Metamorphism and Deformation History of Precambrian Rocks of Sorobo, Konso Area, Southern Ethiopia
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Date
2015-06
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Addis Ababa Universty
Abstract
Metamorphism and deformation evolution history of Konso Sorobo is described, which is part of
the Pan-African Orogeny, Mozambique Belt of southern Ethiopia. It comprises polydeformed
and metamorphosed mafic-ultramafic to felsic rocks, high grade complex gneiss rocks. Also synto
post-tectonic intrusives that range from ultramafic to granitic in composition and various preto
post-rift deposits are geologically described.
From field observations and petrological studies four phases of deformation and two
metamorphic events are differentiated. D1 predated migmatization and high grade metamorphism
of the paragenesis. It has resulted large open recumbent isoclinal folds with nearly horizontal
axial surface. D2 phase formed open-reclined folds having NE axial surface. During D3 phases,
the rocks were intensively sheared creating tight flexures having NW axial surface and local
mineral lineations were developed. Whereas D4 was brittle-ductile deformation resulting faults
owning several strike orientations.
Mineral assemblage of the area shows high grade metamorphism, which is represented by
amphibolite facies to granulite facies. D1 and D2 phases were enhanced the progression of the M1
metamorphism. Conversely, the existence of low temperature minerals in shear zones evidenced
that there was retrograde metamorphism M2. This M2 retrograde event was syn-D3 and shows
that late Pan-African Orogen-parallel shearing occurred, with the shear zones acting as important
fluid conduits.
Epidotization, chloritization, serpentinization alterations are common at plcaes. Thin section
studies evidenced (1) partial melting as the temperature raised and (2) drop in temperature led
high pressure-temperature minerals to alter into low grade minerals.
Keywords: Metamorphism, Deformation, Progression, Retrogression
Description
Keywords
Metamorphism, Deformation, Progression, Retrogression