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Geochemical characterization of the metasedimentary rocks of the Yaounde Group within the southernmost North Equatorial tectonic belt:insights into geodynamic evolution
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作者 Simon Pierre Mbola Ndzana Moise Christian Balla Ateba +8 位作者 Germain Marie Monespérance Mboudou Moussa Nsangou Ngapna Jean Paul Sep Nlongang Solange Ipan Moise Bessong Jean Bosco Olinga Joseph Mvondo Ondoa Sébastien Owona Paul Bilong 《Acta Geochimica》 EI CAS CSCD 2023年第6期1017-1034,共18页
The Proterozoic metasedimentary rocks of the Yaounde Group on the northern edge of the Congo Shield in Central Africa were investigated to understand their provenance and depositional environment.Petrography,geochemis... The Proterozoic metasedimentary rocks of the Yaounde Group on the northern edge of the Congo Shield in Central Africa were investigated to understand their provenance and depositional environment.Petrography,geochemistry,and field evidence helped to subdivide the metasediments into paragneiss,mica schist,chlorite schist,and quartzite which were derived from greywacke,shale,quartz arenite,litharenite protoliths.They are immature with some mature samples,moderately weathered and reworked Neo-and Post-Archean metasediments.Rare earth element signatures(Chondrite Eu/Eu^(*)≤1),enrichment of light rare earth elements over the heavy ones,and the La/Sc ratio(>0.7)are compatible with those of the intermediate and felsic sources from the upper continental crust.These metasediments were deposited in the continental arc setting and have evolved during Proterozoic times according to the Wilson cycle to form the West Gondwana including NE Brazil. 展开更多
关键词 West Gondwana North Equatorial orogenic belt Yaounde Group Neoproterozoic basin Geochemistry of metasedimentary rocks geodynamic evolution
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Petrology and Geochemistry of Some Ophiolitic Metaperidotites from the Eastern Desert of Egypt:Insights into Geodynamic Evolution and Metasomatic Processes
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作者 Abdel-Aal M.ABDEL-KARIM Mokhles K.AZER Shaimaa A.EL-SHAFEI 《Acta Geologica Sinica(English Edition)》 SCIE CAS CSCD 2021年第4期1139-1157,共19页
Ophiolitic peridotites exposed in the Eastern Desert(ED)of Egypt record multiple stages of evolution,including different degrees of partial melting and melt extraction,serpentinization,carbonatization and metamorphism... Ophiolitic peridotites exposed in the Eastern Desert(ED)of Egypt record multiple stages of evolution,including different degrees of partial melting and melt extraction,serpentinization,carbonatization and metamorphism.The present study deals with metaperidotites at two selected localities in the central and southern ED,namely Wadi El-Nabáand Wadi Ghadir,respectively.They represent residual mantle sections of a Neoproterozoic dismembered ophiolite that tectonically emplaced over a volcano-sedimentary succession that represents island–arc assemblages.The studied metaperidotites are serpentinized,with the development of talc-carbonate and quartz-carbonate rocks,especially along shear and fault planes.Fresh relics of primary minerals(olivine,orthopyroxene and Cr-spinel)are preserved in a few samples of partiallyserpentinized peridotite.Most of the Cr-spinel crystals have fresh cores followed by outer zones of ferritchromite and Crmagnetite,which indicates that melt extraction from the mantle protolith took place under oxidizing conditions.The protoliths of the studied metaperidotites were dominated by harzburgites,which is supported by the abundance of mesh and bastite textures in addition to some evidence from mineral and whole-rock chemical compositions.The high Cr#(0.62–0.69;Av.0.66)and low TiO_(2)(<0.3 wt%)contents of the fresh Cr-spinels,the higher Fo(89–92;Av.91)and NiO(0.24–0.54 wt%,Av.0.40)contents of the primary olivine relics,together with the high Mg#(0.91–0.93;Av.91)and low CaO,Al2 O3 and TiO_(2)of the orthopyroxene relics,are all comparable with depleted to highly depleted forearc harzburgite from a suprasubduction zone setting.The investigated peridotites have suffered subsequent phases of metasomatism,from oceanfloor hydrothermal alteration(serpentinization)to magmatic hydrothermal alteration.The enrichment of the studied samples in light rare earth elements(LREEs)relative to the heavy ones(HREEs)is attributed to most probably be due to the contamination of their mantle source with granitic source hydrothermal fluids after the obduction of the ophiolite assemblage onto the continental crust.The examined rocks represent mantle residue that experienced different degrees of partial melting(~10%to 25%for W.El-Nabárocks and~5%to 23%for W.Ghadir rocks).Variable degrees of partial melting among the two investigated areas suggest mantle heterogeneity beneath the Arabian-Nubian Shield(ANS). 展开更多
关键词 ophiolitic metaperidotites partial melting melt extraction geodynamic evolution Eastern Desert EGYPT
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Cretaceous Stress Fields Evolution and Its Geodynamic Implications in Jiaolai Basin, Northern China
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作者 LI Jie HOU Guiting 《Acta Geologica Sinica(English Edition)》 SCIE CAS CSCD 2016年第S1期162-,共1页
The Tan-Lu fault zone(TLFZ)along the East China continental margin experienced sinistral movement at the beginning of Early Cretaceous(ca.145)due to fast oblique subduction of the Izanagi Plate in the Pacific Ocean.It
关键词 Cretaceous Stress Fields evolution and Its geodynamic Implications in Jiaolai Basin Northern China
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