Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Sample decomposition using inverse aqua regia at elevated temperatures and pressures (e.g., Carius tube or high-pressure asher) is the most common method used to extract highly siderophile elements (HSEs: Ru, Rh, Pd, Re, Os, Ir, Pt and Au) from geological samples. Recently, it has been recognised that additional HF desilicification is necessary to better recover HSEs, potentially contained within silicate or oxide minerals in mafic samples, which cannot be dissolved solely by inverse aqua regia. However, the abundance of interfering elements tends to increase in the eluent when conventional ion-exchange purification procedures are applied to desilicified samples. In this study, we developed an improved purification method to determine HSEs in desilicified samples. This method enables the reduction of the ratios of isobaric and polyatomic interferences, relative to the measured intensities of HSE isotope masses, to less than a few hundred parts per million. Furthermore, the total procedural blanks are either comparable to or lower than conventional methods. Thus, this method allows accurate and precise HSE measurements in mafic and ultramafic geological samples, without the need for interference corrections. Moreover, the problem of increased interfering elements, such as Zr for Pd and Cr for Ru, is circumvented for the desilicified samples.

DOI： 10.1111/ggr.12280

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN ACAD  

A comprehensive geochemical study of the Chelyabinsk meteorite reveals further details regarding its history of impact-related fragmentation and melting, and later aqueous alteration, during its transit toward Earth. We support an similar to 30 Ma age obtained by Ar-Ar method (Beard et al., 2014) for the impact-related melting, based on Rb-Sr isotope analyses of a melt domain. An irregularly shaped olivine with a distinct 0 isotope composition in a melt domain appears to be a fragment of a silicate-rich impactor. Hydrogen and Li concentrations and isotopic compositions, textures of Fe oxyhydroxides, and the presence of organic materials located in fractures, are together consistent with aqueous alteration, and this alteration could have pre-dated interaction with the Earth's atmosphere. As one model, we suggest that hypervelocity capture of the impact-related debris by a comet nucleus could have led to shock-wave-induced supercritical aqueous fluids dissolving the silicate, metallic, and organic matter, with later ice sublimation yielding a rocky rubble pile sampled by the meteorite.

DOI： 10.2183/pjab.95.013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Platinum-group element (PGE) geochemistry may be used to constrain the timing of sulfide saturation in magmas, which influences the Cu and Au fertility of evolving magmatic systems. We report new geochronological and geochemical data, with emphasis on PGE geochemistry, for a suite of regional porphyritic hornblende-diorite intrusions and ore-bearing porphyries from the super-giant Escondida and smaller Zaldivar Cu deposits of Northern Chile. The regional dioritic intrusions have zircon U-Pb ages between 396 to 371Ma, which overlap with the ages of the ore-bearing Escondida and Zaldivar porphyries (381 to 350Ma). Whole-rock major and trace element, and Sr-Nd-Pb and zircon O-Hf isotope geochemistry indicate that the regional diorites and ore-bearing porphyries are co-magmatic and originated from the same mantle-derived magma by fractional crystallization, with minor contamination by Paleozoic crust (approximate to 10%). The low concentrations of PGE in the regional diorites show that they reached sulfide saturation before the MgO content of the melt fell to 47wt %, the MgO content of the most primitive sample analysed. The fraction of sulfide melt which separated from the melts that formed the regional diorites is estimated to be approximate to 012wt %; this resulted in the partitioning of highly chalcophile elements (Au and PGE) into a sulfide phase that was retained in cumulus rocks at depth. However, the fraction of sulfide melt was too low to have a significant effect on the Cu content of the fractionating melt. As a consequence, when the evolving melt eventually reached volatile saturation, it contained enough Cu (40 +/- 10ppm) to form a super-giant Cu deposit. In contrast, Au was largely stripped from the melt by sulfide precipitation, with the result that the mineralization at Escondida is Cu dominant, with only minor Au. The Zaldivar deposit, on the other hand, contains even less Au, which is attributed to a longer fractionation interval between sulfide and volatile saturation. This study provides evidence to support previously proposed models which suggest that the timing of sulfide saturation, the amount of sulfide melt produced, the water content and oxidation state of the melt, and the magma volume are critical factors in determining the potential to form a porphyry Cu deposit. Plots of Pd/MgO against Y can be used as empirical indicators of magma fertility for porphyry mineralization, and to discriminate between Cu-Au and Cu-dominated systems, but cannot predict the size of the deposit. The super-giant status of the Escondida deposit is attributed to it being underlain by a large batholith with a calculated minimum mass of 10(12) tonnes (approximate to 400km(3)).

