High pressure experimental investigation of clinopyroxene dissolution in a K-basaltic melt

Dissolution of clinopyroxene (cpx) in a K-basaltic melt from the Campi Flegrei Volcanic District (Italy) has been
investigated through dissolution and dissolution-crystallization experiments at pressure of 0.8 GPa, superliquidus
temperature of 1350 ◦C, and dwell times between 0.5 and 1 h. The obtained dissolution rates range from
7.9⋅10− 6 cm s− 1 to 6.1⋅10− 6 cm s− 1 as a function of dwell time. In the dissolution-crystallization experiment
(1300 ◦C; 0.8 GPa; 2 h), the formation of overgrowth rims accompanied by new cpx crystals suggests that the
injection of recharge magmas in basaltic reservoir may lead to inverse or oscillatory zonation. The interaction
between cpx and K-basaltic melt at ~1570 ◦C was studied by in situ radiography using synchrotron radiation
combined with the Paris-Edinburgh press. This resulted in cpx resorption to occur depending on the temperature
conditions with respect to the liquidus temperature of the cpx (TcpxL). The calculated cpx dissolution rates are
~5⋅10− 3 cm s− 1 at T ≤ TcpxL and ~ 3⋅10− 2 cm s− 1 at T ≥ TcpxL. The role of crystal dissolution in the estimation of
magma residence times has been also tested for a natural magmatic system by interpolating the dissolution rates
(~10− 5–10− 6 cm s− 1) with the textural data of cpx phenocrysts from the Agnano-Monte Spina pyroclastic deposit
at Campi Flegrei caldera (Campanian region, Italy). Results from calculations indicate that the time required for
partial or complete resorption of phenocrysts varies from ~0.5 to ~40 h, and that the effect of crystal dissolution
may be relevant to estimate magma residence times whether signifcant dissolution occurs during magma mixing
processes.