Mafic–Ultramafic Complexes of the Stalemate Ridge, NW Pacific, and the Shirshov Rise, Bering Sea: Geochemical Similarities and Differences

• Published in: Petrology 2021, Vol.29 (1), p.1-13
• Main Authors: Silantyev, S. A., Kubrakova, I. V., Nabiullina, S. N.
• Format: Article
• Language: English
• Subjects: Bottom trawling; Data acquisition; Dredging; Earth and Environmental Science; Earth Sciences; Geochemistry; Island arcs; Isotopes; Lava; Lithosphere; Magma; Mineralogy; Rocks; Sediment samples; Segments; Spreading centres; Strontium 87; Strontium isotopes; Subduction (geology); Tectonics; Ultramafic materials; Ultramafic rocks
• ISSN: 0869-5911; 1556-2085
• DOI: 10.1134/S0869591121010057

This study was focused on the estimation and geodynamic interpretation of the contents and character of distribution of highly siderophile and chalcophile elements in rock samples from mafic–ultramafic assemblage sampled at the Stalemate Ridge in the NW Pacific and the Shirshov Rise in the Bering Sea. All of the samples were collected during Cruise 249 of German R/V Sonne . These mafic–ultramafic rock complexes situated at the opposite sides of Aleutian Island Arc may carry important information on the structure and composition of the old Pacific lithosphere subducted under Aleutian Arc, as well as on the products of suprasubduction magmatism in back-arc basin of the Bering Sea. The newly acquired data presented in this paper indicate that the real structure of the northwestern segment of the Stalemate Ridge is inconsistent with the currently widely assumed model that the local lithosphere corresponds to the canonic oceanic type. The lithosphere in the area includes mafic–ultramafic complexes whose origin was not related to mantle reservoirs of the oceanic type (e.g., DM). At the same time, the tectonic remobilization of the lithosphere in this part of the NW Pacific suggested in (Lonsdale, 1988) is confirmed by results of dredging at sites on the northwestern flank of the Stalemate Ridge. Vertical tectonic motions in this region combined lithospheric blocks that might have been formed in contrasting geodynamic settings. These lithospheric blocks may have included fragments of magmatic complexes formed by suprasubduction magmatism and were identical in the their isotope geochemistry ( 87 Sr/ 86 Sr, 143 SNd/ 144 Nd) to the mafic–ultramafic assemblage occurring in the Shirshov Rise, which lies immediately north of the northwestern Stalemate Ridge segment and likely is a relic of a backarc spreading center.