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Pan-African, post-collisional, ferro-potassic granite and quartz–monzonite plutons of Eastern Nigeria |
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| Authors: | E C Ferr R Caby J J Peucat R Capdevila P Moni |
| Institution: | a Department of Geology, Rhodes University, 6140 Grahamstown, South Africa b Laboratoire de Tectonophysique, Université des Sciences et Techniques du Languedoc—Montpellier II, Place E. Bataillon, 34095 Montpellier Cedex 05, France c Géosciences Rennes, UPR 4661 CNRS, Université de Rennes I, 35042 Rennes, France |
| Abstract: | Three Pan-African hypersthene-bearing monzogranitic and quartz–monzonitic plutons from the Eastern terrane of Nigeria have been investigated in detail. New major, trace and REE data, used to constrain their origin and nature, indicate that they display chemical features of ferro-potassic trans-alkaline affinity. Further trace element discrimination suggests (i) production of calc-alkaline medium-K diorite magmas by partial melting of fluid-metasomatised mantle wedge possibly combined with melts from the dehydration partial melting of altered oceanic crust; (ii) simultaneously production of the granite–quartz–monzonite ferro-potassic magmas from partial melting of hornblende-bearing granodioritic crustal sources; (iii) mixing of the two magmas. Sr initial ratios of 0.707 to 0.711 witness that the source of the granite magmas is the lower crust. Ages of the lower crustal granulitic protoliths is bracketed by Nd model ages between 1.9 and 2.2 Ga. Pb evaporation ages on single zircons constrain the emplacement of the three plutons around 580 Ma. 40Ar/39Ar ages of amphiboles at about 560 Ma suggest cooling rates around 15°C/Ma. Extensive field work has established that pluton emplacement occurred during a regional north–south dextral strike-slip tectonics following the 630–610 Ma stage of oblique continent–continent collision in this part of west Africa. |
| Keywords: | Granite Pan-African Ferro-potassic Post-collisional Nigeria |
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