Re-Os isotopes in orogenic peridotite massifs in the Eastern Alps, Austria

The Re-Os and Sm-Nd isotopic systematics of polymetamorphic massif peridotite bodies, which have been described as ophiolites, are examined. The serpentinized mantle rocks from different tectonic units of the Eastern Alps reveal that Os isotopes are robust and provide information that field studies, petrographic and major and trace element studies do not. Presumed Paleozoic (e.g., Kraubath and Hochgrössen) and Mesozoic (e.g., Reckner Complex) bodies have uniform ¹⁸⁷Os/¹⁸⁸Os ratios that are slightly higher than, but within the range of, abyssal peridotites, which are presumed to represent the depleted mid-ocean ridge basalt source mantle (DMM). One serpentinite from the Penninic unit yields ¹⁸⁷Os/¹⁸⁸Os much lower than DMM. This mantle rock must have had a source in a long-term Re-depleted reservoir of the upper mantle. Although our understanding of the Re-Os isotope system of upper mantle reservoirs is still limited, this system can be used to help constrain the tectonic evolution of diverse terrains.