Nd In Rocks Research Articles

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

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.

Oceanic anoxic events and global rhythms of endogenic activity during the Phanerozoic history of the Earth

The Phanerozoic history of the Earth was marked by recurrent oceanic anoxic events (OAE) accompa� nied by outbursts of plankton bioproductivity and extinction of more evolved animal and plant groups. Such processes resulted in accumulation of sediments enriched in organic matter and sulfides. For the sake of brevity, let us call them carbonaceous metalliferous sediments (CMS). Some researchers [1–4 and others] noted that accumulation of CMS members was preceded or accompanied by volcanic eruptions, which resulted sometimes in the formation of large magmatic prov� inces. The significant role of volcanic activity during accumulation of such sediments is confirmed by the isotopic analysis of S, Mo, Rb, Sr, Os, and Nd in rocks

Isotopic composition of strontium and neodymium in potassic rocks of the Little Murun complex, Aldan Shield, Siberia

This paper presents the first data on the isotopic composition of Nd and Sr in ultrapotassic rocks of the Little Murun complex, Aldan Shield, Siberia. The samples analysed include a SrBa-carbonatite and rocks belonging to the biotite pyroxenite-shonkinite series. The latter are representative of rocks termed “lamproites” by previous investigators of the complex. The rocks have isotopic compositions that indicate derivation from ancient sources that have higher Rb Sr and lower Sm Nd ratios than those of bulk Earth. The samples define an array on a SrNd correlation diagram, suggesting that the isotopic composition of Sr and Nd in the rocks is a mixture of two components: a dominant one derived from an ancient lithospheric mantle source that has been isolated from convecting mantle, and a minor component of asthenospheric origin. We do not consider that any of the samples analysed are lamproites, although our isotopic data suggest that conditions in the lithospheric mantle in this region are suitable for the generation of lamproites. The potassic rocks from the Aldan shield have isotopic compositions that are similar to those of potassic rocks in the Wyoming craton. It is proposed that the geochemical evolution of the two shields was broadly similar.