Reinterpretation of the Ordovician rotations in NW Argentina and Northern Chile: a consequence of the Precordillera collision?

Abstract

Early Paleozoic paleomagnetic data from NW Argentina and Northern Chile have shown large systematic rotations within two domains: one composed of the Western Puna that yields very large (up to 80°) counterclockwise rotations, and the other formed by the Famatina Ranges and the Eastern Puna that shows (*40°) clockwise rotations around vertical axes. In several locations, lack of significant rotations in younger rocks constrains this kinematic pattern to have occurred during the Paleozoic. Previous tectonic models have explained these rotations as indicative of rigid-body rotations of large para-autochthonous crustal blocks or terranes. A different but simple tectonic model that accounts for this pattern is presented in which rotations are associated to crustal shortening and tectonic escape due to the collision of the allochthonous terrane of Precordillera in the Late Ordovician. This collision should have generated dextral shear zones in the back arc region of the convergent SW Gondwana margin, where systematic domino-like clockwise rotations of small crustal blocks accommodate crustal shortening. The Western Puna block, bordering the Precordillera terrane to the north, might have rotated counterclockwise as an independent microplate due to tectonic escape processes, in a fashion similar to the present-day relationship between the Anatolia block and the Arabian microplate.

Magnetostratigraphy of the Miocene Las Arcas Formation, Santa María Valley, northwestern Argentina

“…The values obtained indicate non-significant rotation of the study locality during the last 9 Ma. Lack of significant Andean tectonic rotations in this area reinforces previous ideas (Aubry et al 1996;de Urreiztieta et al 1996;Beck 1998;Taylor et al 1998;Coutand et al 1999;Spagnuolo et al 2010;Zambrano et al 2010;Ré et al 2001;Japas and Ré 2006;Japas and Ré 2012;Vizán et al 2013) that rotations in this region do not follow a simple and uniform pattern. Beck (1998), Prezzi et al (2004), Japas and Ré (2012) and Somoza and Tomlinson (2002) claim that no significant rotation should be expected in the region since 10 Ma.…”

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

“…Giménez et al, 2000;Introcaso et al, 2004;Álvarez et al, 2016) (Fig. 20a); 2) a counter-clockwise rotation due to tectonic escape for the Western Puna block, located immediately in the northern sector of the indentation, interpreted through paleomagnetic data by Spagnuolo et al (2011); and 3) the style of wrap-around deformation of the shear zones in the indented basement between 30°S and 34°S, which suggests that there was a radial field of the horizontal deviatoric stress vectors (Christiansen et al, 2019).…”

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

“…Although the orogeny was solved primarily by vertically reverse shear zones, lateral movement (strikeslip) associated with a partition of the deformation by large scale scape tectonics occurred in some sites of this orogen. Spagnuolo et al, (2011) investigated a counter-clockwise rotation for the Western Puna block (located immediately in the northern sector of the indentation).…”