Alkaline Rocks and Carbonatites of the World

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Mishbih (Mishbeh)

stripes

Occurrence number: 
049-00-041
Country: 
Egypt
Location: 
Longitude: 34.68, Latitude: 22.72

An approximately circular complex 8 km in diameter is capped in places at higher levels by a roof of lavas and agglomerates. The principal rock types are syenites of widely varying grain size which vary from quartz- to nepheline- and analcime-bearing. Aegirine is the normal mafic mineral but some varieties contain augite, generally surrounded by sodic amphibole, and biotite. Within the southeastern part of the complex is an oval-shaped mass of 3x4 km of basement granite, gneiss and metavolcanics cut by numerous dykes. It is surrounded by a broad peralkaline syenite dyke. A small stock in the central area of the complex consists of umptekites containing a little nepheline and analcime; these pass into foyaites that are very much richer in nepheline. The volcanic rocks underlie a plateau about 3 km in diameter in the northeast of the complex. Basal agglomerates contain some trachybasaltic material, but they pass upwards into agglomerates and tuffs that are essentially of trachytic and latitic fragments. Radial solvsbergite-grorudite, bostonite and nepheline-bearing syenite dykes are widespread among the country rocks. Rock analyses are given by El Ramly et al. (1971), some trace element data for nepheline syenite by Ivanov et al. (1973) and U and Th data on three rocks are in El Reedy (1985).

Age: 
K-Ar on peralkaline syenites gave 141(3 and 143(3 Ma (Serencsits et al., 1979). Three samples of peralkaline quartz syenite gave a Rb-Sr isochron age of 148.3(12.2 Ma (Hashad and El Reedy, 1979). Fission-track dating of apatite from peralkaline syenite yielded ages of 64.9-67.7 Ma and sphene 132 and 133 Ma (Omar et al., 1987).
References: 
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.EL REEDY, M.W. 1985. Preliminary investigation on the distribution of uranium and thorium in some alkaline rocks of south eastern desert, Egypt. Annals of the Geological Survey of Egypt, 15: 115-21.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.SERENCSITS, C.M., FAUL, H., FOLAND, K.A., EL RAMLY, M.F. and HUSSEIN, A.A. 1979. Alkaline ring complexes in Egypt: their ages and relationship to tectonic development of the Red Sea. Annals of the Geological Survey of Egypt, 9: 102-16.
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith