49-2 What drove hinterland uplift and exhumation in the southern central Andes (29–34°S)?

Session: Exploring Feedbacks Between Tectonics and Climate on Lithospheric Evolution Using Multidisciplinary Approaches

Presenting Author:

Chelsea Mackaman-Lofland

Authors:

Mackaman-Lofland, Chelsea A.¹, Fosdick, Julie², Ketcham, Richard A.³, Lossada, Ana⁴, Rodriguez, Maria Pia⁵, Litvak, Vanesa⁶, Bertoa del Llano, Macarena⁷, Suriano, Julieta⁸, Mescua, Jose⁹, Giambiagi, Laura¹⁰, Capaldi, Tomas N.¹¹, Robbins, Samuel¹², Stockli, Daniel F.¹³, Horton, Brian K.¹⁴

(1) University of Tennessee, Knoxville, TN, USA, (2) University of Connecticut, Storrs, CT, USA, (3) Univ Texas, Austin, TX, USA, (4) Instituto de Estudios Andinos Don Pablo Groeber (IDEAN, University of Buenos Aires-CONICET), Buenos Aires, Argentina, (5) Universidad Andrés Bello, Santiago, Chile, (6) Instituto de Estudios Andinos Don Pablo Groeber (IDEAN, University of Buenos Aires-CONICET), Buenos Aires, Argentina, (7) IANIGLA - CONICET, Godoy Cruz, Mendoza, Argentina, (8) UBA-CONICET, Depto. de Ciencias Geológicas, Ciudad Autónoma de Buenos Aires, Argentina, (9) IANIGLA, CCT Mendoza, CONICET, Mendoza, Argentina, (10) CONICET, IANIGLA, Mendoza, Argentina, (11) University of California San Diego, La Jolla, CA, Argentina, (12) Jackson School of Geosciences, University of Texas at Austin, Austin, TX, USA, (13) Dept. of Earth and Planetary Sciences, University of Texas at Austin, Austin, TX, USA, (14) University of Texas at Austin, Jackson School of Geosciences, Austin, TX, USA,

Abstract:

The Andean hinterland at 29–34°S resides above a modern transition from flat-slab to normal subduction and contains the highest peaks associated with a subduction-related mountain belt (Aconcagua, 6961 m; Mercedario, 6720 m). Development of this narrow zone of high topography has been variably attributed to crustal thickening driven by internal (hinterland) shortening, underthrusting during shortening in external (forearc or retroarc) fold-thrust belts, or deeper (dynamic or isostatic) processes associated with increased buoyancy forces and/or plate coupling above the flat slab. Patterns of rock exhumation and topographic relief development may have been further modulated by Miocene–Pleistocene climate changes. We integrate structural, sedimentologic, and geo/thermochronological data that help constrain the timing and magnitude of rock uplift and exhumational cooling necessary to evaluate potential mechanisms of hinterland construction. New and published apatite (U-Th)/He, apatite fission track, and zircon (U-Th)/He data and allied thermal history models from 55 retroarc hinterland samples spanning >400 km along strike record protracted low-temperature (<100–160°C) residence of most samples since the late Mesozoic, followed by >40–80°C of rapid cooling at ~15–5 Ma. Multi-sample thermal history models and other geologic datasets demonstrate the influence of structurally controlled exhumation with important along-strike variations. At 29–31°S, models and structural measurements require ~10° of east-down tilting during topographic growth and exhumational cooling, consistent with patterns predicted in response to hinterland construction via underthrusting linked to retroarc fold-thrust belt shortening. At 31–33°S, signals of underthrusting are superposed by evidence of internal shortening along high-angle, west-dipping faults. At 33–34°S, beyond the southern termination of the retroarc fold-thrust belt, high-angle faults within the hinterland were the most important drivers of rock uplift and exhumation. This research highlights the importance of quantifying spatiotemporal patterns in thermochronology data when testing structural and topographic hypotheses and evaluating the timing, rates, and drivers of exhumational cooling under varied tectonic and climatic conditions.

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

doi: 10.1130/abs/2025AM-8806

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