Unique spinel-garnet lherzolite inclusion in kimberlite from Australia

Ferguson, John; Ellis, David J.; England, R. N.

doi:10.1130/0091-7613(1977)5<278:usliik>2.0.co;2

Cited by 34 publications

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“…In the multicomponent system, the spinel to garnet lherzolite transition is not univariant in P-T space, and therefore, it is possible that garnet and Cr-spinel coexist in the lherzolite assemblage over some pressure interval (MacGregor, 1970). Natural examples of spinel-garnet peridotite are reported from alpine-type peridotites (Lasnier, 1971;Rost & Brenneis, 1978) and nodules in Australian kimberlite (Ferguson et al, 1975).…”

Section: Garnetsmentioning

confidence: 99%

The Ronda Peridotite: Garnet-, Spinel-, and Plagioclase-Lherzolite Facies and the P-T Trajectories of a High-Temprature Mantle Intrusion

Obata¹

1980

Journal of Petrology

244

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The Ronda peridotite is a high-temperature, alpine-type peridotite emplaced in the internal Zone of the Betic Cordilleras, southern Spain. Using the mineral assemblages of the peridotite and mafic layers, the peridotite mass has been subdivided into 4 zones of mineral facies: (l)garnet-lherzolite facies, (2) ariegite subfacies of spinel-lherzolite facies, (3) seiland subfacies of spinel-lherzolite facies, and (4) plagioclase-lherzolite facies. It is proposed that this mineralogical zonation developed through a syntectic recrystallization of a hot (1100 to 1200 °C), solid mantle peridotite during its ascent into the Earth's crust.Coexisting minerals from 12 peridotites covering all the mineral facies above were analysed with an electron microprobe. Core compositions of pyroxene porphyroclasts are constant in all mineral facies and indicate that the peridotite was initially equilibrated at temperatures of 1100 to 1200 °C and pressures of 20 to 25 kb. In contrast, the compositions of pyroxene neoblasts and spinel grains (which appear to have grown during later recrystallization) are well correlated with mineral facies. They indicate that the recrystallization temperature throughout the mass is more or less constant, 800 to 900 °C, but that the pressure ranges from 5-7 kb in the plagioclase-lherzolite facies to 12-15 kb in the garnet-lherzolite facies. Therefore, variation in pressure appears to be primarily responsible for the four mineral facies types.A pressure range of at least 5 kb appears to be too large to have been maintained (at the same time) in a mass as small as the Ronda peridotite. Dynamic cooling may explain the observed variation in the recrystallization pressure; i.e. during the intrusion of the peridotite body, different parts of the body have followed different P-T paths in response to different local cooling rates. Comparing the inferred /"-Tpaths for the peridotite with published melting temperature of peridotite and mafic rocks, it is concluded that the peridotite did not go through partial fusion during the ascent. A hypothetical, diapiric uprise that caused partial fusion and igneous differentiation of the mantle peridotite is considered to be a separate event prior to the ascent that started from about 70 km depth in the upper mantle. Estimates of cooling rates and of Al diffusion rates in pyroxenes suggest that the ascent rate of the peridotite body was greater than 1 meter/year.

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Section: Garnetsmentioning

confidence: 99%

The Ronda Peridotite: Garnet-, Spinel-, and Plagioclase-Lherzolite Facies and the P-T Trajectories of a High-Temprature Mantle Intrusion

Obata¹

1980

Journal of Petrology

244

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“…4; see also Wood, 1977), and of all the A120 3 by ~ 28 kb (O'Neill, 1981). Although coarse grains of garnet and spinel tend to be mutually exclusive in peridotite xenoliths, the following papers report coexisting assemblages: Boyd and Nixon (1978), Kimberley, S. Africa; Carswell et al (1979) and Mitchell et al (1980), Pipe 100, Lesotho; Danchin (1979), Premier, S. Africa; Ferguson et al (1977), NSW, Australia; MacGregor (1979), Kao, Lesotho; Nixon and Boyd (1973), Thaba Putsoa and Mothae, Lesotho; Smith and Dawson (1975), Matsoku; Nixon and Boyd (1979), Malaita, Solomon Islands: Sobolev (1977), occurrences in Russia. Spinel and garnet pairs in alkremites (Nixon et al, 1978), and in a spinelgarnet websterite (Irving, 1974) were not considered because their bulk compositions are much richer in A1 and Ca, and lower in Cr, than typical ultramafic peridotites, and because they lack the olivine and pyroxene of lherzolite assemblages.…”

mentioning

confidence: 99%

“…2 Carswell et al (1979); filled triangle, Kao, MacGregor (1979); R, Mir, Russia, Sobolev (1977); M, Malaita, Solomon Islands, Nixon and Boyd (1979); A, SE Australia, Ferguson et al (1977); D, Dish Hill, California, Shervais et al (1973); open square, Pipe 200, Carswell et al (1979); open circle, Letseng, Lock and Dawson (1980); horizontal and inclined crosses, 73-106 and 73-109, this paper. Small numbers show t00 mg of spinel.…”

