Magnitude and Q determinations in southern Africa using Lg wave amplitudes     

R. A. C. Chow  J. D. Fairhead  N. B. Henderson  P. D. Marshall 《Geophysical Journal International》1980,63(3):735-745

b
The amplitude of vertical, short period (1 s) Lg -waves from 575 shallow earthquakes recorded within the distance range 0|Mo-30|Mo by the Rhodesian seismograph network during the period 1968–77 are analysed to separate the effects of earthquake size, epicentral distance and station structure.
When corrected for geometrical spreading and Airy phase dispersion the decay of amplitude with distance yields an estimate of anelastic attenuation of 0.160 deg^-1 which gives an average value of Q (the specific quality factor) of 603 |Mp 50 for propagation paths that lie along and across the East African Rift System. Inversion of the amplitude—distance curve gives the calibration or distance normalizing function. Thereby the amplitude of Lg can be used to provide an estimate of the size of small, local earthquakes in terms of the teleseismic body wave magnitude m_b (after Henderson). The station effects of the six seismograph stations making up the network all lie within |Mp0.1 magnitude units. Since three of the stations lie on the Rhodesian craton while the remaining three lie on Precambrian mobile belts adjacent to the craton, the Precambrian basement geology does not significantly affect the amplitude of Lg  相似文献   

Elemental abundance data for the Manitouwabing iron meteorite     

R. R. Brooks  X. Guo  M. Hoashi  R. D. Reeves  D. E. Ryan  J. Holzbecher  G. S. Henderson 《Meteoritics & planetary science》1992,27(2):186-186

Abstract The Manitouwabing meteorite whose trace constituents have not been previously quantified was analysed for Au, As, Ga, Ge, Ir, Ni, Os, Pd, Pt, Rh and Ru. Our data confirm that it belongs to subgroup IIIA of the IIIAB group and on the basis of the much higher concentrations of As, Ir, Os, Pt, Rh and Ru, it is not paired with Madoc as had previously been proposed.  相似文献   

Measuring quartz solubility by in situ weight-loss determination using a hydrothermal diamond cell     

Halan M. Wang  Grant S. Henderson 《Geochimica et cosmochimica acta》2004,68(24):5197-5204

The solubility of quartz was determined using a hydrothermal diamond anvil cell (HDAC) within the temperature and pressure ranges of 126 to 490°C and up to 8.9 kbar, respectively. A novel approach has been used to measure the amount of dissolved silica. The quartz was abraded into spheres which have a diameter of ∼40 μm. The spheres were then placed in pure water inside the diamond anvil cell and heated externally. Because the transparency of the diamonds allows direct observation of the sample chamber during the experiment, we were able to estimate the amount of quartz dissolved in the water at various stages of the dissolution process by measuring the decrease in the sphere’s diameter over time. Experiments were performed along isochores between 0.92 and 0.99 g/cm³. The maximum solubility measured was 0.165 molal. The experimental solubility data were limited to 370°C because of overestimation of solubilities above this temperature. Reprecipitation of silica inside the HDAC sample chamber and the refaceting of the spheres to trigonal form at temperatures above 350°C are major contributors to the overestimation.  相似文献   

A lithostratigraphic revision and palaeoenvironmental assessment of the Cretaceous System exposed in the onshore Cauvery Basin, southern India     

