Peridotite xenoliths from the Jagersfontein kimberlite pipe: I. Primary and primary-metasomatic mineralogy

Journal Article · Wed Jan 31 23:00:00 EST 1990 · Geochimica et Cosmochimica Acta; (USA)

OSTI ID:6935801

Harte, B ^[1]; Gurney, J J ^[2]; Winterburn, P A ^[3]

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1. Univ. of Edinburgh (England)
2. Univ. of Cape Town (South Africa)
3. Univ. of Edinburgh (England) Isotope Geochemistry Facility, Pretoria (South Africa)

The geochemistry and textures of peridotite xenoliths from the Jagersfontein kimberlite pipe are reported. The xenoliths have a primary mineralogy of olivine {plus minus} orthopyroxene {plus minus} clinopyroxene {plus minus} garnet {plus minus} spinel. They are subdivided into coarse and deformed xenoliths corresponding to high- and low-temperature estimates, respectively. Coarse-grained xenoliths are further subdivided into low- and medium-temperature groups. Mineral chemistry of these two groups is distinct, e.g., clinopyroxene 100 Al/(Al + Cr) 24 to 60 and 60 to 70 in the medium- and low-temperature groups, respectively. Low-temperature xenoliths have undergone exsolution of pyroxene, spinel, and garnet in their pyroxenes. Primary modal metasomatism has occurred in the coarse xenoliths with the replacement of orthopyroxene by edenitic amphibole in the low-temperature xenoliths and of clinopyroxene by low-Ti phlogopite in the medium-temperature xenoliths. The amphibole stability limit confines it to shallower depths. Metasomatized xenoliths have been enriched in K, Na, Al, and Ca, and trace incompatible elements. Metasomatism is considered to have occurred at round 1 Ga by the infiltration of, and reaction with, ascending H{sub 2}O-rich fluids with Sr and Nd isotopic characteristics similar to group II kimberlites. The widespread chemical equilibrium seen in metasomatized xenoliths suggests that the particularly distinctive features of the low-temperature Jagersfontein xenoliths, namely exsolution and very low equilibration temperatures, may also be a result of the primary metasomatism.

• OSTI ID: 6935801
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 54:2; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
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ALKALINE EARTH METAL COMPOUNDS
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ALUMINIUM OXIDES
CHALCOGENIDES
IGNEOUS ROCKS
IRON COMPOUNDS
IRON SILICATES
ISOTOPES
KIMBERLITES
LAMPROPHYRES
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MAGNESIUM OXIDES
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METAMORPHISM
MINERALOGY
MINERALS
NEODYMIUM ISOTOPES
OLIVINE
OXIDE MINERALS
OXIDES
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PERIDOTITES
PETROCHEMISTRY
PETROGENESIS
PLUTONIC ROCKS
PYROXENES
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
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STRONTIUM ISOTOPES
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