TY - JOUR

T1 - Chemical variability in peralkaline magmas and magma reservoirs

T2 - insights from the Khaggiar lava flow, Pantelleria, Italy

AU - Neave, David A.

N1 - Funding Information: Thanks to Margaret E. Hartley and Michael J. Stock for providing feedback on an earlier version of this manuscript. Thanks also to Ray Macdonald and one anonymous reviewer for their insightful and constructive comments that improved the manuscript’s clarity considerably, as well as to Othmar Müntener for his efficient editorial handling. Many thanks to Agnes F. Upshall, field assistant and knitter in residence, for her help during fieldwork. Fieldwork and XRF analyses were supported by a grant from the Elspeth Matthews Fund of the Geological Society of London. I also acknowledge support from the Alexander von Humboldt Foundation (Postdoctoral Research Fellowship) and the University of Manchester (Presidential Fellowship).

PY - 2020/4/3

Y1 - 2020/4/3

N2 - Silicic volcanoes are increasingly understood to be underlain by crystal-rich and vertically extensive magma reservoirs within which disequilibrium is widespread. Observations from ignimbrite deposits demonstrate that silicic magma reservoirs are often compartmentalised and compositionally stratified. However, it is currently unclear whether the small (i.e., < 0.1 km3 dense rock equivalent) eruptions that dominate activity at many volcanoes, and peralkaline volcanoes in particular, are fed from similarly complex magma reservoirs as their larger counterparts. Here I report petrographic and geochemical observations from the products of a small peralkaline eruption on Pantelleria, Italy, with the aims of unravelling peralkaline magma assembly processes and evaluating the complexity of reservoirs feeding small silicic eruptions. Matrix glass and whole-rock compositions from the Khaggiar lava flow and Cuddia Randazzo pumice cone reveal that erupted magmas were assembled from at least three distinct magma types stored within a compartmentalised magma reservoir: trachytes, less-evolved pantellerites and evolved pantellerites. Chemical variability in the Khaggiar lava flow was created by at least three distinct processes: the accumulation of evolved macrocrysts into evolved pantellerites; the injection of trachytic magmas into less evolved pantellerites; and the accumulation of relatively primitive macrocrysts into trachytic magmas. Macrocryst textures indicate that both trachytic and pantelleritic domains of the magma reservoir experienced numerous recharge events prior to the one that ultimately triggered eruption. Overall, magmas forming the Khaggiar lava flow and Cuddia Randazzo pumice cone appear to have been assembled in analogous ways to those erupted in much larger events. My observations are in good agreement with those from other peralkaline volcanoes and confirm that magma mingling, crystal cannibalism and macrocryst entrainment are as ubiquitous in peralkaline systems as they are in their calc-alkaline counterparts.

AB - Silicic volcanoes are increasingly understood to be underlain by crystal-rich and vertically extensive magma reservoirs within which disequilibrium is widespread. Observations from ignimbrite deposits demonstrate that silicic magma reservoirs are often compartmentalised and compositionally stratified. However, it is currently unclear whether the small (i.e., < 0.1 km3 dense rock equivalent) eruptions that dominate activity at many volcanoes, and peralkaline volcanoes in particular, are fed from similarly complex magma reservoirs as their larger counterparts. Here I report petrographic and geochemical observations from the products of a small peralkaline eruption on Pantelleria, Italy, with the aims of unravelling peralkaline magma assembly processes and evaluating the complexity of reservoirs feeding small silicic eruptions. Matrix glass and whole-rock compositions from the Khaggiar lava flow and Cuddia Randazzo pumice cone reveal that erupted magmas were assembled from at least three distinct magma types stored within a compartmentalised magma reservoir: trachytes, less-evolved pantellerites and evolved pantellerites. Chemical variability in the Khaggiar lava flow was created by at least three distinct processes: the accumulation of evolved macrocrysts into evolved pantellerites; the injection of trachytic magmas into less evolved pantellerites; and the accumulation of relatively primitive macrocrysts into trachytic magmas. Macrocryst textures indicate that both trachytic and pantelleritic domains of the magma reservoir experienced numerous recharge events prior to the one that ultimately triggered eruption. Overall, magmas forming the Khaggiar lava flow and Cuddia Randazzo pumice cone appear to have been assembled in analogous ways to those erupted in much larger events. My observations are in good agreement with those from other peralkaline volcanoes and confirm that magma mingling, crystal cannibalism and macrocryst entrainment are as ubiquitous in peralkaline systems as they are in their calc-alkaline counterparts.

KW - Chemical variability

KW - Crystal mush

KW - Magma mixing

KW - Pantellerite

KW - Peralkaline

UR - http://www.scopus.com/inward/record.url?scp=85082935656&partnerID=8YFLogxK

U2 - 10.1007/s00410-020-01678-0

DO - 10.1007/s00410-020-01678-0

M3 - Article

AN - SCOPUS:85082935656

VL - 175

JO - Contributions to Mineralogy and Petrology

JF - Contributions to Mineralogy and Petrology

SN - 0010-7999

IS - 4

M1 - 39

ER -