Re-Os

The Rhenium-Osmium (Re-Os) system is a chronometer and geochemical tracer that has been successfully applied to a range questions in planetary and Earth sciences. The technique has provided much-needed age constraints for a wide variety of problems such as: planetary accretion and differentiation; tracing mantle evolution through time; dating sedimentary rocks; areas of economic geology such as ore genesis and hydrocarbon generation and migration. The Re-Os system differs from other radiogenic isotope systems in that Re and Os display chalcophilic, organophilic and siderophilic behavior with a very long half-life of ~42 Gyr (beta decay of ¹⁸⁷Re to ¹⁸⁷Os). Together, these factors make the Re-Os system a unique tool for interrogating the geological record of the Earth and planetary materials.

Advances in analytical procedures and instrument development over the past 25 years have improved the reliability and accuracy of the Re-Os geochronometer with many laboratories capable of generating ages with total uncertainties <0.5%.

Mantle and high-temperature geochemistry
By coupling the Re-Os system with data from other Platinum Group Elements the techniques is routinely used to study the geochemical evolution of the terrestrial planets. Highlights in this area of research include, but are not limited to; exploring the links between continental crust growth and mantle melting; constraining diamond formation events; and elucidating the processes driving plume magmatism and forming chemical heterogeneities in the mantle.

Crustal sulfides
Dating of molybdenite and other sulfides (e.g., pyrite, arsenopyrite, bornite, marcasite) using the Re-Os geochronometer has been highly successful in providing precise and accurate age constraints on ore formation as well as associated tectonic events (e.g., fluid-flow and metamorphism) from the early Archean to younger than 1 Ma.

Sedimentary rock geochronology
Organic-rich strata are often greatly enriched in Re and Os thus providing the foundation for Re-Os sedimentary rock geochronology. The Re-Os geochronometer has shown great promise in dating successions lacking suitable material for traditional geochronology techniques such as Ar-Ar or U-Pb zircon geochronology. Target lithologies such as black shales and organic-rich carbonates are often coincident with events such as mass extinctions, which have been dated using Re-Os geochronology. Additionally, application of the Re-Os sedimentary geochronometer has helped refine the temporal framework of the Proterozoic “Snowball Earth” events and the tempo of eukaryotic evolution.

Hydrocarbon generation
Concentrations of Re and Os in source rocks and related hydrocarbons can be much higher than average crustal rocks. As such, the Re-Os geochronometer may yield age constraints on deposition of the source rock as well as hydrocarbon generation and migration ages. Coupling these ages with reservoir rock geochronology, petrography, and organic geochemistry can improve our understanding of the evolution of petroleum basins thereby greatly reducing uncertainties associated with hydrocarbon exploration.

Os isotopes as a paleoseawater and paleoweathering proxy
In addition to geochronological data, Os isotope data from sedimentary rocks can be used to track the changing redox state of the oceans from the Archean through to the modern. With a seawater residence time of ~10 kyr, Os isotopes from sedimentary strata can yield high-resolution chemostratigraphy that can further our understanding of processes driving OAEs; ice sheet advance and retreat; the transition from lacustrine to marine environments and detecting extraterrestrial impact events.