REE Data Research Articles

Hydrothermal CO 2 degassing in seismically active zones during the late Quaternary

Natural CO 2 discharges are abundant in Turkey as evident from ongoing deposition of recent terrace-mound travertines and emplacement of significant travertine vein and breccia deposits in fractured damage zones of active fault systems. We report high-precision U-series age data for the vein carbonates combined with important field observations and geochemical data to evaluate the travertine veining and CO 2 degassing history in seismically active areas. Field evidence suggests that travertine-filled veins and associated breccias represent hydrothermal eruption products, which probably formed by hydraulic fracturing in response to overpressure of CO 2-rich fluids. Stable isotope and REE data support the field observations and indicate that travertine veins formed as thermogene deposits from rapidly ascending CO 2-rich fluids. Travertine veins from the Kirsehir geothermal field give U-series ages in a range from 10.6 ± 0.3 ka to 86.16 ± 1.24 ka, with a majority of ages falling between 10.6 ± 0.3 and 11.3 ± 0.2 ka. Vein samples from the Pamukkale geothermal field yield U-series ages between 21.1 ± 0.1 ka and 73.6 ± 0.6 ka. Two major age groups are evident in Pamukkale that cluster coherently around 21 ka and 25 ka. A large number of travertine veins we dated by high-precision U-series technique coincide with times of cold/dry climate events. This is different from surface sinter deposits in geothermal fields, which more frequently form during warm and wet periods. We propose that a significant reduction in surface discharge of CO 2 by spring or geothermal waters during dry climate periods may promote oversaturation of CO 2 in deep reservoirs. Host rock fracturing in response to seismic shaking and fluid overpressure results in rapid exsolution and expansion of the dissolved gas and may lead to hydrothermal eruptions.

Adakite–TTG connection and fate of Mesoarchaean basaltic crust of Holenarsipur Nucleus, Dharwar Craton, India

Holenarsipur Nucleus (HN) is one of the oldest part (3.5–3.1 Ga) of the continental crust of India. It is made up of mafic–ultramafic-komatitic (3.35 Ga) greenstone belts, migmatitic TTG (tonalite–trondhjemite–granodiorite 3.3 Ga) and diapiric trondhjemites (3.1 Ga). New major, trace and REE data on these rocks presented here provide constraints on adakite–TTG connection model and petrogenesis of these rocks of HN, in addition to recycling of the Early-Mesoarchaean basaltic crust and evolution of Mesoarchaean continental crust. Although of two different ages, the chemical characteristics of the migmatitic TTGs and diapiric trondhjemites of the HN resemble with the Archaean and Cenozoic high silica adakites (HSA), and the adakites from two Neoarchaean greenstone belts of Dharwar Craton, they also display similarities with the Early-Mesoarchaean TTGs from different cratons. Based on the compositional variations observed in TTG and diapiric trondhjemites of HN, we propose that plume fed, basaltic and/or basaltic komatiitic oceanic crust/slab flatly (shallow angle) subducted and melted under high Archaean geothermal regime to produce TTGs. Identification of HSA in 2.7 Ga old greenstone belt subduction complexes that are compositionally similar to TTG, suggests the possibility of continuation of this process into Neoarchaean and supports a genetic connection between TTG and adakites.

