Petrology of spinel lherzolite xenoliths and host basaltic lava from Ngao Voglar volcano, Adamawa Massif (Cameroon Volcanic Line, West Africa): equilibrium conditions and mantle characteristics

Tesis (Ingeniero Industrial y de Sistemas)--Universidad de Piura. Facultad de Ingeniería. Programa Académico de Ingeniería Industrial y de Sistemas, 2006.El presente trabajo estudia los parámetros y mejoras de las etapas del proceso de obtención de harina de lúcuma, aplicados al proyecto productivo que desarrolla el Programa de de Desarrollo Sostenible de Ecosistemas de Montaña en el Perú (PDSEMP) en varios caseríos del distrito de Chalaco, Piura. Para ello se estableció el uso de indicadores de tiempo, rendimiento, clima y calidad así como el cursograma analítico del material. Además, se evaluó la calidad del producto a través de pruebas de sólidos solubles, humedad, granulometría, etc

Pétrologie du volcanisme cénozoïque au nord et à l'est de Ngaoundéré (Adamaoua, Cameroun)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Géochimie des laves basaltiques récentes des zones Nord et Est de Ngaoundéré (Cameroun, Plateau de l’Adamaoua, Afrique centrale): pétrogenèse et nature de la source

Des coulées et projections basaltiques récentes (basaltes: I.D

Sub-continental lithospheric mantle structure beneath the Adamawa plateau inferred the petrology of ultramafic xenoliths from Ngaoundéré (Adamawa Plateau, Cameroon, Central Africa)

International audienceUltramafic xenoliths (lherzolite, harzburgite and olivine websterite) have been discovered in basanites close to Ngaoundéré in Adamawa plateau. Xenoliths exhibit protogranular texture (lherzolite and olivine websterite) or porphyroclastic texture (harzburgite). They are composed of olivine Fo89-90, orthopyroxene, clinopyroxene and spinel. According to geothermometers, lherzolites have been equilibrated at 880 to 1060 °C; equilibrium temperatures of harzburgite are rather higher (880―1160 °C), while those of olivine websterite are bracketed between 820 and 1010 °C. The corresponding pressures are 1.8―1.9 GPa, 0.8―1.0 GPa and 1.9―2.5 GPa, respectively, which suggests that xenoliths have been sampled respectively at depths of 59―63 km, 26―33 km and 63―83 km. Texture and chemical compositional variations of xenoliths with temperature, pressure and depth on regional scale may be ascribed to the complex history undergone by the sub-continental mantle beneath the Adamawa plateau during its evolution. This may involve a limited asthenosphere uprise, concomitantly with plastic deformation and partial melting due to adiabatic decompression processes. Chemical compositional heterogeneities are also proposed in the sub-continental lithospheric mantle under the Adamawa plateau, as previously suggested for the whole Cameroon Volcanic Line

Petrology and geochemistry of doloritic dyke of Likok (Cameroon, Central Africa).

International audienc

First occurrence of pigeonite in the Cameroon Volcanic Line

International audienceLow-Ca clinopyroxene crystal of pigeonite composition has been discovered in the Tchabal Mbabo volcano massif of the Cameroon Volcanic Line (CVL), a long active N30° chain of volcanic centres and ring complexes in Central Africa. The Tchabal Mbabo is a huge Eocene-Oligocene volcano, at the junction with Adamawa Plateau (AP), made of lava flows and domes, which display a rather complete alkaline series from basanite and basalt to peralkaline trachyte and rhyolite. Pigeonite phase was found, as small crystals (30–50 μm) included in K-feldspar, which is in turn included in a biotite, in the Gouri peralkaline trachytic dome-flow. We describe in this paper for the first time the occurrence of modal pigeonite phase in the CVL. Occurrence of pigeonite phase in peralkaline trachyte does not evidence tholeiitic/transitional affinities but is considered resulting from silica saturation during differentiation of the alkaline series. Low (87Sr/86Sr)i (0.704277) and high εNdi (+ 1.25) of trachyte, close to OIB rather than FOZO reservoir, preclude any important crustal contamination

Pétrologie du volcanisme Eocène-Oligocène du Massif de Tchabal Mbabo, Adamaoua-Cameroun, Afrique centrale

International audienc

Petrology of lherzolite xenoliths of Hosséré Sédé volcano (Adamawa plateau, Ngaoundéré area, Cameroon)

International audienceNumerous mantle xenoliths 6–12 cm in size and sub-angular to rounded in shape occur within Mio-Pliocene basanite lavas of the monogenic volcano of Hosséré Sédé in the Adamawa plateau. Xenoliths of spinel lherzolite exhibit protogranular, equigranular or porphyroclastic texture. Microprobe chemical analyses show that olivine is highly magnesian (Fo88-90), clinopyroxene crystals are diopside and augite (Wo41.6–49.6 En45.3–53.7 Fs4.2–6.2), orthopyroxene crystals are enstatite (Wo1.4–1.5 En88.6–89.0 Fs9.6–9.9) and spinel crystals are mainly Al-spinel associated to minor Cr-spinel. Estimated temperatures and pressures through empirical formulas show that Hosséré Sédé xenoliths have equilibrated between 1085 and 1204 °C and 1.08 to 1.57 GPa, corresponding to sampling depths of 36 and 52 km. Detailed petrographical and mineral chemistry of Hosséré Sédé xenoliths evidences the complex nature and composition of the subcontinental lithosphere under the Adamawa plateau. This may involve a probable uplift of the whole area after a limited extensional event, possible metasomatism through melt infiltration during shearing of the lithospheric mantle along the Pan African strike-slip fault system