DOI： 10.1093/petrology/egz004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

To precisely determine the abundances of fifty-two elements found within natural water samples, with mass fractions down to fg g(-1) level, we have developed a method which combines freeze-drying pre-concentration (FDC) and isotope dilution internal standardisation (ID-IS). By sublimation of H2O, the sample solution was reduced to < 1/50 of the original volume. To determine element abundance with accuracy better than 10%, we found that for solutions being analysed by mass spectrometry the HNO3 concentration should be > 0.3 mol l(-1) to avoid hydrolysis. Matrix-affected signal suppression was not significant for the solutions with NaCl concentrations lower than 0.2 and 0.1 cg g(-1) for quadrupole ICP-MS and sector field ICP-MS, respectively. The recovery yields of elements after FDC were 97-105%. The detection limits for the sample solutions prepared by FDC were <= 10 pg g(-1), except for Na, K and Ca. Blanks prepared using FDC were at pg-levels, except for eleven elements (Na, Mg, Al, P, Ca, Mn, Fe, Co, Ni, Cu and Zn). The abundances of fifty-two elements in bottled drinking water were determined from five different geological sources with mass fractions ranging from the fg g(-1) to mu g g(-1) level with high accuracy.

DOI： 10.1111/ggr.12245

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Field, petrographic-structural and geochemical data are reported for spinel and plagioclase peridotites from the northern domain of the Lanzo peridotite massif (Western Alps). The North Lanzo peridotites are extremely heterogeneous in terms of mineral mode, texture and chemistry. They can be referred to four major groups: (1) spinel harzburgites with coarse granular to porphyroclastic structures; (2) pyroxene-depleted spinel harzburgites recording olivine-forming or pyroxene-consuming microtextures; (3) spinel lherzolites with porphyroclastic to foliated and banded structures; (4) plagioclase-enriched spinel lherzolites. Major and trace element characterization of whole-rocks and their constituent minerals allows reconstruction of the complex series of pre- to syn-rift events this mantle sector underwent. Sr, Nd and Hf isotope data provide information on the nature of infiltrating melts and time constraints. More depleted harzburgites represent refractory protoliths that after melt extraction, possibly in the presence of residual garnet, underwent a first episode of refertilization by enriched mid-ocean ridge basalt (E-MORB)-like melts, whereas harzburgites and spinel lherzolites with ocean island basalt (OIB) signatures document the successive migration of alkaline melts. The most noticeable feature of this group of rocks is their Nd-Hf decoupling, specifically the very high Hf-176/Hf-177 coupled with very low Nd-143/Nd-144. Lu-Hf data for these peridotites define an similar to 260 Ma errorchron that is interpreted as evidence of mixing during relatively recent times between old (most probably Proterozoic) refractory subcontinental mantle and OIB-type melts. This event most probably occurred during extension (Triassic times) or during the onset of exhumation (Liassic times). Plagioclase peridotites document the last refertilization episode, involving the shallow-level impregnation of harzburgite mantle by evolved MORB melts before its sea-floor emplacement. This Middle Jurassic event caused the almost complete resetting of the original trace element and Sr-87/Sr-86 composition. The combination of structural, petrological and geochemical information for a north-south Lanzo traverse, from the North Massif to the South Massif, notwithstanding the effects of the alpine orogeny, allows the study of the complete evolution of a sector of old (Proterozoic?) mantle since the early stages of melt removal and allows reconstruction of the tectonic and magmatic events during continental extension leading to the opening of the Jurassic Ligurian-Piedmontese basin. North Lanzo fundamentally preserves the record of pre-syn-rift ancient episodes, whereas South Lanzo better highlights the processes that deeply modified and refertilized the older lithosphere during subsequent lithosphere extension. Slow to very slow extension led to sea-floor exposure of the subcontinental lithospheric mantle (North Lanzo) at a marginal position, close to the Adria continental margin, and of the deeply melt-modified lithospheric mantle (Lanzo South) in a more distal setting of the basin. In this respect, the Lanzo traverse is closely similar to the ocean-continent transition in slow- or ultraslow-spreading oceanic basins, such as the North Atlantic.

