Age and substance sources of the Ilmeno-Vishnevogorsky Alkaline Complex (South Urals): Rb-Sr, Sm-Nd, U-Pb, and Lu-Hf isotope data

Abstract

) ofmiaskites, fenites, and carbonatites with REE–Zr–Nb mineralization located in the Uralian foldbelt.Although the IVC is well studied, a number of important genesis and geochronological problems are currently debatable. Thus, because of the wide dispersionof datings obtained by the different isotope–geochronological methods on various rocks and minerals, ofcritical concern are the problems of geochronology ofalkaline rocks and carbonatites of the IVC. The keyquestion of the IVC genesis is the role of mantle andcrustal sources for rock and ore formation. Theseproblems may be solved on the basis of the complexand systematic study of the Rb–Sr, Sm–Nd, U–Pb,and Lu–Hf isotope systems of rocks and minerals,which currently have become an important and indispensable instrument for reconstruction of the sourceof magmatic rocks and solution of the problems oftheir origin.We applied the isochron methods based on theSm–Nd and Rb–Sr isotope systems of bulk samplesand rockforming minerals of miaskites and carbonatites (TIMS method, Institute of Geology andGeochemistry, Yekaterinburg; Institute of Precambrian Geology and Geochronology, Saint Petersburg;Institute of Geology, Apatity), as well as the local U–Pb isotope dating of zircons from carbonatites andmiaskites from Vishnevogorsky and Buldym massifs(ion microprobe SHRIMPII, Russian GeologicalResearch Institute, Saint Petersburg; laser ablationLaICPMS, GEMOC, Sydney) for dating of themain rock types of the IVC. The U–Pb isotope systems of pyrochlores from the IVC (TIMS, AllRussianGeological Research Institute, SaintPetersburg) wereused for dating as well. The initial isotope characteristics of rocks and minerals of the IVC were obtained inorder to establish the sources of substances for magmatic rocks and ores and the role of mantle in theirformation.The Ilmeno–Vishnevogorsky Complex is locatedat the boundary between the South and Middle Uralsin the Sysertsko–Ilmenogorsky block of Precambrianrocks occurring in the Uralian paleooceanic complexes. The core of this block is composed of granuliticgneisses and migmatites of the Selyankinskaya Series,as well as plagiogneisses and amphibolites of the Vishnevogorskaya Series (