The pulse of large silicic magmatic systems

Large silicic volcanic fields (LSVFs) are considered windows into the tops of upper crustal batholiths that are the foundations of the continental crust. The space-time-volume records of volcanism in LSVFs are therefore assumed to mirror the accumulation record of the associated upper crustal batholith. However, key questions about the link between the volcanic and plutonic realms remain to be addressed if this view is to be substantiated. Among these are: 1) What does the surface pattern of volcanism really tell us about the development of the plutonic system below? Do these eruptions represent evacuation from a distinct batch of magma that formed just prior to eruption or do they represent the periodic tapping of a long lived regional magma body? 2) What does the cyclicity of the large caldera systems and the regional concordance of eruptions tell us about the development of the magmatic systems beneath? Does the repose period represent the time scale of development of the next magma batch or does the erupted magma develop in a timescale much shorter than the repose period? 3) What does the self-organization of single batholithic scale magmatic systems, for instance the development of a zoned system, tell us about the dynamics and time scales over which these systems differentiate and evolve? We are addressing some of these questions in the Altiplano-Puna Volcanic Complex of the Central Andes. Here, time scales of assembly and organization of batholith-scale silicic magma systems investigated using 40Ar/39Ar and U-Pb in zircon connote: 1) Supereruptions in the APVC evacuated distinct magma batches that accumulated within a few hundred thousand years prior to eruption 2) The repose period of cyclic supervolcanic systems is considerably longer than the time scale to develop the next eruptible magma batch 3) Batholith scale-silicic magma chambers can develop significant zonations in time scales of a few hundred thousand years. Additionally, our data suggest quasi-absent or dominant pre-eruptive zircon crystallization in otherwise compositionally highly similar magmas. This is in contrast to smaller arc volcanic systems like Crater Lake, Mt St Helens, and Aucanquilcha where abundant evidence for cannibalization and antecrysts are found. Larger magmatic systems may instead evolve into thermally buffered, and comparatively hot magma systems, thus acting against preservation of any prehistory in the system.