The Cenozoic tectonic evolution of the Kurile-Kamchatkan arc system has been reconstructed based on the spatial-tectonic setting of the volcanic-rock formations and their petrologic-geochemical characteristics, using gravity and seismic data. Three volcanic arc trench systems of different ages that become successively younger toward the Pacific have been recognized in the region: the West Kamchatka (Eocene), Mid-Kamchatka-Kurile (Late Oligocene-Quaternary), and Recent Kurile-Kamchatka systems. The Kamchatka volcanic belts are viewed as the products of these systems, which originated above the subduction zones. The geometry of the present-day Kurile-Kamchatka subduction zone and dynamics of contemporary volcanism can be defined from seismic data. The contemporary Kurile-Kamchatka arc can be subdivided into individual segments in accord with its tectonic evolution and geodynamics. The East Kamchatka segment represents the initial subduction stage (7-10 Ma ago) of the Pacific Plate. The Petropavlovsk segment (the Malka-Petropavlovsk zone of transverse faults) is a zone of discordant superposition of the contemporary Kurile-Kamchatka arc over the older Mid-Kamchatka arc. Within the South Kamchatka segment subduction remained practically unchanged since the Late Oligocene, i.e., since the origin of the Mid-Kamchatka-Kurile arc system, as well as within the three Kurile segments. Geodynamics controlled magma generation and is imprinted in the petrochemical properties of the volcanic rocks. Typical arc magmas are generated at the steady-state geodynamic regime of subduction. Lavas of an intraplate geochemical type are generated at initial and final stages of subduction, and also at the Kamchatka-Aleutian junction.

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Silicate-sulfide liquid immiscibility in mantle-derived magmas has important control on the budget of siderophile and chalcophile metals, and is considered to be instrumental in the origin orthomagmatic sulfide deposits. Data on primitive sulfide melts in natural samples, even those This is a preprint, the final version is subject to change, of the American Mineralogist (MSA) Cite as Authors (Year) Title. American Mineralogist, in press.

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