ORCID Profile
0000-0001-6343-2482
Current Organisation
University of Manchester
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Publisher: Springer Science and Business Media LLC
Date: 23-07-2018
Publisher: Springer Science and Business Media LLC
Date: 08-2015
Publisher: Oxford University Press (OUP)
Date: 18-06-2021
DOI: 10.1093/PETROLOGY/EGAB054
Abstract: Establishing the conditions and dynamics of pre-eruptive magma storage and transfer within transient transcrustal storage networks is a major focus of quantitative volcanic petrology. In Iceland, the behaviour, conditions and timescales of magmatic processes within on-rift plumbing systems are increasingly well constrained. However, relatively little is known about magma storage and transfer in off-rift zones, despite off-rift volcanoes being able to generate hazardous explosive eruptions after centuries or millennia of dormancy (e.g. 2010 AD Eyjafjallajökull 1362 AD Öræfajökull 3.0 ka, 4.2 ka and 1104 AD Hekla). We present a combined geochemical and geothermobarometric study of magma storage and transfer recorded in the products of the postglacial Búðahraun (∼5.0–8.0 ka) and Berserkjahraun (∼4.0 ka) eruptions within the Snæfellsnes volcanic zone. The eruption products contain erse and compositionally heterogeneous macrocryst cargoes recording complex petrogenetic histories of crystal evolution and inheritance from different parts of the sub-volcanic plumbing systems. Geothermobarometry indicates two compositionally and thermally heterogeneous magma storage regions located in the lower (20 ± 4 km) and upper-mid (11 ± 3 km) crust. Crystallization pressure and depth estimates coincide with comparable data from Vatnafell, a small sub-glacial table mountain (tuya) in the centre of the Snæfellsnes volcanic zone, indicating that the nature and conditions of magma storage have remained unchanged since the Upper Pleistocene. Trace element zoning of clinopyroxene macrocrysts indicates that mafic recharge into the upper-mid-crustal storage zone triggered the eruptions of Búðahraun and Berserkjahraun. Evidence for eruption-triggering mafic recharge and basaltic cannibalism involving the transfer and amalgamation of crystals with different evolutionary histories sets the Búðahraun and Berserkjahraun eruptions apart from other studied eruptions in Iceland. We propose that the compositional and textural ersity preserved within the crystal cargoes are a direct consequence of the reduced heat flow beneath the Snæfellsnes volcanic zone, which favours the formation of isolated melt pockets in which compositionally erse macrocryst populations formed. Periodic flushes of primitive basaltic magma from depth promote widespread mixing with evolved melts, resulting in the assembly of crystals with erse ancestries from different parts of the sub-volcanic systems. Insights gained from the erse macrocryst cargoes of Búðahraun and Berserkjahraun and comparisons with recent off-rift volcanism in Iceland are essential for the development of future monitoring efforts and hazard evaluation. Although volcanism within the Snæfellsnes volcanic zone differs fundamentally from that in rift zones where eruptions are controlled by extensional spreading, magma ascent from depth still appears to follow pre-existing tectonic escape routes. This could result in extremely short advance warning times on the order of a few days.
