AN ISOSTATIC MASS BALANCE MODEL OF CONTINENTAL ARCS AND ITS APPLICATION TO PALEOZOIC-MESOZOIC ARGENTINEAN CORDILLERAN OROGENIC SYSTEMS

Magma additions, tectonic shortening/thickening, rate of crustal root development, and surface erosion affect the crustal thickness and elevation of continental arcs. Studying the interplay between these driving forces helps us better predict the future behaviors of arc systems. An isostatic mass balance model, which incorporates the above variables, has been recently proposed (Lee et al., 2015) and has been shown to capture the first-order variability of the Mesozoic Sierra Nevada arc, California (Cao et al., in review). Here we apply the model to the Argentinean Cordilleran orogenic system from Neoproterozoic to Cretaceous. We based the magma addition parameter on age controlled map distributions of plutons, the tectonic shortening on retrodeformation of cross sections, root growth on published studies of lower crustal magmatic processes and erosion rates estimated from regional paleoclimatology. We found that Pampean (980-490 Ma) experienced little elevation and arc thickness change due to a moderate amount of both magmatic and tectonic thickening. During Famatinian (490-340 Ma), crustal and total thickness dramatically increased along with an increased thickening forces and mild erosion rates. Elevation did not increase as much as arc thickness, however. Elevation reached its highest during Gondawanian (340-290 Ma), to 3.5 kilometers, thanks to the dropping of the thick Famatinian arc root. Because of the resulted increase in erosion rates, crustal and total thickness increases were modest. During Andean (290-120 Ma), the last period of this study, elevation and arc thickness returned to Pampean level as thickening forces weakened. Compared with the Mesozoic Sierra Nevada arc, the Argentinean Cordilleran arc’s elevation, crustal thickness and total thickness have persistently lower numbers and less variability. The Argentinean Cordilleran arc’s crustal and total thickness are also more susceptible to magmatic thickening.