DOI： 10.1093/petrology/egs049

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL ACAD SCIENCES  

Records of micrometeorite collisions at down to submicron scales were discovered on dust grains recovered from near-Earth asteroid 25143 (Itokawa). Because the grains were sampled from very near the surface of the asteroid, by the Hayabusa spacecraft, their surfaces reflect the low-gravity space environment influencing the physical nature of the asteroid exterior. The space environment was examined by description of grain surfaces and asteroidal scenes were reconstructed. Chemical and O isotope compositions of five lithic grains, with diameters near 50 mu m, indicate that the uppermost layer of the rubble-pile-textured Itokawa is largely composed of equilibrated LL-ordinary-chondrite-like material with superimposed effects of collisions. The surfaces of the grains are dominated by fractures, and the fracture planes contain not only sub-mu m-sized craters but also a large number of sub-mu m-to several-mu m-sized adhered particles, some of the latter composed of glass. The size distribution and chemical compositions of the adhered particles, together with the occurrences of the sub-mu m-sized craters, suggest formation by hypervelocity collisions of micrometeorites at down to nm scales, a process expected in the physically hostile environment at an asteroid's surface. We describe impact-related phenomena, ranging in scale from 10(-9) to 10(4) meters, demonstrating the central role played by impact processes in the long-term evolution of planetary bodies. Impact appears to be an important process shaping the exteriors of not only large planetary bodies, such as the moon, but also low-gravity bodies such as asteroids.

DOI： 10.1073/pnas.1116236109

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Measurements of U-238-Th-230-Ra-226 disequilibria, Sr-Nd-Pb-Hf isotopes and major-trace elements have been conducted for lavas erupted in the last quarter-millennium at Hekla volcano, Iceland. The volcanic rocks range from basalt to dacite. Most of the lavas (excluding dacitic samples) display limited compositional variations in radiogenic Sr-Nd-Pb-Hf isotopes (Sr-87/Sr-86 = 0.70319-0.70322; Nd-143/Nd-144 = 0.51302-0.51305; Ph-206/Pb-204 = 19.04-19.06; Pb-207/Pb-204 = 15.53-15.54; Pb-208/Pb-204 = 38.61-38.65; Hf-176/Hf-177 = 0.28311-0.28312). All the samples possess (Th-230/U-238) disequilibrium with Th-230 excesses, and they show systematic variations in (Th-230/Th-232) and (U-238/Th-232) ratios. The highest Ra-226 excesses occur in the basalt and most differentiated andesite lavas, while some basaltic-andesite lavas have (Ra-226/Th-230) ratio that are close to equilibrium. The U-238-Th-230-Ra-226 disequilibria variations cannot be produced by simple closed-system fractional crystallization with radioactive decay of Th-230 and Ra-226 in a magma chamber. A closed-system fractional crystallization model and assimilation and fractional crystallization (AFC) model indicate that the least differentiated basaltic andesites were derived from basalt by fractional crystallization with a differentiation age of similar to 24 +/- 11 kyr, whereas the andesites were formed by assimilation of crustal material and fractionation of the basaltic-andesites within 2 kyr. Apatite is inferred to play a key role in fractionating the parent daughter nuclides in Th-230-U-238 and Ra-226-Th-230 to make the observed variations. Our proposed model is that several batches of basaltic-andesite magmas that formed by fractional crystallization of a basaltic melt from a deeper reservoir, were periodically injected into the shallow crust to form individual magma pockets, and subsequently modifying the original magma compositions via simultaneous assimilation and fractional crystallization. The assimilant is the dacitic melt, which formed by partial melting of the crust. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2010.10.001

