Palaeomagnetism of the transition Upper Carboniferous-Lower Permian from Paganzo Basin, Argentina

GEUNA, SILVANA; ESCOSTEGUY, LEONARDO

GEOPHYSICAL JOURNAL INTERNATIONAL

Blackwell Publishing

Lugar: Londres; Año: 2004 vol. 157 p. 1071 - 1089

0956-540X

A palaeomagnetic study of Upper Palaeozoic rocks was performed on Paganzo basin, central-western Argentina and its western extension, Río Blanco sub basin. Volcanic-volcaniclastic Río del Peñón Formation and marine sedimentary Punta del Agua Formation were sampled in Rincón Blanco syncline. Both units represent the transition Upper Carboniferous-Lower Permian according to palaeontological and geochronological evidence. Chancaní Formation and Cerro Colorado-Caminiaga Formation were sampled in their type localities, in eastern Paganzo basin. All-reversed, pretectonic characteristic magnetisations were isolated in all three localities, spanning a wide lithological variation. Particularly in Rincón Blanco syncline, the same reversed magnetisation is observed in the entire 1,500 meters-thick sequence, in volcanic and sedimentary rocks; at least part of the deformation there is thought to be Permian in age, related to the San Rafael Orogenic Phase (SROP). The palaeomagnetic poles are: Rincón Blanco (RB) Lat. 77oS, Long. 294oE, N=19, A95=4.9, K=47; Chancaní (CH) Lat. 85oS, Long. 359oE, N=3, A95=8.8, K=196; Cerro Colorado-Caminiaga (CC) Lat. 79oS, Long. 291oE, N=6, A95=8.0, K=71. Neither of the poles is coincident with expected Late Carboniferous-Early Permian directions according to accepted apparent polar wander paths (APWPs) from South America and from other plates forming Pangaea in Late Palaeozoic times. This discrepancy could be due to 1) Polar wander affecting the western Gondwana margin, probably related to SROP, 2) Tectonic rotations related to strike-slip faults active in the area since the Palaeozoic and controlling the position of the main depocenters, 3) Incorrect age assignment for the sedimentary sequences or for the remanence acquisition, i.e. local remagnetisations. Tectonic rotations and local remagnetisation have both been proven in particular localities and further work needs to be done to establish the Late Palaeozoic APWP for South America, but SROP seems to have played a major role controlling both processes, rotation and remagnetisation.   Keywords: Palaeomagnetism, Argentina, Block rotations, Remagnetisation, Upper Palaeozoic, South America, San Rafael Orogenic Phase