The Bi'r Umq-Nakasib Suture Zone in the Arabian-Nubian Shield: A Key to Understanding Crustal Growth in the East African Orogen
The Bi'r Umq-Nakasib suture zone, 5-65 km wide and over 600 km long, consists of highly deformed ophiolite nappes and metavolcanic, metasedimentary, and intrusive rocks contained in one of the longest ophiolite-decorated shear zones in the Arabian-Nubian Shield. The rocks originated in a variety of juvenile oceanic environments and include assemblages formed in mid-ocean-ridge, subduction-zone, passive-margin, and continental-slope settings. Dating of the ophiolites, volcanic rocks, and pre- and syntectonic plutons indicates that oceanic magmatism in the region was active ~870-830 Ma whereas suturing occurred ~780-760 Ma. This chronology suggests that suturing involved the closure of a relatively long-lived oceanic basin and makes the Bi'r Umq-Nakasib shear zone the oldest accretionary structure known among the juvenile Neoproterozoic rocks of the northern East African Orogen. Creation of the shear zone dates the onset of arc-arc convergence in what eventually became the Arabian-Nubian shield, and marks the beginning of the complex, heterogeneous process of terrane amalgamation and continental accretion that led to the eventual accretion of East and West Gondwana.
P. R. Johnson et al., "The Bi'r Umq-Nakasib Suture Zone in the Arabian-Nubian Shield: A Key to Understanding Crustal Growth in the East African Orogen," Gondwana Research, vol. 6, no. 3, pp. 523-530, Elsevier Inc., Jul 2003.
The definitive version is available at http://dx.doi.org/10.1016/S1342-937X(05)71003-0
Geosciences and Geological and Petroleum Engineering
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