27-6 Magmatic arc advance regulates orogenesis in the southern Central Andes

Session: Evolution of Cordilleran-type orogenic systems

Presenting Author:

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Abstract:

No consensus exists on the mechanisms that govern the tempo and style of arc magmatism and retroarc shortening along Cordilleran-type margins. We integrate geochronological and geochemical records of Cenozoic arc magmatism in the southern Central Andes with reconstructions of retroarc shortening and flexural subsidence to evaluate how subduction, magmatism, and crustal deformation interact through time. A synthesis of igneous εHf and εNd compositions, magmatic activity, fold-thrust belt shortening, and sediment accumulation reveals recurring 5-8 Myr cycles marked by enhanced arc magmatism, retroarc underthrusting, and foreland basin development. The periodic advance of retroarc deformation was focused within discrete Andean tectonic provinces, of contrasting pre-Andean inheritance, that were sequentially activated inboard toward the foreland along newly formed middle/upper-crustal décollements. Inboard migration of arc magmatism consistently preceded deformation advance, suggesting that fluid-assisted weakening above the subducting slab promoted focused shortening and orogenic growth toward the cratonic interior. Comparisons with both high- and low-shortening segments of the North and South American Cordillera indicate that magmatic arc advance and fluid-assisted retroarc weakening are vital components of Cordilleran mountain building. We propose that variations in the periodicity of magmatism and shortening reflect not only evolving slab dynamics, but also structural and stratigraphic heterogeneities embedded within the overriding continental crust.

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

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