Klaus Peter Jochum

MPI‐DING reference glasses for in situ microanalysis: New reference values for element concentrations and isotope ratios

We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different 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.

Trace element fractionation during dehydration of eclogites from high-pressure terranes and the implications for element fluxes in subduction zones

The trace element compositions of eclogites, blueschists and mafic granulites from high-pressure terranes have been analysed to investigate element losses and fractionation that occur during dehydration of oceanic basalt in subduction zones. Abundances of elements that are suggested to be near-immobile (e.g., Nb, Zr, Ti), Sr-Nd isotopic compositions, and major element compositions indicate that most samples had altered MORB protoliths. The samples show only limited retrograde alteration, and cover a range in pressure-temperature conditions (1.2–4 GPa, 300–1000°C). In ratio diagrams, strong depletions (95–98%) of K, Rb and Ba relative to Nb and Th in most samples are obvious when compared with unaltered and altered MORB or ocean island basalts. The largest fraction of K, Rb and Ba appears to be lost at temperatures < 600–700°C. In contrast, elements such as Th, Nb, Ti, Zr, Nd, Sm and compatible elements show no evidence of significant losses (<10–20%). U and Pb also show losses, but these are significantly less than those for K and Ba. Eclogites retain nearly all Nb during dehydration. Consequently, the depleted nature of sub-arc mantle is the most likely cause for the low Nb abundances in arc lavas. The addition of U during sub-seafloor alteration and its restricted loss during subduction zone metamorphism substantially decreases Th/U and Nb/U in subducted altered MORB. The latter observation suggests that high U/Pb of many metabasaltic eclogites may have been caused by addition of U during sub-seafloor alteration. However, the correlation of U/Pb with Nd/Pb indicates that Pb loss during dehydration is the major cause of increased U/Pb in the eclogites. Model compositions of subducted altered oceanic crust have been established at 600°C and 900°Con the basis of the composition of the high-pressure rocks. Using these data, flux models indicate that Ba and Th in typical arc magmas must be mainly sediment-derived (fluids or melts from subducted sediment or shallow crustal contamination). In contrast, a large fraction of Rb and K and < 40% of the U in arc front magmas may be provided by fluids from subducted altered basalt. The models indicate that subducted altered oceanic basalt provides less than ca. 10% of the Pb and less than 5% of Sr to average arc front magma compositions. The low estimate for Sr confirms previous indications that contributions [page end] from average altered MORB cannot explain the Sr enrichment in arc lavas. Most of the Nd, heavy rare earth elements (REE), Y, high-field strength elements (HFSE) and compatible elements in primitive arc front magmas must be supplied by the depleted mantle wedge and a sedimentary component in arc lavas.

Fluid- and melt-related enrichment in the subarc mantle: Evidence from Nb/Ta variations in island-arc basalts

The single most distinctive feature of volcanic rocks from convergent-margin settings is a marked depletion of the high field strength elements (HFSE) Nb, Ta, and Ti relative to large ion lithophile and light rare earth elements when compared with basalts from mid-oceanic ridges (MORB) and the oceanic islands. A major impediment to a better understanding of this problem has been a lack of high-quality data for the HFSE (particularly Nb and Ta) that occur in very low concentrations in most volcanic rocks from convergent-margin settings. We report new analyses of Nb and Ta for a suite of island-arc volcanic rocks as well as some sea-floor sediments. Our data show that Nb/Ta values for relatively depleted island-arc volcanic rocks are similar to MORB and essentially chondritic (Nb/Ta ∼ 17), whereas more potassic arc volcanics have substantially higher Nb/Ta values (up to 33). We interpret these high values as due to modification of the subarc mantle source by silicic melts derived from the subducting slab, whereas enrichment of the source regions of the less potassic arc rocks involved a slab-derived fluid.

