Brittle shear deformation in northern Kordofan, Sudan: late carboniferous to triassic reactivation of precambrian fault systems

Abstract

Analysis of folding and faulting in the basement of the Umm Badr and Sodiri areas of Northern Kordofan, Sudan, revealed the existence of four major deformational episodes. A late Proterozoic deformation (D1) produced isoclinal folds in high-grade migmatitic-gneissic basement and in the metasedimentary belt of Umm Badr. A phase of intense NNE—SSW ductile shearing (D2) in the Umm Badr belt refolded the earlier structures in the metasediments and is of late Pan-African age. Dextral ENE—WSW brittle shearing (D3) of latest Pan-African age also affected the metasedimentary belt of Umm Badr.A late Carboniferous to Triassic brittle shearing (D4) reactivation event in the Umm Badr and Jebel Nehud areas (dextral?) and in the Sodiri area (sinistral) extensively reactivates structures of the previous episodes of deformation, exploiting part of the anisotropic zones of weakness. Age limits for brittle shear deformation in the Umm Badr and Sodiri areas were established from KAr isotopic ages of igneous rocks with varying field relationships to the shearing.