Zircons, zircon geochronology, and petrogenetic problems of the lherzolite massifs of the South Urals |
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| Authors: | A A Krasnobaev A I Rusin I A Rusin S V Busharina |
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| Institution: | 1. Zavaritskii Institute of Geology and Geochemistry, Ural Branch, Russian Academy of Sciences, Pochtovyi per. 7, Yekaterinburg, 620219, Russia
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| Abstract: | The paper reports the results of mineralogical and isotope-geochronological study of zircons from the Uzyansky Kraka (UK) Massif, which represents the part of the large (more than 900 km2) lherzolite allochthon thrusted onto the Paleozoic sequences of the East European margin. The massif shows a distinct stratification (from the top downward): spinel lherzolites, garnet pyroxenites, and dunites. The formation of stratified section is considered to be related to the decompression uplift of mantle lherzolite block. Zircons from the massif rocks were dated using SHRIMP-II ion microprobe. The oldest relict datings characterizing endogenous transformations of protolith were established in the zircons from the lherzolites (2037 ± 20 and 1132 ± 6 Ma), garnet pyroxenites (953 ± 11 Ma), and dunites (632 ± 11 Ma). All rock associations contain zircons with ages within 590–550 and 445–390 Ma, which mark the stages of mantle stratification of lherzolite block into complementary series and their emplacement at the upper crustal level. Age values within 299–196 Ma were found only in the dunites and date the influence of the Paleozoic strike-slipping. Our studies led us to conclude that the modern structure of the Ural collision orogen contains the fragments of subcontinental lithosphere, which were previously described only for the massifs of the root zones of the Western and Central Europe. Some general petrogenetic questions of lherzolite massifs from orogenic regions are discussed. |
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