Rare Earth Element Abundances Research Articles

Abnormal variation of magnetic properties with Ce content in (PrNdCe)2Fe14B sintered magnets prepared by dual alloy method**Project supported by the National Natural Science Foundation of China (Grant Nos. 51461033, 51571126, 51541105, and 11547032), the Natural Science Foundation of Inner Mongolia, China (Grant No. 2013MS0110), and the Inner Mongolia University of Science and Technology Innovation Fund, China.

Resource-saving (PrNdCe)2Fe14B sintered magnets with nominal composition (PrNd)15−xCexFe77B8 (x = 0−10) were prepared using a dual alloy method by mixing (PrNd)5Ce10Fe77B8 with (PrNd)15Fe77B8 powders. For Ce atomic percent of 1% and 2%, coercivity decreases dramatically. With further increase of Ce atomic percent, the coercivity increases, peaks at 6.38 kOe in (PrNd)11Ce4Fe77B8, and then declines gradually. The abnormal dependence of coercivity is likely related to the inhomogeneity of rare earth chemical composition in the intergranular phase, where PrNd concentration is strongly dependent on the additive amount of (PrNd)5Ce10Fe77B8 powders. In addition, for Ce atomic percent of 8%, 7%, and 6% the coercivity is higher than that of magnets prepared by the conventional method, which shows the advantage of the dual alloy method in preparing high abundant rare earth magnets.

Sm-Nd dating and REE Composition of scheelite for the Honghuaerji scheelite deposit, Inner Mongolia, Northeast China

Sm-Nd analyses of seven scheelite samples from scheelite-quartz veins in the Honghuaerji scheelite deposit produce a well-defined linear array on an isochron diagram with a mean square weighted deviation (MSWD) of 0.87 corresponding to an age of 178.4±2.9Ma with εNd(t)=+1.50. This age is interpreted to represent the age of scheelite mineralization. The scheelite Sm-Nd age is in good agreement with U–Pb ages obtained from a mineralization-related granite (179.4~178.6Ma), indicating that there is no apparent age gap between granite crystallization and ore formation. Rare earth element (REE) abundances in the scheelite were determined by in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and the scheelite samples contain elevated REE concentrations with total ΣREE + Y contents in the range of 3339 to 6321ppm. The chondrite-normalized REE distribution patterns of all scheelites are middle REE (MREE)-enriched, with strong negative Eu-anomalies (Eu/Eu*=0.09~0.23). The REE characteristics of the Honghuaerji scheelite suggest that REE3+ substituted into the Ca site along with Na and Nb (dominated by Na), whereas Eu is predominantly present as Eu2+ in the scheelite and may have crystallized from relatively reduced fluids. All sulfur isotope data (δ34S) for sulfide separates range from +2.0 to +3.8‰, with an average of 3.2‰. Measured 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios vary from 18.243 to 18.451, 15.494 to 15.574, and 37.933 to 38.340, respectively. On the basis of common Sr-Nd-Pb-Hf isotopic characteristics between the scheelite and the host granite and the positive initial Nd isotope ratios (+1.46−+1.52), low 87Sr/86Sr ratios (0.704983–0.705297) in the scheelites, it is inferred that the hydrothermal fluids responsible for tungsten mineralization at Honghuaerji were of magmatic origin with a mantle-derived signature. Based on the regional geology, tectonic evolution, and geochemical evidence, the Honghuaerji granite is thought to have been derived from the partial melting of thickened lower crust produced during post-collisional orogenic events associated with the closure of the Mongol-Okhotsk Ocean.

