海拉尔盆地基底晚古生代adakite的发现及其地质意义

海拉尔盆地的前中生代基底隶属中亚造山带东段的兴蒙造山带。 在盆地基底地层中发现了具有adakite成分特征的粗面安山岩、英安岩和闪长玢岩。 这些火成岩与晚古生代沉积地层交互或伴生, 共同构成晚中生代裂陷盆地的基底。 地球化学研究表明, 这些火成岩基本上属于高钾钙碱性和准铝质岩石系列, 具有高SiO₂和Al₂O₃含量, 高Sr、Sr/Y和La/Yb值, 富集轻稀土(LREE), 亏损重稀土(HREE)、Y和高场强元素(HFSE),Eu表现弱的负异常或轻微的正异常, 相容元素Mg、Cr和Ni含量低, 这些特征与增厚下地壳部分熔融成因的adakite非常相似, 而明显不同于典型的由俯冲洋壳熔融形成的adakite。 样品的(⁸⁷Sr/⁸⁶Sr)_i值基本一致,为0.7041, (¹⁴³Nd/¹⁴⁴Nd)_i值为0.51243~0.51247, ε_Nd (t)为正值(+3.7~+4.5), 显示其岩浆源区可能源于弱亏损地幔, 或亏损地幔受到地壳物质混染。 本文认为海拉尔地区晚古生代adakite型岩浆很可能是由当时新底侵的玄武质下地壳在角闪岩相向榴辉岩相过度或榴辉岩相条件下部分熔融形成。 这些adakite岩石的出现反映了兴蒙造山带晚古生代受到了古亚洲洋的俯冲消减引起的强烈的地幔玄武质岩浆底侵作用, 并由此导致地壳垂向上显著的增生加厚过程。     

Abundance patterns of thirteen trace elements in primitive carbonaceous and unequilibrated ordinary chondrites

A neutron activation analysis technique was used to determine Au, Re, Co, Mo, As, Sb, Ga, Se, Te, Hg, Zn, Bi and Tl in 11 carbonaceous chondrites, 12 unequilibrated ordinary chondrites (UOC), and 4 equilibrated ordinary chondrites. The first 6 elements are ‘undepleted’, the next 3 ‘normally-depleted’ and the last 4 ‘strongly-depleted’. Except for Hg, ‘depleted-element’ abundances in carbonaceous chondrites lead to mean relative ratios of C1:C2:C3 = 1.00:0.53:0.29, i.e. those predicted by a two-component (mixing of high-temperature and low-temperature fractions) model. The last 4 nominally ‘undepleted’ elements are somewhat depleted in ordinary chondrites, As and Sb showing partial depletion in C3 and the latter in C2 chondrites as well. This requires a modification of the two-component model to indicate that deposition of elements during condensation of high temperature material was not an all-or-nothing process.Apart from Bi and Tl, the elements studied have similar abundances in unequilibrated and equilibrated ordinary chondrites and only the former are unquestionably correlated with the degree of disequilibrium in silicate minerals. Only some ‘strongly-depleted’ elements exhibit at least one of the following—proportional depletion in UOC, progressive depletion in petrographic grades 3–6 ordinary chondrites and enrichment in the gas-containing dark portion of gas-rich, light-dark meteorites—indicating that such depletion does not ensure that an element will exhibit these trends. Partly or completely siderophile As, Au, Co, Ga, Mo, Re and Sb vary with chemical type in the same manner in both unequilibrated and equilibrated ordinary chondrites and doubtless reflect a process involving fractionation of metallic iron.     

Vanadium isotopic composition and contents in gas-rich meteorites

We report ⁵⁰V/⁵¹V abundance ratio measurements and V concentrations for the dark portions of six gas-rich meteorites. These data and previous results for meteoritic, lunar and terrestrial samples indicate the same vanadium isotopic composition within the limits of error and, hence, place severe limits on possible differences in the irradiation histories of these materials. After application of necessary corrections, an average absolute abundance ratio of ⁵⁰V/⁵¹V= (2.425 ± 0.030) × 10^?3 is obtained.     

Petrogenesis of A-type granites and origin of vertical zoning in the Katharina pluton, Gebel Mussa (Mt. Moses) area, Sinai, Egypt

The central pluton within the Neoproterozoic Katharina Ring Complex (area of Gebel Mussa, traditionally believed to be the biblical Mt. Sinai) shows a vertical compositional zoning: syenogranite makes up the bulk of the pluton and grades upwards to alkali-feldspar granites. The latters form two horizontal subzones, an albite–alkali feldspar (Ab–Afs) granite and an uppermost perthite granite. These two varieties are chemically indistinguishable. Syenogranite, as compared with alkali-feldspar granites, is richer in Ca, Sr, K, Ba and contains less SiO₂, Rb, Y, Nb and U; Eu/Eu* values are 0.22–0.33 for syenogranite and 0.08–0.02 for alkali-feldspar granites. The δ¹⁸O (Qtz) is rather homogeneous throughout the pluton, 8.03–8.55‰. The δ¹⁸O (Afs) values in the syenogranite are appreciably lower relative to those in the alkali–feldspar granites: 7.59–8.75‰ vs. 8.31–9.12‰. A Rb–Sr isochron (n = 9) yields an age of 593 ± 16 Ma for the Katharina Ring Complex (granite pluton and ring dikes).

