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The evolution of pore connectivity in volcanic rocks.

Colombier, Mathieu and Wadsworth, Fabian B. and Gurioli, Lucia and Scheu, Bettina and Kueppers, Ulrich and Di Muro, Andrea and Dingwell, Donald B. (2017) 'The evolution of pore connectivity in volcanic rocks.', Earth and planetary science letters., 462 . pp. 99-109.

Abstract

Pore connectivity is a measure of the fraction of pore space (vesicles, voids or cracks) in a material that is interconnected on the system length scale. Pore connectivity is fundamentally related to permeability, which has been shown to control magma outgassing and the explosive potential of magma during ascent in the shallowest part of the crust. Here, we compile a database of connectivity and porosity from published sources and supplement this with additional measurements, using natural volcanic rocks produced in a broad range of eruptive styles and with a range of bulk composition. The database comprises 2715 pairs of connectivity C and porosity φ values for rocks from 35 volcanoes as well as 116 products of experimental work. For 535 volcanic rock samples, the permeability k was also measured. Data from experimental studies constrain the general features of the relationship between C and φassociated with both vesiculation and densification processes, which can then be used to interpret natural data. To a first order, we show that a suite of rocks originating from effusive eruptive behaviour can be distinguished from rocks originating from explosive eruptive behaviour using C and φ. We observe that on this basis, a particularly clear distinction can be made between scoria formed in fire-fountains and that formed in Strombolian activity. With increasing φ, the onset of connectivity occurs at the percolation threshold φcwhich in turn can be hugely variable. We demonstrate that C is an excellent metric for constraining φcin suites of porous rocks formed in a common process and discuss the range of φcvalues recorded in volcanic rocks. The percolation threshold is key to understanding the onset of permeability, outgassing and compaction in shallow magmas. We show that this threshold is dramatically different in rocks formed during densification processes than in rocks formed in vesiculating processes and propose that this value is the biggest factor in controlling the evolution of permeability at porosities above φc.

Item Type:Article
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Available under License - Creative Commons Attribution Non-commercial No Derivatives.
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1016/j.epsl.2017.01.011
Publisher statement:© 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Date accepted:15 January 2017
Date deposited:22 May 2018
Date of first online publication:30 January 2017
Date first made open access:22 May 2018

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