부산대학교 도서관

This study presents major and trace elements, and Sr-Nd-Pb isotope data of the Mokolo-Kossehone volcanic rock (basanite, trachybasalt, trachyte, and rhyolite) from the northernmost segment of the Cameroon Volcanic Line (CVL). The basanite sample exhibits primitive character (MgO: 12-14 wt%; Mg#: 69-72; Ni: 327-427 ppm; Cr: 524-599 ppm; Co: 57-60 ppm). Trace element and isotopic signatures of the mafic lavas are similar to those of OIB. The trends observed in the major oxides and compatible trace elements against Si[O.sub.2] from basanite to rhyolite are attributed to the fractionation of different mineral phases such as Fe-Ti oxides, olivine, clinopyroxene, feldspar, and quartz. The enrichment in LREEs and depletion in HREEs associated with (La/Yb)N > 5 (12.39-32.65), [(Tb/Yb).sub.N] > 1.7 (1.71-2.89), and Dy/Yb > 2 (2.16-3.63), suggest the presence of a garnet phase in a mantle source. The lavas were produced at varying depths by low degrees of partial melting (< 4%) of a source containing less than 5% of garnet peridotite. The [sup.206]Pb/[sup.204]Pb values of basanite (19.69630-19.79122) are similar to those of FOZO ([sup.206]Pb/[sup.204]Pb > 19.5). The trachybasalt samples with [sup.206]Pb/[sup.204]Pb values of 19.25 and 19.37 suggest the probable enrichment of magma with a high-[mu] (HIMU) signature ([sup.206]Pb/[sup.204]Pb < 19.5) by a crustal component. Trace elements and isotopic compositions ([sup.87]Sr/[sup.86]Sr: 0.70308- 0.70378, [sup.143]Nd/[sup.144]Nd: 0.51287-0.51296, [sup.206]Pb/[sup.204]Pb: 19.24652-19.79122) of the Mokolo-Kossehone lavas are consistent with a mixture of different source material from the sub-continental lithospheric mantle (SCLM) and the asthenosphere with minor crustal contamination. The composition of the source is analogous to those described in the northern portion of the CVL and other volcanic massifs along the CVL. Key words: Cameroon Volcanic Line, Mokolo-Kossehone, focal zone, high-[mu] mantle, sub-continental lithospheric mantle
1. INTRODUCTION The administrative Far North Region of Cameroon is situated in the northernmost section of the Cameroon volcanic line (CVL). It is characterized by various volcanic geoforms, which testify [...]