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Chemical and physical characteristics of diamond crystals from Garnet Lake, Sarfartoq, West Greenland; an association with carbonatitic magmatism

Mark T. Hutchison and Larry M. Heaman
Chemical and physical characteristics of diamond crystals from Garnet Lake, Sarfartoq, West Greenland; an association with carbonatitic magmatism (in The mineralogy and petrology of carbonatites; a tribute to John Gittins, Roger H. Mitchell (prefacer), Anton R. Chakhmouradian (prefacer) and David R. Lentz (prefacer))
The Canadian Mineralogist (August 2008) 46 (4): 1063-1078

Abstract

A shallow-dipping kimberlite-ultramafic lamprophyre sheet at Garnet Lake, Sarfartoq, West Greenland, contains diamond crystals in abundance. The crystals are most commonly colorless, and irregular or octahedral in shape. Nitrogen concentrations are unusually high, averaging 1100 ppm, compared to diamond crystals from elsewhere; the nitrogen is not strongly aggregated, however, averaging 26% IaB. This observation points to a short residence-time in the mantle, low temperature of mantle residence, or likely a combination of both conditions. Evidence of two populations is apparent in the relative abundance of different states of aggregation of the nitrogen in the stones. The common octahedral morphologies constrain the minimum temperature of formation for the majority of the crystals to 1375 degrees C, assuming a 41 mWm (super -2) geotherm. Nitrogen concentrations and aggregation states only allow for very short residence-times, however, up to 1 Ma at this temperature. Hence a model of diamond formation quickly followed by ponding within a shallower, cooler mantle at a temperature of approximately 1252 degrees C, supported by the tight clustering of associated mantle xenoliths, is preferred. Under these cooler conditions, the unusually high concentrations of nitrogen, combined with relatively low aggregation, give a calculated spread of diamond residence up to a maximum of 42.3 Ma. An emplacement age of 568+ or -11 Ma (2sigma ) obtained for the Garnet Lake kimberlite is based on the weighted average (super 207) Pb/ (super 206) Pb age for two perovskite fractions. This age is coincident with revised data on emplacement of the neighboring 565 Ma Sarfartoq carbonatite complex. Combined with diamond residence-time, the maximum likely age for diamond formation is ca. 610 Ma. Geographic and petrological similarities between kimberlitic hosts and the Sarfartoq carbonatite are apparent; in view of the close temporal similarity, we propose that CO (sub 2) -rich fertilization of mantle rocks giving rise to the formation of diamond has in this case assisted in the subsequent production of carbonatite magmatism and associated kimberlitic melts acting as transporting medium for the diamond.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 46
Serial Issue: 4
Title: Chemical and physical characteristics of diamond crystals from Garnet Lake, Sarfartoq, West Greenland; an association with carbonatitic magmatism
Title: The mineralogy and petrology of carbonatites; a tribute to John Gittins
Author(s): Hutchison, Mark T.Heaman, Larry M.
Author(s): Mitchell, Roger H.prefacer
Author(s): Chakhmouradian, Anton R.prefacer
Author(s): Lentz, David R.prefacer
Affiliation: Geological Survey of Denmark and Greenland, Copenhagen, Denmark
Affiliation: Lakehead University, Thunder Bay, ON, Canada
Pages: 1063-1078
Published: 200808
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 58
Accession Number: 2009-013094
Categories: Mineralogy of non-silicatesGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, sketch map
N60°00'00" - N65°00'00", W56°00'00" - W47°00'00"
Secondary Affiliation: University of Manitoba, CAN, CanadaUniversity of New Brunswick, CAN, CanadaUniversity of Alberta, CAN, Canada
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200908
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