Lava dating info
However, geologists have found that various eruptive stages of the same volcano often extrude lavas exhibiting somewhat different mineral compositions, particularly if an extensive period of time separated the eruptions.
Evidence of this type led them to look into the possibility that a single magma might produce rocks of varying mineral content. Bowen discovered that as magma cools in the laboratory, certain minerals crystallize first.
This calls the whole radiometric dating scheme into serious question.
Geologists assert that older dates are found deeper down in the geologic column, which they take as evidence that radiometric dating is giving true ages, since it is apparent that rocks that are deeper must be older.
Here I want to concentrate on another source of error, namely, processes that take place within magma chambers.
If you're seeing this message, it means we're having trouble loading external resources on our website.The potassium-argon method is attractive for dating volcanics since it can be applied to rocks of Pleistocene age and older, thus encompassing important periods of general volcanic activity.However it has been found that dates obtained on whole rocks and on included minerals frequently show gross discordances.A number of processes could cause the parent substance to be depleted at the top of the magma chamber, or the daughter product to be enriched, both of which would cause the lava erupting earlier to appear very old according to radiometric dating, and lava erupting later to appear younger.The following quote from The Earth: An Introduction to Physical Geology by Tarbuck & Lutgens, pp.