内蒙古崇根山地区超基性岩岩石地球化学特征及构造环境分析

针对出露在二连浩特-贺根山缝合带东段的崇根山超基性岩进行了野外地质调查、岩石学和岩石地球化学方面的分析研究,结果显示:崇根山超基性岩已发生了强烈蛇纹石化,基本已经蚀变成蛇纹岩;主量元素表现出高Mg(w(MgO)=36.00%~38.25%)、高Cr(w(Cr2O3)=0.17%~0.46%)、高Ni(w(NiO)=0.21%~0.24%)、低Si(w(SiO2)=39.79%~42.35%)、贫Al(w(Al2O3)=1.04%~1.96%)、低Fe(w(FeOT)=6.79%~9.47%)的特征,其Mg#值为90.05~93.04,m/f值为8.72~11.60,属典型的镁质超基性岩,原岩可能为方辉橄榄岩;稀土元素总量很低,w(∑REE)为1.28×10^-6~2.94×10^-6,稀土元素配分模式为轻稀土元素微弱富集的近平坦型,其(La/Yb)N为2.25~5.95,具一定程度的负Eu异常(δEu=0.35~1.16)和负Ce异常(δCe=0.48~0.68);微量元素富集Ba,U,Ta,亏损Nb,Ti。崇根山超基性岩属变质橄榄岩,是SSZ型蛇绿岩的底部组成单元,为原始地幔经5%~15%部分熔融形成的亏损地幔岩,形成于俯冲带环境中的洋内弧后盆地环境。     

液化型路堤边坡动力数值模拟分析

液化型路堤边坡动力稳定性问题涉及岩土工程与工程地震两个学科领域,是边坡工程与砂土液化的交叉课题。采用天然地震记录为输入条件,应用Finn本构关系模型,运用有限差分法,对填土+砂土+卵砾土地层组合的路堤边坡进行了全时程动力分析,探讨了地震作用下路堤边坡的液化初步规律和稳定性。数值模拟结果表明:地震作用引起了路基饱和砂土有效应力急剧减小,并导致路基砂土液化,引起路堤变形破坏。孔隙水压力的积累与消散不仅与地震记录序列存在对应关系,也与砂土所处的位置和深度有密切关系。地表变形破坏主要表现为路堤顶面发生震陷和拉裂破坏,坡底面产生挤压隆起变形。地面以下的变形破坏主要包括土体剪切破坏和深部砂土液化引起的侧向流动破坏。     

Rapid imbibition of water in fractures within unsaturated sedimentary rock

The spontaneous imbibition of water and other liquids into gas-filled fractures in variably-saturated porous media is important in a variety of engineering and geological contexts. However, surprisingly few studies have investigated this phenomenon. We present a theoretical framework for predicting the 1-dimensional movement of water into air-filled fractures within a porous medium based on early-time capillary dynamics and spreading over the rough surfaces of fracture faces. The theory permits estimation of sorptivity values for the matrix and fracture zone, as well as a dispersion parameter which quantifies the extent of spreading of the wetting front. Quantitative data on spontaneous imbibition of water in unsaturated Berea sandstone cores were acquired to evaluate the proposed model. The cores with different permeability classes ranging from 50 to 500 mD and were fractured using the Brazilian method. Spontaneous imbibition in the fractured cores was measured by dynamic neutron radiography at the Neutron Imaging Prototype Facility (beam line CG-1D, HFIR), Oak Ridge National Laboratory. Water uptake into both the matrix and the fracture zone exhibited square-root-of-time behavior. The matrix sorptivities ranged from 2.9 to 4.6 mm s^−0.5, and increased linearly as the permeability class increased. The sorptivities of the fracture zones ranged from 17.9 to 27.1 mm s^−0.5, and increased linearly with increasing fracture aperture width. The dispersion coefficients ranged from 23.7 to 66.7 mm² s⁻¹ and increased linearly with increasing fracture aperture width and damage zone width. Both theory and observations indicate that fractures can significantly increase spontaneous imbibition in unsaturated sedimentary rock by capillary action and surface spreading on rough fracture faces. Fractures also increase the dispersion of the wetting front. Further research is needed to investigate this phenomenon in other natural and engineered porous media.     

