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 distribution and production of the hard clam,Mercenaria mercenaria,in Wassaw Sound,Georgia     

Walker  Randal L.  Tenore  Kenneth R. 《Estuaries and Coasts》1984,7(1):19-27

Estuaries and Coasts - Hard clams,Mercenaria mercenaria, occurred in four intertidal habitats in the outer, high salinity (18‰) region of Wassaw Sound, Georgia: small feeder creeks $$(\bar x...  相似文献   

Melting equilibria in multicomponent systems and liquidus/solidus convergence in mantle peridotite     

D. Walker 《Contributions to Mineralogy and Petrology》1986,92(3):303-307

The melting of undepleted mantle peridotite proceeds through a temperature interval which decreases with increasing pressure. If liquidus and solidus actually meet in the range 100–150 Kb, as suggested by Herzberg (1983), peridotite must transform there directly to a melt of its own composition. Thermodynamic analysis shows that such a liquidus/solidus meeting would be very unlikely in a system as chemically complex as mantle peridotite and would require that unanticipated phase equilibrium relations suppress all incongruent melting behavior. But Takahashi and Scarfe's (1985) preliminary experiments suggest that the upper mantle itself may indeed have a special composition with respect to phase equilibrium relations between liquids and solids at very high pressure. If so, mantle peridotite composition cannot be generated as a crystal accumulate or melting residue, because these two popular theories of origin are difficult to reconcile with a supposed eutecticlike composition. If upper mantle peridotite were itself a solidified liquid composition produced either as a partial melt or, more likely, as a crystallization residue of some more primitive melt composition representative of the whole mantle, an approach of liquidus to solidus might be expected at high pressure although the phase relations of Herzberg (1983) and Herzberg and O'Hara (1985) remain implausible.  相似文献   

Experimental petrology of alkalic lavas: constraints on cotectics of multiple saturation in natural basic liquids     

Richard O. Sack  David Walker  Ian S. E. Carmichael 《Contributions to Mineralogy and Petrology》1987,96(1):1-23

Experimental study of natural alkalic lava compositions at low pressures (pO₂QFM) reveals that crystallization of primitive lavas often occurs in the sequence olivine, plagioclase, clinopyroxene, nepheline without obvious reaction relation. Pseudoternary liquidus projections of multiply saturated liquids coexisting with plagioclase (±olivine±clinopyroxene±nepheline) have been prepared to facilitate graphical analysis of the evolution of lava compositions during hypabyssal cooling. Use of (TiAl₂)(MgSi₂)_–1 and Fe³⁺ (Al)_–1 exchange components is a key aspect of the projection procedure which is succesful in reducing a wide range of compositions to a systematic graphical representation. These projections, and the experiments on which they are based, show that low pressure fractionation plays a significant role in the petrogenesis of many alkalic lava suites from both continental and oceanic settings. However, the role of polybaric fractionation is more evident in the major element chemistry of these lava suites than in many tholeiitic suites of comparable extent. For example, the lavas of Karisimbi, East Africa, show a range of compositions reflecting a polybaric petrogenesis from primitive picrites at 1360° C/18 kb and leading to advanced low pressure differentiates. Evolved leucite-bearing potassic members of this and other suites may be treated in a nepheline-diopside-kspar (+olivine+leucite) projection. Compositional curvature on the plagioclase+clinopyroxene+olivine+leucite cotectic offers a mechanism to explain resorption of plagioclase in alkalic groundmass assemblages and the incompatibility of albite and leucite. This projection is useful for evaluating the extent of assimilation of the alkalic portions of crustal granulites. Assimilation appears to have played some role in the advanced differentiates from Karisimbi.  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   

${}^{40}\text{Ar}{}^{39}\text{Ar}$ and KAr dating of altered glassy volcanic rocks: the Dabi Volcanics,P.N.G.     

David A. Walker  Ian McDougall 《Geochimica et cosmochimica acta》1982,46(11):2181-2190

KAr and ${}^{40}\text{Ar}{}^{39}\text{Ar}$ ages have been determined for altered submarine tholeiitic and boninite (high-Mg andesite) lavas from the Dabi Volcanics, Cape Vogel Peninsula, Papua New Guinea. ${}^{40}\text{Ar}{}^{39}\text{Ar}$ whole rock total fusion and plateau ages identify a Late Paleocene age for the tholeiitic lavas (58.9 ± 1.1 Ma) and also for the boninitic lavas (58.8 ± 0.8 Ma). Apparent KAr ages for the same samples range from 27.2 ± 0.7 to 63.9 ± 4.5 Ma, and young KAr ages for glassy boninites are probably due to variable radiogenic ⁴⁰Ar (⁴⁰Ar¹) loss. These new ages effectively reconcile previously ambiguous age data for the Dabi Volcanics and indicate contemporaneous tholeiitic and boninitic volcanism occurring in southeast PNG during the Late Paleocene.Smectites, developed as alteration products after glass in oceanic lavas commonly do not retain ³⁹Ar during or subsequent to irradiation, but in some cases may contain ⁴⁰Ar1. In the absence of other factors modifying K and Ar contents, samples which have not lost ⁴⁰Ar¹ from smectite and suffer ³⁹Ar loss only, are interpreted to have been altered immediately subsequent to the crystallization of the lava; whereas samples which have lost ⁴⁰Ar¹ as well as ³⁹Ar may be the result of either recent alteration, or of continuous ⁴⁰Ar¹ loss since the time of crystallization.  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   

Reply to A.Y. Glikson     

E.G. Nisbet  D. Walker 《Earth and Planetary Science Letters》1983

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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