Pop-down tectonics, fluid channelling and ore deposits within ancient hot orogens

Denis Gapais (1) , Justine Jaguin (2) , Florence Cagnard (3) , Philippe Boulvais (2)

1 Systèmes Tectoniques
2 Terre, Temps, Traçage
3 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

Many Archaean and Paleoproterozoic deformation zones, often rich in ore resources, show particular structural patterns in particularmarked by regional vertical stretch. These zones are not restricted to greenstone-bearing Archaean domains that may have suffered gravity-driven sagduction of heavy supra-crustals, as extensively discussed since the last twenties. Structures are actually best explained by pop-down tectonics of upper-crustal unitswithin an underlyingweak crust submitted to horizontal regional shortening.Herewe present three complementary examples fromtwo Archaean greenstone belts (Abitibi sub-Province, Quebec, andMurchison belt, South Africa) and one greenstone-lacking Paleoproterozoic belt (Thompson belt,Manitoba). In the three examples, ore is concentrated along steeply dipping deformation zones, rich in syntectonic deposits and marked by substantial sub-vertical crustal stretch. On the other hand, the three regions show differences in age, in metamorphic grade (from sub-greenschist facies to upper amphibolite facies), in metal contents (gold, antimony, nickel), in metal sources, transfers and concentration histories. Our compared analysis emphasizes that pop-down tectonics associatedwith horizontal shortening of weak lithospheres may account for observed geometric patterns and provide a new and promising frame for the analysis of relationships between structural patterns and ore concentrations within old cratons.

Mots clés: Tectonics; Crustal shortening; Weak lithosphere; Fluid transfers; Ore deposits; Ancient cratons

Domaines: Sciences de la Terre

Denis Gapais, Justine Jaguin, Florence Cagnard, Philippe Boulvais. Pop-down tectonics, fluid channelling and ore deposits within ancient hot orogens. Tectonophysics, 2014, 618, pp.102-106. ⟨10.1016/j.tecto.2014.01.027⟩. ⟨insu-00965100⟩