Petrology of peraluminous and peralkaline rhyolites from the SE Lake Chad (northernmost Cameroon Line)

• Location of the peralkaline and peraluminous rhyolites from SE Lake Chad.
• Identify the characteristic of the associated rocks.
• We used the whole-rock data to identify the source of SE Lake Chad rhyolites.

Peraluminous (P.I. < 1) and peralkaline (P.I. > 1) rhyolites from SE Lake Chad consisted of quartz, alkali feldspar and oxides–hydroxides phenocrysts, display negative Eu anomaly. F-arfvedsonite, augite–hedenbergite, aegirine and aegirine-augite are present in peralkaline rhyolites. The peralkaline and peraluminous rhyolitic magmas of the SE Lake Chad derive likely from the same source, according to their coexistence on the same volcano (Hadjer Bigli); their similar Zr/Nb, Zr/Hf ratios and their linear trends established in Zr vs Nb, Zr vs Ta and Zr vs Y diagrams, which linked to removal of successive batches of magma from a mantle source or to different degrees of partial melting. These magmas generated from the partial melting model of the underplated mantle, which would have induced the intrusion of crustal materials, triggering the hydrothermal reactions. Although, the high Zr amounts are not related to bulk assimilation of partially melted crustal materials.

Figure optionsDownload as PowerPoint slide