The Neoproterozoic Shadli metavolcanics in the Eastern Desert of Egypt have been conventionally c... more The Neoproterozoic Shadli metavolcanics in the Eastern Desert of Egypt have been conventionally categorized as a bimodal island-arc association. The present study deals with Shadli metavolcanics of three areas: Hamama in the central and Darhib and Atshan in the southern Eastern Desert of Egypt. They contain both mafic and felsic compositions and display a bimodal nature. Geochemical classification indicates that the mafic end-members are tholeiitic basalt and basaltic andesite whereas the felsic ones comprise calc-alkaline dacite and rhyolite.
Mafic end-members show flat to slightly LREE-depleted patterns comparable to normal MORB produced from a depleted mantle source. Major element data indicates affinity to arc-related non-cumulative mafic rocks. The obvious negative Nb and positive Pb anomalies, the nearly flat REE patterns together with pyroxene chemistry are characteristic of island-arc tholeiitic suite. Accordingly, we suggest that their primary magma was derived from partial melting of a depleted mantle source metasomatized by subduction-related slab fluids/melts.
Felsic end-members exhibit magnesian character consistent with a relatively hydrous, oxidizing magma and subduction-related source. Their weakly peraluminous character and calc-alkalic to calcic compositions are characteristics of arc-related magmas. Moreover, the negative Nb and Ti anomalies suggest an influx of subduction-related slab fluids/melts. Their SiO2 contents are too high to represent magmas directly derived by partial melting of a mantle source. So, the high SiO2 and Al2O3 and the low MgO contents suggest melting crustal source. The high Y/Nb ratios (> 1.2) confirm that they were generated from crustal source. Actually, their Ce/Pb ratios (average of 2.66) are affiliated to those of continental crust and contrast typical mantle values. The weakly peraluminous and sodic nature is a typical feature of I-type magma. Therefore, their magmas were most likely derived by partial melting of thickened low-K mafic lower crust.
Several lines of evidence let us speculate a genetic relationship between mafic and felsic end-members and that the felsic rocks were possibly evolved from the mafic melts that derived from metasomatized mantle. These comprise the close proximity and a coeval nature; the subalkaline character with approximately continuous trend; the similarity of trace element patterns; the arc-like signature, and the well fitness of major element data of the felsic rocks with melts derived from low-K mafic lower crust. The general tendency of silica increase with alkalis from mafic to felsic end-members may indicate that the felsic rocks were generated by fractional crystallization processes of the mafic magmas in the area.
Arabian Journal for Science and Engineering , 2022
The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern D... more The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern Desert shear zones. They are hosted in talc-and tremolite-talc-rich rocks and also in meta-basaltic dykes and quartz-veins. The principal mineralization in Atshan includes sphalerite, pyrite, chalcopyrite, galena and pyrrhotite, whereas that in Darhib comprises chalcopyrite, sphalerite, pyrite, and galena with subordinate bornite and covellite. Darhib mineralization contains traces of altaite and electrum. Altaite has the highest Te concentrations suggesting crystallization under low fS 2 and/or high fTe 2 conditions, probably due to S budget consumption from the hydrothermal fluids in the late stage of deposition. Electrum has the highest Au contents with gold fineness value falling within the range of epithermal Au-Ag deposits. The dominance of recrystallized and replacement textures in the studied mineralizations suggests a secondary or post-depositional metamorphic overprint. The significant Cd contents in sphalerite from remobilized massive mineralizations hosted in tremolite-talc-rich rocks indicate crystallization at ~250-300 °C. Galena hosted in tremolite-talc-rich rocks is characterized by exceptionally high selenium and tellurium contents, indicating its generation from relatively Se-Te-enriched hydrothermal fluids. Pyrrhotite hosted in quartz-veins from Atshan was formed under lower sulfur activity (aS 2) and oxygen fugacity (fO 2). Covellite and bornite were formed due to chalcopyrite oxidation, revealing a role of supergene process. Shear zones, possibly produced during later thrust faulting, were acted as channel ways for hydrothermal mineralizing fluids that may have modified and/or precipitated the mineralization. Mineralizing fluids have probably resulted from dehydration during metamorphism and/or late-magmatic fluids from nearby granitic intrusions.
