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Tom&#x; Magna Uwe Wiechert Timothy L. Grove Alex N. Halliday 《Earth and Planetary Science Letters》2006,250(3-4):428-443
We present lithium (Li) abundances and isotope compositions for a suite of anhydrous olivine tholeiites (HAOTs) and hydrous basalt-andesitic (BA) lavas from the Mt. Shasta and Medicine Lake regions, California. The values of δ7Li vary from + 0.9‰ to + 6.4‰ and correlate inversely with distance from the trench. These data are consistent with continuous isotope fractionation of Li during dehydration of the subducted oceanic lithosphere, an interpretation corroborated by uniformly high pre-eruptive H2O contents in basaltic andesites accompanied by high Li, Rb, Sr, Ba and Pb abundances. The subduction-derived component that was added to these hydrous magmas is shown to be very similar beneath both Mt. Shasta and Medicine Lake volcanoes despite characteristically distinct Li isotope compositions in the magmas themselves. More evolved andesites and dacites from Mt. Shasta have δ7Li from + 2.8 to + 6.9‰ which is identical with the range obtained for HAOTs and BA lavas from Mt. Shasta. Therefore, Li isotopes do not provide evidence for any other crustal component admixed to Mt. Shasta andesites or dacites during magmatic differentiation and magma mixing in the crust. 相似文献
2.
Implications for behavior of volatile elements during impacts—Zinc and copper systematics in sediments from the Ries impact structure and central European tektites 
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下载免费PDF全文 Zuzana Rodovská Tomáš Magna Karel Žák Chizu Kato Paul S. Savage Frédéric Moynier Roman Skála Josef Ježek 《Meteoritics & planetary science》2017,52(10):2178-2192
Moldavites are tektites genetically related to the Ries impact structure, located in Central Europe, but the source materials and the processes related to the chemical fractionation of moldavites are not fully constrained. To further understand moldavite genesis, the Cu and Zn abundances and isotope compositions were measured in a suite of tektites from four different substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia) and chemically diverse sediments from the surroundings of the Ries impact structure. Moldavites are slightly depleted in Zn (~10–20%) and distinctly depleted in Cu (>90%) relative to supposed sedimentary precursors. Moreover, the moldavites show a wide range in δ66Zn values between 1.7 and 3.7‰ (relative to JMC 3‐0749 Lyon) and δ65Cu values between 1.6 and 12.5‰ (relative to NIST SRM 976) and are thus enriched in heavy isotopes relative to their possible parent sedimentary sources (δ66Zn = ?0.07 to +0.64‰; δ65Cu = ?0.4 to +0.7‰). In particular, the Cheb Basin moldavites show some of the highest δ65Cu values (up to 12.5‰) ever observed in natural samples. The relative magnitude of isotope fractionation for Cu and Zn seen here is opposite to oxygen‐poor environments such as the Moon where Zn is significantly more isotopically fractionated than Cu. One possibility is that monovalent Cu diffuses faster than divalent Zn in the reduced melt and diffusion will not affect the extent of Zn isotope fractionation. These observations imply that the capability of forming a redox environment may aid in volatilizing some elements, accompanied by isotope fractionation, during the impact process. The greater extent of elemental depletion, coupled with isotope fractionation of more refractory Cu relative to Zn, may also hinge on the presence of carbonyl species of transition metals and electromagnetic charge, which could exist in the impact‐induced high‐velocity jet of vapor and melts. 相似文献
