A study of strontium in core 119K,Discovery deep,Red Sea     

M.O.U. Ikpeama  P.D. Boger  G. Faure 《Chemical Geology》1974,13(1):11-22

The isotopic composition of strontium of pore water and of authigenic minerals leached from the sediment of core 119K with hot aqua regia is similar to that of the brine in the Discovery deep and differs from that of normal seawater. The average ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of strontium removed by acid leaching is 0.7077 ± 0.0007 (1σ) compared to a value of 0.70904 for the Red Sea. The detrital silicate fraction exhibits an approximate inverse correlation between ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios and strontium concentrations which provides tentative support for a model in which the detrital silicate fraction of deep-sea sediment is considered to be a mixture of terrigenous dust of sialic composition enriched in radiogenic ⁸⁷Sr and of volcanogenic material of basaltic composition and low ⁸⁷Sr abundance. The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of the shells of foraminifers and pteropods, expressed as δ ⁸⁷Sr‰ relative to 0.70904 for seawater, decrease from $\text{?0.23 ± 0.17‰}$ at 90 cm to $\text{?0.82 ± 0.17‰}$ at 273 cm and remain constant at this value to a depth of 450 cm. The lowering of the δ ⁸⁷Sr values is attributed both to the presence of aragonite overgrowths on pteropod shells and to possible isotope exchange with strontium in the connate fluid.  相似文献   

The RbSr isotope system as an index of origin and diagenetic evolution of southern Pacific red clays     

Norbert Clauer  Michel Hoffert  Anne-Marie Karpoff 《Geochimica et cosmochimica acta》1982,46(12):2659-2664

Morphological, mineralogical, chemical and RbSr isotopic studies have been made on Fesmectites (nontronites) from southern Pacific red clays cored near the Marquisas Islands. These minerals have at the top of the core, an ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of 0.70917 ± 0.00007, which indicates an authigenic origin in isotopic equilibrium with seawater. Weak leaching experiments with 1N HCl show that the nontronites also contain a volcanic component with a lower ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio which, combined with the morphology of the particles, suggests a transportation by bottom currents of clay formed elsewhere.During burial, the nontronites experience diagenetic modifications resulting in an increase in Fe, K and Rb contents, a concomitant decrease of Mg, Ca, Ti, Na and Sr, and a preferential migration of radiogenic ⁸⁷Sr from the clays into the surrounding pore waters.The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of the Sr adsorbed on the outermost surfaces of the nontronites does not change with depth in the core, and is, therefore, independent of diagenetic influence, which is rather characterized by the ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of the interstitial waters. The isotopic composition of both the adsorbed Sr and that of the pore fluids may yield useful information on the crystallization environment and subsequent history of deep sea red clays.  相似文献   

A strontium isotopic study of Smackover brines and associated solids,southern Arkansas     

Alan M. Stueber  Paul Pushkar  Ernest A. Hetherington 《Geochimica et cosmochimica acta》1984,48(8):1637-1649

The isotopic composition of Sr has been measured in brine samples from the Upper Jurassic Smackover Formation in southern Arkansas; ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios range from 0.7071 to 0.7101. With one exception, the 32 Smackover brines contain Sr which is significantly more radiogenic than the Sr in Late Jurassic sea water, indicating sizable Sr contributions from detrital sources. Isotopic analyses of core samples from rock units associated with the brines and regional stratigraphic relationships suggest that the radiogenic Sr was released from detrital minerals in Bossier shale to interstitial fluids expelled from the underlying Louann Salt in the North Louisiana salt basin. These fluids migrated through the Bossier Formation updip to the South Arkansas shelf, where they entered the upper Smackover carbonate grainstone. The radiogenic fluids mixed with Sr-rich interstitial marine waters that had the isotopic composition of Late Jurassic sea water; mixing in variable proportions resulted in the random distribution pattern of variable ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios that is observed in Smackover brines within the 5000 km² study area. Isotopic analyses of nonskeletal carbonate grains and coexisting coarse calcspar cement from the upper Smackover grainstone imply that the grains were diagenetically stabilized in the presence of interstitial marine waters, whereas the calcspar cement is a relatively late diagenetic phase precipitated after the arrival of radiogenic fluids.  相似文献   

Isotopic composition of strontium in Indian kimberlites     

D.K Paul 《Geochimica et cosmochimica acta》1979,43(3):389-394

Strontium isotopic studies on twenty three whole rock kimberlites from two petrographic provinces in India show variation of initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios from 0.7027 to 0.7102. The variation is unrelated to the degree of alteration. Between the micaceous and basaltic varieties there is some overlap in the Sr isotopic ratios. Leaching experiments on whole rock samples showed more highly radiogenic Sr in leaches compared to the bulk samples.In two diatremes, the initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios show a positive correlation with $\text{Rb}\text{Sr}$ which is believed to reflect a source event earlier than the formation of the kimberlites. The observed Sr isotopic data can be caused by (i) melting of a heterogeneous source or (ii) disequilibrium partial melting in the source region. In the former case, variable isotopic composition would be a necessary consequence of melting in small subsystems.  相似文献   

