Two diamond-bearing peridotite xenoliths from the finsch kimberlite, South Africa

1982 ◽  
Vol 81 (2) ◽  
pp. 79-87 ◽  
Author(s):  
S. R. Shee ◽  
J. J. Gurney ◽  
D. N. Robinson
Keyword(s):  
South Africa ◽  
Peridotite Xenoliths

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.

Time and Latitude in South Africa

1972 ◽  
Vol 1 ◽  
pp. 27-38
Author(s):  
J. Hers
Keyword(s):  
South Africa ◽  
Cape Town ◽  
Astronomical Observations ◽  
Royal Observatory ◽  
The Republic ◽  
Astronomical Determination ◽  
Limited Accuracy ◽  
Better Than

In South Africa the modern outlook towards time may be said to have started in 1948. Both the two major observatories, The Royal Observatory in Cape Town and the Union Observatory (now known as the Republic Observatory) in Johannesburg had, of course, been involved in the astronomical determination of time almost from their inception, and the Johannesburg Observatory has been responsible for the official time of South Africa since 1908. However the pendulum clocks then in use could not be relied on to provide an accuracy better than about 1/10 second, which was of the same order as that of the astronomical observations. It is doubtful if much use was made of even this limited accuracy outside the two observatories, and although there may – occasionally have been a demand for more accurate time, it was certainly not voiced.

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