达拉布特蛇绿岩带镁铁质岩的地球化学

达拉布特蛇绿岩带的镁铁质岩属亚碱性和碱性系列,可能是弧后盆地火册活动的产物。根据镁铁质岩的层位关系、岩浆来源和微量元素特征,可将该盆地的地质演化概括为扩张阶段和封闭阶段。盆地扩张阶段早、中期喷发的镁铁质岩具有低的稀土和不相容元素丰度,而在盆地封闭阶段晚期喷发的碱性玄武岩,其特点是稀土和大多数不相容元素丰度极大增高,其稀土元素分布模式为轻稀土元素强烈富集型。     

Short-wave radiation flux divergence in arctic cirrus: a case study

Radiation and particle measurements have been performed with an aircraft in deep cirrus cloud fields near the island of Svalbard. The data of 12 March 1993, when measurements at 10 different levels could be obtained, are used in a comparative study with radiative transfer calculations. In a first analysis, the cirrus cloud field was assumed to be horizontally homogeneous and invariable during the time of measurements (frozen properties). Calculations of the up and downward radiative flux densities showed root mean square differences of 9 Wm⁻² from the measurements. To estimate the possible effect of changes of the optical properties of cirrus with time, the flux densities in the upper part (6000–8500 m) and the lower part (3000–5500 m) of the cirrus cloud were analyzed separately. In these simulations, the optical thickness in the lower (upper) part was increased (decreased) by 50%. By this treatment, most of all calculated flux densities were within one standard deviation of the natural variability in each leg. Finally, the effect of inhomogeneities in the cloud field on the solar flux density has been simulated using a Monte Carlo method, since the upper part of the cirrus field has indeed been very inhomogeneous. This paper is a result of a collaborative effort between the MRI in Tsukuba, Japan, and the GKSS in Geesthacht, Germany.     

Hard X-ray emission from the solar corona

This review surveys hard X-ray emissions of non-thermal electrons in the solar corona. These electrons originate in flares and flare-related processes. Hard X-ray emission is the most direct diagnostic of electron presence in the corona, and such observations provide quantitative determinations of the total energy in the non-thermal electrons. The most intense flare emissions are generally observed from the chromosphere at footpoints of magnetic loops. Over the years, however, many observations of hard X-ray and even γ-ray emission directly from the corona have also been reported. These coronal sources are of particular interest as they occur closest to where the electron acceleration is thought to occur. Prior to the actual direct imaging observations, disk occultation was usually required to study coronal sources, resulting in limited physical information. Now RHESSI has given us a systematic view of coronal sources that combines high spatial and spectral resolution with broad energy coverage and high sensitivity. Despite the low density and hence low bremsstrahlung efficiency of the corona, we now detect coronal hard X-ray emissions from sources in all phases of solar flares. Because the physical conditions in such sources may differ substantially from those of the usual “footpoint” emission regions, we take the opportunity to revisit the physics of hard X-radiation and relevant theories of particle acceleration.     

A new approach to evaluation of the effect of the two half-Lambert surfaces composed of different albedoes on the emergent radiation at the top of the atmosphere

A new way is adopted for the evaluation of the upwelling radiation from atmosphere bounded by two half-Lambert surfaces. The atmosphere is assumed to be homogeneous, and is composed of aerosol, molecules, and absorbent gases, where the model aerosol is of the oceanic and water soluble types.In the computational procedure, an iterative doubling-adding equation is expanded into a series of the radiative interaction modes between atmosphere and surface. Next, a probability of radiation interacting with respective half surfaces is calculated based on the assumption of single-scattering in the atmosphere. On the basis of this probability, the emergent radiation at the top of the atmosphere is approximately calculated by considering the radiative intractions to be twice as large. The effect of the multiple-scattering is fully taken into account. A numerical simulation exhibits the extraordinary effect near the two half-surface boundary of different albedoes. The effect of the other half-surface on the radiance decreases monotonically with the distance from the boundary. The present new version enable us to quantitatively discuss radiative transfer near the boundary of two half-surfaces even if the optical thickness is large and (or) surface albedo is great.     

Rhenium and osmium systematics on iron and stony iron meteorites

Abstract— Re and Os abundances and ¹⁸⁷Os/¹⁸⁶Os isotopic ratios in 12 iron meteorites of various groups and five stony iron meteorites have been determined by an inductively coupled plasma mass spectrometry (ICP-MS). The series of iron meteorites studied have Re and Os concentrations ranging from 0.004 to 3.3 ppm and 0.03 to 41 ppm, respectively. The ¹⁸⁷Re/¹⁸⁶Os ratios in these meteorites fall between 3.0 and 6.1 and the ¹⁸⁷Os/¹⁸⁶Os between 1.0 and 1.2, giving an initial ¹⁸⁷Os/¹⁸⁶Os isotopic ratio of 0.790 and a Re-Os age of iron meteorites of 4.30 ± 0.28 Ga when employing the decay constant of 1.64 × 10^?11 yr^?1. The observed Re-Os age for iron meteorites appears somewhat younger than that for chondrites. The resultant younger age might be due either to a very slow cooling of the parental planetesimals or due to a secondary “shock” event. However, for definite conclusions about the Re-Os age, higher precisions of the Re and Os isotopic measurements and of the decay constant of ¹⁸⁷Re are required. Furthermore, the clear elucidation of the mechanisms for the fractionation of the Re/Os abundance ratios are related to the understanding of the meaning of the Re-Os age. The Re and Os abundances in pallasite stony iron meteorites are extremely low compared with those for most iron meteorites. On the other hand, the Re and Os abundances in mesosiderite stony iron meteorites show values comparable with those observed in most iron meteorites. The difference in Re and Os abundances in pallasite and mesosiderite stony iron meteorites strongly suggests that these stony iron meteorites are different in origin or history of chemical evolution. Re and Os abundances in the series of iron and stony iron meteorites were found to have a wide variation covering nearly four orders of magnitude, with a very high correlation coefficient (0.996), and a slope very slightly less than unity. The regression line observed here covers various groups of iron meteorites, stony iron meteorites and also chondrites. Masuda and Hirata (1991) suggested the possible direct mixing process of particles of most refractory metallic elements with gaseous clouds of less refractory matrix elements, since the Re and Os were predicted theoretically to be the first elements to condense as a solid phase from the high temperature solar nebula. The aims of this paper are to present a reliable technique for the Re-Os chronology and to study the cosmochemical sequences of the meteoritic metals.     

