Preliminary Evidence for the Tectonic Influence on the Emplacement of the Gwandara Pluton in the Northcentral Nigeria Basement Complex
Keywords:
Pan African tectonics, tectonic, influence basement complex, granite, deformation microstructuresAbstract
This study presents the nature and pattern of field and microtectonic fabrics engraved in the Gwandara pluton as it relates to its emplacement around the southwest of Keffi, in the Northcentral block of the Nigerian basement complex. The granite pluton is part of the numerous isolated hills around Keffi, upstretched amidst polydeformed gneissic and schistose rocks. The pluton is characterized by patches of granodioritic materials and overlapped by a thermally healed fractural system that shows a hopscotch joint pattern with a sinistral strike-slip displacement pattern. Around the host rock, the deformation shows drag-stretching of early injected leucosome, development of ptygmatic folds, and realignment of veins that were supposedly perpendicular to the pluton. The strain estimate shows a strain partitioning pattern that is relatively homogeneous, defined largely by the mineral grain distribution. Anisotropy of Magnetic Susceptibility data suggests a dominantly NE-SW directional magmatism under transient tectonic conditions typical of a transtensional zone. Mineral quartz and feldspars show mechanical deformation and define the field lone-phased ductility that somewhat formed about the crystallization temperature of feldspars during an active regional deformation. Most of the structures resulted from the combined effects of phase transpose under a protracted deformation episode and magmatic stress field generated during pluton growth.
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