Existence of a possible subsurface ring complex in the northwestern part of the Nigerian Younger Granite province: a con
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ORIGINAL PAPER
Existence of a possible subsurface ring complex in the northwestern part of the Nigerian Younger Granite province: a contribution from aeromagnetic and remote sensing data J. Raimi & B. B. M. Dewu & P. Sule
Received: 23 August 2013 / Accepted: 11 June 2014 # Saudi Society for Geosciences 2014
Abstract The study area lies within the north-western part of the Nigerian Younger Granite province. It is bounded by latitude 10°30′N and 11°00′N and longitude 8°00′E and 9°00′E. Previous geological and geophysical studies that were carried out in the study area focused mainly on the ring complexes with surface exposure while nothing is known about those without the surface exposure. This has resulted in gap in geo-scientific knowledge which this study aimed to fulfill. First vertical derivative (FVD) and Euler deconvolution of the aeromagnetic data along with processed DEM were used to achieve this purpose. Results of the interpretation revealed a magnetic anomaly, almost circular in shape, with characteristics that are similar to the anomalies that spatially coincide with the prominent ring complexes but without the outcrops that are associated with the complexes. This anomaly is interpreted to be an unexposed ring. Lineaments revealed by the results are mainly oriented in the E–W, NE–SW and NW– SE. The lineaments in the NE–SW and its conjugate are the most developed lineament system. Presence of ring complexes on and along the lineaments favours the opinion that the emplacement sites of the complexes are influenced by the reactivated Pan-African shear zones and transcurrent faults. In particular, the cross-over of major lineaments at the nonoutcropping anomaly may suggest a very weak zone that probably allowed the volcanic eruption that initiated the emplacement of the unexposed ring complex. Results of the Euler deconvolution suggest a cylindrical-like body for the unexposed ring complex, which is consistent with pluton geometry, and a depth that range from outcrop to 1,200 m for it. J. Raimi (*) : P. Sule Department of Physics, Ahmadu Bello University, Zaria, Nigeria e-mail: [email protected] B. B. M. Dewu Centre for Energy Research and Training, Zaria, Nigeria
Keywords Aeromagnetic . Digital Elevation Model . Ring complex . Lineaments . First vertical derivative . Euler deconvolution
Introduction Younger Granite is one of the important series of the Nigerian igneous rocks, the others being the Older Granite and the Younger Volcanic series. The Younger Granite occurs characteristically as ring complexes and is wide spread in a region in the north central Nigeria referred to as the Nigerian Younger Granite province. With over 50 complexes in the province (Kinnaird 1985), the northwestern part of the province (study area) consist of prominent ring complexes with well-defined topographic features that manifest as ring intrusions on geological map (Fig. 1) and Digital Elevation Model (DEM) (Fig. 2). They are also known to give rise to prominent magnetic anomalies (Jaques et al. 1997). Their emplacemen
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