Metasomatised Xenoliths from Foster Crater, Antarctica: Implications for Lithospheric Structure and Processes beneath the Transantarctic Mountain Front
Identifieur interne : 001570 ( Main/Exploration ); précédent : 001569; suivant : 001571Metasomatised Xenoliths from Foster Crater, Antarctica: Implications for Lithospheric Structure and Processes beneath the Transantarctic Mountain Front
Auteurs : J. A. Gamble [Nouvelle-Zélande] ; F. Mcgibbon ; P. R. Kyle [États-Unis] ; M. A. Menzies [Royaume-Uni] ; I. Kirsch [États-Unis]Source :
- Journal of Petrology [ 0022-3530 ] ; 1988.
Abstract
Xenoliths in basanite from Foster Crater in the foothills of the Transantarctic Mountains have been used to construct a model of the subcontinental lithosphere and lithospheric processes in this segment of Antarctica. The mafic and ultramafic xenoliths define two mineralogically, texturally and chemically distinct populations. One group is identical to Group II xenoliths, as defined by Frey & Prinz (1978). These have igneous cumulate textures and include wehrlites, rare websterites, dunite and amphibolite. In these xenoliths, the amphibole is always kaersutite and the (very rare) mica a Ti-rich phlogopite (TiO2 > 5%). The other xenoliths have complex metamorphic textures ranging from protogranular to porphyroclastic and are dominated by clinopyroxenites (cpx: Mg/(Mg + Fe) = 0·85–0·95; Ca/(Ca + Mg)>0·53) which show varying degrees of replacement by metasomatic phlogopite. Spinel and anorthite are also present. Collectively, these xenoliths are called the High Calcium Pyroxene Suite (HCPS) in deference to their unusual pyroxene compositions. Moreover, their spinel assemblages indicate equilibrium under variable fO2 conditions contrasting with the Group II spinels which equilibrated at relatively constant fO2. The mineralogy and chemistry of the HCPS xenoliths are unlike meta-igneous rocks and more closely resemble calc-silicate granulites. Thermobarometric calculations on Group II websterite assemblages and comparison with experimental equilibria on granulites and phlogopite stability suggest equilibration temperatures between 850 and 950° at 5 kb pressure, consistent with equilibration at mid to lower crustal depths. A number of processes have acted to modify Group II and HCPS xenoliths including K-metasomatism, dynamic recrystallization, melt generation, melt infiltration and oxidation. The first two are restricted to the HCPS xenoliths whereas the latter affect both groups. The interaction of these processes highlights the differences between Group II and HCPS protolith assemblages and is consistent with derivation from a complex section of lithosphere which has experienced major changes in tectonomagmatic activity since late PreCambrian times.
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DOI: 10.1093/petrology/Special_Volume.1.109
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A." last="Gamble">J. A. Gamble</name><affiliation wicri:level="1"><country xml:lang="fr">Nouvelle-Zélande</country><wicri:regionArea>Research School of Earth Sciences, Antarctic Research Centre, Victoria University, Wellington</wicri:regionArea><wicri:noRegion>Wellington</wicri:noRegion></affiliation></author><author><name sortKey="Mcgibbon, F" sort="Mcgibbon, F" uniqKey="Mcgibbon F" first="F." last="Mcgibbon">F. Mcgibbon</name><affiliation><wicri:noCountry code="subField">MK76AA</wicri:noCountry></affiliation></author><author><name sortKey="Kyle, P R" sort="Kyle, P R" uniqKey="Kyle P" first="P. R." last="Kyle">P. R. Kyle</name><affiliation wicri:level="2"><country xml:lang="fr">États-Unis</country><wicri:regionArea>Dept of Geosciences, New Mexico Institute of Mining and Technology, Socorro, NM 87801</wicri:regionArea><placeName><region type="state">Nouveau-Mexique</region></placeName></affiliation></author><author><name sortKey="Menzies, M A" sort="Menzies, M A" uniqKey="Menzies M" first="M. A." last="Menzies">M. A. Menzies</name><affiliation wicri:level="1"><country xml:lang="fr">Royaume-Uni</country><wicri:regionArea>Dept of Geology, Royal Holloway and Bedford New College, Egham</wicri:regionArea><wicri:noRegion>Egham</wicri:noRegion></affiliation></author><author><name