Abstract:
Gozamin area exposes granitic rocks belonging to eastern corner of the western Ethiopian
Precambrian shield. The aim of this thesis work is to understand the petrography and the
geochemical composition of Gozamin granites and finally to assess their petrogenesis. To
achieve the objectives various methodologies were employed, such as field work for
sampling and mapping, petrographic investigation and geochemical analysis. The major
rock types identified in the studied area represented by medium to coarse grained pink and
gray granite. Petrographically, Gozamin granites range from alkali feldspar to syenogranite and are predominantly composed of alkali feldspar and quartz with subordinate
minerals of plagioclase, biotite, hornblende and opaque. Geochemically, they are
characterized by high silica content, exhibit ranges of SiO2 (70.5-79.5) and are similar to
high k-calc alkaline granites with higher total alkali content (7.52 - 8.81 wt.%) and show
an overall predominance of K2O over N2O. The negative correlation of SiO2 with Al2O3,
FeOt, CaO, TiO2, and P2O5 indicate fractionation nature of these granites during magmatic
differentiation. They have distinctive geochemical features typical of I-type granitoid,
metaluminious feature (A/CNK< 1.3), low P2O5 content, enriched in light rare earth
elements relative to heavy rare earth elements and have fractionated rare earth element
patterns (La/Yb) N=1.77–63.18). In primitive normalized mantle multi element diagram,
the patterns of the samples show enrichment in large ion lithophile elements and depletion
in high field strength elements (e.g., Nb, Ta, and Ti) and enrichment in Pb relative to Ce
are typical of continental crustal magmatism. Additionally, the diagram shows high
concentrations of Th, U, and Pb in the granites point to additional involvement of crustal
components in their generation. Tectonically, the analyzed samples have characteristics of
syn-collision and volcanic arc granitoid or subduction related granitoid rock formation
which suggests that they are formed in syn-collisional and volcanic arc environment. This
indicates the Gozamin granites are one of EAO features. The observed geochemical
features (major element and trace element variation) suggest that the studied granites were
generated by crustal melting and followed by fractional crystallization.
Keywords Petrography, Geochemistry, Neo-Proterozoic granites, tectonic setting,
Gozamin