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791.
Drilling at site 207 (DSDP Leg 21), located on the broad summit of the Lord Howe Rise, bottomed in rhyolitic rocks. Sanidine concentrates from four samples of the rhyolite were dated by the40Ar/39Ar total fusion method and conventional K-Ar method, and yielded concordant ages of 93.7 ± 1.1my, equivalent to the early part of the Upper Cretaceous. At this time the Lord Howe Rise, which has continental-type structure, is thought to have been emergent and adjacent to the eastern margin of the Australian-antarctic continent. Subsequent to 94 my ago and prior to deposition of Maastrichtian (70-65 myBP) marine sediments on top of the rhyolitic basement of the Lord Howe Rise, rifting occurred and the formation of the Tasman Basin began by sea-floor spreading with rotation of the Rise away from the margin of Australia. Subsidence of the Rise continued until Early Eocene (about 50 myBP), probably marking the end of sea-floor spreading in the Tasman Basin. These large scale movements relate to the breakup of this part of Gondwanaland in the Upper Cretaceous. 相似文献
792.
Gerrit van der Kaaden Joost Quakernaat Odd Gjems 《Contributions to Mineralogy and Petrology》1968,19(4):302-308
A pink-colored (HUE 5R-7/4), predominantly calcium saturated, clay mineral from Tirebolu, NE-Turkey, is shown to be a dioctahedral, high-charge manganiferous smectite. It is probably an alteration product of volcanic tuffs of rhyodactitic composition. Ionic formula: (Si7.71Al0.29)IV(Al3.04Fe
0.12
3+
Fe
0.02
2+
Mg0.92Mn
0.07
2+
)VI O20 (OH)4 0.79 M+ Cation exchange capacity: 92 me/100 g (air dry sample). Unit cell parameters (ca. 20 ° C; ca. 40% RH): a09.02 Å b05.21 Å Mg++... Mn-smectite: c014.65 Å Ca++... Mn-smectite: c014.83 Å K+... Mn-smectite: c012.10 Å
Zusammenfassung Ein rosa (HUE 5R-7/4), weitgehend Calcium-gesättigtes Tonmineral von Tirebolu (NO-Türkei) wurde als ein dioktaedrischer, hochgeladener manganhaltiger Smektit identifiziert. Er ist wahrscheinlich ein Umwandlungsprodukt eines rhyodazitischen Tuffs. Strukturformel: (Si7.71Al0.29)IV(Al3.04Fe 0.12 3+ Fe 0.02 2+ Mg0.92Mn 0.07 2+ )VI O20 (OH)4 0.79 M+ Kationaustauschkapazität: 92 me/100 g (luftgetrocknet). Gitterkonstanten (ca. 20° C; ca. 40% RF): a09.02 Å b05.21 Å Mg++... Mn-Smektit: c014.65 Å Ca++... Mn-Smektit: c014.83 Å K+... Mn-Smektit: c012.10 Å相似文献
793.
Willem van der Velden James Baker Sandra de Maesschalck Thea van Meerten 《International Journal of Earth Sciences》1982,71(1):171-181
The Grythytte field sequence forms a NNW belt of acid-basic metavolcanic and metasedimentary rocks. The geology shows characteristics of a dynamic process of trough-forming and infilling which to a large extent post-dates the Hjulsjö volcanoplutonic complex situated to the east. In the latter complex acid metapyroclastics strike around a centre of granite and granophyre, which cut and are cut by basic sills and dykes. Field and petrochemical evidence points to a distinct bimodal magmatism that ist manifested during one short phase of a rifting period.
Zusammenfassung Die Grythytte Schichtenfolge bildet einen NNW verlaufenden Gürtel aus sauren und basischen Metavulkaniten und Metasedimenten. Die geologischen Befunde weisen auf einen dynamischen Entstehungsprozeß von Grabenbildung und Füllung hin. Im weiter östlich gelegenen vulkanisch-plutonischen Hjulsjö-Komplex streichen älteren metamorphen pyroklastischen Gesteine rund ein Granit-Granophyr Zentrum. Dieser Komplex durchschneidet und wird durchschnitten von basischen Sills und Gängen. Feldgeologische und geochemische Untersuchungen weisen deutlich auf einen bimodalen Magmatismus hin, der während einer kurzen Phase der Grabenbildung stattfand.
