Experimental cannibalization of plagioclase by alkaline basalt magmas

Authors

  • Cristina Perinelli Dipartimento di Scienze della Terra, Sapienza Università di Roma, P.le Aldo Moro 5, 00185, Rome, Italy
  • Alessandro Fabbrizio Institute of Petrology and Structural Geology, Faculty of Science, Charles University, Albertov 6, 12843 Prague, Czech Republic
  • Barbara Bonechi Department of Earth and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester, United Kingdom
  • Mario Gaeta Dipartimento di Scienze della Terra, Sapienza Università di Roma, P.le Aldo Moro 5, 00185, Rome, Italy
  • Aida Maria Conte Consiglio Nazionale delle Ricerche, Istituto di Geologia Ambientale e Geoingegneria, Sede Secondaria di Roma, c/o Dipartimento di Scienze della Terra, Sapienza Università di Roma, P.le A. Moro 5, 00185, Rome, Italy

DOI:

https://doi.org/10.13133/2239-1002/17931

Abstract

 

 Time-series crystallization/dissolution experiments were conducted on a natural potassic basalt seeded with bytownitic plagioclases (Plg) at atmospheric pressure, in air, at 1180- 1240 °C and isothermal dwell time up to 20 hours. Plg-seed presence promotes the early formation of new-Plg, dampening the clinopyroxene (Cpx) crystallization. New-Plgs grow at a rate from 10-6 up to 10-8 cm·s-1 as the dwell time increases. Seeds overgrow at similar rate. Cpx crystallizes with a delay of at least 3 hours; this has a significant impact on the composition of both residual melt and new-Plgs. For undercooling >35 °C the Cpx delay causes a strong supersaturation of this phase in the melt resulting in a decrease in the new-Plg nucleation rate by 2 orders of magnitude in the 3 h-experiment. In the 15h-run, Cpx coarsening and the decrease of crystallinity suggest the achievement of a near-equilibrium conditions. Cpx growth rate is in the order of 10-7 cm·s-1 showing very limited variation. Finally, for the investigated superheating (5-15 °C) only the long lasting experiments allows an estimation of Plg dissolution rate (10-9 cm·s-1) although changes in the melt composition are already detectable in the 3h-runs. 

As a whole our results suggest that in natural systems, the takeover of antecrysts/ xenocrysts by a magma can induce on a short time scales, changes in its initial nucleation behavior with remarkable petrological implications for the solidification paths and eruptive dynamics of potassic magmatic systems. 

Published

2023-02-10

Issue

Section

PETROLOGY