CORDILLERAN HIGH FLUX EVENTS: INSIGHTS FROM AN IGNIMBRITE FLARE-UP IN THE CENTRAL ANDES

Continental arc evolution is characterized by steady-state magmatism punctuated by episodic High Flux Events (HFEs) thought to be driven by density instabilities in the lower crust/mantle interface resulting from crustal thickening (e.g. DeCelles et al, 2009). However, the Neogene ignimbrite flare-up of the Central Andes is time and space transgressive responding primarily to the rearrangement of plate and mantle wedge geometry in response to the passage of the Juan Fernandez ridge (e.g. Kay and Coira, 2009; Freymuth et al., 2015). Slab steepening, delamination, and associated elevated mantle power input appear to be the primary drive for the flare-up. The most intense flare-up resulted in the Altiplano Puna Volcanic Complex (de Silva, 1989). The interaction of tectonics and magmatism here also implicate a major for upper crustal processes in the development of the flare-up.

~20 – 15 Ma compressional tectonics resulted in crustal thickening and uplift of the Altiplano-Puna plateau. A transition to orogeny parallel stretching (e.g. Riller et al, 2001) coincident with the passage of the Juan Fernandez ridge enhanced emplacement of magmas into the upper crust leading to development of a major upper crustal mash zone, the Altiplano Puna Magma Body (e.g. Ward et al., 2014; Burns et al., 2015). Consequent magmatic uplift of the plateau accompanied the ignimbrite flare-up (Perkins et al., 2016), probably reflecting the interplay between uplift, extension, and catastrophic caldera-forming eruptions. A broad correlation in tectonism, uplift and magmatism is evident. A more robust finer scale ~2 Ma episodicity in the high flux magmatic and eruptive chronology may be recorded in tectonic proxy coarse clastic sedimentary horizons between major ignimbrites. These relationships connote a strongly integrated history of magma intrusion, plateau uplift and extension, and catastrophic eruption in controlling the spatiotemporal character of this Cordilleran HFE.