R. Sundaram  R. A. Henderson  K. Ayyasami  J. D. Stilwell 《Cretaceous Research》2001,22(6):743

The exposed Cretaceous shelf succession of the Cauvery Basin, southeastern India, has provided a world-class record of mid and Late Cretaceous invertebrates, documented in a substantial literature. However, the lithostratigraphy of the succession has been little studied and previously subject to a range of nomenclature. It is revised here, on the basis of intensive regional mapping, to stabilize the definition and nomenclature of lithostratigraphic units. The Uttattur Group is restricted in outcrop to the Ariyalur district and divided into the Arogypapurum Formation (new; Albian), Dalmiapuram Formation (late Albian), and Karai Formation (late Albian–early Turonian) for which the Odiyam and Kunnam Members are recognized. The Trichinopoly Group follows unconformably and is also restricted in outcrop to the Ariyalur district. It is divided into the Kulakkalnattam Formation (Turonian) and Anaipadi Formation (late Turonian–Coniacian). The Ariyalur Group is more widely distributed. In the Ariyalur district, the Sillikkudi Formation (Santonian–Campanian) and its Kilpaluvari Member, the Kallakurichchi Formation (early Maastrichtian), the Kallamedu Formation (mid and Late Maastrichtian) and the Niniyur Formation (Danian) are recognized. The sequence in the Vriddhachalam area consists of the Parur and Patti formations (Campanian), Mattur Formation (late Campanian–earliest Maastrichtian) and Aladi Formation (Maastrichtian). For the Pondicherry district, the Valudavur and Mettuveli formations (Maastrichtian) and Kasur and Manaveli formations (Paleocene) comprise the succession. The interpreted depositional environments for the succession in the Ariyalur district indicate four eustatic cycles in the mid and Late Cretaceous and earliest Tertiary: late Albian–early Turonian, late Turonian–Santonian, Campanian, Maastrichtian, and Paleocene. Overall the Cauvery Basin sequence is arenaceous and relatively labile in terms of framework grain composition, and contrasts with the pelitic assemblage developed on the west Australian margin from which eastern India separated in the Early Cretaceous (Valanginian). The difference is ascribed to palaeoclimate as controlled by palaeolatitude. For the Late Cretaceous, the Cauvery Basin drifted north on the Indian plate from 40 to 30°S. This zone is inferred to constitute Southern Hemisphere horse latitudes for Late Cretaceous time, characterized by an arid climate, physical weathering and the production of labile sands. By contrast, the west Australian margin of matching tectonic history remained in a high palaeolatitude (>40°S) throughout the Late Cretaceous, experiencing a pluvial climate, the dominance of chemical weathering and the production of clays.  相似文献   

Use of L-edge X-ray absorption spectroscopy to characterize multiple valence states of 3d transition metals; a new probe for mineralogical and geochemical research     

G. Cressey  C. M. B. Henderson  G. van der Laan 《Physics and Chemistry of Minerals》1993,20(2):111-119

2p (L _2,3) X-ray absorption spectra are presented for a range of minerals to demonstrate the usefulness of L-edge spectroscopy as a symmetry- and valenceselective probe. 2p XAS provides a sensitive fingerprint of the electronic states of 3 d transition metals and can be applied to phases containing mixtures of such elements. Calculated spectra for 3d ⁿ → 2p ⁵ 3d ⁿ⁺¹ transitions provide a basis for the interpretation of the measured spectra. Thus, in principle, multiple valence states of a particular 3 d metal can be precisely characterized from a single L-edge spectrum. Examples of vanadium L-edge spectra are presented for a range of minerals; these complex spectra hold information concerning the presence of vanadium in multiple valence states. The Cu L-edge spectrum of sulvanite (Cu₃ VS₄) indicates the presence of both Cu⁺ and Cu²⁺; the V L-edge spectrum of the same sample shows that both V²⁺ and V⁵⁺ are present. Spectral simulations representing mixtures of Fe d ⁵ and Fe d ⁶ states are used to quantify Fe³⁺/∑Fe in a spinel, a glass, and an amphibole, all of which contain Fe as a major component. To illustrate the sensitivity of 2p XAS in a dilute system, the Fe L-edge spectrum of amethyst (α-SiO₂: Fe) has been recorded; this spectrum shows that ～68% of the Fe in amethyst is Fe²⁺, and ～32% is Fe³⁺. Although previous studies on amethyst using other spectroscopic methods cite evidence for Fe⁴⁺, there is no indication in the L-edge spectrum for Fe⁴⁺ in amethyst. Comparison of theoretical and experimental spectra not only allows the valence states of 3 d ions to be recognised, but also provides site-symmetry information and crystal field parameters for each ion site.  相似文献   

