PROVENANCE ANALYSIS OF ORDOVICIAN CLASTIC SEQUENCES OF THE SAN RAFAEL BLOCK, CENTRAL ARGENTINA, WITH EMPHASIS IN THE PONON TREHUE FORMATION: IMPLICATIONS IN WESTERN GONDWANA.

ABRE, P.; CINGOLANI, C.A.; ZIMMERMANN, U.; CAIRNCROSS, B.; CHEMALE JR., F.

GONDWANA RESEARCH

ELSEVIER SCIENCE BV

Año: 2009

1342-937X

PROVENANCE ANALYSIS OF ORDOVICIAN CLASTIC SEQUENCES OF THE SAN RAFAEL BLOCK, CENTRAL ARGENTINA WITH EMPHASIS IN THE PONON TREHUE FORMATION: IMPLICATIONS IN WESTERN GONDWANA. Abre, P.1*; Cingolani, C.2; Zimmermann, U.1, Cairncross, B.1 and Chemale Jr., F.3 1 Department of Geology, University of Johannesburg, PO Box 524, AucklandPark 2006, Johannesburg, South Africa, e-mail: paulinabre@yahoo.com.ar PO Box 524, AucklandPark 2006, Johannesburg, South Africa, e-mail: paulinabre@yahoo.com.ar PO Box 524, AucklandPark 2006, Johannesburg, South Africa, e-mail: paulinabre@yahoo.com.ar PO Box 524, AucklandPark 2006, Johannesburg, South Africa, e-mail: paulinabre@yahoo.com.ar 2 Centro de Investigaciones Geológicas, CONICET-Universidad Nacional de La Plata, Calle 1 n° 644, B1900TAC La Plata, Argentina, e-mail: ccingola@cig.museo.unlp.edu.ar 3 Laboratorio de Geología Isotópica, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil. 1          ABSTRACT             The Ponón Trehué Formation is the only sedimentary sequence known to record a primary contact with the basement of the Cuyania terrane, in its southwards extension named the San Rafael block. Petrographic and geochemical data indicate the contribution from a dominantly upper continental crustal component (including a minor recycled sedimentary component), and a subordinated depleted component. Nd-isotopes indicate an average εNd of -4.6, average ƒSm/Nd -0.36 and average TDM 1.47 Ga. The low recycling along with the narrow range of εNd values are in agreement with a localized source. Pb-isotopes tend to link the unit to sources with high 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios (average 19.15, 15.69 and 38.94 respectively), which are known from Gondwanan areas. Detrital zircon dating from the Ponón Trehué Formation constrains the provenance to have been only from Mesoproterozoic rocks, and more precisely from a Grenvillian-age source. The Pavón Formation instead show a more widespread distribution of detrital zircon ages comprising two Mesoproterozoic peaks as well as Palaeoproterozoic and Neoproterozoic detrital grains. The combination of the different provenance approaches applied to understand the contribution of detritus to the Ponón Trehué Formation is compared with data available from the literature and the newly acquired detrital zircon data from the Pavón Formation. * Corresponding author: +27-727195504; +54-221-4215677 Keywords: Cuyania terrane, provenance, geochemistry, isotope geochemistry, detrital zircon dating, Ordovician Ponón Trehué and Pavón Formations.