Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas   总被引：70，自引：0，他引：70  

Henry J. B. Dick  Thomas Bullen 《Contributions to Mineralogy and Petrology》1984,86(1):54-76

The composition of chromian spinel in alpine-type peridotites has a large reciprocal range of Cr and Al, with increasing Cr# (Cr/(Cr+Al)) reflecting increasing degrees of partial melting in the mantle. Using spinel compositions, alpine-type peridotites can be divided into three groups. Type I peridotites and associated volcanic rocks contain spinels with Cr#<0.60; Type III peridotites and associated volcanics contain spinels with Cr#>0.60, and Type II peridotites and volcanics are a transitional group and contain spinels spanning the full range of spinel compositions in Type I and Type II peridotites. Spinels in abyssal peridotites lie entirely within the Type I spinel field, making ophiolites with Type I alpine-type peridotites the most likely candidates for sections of ocean lithosphere formed at a midocean ridge. The only modern analogs for Type III peridotites and associated volcanic rocks are found in arc-related volcanic and intrusive rocks, continental intrusive assemblages, and oceanic plateau basalts. We infer a sub-volcanic arc petrogenesis for most Type III alpine-type peridotites. Type II alpine-type peridotites apparently reflect composite origins, such as the formation of an island-arc on ocean crust, resulting in large variations in the degree and provenance of melting over relatively short distances. The essential difference between Type I and Type III peridotites appears to be the presence or absence of diopside in the residue at the end of melting.Based on an examination of co-existing rock and spinel compositions in lavas, it appears that spinel is a sensitive indicator of melt composition and pressure of crystallization. The close similarity of spinel composition fields in genetically related basalts, dunites and peridotites at localities in the oceans and in ophiolite complexes indicates that its composition reflects the degree of melting in the mantle source region. Accordingly, we infer from the restricted range of spinel compositions in abyssal basalts that the degree of mantle melting beneath mid-ocean ridges is generally limited to that found in Type I alpine-type peridotites. It is apparent, therefore, that the phase boundary OL-EN-DI-SP +meltOL-EN-SP+melt has limited the degree of melting of the mantle beneath mid-ocean ridges. This was clearly not the case for many alpine-type peridotites, implying very different melting conditions in the mantle, probably involving the presence of water.  相似文献   

Finite strain patterns and their significance in Permian rocks of the Alpes Maritimes (France)     

A.W.B. Siddans  B. Henry  R. Kligfield  W. Lowrie  A. Hirt  M.N. Percevault 《Journal of Structural Geology》1984,6(4):339-368

More finite strain data has been obtained from autochthonous Permian mudstones of the Alpes Maritimes, S.E. France. These new data were computed from field measurements of green spots on all available sections, deformed mudcracks and from the quantitative correlation between magnetic susceptibility anisotropy and finite strain in these rocks. Previously published finite strain data and the new results are presented on a series of structural maps and cross-sections for the Dôme de Barrot, the Tinée and Vionène region and the Roya region. As in previous studies difficulties arise in explaining the apparently variable extension parallel with the 100°, subhorizontal bedding-cleavage intersection: either this is real or there were large volume changes during the tectonic deformation. Study of quartz fibres, developed in deformed mudcracks in the Tinée valley, suggest that early in the tectonic history incremental stretching directions were parallel with the bedding—cleavage intersection, while later they were down-dip in the 100° trending cleavage. Since these Permian rocks have remained stuck to the Argentera basement they also record displacements and deformations in the basement. The early 100°, subhorizontal stretching is consistent with NW-SE dextral, strike-slip basement faulting, while later, down-dip stretching in the cleavage is consistent with contraction faults in the basement. This information and new palaeomagnetic data on the same samples are combined with recent geophysical evidence and regional tectonic studies, to provide a new precision to the tectonic history of this part of the Western Alpine External Zone.  相似文献   

The early Cenozoic tectonic history of the southeast Pacific     

Henry Stommel 《Earth and Planetary Science Letters》1982,61(1):63-67

It is suggested that the hydrothermal vents of the South Pacific Rise produce a beta-governed circulation at mid-depth, and that perhaps the associated plume of excess³He (Lupton and Craig [1]) points westward because of the dynamics of this circulation rather than as a passive tracer.  相似文献   

Iron metal production in silicate melts through the direct reduction of Fe(II) by Ti(III), Cr(II), and Eu(II)     

Henry D. Schreiber  G.Bryan Balazs  Andrew P. Shaffer  P.Lynne Jamison 《Geochimica et cosmochimica acta》1982,46(10):1891-1901

