4.4 billion years of crustal maturation: oxygen isotope ratios of magmatic zircon

• Published in: Contributions to mineralogy and petrology Vol. 150; no. 6; pp. 561 - 580
• Main Authors: Valley, J. W., Lackey, J. S., Cavosie, A. J., Clechenko, C. C., Spicuzza, M. J., Basei, M. A. S., Bindeman, I. N., Ferreira, V. P., Sial, A. N., King, E. M., Peck, W. H., Sinha, A. K., Wei, C. S.
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer Nature B.V 01.12.2005
• Subjects: Earth; Geology; High temperature; Igneous rocks; Isotopes; Low temperature; Mineralogy; Mountains; Oxygen; Oxygen isotopes; Petrology; Recycling; Sediments; Surface water
• ISSN: 0010-7999; 1432-0967
• DOI: 10.1007/s00410-005-0025-8

Analysis of delta 18O in igneous zircons of known age traces the evolution of intracrustal recycling and crust-mantle interaction through time. This record is especially sensitive because oxygen isotope ratios of igneous rocks are strongly affected by incorporation of supracrustal materials into melts, which commonly have delta 18O values higher than in primitive mantle magmas. This study summarizes data for delta 18O in zircons that have been analyzed from 1,200 dated rocks ranging over 96% of the age of Earth. Uniformly primitive to mildly evolved magmatic delta 18O values are found from the first half of Earth history, but much more varied values are seen for younger magmas. The similarity of values throughout the Archean, and comparison to the composition of the "modern" mantle indicate that delta 18O of primitive mantle melts have remained constant (+-0.2 0/00) for the past 4.4 billion years. The range and variability of delta 18O in all Archean zircon samples is subdued (delta 18O(Zrc)=5-7.5 0/00) ranging from values in high temperature equilibrium with the mantle (5.3+- 0.3 0/00) to slightly higher, more evolved compositions (6.5-7.5 0/00) including samples from: the Jack Hills (4.4-3.3 Ga), the Beartooth Mountains (4.0-2.9 Ga), Barberton (3.5-2.7 Ga), the Superior and Slave Provinces (3.0 to 2.7 Ga), and the Lewisian (2.7 Ga). No zircons from the Archean have been analyzed with magmatic delta 18O above 7.5 0/00. The mildly evolved, higher Archean values (6.5-7.5 0/00) are interpreted to result from exchange of protoliths with surface waters at low temperature followed by melting or contamination to create mildly elevated magmas that host the zircons. During the Proterozoic, the range of delta 18O(Zrc) and the highest values gradually increased in a secular change that documents maturation of the crust. After delta 1.5 Ga, high delta 18O zircons (8 to >10 0/00) became common in many Proterozoic and Phanerozoic terranes reflecting delta 18O(whole rock) values from 9 to over 12 0/00. The appearance of high delta 18O magmas on Earth reflects nonuniformitarian changes in the composition of sediments, and rate and style of recycling of surface-derived material into magmas within the crust. [PUBLICATION ABSTRACT]