Natural and anthropogenic sources of atmospheric dust at a remote forest area in Guizhou karst region, southwest China

The abundance and distribution patterns of Rare Earth Elements (REE) in atmospheric dust in a typical karst forest area of the Maolan National Nature Reserve Park in Southwest China were determined during the period from May 2009 to January 2011. Total REE concentrations (ΣREE) recorded moderate seasonal variation, ranging from 31.0 mg kg −1 to 88.2 mg kg −1 , with an average of 53.5 mg kg −1 , similar to the ΣREE of local topsoil. The values of ΣREE were negatively correlated with the corresponding dust deposition fluxes, which may be due to different rates of deposition as a function of particulate size. PAAS-normalized REE patterns of the dust showed slightly positive Ce anomalies and enrichment in light REE. Most dust samples had similar PAAS-normalized REE patterns to local topsoil, whereas others were similar to the anthropogenic input material from urban areas.

Anomalous abundance and redistribution patterns of rare earth elements in soils of a mining area in Inner Mongolia, China.

The Bayan Obo Mine, the largest rare earth element (REE) deposit ever found in the world, has been mined for nearly 60years for iron and rare earth elements. To assess the influences of mining activities on geochemical behavior of REEs in soils, 27 surface soil samples and three soil profile samples were collected from different directions in the vicinity of the mine area. The total concentrations of REEs in surface soils varied from 149.75 to 18,891.81mgkg(-1) with an average value of 1906.12mgkg(-1), which was apparently higher than the average values in China (181mgkg(-1)). The order of the average concentrations of individual REEs in surface soils was similar to that in Bayan Obo ores, which confirmed that the concentration and distribution of REEs in the soils was influenced by the mining activities. The concentrations of single REE in the soil profiles showed a similar trend with depth with an increase at 0-25cm section, then decreased and remained relatively stable in the deep part. The normalized curves inclined to the right side, showing the conspicuous fractionation between the light and heavy REEs, which supported by the North American Shale Composite (NASC) and Post-Archean Australian Shale (PAAS) normalized concentration ratios calculated for selected elements (La N /Yb N , La N /Sm N , Gd N /Yb N ). Slight positive Ce anomaly and negative Eu anomaly were also observed.

Rare earth element distribution in tropical coastal wetland sediments: a case study from Vembanad estuary, southwest India

Rare earth element (REE) geochemistry of sediments from Vembanad Coastal Wetland, southwest India, shows that light rare earth elements (LREEs) are the more abundant compared to middle rare earth element (MREE) and heavy rare earth element (HREE). We suggest that the textural parameters and the biochemical processes lead to the REE variation in this coastal wetland environment. Variations in the REE abundance are mainly controlled by the source materials deposited by riverine input. REE records in sediments showed spatial heterogeneity due to the influence of the physico-chemical conditions like, sedimentological conditions, salinity and depositional flux of the sediments along the wetland. Enriched values observed along the northern and southern stations are due to the increased riverine input. The REE ratios and enrichment factor values suggest that the abundance is in the order of LREE > MREE > HREE. Positive Eu anomaly is linked to the source sediments brought down from the catchment areas of the Periyar River and Muvattupuzha River. However, Ce anomaly suggests no significant variation in the oxidation condition at the sites of deposition.

RARE EARTH ELEMENTS USED AS FINGERPRINTS OF DIFFERENTIATED SEDIMENT SOURCES IN THE RIA DE AVEIRO (PORTUGAL)

This work focuses on the distribution and the controlling factors of rare earth element (REE) total concentrations and fractionation patterns in fine sediment fractions of 53 samples collected along the main channels of the Ria de Aveiro, a northern Portuguese coastal lagoon. Total and available concentrations and residual phases of REE and total concentrations in three chemically partitioned fractions (S1 - adsorbed by clay and co-precipitated with carbonates; S2 - adsorbed by organic matter; S3 - adsorbed by amorphous Mn hydroxides) are analysed. These data are joinly analysed with physicochemical, textural and mineralogical and other geochemical data. Sediment samples mainly consisted of phyllosilicates, quartz, plagioclase and K–feldspars. Cerium (Ce) is the most abundant REE in the residual phase and displays the lowest total available percentage, whereas Yttrium (Y) is the most available. The highest total concentration and residual concentration (R) of Ce, Lanthanum (La), Scandium (Sc) and Y are mostly related to fine grained sediments, suggesting that their distributions are conditioned by lagoon hydrodynamics. The dissimilar distribution of REE-S1, REE-S2 and REES3 indicates differentiated sedimentary processes. The enrichment of REE-S2 and REE-S3 is related essentially to biogeochemical processes inside the lagoon. The REE-S1, as well as Ce-S1/Sc-R, trace sediments supplied from the northern areas suplyed mostly by the Douro River outflow and from the Antuã River. In the past, the sediments suplyed by the Douro River through the litoral drift contributed to the formation of the lagoon islands. Thus the relatatively high Ce-S1/Sc-R values inside the lagoon allowed the identification of: sediments supplied from the litoral drift and deposited near the lagoon mouth, erosional processes of the lagoonal islands and sediments supplied by the Antuã River. This work demonstrates that the available concentrations of rare earth elements can be considered as important tools for investigating sediment sources and dispersion in a coastal system. doi: 10.12957/jse.2016.21444

