EM: dkirschn@eas.slu.edu
AF: Dept. of Earth and Atmospheric Sciences, Saint Louis University, St. Louis, MO 63103 United States
AU: Cuevas-Miranda, D N
EM: camandulo@hotmail.com
AF: Dept. of Earth and Atmospheric Sciences, Saint Louis University, St. Louis, MO 63103 United States
AU: Cuevas-Miranda, D N
EM: camandulo@hotmail.com
AF: Dept. of Marine Science, University of Puerto Rico, Mayaguez, PR 00681 Puerto Rico
AU: El-Shafei, M
EM: elshafeim@hotmail.com
AF: Dept. of Earth and Atmospheric Sciences, Saint Louis University, St. Louis, MO 63103 United States
AU: El-Shafei, M
EM: elshafeim@hotmail.com
AF: Dept. of Geology, Suez Canal University, Ismailia, 41522 Egypt
AU: Garver, J I
EM: garverj@union.edu
AF: Geology Dept., Union College, Schenectady, NY 12308 United States
AB: There has been a longstanding debate regarding the strength of the San Andreas fault and other large faults in the San Andreas system. Some field- and laboratory-derived data are consistent with these faults being anomalously weak, while other data are consistent with these faults having normal strength. One of the most widely accepted and oft-quoted data in support of weak faults is the absence of anomalously high heat flow in the vicinity of these faults. Friction in a normal-strength fault should produce significant amounts of heat, resulting in elevated heat flow in and adjacent to the fault. There is no uniformly high heat-flow along the San Andreas fault, resulting in the well-known "stress / heat-flow" paradox. To provide new data directly related to resolving the stress / heat-flow paradox, we have obtained fission-track data for 41 apatite samples and 8 zircon samples from two inactive strike-slip faults in the San Andreas system (the San Gabriel and Punchbowl faults) that have been exhumed ~2 to 5 kilometers. San Gabriel fault samples were collected in traverses near Whitaker Peak, the "Earthquake locality", and along Bear Creek. Samples were also collected from one traverse in the Devil's Punchbowl County Park. Apatite FT dates are between 51 to 25 Ma from Whitaker Peak, 54 to 24 Ma from the Earthquake locality, and 44 to 6 Ma from Bear Creek. Zircon FT dates from Bear Creek range between 61 and 40 Ma. Apatite FT dates from the Punchbowl fault range between 15 and 7 Ma. FT dates vary systematically with distance from the fault cores along individual traverses. The dates do not, however, young monotonically towards the faults, which would be expected if there had been sustained elevated temperature along the faults. More thermochronologic data (U-Th/He) from the same samples will help resolve factor(s) responsible for the variations in FT dates, and ultimately the strength of these faults when they were active.
DE: 1035 Geochronology
DE: 7209 Earthquake dynamics and mechanics
DE: 8010 Fractures and faults
SC: Seismology [S]
MN: 2003 Fall Meeting