Constraining the timing of deformation in the southwestern Central Zone of the Damara Belt, Namibia

Abstract

AbstractStructural investigations and U–Pb sensitive high-resolution ion microprobe (SHRIMP) dating of rocks from the southwestern Central Zone of the Damara Belt, Namibia, reveal that a major SE-verging deformation event (D2) occurred at between 520 and 508 Ma. During D2, SE-verging simple shear and NE–SW pure shear extension in a constrictional stress field produced recumbent, south- to SE-verging, kilometre-scale folds and ductile shear zones, a NE–SW extensional lineation and conjugate shear bands, and was coeval with granitoid emplacement and high-grade metamorphism. The timing of this event is constrained by anatectic leucosomes in D2 shear zones (511±18 Ma) and extensional shear bands (508.4±8.7 Ma) as well as by syntectonic grey granites (520.4±4.2 Ma), and is similar to ages for high-grade metamorphism in the Central Zone. An upright folding event (D3) occurred at c. 508 Ma, resulting in the formation of basement-cored fold interference domes. The timing of deformation and metamorphism at 520–508 Ma in the mid-crustal SW Central Zone contrasts with ages of 560–540 Ma for shallow crustal NW-verging folding and thrusting elsewhere in the Central Zone that was concomitant with voluminous magmatism. This magmatism led to metamorphism and anatexis of the basement and the emplacement of anatectic red granites at 539±17 to 535.6±7.2 Ma, which contain 1013±21 Ma inherited zircons. The Central Zone therefore contains a record of crustal thickening, heating of the mid-crust, exhumation and orogen-parallel extension over the life of an orogen.