ANDEAN ARC MIGRATION TRIGGERS RAPID RETROARC SHORTENING

The southern Central Andes above the central Chile flat slab record relatively higher strain rates (~2x) than comparable Cordilleran systems in North and South America. However, no consensus exists for the mechanisms that regulates the timing, style, and tempo of Andean mountain building between the latitudes of 30-32 °S. Here we integrate the Oligocene to Pliocene structural and sedimentary records to constrain the spatiotemporal evolution of retroarc shortening, and leverage existing arc magmatism datasets to speculate on the feedbacks and relationships among subduction, magmatism, and deformation along this segment of the Andes. Results reveal four distinct phases of coeval shortening, magmatic activity, and foreland basin development that reoccurred over short 5-8 Myr timescales. Shortening and high basin accumulation rates were spatially focused along distinct Andean fold-thrust belt segments that sequentially activated toward the foreland along new, disconnected decollements that soled into mid-crustal levels. Notably the advancing arc front temporally preceded retroarc shortening suggesting the influx of slab derived fluids during progressive shallowing of the down going plate may have been a critical mechanism that facilitated enhanced crustal deformation toward the foreland.