Late Cretaceous deep-water agglutinated foraminiferal assemblages from the North Atlantic and its marginal seas     

Dr. Wolfgang Kuhnt  Dr. Michael A. Kaminski  Prof. Dr. Michel Moullade 《International Journal of Earth Sciences》1989,78(3):1121-1140

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Evidence for contamination of recent Hawaiian lavas from²³⁰Th-²³⁸U data     

M. Condomines  M. Bernat  C.J. Allegre 《Earth and Planetary Science Letters》1976,33(1):122-125

²³⁰Th-²³⁸U radioactive disequilibrium was studied in the historical lava flows of the Mauna Loa and Kilauea, Hawaii. Large variations of the (²³⁰Th/²³²Th) ratio among lavas of the same volcano that were erupted at a few years' interval are interpreted as due to contamination. The contamination probably occurs by assimilation of zeolitic minerals formed by seawater interaction while the magma resides in a superficial chamber.  相似文献   

Fine chronology of volcanic processes using ²³⁸U-²³⁰Th systematics     

Claude J. Allegre  Michel Condomines 《Earth and Planetary Science Letters》1976,28(3):395-406

The²³⁰Th-²³⁸U radioactive disequilibrium method was applied to the study of recent volcanic rocks from Costa Rica. Most samples are from the Irazu volcano. Some samples were dated by internal isochrons using the (²³⁰Th/²³²Th)-(²³⁸U/²³²Th) diagram, others were studied only by whole rock analyses. The evolution of the parent magma may be followed by the initial (²³⁰Th/²³²Th)₀ ratios of the rocks. A model involving a differentiating magma chamber that existed for 140,000 years under the Irazu volcano correlates well with the observations. Other volcanoes seem to be in earlier stages of their evolution. Continuing study may help to solve the tholeiitic to andesitic volcanism relationship.  相似文献   

A re-appraisal of the use of trace elements to classify and discriminate between magma series erupted in different tectonic settings   总被引：2，自引：0，他引：2  

David A. Wood  Jean-Louis Joron  Michel Treuil 《Earth and Planetary Science Letters》1979,45(2):326-336

The hygromagmatophile element composition of basic lavas from several tectonic environments are compared with the estimated composition of the primordial mantle. The observed variations are used to subdivide mid-ocean ridge basalts (MORB) into two main types according to the tectonic character of the ridge segment from which they were erupted. Ridge segments with positive residual gravity, depth and heat flow anomalies erupt E-type MORB which are predominantly enriched in the more hygromagmatophile elements, but also include magma types which are depleted in most of these elements. Both enriched and depleted E-type MORB can be distinguished from the basalts erupted at normal ridge segments (N-type MORB) by their La/Ta ratios (in E-type MORB La/Ta ～10, in N-type MORB La/Ta is ～15) and by Hf/Ta ratios (in E-type MORB Hf/Ta> 7, in N-type MORB Hf/Ta> 7). E-type MORB can be distinguished from the basalts erupted at ocean islands by their higher Hf/Ta ratios (>2). A Th-Hf-Ta triangular diagram is used to discriminate between the different ocean floor basalts as well as those erupted at destructive plate margins, which are depleted in Ta and Nb. This diagram can also distinguish between silicic lavas from the different tectonic environments as well as identifying lavas that have been contaminated with continental crust.  相似文献   

Rare earths in barites: distribution and effects on aqueous partitioning     

François Guichard  Thomas M. Church  Michel Treuil  Henri Jaffrezic 《Geochimica et cosmochimica acta》1979,43(7):983-997

A large variety of barites collected from marine and continental environments was analyzed by neutron activation for the rare-earth elements (REE) La, Ce, Sm, Eu and Dy. Relative to chondrites, all barites show a decrease of the lighter REE from La toward Eu. The abundance and distribution of rare earths in barites show a distinction of barite types. Deep-sea barites have large REE concentrations as do other authigenic deep-sea minerals and display the chondrite normalized Eu minimum, but not the negative Ce anomaly, of sea water. Other barites, mostly on land, some hydrothermal, and others of shallow marine origin, display lower total Ree concentrations. Chondrite normalized positive Eu anomalies are displayed by those varieties of reducing sedimentary and metamorphic origin.Distribution of REE in barite can be attributed both to crystallographic constraints of substitution, and to solution complexing of REE in the precipitating medium. Plots of rare earth partitioning versus effective ion size suggest that the decreasing enrichment toward Eu for all barite types is caused by crystallographic constraints due to contraction of the substituting REE ion sizes relative to the size of the host Ba ion. Solution effects on REE substitution in barite can be evaluated by writing solid solution distribution equations based on mass action of REE and Ba sulfates and the lanthanide (Ln) solution species Ln (CO₃)^?5₄), LnSO⁺₄, LnCl⁺² and LnF⁺². Under normal sea water conditions, solution complexing plays a minor role. However, increased alkalinities of reducing sediments and increased brine chlorinities could cause significant complexing and deplete REE heavier than Eu. Besides Dy in barites, this could be true for aqueous precipitation of REE in general.  相似文献   

