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The Pan-African Toro Complex (northern Nigeria): magmatic interactions and structures in a bimodal intrusion

Published online by Cambridge University Press:  01 May 2009

J. Déléris ,
A. Nédélec ,
E. Ferré ,
G. Gleizes ,
R.-P. Ménot ,
C. K. Obasi  and
J.-L. Bouchez
J. Déléris
Affiliation:
Pétrophysique, Umr Cnrs 5563, Université Paul-Sabatier, 38 rue des Trente-Six-Ponts, 31400 Toulouse, France
A. Nédélec
Affiliation:
Pétrophysique, Umr Cnrs 5563, Université Paul-Sabatier, 38 rue des Trente-Six-Ponts, 31400 Toulouse, France
E. Ferré
Affiliation:
Pétrophysique, Umr Cnrs 5563, Université Paul-Sabatier, 38 rue des Trente-Six-Ponts, 31400 Toulouse, France Department of Geology and Mining, University of Jos, PMB 2084, Jos, Nigeria
G. Gleizes
Affiliation:
Pétrophysique, Umr Cnrs 5563, Université Paul-Sabatier, 38 rue des Trente-Six-Ponts, 31400 Toulouse, France
R.-P. Ménot
Affiliation:
Département de Géologie–Pétrologie, ura cnrs 10, Université Jean-Monnet, 23 rue du Docteur Paul Michelon, 42023 Saint-Etienne Cedex 02, France
C. K. Obasi
Affiliation:
Department of Geology and Mining, University of Jos, PMB 2084, Jos, Nigeria
J.-L. Bouchez
Affiliation:
Pétrophysique, Umr Cnrs 5563, Université Paul-Sabatier, 38 rue des Trente-Six-Ponts, 31400 Toulouse, France
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Abstract

The Toro Complex is one of the Pan-African Older Granites of Nigeria, first described as a reversely zoned pluton made of a central dioritic mass surrounded by a broad granitic rim. It has been thoroughly reinvestigated both from the petrographic and structural points of view, with the help of systematic anisotropy of magnetic susceptibility (AMS) measurements. The granite main body is a hornblende–biotite porphyritic monzogranite characterized by an early submagmatic fabric displaying a concentric pattern of foliations and west plunging lineations (stage 1). This fabric is overprinted by a later one due to solid-state strain along north-south subvertical dextral shear zones (stage 2). In the vicinity of the diorite, an evengrained granite displays magmatic structures that are contemporaneous with this strike-slip event. The diorite–granite contact is a complex zone where field, petrographic and geochemical data enable recognition of the effects of mixing and mingling between a mafic and a felsic magma. Tonalites cropping out within this contact zone are interpreted as hybrid rocks. The reverse zonation of the diorite itself is also the result of some hybridization process. Magmatic interactions mainly resulted from in situ infiltration of granitic liquid into the dioritic mass. The detailed history of this bimodal intrusion began with the emplacement of the granitic magma acquiring a first stage fabric. Before full crystallization of the granitic core, intrusion of the dioritic magma permitted reheating of the granitic magma that then crystallized with specific structural characters. The second stage structures, whether characterized by magmatic fabric near the diorite or by solid-state strain features in north–south shear zones elsewhere in the granite, are related to late Pan-African dextral strike-slip tectonics in the basement of northern Nigeria. The bimodal Toro Complex is therefore considered as a late Pan-African syntectonic pluton.

Type
Articles
Information
Geological Magazine , Volume 133 , Issue 5 , September 1996 , pp. 535 - 552
Copyright
Copyright © Cambridge University Press 1996

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