Spinels in Leg 37 Basalts and Peridotites: Phase Chemistry and Zoning

Sigurdsson, Haraldur

doi:10.2973/dsdp.proc.37.171.1977

Cited by 29 publications

(28 citation statements)

References 13 publications

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“…This is consistent with the discussion of mineralogical variability for the Mid-Atlantic Ridge peridotites (e.g., Michael and Bonatti, 1985;Bonatti et al, 1992). It is noted that the spinel compositions around Cr# = 29 are slightly higher than those from Site 670 in the MARK area (Fujii, 1990;Juteau et al, 1990;Komor et al, 1990), and lower than those from Site 395 in the western flank of Mid-Atlantic Ridge in the MARK area (Arai and Fujii, 1979;Sinton, 1979), Site 334 (DSDP Leg 37) in the FAMOUS area (Clarke and Loubat, 1977;Sigurdsson, 1977;Symes et al, 1977), and some fracture zones around Mid-Atlantic Ridge (Prinz et al, 1976;Bonatti et al, 1992;Cannat et al, 1992).…”

Section: Characteristics Of Chemical Composition Of Primary Mineralssupporting

confidence: 76%

“…Abbreviations as in Table 1. Clarke and Loubat, 1977;Sigurdsson, 1977;Symes et al, 1977;Arai and Fujii, 1979;Sinton, 1979;Fujii, 1990;Juteau et al, 1990;Komor et al, 1990;Bonatti et al, 1992;Cannat et al, 1992). A highly uniform composition of primary spinel cores (Mg# = 70-75 and Cr# = 27-31) is conspicuous in Hole 920D spinel harzburgites and lherzolites (Fig.…”

Section: Spinelmentioning

confidence: 99%

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Mineralogy of MARK peridotites: replacement through magma channeling examined from Hole 920D, MARK area

Nilia¹

1997

Proceedings of the Ocean Drilling Program, 153 Scientific Results

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Peridotites drilled at Site 920 of Ocean Drilling Program Leg 153 in the Mid-Atlantic Ridge near the Kane Transform (MARK) area were examined to understand the mode of magma channeling and modification of the upper mantle peridotites. This paper presents mineralogical data from a slow-spreading ocean ridge for peridotites that have been modified by magma channeling and for those that are free from the modification.The chemical compositions of primary minerals in spinel harzburgite and lherzolite are highly uniform. Olivine core compositions concentrate around Fo = 91.0 and NiO = 0.37 wt%. Spinel cores also have a small compositional range of Mg# = 70-75 and Cr# = 27-31. Orthopyroxenes with Mg# = 90.5-91.6 have A1 2 O 3 contents of 3.17 to 4.77 wt%. TiO 2 and Na 2 O contents in primary clinopyroxenes are extremely low, less than 0.15 and 0.11 wt%, respectively. These results suggest that the MARK peridotites represent moderately depleted upper mantle peridotite. The chemical compositions of primary minerals are modified where the peridotites are crosscut by gabbro and pyroxenite dikes and veins. Such peridotites are enriched in FeO* and TiO 2 , and depleted in MgO, NiO, and A1 2 O 3 .Spatial variations in chemical composition of minerals were examined across channels in Samples 153-920D-10R-2 (Piece 4, 35-41 cm) and 153-920D-13R-2 (Piece 7, 136-143 cm). Primary minerals in spinel harzburgite are enriched in FeO* and TiO 2 within narrow replacement bands next to websterite veins. No evidence for melt extractions was detected in the harzburgite wall, indicating that the replacement occurred as a one-way modification process by melt addition from the channeling magma. The Fo-NiO systematics for the modified olivines support a model of open-system reaction between the wall harzburgite and the infiltration melt with a highly evolved composition. All of the results emphasize that the final magma channeling occurred in "cold" peridotites at a shallow level of the upper mantle.

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Section: Characteristics Of Chemical Composition Of Primary Mineralssupporting

confidence: 76%

Section: Spinelmentioning

confidence: 99%

Mineralogy of MARK peridotites: replacement through magma channeling examined from Hole 920D, MARK area

Nilia¹

1997

Proceedings of the Ocean Drilling Program, 153 Scientific Results

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“…3) is usually ascribed to changing melt composition owing to crystallization of olivine, plagioclase or chromian spinel before extrusion, or to magma mixing (Allan et al 1988(Allan et al , 1989. It has also been suggested (Bryan 1972, Sigurdsson & Schilling 1976, Sigurdsson 1977, Dick & Bullen 1984 that zoning with respect to Cr/(Cr + Al) may be due to changes in pressure during growth of the chromian spinel, the more aluminous chromian spinel being stable at higher pressures.…”

Section: Introductionmentioning

confidence: 99%

Growth Forms and Composition of Chromian Spinel in Morb Magma: Diffusion-Controlled Crystallization of Chromian Spinel

