Is the exhumation of the Sierras Pampeanas only related to Neogene flat-slab subduction? Implications from a multi-thermochronological approach

This paper presents new thermochronological data and reviews a set of recently published data for the Sierras Pampeanas in central and northwestern Argentina, which constitutes a distinct morphotectonic feature between 27 degrees S and 33 degrees S. Thermochronological data, derived from zircon and apatite (U-Th)/He, as well as apatite fission-track dating, reveal that cooling below 200 degrees C commenced locally during the Carboniferous period. In Permo-Triassic times, pronounced cooling propagated from east to west in the Southern Sierras Pampeanas, being time-equivalent and spatially equivalent to a flat-slab subduction period at these latitudes. Mesozoic rifting, accompanied by sedimentation and burial re-heating, only affected the thermal history of sampled rocks locally, suggesting that substantial sedimentary thicknesses were only accumulated along narrow and spatially-restricted Cretaceous rift basins. Final cooling in the northern Pampean ranges occurred during the Miocene. Contrastingly, in the Southern and Southwestern Sierras Pampeanas, cooling to near-surface temperatures occurred between the Late Cretaceous and the Paleogene, supporting the idea that a positive topography already existed in these areas before the Neogene. This contradicts the previous hypothesis that the uplift of the Pampean ranges is completely related to the Neogene flat-slab subduction. Instead, this process just accentuated a preexisting relief built up by diachronously developed Mesozoic land surfaces. Calculated long-term denudation rates, varying between 0.010 and 0.024 km/Ma, also support the idea of diachronous surfaces preserved since Mesozoic times. (C) 2013 Elsevier Ltd. All rights reserved.