Iron Skarns of the Vegas Peladas District, Mendoza, Argentina

The Andean belt southwest of Mendoza, Argentina, hosts 23 Fe, Fe-Cu, and Cu (Ag) deposits classified variously in the literature as skarn, iron oxide-copper-gold (IOCG), and manto-type Cu deposits. The Vegas Peladas deposit is one of the best exposed Fe skarns with mineral assemblages and hydrothermal features similar to many other calcic Fe skarns of the world. The plutonic rocks of Vegas Peladas consist of a series of diorite to granite stocks, dikes, and sills. The major-, trace-, and rare earth-element geochemistry analyses of these igneous rocks indicate they were derived from subarc mantle sources. The Vegas Peladas deposit formed by the overprinting of two different metamorphic and metasomatic events associated with early diorite and later granite intrusions. Alteration associated with the early diorite intrusion consists of a metamorphic halo (800 m wide) and a zoned calcic skarn with inner garnet (Ad31–89 Py0–2) + clinopyroxene + magnetite + quartz, intermediate garnet (Ad38–51 Py1–2) ± clinopyroxene, and distal veins of garnet (Ad92–100) ± clinopyroxene (Hd72–29 Jo1–4). The latest alteration consists of widespread albite (Ab96–98) ± epidote ± quartz ± calcite ± chlorite ± pyrite ± titanite. Magnetite and hematite are the main iron ore minerals and occur as massive orebodies and veins associated with retrograde epidote and amphibole. Alteration of the diorite consists of early orthoclase + quartz followed by later amphibole ± quartz ± magnetite ± epidote ± feldspar. The granite-related skarn overprints the earlier diorite-related skarn and consists of garnet + clinopyroxene + scapolite (Me28–36) ± quartz ± alkali feldspar endoskarn and a zoned exoskarn with proximal garnet ± clinopyroxene ± quartz, intermediate green garnet (Ad30–81 Py0–1) + clinopyroxene (Di82–93 Jo4–2), and distal scapolite (Me25–36) ± ferroactinolite ± pyrite veins. Based on fluid inclusion, stable isotope, and REE data, the prograde skarn formed at depths of ~ 3.5 km under lithostatic pressure of ~1 kbar, from high temperature (670°–400°C), saline and iron-rich (>50 wt % NaCl equiv, NaCl ± KCl ± FeCl2) magmatic fluids (garnet δ18OH2O = 7.2–8.5‰) with intermediate oxygen fugacity. Iron ore and retrograde exoskarn assemblages formed under hydrostatic condition after the fracturing of early skarn. Fluids in this stage had lower temperature (T 550°C) and also generated saline (30.3 to 45.3 wt % NaCl equiv, H2O-NaCl-FeCl2) + vapor fluids by immiscibility that redistributed some of the iron from the previous skarn.

Petrogenesis of augite-bearing ureilites Hughes 009 and FRO 90054/93008 inferred from melt inclusions in olivine, augite and orthopyroxene

Melt inclusions in ureilites occur only in the small augite- and orthopyroxene-bearing subgroups. Previously [Goodrich C.A., Fioretti A.M., Tribaudino M. and Molin G. (2001) Primary trapped melt inclusions in olivine in the olivine–augite–orthopyroxene ureilite Hughes 009. Geochim. Cosmochim. Acta 65, 621–652] we described melt inclusions in olivine in the olivine–augite–orthopyroxene ureilite Hughes 009 (Hughes). FRO 90054/93008 (FRO) is a near-twin of Hughes, and has abundant melt inclusions in all three primary silicates. We use these inclusions to reconstruct the major, minor and rare earth element composition of the Hughes/FRO parent magma and evaluate models for the petrogenesis of augite-bearing ureilites. Hughes and FRO consist of 23–47 vol % olivine (Fo 87.3 and 87.6, respectively), 7–52 vol % augite ( mg 89.2, Wo 37.0 and mg 88.8, Wo 38.0, respectively), and 12–56 vol % orthopyroxene ( mg 88.3, Wo 4.9 and mg 88.0, Wo 4.8, respectively). They have coarse-grained (⩽3 mm), highly-equilibrated textures, with poikilitic relationships indicating the crystallization sequence olivine → augite → orthopyroxene. FRO is more shocked than Hughes, experienced greater secondary reduction, and is more weathered. The two meteorites are probably derived from the same lithologic unit. Melt inclusions in olivine consist of glass ± daughter cpx ± metal–sulfide–phosphide spherules ± chromite, and have completely reequilibrated Fe/Mg with their hosts. We follow the method of Goodrich et al. (2001) for reconstructing the composition of the primary trapped liquid they represent (olPTL), but correct an error in our treatment of the effects of reequilibration. Inclusions in augite consist of glass, which shows only partial reequilibration of Fe/Mg. The composition of the primary trapped liquid they represent (augPTL) is reconstructed by reverse fractional crystallization of wall augite from the most ferroan glass. Inclusions in orthopyroxene consist of glass + 30–50 vol % daughter cpx. The cpx shows complete, but the glass only partial, reequilibration of Fe/Mg. A range of possible compositions for the primary trapped liquid they represent (opxPTL) is calculated by modal recombination of glass and cpx, followed by addition of wall orthopyroxene and adjustment of Fe/Mg for equilibrium with the primary orthopyroxene. Only a small subset of these compositions is plausible on the basis of being orthopyroxene-saturated. Results indicate that olPTL, assumed to represent the parent magma of these rocks, was saturated only with olivine and in equilibrium with Fo ∼ 83. AugPTL and opxPTL are very similar in composition; both are close to augite + orthopyroxene co-saturation and in equilibrium with Fo 87/8. We suggest that olPTL was reduced to Fo 87/8 due to smelting during ascent, and show that this produces a composition very similar to that of augPTL and opxPTL. REE data for each of the three primary silicates and the least evolved melt inclusions in olivine are used to calculate REE abundances in the Hughes/FRO parent magma. All four methods yield very similar results, indicating a REE pattern that is strongly LREE-depleted (Sm/La = 3.3–3.7), with a small negative Eu anomaly (Eu/Eu* = 0.82) and slight HREE-depletion (Gd/Lu = 1.4–1.6). The Hughes/FRO parent magma provides a robust constraint on models for the petrogenesis of augite-bearing ureilites. Its major, minor and rare earth element composition suggests derivation through mixing and/or assimilation processes, rather than as a primary melt on the ureilite parent body.

