Niobian ilmenite, hydroxylapatite and sulfatian monazite; alternative hosts for incompatible elements in calcite kimberlite from Internatsional'naya, Yakutia

Rare earth element (REE) and yttrium concentrations of coexisting monazite and xenotime were determined from a suite of seven metapelites from the Variscan fold belt in NE Bavaria, Germany. The metapelites include a continuous prograde, mainly low‐ P (3–5 kbar) metamorphic profile from greenschist ( c. 400 °C) to lower granulite facies conditions ( c. 700 °C). The LREE (La–Sm) are incorporated preferentially in monoclinic monazite (REO 9 polyhedron), whereas the HREE plus Y are concentrated in tetragonal xenotime (REO 8 polyhedron). The major element concentrations of both phases in all rocks are very similar and do not depend on metamorphic grade. Monazite consists mainly of La, Ce and Nd (La 0.20–0.23 , Ce 0.41–0.45 , Nd 0.15–0.18 )PO 4 , all other elements are below 6 mol%. Likewise, xenotime consists mainly of YPO 4 with some Dy and Gd solid solutions (Y 0.76–0.80 , Dy 0.05–0.07 , Gd 0.04–0.06 ). In contrast, the minor HREE concentrations in monazite increase strongly with increasing metamorphic grade: Y, Dy and Gd increase by a factor of 3–5 from greenschist to granulite facies rocks. Monazite crystals often show zonation with cores low in HREE and rims high in HREE that is interpreted as growth zonation attained during prograde metamorphism. Similarly, Sm and Nd in xenotimes increase by a factor of 3–4 with increasing metamorphic grade. Prograde zonation in single crystals of xenotime was not observed. The X HREE+Y in monazite and X LREE in xenotime of the seven rocks define two limbs along the strongly asymmetric miscibility gap from c. 400 °C to 700 °C. The empirical calibration of the monazite miscibility gap limb coexisting with xenotime is appropriate for geothermometry. Due to its contents of U and Th, monazite has often been used for U–Pb age determination. The combination of our empirical thermometer on prograde zoned monazite along with possible age determination of zoned single crystals may provide information about prograde branches of temperature–time paths.

Greenschist

Rare-earth element

Allanite

10.1111/j.1525-1314.1997.t01-1-00052.x

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Citations (192)

Oxide minerals in a layered kimberlite-carbonate sill from Benfontein, South Africa

Contributions to Mineralogy and Petrology (1981)

N. Z. Boctor F. R. Boyd

Carbonatite

Ilmenite

Chromite

Baddeleyite

10.1007/bf00375452

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Citations (33)

Petrology of hypabyssal kimberlites: Relevance to primary magma compositions

Journal of Volcanology and Geothermal Research (2008)

Roger H. Mitchell

Phenocryst

Pyroxene

Magma chamber

Phlogopite

10.1016/j.jvolgeores.2007.12.024

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Citations (236)

Trace element geochemistry of phlogopite-rich mafic mantle xenoliths: their classification and their relationship to phlogopite-bearing peridotites and kimberlites revisited

Contributions to Mineralogy and Petrology (2002)

Michel Grégoire Douglas A. Bell Anton le Roex

Phlogopite

Xenolith

Ilmenite

Trace element

10.1007/s00410-001-0315-8

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Citations (281)

Magmatic sedimentation and carbonatitic differentiation in kimberlite sills at Benfontein, South Africa

Journal of the Geological Society (1973)

J. B. Dawson JOHN BARRY HAWTHORNE

At Benfontein, near Kimberley, South Africa, three sills of kimberlite intrude Dwyka shales and overlying Karroo dolerite. Each sill results from numerous injections of kimberlite that have consolidated to give the sill a layered appearance. Many layers show magmatic sedimentation features and cumulus textures, and, although some show in situ differentiation, other layers result from pre-injection differentiation. The transporting, intercumulus liquid was carbonate-rich and some layers have differentiated to form a carbonate rock composed of the intercumulns calcite; this, on trace element and isotopic data, shows strong affinities with carbonatite. In one of the sills one calcite layer has migrated diapirically into overlying layers in the sill. These sedimentation features, combined with thermal metamorphism of country-rock shales and the presence of quench calcite and apatite, are interpreted as evidence that the kimberlite was injected as a highly mobile fluid, comprising megacrysts of olivine, garnet, pyroxene, mica and picroilmenite in a hot carbonatitic liquid from which olivine, magnetic spinel, perovskite, apatite, calcite, dolomite, ankerite and quartz crystallised. The evidence that the transportation medium was a warm carbonatitic liquid is directly opposed to earlier hypotheses proposing that kimberlite is intruded as a cold or plastic paste, and also supports proposals of a genetic link between kimberlite and carbonatite.

Sill

Sedimentation

10.1144/gsjgs.129.1.0061

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Citations (206)