Unravelling the lithospheric-scale thermal field of the North Patagonian Massif plateau (Argentina) and its relations to the topographic evolution of the area

Maria Laura Gomez Dacal,Mauro Cacace,Eugenio Aragón,Magdalena Scheck-Wenderoth,Judith Bott,Claudia Tocho

doi:10.1007/s00531-020-01953-2

Abstract

The North Patagonian Massif (NPM) area in Argentina includes a plateau of 1200 m a.s.l. (meters above sea level) average height, which is 500–700 m higher than its surrounding areas. The plateau shows no evidence of internal deformation, while the surrounding basins have been deformed during Cenozoic orogenic events. Previous works suggested that the plateau formation was caused by a lithospheric uplift event during the Paleogene. However, the causative processes responsible for the plateau origin and its current state remain speculative. To address some of these questions, we carried out 3D lithospheric-scale steady-state and transient thermal simulations of the NPM and its surroundings, as based on an existing 3D geological model of the area. Our results are indicative of a thicker and warmer lithosphere below the NPM plateau compared with its surroundings, suggesting that the plateau is still isostatically buoyant and thus explaining its present-day elevation. The transient thermal simulations agree with a heating event in the mantle during the Paleogene as the causative process leading to lithospheric uplift in the region and indicate that the thermo-mechanical effects of such an event would still be influencing the plateau evolution today. Although the elevation related to the heating would not be enough to reach the present plateau topography, we discuss other mechanisms, also connected with the mantle heating, that may have caused the observed relief. Lithosphere cooling in the plateau is ongoing, being delayed by the presence of a thick crust enriched in radiogenic minerals as compared to its sides, resulting in a thermal configuration that has yet to reach thermodynamic equilibrium.

Highlights

The North Patagonian Massif (NPM) is located in the backarc of the Southern Andes in central Argentina
By comparing the depth map of the 450 °C isotherm (Fig. 4b) with that of the 100 °C, we notice that the deep thermal field follows a similar pattern than the shallow one, variations in temperature are larger in amplitude and wavelength
Temperature differences between the plateau and the surrounding domains increase with depth and reach their maximum at deeper crustal and mantle levels, where additional effects start to overprint the thermal field induced by variations in the Lithosphere Asthenosphere Boundary (LAB) topology (Fig. 2d)

Summary

Introduction

The North Patagonian Massif (NPM) is located in the backarc of the Southern Andes in central Argentina. It includes a plateau of an average altitude of 1200 m a.s.l. The NPM plateau occupies an area of ~ 100,000 km and its rocks appear mostly undeformed (Aragón et al 2011) It is composed of Paleozoic crystalline basement and mid-Jurassic volcanic rocks terminating upward in a regional planation surface (Aragón et al 2010; Gonzalez Díaz and Malagnino 1984) covered by shallow marine sedimentary. This sequence, in turn, is partially overlain by Oligocene to early Miocene mafic volcanic fields, the basalts of Somún Curá (Kay et al 2007), that cover the southern portion of the plateau and erupted over the adjacent region

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Conclusion