Geology of the Rocks Around the Gombe In-Lier, Northern Benue Trough, North –East Nigeria

Abstract

The rocks suite mapped in the study area are mainly Crystalline Rocks, Bima Sandstone,
Yolde Formation and Pindiga Formation. The crystalline rocks found within the Inlier
were metamorphosed by heat, pressure and fluid inclusion (metasomatism) caused by
the strike-slip fault. Based on the petropgraphic study, the mineral constituents of the
rocks are; Quartz, Biotite, K-Feldspars, Orthopyroxene, Plagioclase and some Opaque
minerals. The petrographic examination shows evidence of Crystal Intergrowth, Quartz
overgrowth and Suture grain content in the sandstone that have undergone
metamorphism. Field observation shows the presence of Quartzite along the fault
zone, implying that regional faulting in the study area triggered metamorphism of some
sandstone in the area. The sedimentary rocks of the study area are mostly fluvial, Albian
Bima Formation and fine grain transition of Cenomanian Yolde Formation and marine,
Turonian Pindiga Formation. From the sieve analysis, the sedimentary rocks around the
area were deposited by interchange between fluvial and marine activities. The rocks
were analyzed to be very coarse sand, coarse sand and fine grain sand that are well
sorted to moderately sorted. Coarse grained sands are dominant from the samples. At
the end of the study the area was thoroughly mapped, structural analysis, macroscopic
observations, microscopic analysis, the effect of digenesis and metamorphism of
mineral grains was analyzed. Finally, the environment of deposition was deduced as
fluvial to marine and the arrangement of the grains was archieved using sieve analysis.