Publisher: Oxford University Press (OUP)
Date: 11-05-2013
Publisher: Elsevier BV
Date: 05-2017
Publisher: American Geophysical Union (AGU)
Date: 07-2023
DOI: 10.1029/2022GC010811
Abstract: The compositions of volcanic materials are sensitive to physical conditions in the underlying magmatic system. When basaltic melts are saturated in olivine‐plagioclase‐augite prior to eruption, their compositions can be used to estimate the pressure at which they last equilibrated. We developed PyOPAM, an open‐source tool that runs in Python, and use this refreshed liquid‐barometer to investigate the relationship between final depths of magma storage and magma flux. We first tested PyOPAM using 312 experimental glasses compiled from literature and found that the 1 σ uncertainty is 1.13 kbar (±3 km). PyOPAM was then applied to a data set of 13,400 analyses from Iceland, where suspected controls on magma flux are well constrained. Of these, 3807 analyses return robust pressure estimates, constraining final pre‐eruptive magma storage depths for 23 of the 30 Icelandic volcanic systems. Our results indicate that magma storage pressures on Iceland are linked to melt‐flux from the mantle. This finding is consistent with previous models linking storage depths and spreading rates on the global mid‐ocean ridge system. In addition, we provide clear evidence that the magma flux, rather than spreading rate alone, is the key control on the distribution of melt at spreading centers. Increased melt flux is associated with shoaling of pre‐eruptive storage depths, indicating that mantle melt fluxes dictate the long‐term stabilization of extensive magmatic storage regions at depths shallower than 10 km. Quantitative relationships between mantle melt flux and storage depths can be used to test computational models of transcrustal magmatic systems.
Publisher: Oxford University Press (OUP)
Date: 29-12-0009
DOI: 10.1093/PETROLOGY/EGAC126
Abstract: The composition of clinopyroxene and clinopyroxene-liquid (Cpx-Liq) pairs are frequently used to calculate crystallization/equilibration pressures in igneous systems. While canonical uncertainties are often assigned to calculated pressures based on fits to calibration or test datasets, the sources of these uncertainties (and thus ways to reduce them) have not been rigorously assessed. We show that considerable uncertainties in calculated pressures arise from analytical error associated with Electron Probe Microanalyser (EPMA) measurements of Cpx. Specifically, low X-ray counts during analysis of elements with concentrations & wt% resulting from insufficient count times and/or low beam currents yield highly imprecise measurements (1σ errors of 10–40% for Na2O). Low analytical precision propagates into the calculation of pressure-sensitive mineral components such as jadeite. Using Monte Carlo approaches, we demonstrate that elemental variation resulting from analytical precision alone generates pressures spanning ~4 kbar (~15 km) for a single Cpx and ~6 kbar for a single Cpx-Liq pair using popular barometry expressions. In addition, analytical uncertainties in mineral compositions produce highly correlated arrays between pressure and temperature that have been previously attributed to transcrustal magma storage. Before invoking such geological interpretations, a more mundane origin from analytical imprecision must be ruled out. Most importantly, low analytical precision does not just affect the application of barometers to natural systems it has also affected characterization of Cpx in experimental products used to calibrate and test barometers. The impact of poor precision on each in idual measurement is often magnified by the small number of measurements made within experimental charges, meaning that low analytical precision and true variability in mineral compositions have not been sufficiently mediated by averaging multiple EPMA analyses. We compile the number of Cpx measurements performed in N = 307 experiments used to calibrate existing barometers, and N = 490 new experiments, finding ~45% of experiment charges were characterized by ≤5 in idual Cpx analyses. Insufficient characterization of the true composition of experimental phases likely accounts for the fact that all Cpx-based barometers exhibit large errors (± 3 kbar) when tested using global experimental datasets. We suggest specific changes to analytical and experimental protocols, such as increased count times and/or higher beam currents when measuring low concentration elements in relatively beam resistant Cpx in experiments and natural s les. We also advocate for increasing the number of analyses per experimental charge, resolving interlaboratory analytical offsets and improving data reporting. Implementing these changes is essential to produce a more robust dataset to calibrate and test the next generation of more precise and accurate Cpx-based barometers. In turn, this will enable more rigorous investigation of magma storage geometries in a variety of tectonic settings (e.g. distinguishing true transcrustal storage vs. storage in discrete reservoirs).
Publisher: Frontiers Media SA
Date: 20-08-2021
Publisher: Oxford University Press (OUP)
Date: 31-10-2014
Publisher: Elsevier BV
Date: 08-2014
Publisher: Elsevier BV
Date: 09-2015
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2017
End Date: 2025
Funder: German Research Foundation
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