Neotectonics of Nazret-Dera Area
No Thumbnail Available
Date
1990-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa Universty
Abstract
The Nazret=DGra area forms a segment of the northern
part of the Main Ethiopian Rift. The region is character-'
ized by a complicated morphology which is a result of
several episodes of volcanism and tectonism.
The volcanic rock units outcropping in the area are
principally bimodal in nature and it is possible to sub~
divide them into 6 groups according to their spatial
distribution. The groups include; the stratoid Eastern
Margin and Dera-Nazrot group mainly formed by a series
of flood basalts inter layered with ignimbrites and
Rhyolites; Keleta group, representing the oldest rift
floor product and constituted by Ash flows and Ignimbrities;
Boku and Gedemsa group,'which are rosults of central type
volcanic activity evidenced by preserved caldera of Gedemsa
and destructed caldera of Boku, giving rise to Pantellerites,
Rhyolites and pumice fall deposits and Melkasa group which
is constituted by basaltic spatter concs and associated
'AA' type lavn f1.ow. The nge of the rocks vary from 1.7 my
to 0.06 my.
The large volume of acidic product as compared to the
basaltic one and the lack of transitional rock units suggest
that there is a pnrtial melting of the lower crust probably
induced by intrusion of large bodies of basaltic magma From Tectonic POitit of view, tho area is chAracterized
by right stepping, "8n echelon" halt grabens, grabens and
faults which affect evan the youngest rock outcropping in
the region, The geometry of these structures i,D. an overstepping
towards the right suggest a left lateral motion
along this part of the rifto The theory is substantiated
by meso-scale structural data which has been collected
from, small faults with slicklines, extensional fractures
and joints which show that the area is undergoing an eastnortheast,
west-southwest extensiono Thus strike-slip
system and oblique extension is the major mode of deformation
for this part of the Rift System and possibly may
extend across the whole length of the Main Ethiopian Rift
Description
Keywords
Neotectonics