Sedimentary provenance study of the post-Early Permian to pre-Early Cretaceous metasedimentary Duque de York Complex, Chile

Juan Pablo Lacassie,Francisco Herve,Barry Roser

doi:10.5027/andgeov33n2-a01

Abstract

The Duque de York Complex constitutes a post-Early Permian to pre-Early Cretaceous metasedimentary succession that crops out at the Madre de Dios and Diego de Almagro archipelagos along the Chilean Patagonian Andes. The petrography and geochemistry of sandstones and mudstones of this complex have been analyzed to characterize its source and depositional tectonic regime. Sandstone modal compositions are dominated by feldspar and, in similar but smaller proportions, by quartz. The mineralogical composition of the sandstones and mudstones is compatible with a low-grade sub-greenschist facies metamorphism. This did not affect significantly the geochemical compositions of these rocks. Nevertheless, the geochemical analyses reveal variable K+ enrichment, especially in the mudstones. Chemical Index of Alteration values of the sandstones and mudstones range between 58 and 71, indicating that the sediment underwent moderate chemical alteration in the source area or during transportation. Sandstone modal compositions are consistent with erosion of the plutonic roots of a magmatic arc. Geochemical provenance indices suggest a relatively evolved source, close in composition to typical continental magmatic arc granodiorite. Deposition of the detritus is most likely to have occurred within an active continental margin. Geochronological, petrographic, and geochemical similarities between the metasediments of the Duke de York Complex, the LeMay Group (Western Antarctica) and the Permian-Late Triassic Rakaia terrane (New Zealand) suggest a common geodynamic set-up for these three successions. This likely constituted an extensive late Paleozoic-early Mesozoic active continental margin, possibly along the Antarctic sector of Gondwana.

Highlights

The Duque de York Complex (DYC) is a postEarly Permian to pre-Early Cretaceous metasedimentary succession consisting of sandstones, mudstones, and subsidiary conglomerates
The above petrographic, geochemical and geochronological similarities between the DYC, Rakaia and LeMay Group (LMG) successions show that they were derived from igneous sources of similar compositions, and suggest that they were deposited along the same active continental margin
The arc was likely located at an active continental margin

Summary

INTRODUCTION

The Duque de York Complex (DYC) is a postEarly Permian to pre-Early Cretaceous metasedimentary succession consisting of sandstones, mudstones, and subsidiary conglomerates It crops out in the Madre de Dios and Diego de Almagro archipelagos (49-52oS), at Ramirez and Contreras Islands and at Desolación Island, along the Chilean Patagonian Andes (Fig. 1). All the DYC samples plot in the P3 field of felsic igneous provenance (Fig. 7a) typical of rocks derived from a silicic crystalline (plutonic-metamorphic) terrain with a lesser intermediateacid volcanic component (Roser and Korsch, 1988). SiO -Na O/K O plot of figure 5b all the DYC samples plot in the active continental margin (ACM) field, with a marked linear trend and clear differentiation between sandstones and mudstones This pattern is typical of large ACM accretionary complexes such as the Franciscan and Torlesse terranes (Roser and Korsch, 1986). On the major element-based comparative diagram of figure 12 the DYC sandstones plot exclusively in the P3 field (felsic provenance), with less scatter than on the previous discrimination plots

DISCUSSION

CONCLUSIONS