Abstract The authors present new petrographic and mineralogical data for the Um Zariq Formation w... more Abstract The authors present new petrographic and mineralogical data for the Um Zariq Formation which belongs to Arabian–Nubian Shield metamorphic tracts exposed on the Sinai Peninsula. The formation is believed to be a metasedimentary sequence whose protolith was deposited during the Sturtian Snowball Earth Event (SEE). Our new field data indicate the occurrence of metasomatised limestones/dolostones (calc-silicates) which are not well-reported in the study area. We also reported a lamprophyre body close to the Kid A-type granite; the Malhaq vogesite is a variety of hornblende-phyric lamprophyre with orthoclase feldspar. Based on mineral assemblages, field observations and petrographic study, metapelites record an early greenschist/lower amphibolite facies regional metamorphism. Intrusion of granites (CA1) synchronise with the regional metamorphic overprints on metapelites and calc-silicates. Calc-silicates, on the other hand, record high T metamorphic mineral assemblages with hornfelsic texture and weak anisotropic fabrics. The contact metamorphism formed cordierite and andalusite in the metapelites and pyroxenes in the calc-silicates. The Um Zariq metapelites protoliths were deposited at a deeper stratigraphic level and thus, recorded the regional and contact metamorphism contrary to the shallower carbonates. The Um Zariq igneous activity (Kid A-type Granite and the Malhaq Lamprophyre) marks the transformation from collisional to extensional regime in the Arabian–Nubian Shield at ca. 600 Ma.
The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern D... more The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern Desert shear zones. They are hosted in talc- and tremolite-talc-rich rocks and also in meta-basaltic dykes and quartz-veins. The principal mineralization in Atshan includes sphalerite, pyrite, chalcopyrite, galena and pyrrhotite, whereas that in Darhib comprises chalcopyrite, sphalerite, pyrite, and galena with subordinate bornite and covellite. Darhib mineralization contains traces of altaite and electrum. Altaite has the highest Te concentrations suggesting crystallization under low fS2 and/or high fTe2 conditions, probably due to S budget consumption from the hydrothermal fluids in the late stage of deposition. Electrum has the highest Au contents with gold fineness value falling within the range of epithermal Au–Ag deposits. The dominance of recrystallized and replacement textures in the studied mineralizations suggests a secondary or post-depositional metamorphic overprint. The signi...
Alkaline basaltic volcanism commenced in the Late Pliocene and continued until the early Pleistoc... more Alkaline basaltic volcanism commenced in the Late Pliocene and continued until the early Pleistocene. Moreover, the alkaline basaltic magmas were developed in response to passive upwelling and decompressional melting of asthenospheric mantle material. The volcanism is characterized by mafic rock types ranging from highly undersaturated nephelinites (Stradnerkogel & Waltrafelsen) to basanites and alkali basalts (Burgenland).
Die vorliegende Doktorarbeit beschaftigt sich mit der Petrologie, Mineralogie und Geochemie alkal... more Die vorliegende Doktorarbeit beschaftigt sich mit der Petrologie, Mineralogie und Geochemie alkaliner, mafischer Laven der westlichen Karpaten-Pannonischen Region (Carpathian-Pannonian Region; CPR). Diese Laven sind in kleineren Vulkanprovinzen im Burgenland (Pauliberg, Oberpullendorf) sowie im sudostlichen steirischen Becken (Kloch, Steinberg, Stradnerkogel, Waltrafelsen) aufgeschlossen. Die altesten alkalinen, mafischen Vulkanite (Basalte des Burgenlandes) entstanden im Obermiozan (~ 11 Ma) wahrend spater Extensionsphasen. Die Hauptphase des Vulkanismus verbunden mit der Forderung alkaliner, mafischer Gesteine fand im Pliozan bis zum Quartar nach der Extension und zeitgleich mit der Kompression statt (z. B. steirisches Becken). Dieser in der gesamten Region auftretende Magmatismus folgte dem post-kollisionalen, kalkalkalinen, subduktionsbezogenen Vulkanismus der westlichen Karpaten. Bei den entnommenen Proben handelt es sich um Alkalibasalte, Basanite/Nephelin-Basanite und Nepheli...
