Browsing by Author "Kidane, Tesfaye"

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    Tectonics of the Precambrian Rocks of the Negash Area, Tigrai Region, Northern Ethiopia
    (Addis Ababa Universty, 1993-01) Kidane, Tesfaye; Boccaletti, M ,(Professor)
    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 .