Roeder

Poustovetov

Öskarsson

2001

The Canadian Mineralogist

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Microphenocrysts of chromian spinel in glass from an East Pacific Rise lava and three Icelandic subglacial lavas show a variety of complex skeletal, hopper, vermiform and chain textures. These grains of chromian spinel are larger than those found in most basalts. Many crystals show significant zoning in Cr/(Cr + Al), and the variation in Cr/(Cr + Al) with respect to Fe 2+ /(Fe 2+ + Mg) is distinctive for each sample. The four samples are relatively primitive, with between 9 and 10 wt.% MgO in the glass. One very distinctive texture, a core surrounded by a vermiform rim, has been interpreted by a number of researchers as a reaction texture caused either by changes in pressure or magma mixing. The variety of chromian spinel textures, including the vermiform rim, has been duplicated in an experimental run using the sample from the East Pacific Rise. The sample was held at 1225°C for 67 hours and then cooled slowly over 8 hours to 1147°C. We conclude that the vermiform texture and the other chromian spinel textures in the experimental run and the lavas are growth textures and not reaction textures. The change in growth habit that produces the vermiform rim is interpreted as diffusion-controlled growth, leading to what metallurgists refer to as cellular growth. Chromian spinel is susceptible to diffusion-controlled growth because of the very large difference in concentration of Cr in the melt (0.02-0.06 wt.% Cr 2 O 3 ) and in chromian spinel (30-50 wt.% Cr 2 O 3 ) at equilibrium. Although the chromian spinel in the glass of each natural sample shows a large variation in Cr/(Cr + Al), and thus was not in equilibrium with the bulk melt, its Fe 2+ / (Fe 2+ + Mg) may have been close to equilibrium with the bulk melt before quenching. The chromian spinel crystallized over a span of hours to days before a rapid water quench upon eruption. The complex textures and zoning probably reflect the turbulent conditions during passage of the magma toward the Earth's surface.Keywords: chromian spinel, chromite, basalt, texture, vermiform, hopper, diffusion-controlled crystallization. SOMMAIREDes microphénocristaux de spinelle chromifère sont présents dans une matrice vitreuse d'une lave basaltique provenant de la ride Est-Pacifique et de trois échantillons de coulées mises en place sous un glacier en Icelande. Ces cristaux contiennent une variété de textures complexes en entonnoir, vermiformes et en chaînes; ils sont plus grossiers que ceux qui caractérisent la plupart des basaltes. Plusieurs cristaux montrent une zonation importante en Cr/(Cr + Al), qui varie de façon distincte avec Fe 2+ /(Fe 2+ + Mg) dans chaque échantillon. Les quatre échantillons sont relativement primitifs, le verre contenant entre 9 et 10% (poids) de MgO. On a généralement interprété la présence d'un coeur entouré d'un liseré vermiforme comme résultat d'une réaction suite à des changements en pression ou à un mélange de magmas. La diversité texturale du spinelle chromifère, y inclus la bordure vermiforme, a été reproduite dans un série d'expériences f...

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“…The reverse zoning texture in Cr-spinel has been reported in meteorites [20], mid-ocean ridge basalts (MORBs), [21] and various mafic-ultramafic complexes (e.g., Alpine-type [22]; layered [23]; Alaskan-type [24]). Although this type of texture has been investigated in some mineralogical [25], geochemical [22], and experimental [26,27] studies, its origin is still a matter of continuous debate. The texture has been interpreted as a product of fractional crystallization [21,25,[28][29][30][31][32], reaction with non-homologous melt [33][34][35][36], and elemental exchange with host silicate minerals [22,24,37].…”

Section: Introductionmentioning

confidence: 99%

Origin of Reverse Zoned Cr-Spinels from the Paleoproterozoic Yanmenguan Mafic–Ultramafic Complex in the North China Craton

Bai

Xiao

et al. 2018

Minerals

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Abstract:We conducted petrological and mineral chemistry investigations of Cr-spinel in ultramafic rocks of the Yanmenguan mafic-ultramafic complex in the North China Craton. The Cr-spinel grains occur as inclusions in enstatite, tschermakite, phlogopite, and olivine, or as interstitial grains among the aforementioned silicate minerals, and show concentric or asymmetrical textures. Back-scattered electron and elemental images and compositional profiles of the spinel grains indicate the presence of Cr-and Fe-rich cores and Al-and Mg-rich rims. The host silicate minerals display a decrease in Al and Mg contents accompanied by an increase in Cr and Fe away from the spinel. These textures and compositional variations suggest that subsolidus elemental exchange more likely gave rise to the compositional zonation, resulting in the transfer of Al and Mg from the silicate minerals to the spinel. The Mn, Ni, and Ti contents in spinel and the major elements of olivine-hosted spinel are relatively stable during subsolidus elemental diffusion and thus are more reliable tracers of primary high-temperature processes. The temperature estimates reveal that the subsolidus diffusion might have occurred at 600-720 • C, which could be linked to the regional metamorphic event.

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Spinels in Leg 37 Basalts and Peridotites: Phase Chemistry and Zoning

Cited by 29 publications

References 13 publications

Mineralogy of MARK peridotites: replacement through magma channeling examined from Hole 920D, MARK area

Mineralogy of MARK peridotites: replacement through magma channeling examined from Hole 920D, MARK area

Growth Forms and Composition of Chromian Spinel in Morb Magma: Diffusion-Controlled Crystallization of Chromian Spinel

Origin of Reverse Zoned Cr-Spinels from the Paleoproterozoic Yanmenguan Mafic–Ultramafic Complex in the North China Craton

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