The origin and source of intra-plate anorogenic basaltic magmas has been the subject of discussio... more The origin and source of intra-plate anorogenic basaltic magmas has been the subject of discussion for several decades. The generation of basaltic magma has been ascribed either to decompression melting triggered by lithospheric extension or to addition of heat supplied by an upwelling mantle plume. These magmas could have been produced from lithospheric or asthenospheric mantle source and also could represent mixing between both sources. The lithospheric mantle is too cold to be considered as a source of alkaline basaltic magmas and only under special conditions (steep geothermal gradient) can produce basaltic magmas. To contribute towards solving these problems this book provides additional evidence from alkaline basalts of Burgenland and SE Styrian Basin at the western margin of the Carpathian-Pannonian Region. The study of anorogenic Cenozoic volcanism of the Carpathian-Pannonian Region offers an excellent opportunity to understand the relationship between tectonics, mantle proc...
The authors present new petrographic and mineralogical data for the Um Zariq Formation which belo... more The authors present new petrographic and mineralogical data for the Um Zariq Formation which belongs to Arabian-Nubian Shield metamorphic exposures in the Sinai Peninsula. The formation is believed to be a metasedimentary sequence whose protolith was deposited during the Sturtian Snowball Earth Event (SEE). Our new field data indicate the occurrence of metasomatised limestones/dolostones (calc-silicates) which is distinct from those reported from The Feiran-Solaf Metamorphic Complex. We highlight the presence of a lamprophyre body close to the Kid A-type granite; the Malhaq vogesite-a variety of hornblende-phyric lamprophyre with orthoclase feldspar-. Based on mineral assemblages, field observations and petrographic study, metapelites record an early greenschist/lower amphibolite facies regional metamorphism. Intrusion of the syn-collisional deformed granites (CA1) synchronised with the regional metamorphism at ca. 660±25 Ma. Both of the metamorphic events overprinted on the metapel...
The Arabian Shield of Saudi Arabia represents part of the Arabian–Nubian Shield and forms an expo... more The Arabian Shield of Saudi Arabia represents part of the Arabian–Nubian Shield and forms an exposure of juvenile continental crust on the eastern side of the Red Sea rift. Gabbroic intrusions in Saudi Arabia constitute a significant part of the mafic magmatism in the Neoproterozoic Arabian Shield. This study records the first detailed geological, mineralogical and geochemical data for gabbroic intrusions located in the Gabal Samra and Gabal Abd areas of the Hail region in the Arabian Shield of Saudi Arabia. Geological field relations and investigations, supported by mineralogical and geochemical data, indicate that the gabbroic intrusions are generally unmetamorphosed and undeformed, and argue for their post-collisional emplacement. Their mineralogical and geochemical features reveal crystallization from hydrous, mainly tholeiitic, mafic magmas with arc-like signatures, which were probably inherited from the previous subduction event in the Arabian–Nubian Shield. The gabbroic rocks...
The Sol Hamed (SH) area is a part of the Arabian-Nubian Shield (ANS) ophiolites occurred within O... more The Sol Hamed (SH) area is a part of the Arabian-Nubian Shield (ANS) ophiolites occurred within Onib-Sol Hamed suture zone in the southern Eastern Desert of Egypt. The ophiolitic assemblages in this area are represented by serpentinite, metagabbro and arc assemblages represented by metavolcanics. They later intruded by gabbroes and granites. Geochemically, the compatible trace elements (Cr=2426–2709 ppm, Ni=1657–2377 ppm and Co=117–167 ppm) enrichment in SH serpentinites indicate derivation from a depleted mantle peridotite source. They show affinity to the typical metamorphic peridotites. The normative compositions reflect harzburgitic mantle source. Their Al2O3 contents (0.05–1.02 wt. %) are akin to oceanic and active margin peridotites and Pan-African serpentinites. The Cr and TiO2 contents indicate supra-subduction zone (SSZ) environment. Their Al2O3/SiO2 and MgO/SiO2 ratios support the SSZ affinity and are similar to ANS peridotites with fore-arc setting. Moreover, their Al2O3 ...
