Carita Augustsson

TL;DR: In this article, detrital zircon spectra were used to trace the evolution of the South American continental crust through several Proterozoic and Paleozoic orogenic cycles.

TL;DR: In this article, detrital zircon spectra were used to trace the evolution of the South American continental crust through several Proterozoic and Paleozoic orogenic cycles.

TL;DR: 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 as discussed by the authors.

Abstract: Quartz, the most common mineral in most sandstones, rarely is used in provenance studies. This study demonstrates the provenance-discriminatory potential of combining cathodoluminescence (CL) color wavelength spectra of quartz with morphology and in situ U-Pb ages of zircon. The Cambrian Meson Group in northwestern Argentina is used for the test of this combined methodology, because it is composed of nonmetamorphosed sandstones with > 90% quartz and a dominance of zircon among the heavy minerals. Correlation of the results from the two methods is evident: (1) both CL spectra typical for bright-luminescent quartz (red to blue; > 90%) and oscillatory zircon growth zoning (80–90%) indicate a dominance of magmatic detritus. (2) Upsection, diminishing input from euhedral 510–600 Ma zircons (70% at the base) correlates with lower amounts of volcanic quartz (40% red and violet grains at the base). Instead, plutonic quartz and abraded zircons of 550–700 Ma age prevail. The data point to the occurrence of a (nearly) synsedimentary volcanic phase, which has not been known previously. Furthermore, initial short transportation paths from nearby magmatic bodies (100–200 km) can be assumed, because of the low degree of grain abrasion and an age correlation with magmatic bodies in the region, such as the Santa Rosa de Tastil batholith, here dated at 513 +4/−5 Ma. The proximity to the source area at an initial stage indicates first-cycle sand. The maturity was probably reached by intense chemical weathering. The upsection-diminishing young, volcanic input indicates erosion of the volcanic source within a time period of millions of years. At that stage, mainly up to 1000-km-long coast-parallel transport from the Sierras Pampeanas in the south fed the depositional basin. The change in—and expansion of—the main source areas record a change to production of multicycle sand. Hence, the maturity was partly caused by sedimentary recycling. More generally, the provenance-discriminative effect of the CL of quartz, which has been doubted by some researches, can be confirmed. Therefore, the results imply that both quartz and zircon should be taken into account in provenance studies of quartz arenites.

TL;DR: In this paper, a provenance study of late Palaeozoic metasediments of the Eastern Andean Metamorphic Complex (EAMC) along the south Patagonian proto-Pacific margin of Gondwana is reconstructed.