The Nahuel Niyeu basin: A Cambrian forearc basin in the eastern North Patagonian Massif

GERSON A. GRECO; SANTIAGO N. GONZÁLEZ; ANA M. SATO; PABLO D. GONZÁLEZ; MIGUEL A. S. BASEI; EDUARDO J. LLAMBÍAS; RICARDO VARELA

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2017 vol. 79 p. 111 - 136

0895-9811

Early Paleozoic basement of the eastern North Patagonian Massif includes low- and high grade metamorphic units, which consist mainly of alternating paraderived metamorphic rocks (mostly derived from siliciclastic protoliths) with minor intercalations of orthoderived metamorphic rocks. In this contribution we provide a better understanding of the tectonic setting in which the protoliths of these units were formed, which adds to an earlier suggestedidea. With this purpose, we studied the metasedimentary rocks of the low-grade Nahuel Niyeu Formation from the Aguada Cecilio area combining mapping and petrographic analysis with U-Pb geochronology and characterization of detrital zircon grains. The results and interpretations of this unit, together with published geological, geochronological and geochemical information, allow us to interpret the sedimentary and igneous protoliths of all metamorphic units from the massif as formed in a forearc basin at ~520-510 Ma (Nahuel Niyeu basin). Itprobably was elongated in the ~NW-SE direction, and would have received detritus from a proximal source area situated toward its northeastern side (present coordinates). The basin migth be related to an extensional tectonic regime. Most likely source rocks were: (1) 520-510 Ma, acidic volcanic rocks (an active magmatic arc), (2) ~555->520 Ma, acidic plutonic and volcanic rocks (earlier stages of the same arc), and (3) latest Ediacaran-Terreneuvian, paraderived metamorphic rocks (country rocks of the arc). We evaluate the Nahuel Niyeubasin in an autochthonous position of the eastern North Patagonian Massif, adding to the discussion of the origin of Patagonia.