Mineral and bulk–rock chemistry of Shadli bimodal metavolcanics from Eastern Desert of Egypt: Imp... more Mineral and bulk–rock chemistry of Shadli bimodal metavolcanics from Eastern Desert of Egypt: Implication for tectonomagmatic setting and Neoproterozoic continental growth in the Arabian–Nubian Shield
The Neoproterozoic Shadli metavolcanics in the Eastern Desert of Egypt have been conventionally c... more The Neoproterozoic Shadli metavolcanics in the Eastern Desert of Egypt have been conventionally categorized as a bimodal island-arc association. The present study deals with Shadli metavolcanics of three areas: Hamama in the central and Darhib and Atshan in the southern Eastern Desert of Egypt. They contain both mafic and felsic compositions and display a bimodal nature. Geochemical classification indicates that the mafic end-members are tholeiitic basalt and basaltic andesite whereas the felsic ones comprise calc-alkaline dacite and rhyolite.
Mafic end-members show flat to slightly LREE-depleted patterns comparable to normal MORB produced from a depleted mantle source. Major element data indicates affinity to arc-related non-cumulative mafic rocks. The obvious negative Nb and positive Pb anomalies, the nearly flat REE patterns together with pyroxene chemistry are characteristic of island-arc tholeiitic suite. Accordingly, we suggest that their primary magma was derived from partial melting of a depleted mantle source metasomatized by subduction-related slab fluids/melts.
Felsic end-members exhibit magnesian character consistent with a relatively hydrous, oxidizing magma and subduction-related source. Their weakly peraluminous character and calc-alkalic to calcic compositions are characteristics of arc-related magmas. Moreover, the negative Nb and Ti anomalies suggest an influx of subduction-related slab fluids/melts. Their SiO2 contents are too high to represent magmas directly derived by partial melting of a mantle source. So, the high SiO2 and Al2O3 and the low MgO contents suggest melting crustal source. The high Y/Nb ratios (> 1.2) confirm that they were generated from crustal source. Actually, their Ce/Pb ratios (average of 2.66) are affiliated to those of continental crust and contrast typical mantle values. The weakly peraluminous and sodic nature is a typical feature of I-type magma. Therefore, their magmas were most likely derived by partial melting of thickened low-K mafic lower crust.
Several lines of evidence let us speculate a genetic relationship between mafic and felsic end-members and that the felsic rocks were possibly evolved from the mafic melts that derived from metasomatized mantle. These comprise the close proximity and a coeval nature; the subalkaline character with approximately continuous trend; the similarity of trace element patterns; the arc-like signature, and the well fitness of major element data of the felsic rocks with melts derived from low-K mafic lower crust. The general tendency of silica increase with alkalis from mafic to felsic end-members may indicate that the felsic rocks were generated by fractional crystallization processes of the mafic magmas in the area.
Arabian Journal for Science and Engineering , 2022
The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern D... more The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern Desert shear zones. They are hosted in talc-and tremolite-talc-rich rocks and also in meta-basaltic dykes and quartz-veins. The principal mineralization in Atshan includes sphalerite, pyrite, chalcopyrite, galena and pyrrhotite, whereas that in Darhib comprises chalcopyrite, sphalerite, pyrite, and galena with subordinate bornite and covellite. Darhib mineralization contains traces of altaite and electrum. Altaite has the highest Te concentrations suggesting crystallization under low fS 2 and/or high fTe 2 conditions, probably due to S budget consumption from the hydrothermal fluids in the late stage of deposition. Electrum has the highest Au contents with gold fineness value falling within the range of epithermal Au-Ag deposits. The dominance of recrystallized and replacement textures in the studied mineralizations suggests a secondary or post-depositional metamorphic overprint. The significant Cd contents in sphalerite from remobilized massive mineralizations hosted in tremolite-talc-rich rocks indicate crystallization at ~250-300 °C. Galena hosted in tremolite-talc-rich rocks is characterized by exceptionally high selenium and tellurium contents, indicating its generation from relatively Se-Te-enriched hydrothermal fluids. Pyrrhotite hosted in quartz-veins from Atshan was formed under lower sulfur activity (aS 2) and oxygen fugacity (fO 2). Covellite and bornite were formed due to chalcopyrite oxidation, revealing a role of supergene process. Shear zones, possibly produced during later thrust faulting, were acted as channel ways for hydrothermal mineralizing fluids that may have modified and/or precipitated the mineralization. Mineralizing fluids have probably resulted from dehydration during metamorphism and/or late-magmatic fluids from nearby granitic intrusions.
