Unraveling the Construction of the Northern Puna Plateau: How and When was it Formed?
Abstract
The Altiplano-Puna Plateau has an average elevation of ca. 3.5 km and sits on crust that is 60-70 km thick, twice the thickness of the average continental crust. The timing and mechanisms of the genesis of this geological anomaly are highly debated in the geology community. While shortening is believed to be responsible for the most part of the crustal thickness, the timing, mechanism and therefore magnitude of shortening, is not well constrained in the Northern Puna plateau. There, not only Cenozoic shortening has deformed the region, Ordovician shortening and Early Cretaceous rifting are also recorded. Of particular relevance are the two shortening events which demand detailed observations on the deformation patterns to pull them apart. This study utilized a suite of tools to understand the mechanism and to quantify the timing and tempo of deformation across a 140 km structural transect at 23° S - through the northern Puna plateau. We combined mapping, cross-cutting relationships, geochronology and low-temperature thermochronology to quantify the amount of exhumation and shortening in the Puna plateau. Our results indicate that deformation within the Ordovician section is controlled by highly contrasting lithological strengths. This allowed for accommodation of deformation by simple-shear mechanisms related to multiple detachments within the section. The Cenozoic deformation was controlled by new and inherited structures from both the Ordovician and the Cretaceous event. New cooling ages show that by Eocene times, the western Puna-Plateau was being exhumed due to the development of the thrust belt. The deformation was propagated in a bivergent system until the Oligocene when the orogenic front resumed its propagation to the east. Our study shows that the Eocene-Oligocene thrust belt located in the modern Puna region was controlled by a detachment at the base of the Ordovician section from which shortening was propagated to the surface. This structural feature and a similar kinematics of the deformation have been proposed to the north, east of the Altiplano plateau, evidencing the continuous evolution along the plateau.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T51F0242H
- Keywords:
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- 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8038 Regional crustal structure;
- STRUCTURAL GEOLOGYDE: 8104 Continental margins: convergent;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS