Abstract:
Field, microscopic and X-ray powder diffraction studies have been used to evaluate the
cffects of igneous bodlcs on the sedimentary fills of the Lower Benue rift. The results of the
studies show that sn~allerig neous bodies of basic con~positionsw hose thicknesses range from 1
to 3 m produced mineral assemblages including quartz, calcite, chlorite, muscovite, lepidolite,
cordierite and biotite in the adjacent sedimentary rocks which are predominantly pelitic. The
assemblages gcncrally represent temperature conditions greater than 300" C, but not exceeding
450" C', the upper h i t of the albite-epidote hornfels facies. The minimum width of each
aurcole is 1.5 111. An alkali dioritic rock of 2 ltnl diameter produced a 21 1x1 aureole
characterized by a high temperature assemblage of calcite, enstatite and quartz which represents
temperature condition of more than 600" C. The largest body, a nepheline syenite which is 3.5
x 2.0 Itm in dimensions, produced a zoned 350 m aureole containing cordierite, orthoclase,
biotite and andalus~tc in thc innermost part, orthoclase and biotite