Abstract The authors present new petrographic and mineralogical data for the Um Zariq Formation w... more Abstract The authors present new petrographic and mineralogical data for the Um Zariq Formation which belongs to Arabian–Nubian Shield metamorphic tracts exposed on the Sinai Peninsula. The formation is believed to be a metasedimentary sequence whose protolith was deposited during the Sturtian Snowball Earth Event (SEE). Our new field data indicate the occurrence of metasomatised limestones/dolostones (calc-silicates) which are not well-reported in the study area. We also reported a lamprophyre body close to the Kid A-type granite; the Malhaq vogesite is a variety of hornblende-phyric lamprophyre with orthoclase feldspar. Based on mineral assemblages, field observations and petrographic study, metapelites record an early greenschist/lower amphibolite facies regional metamorphism. Intrusion of granites (CA1) synchronise with the regional metamorphic overprints on metapelites and calc-silicates. Calc-silicates, on the other hand, record high T metamorphic mineral assemblages with hornfelsic texture and weak anisotropic fabrics. The contact metamorphism formed cordierite and andalusite in the metapelites and pyroxenes in the calc-silicates. The Um Zariq metapelites protoliths were deposited at a deeper stratigraphic level and thus, recorded the regional and contact metamorphism contrary to the shallower carbonates. The Um Zariq igneous activity (Kid A-type Granite and the Malhaq Lamprophyre) marks the transformation from collisional to extensional regime in the Arabian–Nubian Shield at ca. 600 Ma.
The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern D... more The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern Desert shear zones. They are hosted in talc- and tremolite-talc-rich rocks and also in meta-basaltic dykes and quartz-veins. The principal mineralization in Atshan includes sphalerite, pyrite, chalcopyrite, galena and pyrrhotite, whereas that in Darhib comprises chalcopyrite, sphalerite, pyrite, and galena with subordinate bornite and covellite. Darhib mineralization contains traces of altaite and electrum. Altaite has the highest Te concentrations suggesting crystallization under low fS2 and/or high fTe2 conditions, probably due to S budget consumption from the hydrothermal fluids in the late stage of deposition. Electrum has the highest Au contents with gold fineness value falling within the range of epithermal Au–Ag deposits. The dominance of recrystallized and replacement textures in the studied mineralizations suggests a secondary or post-depositional metamorphic overprint. The signi...
Alkaline basaltic volcanism commenced in the Late Pliocene and continued until the early Pleistoc... more Alkaline basaltic volcanism commenced in the Late Pliocene and continued until the early Pleistocene. Moreover, the alkaline basaltic magmas were developed in response to passive upwelling and decompressional melting of asthenospheric mantle material. The volcanism is characterized by mafic rock types ranging from highly undersaturated nephelinites (Stradnerkogel & Waltrafelsen) to basanites and alkali basalts (Burgenland).
Die vorliegende Doktorarbeit beschaftigt sich mit der Petrologie, Mineralogie und Geochemie alkal... more Die vorliegende Doktorarbeit beschaftigt sich mit der Petrologie, Mineralogie und Geochemie alkaliner, mafischer Laven der westlichen Karpaten-Pannonischen Region (Carpathian-Pannonian Region; CPR). Diese Laven sind in kleineren Vulkanprovinzen im Burgenland (Pauliberg, Oberpullendorf) sowie im sudostlichen steirischen Becken (Kloch, Steinberg, Stradnerkogel, Waltrafelsen) aufgeschlossen. Die altesten alkalinen, mafischen Vulkanite (Basalte des Burgenlandes) entstanden im Obermiozan (~ 11 Ma) wahrend spater Extensionsphasen. Die Hauptphase des Vulkanismus verbunden mit der Forderung alkaliner, mafischer Gesteine fand im Pliozan bis zum Quartar nach der Extension und zeitgleich mit der Kompression statt (z. B. steirisches Becken). Dieser in der gesamten Region auftretende Magmatismus folgte dem post-kollisionalen, kalkalkalinen, subduktionsbezogenen Vulkanismus der westlichen Karpaten. Bei den entnommenen Proben handelt es sich um Alkalibasalte, Basanite/Nephelin-Basanite und Nepheli...
