U-Pb detrital zircon data from the Paleozoic Sierra Grande Formation, North Patagonian Massif, Argentina

URIZ, N.J., CINGOLANI, C.A., CHEMALE JR., F. AND ARMSTRONG, R.A.

Bariloche

Simposio; VI South American Symposium on Isotope Geology, 4 p. CD Rom y abstract; 2008

INGEIS

U-Pb DETRITAL ZIRCON DATA FROM THE PALEOZOIC SIERRA GRANDE FORMATION, NORTH PATAGONIAN MASSIF, ARGENTINA Uriz, N. J. (1), Cingolani, C. A. (1, 2), Chemale, Jr. F.(3) and Armstrong, R. A.(4) (1)       División Científica de Geología-Facultad Ciencias Naturales y Museo, Universidad Nacional de La Plata, Paseo del Bosque s/n, (1900)-LA PLATA, ARGENTINA. nuriz@fcnym.unlp.edu.ar (2)       CIG (UNLP-CONICET): Centro de Investigaciones Geológicas, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, 1-644, (1900)-LA PLATA, ARGENTINA. (3)       Laboratorio de Geología Isotópica, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, Porto Alegre, Brazil. (4)       The Australian National University, Canberra 0200, ACT, Australia. Key words: U-Pb zircon ages, Sierra Grande Formation, North Patagonian Massif, Silurian – Devonian, provenance ABSTRACT The Sierra Grande Formation is a siliciclastic sedimentary unit with oolithic iron levels of economical importance which crops out in the Argentinean North Patagonian Massif. It was deposited within an open marine environment, with littoral to sub-littoral conditions. A Silurian-Lower Devonian age is assigned based on fossil content. It is mainly composed of medium to fine quartz arenites, wackes, silts, shales and conglomerate beds. In order to establish the source rocks for the Silurian-Devonian basin and also to constrain the sedimentation age, different U-Pb geochronological studies have been carried out on detrital zircons. The zircons have been studied with comparative morphology analysis using SEM images to asses the different population types. For dating using U-Pb isotopes in zircon detrital grains, the high resolution SHRIMP and LA-ICP-MS methodologies were used. The predominant obtained age groups are: Neoproterozoic (547–991 Ma), Cambrian (497-546 Ma) and Ordovician (443-495 Ma). All the analyzed samples also comprise Mesoproterozoic ages of about 1009 to 1382 Ma and smaller proportion Paleoproterozic (1641 to 2248 Ma) and Neo-Archean (2649-2657 Ma) ages. It is important to note that Silurian ages (428 and 440 Ma) were obtained from a group of zircon crystals, constraining the sedimentation age of the Sierra Grande basin to be not older than Middle Silurian. With these isotopic data it is possible to discuss the provenance of the Silurian-Devonian siliciclastic sedimentary cover of the North Patagonian Massif.