The solar-system abundances of Nb, Ta, and Y, and the relative abundances of refractory lithophile elements in differentiated planetary bodies

Abstract Analytical data for Nb, Y, and Ho in 8 carbonaceous chondrites were obtained by spark source mass spectrometry (SSMS). In addition, three carbonaceous chondrites were analyzed for Ta by radiochemical neutron activation analysis (RNAA). From these data and earlier literature data on the C1 -chondrite Orgueil a consistent set of solar-system abundances is derived for Nb, Y, Zr, Ta, Hf and the REE. Ratios among these elements are constant within analytical uncertainties in all groups of carbonaceous chondrites. In particular we do not find a difference in Zr Hf ratios between C1 and C2 chondrites. The new abundances for C1-chondrites are: Nb (0.246 ppm), Y (1.57 ppm), Ta (0.014 ppm), or 0.696, 4.64, 0.020 atoms/106 Si atoms, respectively. Based on a large number of analytical data on oceanic basalts, it is argued that the relative abundances of these elements are chondritic in the bulk Earth. Ratios such as Zr Hf or Nb Ta are constant and chondritic in oceanic basalts and agree with estimates of the continental crust. The constant but non-chondritic Nb U ratio (47 vs. 30) in oceanic basalts is balanced by a lower Nb U ratio (~ 10) in the crust. The bulk Earth ratio may therefore be chondritic. The Zr Hf and Nb Ta ratios are correlated in lunar rocks. Both ratios vary within a factor of two, similar to the variability in terrestrial oceanic basalts. The Zr Nb and Hf Ta ratios, however, are much more constant on the Moon. The available evidence suggests that refractory lithophile elements in the Earth, the Moon and achondritic meteorites occur in the same proportions as in carbonaceous chondrites. Refractory elements have greatly different volatilities. The same pattern of refractory lithophile elements in chondrites and planets therefore indicates that protoplanetary materials have never been subject to high temperature processes that would fractionate refractory elements from each other. The same ratio of Zr Nb in the three types of carbonaceous chondrites, in the Earth, the Moon and in differentiated meteorites is a good example, since the condensation temperature for Zr is 177 K higher than that for Nb.

The Gabal Gerf complex: A Precambrian N-MORB ophiolite in the Nubian Shield, NE Africa

We report geochemical and isotopic data for tectonically dismembered units of the Cabal Gerf mafic-ultramafic complex, the largest Neoproterozoic (Pan-African) ophiolite in the Arabian-Nubian Shield and located near the Red Sea in the border region between Egypt and the Sudan. The complex consists of basaltic pillow lavas, sheeted dykes, isotropic and layered gabbros and an ultramafic melange, all in tectonic contact along thrust sheets. Major- and trace-element data, including REE, for the pillow lavas and sheeted dykes are indistinguishable from modem high-Ti N-MORB. Chemical variations in the various rock types can be ascribed to fractionation and accumulation involving olivine, clinopyroxene and plagioclase. A comparison with chemical data from ophiolites of the Arabian-Nubian Shield and elsewhere in the world shows the Cabal Gerf complex to be the only Precambrian ophiolite with N-MORB chemistry, and we suggest that its basalts and sheeted dykes originally formed in a major ocean basin. Sm and Nd isotope analyses combined with published zircon data suggest an age of -750 Ma for the time of igneous crystallization of the Gabal Gerf complex. Ed,, initial values vary between + 6.5 and + 8.8, some of the highest yet reported for Neoproterozoic mantle-derived rocks. Pb isotopic data for the basalts and sheeted dykes are similar to modem N-MORB, while the gabbros are more akin to island arc and back-arc basin rocks. We ascribe their elevated Z07Pb/2MPb ratios to mixing of a small amount of pelagic sediment with the magma source of the gabbros during subduction and subsequent melt generation above a subduction zone. The pillow basal&, sheeted dykes and gabbros were brought together by tectonic stacking during the abduction process when collision of island arc complexes with the active margin of the African continent occurred during an accretion event - 600-700 Ma ago.

