Petrogenesis,Tectonic Setting,and Mineral Potential Of The Neoproterozoic Volcano-sedimentary And Associated Granitoid Rocks From Central Eritrea,Southern Arabian-Nubian Shield

The metavolcanic-sedimentary assemblages and the associated granitoid intrusions of Central Eritrea are part of the southern Arabian-Nubian Shield that was primarily formed by accretion of juvenile island-arcs during the Neoproterozoic time.The primary aim of the current study is to investigate the petrogenesis and tectonic setting of the volcanic and granitic rocks.The supracrustal rocks in the study area are dominated by mafic to felsic metavolcanic rocks with subordinate metasedimentary units.The metavolcanic rocks show large variable major and trace element compositions with SiO₂?41.63-78.4 wt.%?,Al₂O₃?8.51-23.41 wt.%?,MgO?0.05-13.98 wt.%?,Fe₂O₃?3.11-15 wt.%?,K₂O?0.01-2.59 wt.%?,Cr?2.83-834 ppm?,Ni?1.63-244 ppm?,Zr?16.4-128 ppm?that form linear correlations in the Harker diagrams,suggesting that these rocks were genetically linked,and their variation may have resulted from crustal assimilation and fractional crystallization.In general,they have low?REE?20-144 ppm?and show flat chondrite-normalized REE pattern with slight negative or positive Eu anomalies?Eu/Eu*=0.67-1.36?.The metavolcanic rocks are rich in LILE?Ba,Pb,and U?and depleted in HFSE?Ta,Nb,and Ti?in the primitive mantle normalized trace element diagram.They also have low initial ⁸⁷Sr/⁸⁶Sr?0.70079 to 0.70525?,positive?Nd values?+4.0to+6.4?and moderate Pb isotopic compositions(²⁰⁶Pb/²⁰⁴Pb=17.598 to 19.446,²⁰⁷Pb/²⁰⁴Pb=15.518to 15.639 and ²⁰⁸Pb/²⁰⁴Pb=37.175 to 38.811).These features indicate that slab-derived fluids and melts modified the mantle source.The ca.850 Ma Emba-Derho granites display restricted composition ranges with high SiO₂?71.28-73.64 wt.%?,Al₂O₃?14.93-15.89 wt.%?,Na₂O?3.16-4.15 wt.%?,Fe₂O₃^t?2.84-3.62 wt.%?,low K₂O?1.25-2.04 wt.%?.They have characteristics features of adakitic rocks with high values of Sr/Y?42-86?and low Y?3.75-6.03ppm?.The samples exhibit a highly fractionated REE patterns with La/Yb?14 to 30?and insignificant Eu anomalies?Eu/Eu*=0.89-1.07?,while their primitive mantle normalized spider diagram shows elevated LILE?Ba,Pb,and Sr?and troughs of the HFSE?Ta,Nb,and Ti?.They also have low initial ⁸⁷Sr/⁸⁶Sr ratios?0.7008-0.7026?,and high?Nd values?+4.7 to+7.8?.These geochemical compositions reveal that the granites were originated from partial melting of a subducting slab.Both the metavolcanic rocks and the associated granitic intrusions are suggested to have been formed in a forearc setting.As part of the ANS,the Neoproterozoic granitoid-greenstone volcano-sedimentary rocks are considered to be favorable hosts for numerous metallic mineral deposits.Base metal VMS,orogenic and shear hosted gold deposits are the most significant mineralization types.The world-class Au-rich Cu-Zn Bisha and Cu-Zn±Au±Ag Emba-Derho VMS deposits are typical VMS examples in Western lowlands and central Eritrea,while Koka and Gupo orogenic gold deposits represent large deposits of gold in northwestern and central Eritrea,respectively.Most of the VMS types and orogenic gold±sulfide deposits and occurrences of Eritrea are either deformed or directly hosted by NNE to NNW trending curvilinear crustal scale transpressional shear zones?belts?,the Augaro-Adobha Belt?AAB?,the Asmara-Nakfa Belt?ANB?.