Tectonics of the Precambrian Rocks of the Negash Area, Tigrai Region, Northern Ethiopia
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Date
1993-01
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Addis Ababa Universty
Abstract
The Wukro area is constituted by weakly metamorphosed largely
Precambrian age volcano-sedimentary rock units of Tsaliet Group , Tembien
Group , Didikama Formation , Hatheos Formation and pebbly slate which form
part of the Upper Complex of the Precambrian basement . The younger
Palaeozoic-Mesozoic sedimentary cover consisting of the Enticho Sandstone ,
Edagga Arbi Glacials and Adigrat Sandstone unconformably overlies the
Precambrian units .
Detailed structural analyses at macro , meso and microscale have
revealed three generation of ductile deformational events ( Dj , D2 , & Dj ) and
late faulting . The first phase of deformation Dj is characterized by
transposition phenomena which has obliterated the original stratigraphy
and produced rootless intrafolial foldings . The intensity of
transposition is greatest on the rocks of Tembien Group and Didikima
Formation and is least on the rocks of Hatheos formation and Pebbly slate .
Associated with the Dj deformation is the N -S trending Sj foliation largely
defined by slaty cleavage .
The second phase of deformation Dj is characterized by the.
development, of a (10 * - 20 ‘) — > (170 * -195‘) plunging overturned major folds ,
which has folded the structural elements of the Dj generation . It
developed two synforms and two antiforms , namely North Western Synform ,
Western Antiform , Central Synform and Eastern Antiform from west to east .
The planar fabric element S2 produced by this generation is nearly subparallel
to S « along the limbs of the P2 folds and is nearly perpendicular
to Sj along tne hinge zones of the D2 folds .
The third phase of deformation Dyis the last deformation event in
the study area . Throughout the area its effect is a development of
^ndulations on the previous N-S trending composite ( Sp S( S2 ) surfaces .
Its effect is greatest in the North-Western synform , where the D2 axial
plane appears to have a curvilinear ’' trace .
Following this event, is an intrusion of small granite and dykes into
the rocks of the Tembien group and Didikama formation .
Metamorphism in the area is largely synchronous with the Dj and D2
deformations . Metamorphic conditions during those deformations were
restricted to low gree. nschist facies .
Following peneplanation of the basement and deposition of
Palaeozoic - Mesozoic sediments , numerous normal faults affected the
basement and the younger sedimentary cover succession .
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Keywords
Negash Area, Tigrai Region