共查询到20条相似文献，搜索用时 62 毫秒
1.
Cold Bay and Amak Island, two Quaternary volcanic centers in the eastern Aleutians, are orthogonal relative to the trench and separated by ~50 km. Sr, Nd and Pb isotopic compositions of the calc-alkaline andesite magmas show no sign of contamination from continental crust (average , , , ). These samples plot within the mantle arrays for Sr-Nd and for Pb and are similar to arcs such as the Marianas and New Britain (Sr-Nd) and Marianas and Tonga (Pb). Incompatible element ratios for the Aleutian andesites (K/Rb ~ 332, K/Cs ~ 10,600, K/Sr ~ 22.4, K/Ba ~ 18.3, Ba/La ~ 60) are within the range reported for arc basalts, despite the difference in degree of fractionation.Average K content, K/Rb, K/Ba and K/Sr are approximately the same for basalts from arcs and from oceanic islands (OIB); K/Cs is a factor of 4 lower and Ba/La almost 3 times higher in arcs. Abundance ratio correlations indicate that arcs are enriched in Cs and depleted in La relative to OIB, with other incompatible element abundances very similar. Histograms of Sr and Nd isotopic compositions for MORB, OIB, and intraoceanic arcs show remarkably similar peaks and distribution patterns for intraoceanic arcs and OIB.A “plum pudding” model for the upper mantle best accommodates a) geochemical coherence of OIB and IAV, b) the existence of mantle plumes at some oceanic islands, and c) the presence of a MORB-type source at back arc spreading centers. In this model, OIB plums are imbedded in a MORB matrix; small degrees of melting generate OIB-type magmas while larger degrees of melting dilute the OIB magma with MORB matrix melts.OIB plums are merely less robust lower mantle plumes (i.e., blobs) which are distributed throughout the upper mantle by convection. The existence of at least two types of OIB, as indicated by Sr, Nd, and Pb isotopes, suggests that nuggets of recycled oceanic lithosphère may coexist with lower-mantle plums and that both may be tapped in arcs and intraplate environments. 相似文献
2.
G.Nelson Eby 《Geochimica et cosmochimica acta》1985,49(5):1143-1153
The Monteregian Hills and younger White Mountain alkaline intrusions were emplaced into the Cambro-Ordovician sediments of the St. Lawrence Lowlands and the folded and thrusted Lower Paleozoic sequence of the Appalachian orogen. Age relations indicate that there is a fine-scale structure to the igneous activity, with slightly undersaturated to critically saturated rocks emplaced between 141 and 128 Ma and strongly undersaturated rocks emplaced between 121 and 117 Ma.Sr and Pb isotopic data for the mantle-derived alkali picrite, alkali olivine basalt and basanite magmas, indicate derivation from a depleted mantle similar to that which produces present-day oceanic island basalts. For the most isotopically primitive samples, decay-corrected , , , and . On Pb-Sr isotope correlation diagrams the data define trends similar to those for MOR basalts, implying mantle heterogeneity which requires the presence of a component enriched in radiogenic Pb relative to Sr. The interaction of these isotopically primitive magmas with the crust can be defined in terms of a three component system: depleted mantle-Grenville age crust-Lower Paleozoic age crust. The granitic magmas were apparently derived from the Lower Paleozoic crust of the Appalachian orogen.For the mantle-derived magmas, Th/U ratios vary from 2.5 (estimated ratio for MORB source) to 5.1, with the mean value near that of the bulk earth. The variations in Th/U suggest mantle heterogeneity on a local scale, and the high Th/U of some samples suggests that the mantle was enriched in incompatible elements shortly before melting. The magmas derived by partial melting of the crust have Th/U of 3.3 to 8.7, and the higher ratios are associated with rocks crystallized from magmas that originated by melting of Lower Paleozoic sediments.The Sr and Pb isotopic data support the conclusion of Bellet al. (1982) that the subcontinental mantle under eastern Canada underwent a Precambrian depletion event. This depleted mantle apparently extends under the White Mountain province and is isotopically similar to the mantle which gives rise to oceanic island basalts. In contrast, Pb isotopic ratios for the New England Seamount chain (TARAS and HART, 1983), which apparently represents the oceanic extension of this magmatic activity, are significantly more radiogenic. It is possible that a mantle plume provided the heat energy, and perhaps metasomatic fluids, to trigger melting in the subcontinental mantle, whereas in the case of the oceanic extension the plume directly contributed to the observed magmatism, as reflected in the more radiogenic Pb ratios. 相似文献
3.
