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| 1 | Geochemical constraints on the origin and tectonic setting of the serpentinized peridotites from the Paleoproterozoic Nyong series,Eseka area,SW Cameroon显示文摘Serpentinized rocks closely associated with Paleoproterozoic eclogitic metabasites were recently discovered at Eseka area in the northwestern edge of the Congo craton in southern Cameroon.Here,we present new field data,petrography,and first comprehensible wholerock geochemistry data and discuss the protolith and tectonic significance of these serpentinites in the region.The studied rock samples are characterized by pseudomorphic textures,including mesh microstructure formed by serpentine intergrowths with cores of olivine,bastites after pyroxene.Antigorite constitutes almost the whole bulk of the rocks and is associated(to the less amount)with tremolite,talc,spinel,and magnetite.Whole-rock chemistry of the Eseka serpentinites led to the distinction of two types.Type 1 has high MgO(>40 wt%)content and high Mg#values(88.80)whereas Type 2 serpentinite samples display relatively low MgO concentration and Mg#values(<40 and 82.88 wt%,respectively).Both types have low Al/Si and high Mg/Si ratios than the primitive mantle,reflecting a refractory abyssal mantle peridotite protolith.Partial melting modeling indicates that these rocks were derived from melting of spinel peridotite before serpentinization.Bulk rock high-Ti content is similar to the values of subducted serpentinites(>50 ppm).This similarity,associated with the high Cr contents,spinel-peridotite protolith compositions and Mg/Si and Al/Si ratios imply that the studied serpentinites were formed in a subductionrelated environment.The U-shaped chondrite normalizedREE patterns of serpentinized peridotites,coupled with similar enrichments in LREE and HFSE,suggest the refertilized nature due to melt/rock interaction prior to serpentinization.Based on the results,we suggest that the Eseka serpentinized peridotites are mantle residues that suffered a high degree of partial melting in a subductionrelated environment,especially in Supra Subduction Zone setting.These new findings suggest that the Nyong series in Cameroon represents an uncontested Paleoproterozoic suture zone between the Congo craton and the Sao Francisco craton in Brazil. | Philomene Nga Essomba Tsoungui Sylvestre Ganno Evine Laure Tanko Njiosseu Jean Lavenir Ndema Mbongue Brice Kamguia Woguia Landry Soh Tamehe Jonas Didero Takodjou Wambo Jean Paul Nzenti | 2020 | Acta Geochimica2020，39，3： | 3 |
| 2 | Epidemiology of Skin Disorders in Ethiopian Children and Adolescents: An Analysis of Records from the Italian Dermatological Centre, Mekelle, Tigray, Ethiopia, 2005 to 2009显示文摘 | Rosalia Marrone Pascal Vignally Annalisa Rosso Daniele Didero Emma Pizzini Federica Dassoni Maria Chiara Pajno Elisa Maiani Gennaro Franco Roberta Calcaterra Aldo Morrone Concetta Mirisola | 2012 | Pediatric Dermatology2012，，4： | 1 |
| 3 | Geochemistry and zircon U–Pb ages of the Paleoproterozoic ultramafic rocks of the Mbi Valley, Boali area, Central African Republic显示文摘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 antigorite.Whole-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 82.TheydisplayhighNi(526–865 ppm),Cr(1500–3680 ppm)contents.AFM(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 cumulates.Chondrite-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)anomalies.Primitive 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 Nb.This suggests the generation of the parent melt by slab dehydration and wedge melting processes.In addition,incompatible trace element composition and ratios assumed that the source magma had an enhanced mantle source associated with a prominent influence of continental crust.Metasomatism of mantle wedge by plate-dehydrated,LILE-rich fluids and the incorporation of sediments derived from subduction explain the enhancement of the source.Integrated 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 melting.This result intimate that the remnants of Paleoproterozoic oceanic crust or subduction event and subsequent basins closure extended from the Congo craton in Cameroon to CAR and NE Brazil. | 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 | 2022 | Acta Geochimica2022，41，3： | 0 |
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