Incompatible element

About: Incompatible element is a research topic. Over the lifetime, 2420 publications have been published within this topic receiving 154052 citations.

Geochemical variations in Japan Sea back‐arc basin basalts formed by high‐temperature adiabatic melting of mantle metasomatized by sediment subduction components

Abstract: The Yamato Basin in the Japan Sea is a back-arc basin characterized by basaltic oceanic crust that is twice as thick as typical oceanic crust. Two types of ocean floor basalts, formed during the opening of the Japan Sea in the Middle Miocene, were recovered from the Yamato Basin during Ocean Drilling Program Legs 127/128. These can be considered as depleted (D-type) and enriched (E-type) basalts based on their incompatible trace element and Sr-Nd-Pb-Hf isotopic compositions. Both types of basalts plot along a common mixing array drawn between depleted mantle and slab sediment represented by a sand-rich turbidite on the Pacific Plate in the NE Japan fore arc. The depleted nature of the D-type basalts suggests that the slab sediment component is nil to minor relative to the dominant mantle component, whereas the enrichment of all incompatible elements in the E-type basalts was likely caused by a large contribution of bulk slab sediment in the source. The results of forward model calculations using adiabatic melting of a hydrous mantle with sediment flux indicate that the melting conditions of the source mantle for the D-type basalts are deeper and hotter than those for the E-type basalts, which appear to have formed under conditions hotter than those of normal mid-oceanic ridge basalts (MORB). These results suggest that the thicker oceanic crust was formed by greater degrees of melting of a hydrous metasomatized mantle source at unusually high mantle potential temperature during the opening of the Japan Sea.

Petrologic and geologic variations along the Southern Explorer Ridge, northeast Pacific Ocean

Abstract: Mid-ocean ridge basalts (MORB) from the well-defined Southern Explorer Ridge segment (SER) in the northeast Pacific Ocean are moderately to strongly enriched in incompatible elements. Enriched MORB were erupted at the highest and widest part of the segment (culmination) where the magma supply may be the greatest and also at the northern and southern ends of the SER. Variations in basalts' incompatible element enrichment occur over short distances and suggest that the underlying mantle is heterogeneous on a small scale. The variations also preclude the existence of a long-lived, well-mixed magma chamber beneath the robust culmination. Instead, magma chambers are probably temporally and spatially isolated, as evidenced by the presence of highly differentiated lavas. Less enriched (transitional) MORB were erupted along the central part of the SER, 11–27 km south of the culmination, and were supplied to the ridge separately from a less enriched pan of the mantle. A more continuous magma chamber cannot be ruled out for this section on geochemical grounds. All of the MORB from the SER have undergone significant amounts of fractional crystallization. Unlike certain segments of the East Pacific Rise, the most evolved MORB were erupted near the culmination of the ridge segment. Aphyric lavas have been recovered only from the vicinity of the culmination, while phyric lavas have erupted along the entire length of the SER. There is no correlation between composition and total crystal abundances. Despite the requirement of multiple parental magmas, most of the lavas from the culmination and the distal ends of the ridge fall on a common liquid line of descent, indicating that they formed at similar depths and extents of partial melting. The transitional MORB from the central part of the ridge have probably formed by lesser extents of partial melting and separated from their mantle source at greater depths based on abundances of Na and moderately incompatible elements such as Sm and Zr. Enriched, high-melt fraction lavas at the magma-starved southern end of the SER closely resemble lavas from the culmination. Either the southernmost lavas have flowed laterally within the crust from near the culmination, or there is another melting anomaly that supplies the southern end of the SER. If the latter case is true, correspondence between ridge morphology and mantle thermal state is poor.