Sea water weathering effect on K-Ar age of submarine basalts

K-Ar dating and ⁴⁰Ar-³⁹Ar step heating experiments have been done for successive zones from the surface to the interior in two, altered dredged submarine basalts (16-2-6 and Aries V-23). The K contents show a systematic decrease (surface to the interior), whereas the K-Ar ages show a similar decrease in one sample (16-2-6) and almost no change in the other (Aries V-23).A simple diffusion model suggests that the K content decreases systematically from the surface to the interior, whereas the K-Ar age decreases or remains almost constant, depending on whether the times of solidification and of commencement of K-diffusion are close to each other or differ significantly. Comparison of the observed K content and K-Ar age variations within the rocks with the theoretical model then suggests that the solidification age of the sample Aries V-23 is much older than the commencement of the potassium-diffusion, the latter age perhaps being represented by the Eocene planktonic foraminifera on this sample. The ⁴⁰Ar-³⁹Ar isochron age obtained for the freshest specimen of Aries V-23 is 86.6 ± 3.7 m.y., supporting the above conclusion.The mathematical simulation indicates that an apparent concordance of the K-Ar age observed in some submarine basalts may be an artifact, only reflecting the significant gap between the solidification age and the time of the commencement of the K-diffusion in the rocks. Microprobe examination reveals that the potassium enrichment in the outer margin, is mainly due to K feldspar, which is an alteration product of plagioclase.     

The computation of long geodesics on the ellipsoid by non-series expanding procedure

In this paper the author shows a procedure to settle the computation of very long geodesic lines on the ellipsoid without using the series expansion. The integration of elliptic integrals appearing in the procedure is numerically carried out by means of a mechanical quadrature-the method of Repeated Interval Halving. The author also devises formulae for the numerical solution of the problem, in order to make the amount of significance error least and determine the kind of quadrant for the computation of inverse trigonometric function. The anti-podal problem for the direct and inverse solution is rigorously solved by this method.     

The computation of long geodesics on the ellipsoid through Gaussian quadrature

Formulas for computing geodesics on the bi-axial ellipsoid through Gaussian quadrature are shown; the estimation of computational errors, truncation and roundoff errors, for the quadrature is carried out; and test examples found in [3] together with those which consist of near anti-podal points on the neighborhood of the equator, are computed with the evaluation of the computational errors.     

Equation of state of hexagonal aluminous phase in basaltic composition to 63 GPa at 300 K

A laser-heated diamond-anvil cell that is capable of operating up to a pressure of 63 GPa, with X-ray diffraction facilities using a synchrotron radiation source at the SPring-8, has been developed to observe the compressibility of a hexagonal aluminous phase, [K_0.15Na_1.66Ca_0.11Mg_1.29Fe²⁺ _0.86Al_3.13Ti_0.09Si_1.98] _Σ9.27O₁₂. The hexagonal aluminous phase is a potassium host mineral from the subducted oceanic crust in the Earth's lower mantle. A sample was heated using a YAG laser at each pressure increment to relax the deviatoric stress in the sample. X-ray diffraction measurements were carried out at 300 K using an angle-dispersive technique. Pressure was measured using an internal platinum pressure calibrant. The observed unit-cell volumes were used to obtain a third-order Birch–Murnaghan equation of state: unit-cell volume V _o=185.94(±16) ų, density ρ _o=4.145 g/cm³, and bulk modulus K _o=198(±3) GPa when the first pressure is derivative of the bulk modulus K ^′ _o is fixed to 4. The density of hexagonal aluminous phase is lower than that of coexisting Mg-perovskite in the subducted oceanic crust.     