The production of metallic iron in silicate melts by the chemical reactions, 2Ti³⁺_(melt) + Fe²⁺_(melt) → 2Ti⁴⁺_(melt) + Fe⁰_(crystal)2Cr²⁺_(melt) + Fe²⁺_(melt) → 2Cr³⁺_(melt) + Fe⁰_(crystal)2Eu²⁺_(melt)+ Fe²⁺_(melt) → 2Eu³⁺_(melt) + Fe⁰_(crystal) has been demonstrated under experimental conditions in a simplified basaltic liquid, Such reactions may occur in lunar basalts and other reduced systems, and, thus, may aid in the understanding of the reduced nature of lunar basalts. The reactions were studied in a glass-forming Na-Ca-Mg-Al-silicate composition at a melt temperature of 1250°C and an imposed oxygen fugacity at the C/CO buffer (1 atm total pressure). Microtitrations of individually-doped samples were used in the quantitative assessment of their redox ratios and for the calibration of visible and near-infrared spectral absorptions. These spectral absorptions were then applied to the evaluation of the mutual redox interactions in dual-doped samples.  相似文献   

F-OH exchange equilibria between mica-amphibole mineral pairs     

Henry R. Westrich 《Contributions to Mineralogy and Petrology》1982,78(3):318-323

Fluoride-hydroxyl exchange equilibria between phlogopite-pargasite and phlogopite-tremolite mineral pairs were experimentally determined at 1,173K, 500 bars and 1,073–1,173 K, 500 bars respectively. The distribution of fluorine between phlogopite and pargasite was found to favor phlogopite slightly, G _ex ^. (1,173 K)=–1.71 kJ anion^–1, while in the case of phlogopite-tremolite, fluorine was preferentially incorporated in the mica, G _ex ^. (1,073)=– 5.67 kJ anion^–1 and G _ex ^. (1,173K)=–5.84 kJ anion^–1. These results have yielded new values of entropy and Gibbs energy of formation for fluortremolite, S _f =–2,293.4±16.0JK^–1 mol^–1 and G _f = –11,779.3±25.0 kJ mol^–1, respectively. In addition, F-OH mineral exchange equilibria support a recent molten oxide calorimetric value for the Gibbs energy of fluorphlogopite, G _f =–6,014.0±7.0 kJ mol^–1, which is approximately 40 kJ mol^–1 more exothermic than the tabulated value.This work performed in part at Sandia National Laboratories supported by the U.S. Department of Energy, DOE, under contract number DE-AC04-76DP00789  相似文献   

Organochlorine residues in whales landed at Durban,South Africa     

John Henry  Peter B Best 《Marine pollution bulletin》1983,14(6):223-227

The levels of DDT and its metabolites found in the blubber of 29 minke, 6 fin and 1 sei whale landed at the Durban whaling station in 1974 were on average much lower than those found in baleen whales from the North Atlantic, but of the same order as those measured from the Antarctic and North Pacific. In 12 sperm whales examined at Durban the levels of DDT and its metabolites in the blubber were substantially lower than in any other locality so far examined, including the Antarctic, but this may partly reflect the comparative youth of the animals sampled. Low levels of Dieldrin were found in some minke whales only. No PCB could be detected in any of the whales examined.  相似文献   

Rates of cave and landform development in the Yorkshire Dales from speleothem age data     

Melvyn Gascoyne  Derek C. Ford  Henry P. Schwarcz 《地球表面变化过程与地形》1983,8(6):557-568

Uranium-series ages have been obtained for 87 speleothems collected from nine major cave systems in the Craven district of northern England. Large systems such as Ease Gill Caverns, the West Kingsdale caves, and Gaping Gill-Ingleborough Cave, which contain relict high-level tunnels, are found to be older than 350,000 years (the limit of the ²³⁰Th/²³⁴U dating method). There is little evidence to indicate a significant enlargement of these passages since this time. Estimates of the age of Victoria Cave from ²³⁴U/²³⁸U isotopic ratios suggest that the cave has been fully relict for more than 500,000 years. Ages of in situ speleothems immediately adjacent to local base level cave streams show that mean maximum downcutting rates in limestone channels are about 2 to 5 cm 1000 yr. These rates are significantly lower than those obtained from direct measurements on limestone bedrock in stream channels but are comparable to areal denudation rates based on solute budgets. Using the present elevation of caves with respect to adjacent valley floor levels, mean maximum valley entrenchment rates are found to range between 5 cm/ky and < 20cm/ky, which corresponds to 6 m to < 24 m of lowering per glacial/interglacial cycle. These rates suggest that upper beds of the limestone were incised to form the Yorkshire Dales between 1 and 2 million years ago. The results indicate that the erosional effects of individual glaciations are not as severe as previously proposed in the literature.  相似文献   

