Abstract
Research subject and methods . The work is based on a comparative study of the data obtained by the authors and those published in literature on U-Pb ID-TIMS and “in-situ” isotopic examination of zircons extracted from a number of Ural geological objects (volcanogenic rocks of the Mashak Formation of the Bashkir Meganticlinorium, granitoid massifs of the Northern part of the Uraltau Ridge, Kumba gabbro-norite massif Platinum-bearing belt), as well as Australian diorites and South African mafic xenoliths. Results. Since the methods of ID-TIMS (ID-MC-ICP/MS) and SIMS dating of zircon are fundamentally different, their advantages and disadvantages should be taken into account when solving the corresponding geochronological problems. Conclusions . U-Pb ID-TIMS (ID-MC-ICP/MS) methods allow the analysis of individual crystals, as well as their fragments, with an unprecedented level of uncertainty concerning age dating (up to 0.05%). The main drawback of the U-Pb SIMS method consists in a significant error when dating U-Pb (2–5%), which might disguise possible Pb losses (and / or U-contribution) and lead to appearance of artifacts when interpreting U-Pb zircon data. This, in turn, leads to the identification of non-existent stages of magmatism, metamorphism, false ideas about the length of evolutionary processes, etc. The use of U-Pb SIMS methods should be limited to solving geological problems that do not require a high accuracy of dating (i.e., allowing rough estimation) but involving the need to study a large number of samples and corresponding zircon grains. Such problems arise during examination of clastic material in the process of reconstructing sources and geological conditions of sedimentary basin formation. U-Pb SIMS methods can be used for studying the heterogeneity of zircon crystals having a complex structure under preliminary selection of materials for subsequent high-precision dating using U-Pb ID-TIMS and / or ID-MC-ICP/MS methods. The expansion of the number of laboratories using these high-precision methods seems to be the most important direction in the development of Russian isotope geochronology.
Highlights
The work is based on a comparative study of the data obtained by the authors and those published in literature on U-Pb ID-TIMS and “in-situ” isotopic examination of zircons extracted from a number of Ural geological objects, as well as Australian diorites and South African mafic xenoliths
U-Pb ID-TIMS (ID-MC-ICP/MS) methods allow the analysis of individual crystals, as well as their fragments, with an unprecedented level of uncertainty concerning age dating
The main drawback of the U-Pb SIMS method consists in a significant error when dating U-Pb (2–5%), which might disguise possible Pb losses and lead to appearance of artifacts when interpreting U-Pb zircon data
Summary
Исследования выполнены в рамках темы No АААА-А18-118053090044-1 государственного задания ИГГ УрО РАН. (2020) U-Pb (ID-TIMS) geochronological method and “in-situ” SIMS zircon dating: possibilities and constrains. The use of U-Pb SIMS methods should be limited to solving geological problems that do not require a high accuracy of dating (i.e., allowing rough estimation) but involving the need to study a large number of samples and corresponding zircon grains. Such problems arise during examination of clastic material in the process of reconstructing sources and geological conditions of sedimentary basin formation. The expansion of the number of laboratories using these high-precision methods seems to be the most important direction in the development of Russian isotope geochronology
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