HR: 0800h
AN: T21A-0453    [Abstracts]
TI: Helium Isotope Measurements on Matrix Fluids From the SAFOD Drillcore
AU: * Stute, M
EM: martins@ldeo.columbia.edu
AF: Barnard College, 3009 Broadway, New York, NY 10027 United States
AU: * Stute, M
EM: martins@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 rte 9W, Palisades, NY 10964 United States
AU: Torgersen, T
EM: thomas.torgersen@uconn.edu
AF: University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340 United States
AU: Winckler, G
EM: winckler@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 rte 9W, Palisades, NY 10964 United States
AU: Schlosser, P
EM: schlosser@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 rte 9W, Palisades, NY 10964 United States
AB: Matrix fluids from the SAFOD main hole at ~3060m have been isolated from subcores, core catcher and core fragments for noble gas analysis. Because SAFOD cores are under (hydrostatic to lithostatic) compressive stress, matrix fluids within this material can be released over time by a series of microcracks, diffusive transport, etc. Preliminary results indicate that this release occurs on a time scale of months for a transport scale of 1-3 cm. By placing subcores, core catcher bits, etc. in high vacuum containers as soon as possible after becoming available at the surface (on site), flushing with ultra-pure nitrogen and evacuating, the noble gases from matrix fluids have been measured in several SAFOD samples. ³He/⁴He ratios from these samples (³He/⁴He = 4.9-5.5 e-7) are identical to the ³He/⁴He ratios recovered from fluid samples captured during an open hole flow test (Kennedy, et al. pers. comm.) and indicate a mantle derived He component of ~4%. Assuming ³⁶Ar is at saturation, open hole flow tests suggest ⁴He concentrations of 4-6 e-5 cc⁴He/g-water, which is largely in agreement with matrix fluid concentrations calculated from the measured mass of volatile fluids (evaporated water) and ⁴He amounts (4-7 e-5 cc⁴He/g-water). These data are preliminary, because at this time water and He have not been quantitatively released from the rocks. The results suggest that matrix fluids collected from core material is representative of fracture-filling fluids and represents a viable means for fluid collection when flow tests are restricted by limited permeability and/or drilling schedules. Our preliminary results indicate that our method might be suitable for constraining the long-term dynamics of fluids in the San Andreas Fault.
DE: 1829 Groundwater hydrology
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8155 Plate motions: general (3040)
SC: Tectonophysics [T]
MN: Fall Meeting 2005