U pb dating minerals
The common pre-conditions for application of these methods are: (1) the source areas are characterized by rocks with different tectonic histories recorded by distinctive crystallization and cooling ages, and (2) the source rocks contain the selected mineral.
Whereas zircons occur in most magmatic, metamorphic, and sedimentary rocks, other minerals, such as apatite, monazite, and white mica, are less abundant.
Geochronology and thermochronology applied to detrital minerals such as zircons, monazites, white micas, and apatites have received increasing attention in the past decade for their unique power to determine the timing of crystallization and multiple tectono-thermal events, with relevance for sediment provenance, tectonic processes, and erosion.
Recent breakthroughs in multi-dating (applying different geochronologic and thermochronologic systems to the same detrital grains) allow for unprecedented levels of detail in provenance and tectonic studies of detrital sediments.
This is consistent with the several lines of impeccable evidence that radioisotope decay rates were grossly accelerated during the year-long biblical global Flood cataclysm, and then the decay rates decelerated.
That we may still be detecting the radioisotope decay rates decelerating is likewise consistent with the Flood occurring only about 4300 years ago.
By 1971 the direct counting experiments had provided U half-life values with small uncertainties which ever since have been the recommended values used in all U-Pb age calculations. Extreme U and Pb isotope variations produced by disequilibrium in decay chains of 238U and 232Th are found in calcite, opal/chalcedony, and Mn-oxides occurring as secondary mineral coatings in the unsaturated zone at Yucca Mountain, Nevada.These very slowly growing minerals (mm my-1) contain excess 206Pb and 208Pb formed from excesses of intermediate daughter isotopes and cannot be used as reliable 206Pb/238U geochronometers.All the geological age comparison studies have utilized those recommended values, in spite of the admitted philosophical circularity involved. And the critical reviews and reevaluations have all converged on these same recommended values because of the meticulous care taken in the 1971 direct counting experiments, which then gave those experimental results the dominant weight in the calculation of mean values.