Onset of compressive exhumation of the northern Santa Bárbara System (NW Argentina). Tectonic implications from low-T thermochornology.

VÍCTOR H. GARCÍA; ANTONELLA GALETTO; EDWARD SOBEL; PATRICIO PAYROLA; CAROLINA MONTERO; LEONARDO ELÍAS; AHMAD ARNOUS; FERNANDO HONGN; MANFRED STRECKER

Vienna

Congreso; EGU 2024; 2024

EGU confernece

The Santa Bárbara System (SBS) of the Central Andes of NW Argentina is a thick-skinned fold-and-thrust belt (FTB) that represents the outermost portion of the orogenic wedge and the westernboundary of the undeformed Chaco-Paraná foreland basin. The present-day structural arquitectureof the SBS is mainly governed by the reactivation of basement anisotropies and Cretaceous normalfaults imprinting an overall vergence towards the west. Some of its major faults show signs ofactive tectonics, as recorded by instrumental seismicity and destructive earthquakes.Studies based on seismic interpretation of growth strata in synorogenic deposits have shown that thebasement ranges of the southern SBS began to be uplifted during the late Miocene, although themagnitude of exhumation has not yet been quantitatively established. On the other hand,thermochronological analyses of basement samples from the neighboring Eastern Cordillerahighlighted the relevance of a late Miocene (ca. 10 Ma) exhumation event that propagated theorogenic front into the Mojotoro range, just west of the northern SBS.In this contribution, we present the first thermochronological cooling ages from Paleozoic rocks ofthe northern SBS and from the basement of the Reyes range, in the Eastern Cordillera. Theintegration of these data with previously published cooling ages allowed us to interpret that the lateMiocene event reached the northern SBS onseting their exhumation of the basement-cored rangesby 7-8 Ma. In addition, the Reyes range sample documented a Pliocene cooling phase (ca. 4 Ma)that agrees well with the model of hinterland reactivation of faults due to the recovery of a sub-critical orogenic wedge proposed by previous authors.Taking into account the available structural reconstructions, an average exhumation rate of about0.7 mm/a can be estimated for the western frontal thrusts of the northern SBS. This value agreeswith the late Pleistocene-Holocene rates obtained for Quaternary morphostructures of the LermaValley, the easternmost intermontane basin of the Eastern Cordillera, suggesting a potential steadylong-term deformation pattern for this portion of the Andean backarc.