Crystallization and Breakdown of Metasomatic Phases in Graphite-bearing Peridotite Xenoliths from Marsabit (Kenya)

Kaeser, Benjamin; Kalt, Angelika; Pettke, Thomas

doi:10.1093/petrology/egm036

Cited by 22 publications

(30 citation statements)

References 112 publications

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“…8). This result is in agreement with the fabric of this sample indicating static recrystallisation, most likely in response to the young thermal modification of the Marsabit lithosphere, resulting from Kenya rift magmatism (Kaeser et al 2006(Kaeser et al , 2007. Peridotite-pyroxenite mingling: the result of pyroxenite emplacement and/or sub-solidus reactions?…”

Section: Interpretation Of the P-t Evolutionsupporting

confidence: 87%

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Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite

Kaeser

Olker

Kalt

et al. 2008

Contrib Mineral Petrol

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Garnet-bearing and garnet-free pyroxenite xenoliths from Quaternary basanites of Marsabit, northern Kenya, were analysed for microstructures and mineral compositions (major and trace elements) to constrain the thermal and compositional evolution of the lithospheric mantle in this region. Garnet-bearing rocks are amphibolebearing websterite with *5-10 vol% orthopyroxene. Clinopyroxene is LREE-depleted and garnet has high HREE contents, in agreement with an origin as cumulates from basaltic mantle melts. Primary orthopyroxene inclusions in garnet suggest that the parental melts were orthopyroxene-saturated. Rock fabrics vary from weakly to strongly deformed. Thermobarometry indicates extensive decompression and cooling (*970-1,100°C at *2.3-2.6 GPa to *700-800°C at *0.5-1.0 GPa) during deformation, best interpreted as pyroxenite intrusion into thick Paleozoic continental lithosphere subsequently followed by continental rifting (i.e., formation of the Mesozoic Anza Graben). During continental rifting, garnet websterites were decompressed (garnet-to-spinel transition) and experienced the same P-T evolution as their host peridotites. Strongly deformed samples show compositional overlaps with cpx-rich, initially garnet-bearing lherzolite, best explained by partial re-equilibration of peridotite and pyroxenite during deformation and mechanical mingling. In contrast, garnet-free pyroxenites include undeformed, cumulate-like samples, indicating that they are younger than the garnet websterites. Major and trace element compositions of clinopyroxene and calculated equilibrium melts suggest crystallisation from alkaline basaltic melt similar to the host basanite, which suggests formation in the context of alkaline magmatism during the development of the Kenya rift.

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Section: Interpretation Of the P-t Evolutionsupporting

confidence: 87%

“…A full description of analytical methods is given elsewhere (Pettke et al 2004;Kaeser et al 2007). The results are summarised in Tables 2 (first generation minerals) and 3 (inclusions in grt).…”

Section: Composition Of Mineralsmentioning

confidence: 99%

Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite

Kaeser

Olker

Kalt

et al. 2008

Contrib Mineral Petrol

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“…7b). Magnesiokatophorites from Marasbit (Kenya) reported by Kaeser et al (2007) show a variety of compositions, with, some of them having similar compositions to the magnesiokatophorite from Jabal Karash (Figs. 7a and 7b).…”

Section: Results: Major Elementsmentioning

confidence: 99%

“…The chondrite -normalized pattern of the matrix peridotite clinopyroxenes (chromian diopside) shows lower Kenya peridotite xenoliths (Kaeser et al, 2007) concentrations in REE than euhedral clinopyroxenes, especially kosmochlor -bearing diopside (Ko), in melt pockets after amphiboles (Fig. 8a).…”

Section: Results: Trace Elementsmentioning

confidence: 99%

“…Here, we report the petrographic and chemical characteristics of an unusual amphibole, magnesiokatophorite, and discuss its importance in mantle metasomatism. This report is the second report on magnesiokatophorite from spinel peridotite xenoliths (Kaeser and Pettke, 2007). The metasomatic agent for the formation of magnesiokatophorite will be more thoroughly discussed in this paper.…”

Section: Introductionmentioning

confidence: 85%

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Cr-rich magnesiokatophorite as an indicator of mantle metasomatism by hydrous Na-rich carbonatite

Ali

Arai

2013

Journal of Mineralogical and Petrological Sciences

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Na -and Cr -rich amphibole and clinopyroxene are commonly observed in hydrous mantle xenoliths hosted by Pliocene -Quaternary basalts from Yemen. The amphibole is Cr -rich magnesiokatophorite high in Na 2 O (3.66 -5.65 wt%) and Cr 2 O 3 (2.21 -3.09 wt%), relatively low in K 2 O (0.23 -0.66 wt %) and almost free of Cl and F. The clinopyroxene is characterized by high Cr 2 O 3 (up to 5.64 wt%) and Na 2 O (up to 2.97 wt%), indicating appreciable amounts of kosmochlor. Both minerals show high REE concentrations as well as HFSE depletion, suggesting an involvement of carbonatitic melt in their formation. The magnesiokatophorites and kosmochlor -bearing diopside possibly formed through metasomatism by hydrous Na -rich carbonatite melt. Magnesiokatophorite is an indicator of metasomatism by hydrous Na -rich carbonatite in the upper mantle.

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Graphite‐bearing mineral assemblages in the mantle beneath Central Aldan superterrane of North Asian craton: combined confocal micro‐Raman and electron microprobe characterization

Николенко

Sharygin

Alifirova

et al. 2017

J Raman Spectroscopy

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Mantle‐derived lherzolitic and harzburgitic Cr‐pyropes from lamprophyres of the Chompolo field (Central Aldan superterrane, North Asian Craton) were studied using micro‐Raman spectroscopy and electron microprobe microanalysis. These garnets enclose graphite coexisting with forsterite, diopside, Ba‐Cl‐phlogopite, tschermakite, rutile, magnesiochromite, Mg‐ilmenite, apatite, chalcopyrite, dolomite, magnesite and lindsleyite inclusions. The PT conditions of residence of graphite‐bearing assemblage in the mantle were estimated, using a combination of mineral thermometers and barometers, to be as high as 2.87–3.55 GPa and 710–770 °C. Generally, graphite within inclusions is well ordered; D1 and D2 disordered bands in its spectra are restricted to inclusion edges. The residual pressure up to 2.1 GPa was inferred for graphite assuming pressure dependence of the G‐band upshift (1580 cm−1 at ambient conditions vs 1588.6 cm−1 at 2.1 GPa). Disordered graphite most likely appears due to the stress‐induced distortion of the fully ordered graphite crystal structure. The distortion results from difference in the thermoelastic properties of graphite inclusions and their garnet hosts exposed to decompression during ascent to the surface with lamprophyre magma. The mineralogy of inclusions in the studied garnets strongly suggests an episode(s) of metasomatism by carbon‐rich agent(s) (COH‐fluid or carbonatitic melt) in the lithospheric mantle of the Central Aldan superterrane, which was coeval with the formation of graphite inclusions and the host pyropes. Copyright © 2017 John Wiley & Sons, Ltd.

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Crystallization and Breakdown of Metasomatic Phases in Graphite-bearing Peridotite Xenoliths from Marsabit (Kenya)

Cited by 22 publications

References 112 publications

Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite

Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite

Cr-rich magnesiokatophorite as an indicator of mantle metasomatism by hydrous Na-rich carbonatite

Graphite‐bearing mineral assemblages in the mantle beneath Central Aldan superterrane of North Asian craton: combined confocal micro‐Raman and electron microprobe characterization

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