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Whole-Rock Geochemistry Of Basic And Intermediate Intrusive Rocks In The Ishiagu Area: Further Evidence Of Anorogenic Setting Of The Lower Benue Rift, Southeastern Nigeria, Anthony Chukwu, Smart Chika Obiora

Turkish Journal of Earth Sciences

Petrographic studies on the intrusive rocks from the Ishiagu area show that they are gabbro, dolerites, and diorite. The gabbro and diorite occur as stocks while the dolerites occur as sills in folded sedimentary sequence predominated by shale. Geochemical data confirmed the rocks as basic (gabbro and dolerites) and intermediate (diorite) rocks with silica contents ranging from 42.45 to 50.75 wt.% and 55.03 to 60.24 wt.%, respectively. They are predominantly alkaline (gabbro, dolerites, and diorites) with sparse tholeiites (few gabbro). The basic rocks are made up of calcic plagioclase (An_{49-54}), clinopyroxene, olivine (altered), nepheline, and opaques, while the intermediate rocks …