Extreme enrichment of Sb, Tl and other trace elements in altered MORB

Abstract We have analyzed 25 trace elements (e.g., Sb, Tl, Sn, rare earth elements (REE), Th, U, Nb, Pb, Zr, Hf, and Y) in altered mid-ocean ridge basalts (MORB) from locations near the mouth of the Gulf of California. Our results imply that the heavy REE and Y are not seriously affected by seawater alteration, in agreement with previous studies. The elements Zr, Hf, Nb, light REE and Sr are enriched up to a factor of 2 in some extremely altered samples. However, element ratios between Zr, Hf, and Nb (e.g., Zr/Hf, and Zr/Nb) are not greatly affected, presumably due to the chemical similarity of these elements during any exchange process. The enrichment of Th and Sn is even higher. Antimony, Tl, Cs, Rb, Rb, and Ba are most easily altered by water-rock interaction and are therefore the best indicators for seawater alteration. The enrichment factor of the most mobile element Sb is up to 2000. There is a weak correlation between the concentration in seawater and the enrichment factors. On the other hand, the worldwide pelagic clay pattern matches the enrichment pattern much more closely, and the limited data available for local oceanic sediments give an even better correlation. A plausible model to explain the enrichment pattern may be an elemental exchange between basalt and seawater that had interacted earlier with overlying sediments.

Sponge spicules as blueprints for the biofabrication of inorganic–organic composites and biomaterials

While most forms of multicellular life have developed a calcium-based skeleton, a few specialized organisms complement their body plan with silica. However, of all recent animals, only sponges (phylum Porifera) are able to polymerize silica enzymatically mediated in order to generate massive siliceous skeletal elements (spicules) during a unique reaction, at ambient temperature and pressure. During this biomineralization process (i.e., biosilicification) hydrated, amorphous silica is deposited within highly specialized sponge cells, ultimately resulting in structures that range in size from micrometers to meters. Spicules lend structural stability to the sponge body, deter predators, and transmit light similar to optic fibers. This peculiar phenomenon has been comprehensively studied in recent years and in several approaches, the molecular background was explored to create tools that might be employed for novel bioinspired biotechnological and biomedical applications. Thus, it was discovered that spiculogenesis is mediated by the enzyme silicatein and starts intracellularly. The resulting silica nanoparticles fuse and subsequently form concentric lamellar layers around a central protein filament, consisting of silicatein and the scaffold protein silintaphin-1. Once the growing spicule is extruded into the extracellular space, it obtains final size and shape. Again, this process is mediated by silicatein and silintaphin-1, in combination with other molecules such as galectin and collagen. The molecular toolbox generated so far allows the fabrication of novel micro- and nanostructured composites, contributing to the economical and sustainable synthesis of biomaterials with unique characteristics. In this context, first bioinspired approaches implement recombinant silicatein and silintaphin-1 for applications in the field of biomedicine (biosilica-mediated regeneration of tooth and bone defects) or micro-optics (in vitro synthesis of light waveguides) with promising results.

High-sensitivity Nb analysis by spark-source mass spectrometry (SSMS) and calibration of XRF Nb and Zr

Abstract A new spark-source mass spectrometric (SSMS) technique for precise analysis of low Nb abundances in geological samples has been developed. The main improvements in precision, accuracy and detection power have stemmed from application of isotope dilution for accurate analysis of the internal standard element Zr, high mass resolution for sensitive measurement of low-abundance Nb peaks and precise determination of the element sensitivity of Nb for calibration. Nb concentrations of 5 ppb to 500 ppm (5 orders of magnitude) can be measured by this technique. Only small sample amounts (∼ 50 mg) are needed for an analysis. Precision and accuracy are better than ∼ ± 4%, ∼ ± 8% and ∼ ± 12% for Nb concentrations higher than 1, 0.1 and 0.01 ppm, respectively. To demonstrate the capability of the technique, 16 international standard rocks have been analysed. Our investigations yield the first reliable Nb and Zr abundances of some standard samples. The agreement for most of our data and compiled literature data is within 10% for Nb concentrations > 5 ppm and Zr > 40 ppm. However, for samples with low Nb and Zr concentrations (e.g., DTS- 1 ), differences between our data and the literature can be as large as a factor of 70. These standard data have been used to calibrate X-ray fluorescence (XRF) analyses of Nb and Zr. Careful attention to spectral interferences and matrix corrections combined with long counting times (giving precision between ± 0.4 and ± 0.2 ppm 2σ on Nb) leads to a calibration for 13 standards with MSWD of ∼ 0.9 for Nb, and ∼ 2.7 for Zr. This demonstrates that the SSMS data may be used to obtain consistent, high-precision calibrations for Nb analysis at many XRF laboratories worldwide.

