Alkaline Rocks and Carbonatites of the World

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Mansouri (Gabal Mansouri)

stripes

Occurrence number: 
049-00-045
Country: 
Egypt
Location: 
Longitude: 33.62, Latitude: 22.05

An approximately circular pluton 5 km in diameter is overlain in its central and northeastern parts by lavas, breccias and agglomerates representing the remnants of a volcanic cone. The plutonic rocks are coarse- and fine-grained, mineralogically variable peralkaline aegirine and sodic amphibole syenites and quartz syenites. They are cut by numerous radial and concentric dykes. The volcanic rocks are cut and brecciated by the syenites as well as dykes of solvsbergite, bostonite and syenite porphyries. The volcanics include rhyolites and trachytes with sodic amphiboles. Rock analyses are given by El Ramly et al. (1971). A number of carbonate bodies to the north, west and southeast of the pluton are referred to by El Ramly et al. (1971) as carbonatites. They form sheets and plug-like masses and are described as containing magnesite, forsterite and tremolite and are highly serpentinized. In the mass to the west a variety consisting of alternate bands of calcite and Nb-rich magnetite occurs. Niocalite has been identified in some of these rocks (El Ramly and Hussein, 1982). M.S. Garson (pers. comm., 1988) is convinced that these rocks are indeed carbonatites and he has identified a fenite associated with them. They extend even further to the east than shown on the map of El Ramly et al. (1971, Plate VI). Four carbonatite analyses are quoted in Aly et al. (1983).

Age: 
Rb-Sr determinations on quartz syenite gave 131.6(10 Ma (Hashad and El Reedy, 1979). A fission-track age of 72.0(5.3 Ma was obtained on apatite from quartz syenite (Omar et al., 1987). M.S. Garson (pers. comm., 1988) says that the carbonatites are 'pre-batholith' and therefore Precambrian in age.
References: 
ALY, M. M., EL RAMLY, M.F. and KABESH, M.L. 1983. Analyses of Egyptian rocks. Part 1. Igneous rocks. Geological Survey of Egypt, Paper, 66: 1-119.EL RAMLY, M.F. and HUSSEIN, A.A.A. 1982. The alkaline ring complexes of Egypt. Geological Survey of Egypt, Paper, 63: 1-16.EL RAMLY, M.F., BUDANOV, V.I. and HUSSEIN, A.A.A. 1971. The alkaline rocks of south-eastern Egypt. Geological Survey of Egypt, Paper, 53: 1-111.M.S. Garson, pers. comm., 1988.HASHAD, A.H. and EL REEDY, M.W.M. 1979. Geochronology of the anorogenic alkalic rocks, South Eastern desert, Egypt. Annals of the Geological Survey of Egypt, 9: 81-101.OMAR, G.I., KOHN, B.P., LUTZ, T.M. and FAUL, H. 1987. The cooling history of Silurian to Cretaceous alkaline ring complexes, South Eastern Desert, Egypt, as revealed by fission-track analysis. Earth and Planetary Science Letters, 83: 94-108.
Location: 
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