NMR studies of the leucite analogues X2YSi5O12, where X= K,Rb, Cs; Y = Mg,Zn, Cd     

S. C. Kohn  C. M. B. Henderson  R. Dupree 《Physics and Chemistry of Minerals》1994,21(3):176-190

A number of leucite group materials with the formula X₂YSi₅O₁₂ where X=K, Rb, Cs and Y=Mg, Zn, Cd have been synthesized by dry and hydrothermal crystallization of glass starting materials. ²⁹Si MASNMR has been used to obtain structural information, such as the number of distinct tetrahedral sites, degree of cation ordering, and estimates of the mean T-O-T bond angles of the tetrahedra. X-ray powder diffraction gave information on cell volumes and degree of distortion from cubic symmetry for all the samples and space group and structural information for some samples. Integration of the different length-scale data obtained using these two complementary techniques allows greater reliance to be placed on the structures deduced for these leucite samples, which are only available as fine-grained powders. Hydrothermally synthesized K₂MgSi₅O₁₂, K₂ZnSi₅O₁₂ and Rb₂ZnSi₅O₁₂ have structures with 12 distinct tetrahedral sites (T-sites) and are monoclinic P2₁/c while the dry-synthesized equivalents are disordered with single T-sites and are cubic, Ia3d. Most of the other members of the group have structures with 6 tetrahedral sites with Cs₂CdSi₅O₁₂ being orthorhombic, Pbca. Cs₂ZnSi₅O₁₂ has an intermediate “5+2” structure. Decreasing the size of the X⁺ cation for a given Y²⁺ cation gives more collapsed and distorted frameworks. ¹³³Cs NMR was used to show that samples with 6 T-sites have 2 alkali sites. It is deduced that samples with 12 T-sites will undergo a displacive phase transition to a 6 T-site structure (possibly via a 5+2 intermediate in some cases) with no change in the framework topology or degree of T-site ordering.  相似文献   

Plutonium diffusivity in compacted bentonite     

Kazuya Idemitsu  Katsuhiko Ishiguro  Yasuhisa Yusa  Noriaki Sasaki  Naomi Tsunoda 《Engineering Geology》1990,28(3-4):455-462

Measurements on plutonium diffusivity in water-saturated compacted bentonite were carried out. Representative specimens of sodium bentonite were taken from the Tsukinuno and Kuroishi mines situated in northeast Japan. Tsukinuno bentonite was divided into three types: raw type, purified Na-type, and H-type which was prepared by treating Na-type bentonite with hydrochloric acid. Kuroishi bentonite contained chlorite as impurity. H-type bentonite was used as reference for the convenience of profile measurement in bentonite, since plutonium diffusivity in H-type bentonite was considered to be larger than that in Na-type bentonite because of low pH and low swelling pressure of H-type bentonite.

Sampled bentonite was compacted into pellets of 20 mm in diameter and 20 mm in height. Bulk densities of these specimens were 1200–1800 kg/m³ for purified Na-type and H-type bentonite and 1600 kg/m³ for raw type bentonite.

Plutonium profiles obtained in H-type bentonite can be explained by diffusion equation with constant concentration source. Diffusivity ranges from 10^-13 to 10¹² m²/s for H-type and Kuroishi impure sodium bentonite. Diffusivity in both raw type and purified Tsukinuno bentonite was was estimated to less than 10^-14 M²/s. Diffusivity in H-type bentonite showed a tendency to decrease with increasing density. Influence of in bentonite was also studied. Quartz content up to 50% or hematite content up to 1% did not influence diffusivity significantly in H-type bentonite.

