Constraints on deformation of the Southern Andes since the Cretaceous from anisotropy of magnetic susceptibility

Research output: Contribution to journalArticle

Authors

  • Catalina Hernandez-Moreno
  • Matias C. Ghiglione
  • Fabio Speranza
  • Douwe J J van Hinsbergen
  • Emanuele Lodolo

Colleges, School and Institutes

External organisations

  • Utrecht University
  • Istituto Nazionale di Geofisica e Vulcanologia
  • Universidad de Buenos Aires
  • OGS (Istituto Nazionale di Oceanografia e Geofisica Sperimentale - National Institute of Oceanography and Experimental Geophysics)

Abstract

The southernmost segment of the Andean Cordillera underwent a complex deformation history characterized by alternation of contractional, extensional, and strike-slip tectonics. Key elements of southern Andean deformation that remain poorly constrained, include the origin of the orogenic bend known as the Patagonian Orocline (here renamed as Patagonian Arc), and the exhumation mechanism of an upper amphibolite facies metamorphic complex currently exposed in Cordillera Darwin. Here, we present results of anisotropy of magnetic susceptibility (AMS) from 22 sites in Upper Cretaceous to upper Eocene sedimentary rocks within the internal structural domain of the Magallanes fold-and-thrust belt in Tierra del Fuego (Argentina). AMS parameters from most sites reveal a weak tectonic overprint of the original magnetic fabric, which was likely acquired upon layer-parallel shortening soon after sedimentation. Magnetic lineation from 17 sites is interpreted to have formed during compressive tectonic phases associated to a continuous. ~. N-S contraction. Our data, combined with the existing AMS database from adjacent areas, show that the Early Cretaceous-late Oligocene tectonic phases in the Southern Andes yielded continuous contraction, variable from. ~. E-W in the Patagonian Andes to. ~. N-S in the Fuegian Andes, which defined a radial strain field. A direct implication is that the exhumation of the Cordillera Darwin metamorphic complex occurred under compressive, rather than extensional or strike-slip tectonics, as alternatively proposed. If we agree with recent works considering the curved Magallanes fold-and-thrust belt as a primary arc (i.e., no relative vertical-axis rotation of the limbs occurs during its formation), then other mechanisms different from oroclinal bending should be invoked to explain the documented radial strain field. We tentatively propose a kinematic model in which reactivation of variably oriented Jurassic faults at the South American continental margin controlled the Late Cretaceous to Cenozoic evolution of the Magallanes fold-and-thrust belt, yielding the observed deformation pattern.

Details

Original languageEnglish
Pages (from-to)236-250
Number of pages15
JournalTectonophysics
Volume665
Publication statusPublished - 8 Dec 2015

Keywords

  • Anisotropy of magnetic susceptibility, Cordillera Darwin, Patagonian Orocline, Southern Andes, Tectonics

ASJC Scopus subject areas