HR: 1340h
AN: V13A-0513    [Abstracts]
TI: Refining the Thermal History of the Ecstall Pluton, British Columbia: A Test of the Remagnetization Hypothesis
AU: * Brownlee, S J
EM: sbrownlee@berkeley.edu
AF: University of California, Berkeley Department of Earth and Planetary Science, 307 McCone Hall #4767, Berkeley, CA 94720
AU: Renne, P R
EM: prenne@bgc.org
AF: University of California, Berkeley Department of Earth and Planetary Science, 307 McCone Hall #4767, Berkeley, CA 94720
AU: Renne, P R
EM: prenne@bgc.org
AF: Berkeley Geochronology Center, 2455 Ridge Rd., Berkeley, CA 94709
AU: Hollister, L S
EM: Linc@princeton.edu
AF: Princeton University Department of Geosciences, Guyot Hall, Washington Rd., Princeton, NJ 08544
AB: In the interest of refining the thermal history of the Ecstall Pluton we performed Ar/Ar laser heating analyses of biotite (single crystals) and hornblende (10 grains per aliquot) from samples 001 and 008 of Hollister et al. (2004). These sample locations are on the eastern and western margins of the pluton, and are similar to samples 018 and 008, respectively, of Butler et al. (2002). For the western margin, hornblende yields a plateau age of 85.4 +/- 0.6 Ma, and biotite yields a plateau age of 77.1 +/- 0.5 Ma, approximately 1.2 and 3.8 Ma older than reported by Butler et al. (2002) for the same sample locations. For the eastern margin, sample 001, about 3 km east of sample 018 in Butler et al. (2002), hornblende gives a plateau age of 67.2 +/- 0.4 Ma and biotite gives a plateau age of 52.6 +/- 0.3 Ma, approximately 9.2 and 2.1 Ma younger, respectively, than sample 018 in Butler et al. (2002). The age difference between our sample 001 and Butler et al.'s sample 018 can be explained by reheating of the Ecstall Pluton from the east as proposed by Hollister et al. (2004). The older ages from our western margin sample, and younger ages for our eastern margin sample, may indicate that the reheating event was of greater magnitude and/or duration than originally hypothesized. This would favor the kinetics of exsolution in titanohematites, strengthening the inference of Hollister et al. (2004) that systematic spatial variations in paleomagnetic inclination are a consequence of exsolution-remagnetization during reheating by the hot Coastal Shear Zone.
DE: 1040 Radiogenic isotope geochemistry
DE: 1115 Radioisotope geochronology
DE: 1140 Thermochronology
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1533 Remagnetization
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005