Stream-sediment geochemical prospecting for uranium in the paleozoic of the Belgian ardennes     

H. Martin  J.P. Lefin  L. Dejonghe  J. Henry 《Journal of Geochemical Exploration》1983,19(1-3)

During the years 1979 and 1980, a preliminary program of uranium exploration in the Paleozoic of the Belgian Ardennes was carried out under the sponsorship of the Commission of European Communities. The Laboratory of Mineralogy of the Polytechnic Faculty of Mons was charged with the radiometric section of the program, the Geochemistry Laboratory of the Free University of Brussels with the hydrogeochemical exploration, and the Geochemistry Laboratory of the University of Louvain with the stream sediment exploration. The Geological Survey of Belgium had the responsibility for coordinating the three programs, the statistical and computer treatment of the data, and the compilation of the different maps.Orientation studies at the Geochemistry Laboratory of the University of Louvain showed that a positive geochemical response for uranium could be obtained with bank sampling, which consists of collecting colluvium and alluvium on both sides of the rivers. This necessitates a large sampling density of about one sample per km² (10 205 samples from an area of 11 000 km²).The frequency distribution of the values of uranium follows the lognormal law with a geometric mean of 1.06 ppm and a threshold of 2.36 ppm (P= 0.954). The anomalies (> 3 ppm) fall into three main areas each in a different geological setting: (1) at the periphery of the Cambro-Silurian Massif of Stavelot; (2) within the transition beds between the Visean and Namurian; and (3) in the lower Devonian of the central Ardennes.The first two areas coincide with zones of known radiometric anomalies and of the occurrence of uraniferous minerals.In the third zone, follow-up work has led to the discovery of a uraniferous mineral assemblage consisting of a weathered mass of iron oxide, leucoxene and phosphates.Statistical analyses of the results indicate no significant relationship between U and either organic carbon or Mn, a negative correlation between U and carbonate and pH, and a good positive correlation between U and Cu, V and Fe. The last correlation may indicate an association of U, V, and Cu with iron oxides formed during meteoric alteration.  相似文献   

Subliquidus glass-glass immiscibility along the albite-diopside join     

D.J. Henry  I.D.R. Mackinnon  I. Chan  A. Navrotsky 《Geochimica et cosmochimica acta》1983,47(2):277-282

A calorimetric study has shown that glasses along the albite-diopside join in the system albiteanorthite-diopside have positive enthalpies of mixing. Thermodynamic calculations based on these data describe a nearly symmetric, metastable, subliquidus irascibility gap along the join with a critical temperature at 910 K. The existence of the miscibility gap was tested experimentally by annealing an Ab₅₀Di₅₀ glass at 748 K and 823 K. Annealed glasses were examined by optical microscopy and by scanning and transmission electron microscopy. The glasses showed morphological and chemical features consistent with unmixing of two glass phases. The apparent mechanism of phase separation involves initial spinodal decomposition followed by coarsening to produce 0.1 μm–0.3 μm spherical glass phases.  相似文献   

High-Resolution Seismic Reflection Evidence for Middle Holocene Environmental Change, Owasco Lake, New York   总被引：2，自引：0，他引：2  

Henry T. Mullins  John D. Halfman 《Quaternary Research》2001,55(3):322

Approximately 70 km of new decimeter-resolution seismic reflection profile data from Owasco Lake, New York define a middle Holocene (4600 ¹⁴C yr B.P.) erosion surface in the north end of the lake at water depths as great as 26 m. Beneath the lake, post-glacial sediments are up to 9 m thick and represent about 10% of the total sediment fill. Early to middle Holocene sediments, 6 m thick, contain biogenic gas at the south end of the basin and a large (4 km×300 m×15 m) subaqueous slide deposit along the east-central portion of the lake. Late Holocene sediments are thinner or absent, particularly at the north end of the lake. The middle Holocene erosion surface may have been produced by a drop in lake level. Alternatively, it may represent a change in climate during the transition between the relatively warm Holocene hypsithermal and cool neoglacial. At this time (4600 ¹⁴C yr B.P.) circulation in Owasco Lake appears to have evolved from sluggish to active. The increased circulation, which persists today, probably resulted from atmospheric cold fronts with strong southwesterly winds that piled up water at the north end of the lake. The increased water circulation may have been ultimately driven by decreasing insolation, which produced an increased pole-to-equator thermal gradient and, thus, stronger global winds that began at the transition between the hypsithermal and neoglacial.  相似文献