Rare earth element geochemistry of Late Devonian reefal carbonates, canning basin, Western Australia: Confirmation of a seawater REE proxy in ancient limestones

Rare earth element and yttrium (REE+Y) concentrations were determined in 49 Late Devonian reefal carbonates from the Lennard Shelf, Canning Basin, Western Australia. Shale-normalized (SN) REE+Y patterns of the Late Devonian samples display features consistent with the geochemistry of well-oxygenated, shallow seawater. A variety of different ancient limestone components, including microbialites, some skeletal carbonates (stromatoporoids), and cements, record seawater-like REE+Y signatures. Contamination associated with phosphate, Fe-oxides and shale was tested quantitatively, and can be discounted as the source of the REE+Y patterns. Co-occurring carbonate components that presumably precipitated from the same seawater have different relative REE concentrations, but consistent REE+Y patterns. Clean Devonian early marine cements (n = 3) display REE+Y signatures most like that of modern open ocean seawater and the highest Y/Ho ratios (e.g., 59) and greatest light REE (LREE) depletion (average Nd-SN/Yb-SN = 0.413, SD = 0.076). However, synsedimentary cements have the lowest REE concentrations (e.g., 405 ppb). Non-contaminated Devonian microbialite samples containing a mixture of the calcimicrobe Renalcis and micritic thrombolite aggregates in early marine cement (n = 11) have the highest relative REE concentrations of tested carbonates (average total REE = 11.3 ppm). Stromatoporoid skeletons, unlike modern corals, algae and molluscs, also contain well-developed, seawater-like REE patterns. Samples from an estuarine fringing reef have very different REE+Y patterns with LREE enrichment (Nd-SN/Yb-SN > 1), possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged LREE from a nearby riverine input source. Hence, Devonian limestones provide a proxy for marine REE geochemistry and allow the differentiation of co-occurring water masses on the ancient Lennard Shelf. Although appropriate partition coefficients for quantification of Devonian seawater REE concentrations from out data are unknown, hypothetical Devonian Canning Basin seawater REE patterns were obtained with coefficients derived from modern natural proxies and experimental values. Resulting Devonian seawater patterns are slightly enriched in LREE compared to most modem seawaters and suggest higher overall REE concentrations, but are very similar to seawaters from regions with high terrigenous inputs. Our results suggest that most limestones should record important aspects of the REE geochemistry of the waters in which they precipitated, provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high, non-seawater-like REE contents. Hence, we expect that many other ancient limestones will serve as seawater REE proxies, and thereby provide information on paleoceanography, paleogeography and geochemical evolution of the oceans. Copyright (C) 2004 Elsevier Ltd.

Rare earth element and yttrium variability in South East Queensland waterways

We present data for the rare earth elements and yttrium (REY) in the National Research Council of Canada natural river water reference material SLRS-4 and 19 natural river waters from small catchments in South-East Queensland, Australia, by a direct ICP-MS method. The 0.22 mu m filtered river water samples show a large degree of variability in both the REY concentration, e.g., La varies from 13 to 1157 ppt, and shape of the alluvial-sediment-normalised REY patterns with different samples displaying light, middle or heavy rare earth enrichment. In addition, a spatial study was undertaken along the freshwater section of Beerburrum Creek, which demonstrates that similar to 75% of the total REYs in this waterway are removed prior to estuarine mixing without evidence of fractionation.

Direct quantification of rare earth element concentrations in natural waters by ICP-MS

A direct quadrupole ICP-MS technique has been developed for the analysis of the rare earth elements and yttrium in natural waters. The method has been validated by comparison of the results obtained for the river water reference material SLRS-4 with literature values. The detection limit of the technique was investigated by analysis of serial dilutions of SLRS-4 and revealed that single elements can be quantified at single-digit fg/g concentrations. A coherent normalised rare earth pattern was retained at concentrations two orders of magnitude below natural concentrations for SLRS-4, demonstrating the excellent inter-element accuracy and precision of the method. The technique was applied to the analysis of a diluted mid-salinity estuarine sample, which also displayed a coherent normalised rare earth element pattern, yielding the expected distinctive marine characteristics. (c) 2006 Published by Elsevier Ltd.