The origin and source of intra-plate anorogenic basaltic magmas has been the subject of discussio... more The origin and source of intra-plate anorogenic basaltic magmas has been the subject of discussion for several decades. The generation of basaltic magma has been ascribed either to decompression melting triggered by lithospheric extension or to addition of heat supplied by an upwelling mantle plume. These magmas could have been produced from lithospheric or asthenospheric mantle source and also could represent mixing between both sources. The lithospheric mantle is too cold to be considered as a source of alkaline basaltic magmas and only under special conditions (steep geothermal gradient) can produce basaltic magmas. To contribute towards solving these problems this book provides additional evidence from alkaline basalts of Burgenland and SE Styrian Basin at the western margin of the Carpathian-Pannonian Region. The study of anorogenic Cenozoic volcanism of the Carpathian-Pannonian Region offers an excellent opportunity to understand the relationship between tectonics, mantle proc...
The authors present new petrographic and mineralogical data for the Um Zariq Formation which belo... more The authors present new petrographic and mineralogical data for the Um Zariq Formation which belongs to Arabian-Nubian Shield metamorphic exposures in the Sinai Peninsula. The formation is believed to be a metasedimentary sequence whose protolith was deposited during the Sturtian Snowball Earth Event (SEE). Our new field data indicate the occurrence of metasomatised limestones/dolostones (calc-silicates) which is distinct from those reported from The Feiran-Solaf Metamorphic Complex. We highlight the presence of a lamprophyre body close to the Kid A-type granite; the Malhaq vogesite-a variety of hornblende-phyric lamprophyre with orthoclase feldspar-. Based on mineral assemblages, field observations and petrographic study, metapelites record an early greenschist/lower amphibolite facies regional metamorphism. Intrusion of the syn-collisional deformed granites (CA1) synchronised with the regional metamorphism at ca. 660±25 Ma. Both of the metamorphic events overprinted on the metapel...
The Arabian Shield of Saudi Arabia represents part of the Arabian–Nubian Shield and forms an expo... more The Arabian Shield of Saudi Arabia represents part of the Arabian–Nubian Shield and forms an exposure of juvenile continental crust on the eastern side of the Red Sea rift. Gabbroic intrusions in Saudi Arabia constitute a significant part of the mafic magmatism in the Neoproterozoic Arabian Shield. This study records the first detailed geological, mineralogical and geochemical data for gabbroic intrusions located in the Gabal Samra and Gabal Abd areas of the Hail region in the Arabian Shield of Saudi Arabia. Geological field relations and investigations, supported by mineralogical and geochemical data, indicate that the gabbroic intrusions are generally unmetamorphosed and undeformed, and argue for their post-collisional emplacement. Their mineralogical and geochemical features reveal crystallization from hydrous, mainly tholeiitic, mafic magmas with arc-like signatures, which were probably inherited from the previous subduction event in the Arabian–Nubian Shield. The gabbroic rocks...
The Sol Hamed (SH) area is a part of the Arabian-Nubian Shield (ANS) ophiolites occurred within O... more The Sol Hamed (SH) area is a part of the Arabian-Nubian Shield (ANS) ophiolites occurred within Onib-Sol Hamed suture zone in the southern Eastern Desert of Egypt. The ophiolitic assemblages in this area are represented by serpentinite, metagabbro and arc assemblages represented by metavolcanics. They later intruded by gabbroes and granites. Geochemically, the compatible trace elements (Cr=2426–2709 ppm, Ni=1657–2377 ppm and Co=117–167 ppm) enrichment in SH serpentinites indicate derivation from a depleted mantle peridotite source. They show affinity to the typical metamorphic peridotites. The normative compositions reflect harzburgitic mantle source. Their Al2O3 contents (0.05–1.02 wt. %) are akin to oceanic and active margin peridotites and Pan-African serpentinites. The Cr and TiO2 contents indicate supra-subduction zone (SSZ) environment. Their Al2O3/SiO2 and MgO/SiO2 ratios support the SSZ affinity and are similar to ANS peridotites with fore-arc setting. Moreover, their Al2O3 ...
