Probing the origins of large calderas in Kamchatka: are short-lived large silicic systems in continental arcs produced by periodic delamination of the lower crust?

Many continental arc systems where volcanism is dominated by shield and stratovolcano formation occasionally produce large silicic centers which are characterized by large calderas, short lifespans, and cumulative eruptive volumes which dwarf those of neighboring systems. Recent examples of such systems in the Kamchatka peninsula include the 1.78 Ma Karymshina and 0.43 Ma Pauzhetka systems. In Karymshina, 2-3 Myr of basaltic-intermediate magmatism climaxed in giant caldera-forming eruptions producing >500 km³ of rhyolite after which activity faded into quiescence. In Pauzhetka, no known precursors exist prior to a giant 300 km³ eruption. The heat required to produce such large volumes of magma clearly exceeds that required to sustain more typical stratovolcano volcanism, and requires rates of input of basaltic magma from the mantle which are both unusually voluminous and transient in nature.

For this study, we present preliminary results from a series of high-resolution magmatic-thermomechanical finite difference models which investigate the possible origin of these silicic volcanic flareups, using the Kamchatkan calderas as a benchmark to constrain model behavior. We find that the production of dense mafic cumulates in the mantle produces periodic intermittent dripping or delamination of the lowermost crust into the less dense upper mantle, allowing low-viscosity mantle to ascend several km from its initial position and undergo extensive decompression melting, resulting in a localized pulse of magmatism that may elevate intrusive fluxes of basalt into the crust by as much as an order of magnitude above background rates. This magmatism eventually thickens the crust and forces mantle melting back to deeper levels, and is therefore self-limiting and lasts for only a few Myr at most. These events vary in scale and their occurrence interval depends largely on background intrusion rates, with more active arcs having them more often. Chemical and isotopic mass balances and heat budget require 10 km of cumulates to produce the required silicic volumes, and the lack of extreme cumulative crustal thickening in Kamchatka by repeated silicic caldera formation can be explained by these repeated delamination events.