Résumé La séquence de Grythytte forme une ceinture de roches métavolcaniques et métasédimentaires de direction NNO. La géologie fait apparaître les caractéristiques d'un processus dynamique de formation de fosse et de remplissage, qui s'est produit, pour la plus grande partie, après la formation du complexe volcano-plutonique de Hjulsjö situé à l'Est. Dans ce dernier complexe des produits pyroclastiques acides sont disposés autour d'un centre granitoïde et granophyrique, qui à son tour recoupe et est recoupé par des sills et des dykes basiques. Les observations de terrain et les faits pétrochimiques indiquent un procèssus magmatique distinctement bimodal qui s'est manifesté pendant une phase courte dans une période de «rifting».
Grythytte , NNW . . Hjulsj -- . . , , .相似文献
794.
P. F.?SchofieldEmail author K. S.?Knight J. A. M. van der?Houwen E.?Valsami-Jones 《Physics and Chemistry of Minerals》2004,31(9):606-624
The unit-cell and atomic parameters of perdeuterated brushite have been extracted from Rietveld analysis of neutron powder diffraction data within the temperature range 4.2 to 470 K. The thermal expansion of brushite is anisotropic, with the largest expansion along the b axis due principally to the effect of the O(1)···D(4) and O(3)···D(2) hydrogen bonds. Expansion along the c axis, influenced by the Ow1···D(5) interwater hydrogen bond, is also large. The high temperature limits for the expansion coefficients for the unit-cell edges a, b and c are 9.7(5) × 10–6, 3.82(9) × 10–5 and 5.54(5) × 10–5 K–1, respectively, and for the cell volume it is 9.7(1) × 10–5 K–1. The angle displays oscillatory variation, and empirical data analysis results in = 1.28(3) × 10–6sin(0.0105 T) K–1, within this temperature range. The evolution of the thermal expansion tensor of brushite has been calculated between 50 T 400 K. At 300 K the magnitudes of the principal axes are 11 = 50(6) × 10–6 K–1, 22 = 26.7(7) × 10–6 K–1 and 33 = 7.0(5) × 10–6 K–1. The intermediate axis, 22, is parallel to b, and using IRE convention for the tensor orthonormal basis, the axes 11 and 33 have directions equal to (–0.228, 0, –0.974) and (–0.974, 0, 0.228) respectively. Under the conditions of these experiments, the onset of dehydration occurred at temperatures above 400 K. Bond valence analysis combined with assessments of the thermal evolution of the bonding within brushite suggests that dehydration is precipitated through instabilities in the chemical environment of the second water molecule. 相似文献
795.
The Global Differential GPS (GDGPS) system developed by JPL aims at seamless global real-time positioning at the dm accuracy level for dual-frequency receivers either fixed or mobile, anywhere and at any time. The GDGPS system relies on GPS data transmitted in real-time to a central processing center at JPL from a global network of permanently operating GPS dual-frequency receivers. At the processing center, the Internet-based Global Differential GPS (IGDG) system, the heart of JPLs GDGPS, generates and disseminates over the open Internet special 1-s global differential corrections (IGDG corrections) to the GPS broadcast ephemerides. The IGDG corrections enhance the accuracy of GPS broadcast orbits and clocks down to the dm level and serve as the key-factor for high-precise real-time positioning of a stand-alone receiver. An experimental verification of the dm positional accuracy of the IGDG system was carried out in the Netherlands, by means of both a static and a kinematic test. During the static test GPS data were collected for 5 consecutive days using a fixed immobile receiver and processed as if in real-time. Within the framework of the kinematic test, an experiment was carried out using a kinematic platform. Our tests confirmed the dm accuracy of stand-alone receiver positioning with IGDG. The standard deviation for positioning both in static and kinematic mode appears to be 10 cm in each horizontal component and 20 cm in the vertical component. More than 99% of the IGDG corrections were received with the expected 1-s interval in the field via mobile communication, the latency of the corrections was generally from 7 to 8 s. 相似文献
796.