RbSr studies of CI and CM chondrites     

David W Mittlefehldt  George W Wetherill 《Geochimica et cosmochimica acta》1979,43(2):201-206

RbSr whole rock analyses have been performed on 2 CI and 3 CM chondrites. Four of these stones (Ivuna, Orgueil, Cold Bokkeveld and Erakot) were previously studied in this laboratory and were shown to be discordant from a 4.6 Gyr isochron. The fifth, Murchison, was not previously studied. The new data support the discordance of the first four stones, and indicate that Murchison is also discordant. Studies of Sr isotope ratios in unspiked Orgueil show that the discordance is not due to inhomogeneities in the $\text{Sr}{}^{84}\text{Sr}{}^{86}$ ratio caused by incomplete mixing of nucleosynthesis products.In order to gauge the effects of weathering, two leaching experiments were performed on fresh, interior samples of Murchison; one for a period of 1.5 hr and the other for 117 hr. The results indicate that the relative solubility of nonradiogenic Sr is approximately twice that of Rb and radiogenic Sr is more soluble than the nonradiogenic Sr. This gives the residue a lower model age than the whole rock both by increasing the $\text{Rb}\text{Sr}$ ratio and by decreasing the $\text{Sr}{}^{87}\text{Sr}{}^{86}$ ratio. This result is in contrast to that expected from studies of ordinary chondrite finds, which generally show higher model ages than falls. The constancy of $\text{K}\text{Rb}$ and $\text{K}\text{Sr}$ ratios between the two leaching experiments, and their difference from the unaltered whole rock ratios suggest that the bulk ratios are produced by dissolution of a single phase, and the higher radiogenic Sr content by selective leaching of other phases.  相似文献   

Systematic variations of sialic and volcanic detritus in piston cores from the Red Sea     

Phillip D. Boger  Gunter Faure 《Geochimica et cosmochimica acta》1976,40(7):731-742

The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios and Sr concentrations of the non-carbonate fractions of sediment from two cores taken in the median valley of the Red Sea indicate that the detrital fractions are mixtures of two components originating from old sialic and young volcanic rocks of the surrounding land areas. The mixing equations were derived from the data and were used to estimate the Sr concentrations of the two components. The volcanogenic detritus has a Sr content between 770 and 800 ppm while the component derived from old sialic rocks contains from 50 to 70 ppm. The volcanic component consists primarily of unweathered particles of alkali basalt and volcanic glass while the sialic component is represented by clay minerals and X-ray amorphous material. Systematic variations of the concentration of volcanogenic detritus were used to define layers of sediment which correlate over a distance of about 200 km separating the two cores. The concentrations of quartz, feldspar, amphibole, illite, kaolinite and chlorite were found to vary systematically with the content of volcanogenic detritus as calculated from the Sr data. The carbonate concentrations of the sediment range from 33 to 87% and appear to increase in a southerly direction. The rate of carbonate deposition increased at times of more efficient input of sediment derived from old sialic rocks. This relationship is explained by the hypothesis that both were influenced indirectly by brief warming trends during the Würm glaciation. The occurrence of sediment layers enriched in sediment derived from old sialic rocks correlates approximately with interstadials of the Würm glaciation in northern Europe. Increased input of volcanogenic detritus occurred around 37,000 and 26,000yr ago and during the past 5000 yr. A plot of ${}^{87}\text{Sr}{}^{86}\text{Sr}$ and ${}^{87}\text{Rb}{}^{86}\text{Sr}$ ratios defines a line on the Rb-Sr isochron diagram yielding a fictitious date of about 230 million yr.  相似文献   

Comment on “the statistical analysis and interpretation of imperfectly-fitted Rb-Sr isochrons from polymetamorphic terrains” by M. Cameron et al.     