The behaviour of the rare earth elements during estuarine mixing-revisited

Complete rare earth element (except Eu) and Y concentrations from the estuarine mixing zone (salinity =0.2 to 33) of Elimbah Creek, Queensland, Australia, were measured by quadrupole ICP-MS without preconcentration. High sampling density in the low salinity regime along with high quality data allow accurate tracing of the development of the typical marine rare earth element anomalies as well as Y/Ho fractionation. Over the entire estuary, the rare earth elements are strongly removed relative to a freshwater endmember (60-80% removal). This large overall removal occurs despite a strong remineralisation peak (190% for La, 130% for Y relative to the freshwater endmember) in the mid-salinity zone. Removal and remineralisation are accompanied by fractionation of the original (freshwater) rare earth element pattern, resulting in light rare earth element depletion. Estuarine fractionation generates a large positive La anomaly and a superchondritic Y/Ho ratio. Conversely, we observe no evidence to support the generation of the negative Ce anomaly in the estuary. With the exception of Ce, the typical marine rare earth element features can thus be attributed to estuarine mixing processes. The persistence of these features in hydrogenous sediments for at least 3.71 Ga highlights the importance of estuarine processes for marine chemistry on geological timescales. (c) 2005 Elsevier B.V. All rights reserved.

Aquatic geochemistry of the rare earth elements and yttrium in the Pioneer River catchment, Australia

The rare earth elements are strong provenance indicators in geological materials, yet the potential for tracing provinciality in surface freshwater samples has not been adequately tested. Rare earth element and yttrium concentrations were measured at 33 locations in the Pioneer River catchment, Mackay, central Queensland, Australia. The rare earth element patterns were compared on the basis of geological, topographical and land-use features in order to investigate the provenancing potential of these elements in a small freshwater system. The rare earth element patterns of streams draining single lithological units with minor land modification show strongly coherent normalised behaviour, with a loss of coherence in agricultural locations. Evidence is reported for an anthropogenic Gd anomaly that may provide a useful hydrological tracer in this region since the introduction of magnetic resonance imaging in 2003. Several samples display a superchondritic Y/Ho mass ratio (up to 44), which is not explainable within the constraints imposed by local geology. Instead, it is suggested that the additional Y is derived from a marine source, specifically marine phosphorites, which are a typical source of fertiliser phosphorus. The data indicate that, under some circumstances, scaled and normalised freshwater rare earth patterns behave conservatively.

Effects of rare-earth co-doping on the local structure of rare-earth phosphate glasses using high and low energy X-ray diffraction

Rare-earth co-doping in inorganic materials has a long-held tradition of facilitating highly desirable optoelectronic properties for their application to the laser industry. This study concentrates specifically on rare-earth phosphate glasses, (R2O3)x(R'2O3)y(P2O5)1-(x+y), where (R, R') denotes (Ce, Er) or (La, Nd) co-doping and the total rare-earth composition corresponds to a range between metaphosphate, RP3O9, and ultraphosphate, RP5O14. Thereupon, the effects of rare-earth co-doping on the local structure are assessed at the atomic level. Pair-distribution function analysis of high-energy X-ray diffraction data (Qmax = 28 Å-1) is employed to make this assessment. Results reveal a stark structural invariance to rare-earth co-doping which bears testament to the open-framework and rigid nature of these glasses. A range of desirable attributes of these glasses unfold from this finding; in particular, a structural simplicity that will enable facile molecular engineering of rare-earth phosphate glasses with 'dial-up' lasing properties. When considered together with other factors, this finding also demonstrates additional prospects for these co-doped rare-earth phosphate glasses in nuclear waste storage applications. This study also reveals, for the first time, the ability to distinguish between P-O and PO bonding in these rare-earth phosphate glasses from X-ray diffraction data in a fully quantitative manner. Complementary analysis of high-energy X-ray diffraction data on single rare-earth phosphate glasses of similar rare-earth composition to the co-doped materials is also presented in this context. In a technical sense, all high-energy X-ray diffraction data on these glasses are compared with analogous low-energy diffraction data; their salient differences reveal distinct advantages of high-energy X-ray diffraction data for the study of amorphous materials. © 2013 The Owner Societies.

