CAMBRIAN AND ORDOVICIAN MAGMATISM IN NORTHERN PATAGONIA: A RECORD OF THE PAMPEAN AND FAMATINIAN OROGENS?

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

Medellín

Congreso; VIII South American Symposium on Isotope Geology; 2012

The Georesources, Mining and Environment GEMMA research group of the Universidad Nacional de Colombia (Medellin).

Crustal continuity between the North Patagonian Massif (NPM) and the Pampia terrane is controversial. Two orogens developed in central Argentina in the Early Paleozoic: the Pampean (ca. 560-520 Ma) and Famatinian (ca. 490-460 Ma). Scarcity of well-dated Ordovician plutons in NPM has hampered testing the continuity of the Famatinian magmatic belt in NPM. Besides, no Pampean magmatism has been reported yet. We present new SHRIMP zircon dating for units located at northeastern NPM. They comprise two magmatic units previously considered as Late Paleozoic: the metaigneous Tardugno Granodiorite (TG) and Yaminué Complex (YC), together with detrital zircons on the low grade metaclastic Nahuel Niyeu Fm (NNF). Magmatic zircons from the deformed TG yielded a mean age of 528.5±3.5 Ma. Detrital zircons of NNF indicate a Middle Cambrian (507 Ma) maximum depositional age, in agreement with previous determinations. A period of exhumation and erosion of the Cambrian plutons is inferred from the large Cambrian peak of detrital zircons. A sample from a strongly foliated granodiorite in the southern exposures of the YC yielded 467±7 Ma for magmatic zircons indicating that at least part of the YC is Middle Ordovician. This reduces the extension of the Late Paleozoic magmatism and enlarges that of the Ordovician magmatic activity in NPM. Distribution of outcrops of well-dated Ordovician plutons in NPM suggests a magmatic arc that correlates in age, polarity and location with the Famatinian belt. Our results are consistent with Pampean and Famatinian orogens in NPM and crustal continuity between this and Pampia in the Early Paleozoic. However, a collisional event affecting northern NPM in the Late Paleozoic is supported by a minor Early Devonian peak of detrital zircons in a metaclastic unit interlayered with strongly deformed granitoids exposed in the northern sector of the YC. All this evidence suggests a para-authochtonous nature for NPM.