Temporal and spatial variability of cobalt in the Atlantic Ocean

The spatial and temporal variability of cobalt in the Atlantic Ocean was investigated by means of adsorptive cathodic stripping voltammetry. A vertical profile of total dissolved cobalt at the Bermuda Atlantic Time Series station ranged from 17 to 73 pM and displayed surface depletion indicative of biological utilization. This profile when compared with a cobalt profile from the northeast Pacific shows no increase in deep-water concentrations with thermohaline circulation through the deep ocean basins. Moreover, the middepth maximum observed in northeast Pacific profiles is not present in the Sargasso Sea, perhaps because of the lack of cobalt scavenging by particulate manganese oxides in surface waters and to the absence of a suboxic oxygen minimum zone, which, if present, could dissolve the manganese oxides.Total dissolved cobalt measurements were also made on a surface transect from the Sargasso Sea to coastal Massachusetts, USA, and on time-series samples from the Moored In Situ Trace Element Serial Sampler. Dissolved cobalt on this transect correlated strongly with salinity (r² = 0.93) and ranged from 19 to 133 pM, indicating mixing of cobalt from shelf waters into the Sargasso Sea. Time-series samples near Bermuda did not show an obvious response to the summer maximum in aeolian dust deposition, with an annual average of 20 ± 10 pM at 40- to 47-m depths. By use of this annual value and particulate cobalt data from the literature, 100-m surface-water residence times were calculated to be as low as 0.32 yr for cobalt. Several sharp decreases in cobalt were observed in the time series that occurred simultaneously with a shallowing of the thermocline depth. These decreases could be caused by nutrient drawdown associated with higher productivity mesoscale eddy events.A west-east surface transect across the South Atlantic showed high cobalt concentrations at the boundaries of the transect and low concentrations in the center despite the high precipitation rates in the intertropical convergence zone. Phosphate measurements showed the similar trends as the total cobalt transect. A regression of cobalt vs. phosphate reveals a slope that is an order of magnitude higher than that of the northeast Pacific and that is similar to the slopes observed for zinc vs. phosphate in the Pacific.     

Observation of core discing and in situ stress measurements; Stress criteria causing core discing

Summary Core discing was typically observed in cores recovered from near horizontal holes drilled in Palaeogene sandstones at a depth of 1055 m in the Horonai colliery, Hokkaido, Japan. We have observed disc- and ring-like cores and measured in situ stress where they were recovered. We compared the measured stress state with an empirical criterion of core discing based on Obert and Stephenson (1965) and a theoretical criterion based on Sugawara et al. (1978) and Ishida and Saito (1989). Consequently, we found that disc-like cores were recovered under lower stress state than predicted by both criteria. The stress state where ring-like cores were recovered satisfied the empirical criterion, however, it was below the critical stress state according to the theoretical criterion. These discrepancies indicate that existing stress criteria are not satisfactory and that further experimental, theoretical and field investigations are needed.     

Vibrations of beams with an absorber consisting of a viscoelastic solid and a beam

This paper considers the response of a beam with a dynamic vibration absorber, which consists of a viscoelastic solid and a double-cantilever viscoelastic beam, attached to the centre of the main beam. The ends of the main beam are built in and excited sinusoidally by the base motion. The transfer matrix method is used in the analysis. The displacement transmissibility, i.e. the ratio of the displacement at the centre of the main beam to that of the base is investigated in the numerical example. It is shown that the present absorber is effective to suppress several resonances of the main beam simultaneously by only one compact device. Values of the optimum tuning design parameters are presented in the numerical example.     

济州岛西南泥质区近2300 a来环境敏感粒度组分记录的东亚冬季风变化

对位于东海陆架济州岛西南泥质区的B2孔进行了沉积物粒度分析, 从中提取出了对沉积环境变化敏感的粒度组分. 研究表明该敏感组分的粒级含量和平均粒径变化主要受东亚冬季风的强弱变化制约. 根据以上粒度指标与AMS14C测年相结合建立了近2300 a东亚冬季风高分辨率的时间变化序列. 结果表明近2300 a东亚冬季风变化和中国东部气候变化序列有较好的一致性, 可以划分为四个阶段: 1900 aBP (50 AD)以前和1450 ~ 780 aBP (500 ~ 1170 AD)这两个阶段东亚冬季风相对较弱, 与气候变化的暖期相对应; 1900 ~ 1450 aBP (50 ~ 500 AD)和 780 ~ 219 aBP (1170 ~ 1731 AD)两个阶段为东亚冬季风强盛期, 与气候变化的冷期对应, 后者为近2300 a以来最寒冷的气候阶段, 对应于小冰期. 其中各阶段内部东亚冬季风有明显的次级波动. 在1900 aBP (50 AD)和780 aBP (1130 AD)前后有两次明显的阶段性的气候由暖转冷突变事件, 后者可能与全球尺度大气环流的改变有关.