TY - JOUR

T1 - The origin of Type II diamonds as inferred from Cullinan mineral inclusions

AU - Korolev, Nester

AU - Kopylova, Maya

AU - Gurney, John J.

AU - Moore, Andy E.

AU - Davidson, Jim

PY - 2018/12

Y1 - 2018/12

N2 - We studied a suite of Cullinan diamonds (<0.3 ct) with mineral inclusions, which comprised 266 Type I and 75 blank Type II (<20 ppm N) diamonds, as classified by infrared spectroscopy. More than 90% (n = 68) of Type II diamonds do not luminesce. In contrast, 51.9% (n = 177) of Type I diamonds luminesce, with blue colors of different intensity. Carbon isotopic compositions of Type I and II diamonds are similar, with δ13CVPDB ranging from −2.1 to −7.7‰ for Type I diamonds (n = 25), and from −1.3 to −7.8‰ for Type II diamonds (n = 20). The Type II diamonds are sourced from three parageneses, lithospheric lherzolitic (45%), lithospheric eclogitic (33%), and sublithospheric mafic (22%). The lherzolitic suite contains Cr-pyrope, forsterite, enstatite, clinopyroxene and Cr-spinel formed at 1090–1530 °C and P = 4.6–7.0 GPa. Lithospheric eclogitic diamonds containing garnet, omphacite, kyanite and coesite comprise 33% of Type II diamonds. The sublithospheric mafic paragenesis is mainly represented by Cr-free majorite, various CaSiO3 phases and omphacite equilibrated at 11.6–26 GPa, in the transition zone and the lower mantle. The lherzolitic paragenesis predominates in Type II diamonds, whereas 79% Type I diamonds are sourced from eclogites. The higher incidence of sublithospheric inclusions was found in Type II diamonds, 22% against 6% in Type I diamonds. The similarity of the mineral parageneses and C isotopic compositions in the small Cullinan Type II and Type I diamonds indicate the absence of distinct mantle processes and carbon sources for formation of studied Type II diamonds. The parent rocks and the carbon sources generally vary for Type II diamonds within a kimberlite and between kimberlites.

AB - We studied a suite of Cullinan diamonds (<0.3 ct) with mineral inclusions, which comprised 266 Type I and 75 blank Type II (<20 ppm N) diamonds, as classified by infrared spectroscopy. More than 90% (n = 68) of Type II diamonds do not luminesce. In contrast, 51.9% (n = 177) of Type I diamonds luminesce, with blue colors of different intensity. Carbon isotopic compositions of Type I and II diamonds are similar, with δ13CVPDB ranging from −2.1 to −7.7‰ for Type I diamonds (n = 25), and from −1.3 to −7.8‰ for Type II diamonds (n = 20). The Type II diamonds are sourced from three parageneses, lithospheric lherzolitic (45%), lithospheric eclogitic (33%), and sublithospheric mafic (22%). The lherzolitic suite contains Cr-pyrope, forsterite, enstatite, clinopyroxene and Cr-spinel formed at 1090–1530 °C and P = 4.6–7.0 GPa. Lithospheric eclogitic diamonds containing garnet, omphacite, kyanite and coesite comprise 33% of Type II diamonds. The sublithospheric mafic paragenesis is mainly represented by Cr-free majorite, various CaSiO3 phases and omphacite equilibrated at 11.6–26 GPa, in the transition zone and the lower mantle. The lherzolitic paragenesis predominates in Type II diamonds, whereas 79% Type I diamonds are sourced from eclogites. The higher incidence of sublithospheric inclusions was found in Type II diamonds, 22% against 6% in Type I diamonds. The similarity of the mineral parageneses and C isotopic compositions in the small Cullinan Type II and Type I diamonds indicate the absence of distinct mantle processes and carbon sources for formation of studied Type II diamonds. The parent rocks and the carbon sources generally vary for Type II diamonds within a kimberlite and between kimberlites.

KW - Carbon isotopes

KW - Cullinan kimberlite

KW - Diamond inclusions

KW - Diamond paragenesis

KW - Photoluminescence

KW - Type II diamonds

KW - CARBON ISOTOPES

KW - CALIBRATION

KW - MANTLE PERIDOTITES

KW - KIMBERLITE

KW - NORTHERN SLAVE CRATON

KW - TRANSITION

KW - FINSCH

KW - NITROGEN

KW - GARNET PERIDOTITES

KW - GEOTHERMOBAROMETRY

UR - http://www.scopus.com/inward/record.url?scp=85049155223&partnerID=8YFLogxK

UR - http://www.mendeley.com/research/origin-type-ii-diamonds-inferred-cullinan-mineral-inclusions

U2 - 10.1007/s00710-018-0601-z

DO - 10.1007/s00710-018-0601-z

M3 - Article

AN - SCOPUS:85049155223

VL - 112

SP - 275

EP - 289

JO - Mineralogy and Petrology

JF - Mineralogy and Petrology

SN - 0930-0708

ER -