全球地表热流的产生与分布

全球地表热流是反映地球内部热与动力学过程的一种主要能流.本文在三维球坐标框架下，就几个不同的粘度模型分别研究地幔内部密度异常(基于全球地震层析结果)以及板块运动激发的地幔流动的热效应及其对于观测地表热流产生和分布特征的贡献.由于地幔动力系统具有较高的Pe数，可以期望由板块运动激发的地幔流动将强烈地扰动地幔内部初始传导状态下的温度场以及地表热的热流分布.结果表明，与地幔内部密度异常产生的热效应相比，运动的板块及其激发的地幔流动在全球地表观测热流的产生和分布特征上起着更为重要的作用.观测到的大洋中脊处的高热流在很大程度上可以归因于板块激发的地幔流动的热效应.计算的平均温度剖面较好地揭示了岩石圈和D″层的温度特征，即温度随深度的剧烈变化，这与我们目前通过其他手段对岩石圈和D″层的温度结构了解是一致的.一个下地幔粘度比上地幔高出30倍的粘度结构(文中使用的粘度模型2)较之其余模型的拟合程度似乎更好.     

Two-dimensional modelling of subduction zone anisotropy with application to southwestern Japan

We present a series of 2-D numerical models of viscous flow in the mantle wedge induced by a subducting lithospheric plate. We use a kinematically defined slab geometry approximating the subduction of the Philippine Sea plate beneath Eurasia. Through finite element modelling we explore the effects of different rheological and thermal constraints (e.g. a low-viscosity region in the wedge corner, power law versus Newtonian rheology, the inclusion of thermal buoyancy forces and a temperature-dependent viscosity law) on the velocity and finite strain field in the mantle wedge. From the numerical flow models we construct models of anisotropy in the wedge by calculating the evolution of the finite strain ellipse and combining its geometry with appropriate elastic constants for effective transversely isotropic mantle material. We then predict shear wave splitting for stations located above the model domain using expressions derived from anisotropic perturbation theory, and compare the predictions to ∼500 previously published shear wave splitting measurements from seventeen stations of the broad-band F-net array located in southwestern Japan. Although the use of different model parameters can have a substantial effect on the character of the finite strain field, the effect on the average predicted splitting parameters is small. However, the variations with backazimuth and ray parameter of individual splitting intensity measurements at a given station for different models are often different, and rigorous analysis of details in the splitting patterns allows us to discriminate among different rheological models for flow in the mantle wedge. The splitting observed in southwestern Japan agrees well with the predictions of trench-perpendicular flow in the mantle wedge along with B-type olivine fabric dominating in a region from the wedge corner to about 125 km from the trench.     

The distribution of earthquakes with depth and stress in subducting slabs

We explain the global variation of Benioff zone seismicity with depth and the orientation of stress axes of deep and intermediate earthquakes using numerical models of subducting slabs. Models that match the seismicity and stress require a barrier to flow at the 670 km seismic discontinuity. The barrier may be a viscosity increase of at least an order of magnitude or a chemical discontinuity. Instantaneous flow is subparallel to the slabs for models with a viscosity increase but contorted for models with a chemical barrier. Log N (number of earthquakes) decreases linearly to 250–300 km depth and increases thereafter. Stress magnitude in our models shows the same pattern, in accord with experiments showing N proportional to e^kσ, with k a constant and σ stress magnitude. The models predict downdip compression in the slabs at depths below 300–400 km, as observed for earthquake stress axes.     

The continental tectosphere and Earth's long-wavelength gravity field

To estimate the average density contrast associated with the continental tectosphere, we separately project the degree 2–36 non-hydrostatic geoid and free-air gravity anomalies onto several tectonic regionalizations. Because both the regionalizations and the geoid have distinctly red spectra, we do not use conventional statistical analysis, which is based on the assumption of white spectra. Rather, we utilize a Monte Carlo approach that incorporates the spectral properties of these fields. These simulations reveal that the undulations of Earth's geoid correlate with surface tectonics no better than they would were it randomly oriented with respect to the surface. However, our simulations indicate that free-air gravity anomalies correlate with surface tectonics better than almost 98% of our trials in which the free-air gravity anomalies were randomly oriented with respect to Earth's surface. The average geoid anomaly and free-air gravity anomaly over platforms and shields are significant at slightly better than the one-standard-deviation level: −11±8 m and −4±3 mgal, respectively. After removing from the geoid estimated contributions associated with (1) a simple model of the continental crust and oceanic lithosphere, (2) the lower mantle, (3) subducted slabs, and (4) remnant glacial isostatic disequilibrium, we estimate a platform and shield signal of −8±4 m. We conclude that there is little contribution of platforms and shields to the gravity field, consistent with their keels having small density contrasts. Using this estimate of the platform and shield signal, and previous estimates of upper-mantle shear-wave travel-time perturbations, we find that the average value of ∂lnρ/∂lnν_s within the 140–440 km depth range is 0.04±0.02. A continental tectosphere with an isopycnic (equal-density) structure (∂lnρ/∂lnν_s=0) enforced by compositional variations is consistent with this result at the 2.0σ level. Without compositional buoyancy, the continental tectosphere would have an average ∂lnρ/∂lnν_s≈0.25, exceeding our estimate by 10σ.     

