INVESTIGADORES
LARROVERE mariano Alexis
congresos y reuniones científicas
Título:
Depth-dependent changes in deformation and magmatism in the Famatinian arc, Argentina: implications for isostatic response and mountain building
Autor/es:
RATSCHBACHER, BARBARA; PATERSON, SCOTT R.; ALASINO, PABLO H.; LARROVERE, MARIANO A.; CAO, WENRONG; OKAYA, DAVID
Lugar:
Seattle
Reunión:
Conferencia; GSA Annual Meeting; 2017
Resumen:
Tectonic regimes in magmatic arcs may influence magma transfer, crustal rheology, seismic structure, mountain buildingand erosion. The Ordovician Famatinian arc in the Sierras Pampeanas of Argentina exposes crustal depths from volcanicsto ~ 8 kbar in foreland, main arc and rear-arc sections and preserves the temporal history of arc magmatism,metamorphism and deformation. This allows investigating deformation accommodation and intensity at different crustallevels during arc magmatism. We use constraints on the duration of magmatism, magma addition rates (MARs) anddeformation intensities at different crustal levels to model the predicted isostatic behavior of the Famatinian orogeny.Intrusive rocks dominate (up to 90 %) in the mid to deep crust of the main arc section and make up ~ 40 % of the uppercrust, whereas in the foreland and rear-arc sections, igneous rocks comprise ≤ 30 % of the exposed rocks. MARs into the~ 30 km of vertical exposure increases with depth and are 8.8 km3/Ma/arc-km on average.Tectonic shortening synchronous with magmatism at all crustal levels is recorded by tilted and folded sedimentary andvolcanic strata and at deeper levels by magmatic fabrics and ductile host rock deformation. 10% shortening is determinedin the upper crust, whereas the mid- to deep-mid crustal levels record shortening amounts of ~ 60 % in host rocks. Anincrease in magmatic fabric intensity with depth, related to strain intensities through a study of magmatic folding, is used todetermine depth dependent shortening rates via thermal modeling. Results show regional, east-west shortening andcrustal thickening with stronger intensities in the mid to deep-mid crust (2 to 5 kbar) compared to the upper crust. Theseshortening amounts reflect a vertical deformation gradient, partly accommodated by changing deformation mechanismswith depth, the development of large shear zones in deeper parts and the development of greater shortening at depth dueto emplacement of larger volumes of magmatism.Isostatic mass balance modeling of this hot orogen predicts that tectonic shortening and magmatic thickening during arcmagmatism drives an increase in surface elevation and mountain building from a shallow marine environment at 490 Mato ~ 2 km at 450 Ma with non-coaxial, west-vergent shortening continuing after magmatism ceased.