Oxygen isotope evidence for the origin of discrete granitoid plutons from the Archean western Wabigoon Belt,northwestern Ontario     

F.J. Longstaffe  D. Birk 《Precambrian Research》1981,14(1):21-30

The whole-rock δ ¹⁸O values of samples from twelve discrete Archean plutons intruding the western Wabigoon granite-greenstone belt, northwestern Ontario, range from 6.8 to 9.5‰. Most samples with δ ${}^{18}\text{O}\text{> 8.7‰}$, however, come from portions of the Burditt Lake stock, or the Esox Lake area, that have been affected by deuteric or metasomatic activity. The distribution of δ ¹⁸O values for the remaining samples is very similar to that known for the large batholithic complexes and gneissic terrains that dominate this portion of northwestern Ontario. The generally low δ ¹⁸O values of the discrete granitoid plutons suggest that ¹⁸O-rich supracrustal rocks were unimportant in their genesis. Like the granitoids of the batholithic complexes and gneissic terrains, the discrete granitoid plutons represent new additions to the Archean sialic crust.  相似文献   

Annual periodicity of the 18O16O and 13C12C ratios in the coral Montastrea annularis     

Richard G. Fairbanks  Richard E. Dodge 《Geochimica et cosmochimica acta》1979,43(7):1009-1020

The isotopic ratios ${}^{18}\text{O}{}^{16}\text{O}$ and ${}^{13}\text{C}{}^{12}\text{C}$ show an annual periodicity in the coral Montastrea annularis from Bermuda, Jamaica and Barbados. The abundances of ¹⁸O and ¹³C are positively correlated in the Jamaica and Barbados samples, but inversely related in the Bermuda sample. Annual high density growth bands are formed during the season of warmest water temperature at all 3 sites and are enriched in ¹⁶O. M. Annularis has a constant displacement from oxygen isotopic equilibrium and accurately records seasonal temperature variations via the temperature-dependent aragonite-water fractionation factor. Light intensity, through the activity of the coral's endosymbiotic algae, regulates the depth-dependent and seasonal variations in the skeletal carbon isotopic composition.  相似文献   

Hydrogen,oxygen and carbon isotopic evidence for the origin of rodingites in serpentinized ultramafic rocks     

David B. Wenner 《Geochimica et cosmochimica acta》1979,43(4):603-614

$\text{D}\text{H}$, ${}^{18}\text{O}{}^{16}\text{O}$ and ${}^{13}\text{C}{}^{12}\text{C}$ analyses were made of 14 whole rock and 28 mineral samples of rodingites associated dominantly with lizardite-chrysotile serpentinites from the West Coast of the U.S.A., New Zealand, and the Northern Appalachian Mtns. The δD values of the rodingite minerals are in three groupings: 5 monomineralic veins of pectolite, ?281 to ?429; 8 monomineralic veins of xonotlite, ?112 to ?135; all other minerals, including hydrogarnet, idocrase, prehnite, actinolite, nephrite, and chlorite, ?34 to ?80. Most calcites in rodingites have δ¹⁸O (+9.3 to +14.4) and (δ¹³C (?6.7 to +0.9) values similar to calcites in other Franciscan rocks, but distinct from the very low temperature calcite veins in serpentinites. The $\text{D}\text{H}$ data, combined with δ¹⁸O values of xonotlite (+5.7 to +10.9) and pectolite (+8.9 to +12.4) suggest formation from meteoric-type waters at low temperatures; the $\text{D}\text{H}$ depletion of pectolite, however, is anomalous. Rodingite whole rock values range from δ¹⁸O = +4.1 to +11.5 and δD = ?50 to ?86; one sample containing minor amounts of lizardite-chrysotile serpentinite has δD = ?92, outside this range. However, most rodingites of basaltic or gabbroic parentage are more restricted in δ¹⁸O (+4.1 to +8.6). Such a wide range in δ¹⁸O is consistent with the idea that most rodingites form over a relatively broad range of hydrothermal temperatures. Hydrogen isotopic data for most rodingite minerals (except xonotlite and pectolite) and for whole rocks are suggestive of non-meteoric waters. These $\text{D}\text{H}$ data overlap those observed for veins of hydrous minerals found in Franciscan igneous rocks studied by Margaritz and Taylor (1976, Geochim. Cosmochim. Acta40, 215–234), possibly suggesting evolved D-enriched, connate type metamorphic waters generated during high P, low T Franciscan-type metamorphism at temperatures (250–500°C) comparable to estimates based on mineral stabilities. Such an interpretation is supported by the ${}^{18}\text{O}{}^{16}\text{O}$ and ${}^{13}\text{C}{}^{12}\text{C}$ data for calcite in rodingites.The isotope data appear to contradict some of the conclusions derived from geologic and petrologic studies that indicate concomitant metasomatism and serpentinization of their presently observed host rock. These data appear most consistent with the interpretation that most rodingite minerals, with the exception of late-stage veins of xonotlite and possibly pectolite, may involve metasomatism in association with antigorite serpentinization of ultramafic rock. Subsequent upward tectonic transport in many instances may result in incorporation of the rodingites into their presently observed lizarditechrysotile host rock during or subsequent to pervasive shallow level serpentinization by meteoric waters.  相似文献   

A stable isotope study of serpentinization and metamorphism in the Highland Border Suite,Scotland, U.K.     