Experimental determination of partition coefficients of ten rare earth elements and barium between clinopyroxene and liquid in the synthetic silicate system at 20 kilobar pressure

Two experiments were carried out at 20 kb pressure for the measurement of partition coefficients of ten lanthanides and barium between diopside clinopyroxene and liquid in the synthetic system diopside-enstatite-silica-H₂O. Starting materials are glass of two different compositions CaMgSi₂O₆ 56, MgSiO₃ 14, SiO₂ 30 weight % and CaMgSi₂O₆ 80, MgSiO₃ 20 weight %.In the experiment on the former composition, the partition coefficient increases regularly with decrease of ionic radii from La to Dy and decreases also regularly from Dy to Lu. In the experiment on the latter composition, stepwise shift of partition coefficient was observed between Dy and Er.The results suggest that the lanthanide cations occupy the site of 8-fold coordination in the clinopyroxene and that the partition coefficients depend on the ionic radii of lanthanide elements and also on the chemical composition of the starting material or heating process during the run.     

Trace element concentrations in the isotopically unique Allende inclusion,EK 1-4-1

Concentrations of rare-earth elements (REE), Sc, Fe, Co, Cr, Na and Ir in the bulk sample and mineral separates of the isotopically unique Allende inclusion, EK 1-4-1, were determined by instrumental neutron activation analysis. REE concentrations were also determined by mass-spectrometric isotope dilution for two density separates.The inclusion showed enrichment of light REE over heavy REE with a positive Yb anomaly, thus showing a tendency to resemble group II fine-grained inclusions in REE abundances, although EK 1-4-1 is a coarse-grained inclusion. High Cr concentrations also indicate group II affinity. However, high Ir (6 ppm) and Sc (105 ppm), and low FeO (1.80%), and Co (13.8 ppm) concentrations in the bulk sample and low Na concentrations in mineral separates show group I affinity.Between melilite and pyroxene fractions, the same samples in which mass-fractionated O isotope ratios were observed (Clayton and Mayeda, 1977), REE, Sc, Co and Fe showed distributions which are substantially different from those observed for “ordinary” Allende type B inclusions. These two minerals do not appear to be in equilibrium with respect to trace element distributions.The results indicate that the isotopically unique EK 1-4-1 is also unusual in its elemental abundances and distributions.     

Microstructural development of fine-grained quartz aggregates by syntectonic recrystallization

Experimental study of syntectonic recrystallization of fine-grained quartz aggregates was carried out in order to simulate the development of some natural microstructures of quartz tectonites and to understand their formation condition. Agate was axially compressed with a constant-strain-rate apparatus. Experiments were conducted at 4 kbar solid confining pressure, 700–1000°C and 10⁻⁴-10⁻⁶ sec⁻¹ to 10%–45% strain. In all runs, deformation has proceeded under wet condition caused by dehydration of pyrophyllite used as pressure medium.Two different types of microstructure were distinguished in the deformed specimens. One is P-type which is characterized by equant, equidimensional, and polygonal grains. The other is S-type which is characterized by the highly oblate grains with the largest dimension perpendicular to the compression axis. The P-type microstructure is developed at higher temperatures and slower strain rates, while the S-type developed at lower temperatures and faster strain rates. The transition between the S- and P-types is found to be very sharp.     

Major Element Compositions and Rare—earth Element Abundaces of Cenozoic Basalts in Eastern China：Implications for a Pressure Control over LREE／HREE Fractionation in Continental Basalt

Major element compositions and rare-earth element (REE) and transition element(Ni,Cr and V) abundances have been determined on 44 basalt samples from eastern China.These basalts have SiO2 contents ranging from 38.63 to 55.24(wt.%),and Na2O K2O from 3.1 to 9.4(wt.%).Ni and Cr abundances are largely variable,respectively falling in ranges 60-605 and 78-1150 ppm.REE abundances,especially light rare-earth elements(LREE), are highly variable.La/Sm and La/Yb ratios vary 2.8 to 7.6 and 1.8 to 8.1. Although the segregation mainly of olivine and clinopyroxene is requested to account for the vari-able and low MgO,CaO/Al2O3,Cr and Ni characteristic of these basalts studied here,the differ-ences in REE composition of the basalts are still related mainly to the partial melting process.Obvious varations in REE abundances could be principally attributed to the partial melting process.Obvious variations in REE abundances could be principally attributed to the partial melting processes that took place at different depths,in spite of some variations caused by the fractional crystallization processes.REE abundances and La/Sm and La/Yb ratios systematically decrease with increasing SiO2,which probably indicated that the basaltic magma derived from a deeper level has higher LREE and LREE/HREE ratios than that from a shallower level.As viewed from the fact that the D^Yb/D^La ratios of clinopyroxenes in the basaltic system increase with increasing pressure,the increase of LREE/HUEE ratios with increasing melting depth can be interpreted as the pressure dependence of bulk D^HREE/D^LREE ratios of silicate minerals,in addition to the pressure control over the melting degree.