TITLE:
Fractional Crystallization and Crustal Contamination of Doleritic and Trachytic Dykes Crosscutting the Cretaceous Sedimentary Basins from Figuil (North Cameroon) and Léré (South-Western Chad): Geodynamic Implications
AUTHORS:
Moussa Ngarena Klamadji, Merlin Gountié Dedzo, Rigobert Tchameni, Djamilatou Diddi Hamadjoda, Pierre Christel Biakan à Nyotok, Gervais Onana
KEYWORDS:
Dolerites, Trachyte, Sedimentary Basins, Continental Tholeiites, Figuil and Léré
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.9 No.12,
December
30,
2021
ABSTRACT: Magmatism in the Cretaceous sedimentary basins of
the Figuil and Léré regions constitutes one of the fundamental parameters in
the reconstruction of the history of the Cretaceous sedimentary basins. The
main objective of this paper is to constrain the petrogenetic processes of
hypovolcanic rocks and to determine their geodynamic context of emplacement.
The petrographic study of mafic hypovolcanic and trachytic rocks was carried
out under a polarizing microscope on thin sections. For the geochemical study,
the major oxides and some trace elements were analyzed by ICP-AES. Trace and
rare earth elements were analyzed by ICP-MS. The dolerites of the Cretaceous
sedimentary basins are composed of dykes of amphibole bearing dolerites,
biotite and pyroxene bearing dolerite, pyroxene bearing dolerites and
trachytes. The dykes are in the order of 20 to 100 m wide by several kilometers
long and oriented from N23°E to N90°E. The textures of these rocks are sub-ophitic
to intergranular for dolerites and trachytic for evolved rocks (trachytes). The
geochemical study shows that the dolerites are basaltic in composition with
alkaline to subalkaline character. The sampled dykes have an evolution
dominated by fractional with the minor impact of the crustal assimilation
characterized by low Rb/Y ratios for dolerites (0.36 - 0.97) and high values of
Rb/Y for the Pan-African granitoids’ samples (1.95 - 4.01). The nature of
doleritic and trachytic magma sources is supported by their (Tb/Yb)N > 1.9
(1.91 - 3.79) and Dy/Yb > 2 (2.32 - 3.50) ratios of most samples, which
suggests melting in a garnet-bearing mantle. Concerning the geodynamic context
of the studied rocks, doleritic samples are classified as within-plate tholeiite
and volcanic arc basalt, and within-plate alkali basalts.