The Petrochemistry and Origin of Precambrian Gneisses Around Madaka AndKwana-Bala Area, North Central Nigeria

Abstract: This paper discusses the petrochemistry and origin of gneisses within
basement complex of Nigeria around Madaka and Kwana-Bala area. The
lithological units of rocks from Madaka and Kwana-Bala area comprises of
gneisses (migmatitic, banded, granitic), kyanite-sillimanite schist, semi-pelitic
schist, amphibolites, talcose rock, quartzite, phyllite, granodiorite, fine-mediumgrained granites and porphyritic granite. Seven samples of gneisses were analyzed
for major element oxides using (ICM-MS). The gneisses are often variable in colour
which depending on the nature and proportion of the feldspar and the
ferromagnesian minerals. The variation in textures of these rocks from study area is
due to varying size and amount of the K-feldspar porphyroblasts couple with
varying degree of foliation. In thin section, the characteristics granoblastic textures
were observed in migmatitic and granitic gneisses. The mineral compositions of the
gneisses rocks are variable, the common minerals assemblage includes: migmatitic
gneiss quartz + plagioclase +microcline +biotite + chlorite +garnet, banded gneiss:
quartz + plagioclase+ muscovite +biotite+sphene +chlorite+ garnet and granitic
gneiss contain quartz +plagioclase+microcline + muscovite+ biotite + chlorite
+garnet + opaque minerals. The gneisses of the study area are product of reworked
rocks during the Pan-African with a positive DF values, this suggests igneous
sources for the protoliths of these rocks in the study area. The chemistry of the
gneissic rock also show a variable proportion of Na2O and K2O with alkali-calcic
affinity, which suggests, a closed system behaviour during metamorphism on one
hand, and possibly a co-magmatic origin of the igneous protolith on the other hand.
Keywords: Magmatic, Metamorphism, Petrochemistry, Precambrian, Protoliths,
Tegina.