Selective reopening of low temperature isotopic systems in micas during the Early Jurassic in northeastern Patagonia

MARTÍNEZ DOPICO, CARMEN I.; TOHVER, E; LÓPEZ DE LUCHI, MÓNICA G.; RAPALINI, AUGUSTO E.; WEMMER, KLAUS; CAWOOD, P.

San Miguel de Tucumán

Congreso; XX Congreso Geológico Argentino; 2017

Asociación Geológica Argentina

This contribution presents a new high quality mica K-Ar cooling age ofa coarse grained facies of the Flores Granite close to Nahuel Niyeu town, northeast of the North Patagonian Massif. Biotite separates from this granite, associated with the Treneta Volcanic- Plutonic Complex, yielded a cooling age (250- 300ºC) of 193.9±2.4 Ma (Sinemurian) in agreement with previously published muscovite dating for the finer grained facies. Available well constrained U-Pb zircon data (crystallization ages) coupled with Ar- based cooling agesfrom other different Paleozoic to Jurassic rocks from the area showed an inconsistent relation between their crystallization age, cooling path and exhumation age. Our results show that some of the Paleozoic rocks of the western block (a.k.a Yaminué block; crustal section formed below 3Kbars) have been affected by a thermal event in mid crustal levels that allowed diffusion loss of Ar duringSinemurian to Pliensbachian times. On the contrary, the easternmost and shallower crustal block, between Nahuel Niyeu and Valcheta towns, do not seem to have recorded any low temperature isotope system reopening during these times.