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A hydrous melting and fractionation model for mid-ocean ridge basalts: Application to the Mid-Atlantic Ridge near the Azores

Asimow, Paul D. and Dixon, J. E. and Langmuir, C. H. (2004) A hydrous melting and fractionation model for mid-ocean ridge basalts: Application to the Mid-Atlantic Ridge near the Azores. Geochemistry, Geophysics, Geosystems, 5 (1). 2003GC000568. ISSN 1525-2027. doi:10.1029/2003GC000568.

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The major element, trace element, and isotopic composition of mid-ocean ridge basalt glasses affected by the Azores hotspot are strongly correlated with H2O content of the glass. Distinguishing the relative importance of source chemistry and potential temperature in ridge-hotspot interaction therefore requires a comprehensive model that accounts for the effect of H2O in the source on melting behavior and for the effect of H2O in primitive liquids on the fractionation path. We develop such a model by coupling the latest version of the MELTS algorithm to a model for partitioning of water among silicate melts and nominally anhydrous minerals. We find that much of the variation in all major oxides except TiO2 and a significant fraction of the crustal thickness anomaly at the Azores platform are explained by the combined effects on melting and fractionation of up to ~700 ppm H2O in the source with only a small thermal anomaly, particularly if there is a small component of buoyantly driven active flow associated with the more H2O-rich melting regimes. An on-axis thermal anomaly of ~35°C in potential temperature explains the full crustal thickness increase of ~4 km approaching the Azores platform, whereas a ≥75°C thermal anomaly would be required in the absence of water or active flow. The polybaric hydrous melting and fractionation model allows us to solve for the TiO2, trace element and isotopic composition of the H2O-rich component in a way that self-consistently accounts for the changes in the melting and fractionation regimes resulting from enrichment, although the presence and concentration in the enriched component of elements more compatible than Dy cannot be resolved.

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Asimow, Paul D.0000-0001-6025-8925
Additional Information:Copyright 2004 by the American Geophysical Union. Received 11 April 2003; Revised 21 October 2003; Accepted 18 November 2003; Published 28 January 2004. PDA thanks Mark Ghiorso for allowing his code to be so mercilessly hacked. PDA was supported for part of this work by a postdoctoral fellowship from Lamont-Doherty Earth Observatory and later by the National Science Foundation (OCE 00-95294). CHL and JED acknowledge support by multiple grants from NSF over a period of years. This is Division of Geological and Planetary Sciences contribution number 8913.
Subject Keywords:Mid-Atlantic Ridge; Azores; basalt fractionation; hydrous mantle melting; plume-ridge interaction; 3640 Mineralogy and Petrology: Igneous petrology; 3035 Marine Geology and Geophysics: Midocean ridge processes; 9325 Information Related to Geographic Region: Atlantic Ocean
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Official Citation:Asimow, P. D., J. E. Dixon, and C. H. Langmuir (2004), A hydrous melting and fractionation model for mid-ocean ridge basalts: Application to the Mid-Atlantic Ridge near the Azores, Geochem. Geophys. Geosyst., 5, Q01E16, doi:10.1029/2003GC000568.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1090
Deposited By: Archive Administrator
Deposited On:19 Dec 2005
Last Modified:08 Nov 2021 19:07

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