Incoherent internal tidal currents in the deep ocean 总被引:2,自引:0,他引:2
Eleven months current meter observations from the deep Bay of Biscay were examined for the residual (incoherent internal tidal; icIT) signal, left after harmonic analysis using eight tidal constituents (large-scale barotropic or coherent baroclinic signal) within the semidiurnal band. This residual signal comprised 30% of the total tidal kinetic energy and, due to its flat spectral appearance, it was responsible for typically 5–7 days intermittency. Although icIT was part of the red noise internal wave band continuum, it was not attributable to instrumental noise. It consisted of quasi-harmonics at non-tidal harmonic frequencies having amplitudes larger than N2, the third largest semidiurnal tidal constituent. It is suggested that the kinetic energy at these non-tidal frequencies reflects interaction between semidiurnal tidal motions and the slowly varying background conditions.Responsible Editor: Roger Proctor 相似文献
797.
798.
This paper describes the results of numerical experiments with a three-dimensional hydrodynamic and mud transport model in which sediment–fluid interaction is taken into account through the effects of hindered settling, buoyancy destruction in the turbulence k– model and sediment-induced barocline pressure gradients in the momentum equations. The model was applied to a schematic case representing a coastal area with a tidal river, navigation channel and harbour basin, and a real-world case, viz. Rotterdam harbour area in The Netherlands. The results show that the sediment transport into the harbour area, and subsequent siltation rates, increase by a factor 3 to 5 due to the sediment–fluid interaction. It is shown that the larger contribution stems from an increase in vertical gradients in suspended sediment.Responsible Editor: Jens Kappenberg 相似文献
799.
Wytze?van der WerffEmail author Stephen?D.?Johnson 《International Journal of Earth Sciences》2003,92(5):728-742
Exceptional exposures of Permian basin floor fans (fans 3, 4) and a slope fan (fan 5) in the Tanqua Karoo foreland basin of South Africa have enabled an investigation of the relation between the pinch-out geometries and fan architecture. The pinch-out geometry of fan 3 is characterized by the down dip transition from thin to medium bedded sheet deposits to pinch-out fingers, which are overlain by younger prograding sheet deposits. This geometry reflects the progradational stacking pattern of the fan. In contrast, the fan 4 pinch-out fingers consist of stacked channel fills in the same conduit. This pinch-out configuration relates to the dominant aggradational style observed on the mid and distal parts of fan 4. Fan 5 represents a slope fan comprising an axial channel conduit, which branches down slope into three distributary channels. The distal fan is characterized by larger channel fills, which may represent bypass channels to other basin floor fans. The very thick-bedded nature of the youngest channel fill unit suggests early bypass followed by retrogradation as indicated by the presence of thinner bedded heterolithic channel fill deposits along the axial conduit. Although some of the massive pinch-out channels exhibit basal scour, their depositional morphology suggests that they mainly originated due to the infill of subtle topographic depressions by low concentration turbidity currents. Instead of describing these features as channel fills, the use of the term pinch-out fingers is preferred. 相似文献
800.
We report strong magnetic linear dichroism (MLD) at the Fe L23 and O K edges of the antiferromagnetic compound hematite -Fe2 O3 in high-resolution orientation- and temperature-dependent electron energy-loss spectroscopy (EELS). Large intensity differences of corresponding spectral features are observed when the Fe L23 and O K edges are measured with momentum transfer either parallel or perpendicular to the magnetization. The resultant difference spectra for the Fe L23 edges is consistent with the MLD observed in X-ray absorption spectroscopy. For the first time we have observed MLD at the O K edge, where the magnetic origin of this dichroism is demonstrated by temperature-dependent investigations across the Morin transition temperature TM= 263 K, at which the Fe electron spins, i.e. the magnetic moments, rotate by 90°. The O K edge MLD is interpreted in terms of superexchange between the spins of the Fe 3d and O 2p electrons through overlapping Fe 3d and O 2p orbitals. The experiments were performed in a transmission electron microscope (TEM), yielding information about the anisotropic electronic structure at nanoscale spatial resolution when operated with a focused electron probe. The effects of MLD at the Fe L23 edges on the determination of Fe3+/Fe in hematite at submicrometre scale using different independent quantification methods are discussed. 相似文献