The Gabal Gerf Complex; a Precambrian N-MORB ophiolite in the Nubian Shield, NE Africa

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doi: 10.1016/0009-2541(95)00018-H
Authors:Zimmer, M.; Kröner, A.; Jochum, K. P.; Reischmann, T.; Todt, W.
Author Affiliations:Primary:
Max-Planck-Institut für Chemie, Mainz, Federal Republic of Germany
Other:
Universität Mainz, Institut für Geowissenschaften, Mainz, Federal Republic of Germany
Volume Title:Chemical Geology
Source:Chemical Geology, 123(1-4), p.29-51. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541
Publication Date:1995
Note:In English. 81 refs.; illus., incl. 7 tables, geol. sketch maps
Summary:We report geochemical and isotopic data for tectonically dismembered units of the Gabal Gerf mafic-ultramafic complex, the largest Neoproterozoic (Pan-African) ophiolite in the Arabian-Nubian Shield and located near the Red Sea in the border region between Egypt and the Sudan. The complex consists of basaltic pillow lavas, sheeted dykes, isotropic and layered gabbros and an ultramafic melange, all in tectonic contact along thrust sheets. Major- and trace-element data, including REE, for the pillow lavas and sheeted dykes are indistinguishable from modern high-Ti N-MORB. Chemical variations in the various rock types can be ascribed to fractionation and accumulation involving olivine, clinopyroxene and plagioclase. A comparison with chemical data from ophiolites of the Arabian-Nubian Shield and elsewhere in the world shows the Gabal Gerf complex to be the only Precambrian ophiolite with N-MORB chemistry, and we suggest that its basalts and sheeted dykes originally formed in a major ocean basin. Sm and Nd isotope analyses combined with published zircon data suggest an age of ∼750 Ma for the time of igneous crystallization of the Gabal Gerf complex. εNd initial values vary between +6.5 and +8.8, some of the highest yet reported for Neoproterozoic mantle-derived rocks. Pb isotopic data for the basalts and sheeted dykes are similar to modern N-MORB, while the gabbros are more akin to island arc and back-arc basin rocks. We ascribe their elevated 207Pb/204Pb ratios to mixing of a small amount of pelagic sediment with the magma source of the gabbros during subduction and subsequent melt generation above a subduction zone. The pillow basalts, sheeted dykes and gabbros were brought together by tectonic stacking during the obduction process when collision of island arc complexes with the active margin of the African continent occurred during an accretion event ∼600-700 Ma ago.
Subjects:Alkaline earth metals; Basalts; Chemical fractionation; Dikes; Gabbros; Geochemistry; Igneous rocks; Intrusions; Isotope ratios; Isotopes; Lava; Lithogeochemistry; Major elements; Metals; Mid-ocean ridge basalts; Nd-144/Nd-143; Neodymium; Neoproterozoic; Ophiolite complexes; Pan-African Orogeny; Pillow lava; Plutonic rocks; Precambrian; Proterozoic; Radioactive isotopes; Rare earths; Samarium; Sm-147/Nd-144; Sr-87/Sr-86; Stable isotopes; Strontium; Trace elements; Upper Precambrian; Volcanic rocks; Africa; East Africa; Egypt; North Africa; Nubian Shield; Red Sea region; Sudan; Gabal Gerf Complex
Coordinates:N221500 N224500 E0351500 E0345000
Abstract Numbers:96M/1128
Record ID:1995053623
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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