Литосфера (Aug 2018)
Zircons and zircon’s geochronology of gabbro Nurali massif (the Southern Urals)
Abstract
Object. In the article presents the the results of mineralogy, geochemistry and isotope-chronological investigation of zircons from gabbro Nurali massif. Materials and methods . Amphibole gabbro is the fine-grained and massive texture rock, which cosists of hornblende, the base plagioclase and epidote. The contents of REE in the gabbro significantly exceeds their content in associated ultramafites of the massif. The content of REE and trace elements in zircons was determined by the method of secondary ion mass spectroscopy on the CAMECA-IMS-4F device. U-Pb date of zircons was obtained on the SHRIMP II microprobe. Results. Different variants of complex multiphase zonal structure of gabbro zircons are established. Along with the well known classical fine- and coarse-zonal kinds, a new type of zoning - “polygenic” - is distinguished. It combines the features of both primary growth and superimposed processes. The basis of the material evolution of zircons is progressive process of growth of their refining, reduction of U, Th and REE in later generations. These changes do not go beyond the boundaries of a single geochemical space, due to the connection with a single source. The mechanism of formation of successive zircon generations reflects the anatectic origin of gabbro. The age of zircons from gabbro is 410.5 ± ± 1.1 Ma for the duration of the process of crystallization of rock - 2.0-2.5 Ma. There is on 30-35 million years younger than the zircon from lherzolites of the massif. Conclusion .We consider that this indicates a lack of genetic links between them. The history of the development of gabbro is not associated with the formation of the ultramafic massif.
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