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School of Geosciences, Queen’s University of Belfast, Belfast BT7 1NN, UK
A wide diversity of techniques is now available to help constrain the timing and duration of fluid flow events and fluid-rock interactions in sedimentary basins. Dating methods in rocks traditionally focus on the use of minerals that contain radiogenic isotopes (U-Pb, Pb-Pb, K-Ar, Rb-Sr in particular). I do not intend to dwell on this approach as it is covered adequately elsewhere (e.g. Faure 1986), but it is worthwhile emphasizing that certain phases that are commonly precipitated during diagenesis in sedimentary basins are suitable for such techniques (see below). The range of techniques summarized below were mostly presented in a Queen’s University Geofluids Group International Seminar on Dating of Fluid Flow, incorporated within the Geofluids II conference held at Belfast in March 1997.
There is a limited range of parameters within rocks or minerals which change with time, and which can therefore be used to deduce an age of formation for epigenetic mineral phases. The processes of radioactive decay yield predictable quantities of daughter products (radiometric dating) and particles whose pathways can be observed and whose annealling behaviour is predictable (fission track analysis). In addition we can measure the effects of movement over the Earth’s surface relative to her magnetic field along a well-known polar-wander curve (palaeomagnetism). In some cases we can measure a record of contemporary seawater chemistry that can be related to a well established database of changing stable isotope composition. Furthermore, in young rocks we can measure the consequences of other physico-chemical reactions that are kinetically controlled (electron spin resonance).
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