The chemical species of plutonium in pore water of Na-type and H-type were estimated Pu(OH)₃^-; and PuO₂^- , respectively.  相似文献   

A room-temperature phase transition in maximum microcline     

R. E. Openshaw  C. M. B. Henderson  W. L. Brown 《Physics and Chemistry of Minerals》1979,5(1):83-93

A type of hysteresis, similar to that observed in the heat capacity measurements (Openshaw et al., 1979), has been found in the room temperature unit cell parameters of a microcline sample 71104 and likewise indicates the existence of two forms of this microcline. The A-form (obtained on cooling the sample to approximately 80 K) has significantly different values of b, β and V to the B-form which is the more stable form above 300±10 K. The transition from the A- to the B-form occurs over a period of months and has an associated ΔV of ?0.0011 nm³. The cell parameters of the B-form have been measured up to 1278 K and show significant changes: a and V increase, b constracts, and c is unchanged on increasing temperature. The calculated thermal expansion ellipsoid is nearly uniaxial and similar in shape to that for sanidine. Below room temperature the isobaric thermal expansion coefficent α_p, for a natural microcline is nearly four times as large as that for sanidine. Above room temperature α_p for 71104 microcline decreases markedly with increasing temperature. This implies a rapid change in the thermal expansion behavior of microcline which has been correlated with the proposed phase transition.  相似文献   

The probable occurrence of interstitial Al in hydrous,F-bearing and F-free aluminosilicate melts   总被引：1，自引：0，他引：1  

D. A. C. Manning  D. L. Hamilton  C. M. B. Henderson  M. J. Dempsey 《Contributions to Mineralogy and Petrology》1981,75(3):257-262

Experiments carried out on the system SiO₂-NaAlSi₃O₈-KAlSi₃O₈(Qz-Ab-Or) at 1 kbar in the presence of H₂O and F show that the quartz-alkali feldspar field boundary is progressively displaced towards the feldspar join as F contents increase from 0 to 4 wt. %F. Increasing , in the absence of F, has already been shown to have a similar effect (Tuttle and Bowen 1958; Luth, Jahns, and Tuttle 1964). The increased size of the quartz field in the F-bearing system compared to the hydrous system is believed to be caused by progressive removal of Al from the tetrahedral network of the melt by complexing with F. The residual network in the melt is thus enriched in Si and this stabilizes precipitation of quartz rather than feldspar for certain bulk compositions. The common presence of quench cryolite (Na₃AlF₆) in certain experiments carried out with 4 wt.% F supports this interpretation and indicates that some Al in the melt may be present in six-fold coordination with F^–. The effect of H₂O in the absence of F may be similar, with Al being progressively removed from four-fold coordination as more H₂O is dissolved in the melt. Although a proportion of Al in hydrous melts may occur in six-fold coordination, dry melts predominantly contain Al in four-fold coordination. This major difference in Al complexing may be one of the main causes for differences in the high-pressure phase relations of wet and dry Albearing silicate systems.  相似文献   

Updraft properties deduced statistically from Rawin soundings     

Robert P. Davies-Jones  James H. Henderson 《Pure and Applied Geophysics》1975,113(1):787-801

Between 1966 and 1973, National Severe Storms Laboratory mesonetwork soundings were taken near thunderstorms and squall lines. Thirty-four of these soundings sampled updrafts at various levels. Because of instrumental noise and atmospheric fine structure, many of the individual soundings were hard to interpret. However, significant results were obtained from the data as a whole and from the four fastest updraft cases. Typically, the updrafts were associated with moderate thunderstorms that formed in baroclinic regions with maritime tropical air near the surface overlaid by drier air aloft. The immediate environments were potentially, conditionally, and latently unstable but were stable with respect to parcel displacement from the lifted condensation level. The updrafts were generally located in regions of strong radar reflectivity gradient at 0° antenna tilt. The updraft soundings often showed pseudo-adiabatic lapse rates immediately above the updraft condensation level. Statistical analysis of the data confirms that updrafts are warm core at mid- and upper levels and that they are relatively cool at low levels (below 700 mb). Important effects of perturbation pressure gradient forces are emphasized. We also find that local updraft speed is positively correlated at the 95% confidence level with local potential wet-bulb temperature between 0.9 and 9.3 km MSL. The average vertical velocity is a maximum at a relatively low height (4.8 km MSL); this agrees with other experiments that involve tracking objects released below cloud base. However, flight train icing and other extraneous factors may be influencing this result. The average horizontal winds in the updraft and environment agree with recent conceptual Great Plains thunderstorm models.  相似文献