Solidus reactions in synthetic lherzolite-H2O-CO2 from 20-30 kbar, with applications to melting and metasomatism

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doi: 10.1016/0377-0273(92)90040-K
Authors:White, Bradford S.; Wyllie, Peter J.
Author Affiliations:Primary:
California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA, United States
Other:
University of Leeds, United Kingdom
Volume Title:Essays on magmas and other earth fluids; a volume in appreciation of Prof. Peter G. Harris
Volume Authors:Cox, K. G., editor; Baker, P. E.
Source:Essays on magmas and other earth fluids; a volume in appreciation of Prof. Peter G. Harris, edited by K. G. Cox and P. E. Baker. Journal of Volcanology and Geothermal Research, 50(1-2), p.117-130. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-0273
Publication Date:1992
Note:In English. 36 refs.; illus., incl. 2 tables
Summary:Mixtures of synthetic forsterite, enstatite, diopside and natural dolomite were used to determine solidus reactions for synthetic lherzolite-H2O (passing through 1125, 1060 and 1005 degrees C, at 10, 20 and 30 kbar, respectively), and dolomite-lherzolite with mixed vapour, two curves not previously located experimentally. The vapour-buffered curve for dolomite-lherzolite has a distinctive P minimum, passing down from the CO2 system near 28 kbar and 1230 degrees C to a minimum near 22 kbar and 1075 degrees C, with decreasing CO2/H2O in the vapour, and then up in P through a point at 30 kbar and 990 degrees C. These new results, with others published, permit complete reconstruction of the three divariant solidus and decarbonation surfaces meeting along the vapour-buffered dolomite- lherzolite solidus curve. The vapour phase composition at the P minimum on this curve is approx 85 mol.% CO2; the corresponding curve for natural peridotites is complicated by the addition of amphibole. The three surfaces define boundaries between regions where various kinds of metasomatic fluids can exist, their positions moving to lower T for natural peridotites, and the vapour-buffered solidus ledge occurring at approx 75 km depth. Rapid changes in melt and vapour phase compositions coexisting with peridotite occur within this narrow interval. At <= 75 km silicate magmas coexist with peridotite and vapours range from CO2 to H2O; at >= 75 km near-solidus melts are carbonatitic, with any vapour present being H2O-rich. Rising volatile-rich melts (of moderate T) in equilibrium with peridotite must begin to crystallize and give off vapours near this depth, with compositions changing from H2O- to CO2-rich as depth increases. Melts and vapours separate rapidly from crystals at this and greater depths. [R.E.S.]
Subjects:Experimental studies; High pressure; Igneous rocks; Lherzolite; Mantle; Melting; Melts; Metasomatism; P-T conditions; Peridotites; Petrography; Phase equilibria; Plutonic rocks; Pressure; Ultramafics
Abstract Numbers:93M/561
Record ID:1996025116
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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