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Active or passive continental margin? Geochemical and Nd isotope constraints of metasediments in the backstop of a pre-Andean accretionary wedge in southernmost Chile (46°30′–48°30′S)

By
C. Augustsson
C. Augustsson
1
Geologisch-Paläontologisches Institut, Westfälische Wilhelms-Universität, Corrensstraβe 24, 481 49 Münster, Germany (e-mail: augustss@uni-muenster. de)
2
Zentrallaboratorium für Geochronologie, Institut für Mineralogie, Westfälische Wilhelms- Universität, Corrensstraβe 24, 481 49 Münster, Germany
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H. Bahlburg
H. Bahlburg
1
Geologisch-Paläontologisches Institut, Westfälische Wilhelms-Universität, Corrensstraβe 24, 481 49 Münster, Germany (e-mail: augustss@uni-muenster. de)
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Published:
January 01, 2003

Abstract

Provenance analysis of siliciclastic sedimentary rocks gives indications of the tectonic evolution and setting of source regions and the rocks contained in them. The composition of sedimentary rocks ideally reflects the nature of these regions, and only indirectly the tectonic setting of the basin where the erosional debris is deposited. This makes it possible to interpret Late Devonian to Early Carboniferous metasedimentary basement rocks of the Andes in southernmost Chile as having been deposited at a passive margin, despite geochemical indications of an active margin setting for the source rocks, and the position of the metasediments in the backstop of an accretionary wedge. Major and trace elements point to felsic source rocks from an active margin environment. The Nd model ages of 1170–1490 Ma indicate that the source rocks were part of an old continental crust in the Late Palaeozoic. The εNd(T) values range between −7 and −2. These characteristics, in combination with the regional geology, suggest that the geochemical signal is dominated by rocks formed at an active margin, which later acted as feeders for the sediments deposited in a passive-margin environment. If corroborated by research in progress this emphasizes the problem of deducing the tectonic setting of a depositional basin from provenance data.

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Contents

Geological Society, London, Special Publications

Tracing Tectonic Deformation Using the Sedimentary Record

T. McCann
T. McCann
Geologisches Institut, Bonn, Germany
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A. Saintot
A. Saintot
Instituut voor Aardwetenschappen, Vrije Universiteit, The Netherlands
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Geological Society of London
Volume
208
ISBN electronic:
9781862394568
Publication date:
January 01, 2003

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