Geochemistry of shales of the Upper Cretaceous Hayang Group, SE Korea: Implications for provenance and source weathering at an active continental margin

Shales of the Upper Cretaceous Hayang Group in the Yeongyang Subbasin, southeastern Korea were deposited in fluvio-lacustrine environments as the Paleo-Pacific (Izanagi) Plate obliquely subducted beneath the Asian continent. Major and trace element compositions derived from shales analyzed from the Hayang Group reveal geochemical signatures that are different from Post-Archean average Australian Shale (PAAS), but are typical of igneous rocks found in the continental-margin island arc settings. For example, most major element concentrations are depleted relative to PAAS; among them MgO and MnO depletions are most pronounced in all shales. CaO enrichment is notable in some formations due to the presence of secondary calcite as dispersed micro-calcite nodules. Sc, Y, and Th concentrations are also slightly depleted relative to PAAS while chondrite-normalized REE data for shales from the Hayang Group show moderate to large uniform LREE enrichment but variable HREE depletions. In addition, they are more fractionated than PAAS, and have significant negative Eu anomalies. Moreover, the chemical index of alteration and A–CN–K relations comply that the source area was dominated by non-steady state weathering regimes indicative of active uplift along an active continental margin. These regions were punctuated by two periods of steady-state weathering or alternatively by enhanced recycling of sediments. The latter interpretation is in accord with the timing of exposure of a cherty sequence in the source area. Mixing calculations based on REE data suggest that the average shale in the Hayang Group was derived from sources composed of Precambrian granitic gneiss, arc basaltic rocks, Triassic Yeongdeok Granite in the subbasin, and the Mino accretionary complex of SW Japan with ratios around 43.7 (31.8–73.2):26.4 (15.8–36.7):15.4 (2.8–33.9):14.5 (0.0–33.8). However, these proportions change up sequence.

Rare earth element and yttrium geochemistry applied to the genetic study of cryolite ore at the Pitinga Mine (Amazon, Brazil)

This work aims at the geochemical study of Pitinga cryolite mineralization through REE and Y analyses in disseminated and massive cryolite ore deposits, as well as in fluorite occurrences. REE signatures in fluorite and cryolite are similar to those in the Madeira albite granite. The highest ΣREE values are found in magmatic cryolite (677 to 1345 ppm); ΣREE is lower in massive cryolite. Average values for the different cryolite types are 10.3 ppm, 6.66 ppm and 8.38 ppm (for nucleated, caramel and white types, respectively). Disseminated fluorite displays higher ΣREE values (1708 and 1526ppm) than fluorite in late veins(34.81ppm). Yttrium concentration is higher in disseminated fluorite and in magmatic cryolite. The evolution of several parameters (REEtotal, LREE/HREE, Y) was followed throughout successive stages of evolution in albite granites and associated mineralization. At the end of the process, late cryolite was formed with low REEtotal content. REE data indicate that the MCD was formed by, and the disseminated ore enriched by (additional formation of hydrothermal disseminated cryolite), hydrothermal fluids, residual from albite granite. The presence of tetrads is poorly defined, although nucleated, caramel and white cryolite types show evidence for tetrad effect.