Petrogenetic mixing models and Nd-Sr isotopic patterns 总被引：1，自引：0，他引：1
4.
We report Sr and Pb isotope analyses for an extensive suite of volcanic rocks from the N. Mariana arc together with Sr and Pb isotope analyses of sediments from the nearby Mariana and Nauru basins. In addition ten of the most recent volcanic samples were analysed for 10Be.The Sr isotope compositions cluster tightly around = 0.7035 being slightly but significantly higher than the Pacific ocean floor basalts on either side of the arc and agreeing well with previous data. In contrast, the large number of new Pb isotopic data presented significantly extends the observed range of Pb isotope compositions for volcanic rocks from the Mariana arc to more radiogenic compositions. The concentrations of 10Be were very low (< 0.5 × 106 atom g?1).These new data require either that the Pb and Sr isotopic compositions of the Mariana sub-arc mantle be substantially different from those of the mantle source of ocean floor basalts on either side of the arc, or that the enrichment in radiogenic Pb and Sr relative to the values observed in Pacific ocean floor basalts be related to the subduction process. We prefer the latter hypothesis in which radiogenic Sr and Pb in ocean floor sediments are added to M.O.R.B. type mantle either by direct assimilation of the sediments in partial melts or, more probably, by transfer in a fluid phase into the zone of magma production. The low 10Be concentrations observed suggest the removal of at least the top few metres of sediment during subduction. 相似文献
5.
William K. Hart 《Geochimica et cosmochimica acta》1985,49(1):131-144
Combined elemental and Sr, Nd, Pb and O isotopic data for late Cenozoic olivine tholeiite lavas from the northwestern Great Basin indicate derivation from at least two chemically and isotopically distinct mantle source regions with no significant modification by interaction with continental crust. The lack of crustal involvement is a direct reflection of the extensional tectonic environment which favors rapid ascent of magmas, minimal residence time in crustal magma chambers and scattered fissure eruptions.The observed chemical and isotopic variations in the tholeiite suite are attributed to mixing between depleted oceanic type mantle ( and ) and old, chemically heterogeneous, isotopically enriched subcontinental mantle ( and ). Model incompatible element concentrations suggest strong similarities between the depleted mantle and the mantles beneath normal oceanic ridge segments and back-arc basins and between the enriched mantle and the mantle beneath enriched oceanic ridge segments such as the Azores. Superimposed upon the characteristics derived from the two component mixing model may be the effects of a third mantle source which is identifiable only by its apparent radiogenic ratios. If present, this third source may reflect a component derived from the downgoing slab of an ancient subduction zone. 相似文献
6.
Tertiary-Recent Tasmanian and Newer (Victoria/South Australia) basalts range from quartz tholeiite to olivine melilitite and show systematic increases in their incompatible element abundances with increasing degree of silica undersaturation. These two basalt provinces show similar relative abundances of rare earth elements (REE), differences in the relative concentrations of Rb, Ba, Th, K and Nb, and distinct, restricted isotopic compositions. The Tasmanian basalts have from 0.7026 to 0.7034, and ?Nd from + 7.5 to + 5.8; the Newer basalts have higher from 0.7038 to 0.7045, and lower ?Nd from +4.2 to + 1.7. The range in Sr and Nd isotope compositions can be denned by primary magma compositions for both provinces, using Mg-values, Ni content and the presence of spinel lherzolite nodules. Major and trace element and Sr, Nd and Pb isotope compositions are uniform on a scale of up to 50 km for four separate Newer basanite centers. The chemical and isotopic data are consistent with a model whereby tholeiitic basalts are derived by large degrees of partial melting from a chemically uniform but isotopically variable source, and generation of undersaturated, alkaline basalts by smaller degrees of partial melting of the same source. No isotopic or geochemical evidence was found which would suggest that the more evolved basalts have been contaminated by continental crust.In contrast to tholeiitic and alkalic basalts from Hawaii, there is a continuous spectrum of isotope compositions for the Newer tholeiitic to alkalic basalts. A model is proposed for the generation of these basalts involving mixtures of hotspot mantle plume-derived melt and lithospheric mantle-derived melt, where observed differences between ocean island and continental alkaline basalts are attributed to differences between the sub-oceanic and sub-continental lithospheric mantles. Isotopic differences between tholeiitic and alkalic basalts are interpreted to be due to varying degrees of exchange and mixing between the hotspot plume and lithospheric mantle melt components. The model is consistent with the generation of these basalts from a source which has been recently enriched in the LREE. 相似文献
7.
