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Dating of movement on fault systems is also possible with the Ar method.Different minerals have different closure temperatures; biotite is ~300°C, muscovite is about 400°C and hornblende has a closure temperature of ~550°C.in a sample of a known age can indicate a full or partial melt in the thermal history of the area.Reliability in the dating of a geological feature is increased by sampling disparate areas which have been subjected to slightly different thermal histories.Ar) dating is a radiometric dating method invented to supersede potassium-argon (K/Ar) dating in accuracy.The older method required splitting samples into two for separate potassium and argon measurements, while the newer method requires only one rock fragment or mineral grain and uses a single measurement of argon isotopes. The sample is then degassed in a high-vacuum mass spectrometer via a laser or resistance furnace.Extraneous argon may be incorporated into a rock depending on conditions during cooling.Commonly, gases are not fully removed from magma at the time of crystallization, and so not all of the measured argon will have resulted from Ar include chilled basalts and inclusions of older xenolithic material - such samples should be avoided.
Unless some other process is active at the time of cooling, this is a very good assumption for terrestrial samples.
Both flame photometry and mass spectrometry are destructive tests, so particular care is needed to ensure that the aliquots used are truly representative of the sample.
Argon-argon dating is a similar technique which compares isotopic ratios from the same portion of the sample to avoid this problem.
Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! It is based on measurement of the product of the radioactive decay of an isotope of potassium (K), which is a common element found in many materials, such as micas, clay minerals, tephra, and evaporites, into argon.
Potassium-argon dating or K-Ar dating is a radiometric dating method used in geochronology and archeology.