Palaeomagnetism of Mesozoic magmatic bodies of the Fuegian Cordillera: implications for the formation of the Patagonian Orocline

Abstract

It is not known whether the Patagonian Orocline, the major bend of the southern Andes at the southern tip of South America, is a primary or secondary feature. Palaeomagnetic data along the Patagonian Orocline are still too scarce to provide a reliable and unambiguous answer to this question. New palaeomagnetic results on Late Jurassic–Late Cretaceous magmatic units along the central segment of the Fuegian Cordillera are reported. Data from four Late Cretaceous small intrusions and three sites on Late Jurassic–Early Cretaceous metabasalts and metagabbros showed anticlockwise declination deviations between 21° and 46° with respect to South America. From these and previous data, a picture of a nearly homogeneous post-Late Cretaceous regional rotation of the central Fuegian Cordillera is suggested. This supports a model of nearly 30° of anticlockwise secondary bending of the Patagonian Orocline since the Late Cretaceous (72 Ma). Lack of rotation of post-50 Ma sedimentary rocks exposed to the north of our study region, and larger rotations (of c. 90°) reported to the south of it suggest that a geographical and/or temporal progression of rotation values from south to north in the Fuegian part of the Patagonian Orocline should be investigated.

New Paleomagnetic and 40Ar/39Ar Geochronological Results for the South Shetland Islands, West Antarctica, and Their Tectonic Implications

“…Poblete et al (2016) reconstructed the paleopositions of South America and the Antarctic Peninsula since 120 Ma and proposed the oroclinal bending of southernmost Patagonia (Figure 17a) since the mid-Cretaceous. Paleomagnetic data show a continuous counterclockwise rotation of southernmost Patagonia since the mid-Cretaceous (Figure 17b), supporting the rigid lithospheric blocks rotation model (Poblete et al, 2014(Poblete et al, , 2016Rapalini et al, 2016), in agreement with structural and analog models in Tierra del Fuego (Figure 17a) (Carbonell et al, 2014(Carbonell et al, , 2016Kraemer, 2003). However, based on the new Euler rotations from seafloor spreading data in the Weddell Sea, Eagles (2016b) located a pole for the closure of the Rocas Verdes Basin in equatorial latitudes at mid-Cretaceous (Figure 17a), which precludes the possibility of plate rotations proposed by Poblete et al (2016) and favors a model of regional strike-slip faults movement causing crustal rotation and deformation.…”

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

“…Although alternative hypotheses have also emerged, suggesting a primary origin of the curvature of the Southern Andes (Ramos and Aleman, 2000), oroclinal bending models related to the closure of the Rocas Verdes marginal basin in the Late Cretaceous, proposed originally by Burns et al (1980), represent today a viable mechanism congruent with the known rotation pattern of the Southern Andes (Maffione et al, 2010;Poblete et al, 2014). The regional post-72 Ma 30° CCW rotation of the Fuegian Andes documented by Rapalini et al (2015), although occurring after complete closure of the Rocas Verdes basin, might still be associated to the tip of this major tectonic process.…”

“…8b). During the closure of the Rocas Verdes basin, the originally straight magmatic arc wrapped around the South American continental margin leading to widespread (~ 90° to 30°) counterclockwise (CCW) vertical-axis rotations (Rapalini, 2007;Rapalini et al, 2015). In the early Late Cretaceous (Fig.…”

“…Minor CCW tectonic rotations may have still been active at this stage (Rapalini et al, 2015). Since the Late…”

Introduction: Palaeomagnetism in fold and thrust belts: new perspectives

“…The second part of the volume presents a suite of papers focused on different structural and tectonic problems in the Andes, Pyrenees, the Iberian Range, the Alps and Anatolia. Rapalini et al (2015) show new data focused on unravelling the primary or secondary nature of the Patagonian orocline, Japas et al (2015) discuss Neogene rotations measured in the Andean Precordillera fold and thrust belt. Oliva-Urcia et al (2015) present a new magnetostratigraphic section from the southwestern portion of the Pyrenean main thrust that allows for both the refinement of the chronostratigraphy of the region and dating of primary folding and thrusting events.…”