Origin and source regions of nodule-bearing kimberlites and ultramafic lamprophyres in southern Western Greenland

Llewellyn Howard Pilbeam

Origin and source regions of nodule-bearing kimberlites and ultramafic lamprophyres in southern Western Greenland

Llewellyn Howard Pilbeam

Geology

Abstract

High precision high resolution electron microprobe traverses of olivine grains in the Majuagaa kimberlite sensu stricto from southern West Greenland show that the olivine crystallisation is coupled to digestion of xenocrystic orthopyroxene into the melt. This process was previously suspected but unconfirmed in kimberlite sensu stricto magmas. It is here termed digestion fractional crystallisation (DFC) and it is argued that the DFC process may account for much of the global varia-bility in kimberlite compositions. The bulk rock trace element geochemistry of the Majuagaa kimberlite is used to constrain an inversion of the mixing equation between parental melt and xenocrystic material from the lithospheric mantle. The calculated parental melt is a magnesio-silico-carbonatite. Petrographic, textural, mineral chemical and major and trace element geochemical data show a progression from CO2 rich melts in the kimberlites sensu stricto of the Maniitsoq region to relatively more SiO2, Al2O3, FeOT, TiO2 and K2O enriched ultramafic lamprophyres of the Sarfartoq and Sisimuit regions. Simple mixing modelling supports the formation of this sequence due to variable interaction of the primary melt with depleted lithospheric mantle and glimmerite metasomes in the lithospheric mantle.

Original language	English

Publisher	Faculty of Science, University of Copenhagen
Number of pages	280
Publication status	Published - 22 Jun 2012

Cite this

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title = "Origin and source regions of nodule-bearing kimberlites and ultramafic lamprophyres in southern Western Greenland",

abstract = "High precision high resolution electron microprobe traverses of olivine grains in the Majuagaa kimberlite sensu stricto from southern West Greenland show that the olivine crystallisation is coupled to digestion of xenocrystic orthopyroxene into the melt. This process was previously suspected but unconfirmed in kimberlite sensu stricto magmas. It is here termed digestion fractional crystallisation (DFC) and it is argued that the DFC process may account for much of the global varia-bility in kimberlite compositions. The bulk rock trace element geochemistry of the Majuagaa kimberlite is used to constrain an inversion of the mixing equation between parental melt and xenocrystic material from the lithospheric mantle. The calculated parental melt is a magnesio-silico-carbonatite. Petrographic, textural, mineral chemical and major and trace element geochemical data show a progression from CO2 rich melts in the kimberlites sensu stricto of the Maniitsoq region to relatively more SiO2, Al2O3, FeOT, TiO2 and K2O enriched ultramafic lamprophyres of the Sarfartoq and Sisimuit regions. Simple mixing modelling supports the formation of this sequence due to variable interaction of the primary melt with depleted lithospheric mantle and glimmerite metasomes in the lithospheric mantle.",

author = "Pilbeam, {Llewellyn Howard}",

year = "2012",

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language = "English",

publisher = "Faculty of Science, University of Copenhagen",

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T1 - Origin and source regions of nodule-bearing kimberlites and ultramafic lamprophyres in southern Western Greenland

AU - Pilbeam, Llewellyn Howard

PY - 2012/6/22

Y1 - 2012/6/22

N2 - High precision high resolution electron microprobe traverses of olivine grains in the Majuagaa kimberlite sensu stricto from southern West Greenland show that the olivine crystallisation is coupled to digestion of xenocrystic orthopyroxene into the melt. This process was previously suspected but unconfirmed in kimberlite sensu stricto magmas. It is here termed digestion fractional crystallisation (DFC) and it is argued that the DFC process may account for much of the global varia-bility in kimberlite compositions. The bulk rock trace element geochemistry of the Majuagaa kimberlite is used to constrain an inversion of the mixing equation between parental melt and xenocrystic material from the lithospheric mantle. The calculated parental melt is a magnesio-silico-carbonatite. Petrographic, textural, mineral chemical and major and trace element geochemical data show a progression from CO2 rich melts in the kimberlites sensu stricto of the Maniitsoq region to relatively more SiO2, Al2O3, FeOT, TiO2 and K2O enriched ultramafic lamprophyres of the Sarfartoq and Sisimuit regions. Simple mixing modelling supports the formation of this sequence due to variable interaction of the primary melt with depleted lithospheric mantle and glimmerite metasomes in the lithospheric mantle.

AB - High precision high resolution electron microprobe traverses of olivine grains in the Majuagaa kimberlite sensu stricto from southern West Greenland show that the olivine crystallisation is coupled to digestion of xenocrystic orthopyroxene into the melt. This process was previously suspected but unconfirmed in kimberlite sensu stricto magmas. It is here termed digestion fractional crystallisation (DFC) and it is argued that the DFC process may account for much of the global varia-bility in kimberlite compositions. The bulk rock trace element geochemistry of the Majuagaa kimberlite is used to constrain an inversion of the mixing equation between parental melt and xenocrystic material from the lithospheric mantle. The calculated parental melt is a magnesio-silico-carbonatite. Petrographic, textural, mineral chemical and major and trace element geochemical data show a progression from CO2 rich melts in the kimberlites sensu stricto of the Maniitsoq region to relatively more SiO2, Al2O3, FeOT, TiO2 and K2O enriched ultramafic lamprophyres of the Sarfartoq and Sisimuit regions. Simple mixing modelling supports the formation of this sequence due to variable interaction of the primary melt with depleted lithospheric mantle and glimmerite metasomes in the lithospheric mantle.

M3 - Ph.D. thesis

BT - Origin and source regions of nodule-bearing kimberlites and ultramafic lamprophyres in southern Western Greenland

PB - Faculty of Science, University of Copenhagen

ER -