THE GABAL-GERF COMPLEX - A PRECAMBRIAN N-MORB OPHIOLITE IN THE NUBIAN SHIELD, NE AFRICA

被引：232
作者：
ZIMMER, M
KRONER, A
JOCHUM, KP
REISCHMANN, T
TODT, W
机构：
[1] UNIV MAINZ, INST GEOWISSENSCH, D-55099 MAINZ, GERMANY
[2] MAX PLANCK INST CHEM, D-55020 MAINZ, GERMANY
来源：
CHEMICAL GEOLOGY | 1995年 / 123卷 / 1-4期
关键词：
D O I：
10.1016/0009-2541(95)00018-H
中图分类号：
P3 [地球物理学]; P59 [地球化学];
学科分类号：
0708 ; 070902 ;
摘要：
We report geochemical and isotopic data for tectonically dismembered units of the Cabal 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-TiN-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 Cabal 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 similar to 750 Ma for the time of igneous crystallization of the Cabal Gerf complex. epsilon(Nd) 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 modem N-MORB, while the gabbros are more akin to island are and back-are basin rocks. We ascribe their elevated Pb-207/Pb-204 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 are complexes with the active margin of the African continent occurred during an accretion event similar to 600-700 Ma ago.
引用
收藏
页码：29 / 51
页数：23
相关论文
共 81 条
  • [1] Abdel-Rahman, Geochemical and geotectonic controls of the metallogenic evalution of selected ophiolite complexes from the Sudan, Ber. Geowiss. Abh., Reihe A, 145, (1993)
  • [2] Abdel-Rahman, Harms, Schandelmeier, Franz, Darbyshire, Horn, Muller-Sohnius, A new ophiolite occurrence in NW Sudan — constraints on late Proterozoic tectonism, Terra Nova, 2, pp. 363-376, (1990)
  • [3] Alabaster, Pearce, Malpas, The volcanic stratigraphy and petrogenesis of the Oman Ophiolite complex, Contrib. Mineral. Petrol., 81, pp. 168-183, (1982)
  • [4] Bakor, Gass, Neary, Jabal al Wask, northwest Saudi Arabia, an Eocambrian back-arc ophiolite, Earth Planet. Sci. Lett., 30, pp. 1-9, (1976)
  • [5] Berhe, Ophiolites in Northeast and East Africa: implications for Proterozoic crustal growth, J. Geol. Soc. London, 147, pp. 41-57, (1990)
  • [6] Bodinier, Dupuy, Dostal, Geochemistry of Precambrian ophiolites from Bou Azzer, Morocco, Contrib. Mineral. Petrol., 87, pp. 43-50, (1984)
  • [7] Brouxel, Lapierre, Geochemical study of an early Paleozoic island-arc-back-arc system, Part 1: The Trinity Ophiolite (northern California), Geol. Soc. Am. Bull., 100, pp. 1111-1119, (1988)
  • [8] Cameron, Petrology and origin of primitive lavas from the Troodos ophiolite, Cyprus, Contrib. Mineral. Petrol., 89, pp. 239-255, (1985)
  • [9] Camp, Island arcs and their role in the evolution of the western Arabian shield, Geol. Soc. Am. Bull., 95, pp. 913-921, (1984)
  • [10] Claesson, Pallister, Tatsumoto, Samarium-neodymium data on two late Proterozoic ophiolites of Saudi Arabia and implications for crustal and mantle evolution, Contrib. Mineral. Petrol., 85, pp. 244-252, (1984)
123456789