Salar de Antofalla depression, Puna Plateau, Argentina: an effect of transient extension in a compressional orogen following a mantle lithosphere drip

Abstract:

Removal of dense mantle lithosphere is hypothesized to be an essential component of compressional orogenesis, yet the effects of such removal and their timing and magnitude are debated; one proposed effect is gravitationally-driven extension. In the southern Puna plateau, the late Cenozoic foundering of a lithospheric drip is hypothesized based on tomographic imaging of a dense mass beneath the orogen [1] and Late Miocene to Quaternary bimodal volcanism [2]. Our new field observations, together with published geologic mapping and stratigraphy, suggest that the Salar de Antofalla depression in the southern Puna was formed by a transient episode of tectonic extension that corresponded spatially and temporally with lithosphere foundering.

The Salar de Antofalla depression is a sublinear, ~125 km long, NNE-trending topographic trough, across which topography and stratal ages are asymmetric. The western margin of the depression is a ~1 km tall escarpment that exposes a subhorizontal to gently folded Eocene to Middle Miocene sequence. The east side of the depression slopes more gently and exposes Late Miocene to Pliocene strata at elevations ~1 km below the Middle Miocene strata to the west. We observed a tabular, E-dipping body of fault breccia exposed on the western margin of the Antofalla depression. The fault breccia and juxtaposition of stratal ages suggest normal-sense slip on a basin-bounding fault.

Published paleocurrent directions in Cenozoic strata on both sides of the depression constrain the age of inferred extension. Paleocurrent directions indicate that the extant depression was occupied by a paleotopographic high during the Oligocene to Middle Miocene [3]. In contrast, Late Miocene to Quaternary paleocurrents indicate flow into the Antofalla depression [3]. Quaternary thrusting on the eastern margin of the depression indicates re-establishment of compressional deformation and brackets the age of extension to Late Miocene to (at the latest) Quaternary. The temporal correspondence of inferred extension with Late Miocene to Quaternary, mantle drip-related volcanism [2] suggests that extension may have resulted from mantle lithosphere drip detachment.

[1] Calixto et al., 2013, Geochem. Geophy. Geosy.

[2] Murray et al., 2015, in Geol. Soc. Am. Memoir 212

[3] Kraemer et al., 1999, J. S. Am. Earth Sci.