Episodic intra-continental reactivation during collapse of a collisional orogen: The Damara Belt, Namibia

Collision, high-angle contraction, crustal thickening and heating at 555–516 Ma, primed the Damara Belt ready for collapse, which was triggered by a transition to ENE–WSW contraction along length of belt in response orogenic events east Gondwana 516–505 Ma. Along-orogen shortening reworked thickened high-grade core belt, increasing gravitational instability, establishing an NW–SE extension direction across that conducive reactivation pre-existing structures eventual collapse. This persisted, switch vertical σ1 collapse signalled decompression melting ∼502 Ma subsequent rapid cooling. Collapse focused on exhumed as ∼170 km wide, semi-coherent massif-type metamorphic complex with steep extensional shear zones faults marginal flanks. During exhumation reactivated oblique-slip responded external transient stress fields. Reactivation middle- lower-amphibolite facies dextral-normal ∼500–495 ∼495–490 involved E–W consistent accretionary west margin during Pampean Orogeny. greenschist sinistral-normal ∼485 N–S south Famatinian Orogen. Early stages melting, flattening folds ductile ultramylonite within carbonate formed extension. Late stage brittle field from ∼480 onwards, stress-switch radial directions dominated NE–SW. flat-lying breccia, inclined faults, fractures, oxidizing fluids partitioned into top lower-levels massif. Ongoing drove localized flanking margins hanging-wall, produced low-strain reverse straddle transition. The pressure difference between massif (4.8–5.5 kbar) hanging-wall (3.9–4.2 kbar), indicate ∼3.2–4.6 crust stripped above complex.