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Journal of the Geological Society; 2006; v. 163; issue.6; p. 983-995;
DOI: 10.1144/0016-76492005-149
© 2006 Geological Society of London

Original Article

Provenance of late Palaeozoic metasediments of the SW South American Gondwana margin: a combined U–Pb and Hf-isotope study of single detrital zircons

CARITA AUGUSTSSON1,2, CARSTEN MÜNKER2,3, HEINRICH BAHLBURG1 & C.MARK FANNING4

1 1Geologisch–Paläontologisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 24, 48149 Münster, Germany (e-mail: augustss@uni-muenster.de)
2 2Zentrallaboratorium für Geochronologie, Institut für Mineralogie, Westfälische Wilhelms-Universität, Corrensstrasse 24, 48149 Münster, Germany
3 3Mineralogisch–Petrologisches Institut, Universität Bonn, Poppelsdorfer Schloss, 53115 Bonn, Germany
4 4Research School of Earth Sciences, The Australian National University, Mills Road, Canberra, A.C.T. 0200, Australia

Combined U–Pb and Lu–Hf isotope measurements of single detrital zircon grains in Carboniferous metasediments from Patagonia delineate the source areas of the sediments. The detritus, represented by four metasandstone samples, was deposited prior to onset of subduction in Late Carboniferous time along the south Patagonian proto-Pacific Gondwana margin. A broad series of detrital zircon age peaks (0.35–0.7 Ga, 0.9–1.5 Ga) and a large spread (0.3–3.5 Ga) in the age spectra require numerous sources. A fifth metasediment was deposited after the onset of subduction. This syncollisional sample shows two distinct U–Pb age peaks at c. 290 Ma and 305 Ma. This points to a few sources only (Patagonia, West Antarctica). Initial Hf-isotope compositions of selected U–Pb dated zircons from the Carboniferous metasediments reveal zircon protoliths originating from both recycled crust and juvenile sources ({varepsilon}Hf(T=0.4–3.5Ga)=–14 to +12). A comparison with crustal compositions of possible source areas indicates that the detritus mainly originated from the interior of Gondwana (Extra-Andean Patagonia, the Argentine Sierra de la Ventana, southernmost Africa, East Antarctica), as well as northern Chile and northwestern Argentina. The sediment transportation paths are consistent with an autochthonous palaeogeographical position of Patagonia with respect to Gondwana in Carboniferous time.




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