A Simple Thermodynamic Model for Melting of Peridotite in the System NCFMASOCr

Jennings, Eleanor S. and Holland, Tim J. B. (2015) A Simple Thermodynamic Model for Melting of Peridotite in the System NCFMASOCr. Journal of Petrology, 56 (5). pp. 869-892. ISSN Print ISSN 0022-3530 - Online ISSN 1460-2415 DOI 10.1093/petrology/egv020

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Official URL: http://petrology.oxfordjournals.org/content/early/...

Abstract

A new thermodynamic model is presented for calculating phase relations in peridotite, from 0·001 to 60 kbar and from 800°C to liquidus temperatures, in the system NCFMASOCr. This model system is large enough to simulate phase relations and melting of natural peridotite and basaltic liquids. Calculations in the program THERMOCALC illustrate mantle phase relationships and melting conditions, specifically for the peridotite composition KLB-1. The garnet–spinel transition zone intersects the solidus at 21·4–21·7 kbar, where both Fe3+ and Cr increase spinel stability, expanding the width of the transition. Orthopyroxene is lost at the solidus at 42 kbar in KLB-1, although this pressure is very sensitive to bulk composition. Calculated oxidation states are in excellent agreement with measured log fO2 for xenolith suites with mantle Fe2O3 contents in the range 0·1–0·3 wt %. It appears that mantle oxidation state is not just a simple function of P and T, but depends on phase assemblage, and may vary in a complex way within a single assemblage. The liquid model performs well, such that calculated solidus, melt productivity and liquid compositions compare favourably with those of experimental studies, permitting its use in interpolating between, and extrapolating from, experimental P–T conditions. Experimentally challenging but geologically useful regimes can be explored, such as subsolidus samples and very low melt fractions, with application to both mantle xenoliths and the origin of basalt.

Item Type: Article
Uncontrolled Keywords: 2015AREP; IA69;
Subjects: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
Divisions: 05 - Petrology - Igneous, Metamorphic and Volcanic Studies
07 - Gold Open Access
Journal or Publication Title: Journal of Petrology
Volume: 56
Page Range: pp. 869-892
Identification Number: 10.1093/petrology/egv020
Depositing User: Sarah Humbert
Date Deposited: 13 Aug 2015 17:25
Last Modified: 25 Aug 2015 14:31
URI: http://eprints.esc.cam.ac.uk/id/eprint/3417

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