Rare-earth element distribution and genesis of manganese ores associated with Tethyan ophiolites, Iran: A review

AbstractThe Zagros orogenic and metallogenic belt is characterized by the widespread occurrence of manganese and ferromanganese deposits. These deposits are spatially associated with radiolarian cherts and basaltic rocks, which cap the ophiolite sequences. The present work provides a review on the rare-earth element (REE) geochemistry coupled with major- and trace-element geochemical characteristics of the Nasirabad and Abadeh Tashk manganese deposits (associated with the Neyriz ophiolite), and Sorkhvand manganese deposit (associated with the Kermanshah ophiolite). These data are used to gain an insight into the primary ore-forming processes that control the deposition of manganese ores. All of the selected manganese deposits have consistently high Ba contents and low concentrations of trace elements (Co, Cu and Ni) with high Mn/Fe ratios typical of hydrothermal activity. A relatively low REE abundance, Lan/Ndn ratios (>3), and position on a Lan/Cen vs. Al2O3/(Al2O3 + Fe2O3) discrimination plot indicate a distal hydrothermal source for almost all of the selected manganese deposits. Most of the deposits are characterized by Ceanom < –0.1 which reflects the prevailing oxidative conditions during the deposition of manganese ores. Importantly, this is consistent with the occurrence of non-sulfide oxic Mn mineralization in all the manganese deposits of the Zagros orogeny. The comparison of the Sorkhvand, Abadeh Tashk and Nasirabad manganese deposits with other manganese deposits elsewhere in the world indicates that major- and trace-element characteristics, as well as the REE composition of the Zagros manganese deposits are analogous to those typical of hydrothermal deposits.

Tracking the redox history and nitrogen cycle in the pelagic Panthalassic deep ocean in the Middle Triassic to Early Jurassic: Insights from redox-sensitive elements and nitrogen isotopes

In order to clarify the redox history of the central Panthalassic Ocean in the Middle Triassic (Anisian) to Early Jurassic (Toarcian), we determined the abundances of major, trace and rare earth elements, and organic carbon and total nitrogen isotopes from well-exposed shales interbedded with deep-sea cherts from Inuyama, southwest Japan. A distinct positive Ce anomaly accompanying high Mn and weak Mo enrichments was detected in the transitional sequence across the Tr–J boundary, which indicates deposition under a more oxic condition than at any other period in the study section. The oxic period lasted for 130–170kyr, and coincided with a faunal turnover at the end of the Triassic. On the other hand, strong enrichments of U, V, Mo, TOC and TN in Anisian and Toarcian black shales suggest deep ocean anoxia in both intervals. Highly concentrated Mo contents in some black shales indicate euxinia in the pelagic Panthalassic deep ocean. δ15NTN values are low, down to −2.0‰, in such black shales enriched in redox-sensitive elements, compared with other shales. This low δ15NTN values during recurrent oceanic euxinic events in the Anisian may indicate strong assimilation of ammonium, but the possibility of enhanced nitrogen fixation cannot be ruled out especially for the Toarcian anoxic event. This work provides the first documentation of the long-term redox history in the pelagic Panthalassic deep ocean, from the Middle Triassic to the Early Jurassic, based on redox-sensitive elements in shales, and it reveals probable links between oceanic redox changes and biological activity.

