Pan-African and Red Sea tectonics of eastern Eritrea
Sammanfattning: This thesis proposes that the Pan-African tectonic grain in eastem Eritrea influenced theCenozoic opening of the Red Sea. Evidence is based on studies of the structures and fabrics of various phases associated with both the Pan-African orogeny and subsequent Red Sea extension.Rocks of the East African Orogen in eastem Eritrea comprise two lithotectonic domains, Ghedem and Bizen. A major low-angle discontinuity separates the two domains, with the Bizen domain in the hangingwall. Three Pan-African PAD1-3 phases of deformation are recognised. PAD1 deformation is characterised by a steep penetrative foliation S1 which is axial planar to upright F1 folds. F1 folds were distorted by low-angle shear zones and F2 recumbent folds during PAD2. PAD3 resulted in steep strike-slip shear zones and a steep rare S3 spaced cleavage axial planar to open upright F3 folds.Garnet rim-matrix and inclusion geothermobarometry indicate that rocks of the Ghedem domain experienced synmetamorphic deformation and were exhumed from as deep as 48 km. Exhumation was accomplished by erosion and gravity-driven orogenic collapse and isostatic root recovery. Geothermobarometric studies further indicate peak metamorphism during early PAD2 when P-T conditions were at 12 kbar and 650ºC, probably due to terminal convergence between East and West Gondwana.Both steep and low-angle Pan-African structures and fabrics were exploited during the Cenozoic by three, RSEl-3, Red Sea phases of NE-SW lateral extension. RSE1 extension occurred along a stack of top-to-basin low-angle normal faults that sole out to a semi-brittle subhorizontal basal detachment locally seen at exposure levels. Further asthenospheric upwelling off-shore resulted in RSE2 extension that involved seaward block tilting on a new system of coast-parallel domino-style normal faults and dikes rotated landward up to 40º by inferred detachment shear at depth. RSE3 extension involved significant strike-slip and dip-slip faulting perhaps related to the counterclockwise rotation of the Danakil block.The overall tectonic setting indicates that the Red Sea escarpment in eastem Eritrea is a RSE2 monocline that flexed most along the discontinuity between the Ghedem and Bizen domains.Keywords: Pan-African tectonic grain; geothermobarometry; Red Sea extension; flexure.
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