Geochemical and oxygen isotope signatures of mantle corundum megacrysts from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China

Giuliani, Gaston; Pivin, Marjorie; Fallick, A.E.; Ohnenstetter, Daniel; Song, Yucai Y.; Demaiffe, Daniel

doi:10.1016/j.crte.2014.12.003

Cited by 14 publications

(24 citation statements)

References 36 publications

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“…This suggests that by the point that fO 2 had dropped to near that of the CrO-Cr 0 buffer, most Fe, Ni and Ga had been removed from the system. It is notable that the Ga contents of the corundum varieties described here (< 0.3 ppm;Table 3) are dramatically lower than those of other mantle-derived corundum (typically 50-150 ppm Ga 2 O 3 ;Giuliani et al 2015;Sutherland et al 2009). This depletion may reflect the sequestration of Ga in the metallic alloys at fO 2 ≤IW.…”

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confidence: 67%

Cr2O3 in corundum: Ultrahigh contents under reducing conditions

Griffin

Gain

Saunders

et al. 2021

American Mineralogist

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Xenocrysts and xenoliths in Upper Cretaceous pyroclastics on Mount Carmel (N. Israel) represent a series of similar magma-fluid systems at different stages of their evolution, recording a continuous decrease in oxygen fugacity (fO 2) as crystallization proceeded. Corundum coexisting with Fe-Mg-Cr-Al spinels , other Fe-Mg-Al-Na oxides and Fe-Ni alloys in apparent cumulates crystallized at fO 2 near the iron-wüstite (IW) buffer (fO 2 = IW±1) and is zoned from high-Cr cores to lower-Cr rims, consistent with fractional crystallization trends. The reconstructed parental melts of the cumulates are Al-Cr-Fe-Mg oxides with ca 2 wt% SiO 2. Corundum in other possible cumulates that contain Cr-Fe (Fe 45 wt%) alloys has low-Cr cores and still lower-Cr rims. Corundum coexisting with Cr 0 (fO 2 = IW-5) in some possible cumulates has low-Cr cores, but high-Cr rims (to >30% Cr 2 O 3). These changes in zoning patterns reflect the strong decrease in the melting point of Cr 2 O 3 , relative to Al 2 O 3 , with decreasing fO 2. EELS analyses show that all Cr in corundum that coexists with Cr 0 is present as Cr 3+. This suggests that late in the evolution of these reduced melts, Cr 2+ has disproportionated via the reaction 3Cr 2+ (melt) → 2Cr 3+ (Crn) + Cr 0. The most Cr-rich corundum crystallized together with -alumina phases including NaAl 11 O 17 (diaoyudaoite) and KAl 11 O 17 (kahlenbergite) and "-alumina phases; residual melts crystallized a range of (K,Mg) 2 (Al,Cr) 10 O 17 phases with the kahlenbergite structure. The parental melts of these assemblages appear to have been Al-Cr-K-Na-Mg oxides, which may be related to the Al-Cr-Fe-Mg oxide melts mentioned above, through fractional crystallization or liquid immiscibility. This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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confidence: 67%

Cr2O3 in corundum: Ultrahigh contents under reducing conditions

Griffin

Gain

Saunders

et al. 2021

American Mineralogist

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“…This tool received wider use being extended to sapphire of other colors and even ruby, as it is normally a metamorphic/metasomatic corundum and seemed to conform to the classification boundaries. [9,68,69]. Recent studies show that individual corundum crystals can show significant ranges in their Ga/Mg ratio [70], and that rare rubies from Myanmar and East Australia show high Ga/Mg ratios that lie in the magmatic field [13,48].…”

Section: Myanmar and East Australian Ruby Trace Element Comparisonsmentioning

confidence: 99%

Diversity in Ruby Geochemistry and Its Inclusions: Intra- and Inter- Continental Comparisons from Myanmar and Eastern Australia

et al. 2019

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Ruby in diverse geological settings leaves petrogenetic clues, in its zoning, inclusions, trace elements and oxygen isotope values. Rock-hosted and isolated crystals are compared from Myanmar, SE Asia, and New South Wales, East Australia. Myanmar ruby typifies metasomatized and metamorphic settings, while East Australian ruby xenocrysts are derived from basalts that tapped underlying fold belts. The respective suites include homogeneous ruby; bi-colored inner (violet blue) and outer (red) zoned ruby; ruby-sapphirine-spinel composites; pink to red grains and multi-zoned crystals of red-pink-white-violet (core to rim). Ruby ages were determined by using U-Pb isotopes in titanite inclusions (Thurein Taung; 32.4 Ma) and zircon inclusions (Mong Hsu; 23.9 Ma) and basalt dating in NSW, >60–40 Ma. Trace element oxide plots suggest marble sources for Thurein Taung and Mong Hsu ruby and ultramafic-mafic sources for Mong Hsu (dark cores). NSW rubies suggest metasomatic (Barrington Tops), ultramafic to mafic (Macquarie River) and metasomatic-magmatic (New England) sources. A previous study showed that Cr/Ga vs. Fe/(V + Ti) plots separate Mong Hsu ruby from other ruby fields, but did not test Mogok ruby. Thurein Taung ruby, tested here, plotted separately to Mong Hsu ruby. A Fe-Ga/Mg diagram splits ruby suites into various fields (Ga/Mg < 3), except for magmatic input into rare Mogok and Australian ruby (Ga/Mg > 6). The diverse results emphasize ruby’s potential for geographic typing.

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“…In situ occurrences where the sapphires are still inside their host basalts are rarely found (e.g., MacNevin 1972;Stephenson 1976;Vichit 1987). The best known example is a basalt flow at Changle, China (Guo et al 1992;Zelong et al 2007;Giuliani et al 2015), while numerous corundum, including gem crystals, were recorded in extensive flows south of Jos Plateau, Nigeria (Wright 1985).…”

Section: Introductionmentioning

confidence: 99%