Petrography and geochemical behaviour of trace element, REE and precious metal signatures of sulphidic banded iron formations from the Chikkasiddavanahalli area, Chitradurga schist belt, India

The ∼1.2 km long and ∼250 m wide Chikkasiddavanahalli (C.S. Halli) hill range consists of mixed sulphidic-oxide banded iron formations (BIFs) and Fe-rich phyllites (±carbonaceous), which overlie carbonated schistose and massive meta volcanics. In stratigraphic succession, the lithologies represent the Ingaldhal Formation and are an integral part of the Chitradurga schist belt in the Western Dharwar Craton. The general strike at C.S. Halli varies from N–S to 340° with vertical to steep dips towards east and west. The sulphides, oxides and silicates exhibit intergrowth replacement textures developed during regional greenschist- and amphibolites- facies metamorphism. The BIFs show mesobands of recrystallised cherts and iron sulphides such as pyrite, arsenopyrite, and silicates such as subordinate grunerite, hornblende, chlorite, muscovite, actinolite and minor carbonates such as ankerite, calcite and magnesian siderite. Chemical data indicate depletion in Ti, Mn, Co, Cu, Cr and Ni in these iron formations. Most chondrite normalized REE patterns of the iron formation show moderate LREE and HREE enrichment coupled with strong positive Eu anomaly; the mineralized portions exhibit characteristic negative Ce and Eu anomalies (Eu/Eu∗ 0.21 to 3.00). The total REE abundance varies, correlates well with the iron contents of the BIFs, and similar to those exhibited by hydrothermal plumes [Chown, E.H., Dah, E.N., Mueller, W.G., 2000. The relation between iron formation and low temperature alteration in a Archean volcanic environment. Precambrian Research 101, 263–275]. Trace and REE data suggest that primary mantle-derived hydrothermal solutions were added to the pore fluids of sediments of the Chitradurga basin and supplied chemical constituents such as FeO, SiO 2 and REE. Oxidation of FeO to Fe 2O 3 was caused by the photosynthesis of primitive stromatolite-building cyanobacteria. Geochemical data suggest a model involving epigenetic gold mineralisation in close association with shear zone deformation, quartz-calcite vein activity and sulphidation in the mixed sulphide oxide facies BIF and associated iron phyllites in the C.S. Halli area, Western Dharwar Craton, India.

U–Pb geochronology of paragneisses and metabasite in the Xitieshan area, north Qaidam Mountains, western China: Constraints on the exhumation of HP/UHP metamorphic rocks

The Xitieshan HP/UHP metamorphic unit is a polyphase paragneiss–orthogneiss–metabasite complex preserving relics of an early eclogite facies metamorphism (as deduced from the presence of clinopyroxene + plagioclase symplectite after omphacite in metabasite) followed by decompression through the granulite and amphibolite facies. Paragneisses contain garnet, kyanite (partially replaced by sillimanite), feldspar, quartz and biotite, with minor rutile and zircon. The metabasite consists of garnet, amphibole and plagioclase with relict clinopyroxene + plagioclase symplectite. Two main high-temperature metamorphic stages are distinguished: (1) a high-pressure granulite stage, characterized by the assemblage garnet–kyanite–K-feldspar–plagioclase–quartz–rutile in the paragneisses and garnet–clinopyroxene–plagioclase–quartz in the metabasite; (2) a medium–low pressure granulite to upper amphibolite facies stage, leading to the formation of sillimanite in the paragneisses and overgrowth of amphibole on Cpx–Pl symplectite in the metabasite. SHRIMP U–Pb analyses of metamorphic zircons, in conjunction with LA-ICPMS REE data and rare mineral inclusions in zircons, show that the high-pressure granulite metamorphism recorded by these rocks occurred between 451 and 461 Ma and the medium–low pressure granulite–upper amphibolite facies metamorphic overprint between 423 and 427 Ma, suggesting about 30 Ma residence time in medium–lower crustal levels after an earlier eclogite facies metamorphism (ca. 480 Ma). Based on comparison with other HP/UHP metamorphic units in the North Qaidam Mountains (NQD), these results suggest diachronous subduction and exhumation in the different units of the NQD.