Håakon Austrheim 《Geochimica et cosmochimica acta》1983,47(3):655-658

Cameronet al. (1981) proposed a “Free Line Model” for calculating formation ages for rock systems that have undergone local scale homogenization by ⁸⁷Sr migration. This model is valid only if the variation in the ${}^{87}\text{Rb}{}^{86}\text{Sr}$ ratio is independent of the variation in Sr-content within the rock system. If Sr increases linearly with increasing ${}^{87}\text{Rb}{}^{86}\text{Sr}$ the calculated age will be too high. If Sr decreases linearly with increasing ${}^{87}\text{Rb}{}^{86}\text{Sr}$, the calculated age will be systematically too low. If the rate of change in Sr with increasing ${}^{87}\text{Rb}{}^{86}\text{Sr}$ varies systematically through a rock system the “isochron” will be curved and the calculated ages will be younger or older than the real age, depending on the position of samples in relation to the curvature of the “isochron.” This problem with the “Free Line Model” is inherited in both the “Bulk Earth Model 1” and the “Bulk Earth Model 2.”  相似文献   

Strontium isotopic studies of the volcanic rocks of the Saunda arc,Indonesia, and their petrogenetic implications     

D.J Whitford 《Geochimica et cosmochimica acta》1975,39(9):1287-1302

Pleistocene and Recent lavas from the Sunda arc range from those showing affinities with the island arc tholeiitic series, through a spectrum of calc-alkaline to high-K alkaline rocks. The tholeiitic rocks have relatively low ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios averaging 0–7043; the calc-alkaline rocks show a wide range (from 0.7038 to 0.7059, averaging 0.7048); the high-K alkaline rocks average 0.7045. A rhyolitic ignimbrite from Sumatra has an ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of 0.7139.The relationship between ${}^{87}\text{Sr}{}^{86}\text{Sr}$ and major and trace element geochemistry is variable and complex. Lavas from the same volcano sometimes show significant differences in ${}^{87}\text{Sr}{}^{86}\text{Sr}$ despite close geochemical relationships. Rocks of the calc-alkaline suite show a regular decrease in ${}^{87}\text{Sr}{}^{86}\text{Sr}$ from West Java to Bali and there is some evidence for increasing ${}^{87}\text{Sr}{}^{86}\text{Sr}$ with increasing depth to the Benioff zone. Calc-alkaline and tholeiitic rocks from the Sunda arc have significantly higher ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios than those from other island arcs, except from those arcs where continental crustal involvement has been inferred (e.g. New Zealand).A model of ⁸⁷Sr enrichment due to isotopic equilibration of oceanic crust with sea water and disequilibrium melting in the slab and/or mantle is favoured to explain the Sr isotopic composition of the tholeiitic and normal calc-alkaline lavas. Calc-alkaline lavas with high ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios are best explained by either sialic contamination, or the presence of alkali basalt as a component of the downgoing slab. The Sr isotopic data for the high-K alkaline lavas suggest a mantle origin. The high ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio in the Lake Toba rhyolite implies a crustal origin.  相似文献   

⁸⁷Sr/⁸⁶Sr composition of seawater during the Phanerozoic     

Ján Veizer  William Compston 《Geochimica et cosmochimica acta》1974,38(9):1461-1484

${}^{87}\text{Sr}{}^{86}\text{Sr}$ measurements of 108 sedimentary carbonate rocks have been used to trace variations in the strontium isotopic composition of seawater during the Phanerozoic. The lowest ⁸⁷Sr/⁸⁶Sr observed for any suite of carbonates is taken as the best approximation to the value in well-mixed contemporary seawater. Our data support the existence of low ${}^{87}\text{Sr}{}^{86}\text{Sr}$ in the Cretaceous and Late Jurassic but they do not support further structure beyond a general trend through the Phanerozoic, which may correlate with the continental denudation rate.  相似文献   

⁸⁷Rb-⁸⁷Sr age of fragments and soils from the lunar sea of fertility     

Jean Louis Birck  Claude J Allegre 《Geochimica et cosmochimica acta》1973,37(9):2025-2031

The Luna 16 materials were dated by the Rb-Sr method.An internal isochron age of 3.4 ± 0.2 has been determined for a 6 mg fragment.The Luna 16 total soil is poorer in radiogenic Sr than any other analyzed soil from the Moon. Apollo 14 and 15 soils have also been studied; all of them fall nearly on a 4.65 b.y. isochron with the ADOR initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio.A comparison of the integrated $\text{Rb}\text{Sr}$ of the basalt source region and the $\text{Rb}\text{Sr}$ of the rocks suggests that these basaltic fragments have been generated with only minor $\text{Rb}\text{Sr}$ fractionation.The existence of an old Rb-rich subcrust which contaminated the basalts is also in agreement with the present results.  相似文献   

The statistical analysis and interpretation of imperfectly-fitted Rb-Sr isochrons from polymetamorphic terrains     

M. Cameron  K.D. Collerson  W. Compston  R. Morton 《Geochimica et cosmochimica acta》1981,45(7):1087-1097

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Strontium isotope evidence on the history of oilfield brines,Mediterranean Coastal Plain,Israel     

A Starinsky  M Bielski  B Lazar  G Steinitz  M Raab 《Geochimica et cosmochimica acta》1983,47(4):687-695

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Geochronology of high-K aluminous mare basalt clasts from Apollo 14 breccia 14304     

《Geochimica et cosmochimica acta》1987,51(12):3255-3271

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The effect of weathering on the distribution of strontium isotopes in weathering profiles     

