Links between orogenic wedge deformation and erosional exhumation: Evidence from illite age analysis of fault rock and detrital thermochronology of syn-tectonic conglomerates in the Spanish Pyrenees
Van der Pluijm, Ben A., 1955-
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Jeffrey M. Rahl is a professor of Geology at Washington and Lee University.Article; [FULL-TEXT AVAILABLE]We present new geochronologic data illuminating the tectonic and erosional history of the orogenic wedge exposed in the south-central Pyrenees, Spain. We interpret illite-age analyses from four fault gouges that record thrust-belt development and document the importance of out-of-sequence thrusting. Fault activity occurs in pulses, with slip occurring contemporaneously on multiple faults throughout the wedge. New apatite fission-track data from syn-orogenic sediments of the Sis Conglomerate body reveal ages of 48 to 42 Ma, with no consistent variation upsection in strata deposited from 41 to 30 Ma. We interpret these data, as well as thermal modeling of track-length distributions, to imply rapid cooling in the interior of the Pyrenean wedge during the Middle Eocene. The record of fault activity and erosion suggests that orogenic wedges may not evolve in a steady fashion, but generally exhibit significant changes in rates of deformation and exhumation. The observed correlation in the timing of tectonism and erosional exhumation provides evidence for links between tectonic and surface processes.