reos

ReOs, in geochemistry and geochronology, refers to the rhenium-osmium isotopic system used for dating geological materials. The shorthand often appears as Re-Os dating or the Re-Os isotope system, and it is especially applied to sulfide minerals and related rocks.

The dating principle rests on the radioactive decay of rhenium-187 to osmium-187. The decay has a very long half-life, about 41 billion years, which allows dating of events in the Earth’s history on a timescale comparable to the age of the solar system. By measuring the ratios of 187Re to 187Os and comparing them to stableOs isotopes (such as 188Os), scientists construct an isochron that yields an age for the system, ideally independent of the initial Os composition.

Re-Os dating is widely used in sulfide minerals such as molybdenite (MoS2), pentlandite, and other sulfide phases found in ore deposits, as well as in certain meteorites and mantle-derived rocks. It provides information about the timing of ore formation, mantle-crust differentiation, and other geological processes. In practice, dating relies on precise isotope measurements, typically performed with mass spectrometry, and often employs isochron or model-age approaches to interpret the data.

Advantages of the Re-Os system include a high closure temperature in sulfides and its relative resistance to disturbance by later geological events. Limitations include the need for well-preserved, closed-system samples, potential mobility of Re and Os during alteration, and uncertainties in initial Os concentrations. Accurate dating also depends on meticulous laboratory work to measure very small isotope ratios.

See also: isotopic geochronology, 187Re-187Os decay, molybdenite dating, sulfide minerals, mass spectrometry.