EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Magmas of the El Quemado Complex (Chon Aike Silicic Igneous Province, Patagonia): Elevated Oxygen Isotope Signatures Across Space and Time

Michelle Foley, Benita Putlitz, Lukas Baumgartner, Zoé Guillermin, and Florence Bégué
Michelle Foley et al.
  • University of Lausanne, Institute of Earth Sciences, Lausanne, Switzerland (

The generation and source of ~230,000 km3 of total erupted volume of the predominately silicic (>90 %; Pankhurst et al., 2000) magmas which comprise the Jurassic Chon Aike Large Silicic Igneous Province (CASP) of Southern Patagonia is currently debated. In this study, we conducted a widespread sampling of multiple eruptive units, primarily ignimbrites and minor rhyolitic flows, along the Eastern Andean front (~47°S to 49°S), owning to the third and youngest eruptive episode of the CASP (El Quemado Complex; EQC). To determine the magmatic source and potential role of a significant crustal contribution proposed in the generation of these magmas, we analyzed the in-situ δ18O composition of both quartz and zircon by SIMS. We combined these data with LA-ICP-MS U/Pb analyses on single zircon crystals to characterize the potential for changing oxygen isotopic values through time and space within the EQC units along this ~230 km long transect.

The northern-most units sampled have the lightest average δ18O (relative for the EQC) analyzed in zircon and quartz (7.7 and 10.4 ‰, respectively). Oxygen isotope values increase towards the South, with the highest δ 18O values previously reported in El Chaltén, reaching up to 10.1 ‰ for zircon and 12.5 ‰ for quartz (Seitz et al., 2018). Eruptive units from the same locality appear to be homogeneous in their oxygen isotopic composition.

U/Pb zircon ages for the EQC range overall from ~148 to 155 Ma, though no obvious trend from North to South in zircon crystallization ages is noticeable. Multiple inherited zircon cores (at ~230, 460, 500, 1300 Ma) with Jurassic magmatic overgrowths were discovered. Isotopic compositions of these inherited magmatic cores are variable in their δ18O values throughout time. However, and more significantly, most of these inherited cores record high δ 18O values, with the highest value at 9.5 ‰ measured for a ~460 Ma core. These high values measured within inherited cores are found at all locations sampled for the EQC.

The δ18O values of the EQC rocks are significantly higher than what would be expected for silicic magmas formed by simple closed-system fractionation from any mantle-derived melt (6­-7‰; Valley, 2003). Thus, our oxygen isotope data support significant input of crustal material - of either a sedimentary origin or from hydrothermally altered crust - to generate these ignimbrites and rhyolites with elevated δ18O values all along this transect.

How to cite: Foley, M., Putlitz, B., Baumgartner, L., Guillermin, Z., and Bégué, F.: Magmas of the El Quemado Complex (Chon Aike Silicic Igneous Province, Patagonia): Elevated Oxygen Isotope Signatures Across Space and Time, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21265,, 2020