Abstract
Characterising equilibrium and disequilibrium crystal-melt processes is critical in determining the extent of magma mixing and crystallization conditions in the roots of volcanoes. However, these processes remain poorly investigated in most Pacific intraplate ocean settings that are difficult to access and study. To help address this issue, we investigated crystallization conditions of clinopyroxene phenocrysts in an accreted Palaeogene oceanic island in Panama. Petrographic and geochemical observations, petrological modelling of major and trace elements, and liquid-mineral multicomponent equilibrium tests were carried out using basalts, picrites, and hawaiites of the transitional tholeiitic shield to alkaline post-shield volcanic stages of the island. Five types of clinopyroxene crystals were identified, including (1) microphenocrysts with micron-scale oscillatory zoning, (2) primitive, yet resorbed picrite-hosted phenocrysts, (3) chemically homogeneous, anhedral crystals found in the remaining basalts, (4) Ti–rich euhedral hawaiite-hosted phenocrysts, and (5) evolved sector-zoned phenocrysts. Liquid-clinopyroxene multicomponent equilibrium tests in combination with textural analysis show that ~ 74% of the studied clinopyroxenes are in possible major element equilibrium with one of the available whole rock magma compositions, of which only 21% are equilibrated with their carrier liquid. To deconvolute clinopyroxene-melt pairings and determine plumbing system conditions, we combine rhyolite-MELTS modelling, geothermobarometry, and major- and trace-element equilibrium evaluations, limiting crystallization conditions to crustal levels (< 23 km depth). No migration of magmatic reservoirs to deeper levels is observed during the shield- to post-shield transition. These results suggest the occurrence of an extensive crystal mush system during the late shield to post-shield volcanic stages of this intraplate volcanic system, with both primitive and evolved crystallization domains sampled during eruptions.
| Original language | English |
|---|---|
| Article number | 30 |
| Pages (from-to) | 1-23 |
| Journal | Contributions to Mineralogy and Petrology |
| Volume | 177 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - 10 Feb 2022 |
Bibliographical note
Funding Information:We thank Cardiff University’s professional service staff Anthony Oldroyd and Dr. Duncan Muir for their help with sample preparation and SEM analysis, respectively. We are grateful to Dr. Stuart Kearns of Bristol University for his guidance in EMP analysis. Thanks are given to Ing. Helen de Waard of Utrecht University with her assistance with LA-ICP-MS. Lastly, we would like to thank Dr. David A. Neave for his external consultation on geothermobarometry. JB acknowledges support from a Royal Society Research Professorship. We would additionally like to thank Francesca Forni, Martin Streck, Silvio Mollo, an anonymous reviewer, and the handling editor for their invaluable feedback which allowed us to greatly improve this work.
Publisher Copyright:
© 2022, The Author(s).
Funding
We thank Cardiff University’s professional service staff Anthony Oldroyd and Dr. Duncan Muir for their help with sample preparation and SEM analysis, respectively. We are grateful to Dr. Stuart Kearns of Bristol University for his guidance in EMP analysis. Thanks are given to Ing. Helen de Waard of Utrecht University with her assistance with LA-ICP-MS. Lastly, we would like to thank Dr. David A. Neave for his external consultation on geothermobarometry. JB acknowledges support from a Royal Society Research Professorship. We would additionally like to thank Francesca Forni, Martin Streck, Silvio Mollo, an anonymous reviewer, and the handling editor for their invaluable feedback which allowed us to greatly improve this work.
Keywords
- Clinopyroxene zoning
- Cumulate recycling
- Geothermobarometry
- Magma mixing