Abstract
We created PyOPAM, an open-source software that runs in Python, to estimate the final storage depths of basaltic melts prior to eruption. This improved configuration of the Olivine-Plagioclase-Augite-Melt barometer can be used to estimate the depth where basaltic melt was last three-phase-saturated. Using 366 experimental glass compositions compiled from literature, we calibrate this barometer and constrain 1 σ to 1.26 kbar. We apply PyOPAM to a dataset of ~13,400 analyses of glass and whole-rock samples from Iceland. Of these, 3807 analyses generate robust pressure estimates, constraining final pre-eruptive magma storage depths for 23 of the 30 volcanic systems across Iceland.
Magma storage pressure is linked to input melt flux from the mantle as estimated from the product of crustal thickness and spreading rate. Independent increases in either spreading rate or crustal thickness are associated with shallowing of pre-eruptive storage depths, indicating that mantle melt fluxes dictate the long-term stabilisation of extensive magmatic storage regions at depths shallower than 10 km. The inherited thermal structure of the crust provides a secondary control on basaltic magma storage depths. Crust away from regions of long-term magma flux (e.g. off-axis) is less likely to host basaltic melt in shallow storage regions because the upper crust has cooled. The quantitative relationships between mantle flux and storage depths can be used to test computational models of transcrustal magmatic systems.