Model for andean orogenic volume variation and shortening in the 20°-46°S sector

Abstract

The orogenic volume of the Andes is the result of the equilibrium between the tectonic uplift and erosion. The different rates of shortening along the western margin of the South American continent have defined contrasting morphostructural settings. The orogenic volume along the southern Central Andes and northern Patagonian Andes (20°-46°S) decreases linearly, from north to south. At 38°S, we have separated two segments with different rates of variation in the andean volume. The northern sector (20°-38°S) shows a steeper linear law than the southern sector. Even though the andean volume varies together with the decrease from north to south of the subducted oceanic slab age, latitude 38°S coincides with a sudden change related to this late parameter. This observation has led us to propose a linkage between subducted parameters and variation of Andean volume, which contrasts with other hypotheses that assume that climate, is the principal cause for the variations in the observed orogenic volume. We also present two empiric equations to calculate the orogenic volume at determined latitude, beyond the area of influence of two anomalies centered around 27°S and 33°S respectively. Those sectors are considered to be influenced by other factors related to isostatic rebounds, superposed to shortening. Additionally, we discuss a law for the latitudinal variation of the orogenic shortening away from the location of the mentioned anomalies.