Geochemistry and Sr, Nd, and Pb Isotopic Composition of Early Cretaceous Volcanic Rocks of the Mendeleev Rise, Arctic Ocean

The paper presents newly obtained data on geochemistry and Sr, Nd, and Pb isotopic composition of Early Cretaceous volcanic rocks of the Mendeleev Rise in the Arctic Ocean. Cretaceous igneous rocks from this rise have been previously characterized only by a few samples of the Arctic-2012 collection (Morozov et al., 2012; Kremenetsky et al., 2015). The studied volcanic rocks belong to the unique Arctic-2014 and Arctic-2016 collections, compiled by sampling bedrock exposures during the 2014 and 2016 research submarine deep-sea dives under the ice cover. The rocks are variably altered moderately to highly differentiated volcanics that differ in their phenocryst and groundmass mineral assemblages, the distribution of trace elements, and the Sr, Nd, and Pb isotopic composition. Based on these findings and data, the rocks were classified into three groups: (a) olivine trachybasalts; (b) pyroxene basaltic trachyandesites and ferrohortonolite trachyandesites; and (c) lamprophyre. The compositional diversity of these rocks is likely due to the heterogeneity (including isotopic one) of their mantle sources, which were melted at different depths in the presence/absence of garnet in the mineral residue assemblages, as well as due to differences in a degree of magma fractionation, which was in most cases combined with the assimilation of crustal rocks (carbonate-bearing and siliceous terrigenous rocks). The studied volcanic rocks are compositionally similar to continental tholeiitic and alkaline igneous rocks of the High Arctic Large Igneous Province (HALIP), a fact consistent with that the Mendeleev Rise and Alpha Ridge belong to one of its areas. These volcanic rocks were probably produced in a plume geodynamic setting. The obtained data do not contradict the model of upper mantle convection due to the significant lateral displacement of the subducted lithosphere of the Pacific plate along the boundary of the upper and lower mantle (Laverov et al., 2012; Lobkovsky et al., 2021).