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Crystallisation of an alkali-olivine basalt under controlled PO2, PH2O conditions

Crystallisation of an alkali-olivine basalt under controlled PO2, PH2O conditions
Crystallisation of an alkali-olivine basalt under controlled PO2, PH2O conditions
An alkali-basalt from Hualalai, Hawaii, previously examined by Yoder and Tilley (1962) has been crystallised under controlled PO2 at 2 kb total pressure. Significant differences, in the order of appearance of the phases result from lowering the PO2 from 10?0.7 to about 10?10 atm. In particular magnetite, present at 1100 °C in the unbuffered runs does not crystallise until below 900 °C in the oxygen controlled runs. There is a drop of up to 50 °C on the liquidus of the system if the oxygen is controlled at the quartz-fayalite-magnetite buffer. Calcium amphiboles crystallised under such conditions are nepheline normative and rich in titanium and aluminium. Decreasing the water content but maintaining total pressure at 2 kb results in an increase in the melting point of the amphibole. There is no data in the runs to support the concept of a primary amphibole gabbro crystallising from a basaltic melt of this composition. Rather, the amphibole would form by reaction of the pyroxene with the liquid, or direct growth at lower temperatures from a basaltic mineralogy.
0031-9201
309-315
Nesbitt, R.W.
6a124ad1-4e6d-4407-b92f-592f7fd682e4
Hamilton, D.L.
b42f01c1-f95a-47e1-9199-2d1523ee9214
Nesbitt, R.W.
6a124ad1-4e6d-4407-b92f-592f7fd682e4
Hamilton, D.L.
b42f01c1-f95a-47e1-9199-2d1523ee9214

Nesbitt, R.W. and Hamilton, D.L. (1970) Crystallisation of an alkali-olivine basalt under controlled PO2, PH2O conditions. Physics of the Earth and Planetary Interiors, 3, 309-315.

Record type: Article

Abstract

An alkali-basalt from Hualalai, Hawaii, previously examined by Yoder and Tilley (1962) has been crystallised under controlled PO2 at 2 kb total pressure. Significant differences, in the order of appearance of the phases result from lowering the PO2 from 10?0.7 to about 10?10 atm. In particular magnetite, present at 1100 °C in the unbuffered runs does not crystallise until below 900 °C in the oxygen controlled runs. There is a drop of up to 50 °C on the liquidus of the system if the oxygen is controlled at the quartz-fayalite-magnetite buffer. Calcium amphiboles crystallised under such conditions are nepheline normative and rich in titanium and aluminium. Decreasing the water content but maintaining total pressure at 2 kb results in an increase in the melting point of the amphibole. There is no data in the runs to support the concept of a primary amphibole gabbro crystallising from a basaltic melt of this composition. Rather, the amphibole would form by reaction of the pyroxene with the liquid, or direct growth at lower temperatures from a basaltic mineralogy.

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Published date: 1970
Organisations: Geochemistry

Identifiers

Local EPrints ID: 361876
URI: http://eprints.soton.ac.uk/id/eprint/361876
ISSN: 0031-9201
PURE UUID: 0d789731-9077-4444-a0ab-6ec3d5a69500

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Date deposited: 04 Feb 2014 17:13
Last modified: 21 Oct 2017 18:55

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