Quaternary deformation in the Payogasta-Palermo area, Calchaqui Valley, Eastern Cordillera, NW Argentina

SARA FIGUEROA; LEONARDO ESCALANTE; MANFRED R STRECKER; FERNANDO HONGN

Geissen

Conferencia; Central European Conference on Geomorphology and Quaternary Sciences; 2018

University of Giessen

The approximately N-S-oriented intermontane sedimentary basins of the Eastern Cordillera (EC) of the NW Argentine Andes are an integral part of the southern Central Andes tectonic domain. These basins are the vestiges of formerly contiguous Cenozoic foreland areas that were increasingly compartmentalized into smaller depositional basins by protracted shortening that has continued until the present. The intermontane basins are bordered by reverse faults that have been tectonically active during the Quaternary but increasing field evidence documents that reverse faulting and folding have also affected the basin interiors, causing tilted landforms and changes in the fluvial network. The Calchaquí Valley in the southern sector of the EC (approx. 25° S lat) is one of these basins that exhibit ample evidence for protracted neotectonic activity and seismicity that has caused damage in the past century. Different levels of conglomeratic alluvial fans and fluvial terraces at successively lower elevations, and sculpted into the underlying deformed Tertiary sedimentary strata, are ideally suited strain markers to assess the impact of tectonism onbasin and landscape evolution and thus further contraction of the basins.We present new evidence of Quaternary deformation from the Payogasta-Palermo area in the northern Calchaqui Valley based on 1) the analysis of high-resolution digital elevation models (12,5 m ALOS DEM and 1 m data generated by drone-based photography) to unravel changes in the drainage network, river-profiles anomalies, and topographic anomalies in the terrace sequences to detect deformation; and 2) the collection of field data of potentially reactivated structures (faulting and re-folding), and the analysis of paleocurrents and provenance to detect changes in the Quaternary fluvial network. The alluvial fan and fluvial terrace conglomerates overlie or are faulted by the metamorphicrocks of the ubiquitous Puncoviscana Formation and its metamorphic basement equivalents that constitute the ranges; in the basin, these units cover rocks of the late Cretaceous-Paleogene Salta Group and the Tertiary Payogastilla Group and it appears that a reactivation of older structures has contributed to the deformation. Currently, we are in the process of improving the geochronology of the Quaternary units by U-Pb dating of volcanic ashes and U-Th dating of pedogenic calcretes that have formed in the conglomerates of the different terrace surfaces. Our preliminary results unambiguously document sustainedtectonic deformation in this region, which continues to impact the basin margins and interiors alike. Ultimately, this deformation style may result in severing of foreland connectivity of the fluvial network and associated sediment evacuation from the orogenic interior.