Oceanization starts from below during continental rupturing in the northern Red Sea

Thursday, 17 December 2015: 09:30
304 (Moscone South)
Marco Ligi1, Enrico Bonatti2, William Bosworth3, Yue Cai4, Anna Cipriani5, Camilla Palmiotto1, Najeeb MA Rasul6, Sara Ronca7, Alessio Sanfilippo8, Monique Seyler9, Salem Nomani6 and Abdulnasser S AlQutub6, (1)CNR Institute for Marine Science, Venice, Italy, (2)Lamont Doherty Earth Observatory, Columbia University, Palisades, NY, United States, (3)Apache Corporation, Houston, TX, United States, (4)Lamont -Doherty Earth Observatory, Palisades, NY, United States, (5)University of Modena and Reggio Emilia, Modena, Italy, (6)Saudi Geological Survey, Jeddah, Saudi Arabia, (7)Universita' La Sapienza, Scienze della Terra, Roma, Italy, (8)Kanazawa University, Kanazawa, Japan, (9)University of Lille 1, Villeneuve d'Ascq, France
The role of magmatism in continental rupturing and in the birth of a new ocean is not well understood. Continental rupture can take place with intense and voluminous volcanism, as in the Southern Red Sea or in a relatively amagmatic mode, as in the Northern Red Sea. Mantle upwelling and melting may be affected by the south to north decreasing opening rate of the Red Sea and by the influence of the Afar plume, also decreasing from south to north. The tholeiitic basalts of the Red Sea spreading system contrast with the extensive Cenozoic basaltic lava fields of the western part of the Arabian peninsula that form one of the largest alkali basalt provinces in the world. In order to establish possible relationship between the Red Sea rift evolution and the western Saudi Arabia intraplate alkali volcanism, field work was carried out on Lunayyir, Ishara, al Kura and Khaybar volcanic fields. Collected samples cover a wide range of chemical diversity (from olivine basalt to trachyte) and span over a 20 Ma interval. We attempt a comparison of the geochemistry of igneous rocks from western Arabia dykes and volcanic fields with those from the Red Sea axis and from the islands of Zabargad and Brothers in the northern Red Sea, that represent basaltic melts injected into the thinned continental crust before continental rupturing and initiation of seafloor spreading. Gabbros drilled in the western Red Sea and exposed on the Brothers islands suggest that continental break up in the northern Red Sea, a relatively non-volcanic rift, is preceded by intrusion of oceanic-type basaltic melts that crystallize at progressively shallower crustal depths as rifting progresses towards continental break-up. A seismic reflection profile running across the central part of the southern Thetis basin shows a ~5 km wide reflector that marks the roof of a magma chamber located ~3.5 km below seafloor. The presence of a few kilometers deep subrift magma chamber soon after the initiation of oceanic spreading implies the crystallization of lower oceanic crust intrusives as a last step in a sequence of basaltic melt intrusion from pre-oceanic continental rifting to oceanic spreading. Thus oceanic crust accretion in the Red Sea rift starts at depth before continental break up, emplacement of oceanic basalt at the sea floor, and development of Vine-Matthews magnetic anomalies.