Coupes sismiques des structures superficielles dans les petites antilles—I: Guadeloupe     

Jacques Dorel  Sylvain Eschenbrenner  Michel Feuillard 《Pure and Applied Geophysics》1979,117(5):1050-1069

Summary In 1976 and 1977, seismic profiles were carried out in Guadeloupe. Two profiles were established in the area of La Soufriére volcano and one profile through the northern part of Guadeloupe and southern part of Grande Terre. The two first profiles were occupied from 1 to 30 km and the third profile between 5 and 50 km.The interpretation shows that the superficial structures are characterized by a three-layers model: the compressional velocity is about 2.7 to 3.0 km/s down to a depth from 1 to 3 km. Below this, the velocity is between 4.0 and 4.5 km/s in a layer whose thickness varies from 1 to 2.5 km. Under this layer we find a 6.0–6.1 km/s layer which is one of the two known crustal layer under Lesser Antilles. The boundary between the old and new are which form the Lesser Antilles arc, is marked by a thicker layer of sediments on the eastern flank of recent volcanic chain.

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Large intensity changes of the non-dipole field during a polarity transition     

Michel Prévot 《Physics of the Earth and Planetary Interiors》1977,13(4):342-345

Directional and paleointensity data for the Steens Mountain geomagnetic polarity transition do not agree with the two simplest models of reversals: rotation of undiminished dipole or gradual diminution followed by change in polarity of the dipole moment. Instead, large and rapid changes in the intensity and direction of the field occur, probably as a result of non-dipole variations.  相似文献   

Erratum: Solar cosmic-ray-produced radionuclides in meteorites     

R. Michel  G. Brinkmann  R. Stück 《Earth and Planetary Science Letters》1983,64(1):174

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Ground water geochemistry of ²²⁸Ra, ²²⁶Ra and ²²²Rn     

Philip T. King  Jacqueline Michel  Willard S. Moore 《Geochimica et cosmochimica acta》1982,46(7):1173-1182

²²⁸Ra, ²²⁶Ra, and ²²²Rn activities were determined on over 150 ground water samples collected from drilled, public water supply wells throughout South Carolina. A wide range of aquifer lithologies were sampled including the crystalline rocks of the Piedmont and sedimentary deposits of the Coastal Plain. A significant linear relationship between log ²²⁸Ra and log ²²⁶Ra (n = 182, r = 0.83) was indistinguishable between Piedmont and Coastal Plain ground water. Median ${}^{228}\text{Ra}{}^{226}\text{Ra}$ activity ratios for the Piedmont, 1.2, and Coastal Plain, 1.3, ground water are close to estimated average crustal ${}^{232}\text{Th}{}^{238}\text{U}$ activity ratios of 1.2 to 1.5 corresponding to Th/U weight ratios of 3.5 to 4.5. A linear correlation was also found between log ²²²Rn and log ²²⁶Ra for Piedmont (n = 68, r = 0.62) and Coastal Plain (n = 89, r = 0.64) ground water. However, the median ${}^{222}\text{Rn}{}^{226}\text{Ra}$ activity ratio for Piedmont ground water, 6100, was much higher than for Coastal Plain ground water, 230. Higher excess ²²²Rn activities may be due to greater retention of ²²⁶Ra by the chemically active Piedmont aquifers compared to the more inert sand aquifers sampled in the Coastal Plain. The relationship between log ²²⁸Ra and log ²²⁶Ra was used to predict total Ra (${}^{228}\text{Ra +}{}^{226}\text{Ra}$) distributions in Appalachian and Atlantic and Gulf Coastal Plain ground water. Predictions estimate that 2.4% of Appalachian and 5.3% of Atlantic and Gulf Coastal Plain ground water supplies contain total Ra activities in excess of the 5 pCi/l limit established by the U.S. Environmental Protection Agency. These predictions also indicate that 40–50% of these ground water wells may be overlooked using the presently suggested screening activity of 3.0 pCi/l of ²²⁶Ra for ²²⁸Ra analysis.  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