MAGMATIC EVOLUTION OF AN ACTIVE CORDILLERAN MAGMATIC FLARE-UP EPISODE (Invited Presentation)

To better examine the role of crustal magmatic processes and its relationship to erupted material in Cordilleran systems, we present a continuous high-resolution crustal seismic velocity model for an ~800 km section of the active South American Cordillera (Puna Plateau). The main driving mechanism responsible for the magmatic flare-up in the Puna Plateau is thought to be the southward passage of flat-slab subduction, subsequent re-steepening of the slab, and associated lithospheric delamination. Our seismic velocity model provides evidence that is consistent with this interpretation and observations include: (1) the volumes of low-velocity zones associated with magmatic reservoirs decreases from north to south across the Puna Plateau, (2) the lowest velocities observed in the core of any reservoir progressively increases from north to south, (3) the depths (b.s.l.) at which the lowest velocity (center of low-velocity zone) is imaged in each of the five low-velocity zones systematically deepens from north to south. Finally, we are able to calculate a plutonic-to-volcanic ratio for the entire Puna Plateau, for which we obtain an estimate of ~34:1, which compares extremely well to recent estimates in the Sierra Nevada arc or the Ordovician arc at the Sierra de Valle Fértil titled exposure site.

Although our seismic velocity model only reveals the current magmatic state of the crust in the Puna, the unique southward migration of the mechanism responsible for the magmatic flare-up allows us to interpret along-strike variations as different stages in the magmatic evolution of the Puna Plateau. Under this paradigm, the sequence of south to north cross-sections illustrates the magmatic evolution in a thermally warming and tectonically widening thickened crust. Using the plutonic volumes imaged from our velocity model as a proxy for the spatial distribution of future ignimbrite eruptions, numerous spatial-temporal similarities are observed between the evolution of the APVC magmatic flare-up and the augmented magmatic history inferred for the southern Puna. We therefore suggest the crust in the APVC represents a thermally evolved version of the southern Puna crust. A corollary of this interpretation is that silicic magmatism in the southern Puna will eventually resemble the APVC ignimbrite flare-up episode.