Garrett W Brass 《Geochimica et cosmochimica acta》1975,39(12):1647-1653

The strontium isotope ratio in sea water has varied through geologic time owing to the input of strontium from rock weathering. To evaluate the possibility that $\text{Sr}{}^{87}\text{Sr}{}^{86}$ ratios might be altered during weathering, seven weathering profiles developed on Mesozoic arkoses located along the length of New Zealand were investigated. The rubidium-strontium-strontium isotope relations in these profiles give ‘isochron’ ages less than the ages of deposition of the arkoses. These ages appear to result from the weathering of a homogeneous source rock. The age calculated from the rubidium-strontium system (t′) is related to the original age (t) by the equation t′/t = (n ? 1)/n, where n is the ratio of the amounts of common and radiogenic strontium leached from the rock. Shales formed by the accumulation of these residual solids may inherit misleading isochron relationships which may not be erased during deposition or early diagenesis. The strontium which goes into solution and is transported to the sea is slightly less radiogenic than the strontium in the unweathered rock, while the residual clays may be much more radiogenic.  相似文献   

SR-isotopic composition of clinopyroxenes from some mediterranean alpine lherzolites     

Martin A Menzies  V Rama Murthy 《Geochimica et cosmochimica acta》1976,40(12):1577-1581

Clinopyroxenes in the metamorphic alpine peridotites from Ronda, Béni Bouchera, Lanzo and Othris have ${}^{87}\text{Sr}{}^{86}\text{Sr}$ 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   

Vredefort core: a cross-section of the upper crust?     

W.F Slawson 《Geochimica et cosmochimica acta》1976,40(1):117-121

Sixty-three samples from the granitic core of the Vredefort ring structure have been analyzed for K, Rb, and Sr. The $\text{Sr}{}^{87}\text{Sr}{}^{86}$ ratios were determined for thirteen of these. An isochron yielding an age of 2.85 × 10⁹ yr was obtained. The $\text{Rb}\text{Sr}$ and $\text{K}\text{Rb}$ ratios exhibit a ‘bulls-eye’ pattern in the granite suggesting the central portion has been extruded from depth. Diapiric flow and subsequent erosion has exposed a section of the continental crust within the Vredefort core.  相似文献   

Strontium isotopic composition of several oilfield brines from Kansas and Colorado     

S. Chaudhuri 《Geochimica et cosmochimica acta》1978,42(3):329-331

The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of several oilfield brines associated with Paleozoic dolomites, cherty dolomites and sandstones from Kansas and Colorado range from 0.7113 to 0.7341. Two brines in the Mississippian dolomites from Colorado were found to contain the most radiogenic strontium. The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of brines in a small oilfield in eastern Kansas are constant, and the ratios may suggest that in this field there may be only one oil pool. The isotopic composition of strontium in subsurface waters could be useful in determining hydrologic continuity among reservoirs and for obtaining additional information on the origin and migration of these fluids.  相似文献   

Pb,Sr and ¹⁰Be isotopic studies of volcanic rocks from the Northern Mariana Islands. Implications for magma genesis and crustal recycling in the Western Pacific     

Jon D. Woodhead  Donald G. Fraser 《Geochimica et cosmochimica acta》1985,49(9):1925-1930

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 ${}^{87}\text{Sr}{}^{86}\text{Sr}$ = 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   

Strontium isotope ratios in volcanic rocks from the northwestern part of the Hellenic arc     

G.G. Pe 《Chemical Geology》1975,15(1):53-60

${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios have been determined in fifteen volcanic rocks from the northwestern part of the Hellenic arc. They range from 0.7041 to 0.7134. There is no apparent correlation of strontium isotope values with any major chemical component or with Rb/Sr ratios. The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios appear to increase in a general way with increasing depth to the Benioff zone. The strontium isotope ratios are higher than from most island arcs; this is believed to be due to contamination.  相似文献   

Sr and Nd isotopic evidence for petrogenesis of mid-tertiary felsic volcanism in the mineral district of Zacatecas,Zac. (Sierra Madre Occidental), Mexico     

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 ${}^{87}\text{Sr}{}^{86}\text{Sr}$, K, Rb, and Sr. Eight selected samples are also analyzed for ${}^{143}\text{Nd}{}^{144}\text{Nd}$. A linear regression of the present-day ${}^{87}\text{Sr}{}^{86}\text{Sr}\text{and}{}^{87}\text{Rb}{}^{86}\text{Sr}$ of the felsic volcanic rocks in Zacatecas gives an approximate date of 30 ± 8 Ma. The initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios are high and widely distributed (from 0.705 to 0.712 or higher) whereas the initial ${}^{143}\text{Nd}{}^{144}\text{Nd}$ 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