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" Geologic studies on the Tibesti Massif, south central Libya "
A. A. El-Makhrouf
P. G. Feiss
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Latin Dissertation
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English
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| Record Number
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1112600
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TLpq303934263
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| Main Entry
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A. A. El-Makhrouf
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P. G. Feiss
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| Title & Author
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Geologic studies on the Tibesti Massif, south central Libya\ A. A. El-MakhroufP. G. Feiss
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| College
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The University of North Carolina at Chapel Hill
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| Date
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1991
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| student score
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1991
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| Degree
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Ph.D.
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| Page No
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292
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| Abstract
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The Tibesti massif evolved during Middle to Late Proterozoic as a result of complex subduction processes. It is composed of two orogenic belts, the Eastern Tibesti (Eghei area and southward) and Western Tibesti (Bin Ghanimah batholith), which were amalgamated during the Early to Middle Cambrian. The Super Tibestian Magmatic Series (>600 Ma) developed on a destructive plate margin and includes calc-alkalic gabbro to granite. Then followed by the Eghei Magmatic Series (570-500 Ma). This series includes post-orogenic granites and cogenetic volcanics. They are widespread along the Eastern Tibesti orogenic belt. They were formed during a period of stress relaxation and were followed by diabase dikes (500 Ma) during a rifting stage. The Addaba Mohamed Salah (AMS), Kangara (KAN), and Kangara-Tushidi (K-T) plutons are mesozonal and post-orogenic. The Eghei Magmatic Series of the Jabal Eghei area have an age range of 554 to 528 Ma. The initial Sr/Sr of 0.7044 to 0.7079, suggests that these rocks were derived from a middle crustal source that had an initial Sr/Sr ratio 1000 Ma ago of 0.7030-0.7032 with a range of Rb/Sr ratios of 0.014 to 0.53. The mineral chemistry of the three plutons show that the biotites have a silica range 5.5 to 5.8 and are iron rich and their hornblendes are ferro-edenite. The Al-hornblende geobarometry and the ternary feldspar geothermometer show that these plutons intruded the upper crust at various levels: AMS = 3.0 0.2 Kbar (10 km), KAN = 3.3 0.3 Kbar, and K-T = 3.9 0.2 Kbar (13 km) and crystallized over a temperature range of 620 to 700C. The degree of partial melting, depth and temperature of generation were obtained for AMS, KAN, and K-T plutons: 31%, 24.8 km, 740C; 25%, 24 km, 710C; and 20%, 23.5 km, 695C, respectively. The post-orogenic magmas were generated in the middle crust. The post-orogenic magmatism associated with the stabilization and crationization of the Tibesti massif was followed by an extensional tectonics which prevailed in the Pan-African orogenic belts of northern Africa.
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| Subject
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Earth sciences
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Geochemistry
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Geology
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Geology
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Mineralogy
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