Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

Journal of the Geological Society

This Article Full Text (PDF) References Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Bonatti, E. Articles by El Tahir, M. A. Search for Related Content GeoRef GeoRef Citation

Zabargad (St. John’s) Island: an uplifted fragment of sub-Red Sea lithosphere

Zabargad is a small island located in the Red Sea about 50 km W of its axis, between 23º and 24ºN. The island is not volcanic but probably represents an uplifted block of upper mantle and crustal rocks, and yields information on the nature of the underlying lithosphere.

Peridotites are the main rock type, consisting of exceptionally fresh spinel lherzolites, which equilibrated last at a depth >30 km in the mantle. Other ultramafic facies, some representing rocks which mixed with a basaltic melt fraction, and some which underwent metasomatic exchange at depth, are also present. The peridotite bodies are in tectonic contact with a metamorphic formation consisting of gneissic and amphibolitic rocks similar to those outcropping in the Pan African metamorphic basement of eastern Egypt, Peridotites and metamorphic rocks are both crossed by several generations of basaltic dykes. The sedimentary Zabargad Formation, of probable Cretaceous or Palaeocene age, consists of alternations of silicified limestones, sandstones, black shales and phosphoritic lenses, and is overlain by evaporites, probably of Miocene age, and by reef limestone units, one probably of early Pleistocene age, the other probably deposited during the last interglacial. Various formations are affected by localized metasomatic mineralizations (recrystallized large, gem-quality olivine, cancrinite, scapolite. garnierite). The uplift of upper mantle ultramafic bodies with fragments of crust, which created the island, might have occurred in connection with the early stages of development of the rift which preceded the formation of the Red Sea. An alternative explanation, that the Zabargad peridotites are remnants of a Pan-African Palaeozoic ophiolitic complex, is possible but less likely.

This article has been cited by other articles:

				O. Muntener and G. B. Piccardo Melt migration in ophiolitic peridotites: the message from Alpine-Apennine peridotites and implications for embryonic ocean basins Geological Society, London, Special Publications, January 1, 2003; 218(1): 69 - 89. [Abstract] [PDF]

				T. B. ANDERSEN, K. P. SKJERLIE, and H. FURNES The Sunnfjord Melange, evidence of Silurian ophiolite accretion in the West Norwegian Caledonides Journal of the Geological Society, February 1, 1990; 147(1): 59 - 68. [Abstract] [PDF]

				K. CRANE and E. BONATTI The role of fracture zones during early Red Sea rifting: structural analysis using Space Shuttle radar and LANDSAT imagery Journal of the Geological Society, June 1, 1987; 144(3): 407 - 420. [Abstract] [PDF]