Plagioclase buoyancy in basaltic liquids as determined with a centrifuge furnace     

I. H. Campbell  P. L. Roeder  J. M. Dixon 《Contributions to Mineralogy and Petrology》1978,67(4):369-377

Plagioclase buoyancy experiments have been carried out in a high-temperature centrifuge furnace using seventeen basaltic liquids and plagioclase crystals of three compositions: An₈₉, An⁷⁶ and An₅₅. The results show that the floating tendency of plagioclase in basaltic liquids is at least 0.03 g/cm³ greater than indicated by the calculations. If this correction factor is applied to calculations of plagioclase buoyancy in the Skaergaard Intrusion, it is found that the plagioclase crystals in the lower and middle zones were less dense than the coexisting liquids.Other phenomena relevant to crystal transport in basaltic liquids were observed in the centrifuge experiments. These included crystal flotation by rising bubbles, plagioclase sinking because of the formation of plagioclase-magnetite composite grains, graded bedding of olivine and magnetite, and more than 60% intercumulus basaltic liquid between settled olivine crystals.  相似文献   

Seismische Anisotropie des oberen Erdmantels und Intraplatten-Tektonik     

Prof. Dr. Karl Fuchs 《International Journal of Earth Sciences》1975,64(1):700-716

Specially planned explosion seismic measurements in the oceans provided conclusive evidence that the velocity of P_n-waves depends on the azimuths of the direction of propagation through the upper mantle. The orientation of this azimuthal anisotropy suggests a close connection with the generation of the oceanic lithosphere: in the Pacific the maximum and minimum velocities are measured in a perpendicular and parallel direction to the axis of the oceanic ridges respectively. The observed anisotropy is so strong that a number of models for the generation of anisotropy can be discarded. The most likely cause is a preferred orientation of minerals. The generation of the anisotropy can be simulated in the laboratory under P-T-conditions of the upper mantle. The influence of the rate of deformation can be studied as well. A recent analysis of explosion seismic data in Southern Germany suggests that the continental upper mantle possesses also a velocity anisotropy dependent on azimuth.  相似文献   

Mitteilungen     

Dr. Dieter Stadler  Karl Schomaker 《Ocean Dynamics》1975,28(3):117-120

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A method to determine crystallization temperatures of hydrated crystals by intracrystalline oxygen isotope effects     

Karl Heinzinger  Dieter Götz 《Earth and Planetary Science Letters》1975,27(2):219-220

The fractionation of the oxygen isotopes between water molecules from different sites in CuSO₄ · 5H₂O has been measured for crystallization temperatures of 25, 40 and 50°C. The temperature dependence found provides a basis for the determination of crystallization temperatures from such intracrystalline oxygen isotope effects; also for hydrated crystals of mineralogical and geological interest. Necessary suppositions for the application of this method are discussed.  相似文献   

Petrology and chemistry of recent lavas in the northern Marianas: Implications for the origin of island arc basalts   总被引：3，自引：0，他引：3  

T. H. Dixon  R. Batiza 《Contributions to Mineralogy and Petrology》1979,70(2):167-181

Petrologic and chemical data are presented for samples from five volcanically active islands in the northern Marianas group, an intra-oceanic island arc. The data include microprobe analyses of phenocryst and xenolith assemblages, whole rock major and trace element chemistry including REE, and Sr isotope determinations (⁸⁷Sr/⁸⁶Sr=0.7034±0.0001). Quartz-normative basalt and basaltic andesite are the most abundant lava types. These are mineralogically and chemically similar to the mafic products of other intra-oceanic islands arcs. It is suggested, however, that they are not typical of the ‘island arc tholeiitic’ series, having Fe enrichment trends and K/Rb, for example, more typical of calc-alkaline suits. Major and trace element characteristics, and the presence of cumulate xenoliths, indicate that extensive near surface (< 3 Kb) fractionation has occurred. Thus, even least fractionated basalts have low abundances of Mg, Ni and Cr, and high abundances of K and other large cation, imcompatible elements, relative to ocean ridge tholeiites. However, abundances of REE and small cation lithophile elements, such as Ti, Zr, Nb, and Hf are lower than typical ocean ridge tholeiites. The REE data and Sr isotope compositions suggest a purely mantle origin for the Marianas island arc basalts, with negligible input from subducted crustal material. Thus, subduction of oceanic lithosphere may not be a sufficient condition for initiation of island arc magmatism. Intersection of the Benioff zone with an asthenosphere under appropriate conditions may be requisite. Element ratios and abundances, combined with isotopic data, suggest that the source for the Marianas island arc basalts is more chondritic in some respects, and less depleted in large cations than the shallow (?) mantle source for ocean ridge tholeiites.  相似文献   

Mikrofazielle Untersuchungsmethoden von Kalken | Flügel,E., 1978. (Methods of Investigation of Limestone Microfacies.) Springer-Verlag,Heidelberg, Berlin,New York, 454 pp., D.M. 78.00, U.S. $39.00     

