Palaeomagnetism and 40Ar/39Ar dating from Lower Jurassic rocks in Gastre, central Patagonia: further data to explore tectonomagmatic events associated with the break-up of Gondwana

CLAUDIA BEATRIZ ZAFFARANA; RUBÉN SOMOZA

JOURNAL OF THE GEOLOGICAL SOCIETY

GEOLOGICAL SOC PUBL HOUSE

Lugar: Londres; Año: 2012 vol. 169 p. 371 - 379

0016-7649

New 40Ar/39Ar data indicate ages of ca 185 Ma for the Lonco Trapial volcanic field in Gastre, north-central Patagonia, implying this andesitic unit is roughly coeval with the Marifil silicic province that crops out in north eastern of Patagonia. These volcanic fields are therefore part of the Karoo-Ferrar LIP, further contributing to the huge, 185-180 Ma magmatic outpouring in southern Gondwana. The comparison of palaeomagnetic results from the unit with Early Jurassic reference palaeopoles suggests that Gastre records a small, anticlockwise finite rotation with respect to stable South America. This contrasts sharply with the large clockwise rotation recorded by roughly coeval dolerites from the Malvinas/Falkland Islands and argues against a direct relationship between the rotation of the islands and the tectonic activity in Gastre. The results support previous suggestions that the Gastre Fault System is not the locus of major strike-slip displacement activity in the Jurassic as some authors have suggested. Taken as a whole palaeomagnetic data from Patagonia suggest a more complex than previously thought pattern of distributed and variable deformation during the early stages of Gondwana break-up. The crustal-block boundaries in the region remain cryptic.