The Hidra Massif (Rogaland complex, S.W. Norway) is a massif-type anorthositic-charnockitic body. It consists of undeformed anorthosites and leuconorites, grading into fine-grained jotunites at the contact with the granulite facies gneisses of the metamorphic envelope. A stockwork of charnockitic dykes cross-cuts the massif. The Pb isotopic compositions of the anorthosites and leuconorites are comparable or slightly less radiogenic than those of the jotunites ( from 18.079 to 19.307,( from 15.568 to 15.657 and from 37.617 to 38.493). These values are compatible with an upper mantle origin for the parental magma of jotunitic composition and for the plagioclasic cumulates, but show the incorporation of lower crustal material (U-depleted and thus less radiogenic). The charnockitic dykes have significantly less radiogenic Pb isotopic compositions ( from 17.472 to 19.171, from 15.489 to 15.620and from 36.991 to 40.922) which can be explained by a larger proportion of lower crustal contamination material. The contaminant could be the granulite facies gneisses of the metamorphic envelope. This interpretation is compatible with the K-Rb relationships of these rocks and with the O and Sr isotopic geochemistry.The proportion of contaminating lead in the charnockitic dykes can be estimated at 55 ± 15% considering the border facies jotunite as the uncontaminated parental magma and the least radiogenic gneiss of the metamorphic envelope as the contaminant. 相似文献
8.
Basalts from the Columbia River flood basalt province of the northwestern U.S.A. show a large diversity in chemical and Nd and Sr isotopic compositions. ranges from 0.51303 to 0.51208 and is strongly correlated with variations in . This correlation suggests mixing between two end member compositions, one characterized by and , and the other with and . The more radiogenic component could be mantle enriched in incompatible elements during the Precambrian, or Precambrian materials of the continental crust. A quartz-rich xenolith found in the Columbia lavas has Rb-Sr and Sm Nd model ages of ≈ 1.4Æ, implying the existence of old, isotopically evolved crustal basement which could serve as contaminant. Nevertheless, crustal contamination alone cannot explain the chemical variation of the samples studied, and other fractionation processes must have occurred simultaneously. A model involving combined assimilation and crystal fractionation reproduces the chemical and isotopic characteristics of the volumetrically dominant Grande Ronde unit for an assumed crystallizing component of plagioclase, low calcium pyroxene and minor olivine. The data are not consistent with the suggestion that a ‘primordial’ mantle is the source for this continental flood basalt province. Rather they suggest that the main volume of these lavas was originally derived from a mantle similar in isotopic composition to island arc and ocean island basalts of the north Pacific. The primary magma was modified chemically and isotopically by crystal fractionation and assimilation of sialic crustal materials during its transport through, or storage in the continental crust. 相似文献
9.
Major-element, trace-element and isotopic compositions of approximately 1200 basalts (< 53 wt. % SiO2) from intra-oceanic island arcs have been compiled to assess the nature and possible sources of primitive island-arc basalts (IAB). The chemical characteristics of IAB are examined with reference to those of mid-ocean ridge basalts (MORB) and intraplate oceanic basalts (IPB). Major-element compositions of primitive [] IAB and MORB are similar, but differ significantly from IPB. In general, IAB do not have higher Al2O3, lower TiO2 or a lack of Fe enrichment compared to primitive MORB but many do have greater K2O contents. Differences in major- and minor-element contents between more evolved IAB and MORB result from the dominance of plagioclase + olivine crystal fractionation in MORB magmas vs. clinopyroxene + olivine controlled fractionation in IAB suites. This difference in crystallization history may be related to the higher PH2O or greater depth of crystallization of IAB magmas compared to those inferred for MORB.IAB are characteristically enriched in large-ion-lithophile (LIL) elements and depleted in high-field-strength ions (e.g., Zr, Nb and Hf) relative to normal MORB (N-type) and IPB. The enrichment of some LIL elements (e.g., Sr, Rb, Ba and Pb) relative to the rare-earth elements in IAB is difficult to explain by simple partial melting alone and suggests a multistage petrogenesis involving an LIL-enriched component. Low abundances of high-field-strength ions in evolved IAB are explicable in terms of fractional crystallization, but the cause for consistently low abundances in primitive IAB remains problematic.Island-arc lavas contain greater concentrations of volatiles and have higher and Cl/F ratios than either MORB or IPB, suggesting involvement of a slab-derived volatile component. However, this is not consistent with data which indicate that only near-trench volcanics have been significantly affected by dehydration of the oceanic crust.Sr-, Nd-, Pb- and O-isotopic data, in conjunction with the trace-element data, clearly indicate that IAB are derived from heterogeneous, LIL-depleted mantle sources most similar to those which give rise to enriched MORB (E-type). The marked shift towards higher in IAB compared to oceanic lavas with similar values cannot be explained simply by the addition of radiogenic Sr from the slab. Variable degrees of contamination from a crustally-derived sedimentary component is consistent with the isotopic and trace-element data from a number of arcs. However, the lack of correlation between LIL/REE ratios and more radiogenic isotopic ratios suggests that this enrichment/contamination process is complex. A multi-stage petrogenetic model involving subducted oceanic crust (± sediments), dehydration/volatile transfer, and partial melting of metasomatized mantle beneath island arcs is considered the most reasonable, although least constrained, method to generate a variety of primitive IAB. 相似文献
10.
