High strain-rate deformation fabrics characterize a kilometers-thick Paleozoic fault zone in the Eastern Sierras Pampeanas, central Argentina

Regional deformation of the Sierra de San Luis, Argentina: Implications for the Paleozoic development of western Gondwana

“…[25] The kilometers thick Tres Arboles mylonite zone likely facilitated the juxtaposition of the Sierra de San Luis against the Sierras de Córdoba along the western margin of the Sierra de Comechingones [Whitmeyer and Simpson, 2003]. Maximum age of deformation is constrained by the Early to Middle Ordovician peak metamorphic event in the Sierra de San Luis.…”

“…Sigma and delta porphyroclasts record east over west movement, although dextral movement indicators and subhorizontal lineations can be seen within nearby, and presumed coeval, small-scale shear zones. Despite the lack of preserved transcurrent kinematic indicators within the main fault zone rocks, Whitmeyer and Simpson [2003] presented arguments that the zone overall records significant transpressive movement. Quartz and feldspar microstructures, syntectonic sillimanite needles and garnet-biotite geothermometry suggest deformation at temperatures of 500+°C in the hangingwall to 350°-450°C in the footwall [Whitmeyer and Simpson, 2003].…”

“…[31] Movement of the Sierra de San Luis toward its current position was facilitated by the Tres Arboles fault zone along the western border of the Sierra de Comichingones [Whitmeyer and Simpson, 2003]. Fabrics within the fault zone indicate amphibolite-facies deformation conditions and predominantly east-over-west and dextral oblique movement, at least initially.…”

“…[18] The Tres Arboles fault zone extends for 200+ km along the western boundary of the Sierras de Córdoba and is considered to be the eastern boundary of San Luis-related metasedimentary rocks [Whitmeyer and Simpson, 2003] (Figures 2 and 7). Here, a 16-km-thick zone of mylonites and ultramylonites thrusts granulite-grade gneisses and migmatitic rocks to the west over biotite gneisses, quartzites and migmatites.…”

“…Most previous work has viewed the Sierras de Córdoba and the Sierra de San Luis as an interrelated unit throughout the early Paleozoic [Ramos, 1988;Prozzi, 1990;Von Gosen and Prozzi, 1998], and therefore subject to consistent styles of deformation and metamorphism. However, recent work [Simpson et al, 2001;Whitmeyer and Simpson, 2003] suggests that the Sierra de San Luis was not positioned adjacent to the Sierras de Có rdoba prior to the Late Ordovician, which requires a reevaluation of the Paleozoic tectonic development of western Gondwana.…”