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

• 作者: Abdou Aziz Youpougam Claudial Amane Lagmet Fadimatou Ngounouno Yamgouot Isma?la Ngounouno Mama Ntoumbe
• 来源期刊: 地质学期刊(英文)
• 学科: 地球科学
• 关键词: Metaluminous RHYOLITES LAKE CHAD PETROLOGY Hadjer EL Hamis
• 年，卷（期）: 2018,（9）
• 页码范围: 883-895
• 页数: 13页
• 分类号: P5

摘要

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.