Nicholas P Ikin  Russell S Harmon 《Geochimica et cosmochimica acta》1983,47(2):153-167

$\text{D}\text{H}$ and ${}^{18}\text{O}{}^{16}\text{O}$ ratios have been measured for whole-rock samples and mineral separates from the mafic and ultramatic rocks of the Cambro-Ordovician Highland Border Suite. The H- and O- isotopic compositions of these rocks record individual stages in a relatively complex 500 Myr old hydrothermal/metamorphic history. Lizardite serpentinites (δD ～ ? 105‰; δ¹⁸O ～ + 6.2‰) record a premetamorphic history and indicate that parent harzburgites, dunites, and pyroxenites were serpentinized through low-temperature interaction with meteoric waters during cooling. The other rocks of the Highland Border Suite record subsequent interaction with metamorphic fluids. Amphibolite facies hornblende schists were produced through thrust-related (dynamothermal) metamorphism of spilitic pillow lavas. During dehydration, D-enriched fluids were driven off from the spilites thus leaving the hornblende schists to equilibrate with a relatively D-depleted internal fluid reservoir (δD ～ ? 45‰). The expelled D-enriched fluids may have mixed with more typical Dalradian metamorphic waters which then exchanged with the remaining mafic rocks and lizardite serpentinites during greenschist facies regional metamorphism to produce antigorite serpentinites (δD ～ ? 62‰; δ¹⁸O ～ + 8‰) and greenschist metaspilites (δD ～ ? 57‰; δ¹⁸O ～ + 7.3‰) with similar H- and O-isotopic compositions. Serpentinites which have been only partially metamorphosed show intermediate H-isotopic compositions between that of metamorphic antigorite (δD ～ ? 62‰) and non-metamorphic lizardite δD ～ ? 105‰) end members.  相似文献   

The geochemical evolution of the Pleistocene Lake Lisan-Dead Sea system     

Amitai Katz  Yehoshua Kolodny  Arie Nissenbaum 《Geochimica et cosmochimica acta》1977,41(11):1609-1626

The geochemical history of Lake Lisan, the Pleistocene precursor of the Dead Sea, has been studied by geological, chemical and isotopic methods.Aragonite laminae from the Lisan Formation yielded (equivalent) Sr/Ca ratios in the range 0.5 × 10^?2?1 × 10^?2, Na/Ca ratios from 3.6 × 10^?3 to 9.2 × 10^?3, $\text{δ}{}^{18}\text{O}{}_{\mathrm{PDB}}$ values between 1.5 and 7%. and $\text{δ}{}^{13}\text{C}{}_{\mathrm{PDB}}$ from ?7.7 to 3.4%..The distribution coefficient of Na⁺ between aragonite and aqueous solutions, $\text{λ}{}^{\mathrm{A}}{}_{\mathrm{Na}}$, is experimentally shown to be very sensitive to salinity and nearly temperature independent. Thus, Na/Ca in aragonite serves as a paleosalinity indicator.Sr/Ca ratios and $\text{δ}{}^{18}\text{O}$ values in aragonite provide good long-term monitors of a lake's evolution. They show Lake Lisan to be well mixed, highly evaporated and saline. Except for a diluted surface layer, the salinity of the lake was half that of the present Dead Sea (15 vs 31%).Lake Lisan evolved from a small, yet deep, hypersaline Dead Sea-like, water body. This initial lake was rapidly filled-up to its highest stand by fresh waters and existed for about 40,000 yr before shrinking back to the present Dead Sea. The chemistry of Lake Lisan at its stable stand represented a material balance between a Jordan-like input, an original large mass of salts and a chemical removal of aragonite. The weighted average depth of Lake Lisan is calculated, on a geochemical basis, to have been at least 400, preferably 600 m.The oxygen isotopic composition of Lake Lisan water, which was higher by at least 3%. than that of the Dead Sea, was probably dictated by a higher rate of evaporation.Na/Ca ratios in aragonite, which correlate well with $\text{δ}{}^{13}\text{C}$ values, but change frequently in time, reflect the existence of a short lived upper water layer of varying salinity in Lake Lisan.  相似文献   