Major and trace element and Sr and Nd isotopic results from mantle diapirs in the Oman ophiolite: Implications for off-axis magmatic processes

The Oman ophiolite includes both a fossil fast spreading axis, defined by five mantle diapirs, and an off-axis mantle diapir emplaced 30 km from the axis, providing a natural laboratory for the study of off-axis magmatic processes. We compare field and petrological observations coupled with geochemical and isotopic analyses of samples from the off-axis diapir with those of the nearest on-axis diapir, with a particular focus on the Moho Transition Zone (MTZ). Both diapirs are defined by the presence of steeply plunging lineations, but in the on-axis case, these lineations rotate gradually into parallelism with the horizontal magmatic lineations of the overlying crust, while in the off-axis case, a shear zone separates the steeply plunging lineations from the horizontal lineations of the surrounding mantle. In the on-axis diapir, the MTZ is 50 to 500 m thick and composed of dunite with layered gabbro lenses whereas in the off-axis diapir, the MTZ is thicker and composed of dunite with massive (∼20% of MTZ) clinopyroxenite lenses and a notable absence of plagioclase. Moreover, the off-axis diapir is associated with amphibole-bearing intrusions, consisting of Mg-rich gabbroic sills in the mantle peripheral to the diapir, and microgabbroic lenses of broadly basaltic composition in the overlying crust. The εNd values of the pyroxenites in the MTZ of the off-axis diapir fully overlap with those of the intrusions in the surrounding mantle and crust, suggesting that they are genetically related. Calculated rare earth element (REE) abundances of liquids in equilibrium with clinopyroxene imply that the magmas that traversed the MTZ of the off-axis diapir were more depleted in highly incompatible elements than their counterparts in the MTZ of the on-axis diapir. On the other hand, Nd isotopic compositions of the off-axis samples (εNd=6.2–7.9 in 18 of 19 samples) indicate derivation of their parental magmas from a less depleted source than that which produced the magma associated with the on-axis gabbro (εNd=7.8–9.2, 10 analyses).To explain these observations, we suggest that the earliest magmas in the uprising off-axis diapir formed from the partial melting of pyroxenite veins with less radiogenic Nd isotopic compositions than those of the ambient peridotite. As the diapir traversed the cool, hydrated lithosphere these early melts interacted with depleted harzburgites, lowering the incompatible element contents of the melt products while having little effect on their Nd isotopic compositions. The great abundance of clinopyroxene in the off-axis MTZ might be explained by the high pyroxene component in the original melt but perhaps also by the presence of water in the lithosphere, which would favor the crystallization of clinopyroxene while inhibiting that of plagioclase. The intrusions in the overlying crust could represent, to first order, the secondary melts produced by the melt–harzburgite reaction, while the sills in the surrounding mantle may be cumulates from such secondary melts.These results shed light on processes occurring during interaction between rising off-axis material and depleted, hydrated lithospheric mantle. Furthermore, if our interpretation is correct, the low εNd values of the off-axis samples contribute to the growing body of evidence for the presence of pyroxenite veins in the MORB mantle source.

Geochemistry and Re–Os geochronology of the organic-rich sedimentary rocks in the Jingtieshan Fe–Cu deposit, North Qilian Mountains, NW China

