Abstract.Footwall necessary in order to unroof the samples by 2 Ma. Additional extension, of unknown magnitude, has probably occurred subsequently. Geodetically measured horizontal extension rates are considerably higher than the long-term extension rate that can be attributed to detachment faulting.

Abstract. We have developed a two-dimensional, thermokinetic model that predicts the closure age distributions of detrital minerals from pervasively intruded and differentially exhumed basement. Using this model, we outline a method to determine the denudation history of orogenic regions on the basis of closure age distributions in synorogenic to -1 postorogenic forearc strata. At relatively high mean denudation rates of 0.5 km m.y. sustained over millions of years, magmatic heating events have minimal influence upon the age distributions of detrital minerals such as K-feldspar that are moderately retentive of radiogenic Ar. At lower rates, however, the effects ofbatholith emplacement may be substantial. We have applied the approach to detrital K-feldspars from forearc strata derived from the deeply denuded Peninsular Ranges batholith (PRB). Agreement of the denudation history deduced from the detrital K-feldspar data with thermochronologic constraints from exposed PRB basement lead us to conclude that exhumation histories of magmatic arcs should be decipherable solely from closure age distributions of detrital minerals whose depositional age is known.

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