Heavy Minerals and Rare Earth Elements in Coastal and Inland Dune Sands of El Vizcaino Desert, Baja California Peninsula, Mexico

A heavy mineral (HM) study and light and heavy rare earth elements (LREE and HREE) analysis were performed in coastal and inland dune sands, El Vizcaino Desert, Central Baja California Peninsula, Mexico. Our study shows high abundances of hornblende and apatite in the El Vizcaino dune sands, suggesting a dominance of granodiorites/intermediate plutonic rocks and marine authigenic phosphorite in the dune sands. There is a relationship between unstable heavy minerals like hornblende, pyroxenes, and sphene, and heavy rare earth elements (HREE) that suggests that unstable heavy minerals are potential carriers of HREE in the dune fields. However, there is a slight depletion of HREE in relation to LREE, especially in one locality of the inland dunes probably associated with the wind regime and weathering of unstable heavy minerals in the sands. Inland, transitional, and coastal dune fields can be observed as different dune provinces by means of grouping HM and REE data in two separate dendograms. It seems that HREE are correlated with fine-grained sand sizes and correlated with high CIA values linked to slightly weathered sands.

Geochemical constraints on the origin of sulfide mineralization in the Duke Island Complex, southeastern Alaska

Magmatic Cu‐Ni‐PGE sulfide mineralization associated with mafic to ultramafic igneous rocks is rare in convergent plate settings. However, recent exploration in the Duke Island Complex of southeastern Alaska has detected horizons of sulfide mineralization primarily in the olivine clinopyroxenite unit. The composition of the sulfides, recalculated to 100% sulfide, averages 0.48% Ni and 1.4% Cu. The Duke Island Complex was generated by the emplacement of multiple pulses of variably fractionated magma ranging in composition from picrite to ankaramite that originated in deeper staging chambers. The presence of sulfides in the complex indicates that fO2 conditions were more reduced than those commonly ascribed to arc‐related magmas. The mass of sulfide mineralization together with the sulfur isotopic values indicates that external sulfur was added to the parent magmas at staging chambers. Os isotopic data from sulfides and C isotopic compositions of graphite in the olivine clinopyroxenites also indicate that the parental magmas were contaminated by crustal material. However, oxygen isotopic values of clinopyroxene together with the REE data suggest that bulk assimilation of country rocks has not occurred and the contamination was selective, involving C‐ and S‐bearing fluids or graphitic sulfides. The observed enrichment in Cu and S isotopic values of the sulfides is best explained by assimilation of sulfides from metal‐bearing rock types such as black shales or volcanogenic massive sulfide deposits that occur in terranes above the mantle wedge.

REE Compositions of Lower Ordovician Dolomites in Central and North Tarim Basin, NW China: A Potential REE Proxy for Ancient Seawater

Abstract: Rare earth element compositions of Lower Ordovician dolomites in the Central and Northern Tarim Basin are studied. Most dolomite samples are more or less contaminated by clay minerals. Their rare earth element compositions have been consequently changed, showing both seawater‐like and non‐seawater‐like features. The clay contamination should be disposed before the REE data are used. Through ICP‐MS and ICP‐AES analyses, the REE features are well documented. The clay contamination is quantitatively determined by microscopic investigation, trace elements and REE contents. The dolomites, at least in the Tarim Basin, are thought to be pure when their total LREE contents are less than 3times10−6. Through comparison, the pure dolomites show similarities in REE patterns but differences in REE contents with co‐existing pure limestone, which indicates that dolomitization may slightly change the REE compositions. Nevertheless, whatever the change is, the pure dolomites may act as a potential REE proxy for Ordovician seawater, which would be significant for ancient massive dolomite strata that lack limestone.