The Jingtieshan Group in the North Qilian Mountains, NW China, is dominantly composed of banded iron formations (BIFs), copper deposits and organic-rich sedimentary rocks (ORS, carbonaceous phyllite). X-ray diffraction analysis of the ORS shows the mineral assemblage to be quartz+clay minerals. The total organic carbon contents show a range of 0.44–1.72%. Here we present the results of the geochemistry and Re–Os geochronology of the ORS from the Jingtieshan Group. The high values of Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Plagioclase Index of Alteration (PIA), and Th/U ratio, indicate intense weathering. The Al2O3/TiO2, Zr/Sc, Th/Sc, La/Th ratios, high rare earth elements abundances, light rare earth elements enrichment (normalized to chondrite), and distinctly negative Eu anomalies, suggest that the Jingtieshan Group ORS were derived mainly from felsic volcanic units. The new Re–Os isochron age of 1308±100Ma (2σ, n=6, MSWD=23) broadly overlap with the previous published ages determined using Sm–Nd and U–Pb isotope systems. The new age represents the depositional age of the Jingtieshan Group, as well that of BIF in the Jingtieshan area. Furthermore, the initial 187Os/188Os ratios (0.44±0.07) indicate that the Os in the seawater was dominantly derived from hydrothermal fluids (∼75%). The Ce anomaly (Ce/Ce∗=0.95–1.00) and V/(V+Ni) ratios (0.71–0.86), as well as the lack of enrichment in redox-sensitive trace elements such as U, V, Zn, Pb, Cu, Ni, Cr, Co and Mn, together with the presence of overlying BIF, suggest that the Jingtieshan area represents a ferruginous deep-water succession. This, and intense submarine hydrothermal activities contributed to the deposition of the Jingtieshan BIF.

大洋富钴结壳采样技术革新及发展趋势

大洋富钴结壳富含多种陆地稀缺的金属及稀土元素，是具有重要战略意义的深海矿产资源。本文综述了我国大洋富钴结壳勘探研究现状，全面介绍了不同采样设备特点及新式采样技术革新，同时展望了相关技术的发展趋势和前景。 Ocean cobalt-rich crust contains abundant metal elements and rare earth elements which make it a kind of deep-sea mineral resources with strategic significance. In this paper, we reviewed the actuality of cobalt-rich crust exploration in China, and present a comprehensive introduction of the characteristics of different sampling equipment and the innovation of new sampling techniques. The technological trend and prospects were also analyzed.

Paleoenvironments revealed by rare-earth element systematics in vertebrate bioapatite from the Lower Devonian of Svalbard

In situ rare-earth element (REE) compositions have been measured in early vertebrate microremains from the Lower Devonian basin of Andrée Land (Svalbard), with the aim of obtaining information about their early depositional environment and potential reworking. Vertebrate microremains with different histology were used for the analyses, sourced from two different localities of marginal marine to freshwater sediments from geographically distant parts of the Grey Hœk Formation (Skamdalen and Tavlefjellet members). We selected thelodont and undescribed ?chondrichthyan scales, which allowed us to define potential taxonomic, histological, and taphonomic variables of the REE uptake. Results showed REE concentrations to be relatively uniform within the scales of each taxon, but apparent discrepancies were visible between the studied localities and separate taxa. The compilation of REE abundance patterns as well as REE ratios have revealed that thelodont and ?chondrichthyan originating from the same locality must have had different burial and early diagenetic histories. The shapes of the REE profiles, together with the presence and absence of the Eu and Ce anomalies, equally suggested different depositional and diagenetic environments for these two sympatric taxa resulting from either stratigraphical or long-distance reworking. The REE concentrations appear to have visible differences between separate dental tissues, particularly between enameloid and dentine of thelodonts, emphasizing the importance of in situ measurements in microfossil biomineral geochemistry.

Evidence from Tm anomalies for non-CI refractory lithophile element proportions in terrestrial planets and achondrites