Karl H. Wolf 《Earth》1979,14(4):368-370

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Plagiogranites as late-stage immiscible liquids in ophiolite and mid-ocean ridge suites: An experimental study   总被引：1，自引：0，他引：1  

Susan Dixon  M.J. Rutherford 《Earth and Planetary Science Letters》1979,45(1):45-60

Chemical studies of two ophiolite suites and of selected mid-oceanic rift (MOR) regions indicate the presence of certain magmatic compositions: basalt, Fe-enriched basalt, and sodium granite (plagiogranite). There is a notable lack of evidence for melts of intermediate composition (i.e. 50–60 wt.% SiO₂). To determine possible relationships between basic rocks (basalts and gabbros) and acidic rocks (plagiogranites) a primitive basalt was fractionated at low pressure, under anhydrous conditions, and at different oxygen fugacities near the iron-wustite buffer and slightly above the quartz-fayalite-magnetite buffer. Samples of this basalt were taken to slightly above liquidus temperatures and then cooled at rates ranging from 1 to 2°C/hr. A liquid line of descent characterized by an Fe enrichment was delineated by quenching these experiments from a final temperature in the range of 1200 to 1000°C and analyzing the residual liquid (glass). After 95% crystallization of olivine, plagioclase, calcium pyroxene, and ilmenite, the residual liquid was an Fe-enriched basalt. This Fe-enriched basalt became immiscible at a temperature of about 1010°C. The immiscible phases produced were a more Fe-enriched basaltic liquid and a granitic liquid. The granitic liquid is similar in composition to the naturally occurring plagiogranites found in small volumes in ophiolites and in certain MOR regions. It is therefore concluded that silicate liquid immiscibility could be the petrogenetic process responsible for producing plagiogranite in some MOR regions and in some ophiolites. On the other hand, plagiogranites in ophiolites and MOR rock suites having andesitic and dacitic composition rocks may have evolved under conditions more closely approximating equilibrium crystallization and/or they may have evolved at high water pressures. The available experimental data suggest that amphibole would crystallize early and yield SiO₂-enriched liquids at depths greater than 4.5 km for P_H2O's in the range 0.6–1.0 P_total.The major problem in interpreting any of the natural plagiogranites as products of silicate liquid immiscibility is the fact that neither the Fe-enriched conjugate liquid or its crystalline equivalent has been described in the ophiolite or MOR literature. The identification of this Fe-rich conjugate magma is essential in any rock suite if a completely convincing case for silicate liquid immiscibility is to be made.  相似文献   

Prospecting and exploration of mineral deposits | M. Kuz`vart and M. Böhmer, 1978. Elsevier,Amsterdam, 431 pp., Dfl. 130.00, U.S. $ 55.00     

Karl H. Wolf 《Earth》1980,15(4):406-407

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A reported early-man site adjacent to southern Alaska's continental shelf: A geologic solution to an archeologic enigma     

Robert M. Thorson  David C. Plaskett  E.James Dixon 《Quaternary Research》1980,13(2):259-273

An extensive ancient archeologic site containing lithic artifacts and associated with mammoth remains was reported at Chinitna Bay, southern Alaska in 1943. The presence of such a site adjacent to the continental shelf at the base of the rugged Aleutian Range suggested that humans may have inhabited the inner shelf environment during the late Pleistocene at times of lowered sea level. Because of the site's potential significance, an interdisciplinary research team relocated and reinvestigated the area in 1978, but failed to find evidence of prehistoric human habitation. Geologic studies and radiocarbon dating indicate that the strata reported at the site are intertidal in origin, very late Holocene in age, and have undergone significant tectonic movement in the recent past. These observations indicate that the previously published observations of the Chinitna Bay site are probably invalid.  相似文献   

²¹⁰Po and ²¹⁰Pb distributions in ocean water profiles from the Eastern South Pacific     

John Thomson  Karl K. Turekian 《Earth and Planetary Science Letters》1976,32(2):297-303

Two ocean profiles from the Peru Basin from regions with different surface productivities were analyzed for total²¹⁰Pb and²⁰¹Po to evaluate the influence of particulates in the water column on their distribution. Comparison with a published²²⁶Ra profile for the region was made. The profile closest to the coast, where upwelling and productivity are high, shows depletion of²¹⁰Pb relative to²²⁶Ra at all depths, with particularly marked excursions from radioactive equilibrium at the surface and in the bottom water.²¹⁰Po appears to be deficient relative to²¹⁰Pb at depth as well. Mean residence times in the deep water, relative to particulate removal from the water column to the sediments, of about 100 years for²¹⁰Pb and about two years for²¹⁰Po are indicated. The profile northwest of the upwelling region shows the²²⁶Ra²¹⁰Pb²¹⁰Po system close to equilibrium at all depths to 1500 m (except for the effect of atmospheric²¹⁰Pb input seen at the surface.  相似文献