To better understand the process of crustal contamination/assimilation, 23 Pb isotopic compositions and 12 concentrations have been measured on lavas and basement rocks from the Edgecumbe volcanic field, SE Alaska. Measured isotopic ratios have the following ranges: ; ; . While the data form well-constrained linear arrays on Pb-Pb diagrams, no simple correlation exists with major element composition. Basaltic lavas (≤ 51 wt% SiO2) are characterized by two isotopic groups. The olivine basalt (≤ 48% SiO2) is more radiogenic than the plagioclase basalt (48–51%) which also shows more heterogeneity. In the silica range 52–55%, Pb isotopic ratios increase significantly but remain fairly constant in the range 55–70% SiO2. Lead concentrations vary from 1 ppm in the basalts to 7 ppm in the rhyodacites. Analyzed basement rocks are more radiogenic than any of the lavas ; ; . The Pb isotopic data are qualitatively consistent with the contamination process described by Myerset al. (1984). However, because of fundamental differences in the mixing relations between the Sr system studied earlier and the Pb system, the new Pb data have revealed details of the process not apparent from the Sr data alone. In particular, it has been shown that the parent magma was more primitive than originally assumed, and that two contamination events are recorded in the lavas. The first event, involving a mafic parent and different crustal contaminants, produced the intermediate and siliceous hybrids in cupolas located above the main basaltic chamber. The types of country rock intruded as well as the degree of partial fusion achieved in individual cupolas controlled the range of hybrid compositions produced while the eruption sequence was determined by the order in which the cupolas were tapped. The second contamination event produced the plagioclase basalt, the most voluminous basaltic unit, by mixing the mafic parent with the olivine basalt, an independent, primary magma. Our results suggest crustal contamination models that assume bulk assimilation of crustal end members may be too simplistic. 相似文献
11.
H Elderfield C.J Hawkesworth M.J Greaves S.E Calvert 《Geochimica et cosmochimica acta》1981,45(4):513-528
Analyses have been made of REE contents of a well-characterized suite of deep-sea (> 4000 m.) principally todorokite-bearing ferromanganese nodules and associated sediments from the Pacific Ocean. REE in nodules and their sediments are closely related: nodules with the largest positive Ce anomalies are found on sediments with the smallest negative Ce anomalies; in contrast, nodules with the highest contents of other rare earths (3 + REE) are found on sediments with the lowest 3 + REE contents and vice versa. ratios in the nodules (～0.51244) point to an original seawater source but an identical ratio for sediments in combination with the REE patterns suggests that diagenetic reactions may transfer elements into the nodules. Analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to REE contents of nodules and sediments is negligible. Inter-element relationships and leaching tests suggest that REE contents are controlled by a P-rich phase with a REE pattern similar to that for biogenous apatite and an Fe-rich phase with a pattern the mirror image of that for sea water. It is proposed that 3 + REE concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate. Processes which favour the enrichment of transition metals in equatorial Pacific nodules favour the depletion of 3 + REE in nodules and enrichment of 3 + REE in associated sediments. In contrast, Ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions. 相似文献
12.
