A comparative review of petrogenetic processes beneath the Cameroon Volcanic Line: Geochemical constraints

The origin and petrogenesis of the Cameroon Volcanic Line (CVL), composed of volcanoes that form on both the ocean floor and the continental crust, are difficult to understand because of the diversity, heterogeneity, and nature of available data. Major and trace elements, and Sr-Nd-Pb isotope data of volcanic rocks of the CVL spanning four decades have been compiled to reinterpret their origin and petrogenesis. Volcanic rocks range from nephelinite, basanite and alkali basalts to phonolite, trachyte and rhyolite with the presence of a compositional gap between SiO2 58–64 wt.%. Similarities in geochemical characteristics, modeled results for two component mixing, and the existence of mantle xenoliths in most mafic rocks argue against significant crustal contamination. Major and trace element evidences indicate that the melting of mantle rocks to generate the CVL magma occurred dominantly in the garnet lherzolite stability field. Melting models suggest small degree (<3%) partial melting of mantle bearing (6–10%) garnet for Mt. Etinde, the Ngaoundere Plateau and the Biu Plateau, and <5% of garnet for the oceanic sector of the CVL, Mt. Cameroon, Mt. Bambouto, Mt. Manengouba and the Oku Volcanic Group. The Sr-Nd-Pb isotope systematics suggest that mixing in various proportions of Depleted MORB Mantle (DMM) with enriched mantle 1 and 2 (EM1 and EM2) could account for the complex isotopic characteristics of the CVL lavas. Low Mg number (Mg# = 100 × MgO/(MgO + FeO)) and Ni, Cr and Co contents of the CVL mafic lavas reveal their crystallization from fractionated melts. The absence of systematic variation in Nb/Ta and Zr/Hf ratios, and Sr-Nd isotope compositions between the mafic and felsic lavas indicates progressive evolution of magmas by fractional crystallization. Trace element ratios and their plots corroborate mantle heterogeneity and reveal distinct geochemical signatures for individual the CVL volcanoes

Children's cultural background knowledge and story telling performance

Contains fulltext : 62989.pdf (publisher's version ) (Closed access)The cultural context in which a child is raised influences her cognitive system and language behavior. In this paper, we explored the influence of cultural back ground knowledge on story telling performance of two groups of children living in the Netherlands: (1) bilingual ethnic minority children from immigrant families of Islamic background(2) monolingual Dutch children. Using a within-subject design, all children retold, continued, and finished three story beginnings: One story dealt with a topic related to the ethnic minority children's cultural background(Ramadan), one story dealt with a topic related to the Dutch children's cultural background(Carnival), and one story dealt with a topic both groups of children were familiar with (playing at the schoolyard). All children spoke in Dutch, which implies that the ethnic minority children performed all tasks in a language other than their family language, whereas the Dutch children performed the same tasks in their native language. It appeared that both quantitative and qualitative characteristics of the stories were influenced by the children's cultural background knowledge. Measurements of story length showed that ethnic minority children's Ramadan stories were longer than their Carnival stories, whereas Dutch children's Carnival stories were longer than their Ramadan stories. Likewise, the ethnic minority children's Ramadan stories containedmore connective ties(as indexed by the number of conjunctions used) than their Carnival stories, whereas the reverse pattern was observed in Dutch children. These findings indicate that cultural familiarity with a topic influences story telling performance in terms of story length and coherence.21 p