Thulium is a heavy rare earth element (REE) whose geochemical behavior is intermediate between Er and Yb, and that is not expected to be decoupled from these elements during accretion of planetary bodies and geological processes. However, irregularities in REE volatilities at higher temperature could have decoupled the REEs relative to one another during the early stages of condensation of the solar nebula. Indeed, positive Tm anomalies are found in some refractory inclusions from carbonaceous chondrites, and it is possible that large scale nebular reservoirs displaying positive or negative Tm anomalies were formed during the early history of the solar system. We analyzed a series of meteorites and terrestrial rocks in order to evaluate the existence of Tm anomalies in planetary materials. Relative to CIs (Ivuna-type carbonaceous chondrites), carbonaceous chondrites display unresolved or positive Tm anomalies, while most of the noncarbonaceous chondrites show slightly negative Tm anomalies. Quantification of these anomalies in terrestrial samples is complicated when samples display fractionated heavy REE patterns. Taking this effect into account, we show that the Earth, Mars, Vesta, the aubrite and ureilite parent bodies display small negative anomalies (Tm/Tm∗≈0.975), very similar to those found in ordinary and enstatite chondrites. We suggest that a slight negative Tm anomaly relative to CI is a widespread feature of the materials from the inner solar system. This finding suggests that CI chondrites may not be appropriate for normalizing REE abundances of most planetary materials as they may be enriched in a high-temperature refractory component with non-solar composition. The presence of Tm anomalies at a bulk planetary scale is, to this day, the strongest piece of evidence that refractory lithophile elements are not present in constant CI proportions in planetary bodies.

Rare Earth Elements: Review of Medical and Biological Properties and Their Abundance in the Rock Materials and Mineralized Spring Waters in the Context of Animal and Human Geophagia Reasons Evaluation

New data on the abundance of rare earth elements (REE) and their biological properties, which appeared in recent decades, force the researchers to reconsider the facts previously collected by different researchers related to the study of the geophagia phenomenon in animals and humans. From the standpoint of the new data it becomes apparent that one of the reasons for instinctively traditional form of geophagia, as well as for drinking water from mineralized sources by animals and a man with lengthy visits to the same places could be an instinctual drive of a specific organism to adjust in their bodies and tissues the concentration and ratio of the rare earth elements which are able to actively influence, either directly or indirectly (through the effects on metabolism of other chemical elements in the body) the biochemical and physiological processes that determine the quality of health. Since REE influence at the level of nerve tissue biochemistry, hormonal regulation of the body and even at the genetic level, it all can point to a higher order which they occupy in the hierarchy of elements in the composition of any organism. It seems that REE have reasons to claim to be the main causes of all instinctive forms of traditional geophagia and related consumption of mineralized water.

Impact of the decarboxylation reaction on rare earth elements binding to organic matter: From humic substances to crude oil

The rare earth elements (REEs) are widely used as tracers in studies of various geochemical systems. Their behavior in natural systems such as groundwater and river water is strongly influenced by organic complexation. The behavior of REE during the maturation of organic compounds (e.g., during decarboxylation reaction) is not well understood, and thus forms the topic of this study. In this study, the behavior of REEs during the maturation of organic matters was examined by heating experiments and analysis of crude oil. Heating increased the release of REEs from humic acid, and was associated with a decreased concentration of carboxyl groups in the humic acid. Ternary heating experiments (humic acid+REE+slate) led to the re-adsorption of released REEs to the slate.Carbon-13 nuclear magnetic resonance spectroscopy (13C NMR) did not show peaks corresponding to carboxyl groups in the natural crude oils examined here, meaning that the oils are more highly mature than other oils containing carboxyl groups. The abundances of REEs in the oils without carboxyl groups (this study) were about three orders of magnitude lower than those previously found in oils with carboxyl groups, suggesting that the carboxyl group is important to REE retention in crude oil. These findings suggest that a considerable amount of REEs is released during the early stage of diagenesis, or during decarboxylation, and is likely to be subsequently adsorbed to the petroleum source rock. The variation in the Y/Ho ratio among oils suggests the occurrence of a secondary distribution to the oil-hosting rock. Other metallic elements that behave similarly to REEs, such as Ca, Al, and Fe, can also be released from the organic phase, whereas those that behave differently from the REEs may be retained.

