The Coastal Terrane of the Kaoko Belt, Namibia: Outboard arc-terrane and tectonic significance

摘要: Abstract The Coastal Terrane, or westernmost part of the Kaoko Belt outboard Three Palms Mylonite Zone, has distinct feldspathic arenite sedimentary sequences, no basement, ɛNd sediment signatures excluding Archaean and suggesting Mesoproterozoic–Neoproterozoic provenance sources, primitive arc-like geochemical for I-type granitoids. It contains evidence an older metamorphic event at ∼650–645 Ma not present in any other Belt. This metamorphism (M1) was high-T/low-P granulite to upper-amphibolite facies includes migmatisation associated with granitic magmatism arc affinity. Arc growth 650–640 Ma took place within Adamastor Ocean while Swakop Group turbidite sedimentation continued inboard along passive margin. Overprinting M1 M2 fabrics assemblages constrain docking have occurred between 650 580 Ma. Lack ophiolite fragments intermediate- high-P Zone suggest that it is a suture more likely be arc–backarc wrench–shear system developed E-dipping subduction where subducted beneath leading edge attenuated Congo Craton. Oblique collision 580 Ma, due this Terrane affinities, caused: (i) crustal scale oblique-overriding terrane over margin Craton; (ii) sinistral shear partitioned into two major ductile zones; (iii) high-T extruded, zone-bounded core; (iv) outwards- cratonwards-verging basement-cored fold nappes.