TITLE:
Petrology, Age and Geodynamic Implication of the Panafrican Granitoids Associated with the Glito-Kpatala Shear Zone (South-East Togo)
AUTHORS:
Gnanwasou Alayi, Sarakawa Abalo Malibida Kpanzou, Yao Agbossoumondé, Essodina Padaro, René-Pierre Menot, Mahaman Sani Tairou
KEYWORDS:
Pan-African Granitoids, Post-Collisional, Shear Zone, South-East Togo
JOURNAL NAME:
International Journal of Geosciences,
Vol.14 No.12,
December
29,
2023
ABSTRACT: The granitic plutons associated with the
Glito-Kpatala shear zone are composed of biotite and amphibole granodiorites,
biotite granites, two-mica granites and aplitic granites, which are very poorly represented.
The chemical and mineralogical compositions of these facies indicate
that they are I type and belong to high-K calc-alkaline series, with a chemical
metaluminous character displayed by the granodiorites relative to the biotite
and two-mica facies whose chemical compositions vary between metaluminous and
peraluminous caracter. The Th/Ta (14.04 - 43.82
ppm, mean = 26.05), Th/U (2.58 to 15.05 ppm, mean = 5.85 ppm), Zr/Hf (25.27 to
37.21, mean = 30.67 ppm) and Rb/Sr (0.16 to 4.32; mean = 1.67 ppm) ratios of
these granitoids reveal a strong crustal involvement in their magmatogenesis.
Variations in CaO/Na2O (0.47 - 1.44
ppm), Rb/Sr (0.14 - 0.27 ppm), Rb/Ba (0.07 - 0.14 ppm) and Sr/Y (38.21 - 174.42
ppm) ratios indicate that biotite and amphibole granodiorites with their excessive
Ni (135.37 - 139.51 ppm)
and Cr (395.73 - 447.74 ppm) were derived from a mafic to intermediate lower
continental crust where garnet and/or
amphibole were stable residual assemblage minerals. The moderate Sr/Y ratios
(1.81 - 9.47 ppm) and low transition
elements Ni (1 - 6.44 ppm) and Cr (7.89 - 13.47 ppm) contents in both the two-mica and biotite
granites are consistent with their emplacement at relatively shallow depths in
the upper to mean continental crust, at pressures below 10 Kbar. In the two-mica
granites, moderate CaO/Na2O (0.20 - 0.57 ppm,
mean = 0.38 ppm) and Rb/Ba (0.39 - 1.37,
mean = 0.84 ppm) ratios and quite varied Rb/Sr (1.53 - 4.23 ppm,
mean = 2.85 ppm) ratios indicate a predominant derivation from psammitic and
pelitic metasediments rather than metagreywackes. These low ratios (0.25 ≤
CaO/Na2O ≤ 0.32, mean = 0.28 ppm; 0.31 ≤ Rb/Ba ≤ 0.44, mean = 0.39 ppm; 1.11
≤ Rb/Sr ≤ 1.78, mean = 0.39 ppm) in biotite granites are more consistent with
melting from a metagreywacke-derived source. Evidence
for the contribution of mantle-derived mafic magma with granitic magma in the
plutons studied is materialized by the presence of magmatic enclaves in both
granodiorites and two-mica granites, the volcanic arc geochemical signatures
displayed by the plutons in geotectonic diagrams and Nb/Ta ratios (14.14 - 34.61 ppm) closer to mantle estimates.
Geochemical data and radiometric dating elements suggest that the granitoids
studied can be integrated into the pan-African late magmatic episode, which
corresponds between 606 and 583 Ma, to the activity of transcurrent ductile
strike-slips and to the synchronous emplacement of high K calc-alkaline plutons
in a post-collisional context.