Mineral and bulk–rock chemistry of Shadli bimodal metavolcanics from Eastern Desert of Egypt: Imp... more Mineral and bulk–rock chemistry of Shadli bimodal metavolcanics from Eastern Desert of Egypt: Implication for tectonomagmatic setting and Neoproterozoic continental growth in the Arabian–Nubian Shield
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Papers by Shehata Ali
Mafic end-members show flat to slightly LREE-depleted patterns comparable to normal MORB produced from a depleted mantle source. Major element data indicates affinity to arc-related non-cumulative mafic rocks. The obvious negative Nb and positive Pb anomalies, the nearly flat REE patterns together with pyroxene chemistry are characteristic of island-arc tholeiitic suite. Accordingly, we suggest that their primary magma was derived from partial melting of a depleted mantle source metasomatized by subduction-related slab fluids/melts.
Felsic end-members exhibit magnesian character consistent with a relatively hydrous, oxidizing magma and subduction-related source. Their weakly peraluminous character and calc-alkalic to calcic compositions are characteristics of arc-related magmas. Moreover, the negative Nb and Ti anomalies suggest an influx of subduction-related slab fluids/melts. Their SiO2 contents are too high to represent magmas directly derived by partial melting of a mantle source. So, the high SiO2 and Al2O3 and the low MgO contents suggest melting crustal source. The high Y/Nb ratios (> 1.2) confirm that they were generated from crustal source. Actually, their Ce/Pb ratios (average of 2.66) are affiliated to those of continental crust and contrast typical mantle values. The weakly peraluminous and sodic nature is a typical feature of I-type magma. Therefore, their magmas were most likely derived by partial melting of thickened low-K mafic lower crust.
Several lines of evidence let us speculate a genetic relationship between mafic and felsic end-members and that the felsic rocks were possibly evolved from the mafic melts that derived from metasomatized mantle. These comprise the close proximity and a coeval nature; the subalkaline character with approximately continuous trend; the similarity of trace element patterns; the arc-like signature, and the well fitness of major element data of the felsic rocks with melts derived from low-K mafic lower crust. The general tendency of silica increase with alkalis from mafic to felsic end-members may indicate that the felsic rocks were generated by fractional crystallization processes of the mafic magmas in the area.
Mafic end-members show flat to slightly LREE-depleted patterns comparable to normal MORB produced from a depleted mantle source. Major element data indicates affinity to arc-related non-cumulative mafic rocks. The obvious negative Nb and positive Pb anomalies, the nearly flat REE patterns together with pyroxene chemistry are characteristic of island-arc tholeiitic suite. Accordingly, we suggest that their primary magma was derived from partial melting of a depleted mantle source metasomatized by subduction-related slab fluids/melts.
Felsic end-members exhibit magnesian character consistent with a relatively hydrous, oxidizing magma and subduction-related source. Their weakly peraluminous character and calc-alkalic to calcic compositions are characteristics of arc-related magmas. Moreover, the negative Nb and Ti anomalies suggest an influx of subduction-related slab fluids/melts. Their SiO2 contents are too high to represent magmas directly derived by partial melting of a mantle source. So, the high SiO2 and Al2O3 and the low MgO contents suggest melting crustal source. The high Y/Nb ratios (> 1.2) confirm that they were generated from crustal source. Actually, their Ce/Pb ratios (average of 2.66) are affiliated to those of continental crust and contrast typical mantle values. The weakly peraluminous and sodic nature is a typical feature of I-type magma. Therefore, their magmas were most likely derived by partial melting of thickened low-K mafic lower crust.
Several lines of evidence let us speculate a genetic relationship between mafic and felsic end-members and that the felsic rocks were possibly evolved from the mafic melts that derived from metasomatized mantle. These comprise the close proximity and a coeval nature; the subalkaline character with approximately continuous trend; the similarity of trace element patterns; the arc-like signature, and the well fitness of major element data of the felsic rocks with melts derived from low-K mafic lower crust. The general tendency of silica increase with alkalis from mafic to felsic end-members may indicate that the felsic rocks were generated by fractional crystallization processes of the mafic magmas in the area.