A plastic rheology phenomenological 201 . model that explains the Andes evolution in northern Argentina

A plastic rheology, partially phenomenological model is presented to explain the isostatically compensated Andean relief formation. This model considers a combination of lithospheric heating with long period relaxation and successive crustal shortenings on a north section of Argentina located at 24°S latitude. The present size of the Andean root –related to the Andes construction– was obtained by inverting regionalized Bouguer anomalies, also consistent with geoid undulations. The relief of 1520 km is balanced both with a thermal root of 70.63 km located at the lithospheric mantle and 2 with an evolutionary crustal root originated by shortenings. A pretended contradiction must be noted: lateral compressive shortenings and side moving tending to squash and to widen the high relief. For better understanding the problem, a linear model is first presented. Then, a nonlinear model of plastic rheology is considered with a stability coefficient depending on width and elevation. We have assumed that isostatic balance keeps on the whole orogenic construction. We also impose an empirical stability relationship. If this relationship does not hold, there will be an extra relief and therefore an extra root that will plastically flow until reaching stability.