Barbara Barreiro 《Geochimica et cosmochimica acta》1983,47(4):817-822
Pb isotope ratios have been measured in 12 volcanic rocks from the South Sandwich Islands. The ranges are . In and correlation diagrams, the South Sandwich data plot distinctly above the fields for ocean ridge basalts, and yield trends showing apparent mixing with a sedimentary end member similar to South Atlantic pelagic sediments as reported by Chow and Patterson (1962) and this study. Armstrong and Cooper (1971) have likewise shown that volcanics from the Lesser Antilles show mixing trends with North Atlantic sediments in Pb isotope correlation diagrams. The North Atlantic sediments have distinctly higher and ratios compared to the South Atlantic sediments. The parallel relationships between sediments and volcanic island arc rocks of the North and South Atlantic provide strong evidence for a component of Pb from subducted sediments in the lavas of the west Atlantic basin. In contrast to these data, lavas from the Mariana Arc in the western Pacific show little or no component of Pb from pelagic sediments. The reason for the different behaviors in the two settings is speculative. 相似文献
13.
Kenneth D Collerson Malcolm T McCulloch David Bridgwater 《Geochimica et cosmochimica acta》1984,48(1):71-83
Samples from the core to the margin of a 20 cm wide meta-dolerite dyke are sequentially enriched in K, Rb, Sr, and the light REE's. Rb-Sr and Sm-Nd compositional and isotopic profiles in the dyke are interpreted to be the result of selective contamination with components of country rock derivation, rather than the result of simple bulk mixing. ratios are higher at the edge of the dyke than at its centre, although they are somewhat irregular, due probably to the effects of subsequent alteration. This profile and one shown by unsupported 87Sr are both consistent with contamination of the dyke by a fluid phase derived by the breakdown of biotite. Common Sr shows a parallel, albeit weaker, contamination profile which is interpreted to reflect the contribution of a Sr-bearing phase such as plagioclase. Nd ratios and 144Nd concentrations increase and decrease respectively from the margin to the core of the dyke. In addition, the margin of the dyke is significantly less radiogenic than the interior. This contrasts with the relatively radiogenic character of an adjacent pegmatite vein. As this sample does not lie on an anticipated contamination profile between the Uivak gneisses and the dyke it is concluded that the REE contamination of the dyke occurred by the addition of a REE-enriched fluid phase which gained access to the dyke by flow along the dyke-pegmatite interface. If it is assumed that both the Rb-Sr and Sm-Nd contamination profiles are the result of diffusion limited processes, then the observations of scale made in this paper suggest that the rate of diffusion of Nd is an order-of-magnitude slower than that for Sr. In view of the scale and nature of these profiles, ages obtained from isotopic data for such mafic dykes must be interpreted with some care. Nevertheless, in spite of these limitations the ?Nd values for the least contaminated specimens provide a clear indication that the Saglek dykes were derived from a depleted mantle source with ?Nd? +2. 相似文献
14.
Surendra P. Verma 《Chemical Geology》1984,46(1):37-53
Twelve samples of mid-Tertiary felsic volcanic rocks from Zacatecas and San Luis Potosí (both belonging to the Sierra Madre Occidental) and one sample of Lower Tertiary porphyritic andesite from Zacatecas are analyzed for , K, Rb, and Sr. Eight selected samples are also analyzed for . A linear regression of the present-day of the felsic volcanic rocks in Zacatecas gives an approximate date of 30 ± 8 Ma. The initial ratios are high and widely distributed (from 0.705 to 0.712 or higher) whereas the initial ratios are somewhat low and show a narrow range (0.5125–0.5127). The available isotopic and trace-element data are best explained in terms of a binary mixing model in which the magmas derived from a slightly depleted-mantle fractionate and mix with varying proportions of the overlying middle/upper continental crust and undergo further shallow-level fractional crystallization before eruption. This model is also compatible with the trace-element and Sr isotopic data published from other areas of the Sierra Madre Occidental for which a purely mantle origin has been proposed. 相似文献
15.
UThPb systematics of the eucrite “Juvinas”: Precise age determination and evidence for exotic lead
The U-Th-Pb isotope systematics of the eucrite “Juvinas” have been studied in whole rock fragments as well as in plagioclases and pyroxenes. The results show that this monomict breccia crystallized with a very high initial ratio at T = 4.539 ± 0.004 AE ago. There is evidence for a less radiogenic Pb component (; ; ) interpreted as “exotic lead” induced by a meteoritical impact at the surface of the Juvinas parent body, 1.92 ± 0.06 AE ago. 相似文献
16.
