13-6 Miocene extension of the hinterland Antofalla Basin, southern central Andes: Relationship to lithospheric foundering

Session: Toe to Toe: Cordilleran Systems from Trench to Retroarc Domains

Presenting Author:

Alexander Tye

Authors:

Tye, Alexander¹, Payrola, Patricio², Hardy, Aiden³, Casas, Alexis⁴, Ledesma, Jonathan⁵, McMillan, Mitchell⁶, Schoenbohm, Lindsay⁷, Sim, Shi⁸, Tremblay, Marissa⁹

Abstract:

In the Southern Puna Plateau, NW Argentina, Miocene to Quaternary lithospheric foundering is inferred from a combination of backarc volcanism and geophysically imaged detached lithosphere.  Anomalous tectonic extension or transtension may be key to better constraining the dynamics of foundering, but the timing and scale of such extension remains enigmatic.  We present new mapping and geochronology that document Middle to Late Miocene extension of the Antofalla Basin, which is centrally located in the area affected by foundering.

The Antofalla Basin is a ~125 km long, ~800 m deep linear basin that trends NNE within the Southern Puna Plateau and is internally drained.  Synorogenic conglomerates presently 800 m above the basin floor indicate that during Early Miocene time an uplifted basement block, supported by a thrust system, was located where the basin is now. 

New mapping and stratigraphic data from the Vega Antofalla region along the western margin of the northern part of the Antofalla Basin grant insight into the tectonic evolution of the basin, particularly via the record of the Early?-Middle Miocene Potrero Grande Formation.  The basal section of Potrero Grande Formation includes cobble-boulder conglomerates with NW-directed paleocurrents and metamorphic and plutonic clasts consistent with sourcing from a Miocene Antofalla paleo-highland to the southeast.  This part of the unit is also offset by N-striking thrusts, probably part of the same system that uplifted the nearby sediment source area.  In contrast, the upper Potrero Grande Formation has E-directed paleocurrents, is dominated by granite clasts, and is offset by a normal fault system that exposed granite basement to the west.  Thus, the Potrero Grande Formation here records a reversal of deformation sense from thrust to normal (or transtensional) faulting and the initial lowering of the Antofalla Basin interior to the east.  The upper Potrero Grande Formation interfingers with an overlying, ca. 11 Ma tuff, providing a minimum age for initiation of extension. 

The onset of extension >11 Ma at Vega Antofalla is consistent with age estimates from the southern part of the Antofalla Basin based on the ages of basal evaporite strata within the basin, suggesting a common evolution for the entire basin.  Extension of the Antofalla Basin several Myr before major backarc volcanism (ca. 8 Ma) is consistent with numerical models of lithospheric foundering.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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