Jurassic cooling ages in Paleozoic to early Mesozoic granitoids of northeastern Patagonia: 40Ar/39Ar, 40K?40Ar mica and U?Pb zircon evidence

MARTINEZ DOPICO, CARMEN; TOHVER, ERIC; LOPEZ DE LUCHI, MÓNICA; WEMMER, KLAUS; RAPALINI, AUGUSTO E.; CAWOOD, PETER

INTERNATIONAL JOURNAL OF EARTH SCIENCES

SPRINGER

Lugar: Berlin; Año: 2017 vol. 106 p. 2342 - 2357

1437-3254

U-Pb SHRIMPzircon crystallization ages and Ar-Ar and K-Ar mica cooling ages for basementrocks of the Yaminué and Nahuel Niyeu areas in northeastern Patagonia arepresented. Granitoids that cover the time span from Ordovician to EarlyTriassic are the main outcrops of the western sector of the Yaminué block. The southernYaminué Metaigneous Complex comprises highly deformed Ordovician and Permian granitoidscross-cut by a locally undeformed leucogranite dike (U-Pb SHRIMP zircon age of 254± 2 Ma). Mica separates from highly deformed granitoids from the southernsector yielded an Ar-Ar muscovite age of 182 ± 3 Ma and a K-Ar biotite age of 186± 2 Ma. Moderately to highly deformed Permian to early Triassic granitoids madeup the northern Yaminué Complex. The late Permian to Early-Triassic (U-PbSHRIMP zircon age of 252 ± 6 Ma) Cabeza de Vaca Granite of the Yaminué block yieldedJurassic mica K-Ar cooling ages (198 ± 2 Ma, 191 ± 1 Ma, and 190 ± 2 Ma).  In the limit between the Yaminué block and theNahuel Niyeu block, K-Ar muscovite ages of 188 ± 3 and 193 ± 5 Ma werecalculated for the Flores Granite whereas the Early Permian Navarrete granodioritelocated in the Nahuel Niyeu block, yielded a K-Ar biotite age of 274 ± 4 Ma.  The Jurassic thermal history is not regionallyuniform. In the supracrustal exposures of the Nahuel Niyeu block, the Early Permiangranitoids of its western sector as well as other Permian plutons and Ordovicianleucogranites located further east show no evidence of cooling age reset sincemica ages suggest cooling in the wake of crystallization of these intrusiverocks. On the contrary cooling ages for Late Permian ?Early Triassic granitoidsfrom deeper crustal level exposures in the Yaminué block are Jurassic (198-182Ma). Jurassic resetting could be reconciled with the massive Lower Jurassic FloresGranite, Marifil and Chon Aike volcanic provinces that affected Patagonia reflectingan intraplate deformational pulse that was responsible for the partial (re)exhumationof the mid crustal Paleozoic basement along reactivated discrete NE-SW toENE-WSW lineaments and the resetting of isotopic systems. This new thermochronological data indicates thatEarly Permian magmatic rocks of the Nahuel Niyeu block were below 300°C for ca.20 Ma prior to the onset of the main magmatic episode of the Late Permian toTriassic igneous and metaigneous rocks of the Yaminué block.