Volatiles beneath mid-ocean ridges: Deep melting, channelised transport, focusing, and metasomatism
Volatiles beneath mid-ocean ridges: Deep melting, channelised transport, focusing, and metasomatism
Deep-Earth volatile cycles couple the mantle with near-surface reservoirs. Volatiles are emitted by volcanism and, in particular, from mid-ocean ridges, which are the most prolific source of basaltic volcanism. Estimates of volatile extraction from the asthenosphere beneath ridges typically rely on measurements of undegassed lavas combined with simple petrogenetic models of the mean degree of melting. Estimated volatile fluxes have large uncertainties; this is partly due to a poor understanding of how volatiles are transported by magma in the asthenosphere. Here, we assess the fate of mantle volatiles through numerical simulations of melting and melt transport at mid-ocean ridges. Our simulations are based on two-phase, magma/mantle dynamics theory coupled to an idealised thermodynamic model of mantle melting in the presence of water and carbon dioxide. We combine simulation results with catalogued observations of all ridge segments to estimate a range of likely volatile output from the global mid-ocean ridge system. We thus predict global MOR crust production of 66–73 Gt/yr (22–24 km3/yr) and global volatile output of 52–110 Mt/yr, corresponding to mantle volatile contents of 100–200 ppm. We find that volatile extraction is limited: up to half of deep, volatile-rich melt is not focused to the axis but is rather deposited along the LAB. As these distal melts crystallise and fractionate, they metasomatise the base of the lithosphere, creating rheological heterogeneity that could contribute to the seismic signature of the LAB.
55-68
Keller, Tobias
d8dfcfa5-89d1-4203-aa2d-8c142c00a169
Katz, Richard F.
01d7145d-41ad-44eb-9671-ac78313e82c2
Hirschmann, Marc M.
fff26edc-f235-4ffa-8a4b-58a9d00de016
24 February 2017
Keller, Tobias
d8dfcfa5-89d1-4203-aa2d-8c142c00a169
Katz, Richard F.
01d7145d-41ad-44eb-9671-ac78313e82c2
Hirschmann, Marc M.
fff26edc-f235-4ffa-8a4b-58a9d00de016
Keller, Tobias, Katz, Richard F. and Hirschmann, Marc M.
(2017)
Volatiles beneath mid-ocean ridges: Deep melting, channelised transport, focusing, and metasomatism.
Earth and Planetary Science Letters, 464, .
(doi:10.1016/j.epsl.2017.02.006).
Abstract
Deep-Earth volatile cycles couple the mantle with near-surface reservoirs. Volatiles are emitted by volcanism and, in particular, from mid-ocean ridges, which are the most prolific source of basaltic volcanism. Estimates of volatile extraction from the asthenosphere beneath ridges typically rely on measurements of undegassed lavas combined with simple petrogenetic models of the mean degree of melting. Estimated volatile fluxes have large uncertainties; this is partly due to a poor understanding of how volatiles are transported by magma in the asthenosphere. Here, we assess the fate of mantle volatiles through numerical simulations of melting and melt transport at mid-ocean ridges. Our simulations are based on two-phase, magma/mantle dynamics theory coupled to an idealised thermodynamic model of mantle melting in the presence of water and carbon dioxide. We combine simulation results with catalogued observations of all ridge segments to estimate a range of likely volatile output from the global mid-ocean ridge system. We thus predict global MOR crust production of 66–73 Gt/yr (22–24 km3/yr) and global volatile output of 52–110 Mt/yr, corresponding to mantle volatile contents of 100–200 ppm. We find that volatile extraction is limited: up to half of deep, volatile-rich melt is not focused to the axis but is rather deposited along the LAB. As these distal melts crystallise and fractionate, they metasomatise the base of the lithosphere, creating rheological heterogeneity that could contribute to the seismic signature of the LAB.
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Accepted/In Press date: 2 February 2017
e-pub ahead of print date: 24 February 2017
Published date: 24 February 2017
Identifiers
Local EPrints ID: 488267
URI: http://eprints.soton.ac.uk/id/eprint/488267
ISSN: 0012-821X
PURE UUID: 20e69873-d958-42e8-82cc-48acc53c99de
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Date deposited: 19 Mar 2024 17:48
Last modified: 21 Mar 2024 03:16
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Author:
Tobias Keller
Author:
Richard F. Katz
Author:
Marc M. Hirschmann
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