Geodynamic nature of magmatic sources of North-West Pacific: an interpretation data on isotope composition of Sr and Nd in rocks dredged at Stalemate ridge, Ingenstrem depression, and Shirshov Rise

Abstract

First data on isotope composition of Sr and Nd in rocks dredged at different areas belong to lithosphere of the NW Pacific are present. All samples examined were obtained from NW termination of Stalemate Ridge (NW Pacific) and Central part of Shirshov Rise (Western Bering Sea). Results of conducted study allow sure enough to judge on geodynamic affinity of the central segment of Shirshov Rise. Mafic-ultramafic rocks dredged here originated due evolution of magmatic melt formed by partial melting of source parental for MORB belongs to mantle wedge perhaps. Thus, this interpretation means that Shirshov Rise is remnant Back-Arc Spreading Center. Data on petrology and isotope chemistry of rocks from Stalemate magmatic assemblage demonstrate geochemical heterogeneity of their possible magmatic sources. The presented data allow to assume participation in magmatism of this region of NW Pacific source that responsible for formation of most older volcanic seamounts from NW Termination of Hawaiian-Emperor volcanic chain. There is petrographic similarity between rock assemblage recovered at NW Stalemate and plutonic rocks composed of xenoliths from volcanic effusions of Aleutian Island Arc exists. Considering the scarcity of existing information about the structure of the lithosphere in the NW Pacific it is possible to assume with caution the participation in the construction of the oceanic slope of the Aleutian Trench and the adjacent segment of the Stelmate Ridge fragments of Aleutian Arc basement.