6) Janine Andrys
Janine Andrys, Postdoctoral Research Fellow in the Department of Geosciences at Boise State University
Janine Andrys, Postdoctoral Research Fellow in the Department of Geosciences at Boise State University
Monday October 23rd; 3 PM
Monday October 23rd; 3 PM
Host: Dorsey Wanless
Host: Dorsey Wanless
Title: Insights on arc magmatic systems drawn from natural melt inclusions and laboratory experiments
Title: Insights on arc magmatic systems drawn from natural melt inclusions and laboratory experiments
Abstract: Glass compositions of mineral-hosted melt inclusions and whole rock compositions from the same volcano may record different compositional trends. These differences are often ascribed to post-entrapment phenomena that modify melt inclusion major elements. Yet, owing to the range of conditions over which melt inclusions may be trapped and preserved, differences between melt inclusion and whole rock chemistry may arise from primary igneous processes within a volcanic system, such as high pressure or polybaric crystallization and/or magma mixing. Buldir volcano in the western Aleutian arc provides a case study. We analyze compositions of olivine-hosted melt inclusions and conduct ƒO2-buffered, water-saturated crystallization experiments on a high-Al, basaltic starting material modeled after a Buldir lava at 8 kb and ƒO2 = QFM+1.6 ± 0.4 (1σ). The experiments produce melts with Si-enrichment and Fe-depletion signatures characteristics of evolved, calc-alkaline magmas, although FeO* remains roughly constant over most of the experimental temperature range. Hornblende saturation generates the largest increase in SiO2 and largest decrease in FeO* in coexisting melts. Compositions of melt inclusions are consistent with experimental melts and reflect crystallization of a basaltic parent magma at high PH2O. Both trends differ from the overall trend of whole rock major elements. The melt inclusions and groundmass compositions analyzed in Buldir tephras preserve a polybaric liquid line of descent. Whole rocks, however, record compositions consistent with the addition of crystal cargo containing plagioclase and mafic olivine and/or hornblende, in addition to possible mixing with residual, evolved melts, such that the whole rocks no longer represent fractional liquids erupted from depth. Both the experimental melts and the Buldir whole rock trend achieve Fe-depletion and Si-enrichment characteristic of calc-alkaline magmas at low MgO (< 4.2 wt.%), but the paths to that endpoint differ. Coupled evidence from melt inclusions and experiments reveals that the Buldir whole rock trend doesn’t reflect a true liquid line of descent, warranting caution in interpretation of volcanic trends globally. Moreover, liquid lines of descent with strong, continuous Si-enrichment and Fe-depletion trends like those of the Buldir whole rocks do not appear to be achievable at arc relevant oxygen fugacities, even at hydrous conditions.
Abstract: Glass compositions of mineral-hosted melt inclusions and whole rock compositions from the same volcano may record different compositional trends. These differences are often ascribed to post-entrapment phenomena that modify melt inclusion major elements. Yet, owing to the range of conditions over which melt inclusions may be trapped and preserved, differences between melt inclusion and whole rock chemistry may arise from primary igneous processes within a volcanic system, such as high pressure or polybaric crystallization and/or magma mixing. Buldir volcano in the western Aleutian arc provides a case study. We analyze compositions of olivine-hosted melt inclusions and conduct ƒO2-buffered, water-saturated crystallization experiments on a high-Al, basaltic starting material modeled after a Buldir lava at 8 kb and ƒO2 = QFM+1.6 ± 0.4 (1σ). The experiments produce melts with Si-enrichment and Fe-depletion signatures characteristics of evolved, calc-alkaline magmas, although FeO* remains roughly constant over most of the experimental temperature range. Hornblende saturation generates the largest increase in SiO2 and largest decrease in FeO* in coexisting melts. Compositions of melt inclusions are consistent with experimental melts and reflect crystallization of a basaltic parent magma at high PH2O. Both trends differ from the overall trend of whole rock major elements. The melt inclusions and groundmass compositions analyzed in Buldir tephras preserve a polybaric liquid line of descent. Whole rocks, however, record compositions consistent with the addition of crystal cargo containing plagioclase and mafic olivine and/or hornblende, in addition to possible mixing with residual, evolved melts, such that the whole rocks no longer represent fractional liquids erupted from depth. Both the experimental melts and the Buldir whole rock trend achieve Fe-depletion and Si-enrichment characteristic of calc-alkaline magmas at low MgO (< 4.2 wt.%), but the paths to that endpoint differ. Coupled evidence from melt inclusions and experiments reveals that the Buldir whole rock trend doesn’t reflect a true liquid line of descent, warranting caution in interpretation of volcanic trends globally. Moreover, liquid lines of descent with strong, continuous Si-enrichment and Fe-depletion trends like those of the Buldir whole rocks do not appear to be achievable at arc relevant oxygen fugacities, even at hydrous conditions.
Bio: Janine Andrys is a Postdoctoral Research Fellow in the Department of Geosciences at Boise State University. Janine received her PhD from the University of Rhode Island Graduate School of Oceanography in 2023 and held an academic fellowship with the National Museum of Natural History, Smithsonian Institution from 2017-2023. Janine is an igneous petrologist and her research revolves around using the mineral assemblages and major, trace, and volatile element compositions of basaltic rocks to interpret a magma’s history before eruption. Her research interests include geochemical cycling between Earth’s surface and the mantle over geologic time, the process of magma evolution as it cools and crystallizes in the crust at different thermodynamic conditions, and the chemistries of primary melts of the mantle at various settings on Earth. Currently, Janine is working on projects in the Galápagos, East-Pacific Rise, Aleutian arc, and global back-arc basins.
Bio: Janine Andrys is a Postdoctoral Research Fellow in the Department of Geosciences at Boise State University. Janine received her PhD from the University of Rhode Island Graduate School of Oceanography in 2023 and held an academic fellowship with the National Museum of Natural History, Smithsonian Institution from 2017-2023. Janine is an igneous petrologist and her research revolves around using the mineral assemblages and major, trace, and volatile element compositions of basaltic rocks to interpret a magma’s history before eruption. Her research interests include geochemical cycling between Earth’s surface and the mantle over geologic time, the process of magma evolution as it cools and crystallizes in the crust at different thermodynamic conditions, and the chemistries of primary melts of the mantle at various settings on Earth. Currently, Janine is working on projects in the Galápagos, East-Pacific Rise, Aleutian arc, and global back-arc basins.