Chemical condition for the appearance of a negative Ce anomaly in stream waters and groundwaters

Nine publications showing REE data in groundwaters and river water were examined to understand the general condition of terrestrial water where a negative Ce anomaly develops. It was found that the negative Ce anomaly only appeared when Fe, Mn and dissolved organic carbon (DOC) concentrations were low (Fe and Mn < 5 × 10-5 mol/L and DOC < 10 mg/L). Assuming that Ce3+ and Fe2+ concentrations were limited by the formation of cerianite and ferrihydrite, respective redox potential (Eh) was calculated from each of Ce3+ and Fe2+ concentrations. For data sets displaying Ce anomalies, the calculated Ehs (cEhs) showed a 1:1 relationship between Ce and Fe. This relationship indicates that the absolute concentration of Ce in natural water may be thermodynamically determined in situ by Eh and pH when concentrations of Fe, Mn and DOC are poor.

Characteristics of bleaching of sandstone in northeast of Ordos Basin and its relationship with natural gas leakage

Bleaching of sandstone has significant applications to tracing hydrocarbon pathways and evaluating the scale of natural gas seepage. Bleaching of sandstones in the northeast of Ordos Basin is mainly distributed in the Mesozoic Yan’an Formation. Studying on petrology, major elements, REEs and trace elements of bleached sandstones and comparing with adjacent sandstones, combining with geologic-geochemical evidences of gas seepage in the northeast of the basin, the bleached sandstones are formed in the acid environment and reducing fluids. Characteristics of petrology show that the contents of kaolinite are high and the color of margin of ferric oxide minerals is lighter than that of the center. Major elements of sandstone samples show high contents of Al2O3 and low ratio of Fe3+/Fe2+. The TFe2O3 content of the bleached sandstone is lower than that of red rock. REE data show that bleached sandstones have low ΣREE contents and Eu-depleted and slightly Ce-enriched. Trace elements show that the bleached sandstones enrich in Co, deplete in Sr, and slightly enrich in Zr and Hf which are close to the values for the green alteration sandstones, and slightly lower than ore-bearing sandstones. Geochemical characteristics of oil-bearing sandstone in the northern basin suggest that the oil-shows are formed by matured Carboniferous-Permian coal bed methane escaping to the surface, and natural gas in field could migrate to the north margin of the basin. The δ 13C (PDB) and δ 18O(PDB) values of calcite cement in the study area range from −11.729‰ to −10.210‰ and −14.104‰ to −12.481‰, respectively. The δ 13C (PDB) values less than −10‰ imply the carbon sources part from organic carbon. Comprehensive study suggests that the gas leakage has occurred in the northeastern basin, which is responsible for bleaching of the sandstone on top of the Yan’an Formation.

Tracing dust input to the Mid-Atlantic Ridge between 14°45′N and 36°14′N: Geochemical and Sr isotope study

A geochemical and Sr isotope study was carried out on sediment cores collected from the Logatchev hydrothermal vent site (14°45′N) on the Mid-Atlantic ridge, with the aim of identifying aeolian inputs into the overlying water column. The Logatchev vent site lies beneath the NE trade winds, which transport large amounts of detrital material across the North Atlantic. Sequential dissolution of the sediments has been used to discriminate the detrital fraction from other types of sediment. REE patterns for the acetic acid fraction at the Logatchev site record contributions from biogenic carbonate (seawater-like REE pattern) and oxy-hydroxides, which exhibit positive Eu and negative Ce anomalies, typical of hydrothermal origin. The Logatchev site leach fractions have similar major element compositions to terrigenous Al–Fe–Mn oxides, whose REE patterns show strong positive Ce and negative Eu anomalies that are comparable to those of “preformed” Fe–Mn oxides of continental origin. Based on major element and REE data and 87Sr/ 86Sr ratios (0.7197–0.7236), the residue fractions at the Logatchev site contain a significant contribution from aeolian sources, whose chemical composition is virtually identical to oligotrophic settling particles in the Equatorial Atlantic Ocean. In comparison, residues from the Rainbow hydrothermal site (36°14′N), have geochemical composition controlled by hydrothermal anhydrite [Chavagnac V., German C.R., Milton J.A., Palmer M.R., 2005. Sources of REE in sediment cores from the Rainbow vent site (36°14′N, MAR). Chem. Geol. 216, 329–352.]. They are characterised by 87Sr/ 86Sr ratios of 0.7087–0.7093, which are significantly less radiogenic than those of the Saharan dust. Hence, the data suggest (1) a significant contribution of aeolian material to the sediments at 14°45′N that is not present at 36°14′N, (2) that this material is most likely of North-African origin, and (3) that this source of aeolian material has remained relatively constant over the last 13 kyr.

