Incompatible element

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

Trace Element Evidence for Mantle Heterogeneity Beneath the Scottish Midland Valley in the Carboniferous and Permian

Abstract: The alkaline rocks of Carboniferous to Permian age in the Midland Valley province range in composition from hypersthene-normative, transitional basalts to strongly undersaturated basanitic and nephelinitic varieties. They were formed by varying degrees of equilibrium partial melting of a phlogopite peridotite mantle. Ba, Ce, Nb, P, Sr and Zr were strongly partitioned into the liquid during melting; K and Rb were retained by residual phlogopite for small degrees of melting only. The composition of the mantle source is inferred to have been broadly similar to that from which oceanic alkaline basalts are currently being generated. It was, however, heterogeneous as regards distribution of the incompatible trace elements, with up to fourfold variations in elemental abundances and ratios. The mantle beneath the province may be divisible into several areas, of some hundreds of square kilometres each, which retained a characteristic incompatible element chemistry for up to 50 Ma and which imparted a distinctive chemistry to all the basic magmas generated within them.

Characteristics of mantle source for Jining Cenozoic basalts from southern Inner Mongolia:evidence from element and Sr-Nd-Pb isotopic geochemistry.Acta Petrologica

Abstract: Jining Cenozoic basaltic field,located on the northern edge of the North China craton and to the west of Hannuoba basaltic field,is mainly made up of subalkaline tholeiitic basalt,alkaline olivine basalt,basanite,and tephrite.Their SiO_2 and TiO_2 contents vary from 44.10～52.27 wt.% and 1.57～2.95 wt.%,respectively,with variable Mg-number (43-63) and Ni contents (27～210ppm).The Primitive-mantle normalized incompatible element diagrams and Chondrite-normalized REE patterns are similar to those of OIB.Sr,Nd isotopic ratios are more enriched than Hannuoba basalts.The basalts were mantle-derived magmas with the fractional crystallization of olivine and clinopyroxene,but their trace-element and St,Nd,Pb isotopic geochemistry preclude the possibility that the magmas were contaminated sigaificantly by crustal materials.The correlations of ~(143)Nd/~(144) Nd,~(87)Sr/~(86) Sr vs. ~(206)Pb/~(204)Pb indicates that Jining basalts were generated by the mixing of at least two mantle components:EMI and PREMA,similar to Hannuoba basalts.The mixing of low degree melts of spinel lherzolite (2～5%) and garnet lherzolite (2%) can explain the REE features in Jining basalts.It can be speculated that EMI mantle component came from the lithospheric mantle of a depth70km,and PREMA mantle component from asthenospheric mantle.It is possible that the differences between the subalkaline and alkaline basalts may be produced by the mixing of the melts from lithospheric EMI mantle and asthenospheric PREMA mantle in different proportion, implying that strong interactions have occurred between lithosphere and asthenosphere beneath Jining area.The similar isotopic ratios and correlations suggest a similar mantle source for Jining and Hannuoba basalts.Therefore,the formation of Hannuoba basalts can be also interpreted by the mixing of the melts from EMI mantle and PREMA mantle in different proportion.

Cretaceous carbonatites of the southeastern Brazilian Platform: a review

Abstract: This paper reviews general aspects of alkaline-carbonatitic rocks of Brazilian, Paraguayan and Bolivian terrains. Although 30 such occurrences are known in literature, only the major ones have been thoroughly investigated. The carbonatites are of Cretaceous age, with two well-defined Lower Cretaceous and Upper Cretaceous generation episodes. A clear tectonic control by ancient structural features such as archs, lineaments and faults characterizes most cases. The rocks exhibit a large compositional variation, in decreasing orders of abundance from calciocarbonatites to magnesiocarbonatites to ferrocarbonatites. In some complexes, they form multistage intrusions. C-O isotopes indicate that, in general, the carbonatites were affected by post-magmatic processes associated with the topographic level of emplacement and low-temperature H 2 O-CO 2 rich fluids responsible for the increased amount of heavy carbon and oxygen. Sr-Nd isotopic compositions similar to those of coeval alkaline silicate rocks, ranging from depleted to enriched mantle sources, have been influenced by two distinct metasomatic events in Proterozoic at 2,0-1.4 Ga and 1.0-0.5 Ga. Sr-Nd-Pb-Os data seem related to an isotopically enriched source, their chemical heterogeneities reflecting a depleted mantle that was metasomatized by small-volume melts and by fluids rich in incompatible elements. Fractional crystallization and liquid immiscibility are believed to be the most effective processes in the formation of the Cretaceous carbonatites, with minor contribution of crustal contamination. Pb isotopic ratios yield evidence that HIMU and EM I mantle components played an important role in the genesis of the carbonatitic magma.