Alkaline Rocks and Carbonatites of the World

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Jabal Al Hasawinah

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Occurrence number: 
097-00-003
Country: 
Libya
Location: 
Longitude: 14.08, Latitude: 28.3

The two structural domes of Wadi Darman and Wadi Badran are aligned north-south and across them are distributed numerous tholoids of phonolite while basalts form dykes, pyroclastic cones and lava flows (Busrewil and Oun, 1991). The lava flows may be related to the adjacent Jabal as Sawda volcanic field (No. 097-00-004). Analyses of 23 specimens, including trace element data and REE for four rocks, enabled Busrewil and Oun (1991) to classify them into basalt, basanite, phonolite and trachyte. Brief petrographic notes on these rocks indicate that the basalts contain phenocrysts of olivine and plagioclase and microphenocrysts of augite and magnetite. The basanites include the same phenocryst assemblage together with phenocrysts of nepheline. The phonolites contain abundant phenocrysts of aegirine-augite with resorbed plagioclase, K-feldspar, nepheline, leucite and amphibole. The trachytes include rare olivine, augite and aegirine-augite, plagioclase, sanidine, euhedral nepheline, biotite and amphibole.

Age: 
K-Ar determinations on phonolites gave dates of 15.7 and 23.2 Ma and a basalt from a cone 24.9 Ma (Busrewil and Oun, 1991).
References: 
BUSREWIL, M.T. and OUN, K.M. 1991. Geochemistry of the Tertiary alkaline rocks of Jabal al Hasawinah, west central Libya. In M.J. Salem, M.T. Busrewil and A.M. Ben Ashour (eds) The geology of Libya, 7: 2587-98. Elsevier, Amsterdam.
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