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The average chemical compositions of the continental crust and the oceanic crust (represented by MORB), normalized to primitive mantle values and plotted as functions of the apparent bulk partition coefficient of each element, form surprisingly simple, complementary concentration patterns. In the continental crust, the maximum concentrations are on the order of 50 to 100 times the primitive-mantle values, and these are attained by the most highly incompatible elements Cs, Rb, Ba, and Th. In the average oceanic crust, the maximum concentrations are only about 10 times the primitive mantle values, and they are attained by the moderately incompatible elements Na, Ti, Zr, Hf, Y and the intermediate to heavy REE. This relationship is explained by a simple, two-stage model of extracting first continental and then oceanic crust from the initially primitive mantle. This model reproduces the characteristic concentration maximum in MORB. It yields quantitative constraints about the effective aggregate melt fractions extracted during both stages. These amount to about 1.5% for the continental crust and about 8-10% for the oceanic crust.The comparatively low degrees of melting inferred for average MORB are consistent with the correlation of Na20 concentration with depth of extrusion [1], and with the normalized concentrations of Ca, Sc, and AI (= 3) in MORB, which are much lower than those of Zr, Hf, and the HREE ( = 10). Ca, A1 and Sc are compatible with clinopyroxene and are preferentially retained in the residual mantle by this mineral. This is possible only if the aggregate melt fraction is low enough for the clinopyroxene not to be consumed.A sequence of increasing compatibility of lithophile elements may be defined in two independent ways: (1) the order of decreasing normalized concentrations in the continental crust; or (2) by concentration correlations in oceanic basalts. The results are surprisingly similar except for Nb, Ta, and Pb, which yield inconsistent bulk partition coefficients as well as anomalous concentrations and standard deviations.The anomalies can be explained if Nb and Ta have relatively large partition coefficients during continental crust production and smaller coefficients during oceanic crust production. In contrast, Pb has a very small coefficient during continental crust production and a larger coefficient during oceanic crust production. This is the reason why these elements are useful in geochemical discrimination diagrams for distinguishing MORB and OIB on the one hand from island arc and most intracontinental volcanics on the other.The results are consistent with the crust-mantle differentiation model proposed previously [2]. Nb and Ta are preferentially retained and enriched in the residual mantle during formation of continental crust. After separation of the bulk of the continental crust, the residual portion of the mantle was rehomogenized, and the present-day internal heterogeneities between MORB and OIB sources were generated subsequently by processes involving only oceanic crust an...

More than 50 per cent of the Earth's upper mantle consists of olivine and it is generally thought that mantle-derived melts are generated in equilibrium with this mineral. Here, however, we show that the unusually high nickel and silicon contents of most parental Hawaiian magmas are inconsistent with a deep olivine-bearing source, because this mineral together with pyroxene buffers both nickel and silicon at lower levels. This can be resolved if the olivine of the mantle peridotite is consumed by reaction with melts derived from recycled oceanic crust, to form a secondary pyroxenitic source. Our modelling shows that more than half of Hawaiian magmas formed during the past 1 Myr came from this source. In addition, we estimate that the proportion of recycled (oceanic) crust varies from 30 per cent near the plume centre to insignificant levels at the plume edge. These results are also consistent with volcano volumes, magma volume flux and seismological observations.

We have developed a new database named GeoReM (http://georem.mpch-mainz.gwdg.de) for reference materials and isotopic standards of geochemical and mineralogical interest. Reference samples include rock powders originating from the USGS, GSJ, GIT‐IWG, synthetic and natural reference glasses originating from NIST, USGS, MPI‐DING, as well as mineral (e.g., 91500 zircon), isotopic (e.g., La Jolla, E&A, NIST SRM 981), river water and seawater reference materials. GeoReM is a relational database, which strongly follows the concept of the three EARTHCHEM databases. It contains published analytical and compilation values (major and trace element concentrations, radiogenic and stable isotope ratios), important metadata about the analytical values, such as uncertainty, uncertainty type, method and laboratory. Sample information and references are also included. Three different ways of interrogating the database are possible: (1) sample names or material types, (2) chemical criteria and (3) bibliography. Some typical applications are described. GeoReM currently (October 2005) contains more than 750 geological reference materials, 6000 individual sets of results and references to 650 publications.

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Subducted oceanic crust, transformed into dense mineral assemblages at high pressure, may gravitationally segregate at the bottom of the convecting mantle, for example, the D″ layer. Here it could be stored for a long enough time to develop an “enriched” isotopic signature, before it is recycled in mantle plumes and hence control the geochemical character of hot‐spot basalts. We study both the geodynamical and geochemical aspects of this hypothesis in two‐dimensional numerical convection models, in which plate motion is imposed by a velocity boundary condition. About 250,000 tracer particles are used to identify the basalt fraction in the oceanic crustmantle system. High‐, average‐, and low‐tracer densities indicate basalt or eclogite, peridotite, and harzburgite, respectively. The tracers are negatively buoyant to account for the density differences between the rock types. At surface divergence zones, crust formation is simulated by extracting tracers and transferring them into a thin layer at the surface. The tracers carry a certain amount of the relevant nuclides of the U‐Pb and Sm‐Nd systems, which are fractionated between the basalt tracers and a second species of residue tracers during crust formation. Using reasonable parameter values, we find that of the order of 1/6 of the subducted crust accumulates in pools at the bottom, which reside underneath thermal plumes. After 3.6 Ga, the [207Pb]/[204Pb], [206Pb]/[204Pb], and [143Nd]/[ 144Nd] ratios in various parts of the model cover the observed HIMU‐MORB range. A systematic study of the influence of control parameters on the results indicates that the amount of segregation and the diversity of isotope ratios (1) increases strongly with Rρ, the ratio of chemical to thermal buoyancy; (2) decreases moderately with the Rayleigh number Ra, where Ra = 106 is the highest value that we employed; (3) increases strongly with the degree of temperature dependence of the viscosity; and (4) is not very sensitive to the partitioning between internal and bottom heating. The largest uncertainty in applying our model results to the Earth lies in the lack of accurate density data for conditions at the core‐mantle boundary. We conclude that, if our density estimates are correct, segregation and reentrainment of subducted crust is of fundamental importance for the dynamics and chemistry of mantle plumes.

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analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties (at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive (isotope dilution) and comparative bulk (e.g., INAA, ICPMS, SSMS) and microanalytical (e.g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.