spe478-10 1st pgs page 193 193 The Geological Society of America Special Paper 478 2011 Mineralogical and geochemical fingerprints of mantle metasomatism beneath Nyos volcano (Cameroon volcanic line) M.I. Teitchou Institut de Recherches Géologiques et Minières, IRGM/ARGV Ekona, B.P. 370 Buéa, Cameroon, and Département des Sciences de la Terre, Université de Yaoundé-1, B.P. 812, Yaoundé, Cameroon M. Grégoire* GET–UMR 5562 (Géosciences-Environnement-Toulouse–Unité Mixte de Recherche 5562), Observatoire Midi Pyrénées, Université de Toulouse-3, 14, avenue Édouard-Belin, 31400 Toulouse, France R. Temdjim R.T. Ghogomu Département des Sciences de la Terre, Université de Yaoundé-1, B.P. 812, Yaoundé, Cameroon C. Ngwa F.T. Aka Institut de Recherches Géologiques et Minières, IRGM/ARGV Ekona, B.P. 370, Buéa, Cameroon ABSTRACT Basaltic lavas of Nyos volcano (Cameroon) mostly contain mantle peridotite xenoliths consisting of spinel-bearing lherzolites and harzburgites. Based on the trace-element patterns, especially rare earth element (REE) patterns, two groups of samples have been distinguished: group 1 samples are characterized by spoon- shaped REE patterns, and group 2 samples show light (L) REE–enriched patterns. Mineralogical characteristics together with major- and trace-element compositions point to a low degree of partial melting (less than 5%) and metasomatic processes. The latter mechanism explains in particular the LREE content of bulk rocks and clinopyroxenes and the occurrence of hydrous minerals in some samples. All the metasomatic features observed in both groups of samples are related to more or less alkaline—and carbonated—mafic silicate melts. These melts are related to the mag- matic activity of the Cameroon volcanic line, leading in particular to the eruption of the host lava xenoliths. *michel.gregoire@dtp.obs-mip.fr Teitchou, M.I., Grégoire, M., Temdjim, R., Ghogomu, R.T., Ngwa, C., and Aka, F.T., 2011, Mineralogical and geochemical fingerprints of mantle metasomatism beneath Nyos volcano (Cameroon volcanic line), in Beccaluva, L., Bianchini, G., and Wilson, M., eds., Volcanism and Evolution of the African Lithosphere: Geological Society of America Special Paper 478, p. 193–210, doi:10.1130/2011.2478(10). For permission to copy, contact editing@geosociety.org. © 2011 The Geological Society of America. All rights reserved.