Argon argon dating
The quantity of potassium in a rock or mineral is variable proportional to the amount of silica present.
Therefore, mafic rocks and minerals often contain less potassium than an equal amount of silicic rock or mineral.
The isotopes the KAr system relies on are Potassium (K) and Argon (Ar).
Potassium, an alkali metal, the Earth's eighth most abundant element is common in many rocks and rock-forming minerals.
Dalrymple, referring to metamorphism and melting of rocks in the crust, has commented: "If the rock is heated or melted at some later time, then some or all the In a recent study 128 Ar isotopic analyses were obtained from ten profiles across biotite grains in high-grade metamorphic rocks, and apparent Ar-Ar "ages" within individual grains ranged from 161Ma-514Ma.
is known to cause grave problems in regional geochronology studies.
Second, the sample is irradiated along with a standard of a known age. A major advantage of the argon-argon method is that the sample can be heated incrementally.
This process, known as "step heating", provides additional information on the age of the sample.
If so, then the K-Ar and Ar-Ar "dating" of crustal rocks would be similarly questionable.
When muscovite (a common mineral in crustal rocks) is heated to 740°-860°C under high Ar pressures for periods of 3 to 10.5 hours it absorbs significant quantities of Ar, producing K-Ar "ages" of up to 5 billion years, and the absorbed Ar is indistinguishable from radiogenic argon ( In other experiments muscovite was synthesized from a colloidal gel under similar temperatures and Ar pressures, the resultant muscovite retaining up to 0.5 wt% Ar at 640°C and a vapor pressure of 4,000 atmospheres.
I will hopefully soon find time to put something proper in it's place rather than just deleting things and leaving the butchered article.