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Lithium (Li) isotopes are thought to provide a powerful proxy for the recycling of crustal material, affected by low temperature alteration, through the mantle. We present Li isotope compositions for basaltic volcanic rocks from Hengill, Iceland, and Jan Mayen in order to examine possible links between ocean island volcanism and recycled oceanic crust and to address recent suggestions that mantle 3He/4He is also related to recycling of ancient slabs. Basaltic glasses spanning a range of chemical enrichment from the Hengill fissure system define an inverse correlation between δ7Li (3.8-6.9‰) and 3He/4He (12-20 RA). The high-3He/4He basalts have low δ18O as well as excess Eu and high Nb/U, but carry no Li isotope evidence of being the product of recycling of altered slab or wedge material. In fact, there is no clear correlation between Li or He isotopes on the one hand and any of the other fingerprints of recycled slab components. The low-3He/4He samples do have elevated Nb/U, Sr/Nd, positive Eu anomalies and high δ7Li (∼6.9‰), providing evidence of a cumulate-enriched source that could be part of an ancient altered ocean floor slab.Basalts from Jan Mayen are characterized by large degrees of enrichment in incompatible trace elements typical of EM-like basalts but have homogeneous δ7Li typical of depleted mantle (3.9-4.7‰) providing evidence for a third mantle source in the North Atlantic. It appears that oceanic basalts can display a wide range in isotope and trace element compositions associated with recycled components whilst exhibiting no sign of modern surface-altered slab or wedge material from the Li isotope composition. 相似文献
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de Souza Luciana Sandra Bastos Silva Maiara Tatiane Lima Alba Elisiane de Moura Magna Soelma Beserra da Cruz Neto José Francisco de Souza Carlos André Alves da Silva Thieres George Freire 《Theoretical and Applied Climatology》2022,149(1-2):593-602
Theoretical and Applied Climatology - Analysing alternative methods for estimating reference evapotranspiration (ET0) is essential for improving the management of water resources, especially where... 相似文献
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Natalie Gaspers Tom&#x; Magna Luk&#x; Ackerman 《Geostandards and Geoanalytical Research》2020,44(2):363-374
A double‐spike method in combination with MC‐ICP‐MS was applied to obtain molybdenum (Mo) mass fractions and stable isotope compositions in a suite of sedimentary silicate (marine, lake, stream, estuarine, organic‐rich sediment, shales, slate, chert) and carbonate reference materials (coral, dolomite, limestones, carbonatites), and a manganese nodule reference material, poorly characterised for stable Mo isotope compositions. The Mo contents vary between 0.076 and 364 μg g?1, with low‐Mo mass fractions (< 0.29 μg g?1) found almost exclusively in carbonates. Intermediate Mo contents (0.73–2.70 μg g?1) are reported for silicate sediments, with the exception of chert JCh‐1 (0.24 μg g?1), organic‐rich shale SGR‐1b (36.6 μg g?1) and manganese nodule NOD‐A‐1 (364 μg g?1). The Mo isotope compositions (reported as δ98Mo relative to NIST SRM 3134) range from ?1.77 to 1.03‰, with the intermediate precision varying between ± 0.01 and ± 0.12‰ (2s) for most materials. Low‐temperature carbonates show δ98Mo values ranging from 0.21 to 1.03‰ whereas δ98Mo values of ?1.77 and ?0.17‰ were obtained for carbonatites CMP‐1 and COQ‐1, respectively. Silicate materials have δ98Mo values varying from ?1.56 to 0.73‰. The range of δ98Mo values in reference materials may thus reflect the increasingly important relevance of Mo isotope investigations in the fields of palaeoceanography, weathering, sedimentation and provenance, as well as the magmatic realm. 相似文献
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Florian Genier Jean-Luc Epard François Bussy Tomas Magna 《Swiss Journal of Geoscience》2008,101(2):431-452
Detailed field work and zircon analysis have improved the knowledge of the lithostratigraphy at the base of the Siviez-Mischabel nappe in the Mattertal (St-Niklaus-Törbel area). They confirm the existence of an overturned limb and clarify the structure of the St-Niklaus syncline. The following formations can be observed:
- Polymetamorphic gneisses; composed of paragneisses, amphibolites and micaschists (Bielen Unit, pre-Ordovician).
- Fine-grained, greyish quartzite and graywacke with kerogen-rich horizons (Törbel Formation, presumed Carboniferous).
- Green or white micaschists characterized by brown carbonate spots associated with white conglomeratic quartzites (Moosalp Formation, Early Permian).
- Massive, green or white, fine grained, microconglomeratic or conglomeratic quartzites with characteristic pink quartz pebbles (Bruneggjoch Formation, Late Permian-Early Triassic).