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confidence: 99%

Cr-rich spinel and garnet in two peridotite xenoliths from the Frank Smith mine South Africa: Significance of Al and Cr distribution between spinel and garnet

1982

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ABSTRACT. Peridotite xenoliths 73-106 and 73-109 have coarse textures. All minerals in 73-106 are very Ti-rich, and include olivine (Fo 87.6), orthopyroxene (En 90.0), garnet (core TiO2 0.8, Cr203 7; rim 1.4, 4 wt. ~o), spinel (TiO 2 5, Cr203 38), clinopyroxene (A1203 1 8) secondary mica (TiO2 6, Cr203 2.5 near garnet 0.5 away from garnet), and serpentine (FeO 5-12) enclosing perovskiterimmed ilmenite and minute apatites. All minerals in peridotite 73-109 are Ti-poor, and include olivine (Fo 92.6), orthopyroxene (En 93.6), garnet (Cr203 3.1-3.8), spinel (55), ureyitic diopside, primary mica (TiO 2 0.06, CrzO 3 1.0, BaO 0.5, C1 0.04), and serpentine (FeO 2-23).Various thermometers indicate ~ 1350K (73-106) and ll00K (73-109). The low A1203 in the orthopyroxenes gives 39-47 kb for 73-109 from the Wood-Banno barometer. In 73-106, the spinel lies in secondary mica next to the garnet rim, whereas the spinel of 73-109 occurs in grains enclosed by garnet. The former assemblage indicates diffusion-dependent disequilibrium, whereas the latter is attributed to simultaneous growth of spinel and garnet, perhaps consequent upon exsolution from orthopyroxene. Complex behaviour was found for the Cr/AI distribution in published analyses of garnet and spinel. The 73-109 pair lies near the Thaba Putsoa trend, and the 73-106 assemblages are displaced towards the kelyphite region in which garnet and spinel have similar Cr/AI. Spinel and garnet may coexist over a 30 kb pressure interval ranging from ~ 16 kb for low bulk Cr to ~ 40 kb for high Cr.DETAILED study of the texture and mineral chemistry of peridotite xenoliths can provide information on the physical and chemical nature of the upper mantle. Complex textural relationships between garnet, A1,Cr-spinel, and silicates testify to incomplete accommodation to changing physical conditions (Aoki and Prinz, 1974;Basu and MacGregor, 1975; Dawson et al., 1978;Reid and Dawson, 1972;Reid et al., 1975). Occurrence * Present address: Department of Chemistry, Arizona State University, Tempe, Arizona 85281 USA.t~ Copyright the Mineralogical Society of spinel in kelyphitic coronas around garnet is particularly common, but only a few specimens (Lock and Dawson, 1980) have escaped metasomatism which has removed or obscured important textural information. The transition from the spinel-to the garnet-peridotite facies is an important control in the upper mantle (O'Hara et al., 1971), but its position depends greatly on the bulk Cr/A1 ratio. Whereas the transition from spinel-to garnet-peridotite occurs in the CaOMgO-A1203-SiO 2 system near 15 kb at 1200 K and about 20 kb for 1600 K (data collected in Jenkins and Newton, 1979), replacement of half the A120 3 by Cr20 3 raises the pressure by about 16 kb (MacGregor, 1970, fig. 4; see also Wood, 1977), and of all the A120 3 by ~ 28 kb (O'Neill, 1981). Although coarse grains of garnet and spinel tend to be mutually exclusive in peridotite xenoliths, the following papers report coexisting assemblages: Boyd and Nixon (1978), Kimberley, S. Africa;Carswel...

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The Al2O3 contents of enstatite in equilibrium with garnet in the system MgO-Al2O3-SiO2 at 15–40 kbar and 900°–1,600° C

Perkins

Holland

Newton

1981

Contr. Mineral. and Petrol.

122

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Unique spinel-garnet lherzolite inclusion in kimberlite from Australia

Cited by 34 publications

References 0 publications

The Ronda Peridotite: Garnet-, Spinel-, and Plagioclase-Lherzolite Facies and the P-T Trajectories of a High-Temprature Mantle Intrusion

The Ronda Peridotite: Garnet-, Spinel-, and Plagioclase-Lherzolite Facies and the P-T Trajectories of a High-Temprature Mantle Intrusion

Cr-rich spinel and garnet in two peridotite xenoliths from the Frank Smith mine South Africa: Significance of Al and Cr distribution between spinel and garnet

The Al2O3 contents of enstatite in equilibrium with garnet in the system MgO-Al2O3-SiO2 at 15–40 kbar and 900°–1,600° C

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