Palaeomagnetic results from Palaeozoic volcanic and sedimentary units of the Famatina Ranges, in NW Argentina (28.7°S, 67.8°W) are reported. A late Early to late Middle Ordovician palaeomagnetic pole was obtained from a pre-tectonic remanence carried by magnetite and isolated in volcanics of the Molles Formation and the Cerro Morado Group (MCM1, 16.7°S, 357.2°E, A95 = 6.5°, K = 38.5, N = 14 sites). This pole position is rotated 39° clockwise respect to the coeval reference pole for Gondwana but it is consistent with previous Early Ordovician poles from the Famatina belt and the Faja Eruptiva Oriental in the Puna region of NW Argentina. The sedimentary layers of the Molles Formation, however, present a secondary magnetization carried by hematite, which is interpreted of Permian age and yields a pole position (MCM2) at 78.7°S, 330.8°E (A95 = 7.2°, K = 16.1, n = 27 samples). Two additional independent palaeomagnetic poles were obtained from the Permian De La Cuesta Formation, exposed at two different localities in the same area. While one consisted in a exclusively reverse polarity magnetization and a pole position (LC1, 76.9°S, 345.2°E, A95 = 6.0°, K = 21.1, n = 29 samples) compatible with the late Early to early Late Permian palaeomagnetic poles from South America, the other presented only normal polarities and a pole position (LC2, 74.5°N, 275.4°E, A95 = 2.0°, K = 258.3, n = 21 samples) suggestive of a Cretaceous remagnetization. These new palaeomagnetic results confirm on a much more robust database previous proposals that the Ordovician rocks of the Famatina belt have undergone a large clockwise rotation. They also constrain the rotation to pre-Permian times. Different tectonic models involving the Late Ordovician docking of a large para-authochthonous terrane or a pattern of systematic large-scale rotations in the Early Palaeozoic continental margin of Western Gondwana are discussed.
A paleomagnetic study was carried out in the Late Miocene Las Arcas Formation of northwestern Pampean Ranges (26° 45.757’ S, 66° 2.189’ W) in order to contribute with paleomagnetic information to the knowledge of the deformation of the area. The sampled formation is composed of fluvial red sandstones and pelites that were recently dated, near the top, in 6.88 My (Georgieff et al. 2013). It was sampled a stratigraphic section of 340 m thick from bottom to top of the unit. Of 17 sites analyzed, 14 carried a primary magnetization that was used to calculate a paleomagnetic pole (D = 176.2°, I = 34.0°, A 95 = 6.9°) that indicates a rotation of 0.3° ± 5.8°. This result suggests that the area did not undergo rotation since Late Miocene.
Reactivation of Cretaceous structures during the Miocene deformation, Agrio fold and thrust belt, Neuquen. The most recent studies in this area of the Andes of Neuquen have shown the existence of an important deformational event at the end of the early Cretaceous and a later reactivation during the Miocene. Recent Ar-Ar ages have constrained the first event and Miocene synorogenic deposits the second. New evidence from paleomagnetic data and structural information that corroborate both events are presented in this paper. The paleomagnetic data are from Paleocene-Eocene sills of the Collipilli group. They show that these sills were intruded in a deformed sedimentary sequence dipping about 25o and later rotated to their current position. In addition, the analysis of the discordance between the Tralalhue synorogenic conglomerate and the Agrio and Rayoso Formations has verified a 20o angular unconformity at the time of the deposition of the synorogenic deposits. Putting this evidence together demonstrates that the Cretaceous deformation tilted the sedimentary sequence 20-25o and later, in the Miocene, these structures were reactivated..
