Alkaline Rocks and Carbonatites of the World

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Gharib (Gabal Gharib, Mount Gharib)

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Occurrence number: 
049-00-008
Country: 
Egypt
Location: 
Longitude: 32.88, Latitude: 28.02

The crescent-shaped 55 km2 peralkaline Gharib granite cuts Pan-African granodiorites and adamellites and two dyke swarms (Abdel-Rahman and Martin, 1990). The granite has sharp, steep contacts, sends apophyses into the surrounding rocks and has a metasomatised aureole up to 2 km wide. The granite varies from coarse-grained and sparsely miarolitic at the lowest levels of exposure to vacuolar and fine-grained in the roof facies. The characteristic miarolitic cavities increase in size upwards reaching diameters of 50 cm at the highest levels. There are local cognate mafic inclusions. The granite comprises perthite, quartz, sodic amphibole, many grains being zoned from F-rich ferro-richterite cores to arfvedsonitic rims (Abdel-Rahman, 1987), and accessory astrophyllite, biotite, fluorite, aenigmatite, elpidite(?), zircon and ilmenite. A fine-grained roof facies contains acicular arfvedsonite. In the metasomatized aureole there have been major changes to the nature of the feldspar (Abdel-Rahman and Martin, 1990) and the development of fluor-arfvedsonite, astrophyllite and accessory fluorite. Whole rock analyses, including trace element data, are given by Abdel-Rahman and Martin (1990).

Age: 
Stern and Hedge (1985) obtained a Rb-Sr age on a single sample of 544 Ma, while a 13 point Rb-Sr isochron gave 476(2 Ma (Abdel-Rahman and Doig, 1987).
References: 
ABDEL-RAHMAN, A.-F.M. 1987. Crystallization of amphiboles in the plutonic complexes of northeastern Egypt: implications for magma evolution. Neues Jahrbuch fur Mineralogie. Abhandlungen, 157: 319-35. ABDEL-RAHMAN, A.-F.M. and DOIG, R. 1987. The Rb-Sr geochronological evolution of the Ras Gharib segment of the northern Nubian shield. Journal of the Geological Society, London, 144: 577-86ABDEL-RAHMAN, A.-F.M. and MARTIN, R.F. 1990. The Mount Gharib A-type granite, Nubian Shield: petrogenesis and role of metasomatism at the source. Contributions to Mineralogy and Petrology, 104: 173-83.STERN, R.J. and HEDGE, C.E. 1985. Geochronologic and isotopic constraints on late Precambrian crustal evolution in the eastern desert of Egypt. American Journal of Science, 285: 97-127.
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