Linkages between the Southern Patagonia Pre-Permian basements: New insights from detrital zircons U-Pb SHRIMP ages from the Cerro Negro District

PERMUY VIDAL C.; MOREIRA P.; GUIDO DIEGO; FANNING CM.

GEOLOGICA ACTA

UNIV BARCELONA

Lugar: Barcelona; Año: 2014 vol. 12 p. 137 - 150

1695-6133

The Patagonian basement rocks are dominated by Precambian to Early Paleozoic metamorphic rocks intruded by Paleozoic granitoids. Recently discovered basement rocks in the Cerro Negro District are characterized mainly by quartz-muscovite-chlorite schists; the metamorphic grade reaches greenschist facies (biotite-garnet grade) with a regional S1 schistosity sub parallel to the original sedimentary structure S0 and a secondary non-penetrative S2 foliation. New detrital zircon U-Pb geochronology shows that maximum depositional ages for detrital zircons yielded Devonian ages of 379 ± 4 Ma. These results suggest the Cerro Negro basement rocks as the youngest basement ages in the Deseado Massif, overlapping some detrital zircon ages on the Eastern Andean Metamorphic Complex in the Andean region. Most of detrital zircons are igneous origin with a major peak around ~396 Ma, with possible sources on the Devonian granitoids of the Río Deseado Complex (El Laurel and Bahía Laura granites) and equivalent northern Patagonia granitoids (e.g., Colan Conhué and Lago Lolog granites). Secondary peaks correspond to Ordovician to Silurian ages with proposed sources granites of the Río Deseado Complex and the La Modesta Formation (and their igneous contributors) being a possible sources for the Cerro Negro basement from Ordovician to Silurian zircons. The minor oldest peaks yield Cambrian-Neoproterozoic; Mesoproterozoic and Paleoproterozoic-Archean ages respectively, evidencing a common source from the interior of Gondwana. The obtained results provide new insights about between the pre-Permian metasedimentary rocks of the extra-Andean and Andean region during Mid-Paleozoic ages.