Decarbonation and clast dissolution timescales for short-term magma‑carbonate interactions in the volcanic feeding system and their influence on eruptive dynamics: Insights from experiments at atmospheric pressure

Abstract

While long-term interactions of magma with carbonate wall-rock (a.k.a. carbonate assimilation) are well-studied, only recently some experimental studies focused on short-term interactions (seconds to minutes) at magma chamber conditions (0.5 GPa and 1200 °C). They have shown that carbonate assimilation can effectively release CO2 and dissolve the ingested clast in syn-eruptive timescales. Carbonate wall-rock xenoliths in eruptive products can hence be seen as proof of even shallower ingestion (i.e., within the feeding dyke). To study these shallower interactions, we performed 66 experiments at atmospheric pressure (i.e., at the second endmember of the volcanic feeding system) and at 950–1230 °C with varying melt compositions and limestone compositions. Decarbonation was found to be mainly dependent on temperature and limestone composition while clast dissolution is largely dependent on magma composition, temperature, pressure and interaction time. In natural systems during magma ascent and with increasing quantities of assimilated wall-rock, the magma temperature would steadily decrease, limiting its own decarbonation and assimilation ability. But even in the 950 °C-experiments decarbonation (i.e., CO2 release) remained a syn-eruptive process. We subsequently discussed the limits of carbonate assimilation as well as the potential effect of syn-eruptive addition of CO2 to the magmatic mixture on magma ascent and eruption dynamics.