Inboard advance of arc magmatism regulates mountain building in the Andes

Debate continues over the mechanisms that govern the tempo and style of arc magmatism and retroarc deformation along ocean-continent plate boundaries. Here we integrate detrital and bedrock geo/thermochronological and geochemical records of Cenozoic arc magmatism with results on the spatiotemporal evolution of retroarc shortening and flexural subsidence to explore the interactions and feedbacks among subduction, magmatism, and crustal deformation in the southern Central Andes. A synthesis of igneous compositions, magmatic activity, thrust belt shortening, and sediment accumulation reveals recurring phases of increased arc magmatism, retroarc underthrusting, and foreland basin development over short ( < 10 Myr) timescales. Episodic advance of deformation was focused within discrete Andean tectonic provinces (of contrasting pre-Andean inheritance) that were sequentially activated 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 facilitated enhanced shortening and orogenic growth toward the cratonic interior.