Constraints from high-pressure veins in eclogites on the composition of hydrous fluids in subduction zones

Hydrous high-pressure veins formed during dehydration of eclogites in two paleo-subduction zones (Trescolmen locality in the Adula nappe, central Alps and Munchberg Gneiss Massif, Variscan fold belt, Germany) constrain the major and trace element composition of solutes in fluids liberated during dehydration of eclogites. Similar initial isotopic compositions of veins and host eclogites at the time of metamorphism indicate that the fluids were derived predominantly from the host rocks. Quartz, kyanite, paragonite, phengite, zoisite and omphacite are the dominant minerals in the veins. The major element compositions of the veins are in agreement with experimental evidence indicating that the composition of solutes in such fluids is dominated by SiO2 and Al2O3. Relative to N-MORB, the veins show enrichments of Cs, Rb, Ba, Pb, and K, comparable or slightly lower abundances of Sr, U, and Th, and very low abundances of Nd, Sm, Zr, Nb, Ti and Y. The differential fractionation of highly incompatible elements such as K, U and Th in the veins, as well as the presence of hydrous minerals in the eclogites rule out partial melting as a cause for vein formation. These results confirm previous suggestions that fluids derived from subducted basalt may have low abundances of high field strength elements, rare earth elements and Y. Variable vein-eclogite enrichment factors of incompatible alkalis and to a lesser extent Pb appear to reflect mineralogical controls (phengite, epidote-group minerals) on partitioning of these elements during dehydration of eclogite in subduction zones. However, abundance variations of incompatible elements in minerals from eclogites suggest that the composition of fluids released from eclogites at temperatures <700°C may not reflect true equilibrium partitioning during dehydration. Simple models for the trace elements U and Th indicate the relative importance of the basaltic and sedimentary portions of subducted oceanic crust in producing the characteristic chemical signatures of these elements in convergent plate margin volcanism.

Rhodium and other platinum-group elements in carbonaceous chondrites

Five carbonaceous chondrites (including the CI chondrites Orgueil and Ivuna) were analyzed by spark source mass spectrometry (SSMS) for the platinum-group elements Ru, Rh, Os, Ir, Pt, as well as W, Re, An, Th, and U. Conventional photoplate detection and a recently developed multi-ion counting system were used for ion detection. Results obtained for CI chondrites agree with compiled values within 6%. This study contains the first Rh analyses for this chondrite group. Rhodium concentrations for Orgueil and Ivuna agree well, implying a Solar System abundance of 0.140 ± 0.004 ppm and corresponding to 0.359 ± 0.010 atoms relative to 1 × 106 Si atoms. Concentrations in CM2, CV3, and CK4 chondrites are enriched compared to those of CI chondrites. However, the abundances of the refractory siderophile elements Re, Os, Ir with condensation temperatures above 1600 K (at 10−4 atm) are higher by about 15–20% compared to the less refractory elements Ru, Pt, and Rh. Elements with similar condensation temperatures correlate very well resulting in uniform concentration ratios of RhPt = 0.136 ± 0.006, ReOs = 0.0821 ± 0.0019, and IrOs = 0.949 ± 0.039.