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

MARTÍNEZ DOPICO, C.I.; TOHVER, E; LÓPEZ DE LUCHI, M.G.; WEMMER, K.; RAPALINI, A.E.; CAWOOD, P.

INTERNATIONAL JOURNAL OF EARTH SCIENCES

SPRINGER

Lugar: Berlin; Año: 2017 p. 2343 - 2357

1437-3254

U?Pb SHRIMP zircon crystallization ages andAr?Ar and K?Ar mica cooling ages for basement rocksof the Yaminué and Nahuel Niyeu areas in northeasternPatagonia are presented. Granitoids that cover the timespan from Ordovician to Early Triassic constitute the mainoutcrops of the western sector of the Yaminué block. Thesouthern Yaminué Metaigneous Complex comprises highlydeformed Ordovician and Permian granitoids crosscut byundeformed leucogranite dikes (U?Pb SHRIMP zircon ageof 254 ± 2 Ma). Mica separates from highly deformed granitoidsfrom the southern sector yielded an Ar?Ar muscoviteage of 182 ± 3 Ma and a K?Ar biotite age of 186 ± 2 Ma.Moderately to highly deformed Permian to Early Triassicgranitoids made up the northern Yaminué Complex. TheLate Permian to Early Triassic (U?Pb SHRIMP zircon ageof 252 ± 6 Ma) Cabeza de Vaca Granite of the Yaminuéblock yielded Jurassic mica K?Ar cooling ages (198 ± 2,191 ± 1, and 190 ± 2 Ma). At the boundary between theYaminué and Nahuel Niyeu blocks, K?Ar muscovite agesof 188 ± 3 and 193 ± 5 Ma were calculated for the FloresGranite, whereas the Early Permian Navarrete granodiorite,located in the Nahuel Niyeu block, yielded a K?Arbiotite age of 274 ± 4 Ma. The Jurassic thermal history isnot regionally uniform. In the supracrustal exposures of theNahuel Niyeu block, the Early Permian granitoids of itswestern sector as well as other Permian plutons and Ordovicianleucogranites located further east show no evidenceof cooling age reset since mica ages suggest cooling in thewake of crystallization of these intrusive rocks. In contrast,deeper crustal levels are inferred for Permian?Early Triassicgranitoids in the Yaminué block since cooling agesfor these rocks are of Jurassic age (198?182 Ma). Jurassicresetting is contemporaneous with the massive LowerJurassic Flores Granite, and the Marifil and Chon Aike volcanicprovinces. This intraplate deformational pulse thataffected northeastern Patagonia during the Early Jurassic(Sinemurian?Pliensbachian) was responsible for the partial(re)exhumation of the mid-crustal Paleozoic basement alongreactivated discrete NE?SW to ENE?WSW lineaments andthe resetting of isotopic systems. These new thermochronologicaldata indicate that Early Permian magmatic rocks ofthe Nahuel Niyeu block were below 300 °C for ca. 20 Maprior to the onset of the main magmatic episode of the LatePermian to Triassic igneous and metaigneous rocks of theYaminué block.