Rare Earth and Other Trace Element Content of NRCC HISS‐1 Sandy Marine Sediment Reference Material

The National Research Council (NRC), Ottawa, Canada sandy marine sediment reference material HISS‐1 was characterised for thirty‐seven trace elements by neutron activation optimised irradiation, cooling and counting protocols using the low power Miniature Neutron Source Reactor (MNSR) as a neutron source. This INAA methodology quantified twenty additional elements including ten rare earth (Ce, Dy, Eu, Ho, La, Lu, Nd, Sm, Tb and Yb) and ten other elements (Ba, Br, Cs, Ga, Hf, Rb, Sc, Ta, Th and Zr) missing in the final NRCC certification. A large number of values produced by different irradiation schemes together with the use of certified reference materials in the quantification step that showed good precision, provided confidence in the results. The reliability of the REE data was checked by plotting chondrite‐normalised graphs.

Early to Middle Miocene intra-continental basaltic volcanism in the northern part of the Arabian plate, SE Anatolia, Turkey: geochemistry and petrogenesis

Continental basalts ranging in age from 16.5 to 19.08 Ma crop out throughout the northern part of the Arabian plate. The basalts have distinctive petrographic characteristics such as rounded and skeletal olivine phenocrysts with abundant melt inclusions, implying the mixing of two distinct magmas. All of the analysed basalts are tholeiitic in composition. The presence of quartz xenocrysts with clinopyroxene rims in some samples indicates that crustal assimilation was probably an important process during magma ascent to the surface, and low Mg number and high SiO2 contents of the basalts clearly show that they have experienced fractional crystallization as well as crustal contamination. Variations of the major and trace elements versus MgO show that olivine+clinopyroxene+plagioclase were the main fractionating minerals. In terms of incompatible trace elements, the basalts have OIB-like signatures with a slight depletion at Nb–Ta on primitive-mantle-normalized diagrams. The basalts have slightly LREE enriched patterns with La/YbN = 5.5 to 6.7. La/Nb ratios are close to unity, suggesting the melts may have originated in the asthenospheric mantle. Partial melting modelling based on REE data imply that the melts were not produced from a single mantle source depth, which is either purely a spinel- or garnet-peridotite end member. The samples lie on a binary mixing line between low-degree melts (&lt;5%) from garnet-peridotite and higher-degree melts (&gt;10%) from spinel-peridotite sources on a plot of La/Yb v. Dy/Yb, requiring interaction of melts derived from both garnet- and spinel-peridotite fields. Melts originating from both sources were initially tapped by distinct magma chambers, which subsequently hybridized into a single flow. Hybridized magma ascended to the surface along Neogene strike-slip faults, which are linked to the Dead Sea Fault Zone.

Provenance of aeolian sediment in the Taklamakan Desert of western China, inferred from REE and major-elemental data

To identify the provenance of aeolian deposits in the extensive dune field in the Taklamakan Desert is of great importance for understanding the formation of this, the largest sand sea in China. The opinions from earlier studies are quite dipolar and are as follows: (a) local origin of the dune sands in different parts of the desert on the basis of various heavy mineral assemblages; and (b) strong homogenization of the sands in the entire Taklamakan on the basis of geochemical data from whole-rock samples. By separately examining the REE characteristics and major-elemental composition in coarse and fine fractions of the samples from aeolian deposits, this paper provides new data for interpreting sources of aeolian deposits in the Taklamakan. The sampling sites are distributed in four different fluvial systems, i.e. the areas of the Keriya River, Niya River and Cele River in the southern part and the northern margin near the Tarim River (Fig. 1). Our results show that there are some significant differences in concentrations of trace elements and in REE features between the coarse and the fine fractions of the aeolian sediment. The major-elemental and REE data suggest that the coarser sand is different from area to area in the desert rather than a homogenization of the entire basin. The fine fractions (mainly silts) are more homogenized. The regional difference of coarse fractions in the study areas is consistent with the fluvial and wind systems in the basin. This confirms that the sands are often mixed between the northern and southern parts but there is much less mixing along the east–west direction. It should be emphasized that not only glacial and aeolian processes but also fluvial and lacustrine processes have jointly contributed to the formation of the huge sand sea. In addition, little variation is found between old and young sands in two sediment sequences in the central part of the desert, indicating consistency of sand sources in a given site during the last 40 ka.

