Tectonophysics 750 (2019) 45–55 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto New paleomagnetic pole for the Upper Jurassic Chon Aike Formation of T southern Argentina (South America): Testing the tectonic stability of Patagonia with respect to South America, and implications to Middle Jurassic-Early Cretaceous true polar wander ⁎ Víctor Ruiz Gonzáleza, , Carla G. Puigdomenecha, Emiliano M. Rendaa, Bárbara Boltshausera, Rubén Somozaa, Haroldo Vizána, Claudia B. Zaffaranab, Graeme K. Taylorc, Miguel Hallerd, Raúl Fernándeze a IGEBA, UBA – CONICET, Argentina b IIPG, UNRN – CONICET, Argentina c Plymouth University, United Kingdom d CENPAT, CONICET – UNPSJB, Argentina e INREMI, UNLP, Argentina ARTICLE INFO ABSTRACT Keywords: A paleomagnetic pole and a new Ar-Ar date of 156.08 ± 0.05 Ma are reported for the Chon Aike Formation, an Chon Aike Formation extensive plateau of ignimbrites, outcropping in the Deseado Massif (southern Patagonia, Argentina). The Deseado Massif geographic coordinates and statistical parameters for the paleomagnetic pole, validated by a reversal test, are: South America Lat. = 84.3° S, Long. = 191.3° E, A95 = 8.6°, K = 13.3, N = 23. This pole shows a complete coherence with Late Paleomagnetism Jurassic and Early to mid-Cretaceous poles of South America, obtained exclusively from igneous rocks, avoiding Apparent polar wander path any potential inclination shallowing. It is suggested that; a) southern Patagonia was an integral part of South America in the Late Jurassic; b) any reported vertical axis tectonic rotations must pre-date the Late Jurassic in this region; c) according to updated paleomagnetic data from igneous rocks, South America had very limited latitudinal drift between about 160 and 140 Ma; and, therefore, d) its apparent polar wander (APW) path, when compared with global apparent polar wander paths, does not support a large global shift or true polar wander (TPW) between 160 and 140 Ma. 1. Introduction 140 Ma, which should be testable by reliable paleomagnetic poles from well-dated units of different plates around the globe. Paleomagnetism is an important tool for paleogeographic re- The aim of the present work is to constrain the timing of block constructions and geodynamic analysis. This can be achieved by com- tectonic rotations in the Deseado Massif of southern Patagonia and to parison of apparent polar wander (APW) paths which are a temporal test if paleomagnetic data from South America supports the proposal of sequence of paleomagnetic poles, obtained from a variety of rock types. a large shift of the whole rigid Earth during the Late Jurassic. To fulfill APW paths record the tectonic movements of lithospheric plates and, if these goals, paleomagnetic sampling was carried out in the Chon Aike active, true polar wander (TPW) which is the displacement of an entire, Formation. Its outcrops in the Deseado Massif (Santa Cruz Province - rigid Earth with respect to its spin axis (Goldreich and Toomre, 1969; Argentina) are considered an integral part of South American Plate Gordon and Livermore, 1987). Paleomagnetic poles are also very useful during Jurassic times (von Gosen and Loske, 2004; Zaffarana et al., to test tectonic rotations (around a vertical axis) of lithospheric blocks 2010). due to the activity of fault systems with lateral displacements. A reliable paleomagnetic pole was obtained from several volcanic Using an APW track of paleomagnetic poles, Kent et al. (2015) have flows for which geographic coordinates and statistical parameters are: suggested that a TPW episode took place between about 160 and Lat. = 84.3° S, Long. = 191.3° E, A95 = 8.6°, K = 13.3, N = 23. The ⁎ Corresponding author at: Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires, UBA – CONICET, Oficina 27 - Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales – UBA, Intendente Güiraldes 2160, CABA, Argentina. E-mail address: [email protected] (V. Ruiz González). https://doi.org/10.1016/j.tecto.2018.10.028 Received 5 January 