P.Jonathan Patchett 《Geochimica et cosmochimica acta》1983,47(1):81-91
The 176Lu-176Hf isotope method and its applications in earth sciences are discussed. Greater fractionation of Lu/Hf than Sm/Nd in planetary magmatic processes makes a powerful geochemical tracer. In general, proportional variations of exceed those of by factors of 1.5–3 in terrestrial and lunar materials. Lu-Hf studies therefore have a major contribution to make in understanding of terrestrial and other planetary evolution through time, and this is the principal importance of Lu-Hf. New data on basalts from oceanic islands show unequivocally that whereas considerable divergences occur in and diagrams, and display a single, linear isotopic variation in the suboceanic mantle. These discordant relationships may allow, with the acquisition of further Hf-Nd-Sr isotopic data, a distinction between processes such as mantle metasomatism, influence of seawater-altered material in the magma source, or recycling of sediments into the mantle. In order to evaluate the Hf-Nd isotopic correlation in terms of mantle fractionation history, there is a need for measurements of Hf distribution coefficients between silicate minerals and liquids, and specifically for a knowledge of Hf behavior in relation to rareearth elements. For studying ancient terrestrial Hf isotopic variations, the best quality Hf isotope data are obtained from granitoid rocks or zircons. New data show that very U-Pb discordant zircons may have upwardly-biased , but that at least concordant to slightly discordant zircons appear to be reliable carriers of initial . Until the controls on addition of radiogenic Hf to zircon are understood, combined zircon-whole rock studies are recommended. Lu-Hf has been demonstrated as a viable tool for dating of ancient terrestrial and extraterrestrial samples, but because it offers little advantage over existing methods, is unlikely to find wide application in pure chronological studies. 相似文献
17.
R Vollmer 《Geochimica et cosmochimica acta》1976,40(3):283-295
The isotopic composition of Pb and Sr and the abundances of Rb, Sr, U, Th, and Pb were determined for whole rock samples from all major volcanic centres of the Cenozoic alkaline volcanism of Central and South Italy, together with some samples from the contemporaneous anatectic Tuscan volcanism. The Sr and Pb isotopic compositions of the alkaline rocks show a negative correlation combined with a regional trend: the ratios decrease from 0.711 in the north-west to 0.704 in the south-east, while the ratios increase from 18.7 to 20.0. Variations in both isotopic compositions are generally small throughout erupted rock sequences for any volcanic centre.The Pb and Sr isotopic abundance variations are interpreted on the basis of two alternative models, which correspond to two groups of geological processes: variations can result (i) from a time dependent development in subsystems with different or ratios or, (ii) from mixing of Sr or Pb with different isotopic compositions. Combining both Pb and Sr isotope abundance measurements it is shown that the source of each volcanic centre is formed by various degrees of mixing between two components. One component and the most southern Tuscan anatectic rocks most likely have a common source, whereas the other component of the mixing process is suggested to be a liquid fraction derived from a small degree of partial fusion of a hydrous mantle. Thus at least a two-stage evolution of the Italian alkaline rocks is indicated: first a mixing process leading to the formation of the parental material followed by differentiation processes leading to the formation of the erupted rock sequences.The geodynamic model which explains the data best is that of a lateral inhomogeneous mantle. The lateral inhomogeneities in the mantle would be the result of mixing between originally mantle and crustal derived material. The mixing process itself would not have any primary connection with the Quarternary volcanic activity. 相似文献
18.
Precise determination of SmNd ratios,Sm and Nd isotopic abundances in standard solutions 总被引：1，自引：0，他引：1
G.J Wasserburg S.B Jacobsen D.J DePaolo M.T McCulloch T Wen 《Geochimica et cosmochimica acta》1981,45(12):2311-2323
The methods used for precise calibrations of ratios and the average isotopic abundances obtained for normal Sm and Nd are given. A mixed Sm-Nd normal solution with a precisely known ratio close to the nominal average chondritic value is described and the calibration discussed. Aliquots of this standard solution are available on request and may be useful for precise interlaboratory calibration of Sm and Nd. 相似文献
19.
Clinopyroxenes in the metamorphic alpine peridotites from Ronda, Béni Bouchera, Lanzo and Othris have ratios in the range of 0.70228 – 0.70370, similar to ocean ridge tholeiitic rock. Insofar as these lherzolites represent mantle sources, the present data allows simple evolutionary models relating basalt genesis and alpine peridotite. The highly radiogenic Sr reported in many whole rock alpine peridotites may be due to contamination in olivine and thus, earlier models that deny a simple relationship between alpine peridotite and the oceanic gabbros and basalts need a re-evaluation. 相似文献