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The fate of moderately volatile elements in impact events—Lithium connection between the Ries sediments and central European tektites 下载免费PDF全文
下载免费PDF全文 Zuzana Rodovská Tomáš Magna Karel Žák Roman Skála Tomasz Brachaniec Channon Visscher 《Meteoritics & planetary science》2016,51(12):2403-2415
Lithium abundances and isotope compositions are presented for a suite of sediments from the surroundings of the Ries Impact structure, paralleled by new Li data for central European tektites (moldavites) from several substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia), including a specimen from the newly discovered substrewn field in Poland. The data set was supplemented by three clay fractions isolated from sedimentary samples. Moldavites measured in this study show a very narrow range in δ7Li values (?0.6 to 0.3‰ relative to L‐SVEC) and Li contents (23.9–48.1 ppm). This contrasts with sediments from the Ries area which show remarkable range in Li isotope compositions (from ?6.9 to 13.4‰) and Li contents (0.6–256 ppm). The OSM sediments which, based on chemical similarity, formed the major part of moldavites, show a range in δ7Li values from ?2.0 to 7.9‰ and Li contents from 5.8 to 78.9 ppm. Therefore, the formation of moldavites was apparently accompanied by large‐scale mixing, paralleled by chemical and isotope homogenization of their parent matter. The proposed Li mixing model indicates that sands, clayey sediments, and low volumes of carbonates are the major components for tektite formation whereas residual paleokarst sediments could have been a minor but important component for a subset of moldavites. Striking homogenization of Li in tektites, combined with limited Li loss during impacts, may suggest that moderately volatile elements are not scavenged and isotopically fractionated during large‐scale collisions, which is consistent with recent models. In general, whether homogenization of bodies with distinct Li isotope systematics takes place, or collision of bodies with similar Li systematics operates cannot be resolved at present stage but Li isotope homogeneity of solar system planets and asteroidal bodies tentatively implies the latter. 相似文献
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We present a comprehensive geochemical data set for a suite of back-arc alkaline volcanic rocks from James Ross Island Volcanic Group (JRIVG), Antarctic Peninsula. The elemental and isotopic (Sr, Nd, Pb and Li) composition of these Cenozoic basalts emplaced east of the Antarctic Peninsula is different from the compositions of the fore-arc alkaline volcanic rocks in Southern Shetlands and nearby Bransfield Strait. The variability in elemental and isotopic composition is not consistent with the JRIVG derivation from a single mantle source but rather it suggests that the magma was mainly derived from a depleted mantle with subordinate OIB-like enriched mantle component (EM II). The isotopic data are consistent with mantle melting during extension and possible roll-back of the subducted lithosphere of the Antarctic plate. Magma contamination by Triassic–Early Tertiary clastic sediments deposited in the back-arc basin was only localized and affected Li isotopic composition in two of the samples, while most of the basalts show very little variation in δ7Li values, as anticipated for “mantle-driven” Li isotopic composition. These variations are difficult to resolve with radiogenic isotope systematics but Li isotopes may prove sensitive in tracking complex geochemical processes acting through the oceanic crust pile, including hydrothermal leaching and seawater equilibration. 相似文献
9.
T. Magna A. Deutsch R. Skála J. Mizera L. Adolph 《Geochimica et cosmochimica acta》2011,75(8):2137-2158
Lithium (Li) abundances and isotope compositions were determined in a representative suite of tektites (moldavites, Muong Nong-type tektites and an australite, Ivory Coast tektites and bediasites), impact-related glasses (Libyan Desert Glass, zhamanshinites and irghizites), a glass fragment embedded in the suevite from the Ries impact crater and sedimentary materials in order to test a possible susceptibility of Li to fractionation during hypervelocity impact events and to de-convolve links to their potential parental sources. The overall data show a large spread in Li abundance (4.7-58 ppm Li) and δ7Li values (−3.2‰ to 26.0‰) but individual groups of tektites and impact glasses have distinctive Li compositions.Most importantly, any significant high-temperature Li isotope fractionation can be excluded by comparing sedimentary lithologies from central Europe with moldavites. Instead, we suggest that Li isotope compositions in tektites and impact-related glasses are probably diagnostic of the precursor materials and their pre-impact geological histories. The Muong Nong-type tektites and australite specimen are identical in terms of Li concentrations and δ7Li and we tentatively endorse their common origin in a single impact event. Evidence for low-temperature Rayleigh fractionation, which must have operated prior to impact-induced melting and solidification, is provided for a subset of Muong Nong-type tektites. Although Li isotope variations in most tektites are broadly similar to those of the upper continental crust, Libyan Desert Glass carries high δ7Li ?24.7‰, which appears to mirror the previous fluvial history of parental material that was perhaps deposited in lacustrine environment or coastal seawater. Lithium isotopes in impact-related glasses from the Zhamanshin crater define a group distinct from all other samples and point to melting of chemically less evolved mafic lithologies, which is also consistent with their major and trace element patterns.Extreme shock pressures and the related extreme post-shock temperatures alone appear not to have any effect on the Li isotope systematics; therefore, useful information on parental lithologies and magmatic processes may be retrieved from analyses of Martian and lunar meteorites. Moreover, lack of significant Li depletion in tektites provides further constraints on the loss of moderately volatile elements during the Moon-forming impact. 相似文献
10.
L. Gordon Medaris Jr. Lukáš Ackerman Emil Jelínek Tomáš Magna 《International Journal of Earth Sciences》2015,104(8):1925-1956
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