Ammonium in biotite from metamorphic and granitic rocks of Japan     

Yuuko Itihara  Hiroji Honma 《Geochimica et cosmochimica acta》1979,43(4):503-509

Ammonium contents of biotites from metamorphic and granitic rocks of Japan have been determined, and correlated with the ${}^{18}\text{O}{}^{16}\text{O}$ ratios of the rocks.NH₄ contents of biotites averaged 22 ppm in granitic rocks of non-metamorphic terranes, 67 ppm in granitic rocks in the Ryoke metamorphic belt, and 279 ppm in metamorphosed sedimentary rocks of the Ryoke belt. In granitic rocks, enrichment of NH₄ in biotites is a result of the interaction between the granitic magma and surrounding sedimentary rocks. In metasedimentary rocks, the high NH₄ content in biotites is due to inheritance from original organic material in sedimentary rocks.Biotites from migmatites of the Ryoke belt contain more NH₄ (average, 475 ppm) than those from metasedimentary rocks. This suggests the existence of a metamorphic fluid or anatectic magma enriched in NH₄.  相似文献   

Etude systématique des isotopes de l'oxygène,du carbone et du strontium dans les carbonatites     

Françoise Pineau  Marc Javoy  Claude J Allegre 《Geochimica et cosmochimica acta》1973,37(11):2363-2377

${}^{18}\text{O}{}^{16}\text{O}$, ${}^{13}\text{C}{}^{12}\text{C}$ and ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios have been measured on the same samples for carbonatite complexes. The results show that besides the ‘carbonatite box’ of Tayloret al. (1967) there exist higher δ¹⁸O and δ¹³C values than can be explained by late magmatic or deuteric processes. These processes correspond to high concentrations of CO₂ and lead to big enrichments in ¹⁸O and ¹³C as well as in some ‘volatile’ elements. Strontium results are consistent with a model of selective contamination of deep-seated material by highly radiogenic strontium. The whole study leads to the opinion that parent magmas of carbonatites differentiated in a crustal environment with or without significant contamination.  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   

O18O16 of feldspars in carbonate rocks     

J.R Lawrence  M Kastner 《Geochimica et cosmochimica acta》1975,39(2):97-102

Six authigenic feldspars and three detrital feldspars in limestones and dolostones of Eocene to Preeambrian ages were analyzed for their $\text{O}{}^{18}\text{O}{}^{16}$ content. The difference in δO¹⁸ between the authigenic feldspars (δO¹⁸range = + 18.2 to + 24.7%.) and carbonate host rocks, both limestones and dolostones, was found to be ?0.5 to ?1.4%. Detrital feldspars (δO¹⁸ = + 11.2, + 22.5 and + 17.0%.) exhibit Δ^feldspar_carbonate values of ?12.0, ?2.4 and ?1.6‰, respectively, and appear to have undergone increased isotopic exchange as a function of decreased grain size under solid-state conditions.  相似文献   

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

  相似文献   

The extent of oxygen isotope exchange between clay minerals and sea water     

Hsueh-Wen Yeh  Samuel M. Savin 《Geochimica et cosmochimica acta》1976,40(7):743-748

The extent of oxygen isotopic exchange between detrital clay minerals and sea water was investigated by analyzing $\text{O}{}^{18}\text{O}{}^{16}$ ratios of separated fine-grained size fractions of deep-sea sediments from three North Pacific ocean cores. Isotopic results were interpreted according to models based on the assumption that the extent of isotopic exchange should increase with decreasing particle size and increasing time of exchange between the sediment and sea water. The data indicate that information concerning the provenance and mode of formation of detrital clay minerals can be obtained from the $\text{O}{}^{18}\text{O}{}^{16}$ ratios of the coarser-than-0.1 μm fraction of deep-sea sediments younger than several million years and the finer-than-0.1 μm fraction of deep-sea sediments younger than several tens of thousands of years. Furthermore, if the extent of chemical reaction between detrital clays and sea water is similar to the extent of oxygen isotopic exchange, such reaction may be important in regulating the chemistry of sea water.  相似文献   

