Abstract:
This study is aimed to investigate the petrological, geological and geochemical characteristics of
magmatic rocks in the study area. To achieve this objective, detailed field work, geological,
lithostratigraphical, cross sectional mapping, petrographical and geochemical analyses of 15 and
10 samples respectively was done. The geology of the study area has been classified into five
lithological units: Aphanitic and porphyritic basaltic rocks, Gabbroic rock units, felsic
pyroclastic rocks and unwelded ignimbrites. The low Ti basalts of the study area display sub
ophitic texture and together with the presence of glomerophyric aggregates of pyroxene and
plagioclase minerals denote a tholeiitic tendency.
The correlation of MgO and CaO is positive and is an indicative of co-fractionation of olivine
and clinopyroxene. The chondrite normalized values of the REE pattern shows enrichment in
LREE, (La/Yb)N of 9.4 to 18 than MREE ( La/Sm
N
=1.38-1.86) and HREE (Dy/Yb
=1.39-1.72)
and there is fractionation of these HREE and MREE. The Nb/U ratio of the study area largly
ranged from 13.91 to 37.1, which is an indicator for the contamination nature of the outpouring
magma from the source crustal materials. The Koma-Andabet magmatic suits have similar trace
element patterns and trace element ratios as Zr/Nb (12.95-14.37), Zr/Ce (4.53-5.23) and Hf/La
(0.26-0.33) indicating originated from the same magmatic source. The low CaO/Al2O3 ratio
(0.50-0.80) and the relatively flat pattern of HREE ((Dy/Yb)
=1.39-1.72) and the HREE value is
above 10 times greater than the chondrite values is a clue for the source of the Koma-Andabet
magmatic rocks to be spinel containing mantle rather than garnet sourced.
N
N