Petrology of spinel lherzolite xenoliths from Youkou volcano, Adamawa Massif, Cameroon Volcanic Line: mineralogical and geochemical fingerprints of sub-rift mantle processes

Merlin Patrick Wagsong Njombie*, R. Temdjim, Stephen F. Foley

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

The basaltic maar of Youkou, situated in the Adamawa Volcanic Massif in the eastern branch of the continental segment of the Cameroon Volcanic Line, contains mantle-derived xenoliths of various types in pyroclastites. Spinel-bearing lherzolite xenoliths from the Youkou volcano generally exhibit protogranular textures with olivine (Fo89.4−90.5), enstatite (En89 − 91Fs8.7−9.8Wo0.82−1.13), clinopyroxene, spinel (Cr#Sp = 9.4–13.8), and in some cases amphibole (Mg# = 88.5–89.1). Mineral equilibration temperatures in the lherzolite xenoliths have been estimated from three–two pyroxene thermometers and range between 835 and 937 °C at pressures of 10–18 kbar, consistent with shallow mantle depths of around 32–58 km. Trends displayed by bulk-rock MgO correlate with Al2O3, indicating that the xenoliths are refractory mantle residues after partial melting. The degree of partial melting estimated from spinel compositions is less than 10%: evidences for much higher degrees of depletion are preserved in one sample, but overprinted by refertilization in others. Trace element compositions of the xenoliths are enriched in highly incompatible elements (LREE, Sr, Ba, and U), indicating that the spinel lherzolites underwent later cryptic metasomatic enrichment induced by plume-related hydrous silicate melts. The extreme fertility (Al2O3 = 6.07–6.56 wt% in clinopyroxene) and the low CaO/Al2O3 ratios in the spinel lherzolites suggest that they could not be a simple residue of partial melting of primitive mantle and must have experienced refertilization processes driven by the infiltration of carbonatite or carbonated silicate melts.

Original languageEnglish
Article number13
Pages (from-to)1-20
Number of pages20
JournalContributions to Mineralogy and Petrology
Volume173
DOIs
Publication statusPublished - Feb 2018

Keywords

  • Cameroon Volcanic Line
  • Adamawa Massif
  • Youkou volcano maar
  • Spinel lherzolite xenoliths
  • Mantle metasomatism
  • Refertilization

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