Eilish Brennan

Profile

I am a postgraduate researcher at the Institute of Geophysics and Tectonics. My research interests cover the volatiles of magmatic systems as a key driver of volcanic activity. I am funded by the Leeds-York Panorama NERC DTP (2021)  researching the volatile sources of volcanic systems across the Kamchatka volcanic arc, Russia as part of the NERC funded Deep Mantle Volatiles consortia. Collaborating with Dr Alex Iveson at Durham and Dr Tatiana Churikova in Moscow.

I previously completed my Masters at University College London where I carried out the geochemical analysis (FTIR, SEM/EDs & Raman spectroscopy) of olivine hosted melt inclusions to explore the degassing of active basaltic systems in the CAVAs. My interest lies in understanding volcanic processes through the study of magmatic volatiles and their related inputs and outputs. I primarily study the geochemical properties of erupted material at volcanic settings to gain a better understanding of the physical and chemical properties of the underlying mantle, interaction with crust and the associated magmatic systems.

I am also the current student representative for VMSG (the Volcanic and Magmatic Studies Group); all enquiries can be made to my email address.

Research interests

Research Keywords
Geochemistry, Mineralogy, Petrology, Volcanology

The sources of volatiles released across the Kamchatka volcanic arc.

The Kamchatka peninsula is one of the most volcanically active regions on Earth and is a natural laboratory to study the fate of subducted old (cold) oceanic crust and the interplay of magmatism. Uniquely the volcanoes of this arc erupt in several, rather than one, broad volcanic lineaments, possibly sampling magmatic fluid and melt sources in the forearc, beneath the main volcanic front and also from the behind-the-arc region. Geophysical and geochemical results show that the Kamchatka volcanoes sample fluids derived from slab depths from as little as 50km to as deep as 350 km. While the majority of arc volcanoes (here and elsewhere in other arcs) result from flux melting of depleted subarc mantle wedge source, the geochemistry of the arc volcanic rocks (incl. 10Be, U- series, B & Li isotopes, B/Be, B/Nb and Sr/Y ratios, among others) also shows, sometimes significant elemental and isotopic inputs from subducted slabs.

This project aims to address the volatiles sources and interaction across the Kamchatka arc by examining the geochemistry and petrology of volcanic products erupted along a SE-NW oriented depth transect across the Eastern Volcanic Arc Front and deep into the rear arc (Sredinny Ridge) region. In previous fieldwork campaigns we have extensively sampled Avachinsky and Bakening volcanoes that are ideally situated in the middle of cross-arc transect and represent depths to the top of the slab of 120 to 200 km., respectively. Here we will aim to conduct fieldwork and sample and study the volatile and fluid mobile element systematics in additional volcanoes from the same (arc front orthogonal) transect.

Geochemical and petrological studies allow for the quantification of these magmatic processes and insight into which changes drive and control them. The olivine- and pyroxene- bearing mafic samples (preferably scoria) we collect will be used to extract melt inclusions (MI) from the mafic minerals (ol, px, hbl). The new MI will be adding, for the first time, an exceptionally high-resolution look at the petrochemical variations across active volcanic arc. Moreover, we will uniquely have a chance to examine compositional changes of slab derived fluxes with increasing depth-to-slab. The project will involve the use of various in-situ measurement techniques such as SEM, EPMA, LA-ICP-MS and SIMS (for the MI) as well as utilising textural/petrological observations, and geochemical modelling based on bulk rock and MI datasets.

A search for Olivine-hosted Melt Inclusions in the active Central CAVA  to explore the degassing of basaltic systems.

Primitive melt inclusions (MIs) record valuable information about pre-eruptive melt volatile concentrations but finding good MI candidates can be challenging. Olivine-hosted MIs have been identified and characterised in samples that I collected from Cerro Negro and Arenal volcanoes, whereas samples from Concepcion and Masaya volcanoes did not reveal suitable olivine phenocrysts. MIs provide unique information on the volatile budgets of individual magmas and have become established as an important tool to predict eruptive behaviour of active volcanoes. In the laboratory, my aim was to characterise the main volatile phases present and to quantify their relative abundance using spectroscopic techniques. In addition to confirmation of expected H2O and CO2, Raman spectroscopy indicated the presence of additional gaseous CH4, HCl, CO and SO2, as well as occasional crystalline graphite and the textural association of clinopyroxene with MI-bearing olivine phenocrysts. Further quantification of the main phase H2O was embarked on using FTIR spectroscopy. Because the four volcanoes sampled lie at different locations along a subduction-controlled volcanic margin, it was hoped that they may show systematic differences between each other. To the extent which a short project can allow, I showed that lavas sampled at Cerro Negro volcano consistently define more primitive compositions, whereas lavas sampled at Arenal volcano are more evolved, and both these volcanoes are driven by magmas melted from a volatile-rich source in the upper mantle. The preliminary concentrations of H2O obtained are within error of prior studies and consistent with previous degassing estimations based on crystallisation depths, temperatures and pressures. I recognise that further characterisation of these MIs would be desirable, both to establish that they are representative and to evaluate a range of post entrapment effects that can modify or even compromise MI data. The methods used introduced many lines of error; technique-specific improvements such as overestimation of H2O by FTIR are addressed. The inability to obtain and assess quantitative mineral and glass compositions by electron microprobe (due to covid) has meant relying on previous studies as sources of that data, to compare with mineral/melt/gasequilibria. A variety of future methods for improving understanding of the volatile degassing history of these volcanic systems were also presented

Teaching interests

Volcanic processes, volcanic mapping, isotope geochemistry and igneous petrology.

Qualifications

• Msci (Earth Sciences), First Class Honors. University College London

Research groups and institutes

• Institute of Geophysics and Tectonics
• Rocks, Melts and Fluids
• Volcanology