72-4 Hydrogen Isotopes in Volcanic Glass Suggest Significant Spatio-Temporal Variation in Surface Uplift across the Entire Central Andes

Session: Toe to Toe: Cordilleran Systems from Trench to Retroarc Domains (Posters)

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Abstract:

The Central Andean Plateau (CAP) has long served as a case study in the tectonic and geodynamic drivers of Cordilleran systems, with much interest in the history of surface uplift in response to these processes. Paleoelevations have been estimated from geologic materials that record stable isotope compositions of surface water near the time of deposition. Spatio-temporal variation of H isotopes in volcanic glass – the most widely available stable isotope proxy in this area – has been linked to distinct geodynamic mechanisms for different tectonomorphic zones of the northern (Peruvian) CAP, including the Western Cordillera, Eastern Cordillera, and intervening Altiplano. In contrast, mainly eastward-progressing uplift has been inferred from volcanic glass for the Puna region of the southernmost CAP (Argentina and Chile). However, the Bolivian CAP comprises a major gap (~17-22° S) between these published datasets, obscuring the picture of along-strike variation in uplift and its mechanisms. Such variation is increasingly expected based on recent thermochronology and basin evolution work in this region, but its distribution remains unclear.

We present new H isotope data for volcanic glass throughout the Bolivian CAP and compare these to published volcanic glass H and carbonate O data. Results are most consistent with a scenario in which the Western Cordillera has been at high elevation since at least the late Oligocene, with most δD values (corrected to paleowater based on glass-water fractionation) consistently between -115‰ and -150‰. In contrast, a systematic change toward isotopically lighter paleowater in the central-southern Altiplano (a δD shift from ~ -80‰ to ~ -140‰) provides evidence for fairly rapid uplift between ~21 and 16 Ma, which is earlier than inferred for the northern Altiplano and may be associated with lithospheric foundering and/or lower crustal flow. Sparse data from the Eastern Cordillera are isotopically light (~ -105‰) by ~17 Ma and shift gradually lighter (~ -115‰) until ~8 Ma, consistent with previous suggestions that gradual uplift was driven by contractional deformation. Overall, H isotope results from the Bolivian CAP are more similar to results and inferred uplift mechanisms for the northern CAP than for the Puna region, but uplift of the Altiplano was likely more diachronous along strike than previously recognized.

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

doi: 10.1130/abs/2025AM-8288

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