K–Ca dating
Radiometric dating method used in geochronology / From Wikipedia, the free encyclopedia
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Potassium–calcium dating, abbreviated K–Ca dating, is a radiometric dating method used in geochronology. It is based upon measuring the ratio of a parent isotope of potassium (40
K) to a daughter isotope of calcium (40
Ca).[1] This form of radioactive decay is accomplished through beta decay.
Calcium is common in many minerals, with 40
Ca being the most abundant naturally occurring isotope of calcium (96.94%),[2] so use of this dating method to determine the ratio of daughter calcium produced from parent potassium is generally not practical. However, recent advancements in mass spectrometric techniques [e.g., thermal ionization mass spectrometry (TIMS) and collision-cell inductively-coupled plasma mass spectrometry (CC-ICP-MS)] are allowing radiogenic Ca isotope variations to be measured at unprecedented precisions in an increasing variety of materials,[3] including high Ca minerals (e.g., plagioclase, garnet, clinopyroxene)[4] and aqueous (e.g., seawater and riverine) samples.[5] In earlier studies, this technique was especially useful in minerals with low calcium contents (under 1/50th of the potassium content)[2] so that radiogenic ingrowth of 40-Ca could be more easily quantified. Examples of such minerals include lepidolite, potassium-feldspar, and late-formed muscovite or biotite from pegmatites (preferably older than 60 million years ago). This method is also useful for zircon-poor, felsic-to-intermediate igneous rocks, various metamorphic rocks, and evaporite minerals (i.e. sylvite).[6][7]