U-series dating and geochemical tracing of late Quaternary travertine in co-seismic fissures

We present a method to constrain the timing of fissure generation related to late Quaternary seismic events using the uranium-series technique. Dated samples were from travertine deposits precipitated in co-seismic extensional fissures along major active faults in Western Turkey. Stable isotope and REE data indicate that the precipitation of the fissure travertines was not controlled by the hydrologic regime that is responsible for the speolethem deposition in the same region. Moreover, the REE composition and concentration of the water from which the fissure travertine precipitated were significantly different from those of the current geothermal waters in the study area. The carbonate generation in the co-seismic fissures is interpreted to be the product of rapid precipitation from deeply infiltrated and CO 2-enriched surface water during seismic strain cycles. Results show that U-series dating of fracture-filling travertine deposits from seismically active areas provide important temporal information relevant to establishing recurrence intervals of late Quaternary and prehistoric major earthquake events. Precise dating of prehistoric earthquakes may be of great value for seismic hazard studies and earthquake forecasting research, for which accurate estimates of recurrence intervals are critical.

Comments on: “Trace element and isotopic evidence for Archean basement in the Lonar crater impact breccia, Deccan volcanic province” by Ramananda Chakrabarti and Asish R. Basu in Earth and Planetary Science Letters 247 (2006) 197–211

The effect of meteorite impact on basement rocks remains widely debated at Lonar Crater, Central India. We investigate an impact melt-bearing rock from the ejecta layer of Lonar to assess the potential interaction of the projectile with the underlying Archean basement. The investigated sample is a melanocratic, aphanitic melt rock comprising glassy inclusions, and plagioclase and quartz clasts. Plagioclase and quartz show shock-induced features including diaplectic glass and well-developed planar deformation features (PDFs), respectively. The decrease in shock pressure is thus established with the plagioclase of overlying basalt showing shock features like diaplectic glass whereas the quartz from lower Archean basement showing PDF development. Laser Raman spectroscopy reveals the presence of cristobalite. The impact melt-bearing rock shows major element geochemistry similar to that of Deccan basalt with a tholeiitic trend, but the Harker variation plots reveal an independent field for the melt rock between the two end members: Deccan basalt and Archean basement represented by Peninsular gneiss. The REE geochemistry also reveals more fractionation for the melt rock. Zircon U-Pb data indicate an upper intercept age around 3.0 to 3.1 Ga. Chondrite normalized zircon REE data display a positive Eu anomaly indicating a reheating during the impact event. This indicates that the melt rock sample was generated by the incorporation of Archean basement gneiss components, which is compatible with the estimated depth of excavation for an impact structure of this size. This specifies a depth to basement in the range between 522 and 570 m.

Zircon megacrysts from basalts of the Venetian Volcanic Province (NE Italy): U–Pb ages, oxygen isotopes and REE data

Mafic alkaline lavas from the Venetian Volcanic Province (NE Italy) contain orange–brown zircon megacrysts up to 15 mm long, subhedral to subrounded and showing equant morphology, with width-to-length ratios of 1:2–1:2.5. U–Pb ages of zircon (51.1 ± 1.5 to 30.5 ± 0.51 Ma) fit the stratigraphic age of the host lava (Middle Eocene and Oligocene) and their oxygen isotope composition ( δ 18O = 5.31–5.51‰) is similar to that of zircon formed in the upper mantle. Cathodoluminescence images and crystal chemical features, e.g. depletion of incompatible elements such as REE, Y, U and Th at constant Hf content, indicate that centre-to-edge zircon zoning is not consistent with evolution of the melt by fractional crystallization. All the above features, together with the fact that zircon and host basalts are coeval, indicate that the studied Zr megacrysts crystallised from a primitive alkaline mafic magma, which later evolved to the less alkaline host magma.