排序方式: 共有23条查询结果,搜索用时 15 毫秒
1.
Sabah A. Ismail Sarmad A. Ali Allen P. Nutman Vickie C. Bennett Brain G. Jones 《地学前缘(英文版)》2017,8(5):1073-1087
The Pushtashan suprasubduction zone assemblage of volcanic rocks, gabbros, norites and peridotites occurs in the Zagros suture zone, Kurdistan region, northeastern Iraq. Volcanic rocks are dominant in the assemblage and consist mainly of basalt and basaltic andesite flows with interlayered red shale and limestone horizons. Earlier lavas tend to be MORB-like, whereas later lavas display island arc tholeiite to boninitic geochemical characteristics. Tholeiitic gabbros intrude the norites and display fractionation trends typical of crystallisation under low-pressure conditions, whereas the norites display calc-alkaline traits, suggesting their source included mantle metasomatised by fluids released from subducted oceanic crust. Enrichment of Rb, Ba, Sr, Th and the presence of negative Nb anomalies indicate generation in a suprasubduction zone setting. Trondhjemite and granodiorite intrusions are present in the volcanic rocks, gabbros and norites. SHRIMP U-Pb dating of magmatic zircons from a granodiorite yields a mean~(206)Pb/~(238)U age of 96.0 ±2.0 Ma(Cenomanian). The initial ε_(Hf) value for the zircons show a narrow range from +12.8 to+15.6, with a weighted mean of + 13.90±0.96. This initial value is within error of model depleted mantle at 96 Ma or slightly below that, in the field of arc rocks with minimal contamination by older continental crust. The compositional bimodality of the Pushtashan suprasubduction sequence suggests seafloor spreading during the initiation of subduction, with a lava stratigraphy from earlyerupted MORB transitioning into calc-alkaline lavas and finally by 96 Ma intrusion of granodioritic and trondhjemitic bodies with juvenile crustal isotopic signatures. The results confirm another Cretaceous arc remnant preserved as an allochthon within the Iraqi segment of the Cenozoic Zagros suture zone. Implications for the closure of Neo-Tethys are discussed. 相似文献
2.
The seismicity of Algeria since the nineteenth century is relatively well documented. However, compared with the numerous damaging earthquakes that are documented since 1850, fewer than a dozen reports of earthquakes are listed for the pre-1850 ad period, suggesting that the historical record is missing a substantial number of earthquakes. This paper examines the use of literary and epigraphic sources relevant to the investigation of seismicity in Algeria during Roman times. We provide examples where the meager written literary record may be supplemented with appropriate archaeological and epigraphic data describing damage to ancient Roman sites. The examples show that collaboration between earth scientists and archeologists is of utility in improving the seismic record and highlights the need for further study of data sources and repositories located both inside and outside of Algeria. 相似文献
3.
4.
The effect of a reactive azo dye (the hydrolyzed form of Reactive Orange 107, HRO107) on the digestion of municipal waste sludge (WS) was studied. The study also focused on the effect of acclimation of the anaerobic mixed culture on dye treatment. Anaerobic batch assays were carried out in serum bottles under mesophilic conditions. Unacclimated and acclimated anaerobic mixed cultures were used for the study. Both unacclimated and acclimated anaerobic cultures completely reduced HRO107 during WS digestion. Inhibitory HRO107 concentration was found to be 800 mg/L for unacclimated mixed culture. Acclimation increased the inhibitory concentration level from 800 to 3200 mg/L. Sulfanilic acid and four other unidentified dye reduction end products were detected at the end of the assays. The results of this study indicated that anaerobic municipal WS digesters have the potential to be a cost efficient and effective pre treatment method. 相似文献
5.
6.
Presented and discussed in this paper is an exact analytical solution of the nonhomogeneous partial differential equation governing the conventional one‐dimensional consolidation under haversine repeated loading. The derived analytical solution to the 1D consolidation equation is compared with the numerical solution of the same consolidation problem via FEM. The series solution takes into account the frequency of repeated loading through a dimensionless time factor T0. The paper reveals that an increase in the frequency of imposed repeated haversine loading (a decrease in period of repeated loading) causes an increase in the number of cycles required to achieve the steady state, whereas the effect of frequency on the maximum excess pore water pressure at the bottom of a clay layer with permeable top and impermeable bottom for the range of frequencies studied is generally insignificant. The effective stress at the bottom of the clay deposit with permeable top and impermeable bottom increases with time but with some fluctuations without changing the sign. These fluctuations become more pronounced for increasing values of T0. An increase in T0 also causes an increase in maximum effective stress. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
7.