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Abyssal peridotites, the depleted solid residues of ocean ridge melting, are the most direct samples available to assess upper oceanic mantle composition. We present detailed isotope and trace element analyses of pyroxene mineral separates from Southwest Indian Ridge abyssal peridotites and pyroxenites in order to constrain the size and length scale of mantle heterogeneity. Our results demonstrate that the mantle can be highly heterogeneous to <1 km and even <0.1 m length scales. Examination of Nd isotopes in relation to modal, trace, and major element compositions indicate that the length scales and amplitudes of heterogeneities in abyssal peridotites reflect both ancient mantle heterogeneity and recent modification by melting, melt-rock reaction and melt crystallization. The isotopic and trace element compositions of pyroxenite veins in this study indicate that they are not direct remnants of recycled oceanic crust, but instead are formed by recent melt crystallization. Combined with existing data sets, the results show that the average global isotopic composition of peridotites is similar to that of mid-ocean ridge basalts, though peridotites extend to significantly more depleted 143Nd/144Nd and 87Sr/86Sr. Standard isotope evolution models of upper mantle composition do not predict the full isotopic range observed among abyssal peridotites, as they do not account adequately for the complexities of ancient and recent melting processes. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JB006186

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Language：English   Publisher：Institute of Space and Astronautical Science  

We have participated in the analytical competition related to the sample-return mission, MUSES-C of the ISAS, to be launched in May 2003 and returned in summer 2007. In this competition, we have determined major and trace element abundances and isotopes (as many as possible), both for two powdered samples provided by the ISAS and for chondrules separated from Allende meteorite as an additional demonstration of our high-spatial resolution analytical capabilities for fragment samples. 100 mg of each of the competition samples, 1C and 2C, were split into two fractions of approximately 30 and 70 mg for the determinations of elemental abundances and the isotope analyses, respectively. The bulk concentrations of 55 elements in each 30 mg sample were analyzed by quadruple-type ICP-MS and sector-type ICP-MS with analytical uncertainties better than 10 percent (1 sigma). B, Pb, Li, Rb, Sr, Sm and Nd were successively separated from the remaining 70 mg of each of the samples, using a novel integrated, multi-ion exchange column chemistry approach, and then the isotopes of these elements were successfully determined by TIMS with analytical errors similar to those for analyses of terrestrial samples. The Sr, Nd, Re and Os isotopic compositions were also analyzed using the remaining aliquots of the sample solutions for trace element analyses by ICP-MS. The results obtained in this study indicate that 1C and 2C samples are probably ordinary chondrite and the Allende meteorite, respectively. However, extreme W, Ta and Nb enrichments in the 1C were probably caused by contamination during sample preparation. Furthermore, both of the samples were extensively contaminated by B from the borosilicate glass container in which the samples were delivered. Five chondrules were separated from Allende meteorite and then sliced into three pieces using a dicing saw. The center slices were used to petrographically determine the mineral phases, compositionally map these phases by SEM-EDX, and obtain quantitative major and trace element compositions (30 elements) by SEM-EDX and ion microprobe. The two outer slices, for which sample masses were less than 1 mg, were chemically treated to obtain the bulk trace elements and isotope compositions of the chondrules. For the chondrule slices, 24 trace elements and Sr and Nd isotopic compositions were determined with extremely small analytical uncertainties by ICP-MS and TIMS (for Sr and Nd, respectively). Based on the analytical experience, including this competition, we believe that all of the analyses carried out could have been completed within 50 days if we could have concentrated on this project alone during that 50-day period. In this report, we describe the analytical techniques employed for the powdered samples and the chondrules, and we present all of the results obtained during the approximately 3-month period of the analytical competition.

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