TY - JOUR
T1 - Syngenetic inclusions of yimengite in diamond from Sese kimberlite (Zimbabwe) - evidence for metasomatic conditions of growth
AU - Bulanova, G.P.
AU - Muchemwa, E.
AU - Pearson, D.G.
AU - Griffin, Brendan
AU - Kelley, S.P.
AU - Klemme, S.
AU - Smith, C.B.
PY - 2004
Y1 - 2004
N2 - Syngenetic inclusions of yimengite K (Cr, Ti, Mg, Fe, Al)(12)O-19, a potassium member of the magnetoplumbite mineral group, have been recorded in an octahedral macrodiamond from the Sese kimberlite (50 km south of Masvingo, Zimbabwe). One yimengite inclusion carries lamellae of chromite suggesting peridotitic diamond paragenesis. The diamond and inclusions were studied in situ in a plate polished parallel to (011). Cathodoluminescence (CL) imaging has shown blue colour and octahedral zonation of the diamond, lack of cracks and the location of five yimengites in different growth zones. Nitrogen (N) contents (at. ppm) in the diamond determined by Fourier transform infrared spectroscopy (FTIR) steadily decrease from 576 (core) to 146 (rim). N aggregation (%1aB) is correspondingly 40% in the core and 30% in the rim. Hydrogen (H) content is high in the core, moderate in the intermediate and very high in the rim zones. Four yimengites were dated using the laser Ar-40/Ar-39 method. Three inclusions yielded total gas ages that agree with, or are younger than, or within error of, the Sese kimberlite eruption age (538 +/- 11 Ma) but may be compromised by gas loss. One inclusion, with the highest tapped interface gas yield, gave a total gas age of 892 +/- 21 Ma that is a likely minimum yimengite age. Time-T degreesC constraints from N aggregation systematics give a range of possible ages from kimberlite eruption date back to Archean and do not resolve the variable results of the Ar-40/Ar-39 dating. Compared with the published chemistry of yimengite from kimberlites, inclusions from the Sese diamond contain higher Al, Mg, and Sr and have lower concentration of Fe3+. The chondrite-normalised REE pattern of the yimengite shows enrichment in LREE and depletion in HREE, but LREE/HREE fractionations are lower than for lindsleyite-mathiasite series mantle titanates and rather similar to the REE concentrations in kimberlite and lamproite rocks. It is suggested that Sese yimengite formed in the lithospheric mantle from metasomatism of chrome spinel by a fluid rich in Ti, K, Ba and LREE. (C) 2004 Elsevier B.V. All rights reserved.
AB - Syngenetic inclusions of yimengite K (Cr, Ti, Mg, Fe, Al)(12)O-19, a potassium member of the magnetoplumbite mineral group, have been recorded in an octahedral macrodiamond from the Sese kimberlite (50 km south of Masvingo, Zimbabwe). One yimengite inclusion carries lamellae of chromite suggesting peridotitic diamond paragenesis. The diamond and inclusions were studied in situ in a plate polished parallel to (011). Cathodoluminescence (CL) imaging has shown blue colour and octahedral zonation of the diamond, lack of cracks and the location of five yimengites in different growth zones. Nitrogen (N) contents (at. ppm) in the diamond determined by Fourier transform infrared spectroscopy (FTIR) steadily decrease from 576 (core) to 146 (rim). N aggregation (%1aB) is correspondingly 40% in the core and 30% in the rim. Hydrogen (H) content is high in the core, moderate in the intermediate and very high in the rim zones. Four yimengites were dated using the laser Ar-40/Ar-39 method. Three inclusions yielded total gas ages that agree with, or are younger than, or within error of, the Sese kimberlite eruption age (538 +/- 11 Ma) but may be compromised by gas loss. One inclusion, with the highest tapped interface gas yield, gave a total gas age of 892 +/- 21 Ma that is a likely minimum yimengite age. Time-T degreesC constraints from N aggregation systematics give a range of possible ages from kimberlite eruption date back to Archean and do not resolve the variable results of the Ar-40/Ar-39 dating. Compared with the published chemistry of yimengite from kimberlites, inclusions from the Sese diamond contain higher Al, Mg, and Sr and have lower concentration of Fe3+. The chondrite-normalised REE pattern of the yimengite shows enrichment in LREE and depletion in HREE, but LREE/HREE fractionations are lower than for lindsleyite-mathiasite series mantle titanates and rather similar to the REE concentrations in kimberlite and lamproite rocks. It is suggested that Sese yimengite formed in the lithospheric mantle from metasomatism of chrome spinel by a fluid rich in Ti, K, Ba and LREE. (C) 2004 Elsevier B.V. All rights reserved.
U2 - 10.1016/j.lithos.2004.04.002
DO - 10.1016/j.lithos.2004.04.002
M3 - Article
SN - 0024-4937
VL - 1-4
SP - 181
EP - 192
JO - Lithos
JF - Lithos
IS - 77
ER -