Ferdi?L.?HellwegerEmail author Alan?F.?Blumberg Peter?Schlosser David?T.?Ho Theodore?Caplow Upmanu?Lall Honghai?Li 《Estuaries and Coasts》2004,27(3):527-538
The effects of estuarine circulation and tidal trapping on transport in the Hudson estuary were investigated by a large-scale,
high-resolution numerical model simulation of a tracer release. The modeled and measured longitudinal profiles of surface
tracer concentrations (plumes) differ from the ideal Gaussian shape in two ways: on a large scale the plume is asymmetric
with the downstream end stretching out farther, and small-scale (1–2 km) peaks are present at the upstream and downstream
ends of the plume. A number of diagnostic model simulations (e.g., remove freshwater flow) were performed to understand the
processes responsible for these features. These simulations show that the large-scale asymmetry is related to salinity. The
salt causes an estuarine circulation that decreases vertical mixing (vertical density gradient), increases longitudinal dispersion
(increased vertical and lateral gradients in longitudinal velocities), and increases net downstream velocities in the surface
layer. Since salinity intrusion is confined to the downstream end of the tracer plume, only that part of the plume is effected
by those processes, which leads to the largescale asymmetry. The small-scale peaks are due to tidal trapping. Small embayments
along the estuary trap water and tracer as the plume passes by in the main channel. When the plume in the main channel has
passed, the tracer is released back to the main channel, causing a secondary peak in the longitudinal profile. 相似文献
8.
The effects of rate of strain on strength and deformation characteristics of soil–lime were investigated. Five strain rates (0.1, 0.8, 2.0, 4.0 and 7.0 %/min), five lime contents (0, 3, 6, 9 and 12 %) by dry soil weight and three cell pressures (100, 200 and 340 kN/m2) were carried. Triaxial tests, under unconsolidated condition, were used to study the effect of strain rate on strength and initial modulus of elasticity of soil and soil–lime mixture after two curing periods 7 and 21 days, respectively. A total of 405 triaxial specimens have been tested, where 225 specimens have been tested with first curing period (7 days). The testing program includes nine specimens for each strain rate, and each lime content was carried out, including natural soil with zero lime content. Another set of triaxial tests with a total of 180 specimens for the second curing period (21 days) was prepared at optimum moisture content, and the corresponding maximum dry density was also tested. The effects of strain rate and curing period on each of stress–strain behavior, type of failure, deviator stress at failure, cohesion and angle of internal friction and initial modulus of elasticity were studied thoroughly for the natural soil as well as soil–lime mixtures. For natural soil, the test results showed that the undrained shear strength, the initial modulus of elasticity and the cohesion increase significantly as the strain rate increase, while for soil–lime mixture at different curing periods, the undrained shear strength, initial modulus of elasticity and the cohesion increases to a maximum and then decreases as the strain rate and lime content increase. Also, the same variables and angle of internal friction increase with increasing curing period. 相似文献
9.
Ophiolitic rocks (chromitites and serpentinized peridotites) were petrologically examined in detail for the first time from Rayat, in the Iraqi part of the Zagros thrust zone, an ophiolitic belt. Almost all the primary silicates have been altered out, but chromian spinel has survived from alteration and gives information about the primary petrological characteristics. The protolith of the serpentinite was clinopyroxene-free harzburgite with chromian spinel of intermediate Cr# (= Cr/[Cr + Al] atomic ratio) of 0.5 to 0.6. The harzburgite with that signature is the most common in the mantle section of the Tethyan ophiolites such as the Oman ophiolite, and is the most suitable host for chromitite genesis. Except for one sample, which has Cr# = 0.6 for spinel, the Cr# of spinel is high, around 0.7, in chromitite. The variation in Cr# of spinel in chromitite observed here has been also reported in the Oman ophiolite. The peridotite with chromitite pods exposed at Rayat was derived from an ophiolite similar in petrological character to the Oman ophiolite, one of the typical Tethyan ophiolites (fragments of Tethyan oceanic lithosphere). This result is consistent with the previous interpretation based on geological analysis. 相似文献
10.
Presented in this paper is a study of the one-dimensional consolidation process under haversine repeated loading with and
without rest period. The analysis was carried out using a hybrid coupled, analytical and numerical implicit finite difference
technique. The rate of imposition of excess pore-water pressure was determined analytically, and the remaining part of the
governing differential equation was solved numerically. The clay deposit considered was a homogeneous clay layer with permeable
top and/or impermeable bottom hydraulic boundary conditions with constant coefficients of permeability and of consolidation.
The study reveals that although the loading function is positive for all times, the excess pore-water pressure at the base
of the clay deposit with permeable top and impermeable bottom oscillates with time reaching a ‘steady state’ after few cycles
of loading depending on whether there is a rest period or not. An increase in the rest period causes a decrease in the number
of cycles required to achieve the steady state. The paper shows also that the rest period in the haversine repeated loading
decelerates the consolidation process. Similarly, the paper reveals that the effective stress at the bottom of the clay layer
with permeable top and impermeable bottom increases with time but showing mild fluctuations that do not change the sign. The
maximum positive effective stress achieved depends on the rest period of the haversine repeated loading. A haversine repeated
loading without a rest period gives the highest value for the positive effective stress. 相似文献