3D litho-constrained inversion model of southern Sierra Grande de San Luis: New insights into the Famatinian tectonic setting

Abstract

Unravelling the orogenic structure of the Sierra Grande de San Luis (Argentina) is essential to understand the geological evolution of the Famatinian orogen and the western margin of Gondwana. However, its structural organization is still poorly known and widely debated. In this contribution, a new interpretation of the complex geological structures in the southern sector of the Sierra Grande de San Luis is presented. This work is based on a lithoconstrained joint inversion of gravity and magnetic datasets combining lithological, structural and rock properties information. Results are consistent with a large-scale doubly-vergent structure caused by a compressional tectonic setting as a consequence of the collision between an allochthonous terrane (Cuyania/Precordillera) and the proto margin of Western Gondwana. A convex morphology of the indenter is proposed to be responsible for producing a significant clockwise rotation of the horizontal deviatoric stresses. This stress field caused a small sinistral component of movement and gave rise to the doubly-vergent transpressive mega-structure.

Upper-crustal architecture and record of Famatinian arc activity in the Sierra de Narváez and Sierra de Las Planchadas, NW Argentina

“…Low energy deep to shallow marine sedimentation was interrupted by high-energy volcaniclastic and volcanicsedimentary processes proximal to volcanic centers (Cisterna et al, 2010a;Cisterna and Coira, 2014). In total, the Famatinian orogen (e.g., arc and back-arc regions) is suggested to have been shortened by 50% during orogenesis (Christiansen et al, 2019). Here, we present new mapping, geochemistry, and age dating of rocks exposed in the Sierra de Narváez -Las Planchadas to evaluate and refine this model by further characterizing the eruptive, depositional, magmatic, and deformational processes occurring in the upper crust during Famatinian arc activity.…”

Architecture and kinematics of the Famatinian deformation in the Sierra Grande de San Luis: A record of a collisional history at 33° S latitude

“…Furthermore, this collision produced the current exposures of the Famatinian deep paleo-arc that show a continuous deepening from north to south (Otamendi et al, 2010;Tibaldi et al, 2013;Cristofolini et al, 2014) and from east to west (Camilletti et al, 2020). During the Famatinian belt construction, the deformation was regionally resolved in different ways; through large scale fold and thrust belts in the upper crust (Astini and Dávila, 2004), along major shear zones in the front and margins of the Famatinian paleo-arc (von Gosen and Prozzi, , 2005Höckenreiner et al, 2003;Cristofolini et al, 2014;Mulcahy et al, 2014), through large-scale west-verging shear zones located in the Pampean basement (Sims et al, 1997;Martino, 2003;Cristofolini et al, 2017;Semenov et al, 2019), and double-vergent structures developed in the paleo-backarc (Larrovere et al, 2017;Christiansen et al, 2019). Further, contraction at mid-crustal level in the paleo-backarc was predominately focused along west-verging reverse ductile shearing and folding (Finch et al, 2017;Larrovere et al, 2020).…”

“…The processes that affected the basement units in the Sierra Grande de San Luis (SGSL) have been the subject of extensive discussions in the last 20 years (e.g. Sims et al, 1998;von Gosen and Prozzi, 1998;Sato et al, 2003;Ortiz Suárez and Casquet, 2005;Delpino et al, 2007;Steenken et al, 2008;Morosini et al, 2014;Christiansen et al, 2019). These units represent the root of the Famatinian orogen, which was associated with a convergent plate motion at the Western Gondwana margin in Ordovician-Silurian times.…”

“…Although very detailed studies about the shear zones were carried out by these authors, the architecture of southern SGSL was better understood after the construction of a three-dimensional model using the structural data with geophysical and petrophysical constraints (Christiansen et al, 2019).…”

“…The shear zones in the western portion of the SGSL were studied in this work, incorporating new structural and geophysical data of the northern sector, which were not considered in Christiansen et al (2019). New evidence about the ductile deformation style and the tectonic setting during the Famatinian orogeny is presented in a three-dimensional model in order to establish the geodynamic evolution of the western proto-margin of Gondwana.…”