The history of Nepluyevka batholith: A glimpse into Laurussia-Kazakhstania interactions during the Early Carboniferous

Introduction. The Early Carboniferous Nepluyevka polyphase granitic batholith is situated in the East Ural zone. Its emplacement happened during the Sudetian orogeny, which initially shaped the structure of the southwestern segment of the Ural-Mongolian fold belt. As such, the pluton is a repository of information on tectonic evolution and geodynamics of said orogen, which can be used to enhance our understanding of interactions between Laurussia and the microcontinent of Kazakhstania during the Early Carboniferous.

Methods and materials. We have investigated the existing data on the petrology, petrochemistry, isotope systems, and U-Pb geochronology of Nepluyevka batholith, and performed our own analysis of the trace element distribution of the constituting rocks using ICP-MS method. The mechanism of emplacement and its kinematic setting were investigated through an analysis of oriented fabrics and anisotropy of magnetic susceptibility (AMS) for each phase. Paleomagnetic methods were employed for establishing the position of pluton’s host terrain during its emplacement. A total of five specimen, characterizing all of the phases of the batholith, were chosen for petrochemical analyzes, and 186 oriented specimen from 16 sites were used for rock- and paleomagnetic studies.

Results. Combinations of ⁸⁷Sr/⁸⁶Sr (0,70491–0,70504) and εNd (-0,29-0,5) ratios for different phases indicate that both depleted mantle and crustal sources were involved in petrogenesis. Trace element distribution is characteristic of subduction settings. AMS parameters’ spatial distribution and observed fabric features show that the batholith was emplaced in a kinematic setting of sinistral transtension. Virtual geomagnetic poles (VGPs) obtained from ChRM components of remanent magnetization do not fall anywhere on the Carboniferous-Quaternary sections of apparent polar wander paths (AWP) for Eastern Europe or Siberia.

Discussion. Combined data on geological structure of the pluton, isotope systems, petrochemistry, and rock magnetic properties of rocks lead us to the conclusion that the batholith had developed as a part of a magmatic system associated with an oblique subduction setting. Paleotectonic reconstructions of pluton’s host terrane Visean location derived from our paleomagnetic data contradict the traditional models for the region. We suggest a model featuring rotation of the host terrane in a strike-slip displacement zone to deal with the contradiction. A paleotectonic reconstruction corrected for such a rotation puts the host terrane into the Visean paleo-position of Kazakhstanian microcontinent. This reconstruction agrees well with the the model proposed by Sengor, Natalin and Burtman in [Sengor et al., 1993], featuring a single subduction system (“Kipchak arc”) stretching from Laurussia to Siberia, which existed through much of the Paleozoic and controlled the crustal growth and development of what is now known as Ural-Mongolian fold belt.

Financial support. The research has been funded by RFBR and CNF as a part of the research project № 19-55-26009 with the use of materials of the "Geoportal" Center of the Lomonosov Moscow State University.