Geochemistry and Petrogenetic Affinity of the Rocks of Pella and Environs, Hawal Massif Northeast Nigeria

Publication Date : 24/05/2022

Author(s) :

Kwache, J.B.

Volume/Issue :
Volume 58
Issue 1
(05 - 2022)

Abstract :

Pella and environs is situated on Hawal Massif of northeastern Basement Complex of Nigeria. It covers an area of 2 about 216.8km . The rocks in the area has for long been described as undifferentiated Basement Complex. This paper is aimed at differentiating and suggesting the petrogenetic affinity of the rocks by combing field data with petrography and geochemistry. Stream, compass and road traversing were employed to geologically map outcropping components. Petrographic studies of four thin sections were studied using Steindorff Mel Sobel Petrological Microscope. Atomic Absorption Spectrometry (AAS) method was employed to analyze eighteen pulverized samples. The geochemical results were interpreted using PetroGraph version 2 beta software. These results differentiated the rocks into migmatite-gneiss, granite gneiss, Older Granites and basalts. Major mineral modes in migmatite-gneiss, granite gneiss and the Older granites are quartz, feldspars and biotite while basalt is dominated by plagioclase, olivine and sanidine. Migmatite-gneiss, granite gneiss and the Older Granites have similarities of geochemical data with enrichment in SiO ranging from 67.52 - 71.02 wt. %, K O ranges from 3.35 - 2 2 4.40 wt. % and Na O ranges from 1.87 - 4.00 wt. %. Basalts are enriched in MgO with ranges from 5.99 - 6.78 wt. %, 2 TiO ranges from 3.27 - 4.35 wt. %, Fe O3 ranges from 14.1 - 15.5 wt. % and CaO ranges from 7.11 - 7.64 wt. %. 2 2 Pegmatite are enriched in K O with ranges from 9.98 - 11.4 wt. % but depleted in CaO with ranges from 0.40 - 0.76 wt. 2 % and TiO from 0.06 - 0.12 wt. %. Some selected oxides and trace elements plotted on Harker using SiO for gneisses, 2 2 granites and pegmatite and MgO for basalts as fractionation index revealed that Fe O , CaO, Co, Sr, Al O and K O 2 3 2 3 2 shows a continuous negatively correlated well-defined linear trend. The chondrite-normalized Rare Earth Elements (REE) patterns of most of the rocks are characterized by enrichment in Light Rare Earth Elements (LREE) relative to depletion in Heavy Rare Earth Elements (HREE). The negative anomalies shown by Eu are prominent in the rocks. Total-Alkaline-Silica (TAS) discrimination plot of SiO vs. Na O + K O revealed that granite gneiss and granite falls 2 2 2 within granitic field. Alumina-Iron-Magnesium (AFM) diagrams for gneisses, granites and pegmatite revealed Calcalkaline while basalt is tholeiitic. Discrimination plots of Rb vs. (Yb + Ta) for granite gneiss and granites revealed Syn-Collision (Syn-COLG) and Volcanic Arc Granite (VAG). The granites are I-type, metaluminous to weakly peraluminous and have continental crust affinity. Basalts are Mid Oceanic Ridge (MORB) with mantle affinity. All the rocks suggest fractionation and igneous progenitor.

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