The Wadi Onib Mafic-Ultramafic Complex: A Neoproterozoic Supra-Subduction Zone Ophiolite in the Northern Red Sea Hills of the Sudan

Abstract:

The Wadi Onib mafic-ultramafic complex is an exceptionally well-preserved though tectonically fragmented ophiolitic sequence in the northern Red Sea Hills (NRSH) of the NE Sudan. It is characterized by a number of internal stratigraphic, structural and compositional features some of which are: (A) an exceptionally thick (ca. 2.5 km) transitional zone of interlayered and laminated cumulates showing gravity stratification; (B) an abundance of olivine-bearing pyroxenites and wherlitic (?) transitions relative to troctolites; (C) podiform bimodal chromite (high Cr/high-Al); (D) isoclinal folding of magmatic layering (intrafolial folding) suggesting high-temperature ductile deformation; (E) sea water/rock interaction (hydrothermal) alteration. The Onib lavas and dykes are predominantly Ti-rich, have a transitional IAT-MORB character and are indistinguishable from anomalous MORB and/or marginal basin basalts. The Onib ophiolite was subjected to successive metamorphic episodes which are difficult to distinguish. Vertical zonation of metamorphic grades, albitization and/or saussuritization of plagioclase, uralitization of pyroxene as well as preservation of igneous textures in spite of replacement of primary minerals indicate that sea-floor hydrothermal alteration must have taken place prior to basin closure and ophiolite obduction. Exceptionally thick transition zones have also been reported from other ophiolitic sequences (e.g., see Kröner et al., 1987; Hussein, 2000), and such transitional zones of interlayered cumulates and associated podiform chromite seem to be characteristic of marginal basin ophiolites (Hawkin and Evans, 1983). All these data imply a back-arc (marginal) basin setting in a supra-subduction zone (SSZ) environment. The ophiolite sequence was generated some 808 Ma ago. Partial melting conditions were most probably of multi-stage, and the magma chamber was of an open system type. Thus, the evolution of the ophiolite sequence attests to the fact that modern-type plate tectonic regimes can be extended back into the early Neoproterozoic. The ophiolite forms the major part of the Onib-Sol Hamed ophiolite-decorated suture the northeastern extension of which concurs with the Jabal Al Wask ophiolite complex in Saudi Arabia. © 2004 Elsevier B.V. All rights reserved.

Año de publicación:

2004

Keywords:

Fuente:

scopus