Prolonged Movement on a > 10‐km‐Wide Thrust During Early Paleozoic Orogens in the Gondwana Margin of NW Argentina

Abstract

The >10‐km thick Paleozoic Guacha Corral shear zone in Central Argentina is arguably one of the thickest thrust zones anywhere. It played a key role during the two early Paleozoic orogenies of western Gondwana and currently separates two terranes: one dominated by events related to the >510‐Ma Pampean Orogeny and the other by the <500‐Ma events of the Famatinian Orogeny. The combination of structures and geochronometry suggests that the shear zone was active for over 100 Ma. Thrusting started during migmatization at 520 Ma as recorded by U‐Pb ages in zircon and monazite and was demonstrably active also at 480 and 470 Ma. The age coincidence between Ar plateau ages of muscovite and biotite at 420 Ma in the upper part of the shear zone, and at 405 Ma in the lower part suggests two intense cooling pulses. These are ascribed to thrusting, rapid exhumation, and cooling. Its anomalous width is likely a result of this prolonged kinematic history related to its role in transferring shortening to the Pampean forearc possibly as a basal detachment and later by acting as the main boundary between the Pampean and Famatinian tectonometamorphic terranes. The two low‐temperature shearing events inferred from the Ar ages suggest that deformation continued during the period between the end of the Famatinian cycle at ~440 Ma and the start of the Chanic or Achalian Orogeny and its magmatism after 400 Ma.

From Crustal Thickening to Orogen‐Parallel Escape: The 120‐Myr‐Long HT‐LP Evolution Recorded by Titanite in the Paleozoic Famatinian Backarc, NW Argentina

“…This event was triggered by the arrival and docking of the Laurentian‐derived Precordillera/Cuyania block to the western margin of Gondwana and marked by regional unconformities formed during the inversion of the basins (Astini & Dávila, 2004; Bahlburg & Hervé, 1997a; Davila et al, 2003; Ramos, 2008; Thomas & Astini, 2003). This phase was characterized by folding and development of several wide thrusts at midcrustal levels (Cristofolini et al, 2014; Finch et al, 2015; Larrovere et al, 2016, 2011; Rapela, Pankhurst, Casquet, et al, 1998; Semenov et al, 2019; Semenov & Weinberg, 2017). The Famatinian orogenic cycle is inferred to have finished at around 440–435 Ma when magmatism waned (2009; Bahlburg et al, 2016; Büttner et al, 2005; Mulcahy et al, 2014; Wolfram et al, 2017).…”

“…This orogeny was a long‐lived, wide, and hot accretionary orogeny, located in the active margin of Western Gondwana and part of the regional Terra Australis orogen (Cawood, 2005). The Famatinian backarc is associated with wide shear zones that accommodated shortening from convergence (Finch et al, 2015; Finch et al, 2017; Larrovere et al, 2008; Larrovere et al, 2016; Semenov et al, 2019; Whitmeyer & Simpson, 2004). It records circa 60 million years of magmatism and HT‐LP metamorphism, between ~500 and 440 Ma (Büttner et al, 2005; Finch et al, 2017; Ortiz et al, 2019; Sola et al, 2013, 2017; Steenken et al, 2006; Wolfram et al, 2019).…”

Shear-assisted water-fluxed melting and AFC processes in the foreland of the Early Paleozoic Famatinian orogen: petrogenesis of leucogranites and pegmatites from the Sierras de Córdoba, Argentina

“…It is a ~ 120 km long by 10 km wide shear belt that crops out in the central part of the Sierras de Córdoba, with a North-South trend, eastward dip and moderate dipping angle. The deformational history of the Guacha Corral shear zone points to protracted movements from Cambrian to Devonian times (Semenov et al 2019), with deformational events that reworked the previous gneissic and migmatitic structures. The result of this reworking is the generation of Bt + Sil (fibrolite) mylonites and Chl + Ser phyllonites (mineral abbreviations after Whitney and Evans 2010), formed during two main deformational events that took place at ductile, amphibolitefacies and ductile-brittle, greenschist-facies metamorphic conditions, with an almost reverse motion in a context of a compressive stress field for the ductile event (Martino et al 1995;Martino 2003;Whitmeyer and Simpson 2003;Fagiano and Martino 2004;Otamendi et al 2004;Fagiano 2007;Cristofolini et al 2008;Steenken et al 2010;Demartis et al 2011;Radice et al 2015;Semenov and Weinberg 2017;Semenov et al 2019).…”

“…The Guacha Corral shear zone (Fig. 1b) is the largest and most complex ductile structure in the Sierras de Córdoba (Martino 2003;Whitmeyer and Simpson 2003;Otamendi et al 2004;Fagiano 2007;Radice et al 2015Radice et al , 2020Semenov and Weinberg 2017;Semenov et al 2019). It is a ~ 120 km long by 10 km wide shear belt that crops out in the central part of the Sierras de Córdoba, with a North-South trend, eastward dip and moderate dipping angle.…”

“…The result of this reworking is the generation of Bt + Sil (fibrolite) mylonites and Chl + Ser phyllonites (mineral abbreviations after Whitney and Evans 2010), formed during two main deformational events that took place at ductile, amphibolitefacies and ductile-brittle, greenschist-facies metamorphic conditions, with an almost reverse motion in a context of a compressive stress field for the ductile event (Martino et al 1995;Martino 2003;Whitmeyer and Simpson 2003;Fagiano and Martino 2004;Otamendi et al 2004;Fagiano 2007;Cristofolini et al 2008;Steenken et al 2010;Demartis et al 2011;Radice et al 2015;Semenov and Weinberg 2017;Semenov et al 2019). According to its dimensions (~ 10 km width in its widest part and more than 100 km long) and the fact that it juxtaposes terranes with different tectono-metamorphic histories, the Guacha Corral shear zone is considered to be a crustal-scale structure, and was also proposed to be part of a larger thrust zone which would extend for at least 250 km (Whitmeyer and Simpson 2003;Weinberg et al 2018;Semenov et al 2019).…”