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Geochemistry and zircon U–Pb ages of the Paleoproterozoic ultramafic rocks of the Mbi Valley, Boali area, Central African Republic

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Acta Geochimica 2022年第3期41卷 515-535页

作者： Evine Laure Njiosseu Tanko Prince Emilien Danguene Philomene Nga Essomba Tsoungui Sylvestre Ganno Jonas Didero Takodjou Wambo bertin guy takam tchoupe Gus Djibril Kouankap Nono Timoleon Ngnotue Boniface Kankeu Jean Biandja Jean Paul Nzenti Department of Earth Sciences University of DschangP.O.Box 67DschangCameroon Department of Earth Sciences University of BanguiP.O.Box 908BanguiCentral African Republic Department of Mining Engineering and Mineral Processing School of Mines and Petroleum IndustriesUniversity of MarouaP.O.Box 08Kaélé-MarouaCameroon Department of Earth Sciences University of YaoundéIP.O.Box 812YaoundéCameroon Department of Geology HTTCUniversity of BamendaP.O.Box 39BambiliBamendaCameroon Institute for Geological and Mining Researches(IGMR) P.O.Box 4110YaoundéCameroon

This paper investigates the geochemistry of bulk rock and infers the petrogenesis of ultramafic rocks in the Boali Precambrian terrane in Mbi Valley,in the North of the Central African Republic(CAR).The studied rocks comprise coarse primary olivine and orthopyroxene relics(dominant phase),magnesio-hornblende,magnetite,and ***-rock analysis indicates low SiO_(2)(average of 43.14 wt%)and high MgO(19.84–26.98 wt%)contents and their Mg number(Mg#)ranges from 74 to ***(526–865 ppm),Cr(1500–3680 ppm)***(Na_(2)O-K_(2)O)-FeO-MgO)and ACM(Al_(2)O_(3)-CaO-MgO)ternary diagrams have revealed that the studied samples correspond to arc-related ultramafic ***-normalized REE plots display an increasing trend from La to Sm(CeN/SmN:0.74–1.81),weak negative to no Eu(Eu/Eu*=0.72–1.05)and strong negative Ce(Ce/Ce*=0.33–0.98)*** mantle normalized of multi-element diagrams exhibit LREE enrichment and large ion lithophile elements(LILE)relative to high field strength elements(HFSE),and notable negative anomalies in *** suggests the generation of the parent melt by slab dehydration and wedge melting *** addition,incompatible trace element composition and ratios assumed that the source magma had an enhanced mantle source associated with a prominent influence of continental *** of mantle wedge by plate-dehydrated,LILE-rich fluids and the incorporation of sediments derived from subduction explain the enhancement of the *** major and trace element compositions jointly with the tectonic reconstruction of this region and LA-ICP-MS U–Pb data on zircon constrain the emplacement age at ca.2099 Ma in a continental margin arc setting involving subduction of an oceanic plate beneath the continental lithosphere,dehydration of the slab and mantle wedge *** result intimate that the remnants of Paleoproterozoic oceanic crust or subduction event and subsequent basins closure extended from

关键词： Atlantic supercontinent Central African Republic Ultramafic cumulate LILE-enriched fluids Arc setting

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Origin and intraplate tectonic setting of mafic magmatic enclaves from the Ngaoundal area,Adamawa-Cameroon:Insights from petrography and geochemistry

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China Geology 2022年第4期5卷 579-594页

作者： Aliou Mamouda Sylvestre Ganno guy tchoupe takam bertin Arnold Mbita Motto Steven Hermann Donald Fossi Jean Paul Nzenti Joseph Mvondo Ondoa Department of Earth Sciences University of YaoundéIYaoundéCameroon Institute for Geological and Mining Research(IRGM) YaoundéCameroon

In this contribution,detailed field descriptions together with petrographic and bulk-rock major,trace and rare earth elements(REE)data are used to constrain the origin and geodynamic setting of the mafic magmatic enclaves(MMEs)recently discovered within the Pan-African Ngaoundal pluton,Adamawa area,central *** investigated MMEs are dark-colored with chilled margins,and display medium to coarse-grain igneous *** mineral assemblage is either dominated by K-feldspar and carbonate(group Ⅰ),or by amphibole and plagioclase(group Ⅱ),though the overall mineral phases made of amphibole,plagioclase,K-feldspar,and biotite are similar to that of their host syenite but in different *** MMEs in Ngaoundal area are foid-gabbro in composition with SiO_(2) contents ranging between 41.52% and 43.74% and are contiguous with their host granitoids of intermediate composition(SiO_(2)=57.52% to 58.98%).The host granitoid rocks are metaluminous,and belong to the shoshonitic *** and geochemical data have revealed that the Ngaoundal MMEs derived from rapid cooling of hot injected lithospheric mantle-derived magma within cooler host granitoids magma and were emplaced in the intraplate geodynamic setting.

关键词： Mafic magmatic enclaves(MMEs) Granitoids Lithospheric mantle REE Intraplate Adamawa-Cameroon

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