|
Article |
The Arabian-Nubian shield was produced by the episodic cratonization and accretion of intra-oceanic arc systems over the period 1100–500 Ma BP. The easternmost part of the Arabian shield is dominated by the N-S Al Amar fault zone, long believed to represent an easterly-inclined Upper Proterozoic suture between either two island arc systems or oceanic and continental lithosphere. In the area studied there are two N–S ophiolitic mélange zones which separate a central belt of metamorphosed trench sediments (Abt Schists) from flanking granitoid zones that represent the plutonic cores of arc systems. The mélange blocks are of layered gabbro, chromitite, homogeneous gabbro with dykes, plagiogranite, sheeted dykes and pillow lavas set in a sheared serpentinite matrix. The blocks are large (c. 1 km) and gabbroic in the western zone and smaller (1–100 m) and of fine-grained basic rocks in the eastern zone; all are compositionally similar and petrographically typical of rock types found in ophiolite complexes elsewhere. However, the Zr, Ti and Nb content of all these rocks is too low even for the back-arc, marginal basin setting commonly invoked for ophiolite genesis. To explain the unusually low high field strength element abundances, it is suggested that either these rocks were generated in or near a transform fault zone and then deposited in an oceanic trench when they began to be subducted, or that their boninitic character identifies them as the products of fore-arc igneous activity and, by analogy with the tectono-magmatic evolution of the W. Phillipine-Mariana region in the W Pacific, they mark the site of arc separation prior to back-arc sea-floor spreading; the latter explanation is preferred.
This article has been cited by other articles:
 |
|
 |
|
  P. R. Johnson and B. Woldehaimanot Development of the Arabian-Nubian Shield: perspectives on accretion and deformation in the northern East African Orogen and the assembly of Gondwana Geological Society, London, Special Publications, 2003; 206: 289 - 325. [Abstract] [PDF]
|
|
|
|
|
|
Y. Dilek and Z. Ahmed Proterozoic ophiolites of the Arabian Shield and their significance in Precambrian tectonics Geological Society, London, Special Publications, 2003; 218: 685 - 700. [Abstract] [PDF]
|
|
|
|
 |
|
 A. M. AL-SALEH, A. P. BOYLE, and A. E. MUSSETT Metamorphism and 40Ar/39Ar dating of the Halaban Ophiolite and associated units: evidence for two-stage orogenesis in the eastern Arabian Shield Journal of the Geological Society, 1998; 155: 165 - 175. [Abstract] [PDF]
|
|
|
|
|
|
M. M. MILLER and T. H. DIXON Late Proterozoic evolution of the northern part of the Hamisana zone, northeast Sudan: constraints on Pan-African accretionary tectonics Journal of the Geological Society, 1992; 149: 743 - 750. [Abstract] [PDF]
|
|
|
|
|
|
R. M. Shackleton Precambrian collision tectonics in Africa Geological Society, London, Special Publications, 1986; 19: 329 - 349. [Abstract] [PDF]
|
|
|
|
|
|
J. S. Stacey, D. B. Stoeser, W. R. Greenwood, and L. B. Fischer U-Pb zircon geochronology and geological evolution of the Halaban-Al Amar region of the Eastern Arabian Shield, Kingdom of Saudi Arabia Journal of the Geological Society, 1984; 141: 1043 - 1055. [Abstract] [PDF]
|
|
|
|
|
|
Discussion on the Upper Proterozoic ophiolite melange zones of the easternmost Arabian Shield Journal of the Geological Society, 1984; 141: 1083 - 1087. [Abstract] [PDF]
|
|
|
|
|
|
M. O. Nassief, R. Macdonald, and I. G. Gass The Jebel Thurwah Upper Proterozoic Ophiolite Complex, western Saudi Arabia Journal of the Geological Society, 1984; 141: 537 - 546. [Abstract] [PDF]
|
|
