scholarly journals Garnet peridotite xenoliths from the Koffiefontein mine, South Africa

2019 ◽  
Keyword(s):  
South Africa ◽  
Garnet Peridotite ◽  
Peridotite Xenoliths

Minor elements in olivine from spinel lherzolite xenoliths: implications for thermobarometry

1997 ◽  
Vol 61 (405) ◽  
pp. 257-269 ◽  
Author(s):  
Suzanne Y. O'Reilly ◽  
D. Chen ◽  
W. L. Griffin ◽  
C. G. Ryan
Keyword(s):  
Trace Element ◽  
Garnet Peridotite ◽  
Spinel Peridotite ◽  
Spinel Lherzolite ◽  
Proton Microprobe ◽  
Minor Elements ◽  
Spinel Lherzolites ◽  
Peridotite Xenoliths ◽  
Trace Element Contents ◽  
Element Contents

AbstractThe proton microprobe has been used to determine contents of Ca, Ti, Ni, Mn and Zn in the olivine of 54 spinel lherzolite xenoliths from Australian and Chinese basalts. These data are compared with proton-probe data for Ni, Mn and Zn in the olivine of 180 garnet peridotite xenoliths from African and Siberian kimberlites. Fe, Mn, Ni and Zn contents are well-correlated; because the spinel lherzolite olivines have higher mean Fe contents than garnet peridotite olivines (average Fo89.6vs. Fo90–92) they also have lower Ni and higher Mn contents. Zn and Fe are well-correlated in garnet peridotite olivine, but in spinel peridotites this relationship is perturbed by partitioning of Zn into spinel. None of these elements shows significant correlation with temperature. Consistent differences in trace-element contents of olivines in the two suites is interpreted as reflecting the greater degree of depletion of Archean garnet peridotites as compared to Phanerozoic spinel lherzolites. Ca and Ti contents of spinel-peridotite olivine are well correlated with one another, and with temperature as determined by several types of geothermometer. However, Ca contents are poorly correlated with pressure as determined by the Ca-in-olivine barometer of Köhler and Brey (1990). This reflects the strong T-dependence of this barometer: the uncertainty in pressure (calculated by this method) which is produced by the ±50°C uncertainty expected of any geothermometer is ca ± 8 kbar, corresponding to the entire width of the spinel-lherzolite field at 900–1200°C.

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 ◽  
Vol 45 (337) ◽  
pp. 129-134 ◽  
Author(s):  
R. A. Exley ◽  
J. V. Smith ◽  
R. L. Hervig
Keyword(s):  
South Africa ◽  
Complex Behaviour ◽  
Peridotite Xenoliths ◽  
Garnet Core ◽  
Al Distribution ◽  
Pressure Interval ◽  
Simultaneous Growth

AbstractPeridotite 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, Cr2O3 7; rim 1.4, 4 wt. %), spinel (TiO2 5, Cr2O3 38), clinopyroxene (A12O3 1–8) secondary mica (TiO2 6, Cr2O3 2.5 near garnet 0.5 away from garnet), and serpentine (FeO 5–12) enclosing perovskite-rimmed ilmenite and minute apatites. All minerals in peridotite 73–109 are Ti-poor, and include olivine (Fo 92.6), orthopyroxene (En 93.6), garnet (Cr2O3 3.1–3.8), spinel (55), ureyitic diopside, primary mica (TiO2 0.06, Cr2O3 1.0, BaO 0.5, Cl 0.04), and serpentine (FeO 2–23). Various thermometers indicate ∼ 1350K (73–106) and 1100K (73–109). The low Al2O3 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/Al 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/Al. 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.

Kimberlite-borne garnet peridotite xenoliths from old enriched subcontinental lithosphere

1985 ◽  
Vol 75 (2-3) ◽  
pp. 116-128 ◽  
Author(s):  
Stephen H. Richardson ◽  
Anthony J. Erlank ◽  
Stanley R. Hart
Keyword(s):  
Garnet Peridotite ◽  
Peridotite Xenoliths ◽  
Subcontinental Lithosphere
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