Petrology of Metaluminous A-Type Rhyolite Discovered from Hadjer el Hamis Volcanoes (Lake Chad Basin)

Autor:	Fadimatou Ngounouno Yamgouot, Ismaïla Ngounouno, Mama Ntoumbe, Claudial Amane Lagmet, Abdou Aziz Youpougam
Rok vydání:	2018
Předmět:	Arfvedsonite Rhyolite engineering Silicic Phenocryst engineering.material Petrology Alkali feldspar Peralkaline rock Geology Hedenbergite Amphibole
Zdroj:	Open Journal of Geology. :883-895
ISSN:	2161-7589 2161-7570
DOI:	10.4236/ojg.2018.89052
Popis:	Metaluminous (P.I. > 1) rhyolite from Hadjer el Hamis consisted of quartz, alkali feldspar, clinopyroxene (hedenbergite), amphibole (F-arfvedsonite) and oxides-hydroxides (ilmenite, magnetite, limonite) phenocrysts is characterized by the negative Eu, Ba, P, Sr and Ti anomalies. This metaluminous rhyolite and the early discovered peralkaline rhyolites in Hadjer el Hamis volcanoes derive likely from the same source, according to their coexistence on the same sector and their similar Zr/Nb ratios. The causes of magma heterogeneity are likely linked to varying amounts of extraction of an earlier melt phase or tectonic juxtaposition or a sudden increasing of fO2 in silicic magmas, triggered from a hydrothermal process, associated with F- and alkali-bearing fluids influx, which promoted the enrichment of Na in the hedenbergite rims and the crystallization of arfvedsonite.
Databáze:	OpenAIRE
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