The alkali–feldspar granites were generated mainly by fractional crystallization of syenogranite magma. The model for residual melt extraction and accumulation is based on the estimated extent of crystallization ( 50 wt.%), which approximates the rigid percolation threshold for silicic melts. The fluid-rich residual melt could be separated efficiently by its upward flow through the rigid clusters of crystal phase. Crystallization of the evolved melt started with formation of hypersolvus granite immediately under the roof. Fluid influx from the inner part of the pluton to its apical zone persisted and caused increase of P_H2O in the magma below the perthite granite zone. Owing to the presence of F and Ca in the melt, P_H2O of only slightly more than 1 kbar allows crystallization of subsolvus Ab–Afs granite. Abundance of turbid alkali feldspars and their ¹⁸O/¹⁶O enrichment suggest that crystallization of alkali-feldspar granites was followed by subsolvus fluid–rock interaction; the δ¹⁸O (Fsp) values point to magmatic origin of fluids.

The stable and radiogenic isotope data [δ¹⁸O (Zrn) = 5.82 ± 0.06‰, I_Sr = 0.7022 ± 0.0064, ε_Nd (T) values are + 3.6 and + 3.9] indicate that the granite magma was generated from a ‘juvenile’ source, which is typical of the rocks making up most of the Arabian–Nubian shield.     

Weathering of fuel oil spill on the east Mediterranean coast, Ashdod, Israel

Residual fuel oil spilled into the sea from the Eshkol power station on 8 February, 1998 contaminated about 9 km of the foreshore north of the Ashdod harbour. A study of the aliphatic, polycyclic alkane and polyaromatic hydrocarbon (PAH) composition of the spilled oil shows rapid weathering in the early stages followed by gradual slowdown after about three months. Weathering of isoprenoids and PAH compounds and variation in Pr/Ph ratio appear to occur almost contemporaneously with that of n-alkanes, at a relatively moderate level of degradation, when much of the >C₂₀ n-alkane envelope is still well preserved. Depletion of various compounds in accordance with molecular size rather than molecular structure appears to imply that physical weathering processes, i.e. evaporation and perhaps flushing due to wave energy, might have played an important role in the degradation of the spilled residual fuel oil in this study case.     

A Mixed-Layer Model Of The Well-Mixed Stratocumulus-Topped Boundary Layer

Recently a range of sophisticated large-eddy simulations of thecloud-topped boundary layer have been intercompared and furthercompared with observations and single column models. Here we comparethese results with perhaps the simplest model of the cloud-toppedboundary layer, namely a mixed-layer model. Results from the model aredescribed with two aims in mind. Firstly, the good results act as areminder of the success of simple models, and, secondly, we suggestthat a simple mixed-layer model could be used as a baseline for futuremodel intercomparisons.The mixed-layer model is based on two assumptions that follow previousstudies. Firstly, the liquid-water potential temperature and the total waterspecific humidity are assumed to be constant with height in the boundarylayer. Secondly, turbulence entrains air across the inversion into the boundarylayer at a rate that is assumed to be proportional to the jump in radiative flux at the cloud top and inversely proportional to the jump in buoyancy at the inversion. The constant of proportionality is called the entrainment efficiency.Results from the model for the entrainment rate and height evolutionof the boundary layer are compared with the observations and modelsconsidered in a EUCREM intercomparison study. Thepresent mixed-layer model accurately predicts the observed heightevolution of the boundary layer, but over-estimates the entrainmentrate to a similar degree as the large-eddy simulations. We show that,if the subsidence rate is reduced to the value given by observationsrather than the value used in the EUCREM intercomparison study,then the model agrees well with observed value of the entrainment rateif the entrainment efficiency is taken to be 0.6. With this value, themodel also agrees well with a further case study byBechtold et al. An entrainment efficiency of 0.6 is a little higherthan suggested by large eddy simulations, but such simulations do notcurrently resolve the entrainment events explicitly. Hence this pointdeserves further study.     

Phosphate beneficiation by calcination. Prediction of P2O5 in the product,mining and plant control

A method is described to predict P₂O₅ content in the product (of phosphate beneficiation by calcination) as a function of the composition of an untreated and also of a washed raw material. The method consisted of: (a) developing an on-line multielement analysis by XRF; (b) finding the elemental and mineralogical relationships in the product, by factor analysis; (c) determination of the independent variables; (d) finding the relationships between the concentrations of the impurity variables in the raw material and in the product; (e) developing a linear model to predict P₂O₅ content. The predictions are used for mining and for plant control.     

Inter-element relationships between trace elements in primitive carbonaceous and unequilibrated ordinary chondrites

The results of a search for significant (95 % confidence level) inter-element relationships among 13 trace elements in carbonaceous chondrites and 26 elements and the disequilibrium parameter for silicate phases in unequilibrated ordinary chondrites (UOC) indicate pronounced differences in the formation processes of these two sorts of primitive chondrites. Twenty-six pairs of elements are correlated in carbonaceous chondrites and these correlations lend support to a model involving mixing in different ratios of material differing in thermal history.Comparison of the 26 elements in UOC shows that 39 pairs of elements are significantly related and only very volatile elements are correlated with the disequilibrium parameter. Each of the inter-element relationships can be specifically ascribed to a metal-silicate fractionation in the solar nebula or to a thermal fractionation. These relationships are about equally consistent with the metamorphism, two-component condensation and simultaneous accretion-condensation models for the origin, of the ordinary chondrites, each requiring adoption of specific ad hoc assumptions for complete consistency.