Structurally-controlled and spatially-restricted Late Neoproterozoic granitoids intrude
a multi-deformed amphibolite-granulite facies terrain in Obudu plateau in a regional
N-S to NE-SW pattern. The mineral contents of the granitoids are mainly potassium
feldspar, quartz, plagioclase and biotite, with subordinate muscovite, hornblende,
garnet, iron ores and zircon. The granitoids show a continuous compositional
variation from largely granites (sensu stricto) to a few granodiorites, with SiO2 range
of 65-75 wt%. They are strongly potassic (K2O/Na2O>1) and show a strong
peraluminous composition (A/CNK>1), S-type feature, mostly corundum normative
composition and low iron enrichment. They are characterized by high and variable
concentrations of the Large Ion Lithophile Elements (LILE) and high field-strength
elements (HFSE). Trace element contents of the granitoids indicate an important
role in partial melting of continental crust played on their petrogenesis, hence their
orogenic affinity. In particular, Y+Nb versus Rb and Y versus Nb discrimination
diagrams suggest a syn-continent-continent collision setting between the West African
craton and the westward drifting and subducted Eastern Sahara plate during the
Pan-African orogeny. The observed paucity of syn-collision granitoids in Obudu
plateau and other Pan-African orogenies suggest that crustal thickening was low but
uniform throughout these orogenies.
The study area is part of the Pan-African remobilized tectono-metamorphic terrain of the
Nigerian Precambrian Basement Complex lying between the West African Craton (WAC)
and Gabon-Congo Craton (GCC) (Kennedy, 1964). The area has attained
amphibolite-granulite facies metamorphism. The terrain is intruded by vast volumes of
enderbites and charnockites, a stock of gabbro, and dykes of pegmatites, aplites, dolerites
and small bodies of granitoids.
Igneous intrusions exercise great influence on the character and geodynamic history of
any remobilized belt. For instance, Ferre and Caby (2007) reported that the crystallization
of granulite facies of the Pan-African northern Nigeria was achieved due to the heat supplied
from the abundant anhydrous charnockites and monzodiorites in the area. Though granites
are common in collision zones, where crustal thickening takes place (Zhao et al., 1997;
Percival and Mortensen, 2002), they are generally rare in medium to high pressure granulite
facies terrains (Pride and Muecke, 1980), such as the study area. However, occurrence of
granites have been scantly reported from such terrains (Holland and Lambert, 1975; and
Rollinson and Windley, 1980). The purpose of this paper is to give a new geochemical
data on a set of representative granitoids from Obudu plateau, attempting to use the trace
elements as geotectonic markers.
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