Alkaline Rocks and Carbonatites of the World

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Azrou Area

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Occurrence number: 
113-00-004
Country: 
Morocco
Location: 
Longitude: -5.32, Latitude: 33.48

Over this large region there are extensive areas of basaltic flows, notably southeast of Azrou, with numerous volcanic centres including maars and particularly abundant scoria cones (Gentil, 1916; Harmand and Cantagrel, 1984). Some individual flows are confined to valleys along which they may extend for tens of kilometres. Among these rocks are alkaline varieties which are described under the general term 'ankaratrite' by Jérémine (1955), meaning melanocratic olivine nephelinite. She lists varieties containing analcime, hauyne and, with one example only, melilite. An occurrence in the south of the area contains phenocrysts of olivine in a groundmass of augite and aegirine-augite, biotite, brown amphibole, nepheline and analcime. A melilite-bearing rock occurring in the volcano of Djebel Anach (Termier, 1936) comprises altered olivine, augite, melilite, perovskite, magnetite, brown amphibole, a little apatite, nepheline and 'primary' analcime. Termier (1936) describes in detail hauyne-bearing rocks which also contain altered olivine together with augite, nepheline, rare biotite and magnetite and these are found at a number of localities (Jérémine, 1955, Fig. 2). To the south of Azrou, 10 km southeast of Ain Leuh, Termier et al. (1948) describe a suite of rocks from the Talzast volcano which comprise ankaratrite, consisting of olivine, augite, biotite, nepheline, accessories and, in some varieties, hauyne, and a coarse rock which is referred to as talzastite. The last is an ijolite with Ti-augite, a chemical analysis of which is given by Cherotzky (1969); specimens dated by Harmand and Cantagrel (1984) are described as melanephelinite, micromelteigite and ijolite.

Age: 
Harmand and Cantagrel (1984) give 14 K-Ar whole rock age determinations on melanephelinite, nephelinite, ijolite, basalt and basanite from localities across the whole area. Apart from the melanephelinite at Zebzat, which gives a date of 35(3 Ma, they lie in the range 14.6 to 0.5 Ma, with three dated Talzast rocks varying from 5.9 to 10.6 Ma. They tabulate previous age determinations (Harmand and Cantagrel, 1984).
References: 
CHEROTZKY, G. 1969. Sur la composition chimique de la talzastite. Notes et Mémoires du Service Géologique Maroc, 213: 97-100.GENTIL, L. 1916. Note sur les régions volcaniques du Maroc central. Bulletin de la Société Géologique de France, Ser. 4, 16: 186-218.HARMAND, C. and CANTAGREL, J.M. 1984. Le volcanisme alcalin Tertiary et Quaternaire du Moyen Atlas (Maroc): chronologie K/Ar et cadre géodynamique. Journal of African Earth Sciences, 2: 51-5.JÉRÉMINE , E. 1955. L'ankaratrite a haüyne du Jebel Tourguejid (Haut Atlas de Midelt). Quelques considérations sur les ankaratrites du Maroc et sur les ankaratrites en général. Notes et Mémoires. Service Géologique Maroc, 125: 59-75.TERMIER, H. 1936. Études géologiques sur le Maroc central et le Moyen Atlas Septentrional. Service des Mines et de la Carte Géologique. Notes et Mémoires. Rabat, 33 (III): 1503-47.TERMIER, H., TERMIER, G. and JOURAVSKY, G. 1948. Une roche volcanique à gros grain de la famille des ijolites: la talzastite. Notes et Mémoires. Service Géologique Maroc, 71: 81-120.
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