Applications of Isotope Ratio Measurements in Geochemistry and Geochronology

9 Applications of Isotope Ratio Measurements in Geochemistry and Geochronology 

The isotope variation of boron isotopic composition in aqueous fluids in environments on the Earth s surface has been reviewed by You.185 The boron isotope composition (8nB) is expressed as a per mil (%o) deviation from the boron isotope standard NIST SRM 951  

Boron isotope ratios have been studied in ageothermal system from New Zealand (Ngawha) by MC-ICP-MS (Axiom with eight movable Faraday collectors, from Thermo Electron).188 The 8nB values range between — 3.1 %o and —3.9%e, which does not indicate any marine input into the system. A direct determination of boron isotopes (8nB) on natural and synthetic glass samples at %o precision at the ng level has been proposed using LA-ICP-MS with multiple electron multipliers.129 

An important application of isotope ratio mass spectrometry is geochronology, which is based on the decay of a radioactive nuclide (e.g., 87Rb,187 Re or 238U) to a stable isotope. The total number of daughter atoms Dt at time t is then equal to the sum of the daughter atoms formed due to the radioactive decay and the number of primordial daughter atoms (D0) at time t = 0  

Geochronological measurements (isochrone methodology) are based on the radioactive decay of the parent nuclide to the daughter nuclide using the fundamental Equation (8.8) for calculating the ages of minerals. 

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