Tectonics Of The Precambrian Rocks Of The Negash Area Tigrai Region Northern Ethiopia

The Wukro area is constituted by weakly metamorphosed largelyrnPrecambrian age volcano-sedimentary rock units of Tsaliet Group , TembienrnGroup , Didikama Formation , Hatheos Formation and pebbly slate which formrnpart of the Upper Complex of the Precambrian basement . The youngerrnPalaeozoic-Mesozoic sedimentary cover consisting of the Enticho Sandstone ,rnEdagga Arbi Glacials and Adigrat Sandstone unconformably overlies thernPrecambrian units .rnDetailed structural analyses at macro , meso and microscale havernrevealed three generation of ductile deformational events ( Dj , D2 , & Dj ) andrnlate faulting . The first phase of deformation Dj is characterized byrntransposition phenomena which has obliterated the original stratigraphyrnand produced rootless intrafolial foldings . The intensity ofrntransposition is greatest on the rocks of Tembien Group and DidikimarnFormation and is least on the rocks of Hatheos formation and Pebbly slate .rnAssociated with the Dj deformation is the N -S trending Sj foliation largelyrndefined by slaty cleavage .rnThe second phase of deformation Dj is characterized by the.rndevelopment, of a (10 * - 20 ‘) — > (170 * -195‘) plunging overturned major folds ,rnwhich has folded the structural elements of the Dj generation . Itrndeveloped two synforms and two antiforms , namely North Western Synform ,rnWestern Antiform , Central Synform and Eastern Antiform from west to east .rnThe planar fabric element S2 produced by this generation is nearly subparallelrnto S « along the limbs of the P2 folds and is nearly perpendicularrnto Sj along tne hinge zones of the D2 folds .rnThe third phase of deformation Dyis the last deformation event inrnthe study area . Throughout the area its effect is a development ofrn^ndulations on the previous N-S trending composite ( Sp S( S2 ) surfaces .rnIts effect is greatest in the North-Western synform , where the D2 axialrnplane appears to have a curvilinear ’' trace .rnFollowing this event, is an intrusion of small granite and dykes intornthe rocks of the Tembien group and Didikama formation .rnMetamorphism in the area is largely synchronous with the Dj and D2rndeformations . Metamorphic conditions during those deformations werernrestricted to low gree. nschist facies .rnFollowing peneplanation of the basement and deposition ofrnPalaeozoic - Mesozoic sediments , numerous normal faults affected thernbasement and the younger sedimentary cover succession .

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