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ABSTRACT
We present newly acquired data on the trace element composition and Sr–Nd–Pb-O isotopes of Pliocene – Holocene basalts of the Medvezhiy caldera located on the Iturup Island, Kuril arc. With its unique rhenium mineralization and high-Mg basalt volcanism, it is the largest caldera on the volcanic front of the Kurile Island arc. The calc-alkaline suite of rocks spanning the range from high-Mg basalts to high-Al basalts, has typical arc rock features, such as Nb-Ta depletion and LILE enrichment. The whole set of the caldera geochemical data is divided into two age units, pre- and postcaldera basalts. The precaldera basalts typify low-K, high-Al, basaltic suite of the frontal zones of «cold» subduction. PRIMACALC2 code and Arc Basalt Simulator version 3.1 forward model points to ~21.7% of partial melting of moderately depleted mantle peridotite with relatively high water content (~0.34 wt%) at the pressure of ~1.37 GPa. With similar isotope and trace element signatures, Late Pleistocene–Holocene basalts are marked by the high abundances of MgO (up to 11 wt %), but low Al2O3. The primary magmas were generated from depleted mantle with lower H2O content (~0.13%) and degree of partial melting (~9.5%), but at higher pressure (~1.77 GPa). The decompression scheme reproduces the fractionation trends of postcaldera magnesian basalts for most major elements but fails to explain the composition variations of the precaldera lavas. Their origin has been the matter of some complex processes in the shallow magma chamber. The abrupt change in the type of eruptions and magma composition of the caldera in Late Pleistocene–Holocene were related to a transformation of both the magma-feeding and melt generation systems as the result of geodynamic reorganization of the vast territory adjacent to the Sea of Japan and Kamchatka.
Acknowledgments
The authors thank T.V. Bunaevu, N. Strom, and H. Strom for their help during the preparation of this manuscript. We are grateful to V. Kaminskaya, M. Blokhin, and G. Gorbach, from FEGI, Russia, for ICP MS analyses. We gratefully acknowledge V.P. Kovach from IPPG, Russia for Sr, Nd and Pb isotope analyses. The manuscript was improved by discussions with Dr. V.V. Golozubov and S.A. Kasatkin, and helpful criticisms from Dr. I. N. Bindeman
Disclosure statement
No potential conflict of interest was reported by the author(s).
Supplementary material
Supplemental data for this article can be accessed here
The new trace elements and Sr–Nd–Pb-O isotopes data of Pliocene–Holocene basalts of the Medvezhia caldera (Iturup Island), the largest in the frontal part of the Kuril arc with unique rhenium mineralization and high-Mg basalt volcanism.
Two pulses of volcanic activity during the Middle Pleistocene and the Late Pleistocene–Holocene have important distinct differences in the style of eruptions and compositions of volcanic products.
Geochemical modeling and computer simulation evidenced for complex dynamic processes magma generation and evolution.
High-Mg basaltic eruptions in the Late Pleistocene–Holocene was linked to the geodynamic reorganization of a vast area of northeastern Eurasia in Late Pleistocene.
