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Structural and metamorphic evolution of the northern Nile province of Sudan
A12
Over 150 massive sulfide Cu prospects have been discovered throughout the ophiolite, but those in the pillow lavas close to the top are the largest. Some show association to faults central to the mineralization. Others lie alongNW-trending faults related to younger tectonics. Along the contact between cumulate gabbro and cumulate peridotite are numerous small Cu prospects. Their occurrence and their Ni-rich ancient slags suggest that these sulfides rriay be related to the history of the cumulate gabbros (cf. the Duluth gabbro). The massive sulfides consist mainly of pyrite and chalcopyrite. The chalcopyrite is always late and often accompanied by sphalerite in fractures. Minor bornite and chalcocite occur in drill cores. The low-grade thermal metamorphism of the volcanics and the upper parts of the gabbro is probably related to hot circulating oceanic waters produced by high heat flow near the spreading center. This thermal event (as in Cyprus) m a y be responsible for the Cu deposits. The imbricate thrusting within the ophiolite, combined with strong deformation along its leading edge and mild deformation at its trailing edge, suggest emplacement by gravity sliding.
STRUCTURAL AND METAMORPHIC PROVINCE OF SUDAN
EVOLUTION
OF THE NORTHERN
NILE
A.S. DAWOUD and S.M. EL-RABA'A
University of Khartoum, Khartoum (Sudan) Lithostructural mapping of the pre-Nubian Basement Complex belt lying west of the Nile between Atbara and A b u H a m e d has revealed at least three phases of deformation and three major phases of regional metamorphism. The relationship between the different phases of deformation and metamorphism is discussed. The lithological units are comparable to those of central Sudan and are essentially composed of orthogneisses, migmatites and a metasedimentary sequence. They are of amphibolite facies grade of metamorphism. A younger metavolcanic group of rocks of only greenschist facies witnessed the latest two phases of deformation and are widespread to the East. Batholithic older granites intrude all the above rock types. Younger granite complexes in the area are located largely along wrench faults.
UPPER PROTEROZOIC VOLCANIC ACTIVITY IN THE NORTH ARABIAN SHIELD, KINGDOM OF SAUDI ARABIA
J. D E LFOUR
B.R. G.M., Orleans (France) The volcanologic and petrochemical characters and paleogeographical setting of the Upper Proterozoic volcanic suites in the northern Arabian Shield reflect various stages of mobile belt evolution. The oldest suite (> 650 Ma) represents the marine outpourings of basalt (probably tholeiitic) of an ophiolitic complex. This is followed (740--640 Ma) by an intermediate to acidic (chiefly quartz-keratophyre) volcanism associated with shallow-water sediments (Hulayfah Group). The lava exhibits calc-alkalic and tholeiitic compositions which are
Over 150 massive sulfide Cu prospects have been discovered throughout the ophiolite, but those in the pillow lavas close to the top are the largest. Some show association to faults central to the mineralization. Others lie alongNW-trending faults related to younger tectonics. Along the contact between cumulate gabbro and cumulate peridotite are numerous small Cu prospects. Their occurrence and their Ni-rich ancient slags suggest that these sulfides rriay be related to the history of the cumulate gabbros (cf. the Duluth gabbro). The massive sulfides consist mainly of pyrite and chalcopyrite. The chalcopyrite is always late and often accompanied by sphalerite in fractures. Minor bornite and chalcocite occur in drill cores. The low-grade thermal metamorphism of the volcanics and the upper parts of the gabbro is probably related to hot circulating oceanic waters produced by high heat flow near the spreading center. This thermal event (as in Cyprus) m a y be responsible for the Cu deposits. The imbricate thrusting within the ophiolite, combined with strong deformation along its leading edge and mild deformation at its trailing edge, suggest emplacement by gravity sliding.
STRUCTURAL AND METAMORPHIC PROVINCE OF SUDAN
EVOLUTION
OF THE NORTHERN
NILE
A.S. DAWOUD and S.M. EL-RABA'A
University of Khartoum, Khartoum (Sudan) Lithostructural mapping of the pre-Nubian Basement Complex belt lying west of the Nile between Atbara and A b u H a m e d has revealed at least three phases of deformation and three major phases of regional metamorphism. The relationship between the different phases of deformation and metamorphism is discussed. The lithological units are comparable to those of central Sudan and are essentially composed of orthogneisses, migmatites and a metasedimentary sequence. They are of amphibolite facies grade of metamorphism. A younger metavolcanic group of rocks of only greenschist facies witnessed the latest two phases of deformation and are widespread to the East. Batholithic older granites intrude all the above rock types. Younger granite complexes in the area are located largely along wrench faults.
UPPER PROTEROZOIC VOLCANIC ACTIVITY IN THE NORTH ARABIAN SHIELD, KINGDOM OF SAUDI ARABIA
J. D E LFOUR
B.R. G.M., Orleans (France) The volcanologic and petrochemical characters and paleogeographical setting of the Upper Proterozoic volcanic suites in the northern Arabian Shield reflect various stages of mobile belt evolution. The oldest suite (> 650 Ma) represents the marine outpourings of basalt (probably tholeiitic) of an ophiolitic complex. This is followed (740--640 Ma) by an intermediate to acidic (chiefly quartz-keratophyre) volcanism associated with shallow-water sediments (Hulayfah Group). The lava exhibits calc-alkalic and tholeiitic compositions which are