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LI Tie-jun.Progress in the Application of Oxygen Isotopes in the Study of Petrogenesis[J].Rock and Mineral Analysis,2013,32(6):841-849
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Progress in the Application of Oxygen Isotopes in the Study of Petrogenesis
Received:June 03, 2013  Revised:June 21, 2013
DOI:
Key words: oxygen isotope  progress in analytical method  granite  metamorphic rock  understanding on genesis
Author NameAffiliation
LI Tie-jun Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 
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Abstract:
      Since different types of rocks on the earth have different oxygen isotope compositions, they can be used to discuss the origins of various rocks and it has become a powerful tool for studying petrology. For example, determination on whether the granite was derived from metasedimentary or metavolcanic rocks based on its oxygen isotope compositions can be established. For a complex massif, if rocks of different stages have significantly different oxygen isotope compositions, the determination that they have been assimilated by other materials during evolution of magmas, because there should be no evident oxygen isotope fractionation (less than 0.3‰) during chemical differentiation of magmas from mafic to felsic composition can be made. Analytical techniques of oxygen isotope compositions include traditional BrF5, laser BrF5 and ion microprobe and they reflect the development from bulk analysis to microanalysis. Granites (rhyolites) and metamorphic rocks are used as examples to show that understandings of the origins of rocks have improved with the development of oxygen isotope composition analyses. For both granites (rhyolites) and metamorphic rocks, the ion microprobe in-situ analysis of oxygen isotope composition gain new insights into the origins of rocks. Based on traditional BrF5 method, the Suzhou granite was suggested to have two different origins, a low-δ18O origin and a normal δ18O origin. However, δ18O values of magmatic zircons acquired by laser BrF5 analysis are 4.92‰±0.26‰, confirming that the Suzhou granite has a low-δ18O magma origin that was derived from the crust. Similarly, the proposal drawn from traditional BrF5 analysis on whole rock and rock-forming minerals cannot explain the intergranular and intraparticle oxygen isotope variations in the low-δ18O rhyolites from the Yellowstone plateau which can only be gained by the ion microprobe method. Based on laser BrF5 analysis, the metamorphic rocks of the Sulu orogenic belt were considered to have acquired their extremely negative δ18O values during the formation of their protoliths in the Neoproterozoic. However, recent ion microprobe in-situ analysis of oxygen isotope compositions on zircon demonstrates that the Sulu metamorphic rocks acquired their extremely negative δ18O values during the ultrahigh pressure metamorphism in the Triassic. The study of distribution of oxygen isotopic composition in single gain is a new trend in the future.