TITLE:
Petrology of Metaluminous A-Type Rhyolite Discovered from Hadjer el Hamis Volcanoes (Lake Chad Basin)
AUTHORS:
Claudial Amane Lagmet, Fadimatou Ngounouno Yamgouot, Mama Ntoumbe, Abdou Aziz Youpougam, Ismaïla Ngounouno
KEYWORDS:
Metaluminous, Rhyolites, Lake Chad, Petrology, Hadjer el Hamis
JOURNAL NAME:
Open Journal of Geology,
Vol.8 No.9,
August
20,
2018
ABSTRACT: 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.