ANALYSIS OF MAGNETIC ANOMALY OVER THE RIRUWAI YOUNGER GRANITE RING COMPLEX: A GEODYNAMIC IMPLICATION

Abstract

The Riruwai Complex constitutes one of the Younger Granite Complexes in Nigeria within the Niger- Nigeria anorogenic belt province, located about 140 Km south of Kano. It provides one of the finest examples of the complete cycle of anorogenicmagmaticactivities in Nigerian Province, and consists of alkaline volcanic and plutonic rocks ranging from p yroxene bearing porphyries, rhyolites and comendite s, to riebeckite granites. The aeromagnetic intensity field anomaly of the Riruwai Younger Granite ring complex has been studied and analyzed to establish the tectonic nature of the complex and its influenc e on the geodynamics. The application of second derivati ve both in the x- and y-directions; (d 2 U / dx 2 ) and (d 2 U / dy 2 ) filters respectively, and Laplacian and polymonia l regression analysis revealed a general NE-SW regional anomaly pattern within the Complex and along which the Riruwai Younger Granite is emplaced. Very low magnetic anomaly is associated with the bi otite granites and the riebeckite bearing granites of the Complex. The very low anomaly is deemed to be attributed to highly evolved, late formed low density residual fluid rich magmatic material that were emp laced as granites as a separate magmatic phase, aft er an initial eruption of not so evolved volcanic phase. The general tectonic stress field traversing the Co mplex coincides with the NE-SW structural fabric within t he Basement Complex of the region.