IMPROVING GEOCHRONOLOGY FOR PRECISE GEOHISTORY DETERMINATION

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However, the Holmes-Houtermans model was superseded by the Stacey and Kramers model, simply because the former was not adequate to explain the Pb isotopic data available from the numerous ongoing research studies. Ironically, the number of ore deposits that meet these stringent requirements of the single-stage model is quite small.

Of course, one of the main problems with automated software is that if users do not understand and appreciate what the software does and what the quality of the input data should be, then the resultant recorded output will not be all it is supposed to be, and thus as good as others are expecting it to be! Thus the common Pb of a region may not become the initial Pb in a rock or mineral inherited from its source within that region. Meanwhile, the other grains lost varying amounts of radiogenic Pb so they plot on a straight-line chord, labelled as discordia A on Fig.

U-Pb zircon geochronology - Unraveling such complications which, depending on their maximum lead-retention temperature, can also exist within other minerals generally requires in situ micro-beam analysis via, say, ion microprobe or laser. As part of the development of the Re-Os method in the John de Laeter Centre, we have recently determined a Re-Os age for molybdenite from the Central Bore gold prospect within the Yamarna terrain, in the eastern Yilgarn craton Fuller et al.

15--Luminescence Geochronology (LIPI Indonesia lectures 2013)
Geochimica et Cosmochimica Acta 164: 481—501. Of course, the ages of these standard and primary reference materials must first be determined by U-Pb and other radioisotope dating methods, which involves the same unknown error factors and unverifiable assumptions in choosing their agreed ages, so these are not independent objective standards at all. We interpret this age as the termination age of the Emeishan flood basalts. U-Pb dating of zircons from ash beds interstratified with fossiliferous strata has become an important means of radiometrically calibrating the chronostratigraphic time scales derived by biostratigraphic zonation. The majority of such lines may converge to meet in a single point, which yields the initial Pb isotope composition of that terrain that is, by his interpretation. The time of separation from the reservoir can supposedly be calculated using the isochron that starts at 3. For zircons, which are claimed to contain very little common Pb, the 204Pb signal is overwhelmingly dominated by isobaric interference of 204Hg. Indeed, apart from common Pb incorporated in zircons from their host rock environments at the time of their formation, common Pb in zircons can originate from several other sources—sub-microscopic mineral inclusions, Pb added to the zircons during or after alteration, Pb physically trapped in microfractures, and laboratory Pb from polishing compounds, aerosols, and coating materials. The sequence of events when subsequent mixing of Pb isotopes would have occurred is also radically different. In the Stacey and Kramers 1975 two-stage Pb isotopic evolution model a major disturbance of the earth occurred at 3.

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Oznake: U-Pb, zircon, geochronology