Palaeomagnetism of the Late Devonian - Early Carboniferous Achala Batholith, Córdoba, central Argentina: implications for the Gondwana apparent polar wander path

GEUNA, S.E.; ESCOSTEGUY, L.D.; MIRÓ, R.

GONDWANA RESEARCH

Elsevier

Año: 2008 vol. 13 p. 227 - 237

1342-937X

The Achala batholith (31o30´S, 64o45´W, Córdoba, Argentina) is a major magmatic complex of the Sierras Pampeanas, emplaced as a post-orogenic pluton in a metamorphic?plutonic basement. It is mainly a porphyritic to coarse-grained equigranular monzogranite, with crystallization age of ~370 and cooling age of ~340 Ma, presently exposed as asymmetric, eastward-tilted blocks. Forty-three sites were sampled in the Achala monzogranite. Overall, it is weakly magnetic, with a mean magnetic susceptibility of 15x10-5 (SI). Twenty-two sites showed unstable magnetic behaviour. The remaining 21 sites have haematite as magnetic carrier of a stable remanence. The ilmeno-haematite appears as an accessory mineral, with exsolved intergrowths of (haemo)ilmenite. Thermal demagnetization up to 620-640oC isolated steeply dipping, dual polarity remanence directions. The palaeomagnetic pole is located at 56oS, 307oE (N=18, A95 10.7, K 11). The remanence was locked on cooling, over a range of temperatures from magnetic ordering to exsolution of ilmenite-haematite (~600 to 390oC). The pole better coincides with the 370-360 Ma segment of the Gondwana apparent polar wander path, suggesting that remanence was acquired quickly. The Achala pole matches a complex mid-Palaeozoic apparent polar wander path (?Y-type?) for Gondwana, which may involve rapid movement, true polar wander episodes and/or continental collisions before the final amalgamation of Pangea. Keywords: Palaeomagnetism, South America, Granite, Late Devonian-Early Carboniferous, APWP