Isotopes - Geochemical Tracers

An additional and related question to address is where exactly is the CO₂ is coming from — the subducting slab, mantle wedge or upper most crust? Fortunately this puzzle can be sorted out using isotope geochemistry, since the different reservoirs have distinct carbon and helium isotope ratios. The ratios of ³He to ⁴He and ¹³C to ¹²C in a sample serve as a diagnostic indicator of a volatile’s provenance. We will be undertaking isotope measurements as part of this work (link to ‘in the lab) using instruments called mass spectrometers. These devices are able to discriminate between atoms based upon their mass: hence, they are used to measure isotope ratios.