This study explores the magmatic and eruptive processes of the Manengouba maars,located along the Cameroon Volcanic Line(CVL).Petrographic analyses of the samples reveal a diverse mineralogical composition with clinop...This study explores the magmatic and eruptive processes of the Manengouba maars,located along the Cameroon Volcanic Line(CVL).Petrographic analyses of the samples reveal a diverse mineralogical composition with clinopyroxenes(20%-35%),plagioclases(19%-35%),olivines(5%-15%),and sanidines(up to 15%).Positive Europium(Eu)anomalies observed suggest crystallization under reducing conditions.X-ray diffraction analyses show a significant presence of smectite(25.99%to 76.05%),kaolinite,and other clay minerals,indicating extensive hydrothermal alteration.Geochemical diagrams reveal clear trends of magmatic fractionation,with an increase in Zr(up to 200 ppm)with increasing SiO_(2)(45%to 60%)and a decrease in MgO(from 10%to less than 5%)accompanied by an increase in Nb(from 10 to 50 ppm).These trends suggest magmatic differentiation prior to the eruption.Explosive interactions between ascending magma and groundwater led to phreatomagmatic explosions,forming complex diatremic structures.The presence of mantle xenoliths and host rock fragments indicates significant assimilation of the host rocks during magma ascent,modifying its chemical composition.The results allow proposing a diatreme growth model,highlighting the importance of phreatomagmatic interactions and magmatic fractionation processes.Compared to other volcanic regions,the geology of Manengouba shows significant similarities with other volcanoes along the CVL and with maars and diatremes studied elsewhere in the world.In conclusion,this study enriches our understanding of volcanic and magmatic processes in the Manengouba region,providing crucial insights into eruptive dynamics and associated geochemical and mineralogical conditions.展开更多
Knowledge on soil properties likely to influence P sorption in tephra soils is very important for sustainable management of available P. Sorption studies on six tephra soils were conducted to relate P sorption to soil...Knowledge on soil properties likely to influence P sorption in tephra soils is very important for sustainable management of available P. Sorption studies on six tephra soils were conducted to relate P sorption to soil characteristics in order to identify those with potential influence on P sorption. Four equilibrium-based sorption models commonly encountered in soil studies (Langmuir, Freundlich, Temkin, and Van Huay) were used to describe P sorption in the soils. P sorption was determined by measuring the residual P content of a clarified equilibrating solution of 0.02 N KCl containing varying concentrations (0, 5, 10, 15, 30, 40, 50, 60, 80, and 100 mg/L) of P as KH2PO4 after mixing with 1 g of soil in duplicates for 16 hours at 25°C. Maximum amount of P sorbed for the varying P concentrations used ranged from 2080 to 5402 mg/kg with a potential for greater P sorption maxima at higher P solution concentrations. P sorption in these soils was best described by the Langmuir and Freundlich models. Allophane and ferrihydrite are the principal species controlling the high P sorption in these soils. pH-NaF proved to be a potentially reliable test for assessing the presence of allophanic materials and thus for estimating P sorbed. This work would guide both effective and efficient P fertilizer management with economic implications for both the study area and similar environments.展开更多
文摘This study explores the magmatic and eruptive processes of the Manengouba maars,located along the Cameroon Volcanic Line(CVL).Petrographic analyses of the samples reveal a diverse mineralogical composition with clinopyroxenes(20%-35%),plagioclases(19%-35%),olivines(5%-15%),and sanidines(up to 15%).Positive Europium(Eu)anomalies observed suggest crystallization under reducing conditions.X-ray diffraction analyses show a significant presence of smectite(25.99%to 76.05%),kaolinite,and other clay minerals,indicating extensive hydrothermal alteration.Geochemical diagrams reveal clear trends of magmatic fractionation,with an increase in Zr(up to 200 ppm)with increasing SiO_(2)(45%to 60%)and a decrease in MgO(from 10%to less than 5%)accompanied by an increase in Nb(from 10 to 50 ppm).These trends suggest magmatic differentiation prior to the eruption.Explosive interactions between ascending magma and groundwater led to phreatomagmatic explosions,forming complex diatremic structures.The presence of mantle xenoliths and host rock fragments indicates significant assimilation of the host rocks during magma ascent,modifying its chemical composition.The results allow proposing a diatreme growth model,highlighting the importance of phreatomagmatic interactions and magmatic fractionation processes.Compared to other volcanic regions,the geology of Manengouba shows significant similarities with other volcanoes along the CVL and with maars and diatremes studied elsewhere in the world.In conclusion,this study enriches our understanding of volcanic and magmatic processes in the Manengouba region,providing crucial insights into eruptive dynamics and associated geochemical and mineralogical conditions.
文摘Knowledge on soil properties likely to influence P sorption in tephra soils is very important for sustainable management of available P. Sorption studies on six tephra soils were conducted to relate P sorption to soil characteristics in order to identify those with potential influence on P sorption. Four equilibrium-based sorption models commonly encountered in soil studies (Langmuir, Freundlich, Temkin, and Van Huay) were used to describe P sorption in the soils. P sorption was determined by measuring the residual P content of a clarified equilibrating solution of 0.02 N KCl containing varying concentrations (0, 5, 10, 15, 30, 40, 50, 60, 80, and 100 mg/L) of P as KH2PO4 after mixing with 1 g of soil in duplicates for 16 hours at 25°C. Maximum amount of P sorbed for the varying P concentrations used ranged from 2080 to 5402 mg/kg with a potential for greater P sorption maxima at higher P solution concentrations. P sorption in these soils was best described by the Langmuir and Freundlich models. Allophane and ferrihydrite are the principal species controlling the high P sorption in these soils. pH-NaF proved to be a potentially reliable test for assessing the presence of allophanic materials and thus for estimating P sorbed. This work would guide both effective and efficient P fertilizer management with economic implications for both the study area and similar environments.
