Peraluminous granitoids within the Hangloa area,Adamawa-YadéDomain,Cameroon:Petrogenesis and tectonic implication

Hangloa granitoids form part of the wide range calc-alkaline Pan-African granitic suites within the Adamawa Yade Domain(AYD)in Cameroon.There are several reports on metaluminous granitoids within this domain.The peraluminous suite has been locally reported and their petrogenesis is not fully understood.Petrography and whole-rock geochemistry were used to study the petrogenesis/formation of granitic rocks within this area.The results show that the granitoids are composed of quartzo-feldspathic,made up of granites,monzonites and quartz monzonites which were intruded in the Paleoproterozoic orthogneissic basement.The major and trace element compositions show that they are high-K calc-alkaline to shoshonites,with S-type affinity.The molar ratio A/CNK is>1.1,while the ratio of CaO+Na_(2)O/Al_(2)O_(3) is generally<1 making them strongly peraluminous.The REE shows enrichment in the LREE over the HREE,with(La/Yb)N varying from 11.9 to 53.32,(Dy/Yb)N from 0.77 to 2.13 and moderately negative Eu anomaly((Eu/Eu^(*))N range from 0.42 to 0.93).Most granite samples show depletion in P,with CaO/Na_(2)O<0.3 and Rb/Sr≤1 indicative of clay-poor metapelitic source,while the others show clay-rich metagreywackes sources.The strong peraluminosity,S-type affinity,high Ba/Sr,Ba/Rb and low Rb/Sr indicate they are crustal-derived.The compositional variation might be induced by the partial melting of different source materials followed by fractional crystallization of the granitic magma.The source nature requires fragments of Paleoproterozoic metasedimentary and metaigneous rocks derived from the collision between the north-central Cameroon block and the Congo Craton during the Pan-African.

Geochemical evaluation of mineralization potential of the Somie-Ntem area within the Tikar plain,Cameroon:implication on petrogenesis

Somie-Ntem area of the Tikar plain belongs to the western Cameroon Domain.The lithology of the plain has been characterized,and the mineral potential is still unclear despite previous reports on Sn deposit within one of the magmatic complexes.Our results show two groups of granitic rocks displaying oxidized and reduced character;(1)mesocratic(oxidized)granites including biotitebearing,hornblende-biotite-bearing,hornblende-epidotebearing and pyroxene-bearing;(2)leucogranites(reduced)that are generally amphibole-pyroxene bearing.These granitoids are hosted by gneisses and metasedimentary rocks partially covered by rhyolites.Major element composition shows high-K calc-alkaline to shoshonite affinity,metaluminous to weakly peraluminous I-type granites.Mesocratic granites show moderately negative Eu anomaly,depleted in Nb,P,Ti,and are related to syn-collisional setting.Leucogranites are post-orogenic with strong negative Eu anomaly,depleted in Ba and Sr and enriched in Hf,Nb and Ta.They are fertile in Sn and Zn,enriched through postmagmatic metasomatism and greisenization.Cr–Cu–Ni–V mineralization occurs in hornblende-bearing gneisses and their enrichment suggests a possible Ni–Cutype PGEs mineralization in this area.Meanwhile,their trace element shows high Ni/Cu,very low Rb/Sr,low LILE and LREE which indicates mantle fractionation at subduction.The absence of olivine and pyroxene,and increased SiO_(2)and Al_(2)O_(3)in the Cr–Cu–Ni–V-bearing rocks show that the parent magma experienced fractional crystallization and crustal contamination during evolution.Notwithstanding,the high Zr/Rb and K/Rb ratios show that hydrothermal activity was not intense to enhance mineralization in the area.Variation in the direction of stress during shear deformation inhibited an effective hydrothermal activity and ore deposition in the region.

Relative active tectonic in the metamorphic rocks of the Yaounde group: insights from geomorphic indices and topographic analysis

The Yaounde Group(YG),representing the southern edge of the North Equatorial PanAfrican Belt,consists of quartzites,schists,micaschists,amphibolites,gneisses and migmatites.Tectonism has formed a landscape characterized by the development of linear and folded valleys and ridges,fault scarps,V-shaped valleys,incised rivers and knickpoints.These landforms constitute important markers of the regional tectonic activity,which have been computed from spatial sources such as SRTM,DEM,hydrographical networks and geomorphic indices such as AF,T,Smf,Vf,Bs,Hi,U,SI and Li.The results highlighted a mature relief consisting of asymmetric basins generated by tilting and uplift phenomena.The relative index of active tectonics(RIAT)has been estimated from an average of eight geomorphic indices evaluated on 24 subbasins,in the study area.Four classes have been defined:class 1(1.38),very high active(1.0≤RIAT<1.5);class 2(1.50-1.88),high active(1.5≤RIAT<2.0);and class 3(2.00-2.13)moderate active(2.0≤RIAT<2.5).These three classes,respectively covering 10.20%(458 km2),80.10%(3595 km2)and 9.69%(435 km2)of the study area,have shown a highly active tectonic zone,and imply the existence of a neotectonic event in the YG.This tectonic unit(YG)was also affected by the dextral NW-SE strike-slip faulting,which cross-cut the Sanaga Shear Zone(SSZ)at Ebebda and the foliation oriented NW-SE.The tilting and uplift of rocks related to Moho ascending are responsible for crustal thinning in the Cameroon basement,more important to the Adamawa Plateau from the Cretaceous age and the reactivation of existing tectonic accidents.The presence of hills,fault scarps,reverse faults,knickpoints,V and U shaped valleys and rounded mountains testify to the interaction between tectonic uplift,lithology,climate,weathering and erosion.