Late Jurassic sodium-rich adakitic intrusive rocks in the southern Qiangtang terrane, central Tibet, and their implications for the Bangong–Nujiang Ocean subduction

The lack of magmatic records with high-quality geochronological and geochemical data in the central segment of the southern Qiangtang subterrane in central Tibet inhibits a complete understanding of the subduction polarity of the Bangong–Nujiang Ocean lithosphere during the Mesozoic. In this study, we present the zircon U–Pb age as well as geochemical and Sr–Nd–Pb isotopic data for the Late Jurassic pluton from the Kangqiong area in the central segment of the southern Qiangtang subterrane. The Kangqiong pluton primarily consists of granodiorites (SiO2=62.87–65.17wt.%) and was emplaced in the Late Jurassic (147.6±2.4–149.9±2.1Ma). The granodiorites display high Na2O numbers (Na2O/K2O=1.75–2.24) as well as high MgO (2.21–3.14wt.%) and Mg-numbers (53–58), are characterized by a low abundance of heavy rare earth elements (e.g., Yb=1.05–1.92ppm) and Y (12.63–17.52ppm), and high Sr/Y (29–61) and La/Yb (14–18) ratios, which are comparable in composition to those of slab-derived adakitic rocks. The Kangqiong adakitic granodiorites have initial (87Sr/86Sr)i ratios of 0.70611 to 0.70669, negative εNd(t) values (−1.06 to −0.25), (206Pb/204Pb)t ratios of 18.42 to 18.47, (207Pb/204Pb)t ratios of 15.62 to 15.63, and (208Pb/204Pb)t ratios of 38.50 to 38.60. These geochemical signatures indicate that the magmas were most likely derived from the partial melting of the subducted Bangong–Nujiang oceanic crust and minor contaminants from the accretionary complex. Our results, in combination with the coeval magmatism in the western segment of the southern Qiangtang subterrane, indicate that the Bangong–Nujiang oceanic lithosphere was subducted northward beneath the Qiangtang Terrane, forming a west-east magmatic arc over 800km during the Late Jurassic.

The Late Cretaceous I- and A-type granite association of southeast China: Implications for the origin and evolution of post-collisional extensional magmatism

We present new geochronological, mineralogical, and geochemical data for granitic plutons that crop out within the Zhoushan archipelago, northeastern coastal Zhejiang Province, in order to constrain their origin, and the genetic relationship between the I- and A-type granites. These granites can be divided into two groups: (1) the northern I-type Putuoshan (PTS) and Dadong'ao (DDA) plutons; and (2) the southern A-type Daqingshan (DQS), Taohuadao (THD), and Xiazhidao (XZD) plutons. Zircon LA–ICP–MS U–Pb dating yielded ages of 98–96Ma for the northern I-type plutons and 89–86Ma for the southern A-type plutons. All of these granites are highly siliceous, K-rich, and have similar total alkali and total rare earth element (REE) abundances. However, there are also geochemical differences between the I-type and the A-type granites. The northern I-type alkali-feldspar granites are high-K calc-alkaline, metaluminous to mildly peraluminous, contain low concentrations of the high field strength elements (HFSE; e.g., Nb, Ta, Zr, and Hf), and have low Ga/Al ratios (2.04–2.44). In contrast, the southern A-type granites are peralkaline and F-rich, and have lower CaO and Al2O3 concentrations, and higher Fe2O3T and HFSE concentrations and Ga/Al ratios (3.25–3.86). Meanwhile, they have slightly higher heavy REE (HREE) concentrations, and are more depleted in Ba, Sr, P, Ti, and Eu than the northern I-type granites. Both the I- and A-type granites have homogeneous whole-rock Nd and highly variable zircon Hf isotopic compositions. Of note, the southern peralkaline A-type granites appear to have more radiogenic Nd and Hf isotope compositions than the northern I-type granites. The present data, together with the results of a previous study on mafic enclaves within the PTS pluton, suggest that the northern I-type alkali-feldspar granites were generated by mixing of mantle-derived material with crustal-derived magmas that formed by dehydration melting of mica-bearing basaltic rocks, leaving a granulite residue in the lower crust. Both the I- and A-type granites were emplaced during post-collisional extensional tectonism associated with rollback of the steeply subducting paleo-Pacific Plate. An increase of the dip angle of the subducted palaeo-Pacific plate between the Early and Late Cretaceous resulted in enhanced extension, further thinning the lithosphere and causing more intensive underplating of mantle-derived magmas. This generated high temperatures and caused the partial melting of the residual granulite material, producing relatively anhydrous F-bearing felsic melts. The mixing of these unusual crustal melts with more voluminous mantle-derived mafic magmas generated the parental magmas that eventually formed the peralkaline A-type granites.

