Geochemical Classification, Petrogenetic Association of Magmatic Rocks in the Gboko Area and the Tectono-Magmatic Influence on the Evolution of the (Gboko Area) Lower Benue Trough of Nigeria

摘要

Magmatism in the Gboko area is found to be genetically related to the evolution of the lower sectorial part of the intracratonic sedimentary Benue Trough of Nigeria. Geochemical interpretations of major and trace data show that the rocks which are mainly volcanics with some hypabyssal and plutonic varieties are mainly basaltic (basalts, basaltic trachyandesites, trachydacites), phonolitic (phonolite, tepri-phonolites,), rhyolites and nepheline syenites are generally of calc-alkaline series. They are peraluminous to metaluminous with a few peralkaline. Major and trace elements tectonic discrimination plots reveal that the basaltic rocks are characteristic of Within Plate Basalts (WPB), Oceanic Arc Theoliites (OIT), and Ocean Island Alkalic (OIA) while the nepheline syenites are characteristic of Within Plate Granites (WPG). The plots also show that the tectonic setting is continental in a spreading centre and related to orogenesis. The evolved rocks in the Gboko area of the Lower Benue Trough are products of interaction between magmatism and tectonism which resulted from progressive crustal thining related to a spreading centre that regulated contamination from the crust and/or asthenosphere. Keywords: Tectonism, magmatism, Benue Trough, contamination, magmatic fractionation