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The Significance of Multiple Saturation Points in the Context of Polybaric Near-fractional Melting

Longhi, John and Asimow, Paul D. (2004) The Significance of Multiple Saturation Points in the Context of Polybaric Near-fractional Melting. Journal of Petrology, 45 (12). pp. 2349-2367. ISSN 0022-3530. doi:10.1093/petrology/egh043.

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Experimental petrologists have successfully located basaltic liquid compositions parental to mid-ocean ridge basalt that are, within experimental resolution, multiply saturated with three-phase harzburgite or four-phase lherzolite assemblages on their liquidus at some elevated pressure. Such an experimental result is a necessary consequence of any paradigm in which erupted basalts derive from single-batch primary liquids that equilibrate with a mantle residue and undergo no subsequent magma mixing before differentiation and eruption. Here we investigate whether, conversely, such evidence of multiple saturation is sufficient to exclude dynamic melting models wherein increments of melt are mixed after segregation from residues, during melt transport or in magma chambers. Using two independent models of crystal–liquid equilibria to simulate polybaric near-fractional peridotite melting, we find that aggregate liquids from such melting processes can display near-intersections of liquidus surfaces too close to distinguish experimentally from exact multiple saturation points. Given uncertainties in glass compositions, fractionation corrections, experimental temperature and pressure conditions, and achievement of equilibrium, these results suggest that polybaric mixtures can in fact masquerade as mantle-equilibrated single-batch primary liquids. Multiple saturation points on the liquidus surfaces of primitive basalts do, however, preserve information about the average pressure of extraction of their constituent increments of liquid.

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Asimow, Paul D.0000-0001-6025-8925
Additional Information:Copyright © 2004 Oxford University Press. Reprinted with permission. RECEIVED JULY 2, 2003; ACCEPTED APRIL 6, 2004; Journal of Petrology Advance Access published on August 19, 2004 This paper was motivated by a stimulating conversation with D. H. Green, an invitation to speak at the 2002 Fall AGU Bowen symposium meeting from M. S. Ghiorso and D. Geist, and the hope that M. J. O'Hara will find it intriguing. We acknowledge helpful reviews by C. T. Herzberg and C. C. Lundstrom. It is not our intent to belittle the contributions of experimentalists who have laboured to collect liquidus data over the years in pursuit of multiple saturation points; these experiments have in fact proven essential for calibration of high-pressure melting and fractionation models such as those applied in this study. P.D.A. acknowledges support from the National Science Foundation (OCE-0241716 and EAR-0239513). J.L. acknowledges support from the National Science Foundation (OCE-0084098) and NASA (NAG 5-4649). This is Division of Geological and Planetary Science contribution 8961.
Subject Keywords:mantle melting; basaltic volcanism; experimental igneous petrology; thermodynamic modelling; inverse method
Issue or Number:12
Record Number:CaltechAUTHORS:ASIjpet04
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1461
Deposited By: Archive Administrator
Deposited On:19 Jan 2006
Last Modified:08 Nov 2021 19:10

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