Aragonite from deep sea ultramafic rocks     

E. Bonatti  J.R. Lawrence  P.R. Hamlyn  D. Breger 《Geochimica et cosmochimica acta》1980,44(8):1207-1214

Aragonite mineralization was observed in serpentinized peridotites from the Romanche and Vema Fracture Zones in the Atlantic and the Owen Fracture Zone in the Indian Ocean, either in veins or as radial aggregates in cavities within the serpentinites. Evidence of incipient dissolution of the aragonite crystals was observed in one case. The aragonites tend to have lower Mg content (< 0.03%) and higher Sr content (> 0.95%) relative to other marine aragonites. Their ${}^{18}\text{O}{}^{16}\text{O}$, ${}^{13}\text{C}{}^{12}\text{C}$ and ${}^{87}\text{Sr}{}^{86}\text{Sr}$ isotopic ratios suggest the aragonite was deposited at ocean floor temperatures from solutions derived from sea water circulating in fissures and fractures within the ultramafic rocks. The ${}^{18}\text{O}{}^{16}\text{O}$ ratios of the serpentines indicate serpentinization occurred at higher temperatures, probably deeper in the crust. Low-T reactions between circulating seawater and Mg-silicates (primarily serpentine and pyroxenes) caused high pH and enrichment of Mg and Ca in the solution, conditions favoring carbonate precipitation. Aragonite was formed rather than calcite presumably because the high Mg²⁺ concentration in the solution inhibited calcite precipitation. The high Sr content of the aragonites is probably related, at least in part, to their low temperature of formation. Opaque mineral grains containing over 8% NiO and over 40% MnO were observed concentrated along the margins of some of the aragonite veins, suggesting that Ni is one of the elements mobilized during reactions between ultramafic rocks and circulating seawater.  相似文献   

Strontium isotopic contamination and oxidation during ocean floor hydrothermal metamorphism of the ophiolitic rocks of the Troodos Massif,Cyprus     

E.T.C. Spooner  H.J. Chapman  J.D. Smewing 《Geochimica et cosmochimica acta》1977,41(7):873-890

Twenty-six new high precision ${}^{87}\text{Sr}{}^{86}\text{Sr}$ratio determinations and existing analyses are used to discuss the strontium isotopic composition of the Upper Cretaceous ophiolitic rocks of the Troodos Massif, Cyprus. Relative to initial magmatic ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios (0.70338 ± 0.00010 to 0.70365 ± 0.00005), the hydrothermally metamorphosed pillow lavas and dyke complex have been contaminated by isotopically heavier strontium.This observation confirms the hypothesis that hydrothermal metamorphism was a consequence of sea water-rock interaction, since sea water was the only readily accessible reservoir of isotopically heavier strontium. The fact that metagabbros and altered trondhjemites were also Sr isotopically contaminated shows that sea water penetrated approximately 2 km into the oceanic crust represented by the ophiolitic sequence.The amount of Sr isotopic contamination requires that the bulk sea water: rock ratio was at least ~15:1 and shows that water-rock interaction occurred in a flow system. The degree of oxidation decreases with increasing depth. This shows that the vertical component of fluid flow was downward. The absolute bulk water/rock ratio (for water at S.T.P.), as estimated from the oxidation profile, may have been as large as ~3 × 10³:1 —a large figure which independently confirms that rocks showing strong δ¹⁸O shifts have interacted with large volumes of water.The sites of discharge of the hot fluid, which must have come out of the system, are identified as the cupriferous pyrite ore deposits. This process of mass transfer corresponds to hydrothermal convection in a permeable medium with an open upper boundary surface.  相似文献   

Oxygen isotope fractionations involving pyroxenes: The calibration of mineral-pair geothermometers     

Alan Matthews  Julian R. Goldsmith  Robert N. Clayton 《Geochimica et cosmochimica acta》1983,47(3):631-644

Oxygen isotope fractionations between wollastonite, diopside, jadeite, hedenbergite and water have been experimentally studied at high pressures (1<- PH₂O ≥ 24 kbar) and temperatures (400/dg ≤ T <- 800/dgC) using the three-isotope method (Matsuhisa et al., 1978). Initial ${}^{18}\text{O}{}^{16}\text{O}$ fractionations were made close to equilibrium and initial ${}^{17}\text{O}{}^{16}\text{O}$ ratios were well removed from equilibrium, allowing accurate determinations of the equilibrium ${}^{18}\text{O}{}^{16}\text{O}$ fractionations and of the extent of isotopic exchange. Scanning electron microscope and rate studies show that the wollastonite-water and diopside-water exchange reactions occur largely by solution-precipitation (Ostwald Ripening) mechanisms. Equilibrium ${}^{18}\text{O}{}^{16}\text{O}$ fractionations between water and the minerals wollastonite, diopside, and hedenbergite are in close agreement with one another, whereas significantly more positive fractionations are found for jadeite-water. These isotopic substitution effects can be ascribed to replacement of SiOM bonds (M is a divalent metal cation in octahedral coordination) by higher frequency SiOAl bonds. The fractionations determined in this study can be combined with quartz- and feldspar-water data of Matsuhisa et al. (1979) and revised magnetite-water data of O'NEIL (1963), to provide a coherent set of mineral-pair fractionations satisfactorily represented by straight lines through the origin on a conventional graph of In /ga versus T^?2. Mineral-water data, on the other hand, cannot readily be fitted to the simple relationship suggested by Bottinga and Javoy (1973). Coefficients “A” for the mineral-pair fractionations 1000 ln α = A × 10⁶T^?2 are: