27-13 Hinterland Basin Analysis Highlights Asynchronous, Localized Exhumation of Bolivian Eastern Cordillera

Session: Evolution of Cordilleran-type orogenic systems

Presenting Author:

Samuel Martin

Authors:

Martin, Samuel G.¹, Saylor, Joel², Rafeeza, Muhammad³, Alvarez, Paola⁴, Restrepo, Jimena⁵, Kopystecki, Helen⁶, Jallaza, Ruben⁷, Burga, Rolando⁸

(1) Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada, (2) Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada, (3) Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada; Earth, Energy, and Environment, University of Calgary, Calgary, AB, Canada, (4) Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada, (5) Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada, (6) Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada; Fortescue, Perth, WA, Australia, (7) Ciencias Geológicas, Universidad Mayor de San Andrés, La Paz, La Paz, Bolivia, (8) Ciencias Geológicas, Universidad Mayor de San Andrés, La Paz, La Paz, Bolivia,

Abstract:

The exceptional width, crustal thickness, and shortening magnitude of the central Andes surrounding the Altiplano (~14-22°S) are thought to be tied to an unusual progression of contractional deformation: rather than propagating steadily eastward, active shortening jumped several hundred km inboard from the Western Cordillera to the Eastern Cordillera (EC) in the middle Cenozoic. This structural transition placed part of the former foreland in a hinterland position now occupied by the Altiplano Basin (AB). As the EC grew into a major bivergent fold-thrust belt, it shed sediment westward into the AB and induced flexural subsidence on the basin’s east side. The spatio-temporal progression of EC development should therefore be recorded by AB subsidence patterns and sediment provenance. However, a scarcity of chronostratigraphic constraints has historically precluded using the basin record to track EC development along strike. Recent detrital zircon (DZ) work on the northern AB has suggested initial EC uplift progressed southward through time, but age constraints remain scarce for the central and southern AB.

We present a new regional 3D chronostratigraphic framework for the central and southern AB, constrained largely by new volcanic zircon and DZ maximum depositional ages from multi-km measured sections.

New flexural modeling for across-strike transects at ~21°S and ~18°S indicates the EC began to develop earlier adjacent to the southern AB than the central AB. This result is corroborated by age-constrained DZ provenance, clast counts, and paleocurrent analysis, all indicating an earlier influx of EC-sourced sediment in the south. Results also indicate the volumetric majority of AB strata were deposited in a hinterland rather than a foreland setting; although vertical lithofacies changes are locally consistent with classic foreland sedimentation associated with an advancing tectonic load, sedimentological results place this load to the east, in agreement with published EC thermochronology data.

When combined with published work on the northern AB, results suggest Eocene EC uplift originated along disconnected structures in the north and south, only later merging into a continuous fold-thrust belt along strike. This contrasts with one prevailing structural model in which EC exhumation was driven by kinematically linked, regional-scale basement thrusts whose detachments root west of the Altiplano. It favors, instead, a model in which EC faults were locally rooted, initially discontinuous structures with deformation driven by far-field stresses.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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