Melt compositions and processes in the kimberlite provience of southern West Greenland

The kimberlite province of southern West Greenland (600- 560Ma) comprises kimberlite sensu stricto on the Archean craton and aillikites on the paleoproterzoic sheild to the North. Carbonatite melt and xenocrystic olivine dominate the kimberlite sensu stricto occurrences of the Manitsoq region [1] wh...

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Bibliographic Details
Main Authors: Pilbeam, Llewellyn, Nielsen, Troels, Waight, Tod Earle
Format: Conference Object
Language:English
Published: 2011
Subjects:
Online Access:https://curis.ku.dk/portal/da/publications/melt-compositions-and-processes-in-the-kimberlite-provience-of-southern-west-greenland(ef33464e-198c-4bbf-b1c2-02931e0a8c28).html
http://goldschmidt2011.org/abstracts/finalPDFs/1643.pdf
Description
Summary:The kimberlite province of southern West Greenland (600- 560Ma) comprises kimberlite sensu stricto on the Archean craton and aillikites on the paleoproterzoic sheild to the North. Carbonatite melt and xenocrystic olivine dominate the kimberlite sensu stricto occurrences of the Manitsoq region [1] whilst the silica content and H2O/CO2 ratio of the bulk rocks increases towards Sisimuit [2, 3]. A common carbonatite rich end-member is implicated [2]. This is in contrast to the prevailing dogma of a continuum from carbonatite though aillikite to kimberlite with increasing melting degree [4]. The authors have demonstrated that a process of DFC (digestion fractional crystallisation) whereby the cognate olivine crystallisation is coupled to entrained xenocrystic orthopyroxene assimilation is a key process during the formation of the Majugaa occurrence of the Manitsoq region [5]. Mass balance considerations are here applied to the Majuagaa bulk rock in term of the DFC mechanism obtaining an estimate of parental melt and magma composition for the Majuagaa kimberlite. We use bulk rock major and trace element geochemistry together with mineral chemistry to investigate the range of melt compositions involved in the region. Melting models involving introduction of a carbonatite melt are applied to inferred lithospheric mantle compositions based upon nodule assemblages. Compositional variations across the southern West Greenland province are explained by interaction of an aesthenospheric carbonatite melt with lithospheric mantle. The major and trace element budgets are understood as a combination of melting regime together with mixing and reaction between the primary melts and the dispersed xenocryst assemblages. Variations of the mineral assemblages of the cognate groundmass are similarly explained.