Investigation of Rare-Earth Elements in the Atmosphere of the roAp Star HD 134214: Nd II, Nd III, and Gd II Lines

High-resolution spectra are used to investigate the abundance of rare-earth elements (REE) in the atmosphere of the magnetic, rapidly oscillating, chemically peculiar (roAp) star HD134214. The neodymium abundance is investigated using the lines of neodymium in the first and second ionization states. Disruption of ionization equilibrium REE (mismatch of the contents determined according to the lines of singly and doubly ionized atoms) is found in the atmosphere of the roAp star. Excess abundance of the rare-earth elements (relative to the Sun) is found. The results of an abundance analysis of REE and some other elements are presented. The modulus and the components Br /Bm of the magnetic field are determined.

Diagenetic uptake of rare earth elements by conodont apatite

The rare earth element (REE) composition of bioapatite has long been used as a proxy for ancient seawater chemistry and paleomarine environmental reconstruction, based on the assumption of preservation of a hydrogenous (seawater-derived) REE signal. Recent work, however, has begun to question the provenance of REEs in conodonts, emphasizing the importance of REEs released by the lithogenous fraction of the sediment and subsequently adsorbed onto conodont apatite in the burial environment. Here, we investigate patterns of REE and trace-element abundance in conodonts and their host sediments from the Early to Late Ordovician Huanghuachang and Chenjiahe sections of Hubei Province, South China. Several lines of evidence indicate that REEs in the conodont samples were acquired mainly from clay minerals in the host sediment during burial diagenesis: (1) REEs in conodonts show a strong positive correlation to Th and other lithogenic elements; (2) conodonts and whole-rock samples show general patterns of REE and trace-element enrichment that are highly similar to each other and bear no resemblance to seawater elemental concentrations; (3) similar patterns are observed in Triassic conodonts and whole-rock samples; and (4) Y/Ho ratios in conodonts are mostly <40 (mean ~33), values that are consistent with derivation of >90% of REEs from lithogenous sources. Conodonts show pronounced middle rare earth element (MREE) enrichment, a pattern that is unambiguously of diagenetic origin owing to its association with lower Y/Ho ratios. With increasing MREE enrichment of conodont samples, U concentrations and LaN/YbN ratios shift from high to low, and Mn concentrations from low to high. These patterns suggest that conodont diagenesis was initiated at shallow burial depths under suboxic conditions (i.e., in the zone of Mn(IV) and Fe(III) reduction) but continued at greater burial depths, with most acquisition of secondary REEs at later diagenetic stages. Our findings indicate that (1) conodont apatite frequently does not preserve a recognizable hydrogenous REE signal, and (2) the results of many earlier studies in which REEs in bioapatite were used as a paleoseawater proxy may need re-evaluation.

KIC 4768731: a bright long-period roAp star in theKeplerfield

We report the identification of 61.45 d−1 (711.2 μHz) oscillations, with amplitudes of 62.6 μmag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright (V = 9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of Teff = 8100 ± 200 K, log g = 4.0 ± 0.2, [Fe/H] = +0.31 ± 0.24 and v sin i = 14.8 ± 1.6 km s−1. Line profile variations caused by rotation are also evident. Lines of Sr, Cr, Eu, Mg and Si are strongest when the star is brightest, while Y and Ba vary in antiphase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar Teff and log g. Radial velocities in the literature suggest a significant change over the past 30 yr, but the radial velocities presented here show no significant change over a period of 4 yr.