sortKey="Kirsch, I" sort="Kirsch, I" uniqKey="Kirsch I" first="I." last="Kirsch">I. Kirsch</name><affiliation wicri:level="1"><country xml:lang="fr">États-Unis</country><wicri:regionArea>Institute of Polar Studies, Ohio State University, Columbus, Ohio 43210</wicri:regionArea><wicri:noRegion>Ohio 43210</wicri:noRegion></affiliation></author></analytic><monogr></monogr><series><title level="j">Journal of Petrology</title><title level="j" type="abbrev">Journal of Petrology</title><idno type="ISSN">0022-3530</idno><idno type="eISSN">1460-2415</idno><imprint><publisher>Oxford University Press</publisher><date type="published" when="1988">1988</date><biblScope unit="volume">Special_Volume</biblScope><biblScope unit="issue">1</biblScope><biblScope unit="page" from="109">109</biblScope><biblScope unit="page" to="138">138</biblScope></imprint><idno type="ISSN">0022-3530</idno></series><idno type="istex">99070344513DE793640BC8450189DB35DA8388F0</idno><idno type="DOI">10.1093/petrology/Special_Volume.1.109</idno></biblStruct></sourceDesc><seriesStmt><idno type="ISSN">0022-3530</idno></seriesStmt></fileDesc><profileDesc><textClass></textClass><langUsage><language ident="en">en</language></langUsage></profileDesc></teiHeader><front><div type="abstract">Xenoliths in basanite from Foster Crater in the foothills of the Transantarctic Mountains have been used to construct a model of the subcontinental lithosphere and lithospheric processes in this segment of Antarctica. The mafic and ultramafic xenoliths define two mineralogically, texturally and chemically distinct populations. One group is identical to Group II xenoliths, as defined by Frey & Prinz (1978). These have igneous cumulate textures and include wehrlites, rare websterites, dunite and amphibolite. In these xenoliths, the amphibole is always kaersutite and the (very rare) mica a Ti-rich phlogopite (TiO2 > 5%). The other xenoliths have complex metamorphic textures ranging from protogranular to porphyroclastic and are dominated by clinopyroxenites (cpx: Mg/(Mg + Fe) = 0·85–0·95; Ca/(Ca + Mg)>0·53) which show varying degrees of replacement by metasomatic phlogopite. Spinel and anorthite are also present. Collectively, these xenoliths are called the High Calcium Pyroxene Suite (HCPS) in deference to their unusual pyroxene compositions. Moreover, their spinel assemblages indicate equilibrium under variable fO2 conditions contrasting with the Group II spinels which equilibrated at relatively constant fO2. The mineralogy and chemistry of the HCPS xenoliths are unlike meta-igneous rocks and more closely resemble calc-silicate granulites. Thermobarometric calculations on Group II websterite assemblages and comparison with experimental equilibria on granulites and phlogopite stability suggest equilibration temperatures between 850 and 950° at 5 kb pressure, consistent with equilibration at mid to lower crustal depths. A number of processes have acted to modify Group II and HCPS xenoliths including K-metasomatism, dynamic recrystallization, melt generation, melt infiltration and oxidation. The first two are restricted to the HCPS xenoliths whereas the latter affect both groups. The interaction of these processes highlights the differences between Group II and HCPS protolith assemblages and is consistent with derivation from a complex section of lithosphere which has experienced major changes in tectonomagmatic activity since late PreCambrian times.</div></front></TEI><affiliations><list><country><li>Nouvelle-Zélande</li><li>Royaume-Uni</li><li>États-Unis</li></country><region><li>Nouveau-Mexique</li></region></list><tree><noCountry><name sortKey="Mcgibbon, F" sort="Mcgibbon, F" uniqKey="Mcgibbon F" first="F." last="Mcgibbon">F. Mcgibbon</name></noCountry><country name="Nouvelle-Zélande"><noRegion><name sortKey="Gamble, J A" sort="Gamble, J A" uniqKey="Gamble J" first="J. A." last="Gamble">J. A. Gamble</name></noRegion></country><country name="États-Unis"><region name="Nouveau-Mexique"><name sortKey="Kyle, P R" sort="Kyle, P R" uniqKey="Kyle P" first="P. R." last="Kyle">P. R. 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