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Metasomatism induced by alkaline magma in the upper mantle of northern Victoria Land (Antarctica): An experimental approach

By
C. Perinelli
C. Perinelli
Dipartimento di Scienze della Terra, Università di Pisa, via S. Maria 53, 56100 Pisa, Italy (e-mail: cperinelli@dst.unipi.it)
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A. Orlando
A. Orlando
CNR–IGG, UO di Firenze, via G. La Pira, 4, 50121 Firenze, Italy
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A. M. Conte
A. M. Conte
CNR–IGG, UO di Roma, p.le Aldo Moro 5, 00185 Roma, Italy
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P. Armienti
P. Armienti
Dipartimento di Scienze della Terra, Università di Pisa, via S. Maria 53, 56100 Pisa, Italy (e-mail: cperinelli@dst.unipi.it)
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D. Borrini
D. Borrini
Dipartimento di Scienze della Terra, Università di Firenze, via G. La Pira, 4, 50121 Firenze, Italy
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B. Faccini
B. Faccini
Dipartimento di Scienze della Terra, Università di Ferrara, via Saragat 1, 44100 Ferrara, Italy
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V. Misiti
V. Misiti
INGV Sezione di Sismologia e Tettonofisica, via di Vigna Murata 605, 00143 Roma, Italy
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Published:
January 01, 2008

Abstract

Magma generation in the Ross Sea system is related to partial melting of strongly metasomatized mantle sources where amphibole most probably plays a crucial role. In this context, metasomatism induced by a mela-nephelinite melt in lithospheric mantle of the Mt. Melbourne Volcanic Province (northern Victoria Land (NVL), Antarctica) was investigated experimentally studying the effects of melt interaction with lherzolite at 1.5–2.0 GPa and T=975–1300 °C, and wehrlite at 1.0 GPa and T=1050–1250 °C. The experiments were designed to induce melt infiltration into the ultramafic rocks. The observed modifications in minerals are compared with those found in mantle xenoliths from NVL. The effects of metasomatic modifications are evaluated on the basis of run temperature, distance from the infiltrating melt and the diffusion rates of chemical components. Both in lherzolite and wehrlite, clinopyroxene exhibits large compositional variations ranging from primary diopside to high-Mg–Cr–(Na) augitic and omphacitic clinopyroxenes in lherzolite, and to low-Mg and high-Ti–Al–Fe–Na augites in wehrlite. Olivine (in wehrlite) and spinel (in lherzolite) are also compositionally modified: the former shows enrichment in Fe and the latter displays a higher Cr/(Cr+Al) ratio. The systematic variations in mineral compositions imply modifications of the chemistry of the infiltrating melt as recorded by the glass veinlets and patches observed in some charges. In experiments involving wehrlite paragenesis, the glass composition approaches that of melt patches associated with both amphibole-free and amphibole-bearing natural samples, and is related to olivine + clinopyroxene crystallization coupled with primary clinopyroxene dissolution at the contact between the metasomatizing melt and the solid matrix. Even if amphibole crystallization was not attained in the experiments, we were able to explain the occurrence of amphibole in the natural system considering that in this case a hot metasomatizing melt infiltrates a cooler matrix.

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Geological Society, London, Special Publications

Metasomatism in Oceanic and Continental Lithospheric Mantle

M. Coltorti
M. Coltorti
Università degli Studi di Ferrara, Italy
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M. Grégoire
M. Grégoire
Université Toulouse III, France
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Geological Society of London
Volume
293
ISBN electronic:
9781862395411
Publication date:
January 01, 2008

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