Incompatible element

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

Strontium, neodymium and lead isotope constraints on near-ridge seamount production beneath the South Atlantic

Abstract: STUDIES1–7 of seamounts near the East Pacific Rise (EPR) have shown that, although most seamount lavas are petrographically and chemically identical to mid-ocean-ridge basalt, they are chemically and isotopically more diverse than those erupted on the rise axis. They are also generally more primitive (higher MgO content) and, in some cases, more depleted in incompatible elements than the axial basalts. This indicates that although near-ridge sea-mounts and the EPR share a common mantle source, there must be significant differences in their magma-supply processes. Sea-mounts are probably built by small batches of melt that rise rapidly to the surface, preserving evidence of heterogeneity in the mantle source region. By contrast, the processes of melting and melt segregation, storage and extrusion along the fast-spreading (9–13 cm yr–1) EPR are more efficient in mixing and homogenizing basalt compositions1–7. Here we show that the relationship of strontium, neodymium and lead isotope data between seamounts in the South Atlantic and the nearby axis of the slow-spreading Mid-Atlantic Ridge (MAR) is similar to that seen in the Pacific. This indicates that the processes leading to formation of near-ridge seamounts are similar at a wide range of spreading rates. Differences in the specific isotope signatures of lavas from near-ridge seamounts and axes of the EPR and MAR reflect regional differences in the upper-mantle source of mid-ocean-ridge basalts.

The origin of pristine KREEP: effects of mixing between urKREEP and the magmas parental to the Mg-rich cumulates.

Abstract: The fact that pristine KREEP basalts generally have bulk-rock molar MgO/(MgO+FeO) ratios lower than average for the lunar crust despite their extraordinarily high incompatible element contents is discussed. Pristine KREEP basalts also have primitive Ni contents compared to mare basalts with comparable REE contents. It is suggested that these facts can be explained through mixing between ancient KREEP precursor materials and primitive Mg-rich melts. Finite-difference models of this mixing, followed by anorthosite assimilation and fractional crystallization provide satisfactory fits to the composition of these basalts. It is suggested that this is a further confirmation of the magmasphere hypothesis.

Coexisting calc-alkaline and ultrapotassic magmatism at Monti Ernici,Mid Latina Valley (Latium, central Italy)

Abstract: New major and trace element data, and Sr-Nd-Pb-O isotopic ratios for volcanic mafic rocks outcropping at Monti Ernici in the Mid Latina Valley (southern Latium) are reported, with the aim of investigating the nature and evolution of Plio-Quaternary K-rich volcanism in Central Italy. Petrographical and geochemical studies allow us to identify mafic rocks ranging from ultrapotassic (HKS) to shoshonitic (SHO), and calc-alkaline (CA), these last ones being identified for the first time. The CA rocks exhibit the most primitive signatures for Sr, Nd, and Pb isotopes ( 87 Sr/ 86 Sr =0.706326–0.706654; 143 Nd/ 144 Nd = 0.512388–0.512361; 206 Pb/ 204 Pb = 18.944–18.940). The δ 18 O values are variable (δ 18 O cpx from +5.75 to +7.08 ‰; and δ 18 O ol from +5.50 to +6.23 ‰), suggesting interaction with carbonate wall rocks. Radiogenic isotope ratios and incompatible elements distribution have several characteristic in common with equivalent rocks from Pontine Islands (Ventotene), Campania and Aeolian arc volcanoes. Conversely, the HKS rocks closely resemble the ultrapotassic rocks from the Roman Province ( 87 Sr/ 86 Sr = 0.709679–0.711102; δ 18 O cpx from +6.27 to +7.08 ‰). The high ratios of LILE (Large Ion Lithophile Elements: Rb, Cs, Th, U, K, LREE) and HFSE (High Field Strength Elements: Ta, Nb, Zr, Hf, Ti), and radiogenic isotope compositions of CA to HKS rocks indicate that all suites contain subduction-related components, and suggest a N-MORB-type mantle source variably contaminated by hydrous fluids and/or melts released by undergoing slabs, possibly during two distinct stages of metasomatism. The coexistence of ultra-alkaline and sub-alkaline orogenic magmatism, combined with tectonic, geophysical and geological evidence, support the possibility that the mantle beneath central-southern Italy (Ernici-Roccamonfina Province) was vertically zoned and produced different magma suites during time.