内蒙古太平川铜钼矿成矿斑岩时代、地球化学及地质意义

内蒙古太平川Cu-Mo矿床位于得尔布干成矿带北段额尔古纳地区,为新近发现的斑岩型矿床。矿区内发育环带状热液蚀变,由内向外主要为硅化-绢云母化和泥化。热液蚀变围绕花岗闪长斑岩分布,Cu-Mo矿化主要受控于硅化-绢云母化蚀变,主要分布在花岗闪长斑岩中。本文获得成矿斑岩岩浆锆石U-Pb谐和年龄为202±5.7Ma,指示该矿床可能形成于晚三叠世。同时在样品中也发现继承锆石(784Ma),表明该地区可能存在晚元古基底。成矿斑岩的元素地球化学数据表明,主量元素SiO2(65.86%～68.84%)56%、Al2O3(15.18%～16.28%)15%、MgO(0.84%～1.06%)3%、Na2O/K2O1;微量元素亏损重稀土,Sr(471×10-6～513×10-6)400×10-6、Y(15.0×10-6～17.9×10-6)18×10-6、Yb(1.27×10-6～1.81×10-6)1.9×10-6,表明该花岗闪长斑岩具有明显的埃达克质岩石的地球化学特征。同时成矿斑岩具有相对高的SiO2、Yb含量和Th/Nb、Ce/Nb比值,而相对低的Al2O3、TiO2、MgO、Sr、Th含量和Th/Ce比值,这些特征与源于俯冲板片的埃达克岩相似。然而成矿斑岩(87Sr/86Sr)i(0.70943～0.71019)较大,εNd(t)为-3.4～-3.9,我们推测额尔古纳地块在岩浆上升过程中贡献了部分物质。结合区域构造演化,我们认为该矿区成矿斑岩岩浆形成于俯冲洋壳的部分熔融,矿床形成背景为早中生代蒙古-鄂霍茨克洋向额尔古纳地块俯冲的陆缘弧环境。     

中国四川2008年5月12日汶川地震的地质与地球物理背景

2008年5月12日, 在青藏高原东缘的龙门山, 发生了MW7.9地震. 这一地震是在青藏高原长期隆升和向东推挤的背景下形成的. 发生地震的区域有以下典型的地质特征: 不是陡峭山前的活动汇聚造山带(包括地形起伏大于4 km的情况), 而是缺少高活动强度的低角度逆冲断层;虽拥有年轻的高地形(距今15 Ma)和加厚的地壳, 但是却只有低的GPS缩短率(小于3 mm/a), 并且缺少同时代的前陆沉积. 在我们看来, 青藏高原东部下面的地壳加厚不是因为上部地壳的大范围缩短, 而是由于位于软弱层(低速层)中的深部地壳的韧性增厚. 横跨龙门山的晚新生代缩短量可能仅有10～20 km, 且伴有主要造成青藏高原和四川盆地差异抬升的褶皱和断裂. 5月12日的地震可能反映了青藏高原东部相对四川盆地的带有缓慢的汇聚和右旋走滑的长期抬升. 5月12日地震邻区内GPS确定的速率表明, 该地震的平均复发间隔大约为2 000～10 000年.     

Chitosan – A Sizing Agent in Fabric Production – Development and Ecological Evaluation

Chitosan, a natural polymer, was investigated as a possible sizing agent in fabric production by appropriate modification in the textile industry. Based on recipe developments at a laboratory‐scale, the ecological and economical potential of mainly cotton yarns were demonstrated and developed. Subsequent tests within the scope of industrial production confirmed the findings of the basic developments. As an interesting alternative to the conventional sizing process involving the removal of the size after weaving, the use of appropriate processing technologies makes it possible to apply chitosan in the form of a sizing agent resistant to wash‐out processes. Therefore, the wash‐out process and the combined wastewater loading can be avoided and the properties of chitosan can be used beneficially in the later applications of the fabric. The traditional method of sizing and weaving developments as well as the analyses of material recycling showed the possibilities of using closed circuits in textile production involving sizing agent and water. It is possible that a chitosan‐specific enzyme suitable for production conditions, which facilitates the wash‐out process in combination with the biodegradation of the wastewater in a sewage plant, could be developed.     

华宁暮车露天矿开采对周边地质环境影响评价

现场调查评价区地裂缝特征和成因机制,对形成地裂缝的直接原因——采矿诱发斜坡的失稳进行了定性、定量评价,提出不稳定斜坡的相应防治对策。