'/%3e%3cuse xlink:href='%23a' transform='rotate(45 400 250)'/%3e%3cuse xlink:href='%23a' transform='rotate(67.5 400 250)'/%3e%3cpath id='b' fill='%2385340a' d='M404.31 274.41c.453 9.054 5.587 13.063 4.579 21.314 2.213-6.525-3.124-11.583-2.82-21.22m-7.649-23.757 19.487 42.577-16.329-43.887'/%3e%3cuse xlink:href='%23b' transform='rotate(22.5 400 250)'/%3e%3cuse xlink:href='%23b' transform='rotate(45 400 250)'/%3e%3cuse xlink:href='%23b' transform='rotate(67.5 400 250)'/%3e%3c/g%3e%3cuse xlink:href='%23c' transform='rotate(90 400 250)'/%3e%3cuse xlink:href='%23c' transform='rotate(180 400 250)'/%3e%3cuse xlink:href='%23c' transform='rotate(270 400 250)'/%3e%3ccircle cx='400' cy='250' r='27.778' fill='%23f6b40e' stroke='%2385340a' stroke-width='1.5'/%3e%3cpath id='h' fill='%23843511' d='M409.47 244.06c-1.897 0-3.713.822-4.781 2.531 2.136 1.923 6.856 2.132 10.062-.219a7.333 7.333 0 0 0-5.281-2.312zm-.031.438c1.846-.034 3.571.814 3.812 1.656-2.136 2.35-5.55 2.146-7.687.437.935-1.495 2.439-2.067 3.875-2.094z'/%3e%3cuse xlink:href='%23d' transform='matrix(-1 0 0 1 800.25 0)'/%3e%3cuse xlink:href='%23e' transform='matrix(-1 0 0 1 800.25 0)'/%3e%3cuse xlink:href='%23f' transform='translate(18.862)'/%3e%3cuse xlink:href='%23g' transform='matrix(-1 0 0 1 800.25 0)'/%3e%3cpath fill='%2385340a' d='M395.75 253.84c-.913.167-1.563.977-1.563 1.906 0 1.062.878 1.906 1.938 1.906a1.89 1.89 0 0 0 1.563-.812c.739.556 1.764.615 2.312.625.084.002.193 0 .25 0 .548-.01 1.573-.069 2.313-.625.36.516.935.812 1.562.812 1.06 0 1.938-.844 1.938-1.906 0-.929-.65-1.74-1.563-1.906.513.18.844.676.844 1.219a1.28 1.28 0 0 1-1.281 1.281c-.68 0-1.242-.54-1.282-1.219-.208.417-1.034 1.655-2.656 1.719-1.622-.064-2.447-1.302-2.656-1.719-.04.679-.6 1.219-1.281 1.219a1.28 1.28 0 0 1-1.281-1.281c0-.542.33-1.038.843-1.219zm2.09 5.69c-2.138 0-2.983 1.937-4.906 3.219 1.068-.427 1.91-1.27 3.406-2.125 1.496-.855 2.772.187 3.625.187h.031c.853 0 2.13-1.041 3.625-.187 1.497.856 2.369 1.698 3.438 2.125-1.924-1.282-2.8-3.219-4.938-3.219-.426 0-1.271.23-2.125.656h-.031c-.853-.426-1.698-.656-2.125-.656z'/%3e%3cpath fill='%2385340a' d='M397.12 262.06c-.844.037-1.96.207-3.563.688 3.848-.855 4.697.437 6.407.437h.03c1.71 0 2.56-1.292 6.407-.438-4.274-1.282-5.124-.437-6.406-.437h-.031c-.802 0-1.437-.312-2.844-.25z'/%3e%3cpath fill='%2385340a' d='M393.75 262.72c-.248.003-.519.005-.813.031 4.488.428 2.331 3 7.032 3h.03c4.702 0 2.575-2.572 7.063-3-4.7-.426-3.214 2.344-7.062 2.344h-.031c-3.608 0-2.496-2.421-6.22-2.375zm10.1 6.94a3.848 3.848 0 0 0-3.846-3.846 3.848 3.848 0 0 0-3.847 3.846 3.955 3.955 0 0 1 3.847-3.04 3.952 3.952 0 0 1 3.846 3.04z'/%3e%3cpath id='e' fill='%2385340a' d='M382.73 244.02c4.915-4.273 11.11-4.915 14.53-1.709.837 1.121 1.373 2.32 1.593 3.57.43 2.433-.33 5.062-2.236 7.756.215-.001.643.212.856.427 1.697-3.244 2.297-6.577 1.74-9.746a13.815 13.815 0 0 0-.67-2.436c-4.7-3.845-11.11-4.272-15.81 2.138z'/%3e%3cpath id='d' fill='%2385340a' d='M390.42 242.74c2.777 0 3.419.642 4.7 1.71 1.284 1.068 1.924.854 2.137 1.068.213.215 0 .854-.426.64s-1.284-.64-2.564-1.708c-1.283-1.07-2.563-1.069-3.846-1.069-3.846 0-5.983 3.205-6.41 2.991-.426-.214 2.137-3.632 6.41-3.632z'/%3e%3cuse xlink:href='%23h' transform='translate(-19.181)'/%3e%3ccircle id='f' cx='390.54' cy='246.15' r='1.923' fill='%2385340a'/%3e%3cpath id='g' fill='%2385340a' d='M385.29 247.44c3.633 2.778 7.265 2.564 9.402 1.282 2.136-1.282 2.136-1.709 1.71-1.709-.427 0-.853.427-2.564 1.281-1.71.856-4.273.856-8.546-.854z'/%3e%3c/svg%3e)