2018; Received in revised form 21 October 2018; Accepted 26 October 2018 Available online 15 November 2018 0040-1951/ © 2018 Elsevier B.V. All rights reserved. V. Ruiz González et al. Tectonophysics 750 (2019) 45–55 Table 1 Site: number of paleomagnetic sampling sites; Lat. And Long.: geographic coordinates of these sites; N/n: number of collected samples vs. Number of directions used for the site means; Dec. And Inc.: declination and inclination of the site mean directions; α95: 95% cone of confidence of site mean directions; k: kappa, precision poaramenter of Fisher (1953); Pole Lat. And Pole Long.: geographic coordinates of virtual geomagnetic poles (VGPs). * Discarded because of its large confidence cone (α95 = 37.4°), the site also could correspond to an edge of a volcano caldera. ** Sites with VGPs away from the cutt of angle determined using Wilson et al. (1972) method applied iteratively. Calculated mean directions for 30 and 23 sites used to calculate the reversal test (see text). Site Lat. (°S) Long. (°E) N/n In situ Bedding correction Tilt corrected α95 k VGPs Dec. Inc. Strike Dip Dec. Inc. Pole Lat. Pole Long. 1 47.5800 −69.7710 8/7 201.4 70.8 Horizontal 201.4 70.8 3.1 373.4 −74.7 237.6 2 47.6122 −69.7689 6/6 173.1 67.3 Horizontal 173.1 67.3 5.6 146.6 −84.8 359.5 3 47.6315 −69.7555 5/5 168.2 76.4 Horizontal 168.2 76.4 3.4 516.7 −72.3 307.3 4 47.7587 −69.7041 5/5 167.9 58.8 Horizontal 167.9 58.8 7.2 112.9 −78.0 59.0 5 47.8100 −69.7008 11/9 162.1 65.5 Horizontal 162.1 65.5 4.2 153.7 −78.0 14.4 6** 47.7653 −69.7008 7/7 322.2 85.6 200 10 299.8 76.1 6.6 85.0 −31.0 263.6 7 47.8145 −69.9409 6/6 9.4 −50.0 Horizontal 9.4 −50.0 4.2 259.5 71.5 316.3 8 47.8193 −69.9309 7/7 163.1 52.6 Horizontal 163.1 52.6 4.2 207.7 −70.7 62.9 9 47.9117 −70.0208 5/5 217.5 43.9 Horizontal 217.5 43.9 11.9 42.6 −53.3 176.3 10 47.9228 −69.8090 7/6 322.0 −48.4 Horizontal 322.0 −48.4 9.8 47.7 55.5 218.7 11** 47.9266 −69.6652 5/4 288.6 −64.7 Horizontal 288.6 −64.7 6.8 184.9 43.4 173.8 12 47.9166 −69.6736 6/3 177.2 48.6 Horizontal 177.2 48.6 13.2 88.0 −71.5 102.7 13 47.9259 −69.5375 4/4 192.0 70.9 Horizontal 192.0 70.9 6.0 235.4 −79.5 249.7 14** 47.9249 −69.5410 6/6 89.4 18.8 Horizontal 89.4 18.8 6.1 120.2 −6.8 13.5 15** 47.9336 −69.3577 5/5 157.3 26.7 Horizontal 157.3 26.7 2.6 854.5 −51.3 73.9 16 47.9297 −69.3687 5/5 240.7 71.2 Horizontal 240.7 71.2 2.7 804.8 −52.9 236.2 17 46.9686 −70.5638 7/6 187.6 65.0 Horizontal 187.6 65.0 5.5 151.0 −84.8 202.4 18 47.0178 −70.5098 7/7 342.0 −72.4 Horizontal 342.0 −72.4 3.2 365.5 74.9 148.8 19 46.9023 −70.4732 9/7 23.1 −75.9 Horizontal 23.1 −75.9 11.2 29.9 69.1 80.0 20** 47.0215 −70.5414 7/7 108.2 46.6 Horizontal 108.2 46.6 6.9 82.7 −32.0 11.6 21 46.9457 −70.4842 11/11 171.4 60.2 Horizontal 171.4 60.2 4.0 131.0 −81.5 60.0 22 47.2290 −70.7265 8/4 9.9 −65.0 Horizontal 9.9 −65.0 18.3 26.1 83.3 21.2 23 47.2363 −70.5457 8/8 334.8 −69.7 180 10 3.1 −71.6 4.2 175.2 80.6 98.8 24** 47.4326 −69.5457 9/7 81.6 59.4 Horizontal 81.6 59.4 10.7 33.0 −23.6 345.0 25 47.3211 −68.5457 7/7 207.2 52.6 Horizontal 207.2 52.6 4.6 170.6 −65.0 174.7 26 47.3048 −67.5457 6/6 200.7 27.7 Horizontal 200.7 27.7 4.5 223.1 −53.1 144.2 27** 47.0091 −66.5457 5/5 282.6 74.2 220 5 288.9 69.7 5.1 223.7 −27.1 250.8 28 47.0693 −65.5457 5/4 32.2 −40.7 Horizontal 32.2 −40.7 5.7 265.0 54.9 348.6 29 47.1902 −64.5457 5/3 232.2 79.9 200 5 250.3 76.5 11.2 122.4 −49.5 251.3 30* 47.3898 −63.5457 5/3 136.0 −27.3 225 65 136.1 37.7 37.4 11.9 −58.3 40.3 31 47.0897 −62.5457 5/3 16.3 −60.6 Horizontal 16.3 −60.6 21.1 35.1 77.1 0.6 Mean directions (paleohorizontal) N Dec. Inc. R k α95 23 sites Reverse 15.0 190.2 62.7 14.3 21.0 8.5 Normal 8.0 5.4 −62.6 7.7 21.5 12.2 Chon Aike Formation's paleomagnetic sites belong to a voluminous unit and Santa Cruz Argentinian provinces), as well as parts of Tierra del of ignimbrites, in which fiammes indicate that it was deposited hor- Fuego, Antarctica and the South Atlantic Islands Province (Pankhurst izontal to sub-horizontally and an absence of subsequent deformation.