Pacific Section AAPG, SPE and SEPM Joint Technical Conference

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Exploratory IRSL Thermochronology Of The Yucaipa Ridge Block, San Bernardino Mountains, Southern California

Abstract

New luminescence methods have the potential to provide low-temperature (<100∞C) thermochronomerty for quartz and feldspar grains (Herman et al., 2010). The goal of the present study is to assess advantages and limitations of infra-red stimulated luminescence (IRSL) as a low-temperature thermochronometer, in order to constrain the cooling history of uplifted crystalline basement. The Yucaipa Ridge block of the San Bernardino Mountains, southern California, provides a promising location for preliminary assessment due to its rapid uplift rate of approximately 1.5 mm a-1 (Binnie et al., 2008). Luminescence measurements of feldspar grains, derived from several vertical transects of igneous and metamorphic rocks forming Yucaipa Ridge near Forest Falls, California, provide encouraging preliminary results. These feldspar IRSL measurements yield a strong relationship between the fraction of saturation of each sample and elevation. IRSL measured at 50∞C displayed significant fraction of saturation (90-95%) for samples collected at higher elevations, corresponding to apparent ages in excess of ∼150,000 years. Samples from lower elevations displayed a lower fraction of saturation and lower apparent age estimates, suggesting more recent exhumation and cooling. Fading behavior and other characteristics of the IRSL signal are explored to understand optimal methods to determine sample cooling rates. Binnie, S.A., Phillips, W.M., Summerfield, M.A., Fifield, K.L., Spotila, J.A., 2008, Patterns of denudation through time in the San Bernardino Mountains, California: Implications for early-stage orogenesis, Earth and Planetary Science Letters, v.276, 62-72. Herman, F., Rhodes, E.J., Jean, B.C. and Heiniger, L., 2010, Uniform erosion rates and relief amplitude during glacial cycles in the Southern Alps of New Zealand, as revealed from OSL-thermochronology: Earth and Planetary Science Letters, 297(1-2): 183-189.