Structure of rare-earth phosphate glasses by neutron diffraction

Neutron diffraction was used to measure the structure of the phosphate glasses RAl0.30P3.05O9.62, where R denotes Dy or Ho, and RAl0.34P3.20O10.04, where R denotes La or Ce. For each glass, isomorphic structures were assumed and difference function methods were employed to separate, essentially, those correlations involving the rare-earth ion, R3+, from the remainder. The ratio of bridging oxygen, OB, to terminal oxygen, OT, atoms in the PO4 tetrahedra was quantified and in both materials R3+ and Al3+ are found to act as network modifying cations which bind to the OT. The R–OT coordination number is 6.7(1) and 7.5(2) for the Dy/Ho and La/Ce glasses respectively.

Arc crust-magma interaction in the Andean Southern Volcanic Zone from thermobarometry, mineral composition, radiogenic isotope and rare earth element systematics of the Azufre-Planchon-Peteroa volcanic complex, Chile

The Andean Southern Volcanic Zone (SVZ) is a vast and complex continental arc that has been studied extensively to provide an understanding of arc-magma genesis, the origin and chemical evolution of the continental crust, and geochemical compositions of volcanic products. The present study focuses on distinguishing the magma/sub-arc crustal interaction of eruptive products from the Azufre-Planchon-Peteroa (APP 35°15'S) volcanic center and other major centers in the Central SVZ (CSVZ 37°S–42°S), Transitional SVZ (TSVZ 34.3–37.0°S), and Northern SVZ (NSVZ 33°S–34°30'S). New Hf and Nd isotopic and trace element data for SVZ centers are consistent with former studies that these magmas experienced variable depths of crystal fractionation, and that crustal assimilation is restricted to the lower crustal depths with an apparent role of garnet. Thermobarometric calculations applied to magma compositions constrain the depth of magma separation from mantle sources in all segments of the SVZ to(70-90 km). Magmatic separation at the APP complex occurs at an average depth of ~50 km which is confined to the mantle lithosphere and the base of the crust suggesting localized thermal abrasion both reservoirs. Thermobarometric calculations indicate that CSVZ primary magmas arise from a similar average depth of (~54 km) which confines magma separation to the asthenospheric mantle. The northwards along-arc Sr-Nd-Hf isotopic data and LREE enrichment accompanied with HREE depletion of SVZ mafic magmas correlates well with northward increasing crustal thickness and decreasing primary melt separation from mantle source regions indicating an increased involvement of lower crustal components in SVZ magma petrogenesis. ^ The study concludes that the development of mature subduction zones over millions of years of continuous magmatism requires that mafic arc derived melts stagnate at lower crustal levels due to density similarities and emplace at lower crustal depths. Basaltic underplating creates localized hot zone environments below major magmatic centers. These regions of high temperature/partial melting, and equilibration with underplated mafic rocks provides the mechanism that controls trace element and isotopic variability of primary magmas of the TSVZ and NSVZ from their baseline CSVZ-like precursors.^

Observations and rare earth element composition of manganese nodules during Atlantis cruise AT266, Blake Plateau

An area of about 22,000 km² on the northern Blake Plateau, off the coast of South Carolina, contains an estimated 2 billion metric tons of phosphorite concretions, and about 1.2 billion metric tons of mixed ferromanganese-phosphorite pavement. Other offshore phosphorites occur between the Blake Plateau and known continental deposits, buried under variable thicknesses of sediments. The phosphorite resembles other marine phosphorites in composition, consisting primarily of carbonate-fluorapatite, some calcite, minor quartz and other minerals. The apatite is optically pseudo-isotropic and contains about 6% [CO3]**2- replacing [PO4]**3- in its structure. JOIDES drillings and other evidence show that the phosphorite is a lag deposit derived from Miocene strata correlatable with phosphatic Middle Tertiary sediments on the continent. It has undergone variable cycles of erosion, reworking, partial dissolution and reprecipitation. Its present form varies from phosphatized carbonate debris, loose pellets, and pebbles, to continuous pavements, plates, and conglomeratic boulders weighing hundreds of kilograms. No primary phosphatization is currently taking place on the Blake Plateau. The primary phosphate-depositing environment involved reducing conditions and required at least temporary absence of the powerful Gulf Stream current that now sweeps the bottom of the Blake Plateau and has eroded away the bulk of the Hawthorne-equivalent sediments with which the phosphorites were once associated.