Palaeomagnetic confirmation of Palaeozoic clockwise rotation of the Famatina Ranges (NW Argentina): implications for the evolution of the SW margin of Gondwana

SPAGNUOLO, CECILIA M.; RAPALINI, AUGUSTO E.; ASTINI, RICARDO A.

GEOPHYSICAL JOURNAL INTERNATIONAL

Blackwell Publishing

Lugar: Oxford; Año: 2008 vol. 173 p. 63 - 78

0956-540X

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 early 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, 32.7°S, 4.3°E, dp=5.6°, dm=8.6°, N=14 sites). This pole position is rotated 58° clockwise respect to the coeval reference pole for Gondwana but it is consistent with previous Early Ordovician poles obtained for 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 80.0°S, 349.3°E, dp=7.2°, dm=10.4°, 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, 78.2°S, 349.0°E, dp=4.6°, dm=6.6°, 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, 73.1°S, 90.6°E, dp=2.3, dm=4.3, 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. A brief discussion of tectonic models that suggest docking of a large para-authochthonous terrane or a systematic pattern of large-scale rotations on the Early Palaeozoic Gondwana continental margin is presented.