Tectonic controls on a large landslide complex: Williams Fork Mountains near Dillon, Colorado

An extensive ( 25 km²) landslide complex covers a large area on the west side of the Williams Fork Mountains in central Colorado. The complex is deeply weathered and incised, and in most places geomorphic evidence of sliding (breakaways, hummocky topography, transverse ridges, and lobate distal zones) are no longer visible, indicating that the main mass of the slide has long been inactive. However, localized Holocene reactivation of the landslide deposits is common above the timberline (at about 3300 m) and locally at lower elevations. Clasts within the complex, as long as several tens of meters, are entirely of crystalline basement (Proterozoic gneiss and granitic rocks) from the hanging wall of the Laramide (Late Cretaceous to Early Tertiary), west-directed Williams Range thrust, which forms the western structural boundary of the Colorado Front Range. Late Cretaceous shale and sandstone compose most footwall rocks. The crystalline hanging-wall rocks are pervasively fractured or shattered, and alteration to clay minerals is locally well developed. Sackung structures (trenches or small-scale grabens and upslope-facing scarps) are common near the rounded crest of the range, suggesting gravitational spreading of the fractured rocks and oversteepening of the mountain flanks. Late Tertiary and Quaternary incision of the Blue River Valley, just west of the Williams Fork Mountains, contributed to the oversteepening. Major landslide movement is suspected during periods of deglaciation when abundant meltwater increased pore-water pressure in bedrock fractures.A fault-flexure model for the development of the widespread fracturing and weakening of the Proterozoic basement proposes that the surface of the Williams Range thrust contains a concave-downward flexure, the axis of which coincides approximately with the contact in the footwall between Proterozoic basement and mostly Cretaceous rocks. Movement of brittle, hanging-wall rocks through the flexure during Laramide deformation pervasively fractured the hanging-wall rocks.     

陕西宝鸡高家村—高店断裂的初步研究

通过大比例尺活动断裂地质填图，查明了宝鸡高家村──高店断裂的几何展市及内部结构特征。在多处发现断层露头剖面，断层错断了晚更新世和全新世沉积物，反映出断层具有很新的活动性。     

Thermal evolution of the Northern Cordillera Volcanic Province: implication for heat flow in remnant back-arc regions

ABSTRACT

Active and remnant back-arc regions do not follow a typical conductive lithosphere cooling model, but instead have an apparent two-stage cooling, defined by a high heat flow back-arc region during subduction and a second post-subduction heating event that extends elevated heat flow for several 10s million years. Numerical one-stage cooling models have not reproduced observed heat flow anomalies in active subduction zones using physically realistic parameters and require a secondary post-subduction heating mechanism. Here, an extension driven-volcanism model is developed to examine extension driven heating and volcanism as a mechanism to produce a prolonged thermal anomaly within back-arc lithosphere. This model is tested using the recorded thermal evolution of the Northern Cordillera Volcanic Province (NCVP), a Neogene-Quaternary alkaline volcanic province located in the remnant back-arc region of the Pacific-North American subduction zone in British Columbia, Canada. A single steady-state lithosphere geotherm does not intersect all previously published temperature estimates, suggesting previous data record the thermal evolution of the NCVP. Calculated geotherms at equilibrium with the minimum and maximum MELTS temperatures predict an increase in reduced mantle heat flow (Q_m ) from 43 to 72 mW/m² and lithosphere thinning from a depth of 87 to 48 km. The newly developed extension-volcanism model reproduced the calculated pre- and post-volcanism thermal regimes for the NCVP and supports that extension within the remnant back-arc could produce the present heat flow anomaly and volcanism. The model most readily produces volcanism when Q_m is ~45–65 mW/m², a typical range for back-arcs. Back-arc regions are prime locations for limited volcanism because their warmer thermal regime minimizes tectonic stress requirements to produce volcanism. Additionally, two-stage cooling of back-arcs can be explained with a time-dependent extension-volcanism thermal feedback mechanism that is possible because of the subduction driven pre-heating of back-arc regions.     

1998 Adana-Ceyhan (Turkey) Earthquake and a Preliminary Microzonation Based on Liquefaction Potential for Ceyhan Town

A moderate earthquake (M_s = 6.2) occurred in the Cukurova region in the southern part of Turkey, on 27 June 1998. It resulted in loss of 145 lives and significant damage particularly in the settlements close to the epicenter at the south of Ceyhan town. Widespread liquefaction and associated sand boils, ground fissures and ground deformations due to lateral spreading occurred during this earthquake. In this study, main characteristics of the earthquake are presented and liquefaction throughout the site was assessed. An attempt was also made to establish preliminary microzonation maps for Ceyhan using the data from liquefaction susceptibility analyses. The results of the analyses indicated that the data from the liquefied sites were within the empirical bounds suggested by the field-performance evaluation method. Fortunately, most of the riversides were used for agricultural purposes alone, damage to structures from liquefaction and associated ground failures were rather limited. Preliminary assessments indicated that at depths of about 5 m the liquefaction potential of thin sand layers tends to diminish.     

藏北阿索构造混杂岩的发现及其地质意义

在藏北尼玛县西边阿索一带首次发现最宽约14km的阿索构造混杂岩带。该带西宽东窄，呈喇叭状，由复理石岩片、深海硅质岩、泥质岩岩片、蛇纹质岩片、火山岛弧岩片、碳酸盐岩岩片、大陆碎片岩片等组成。其中以复理石岩片为基质包含其它外来构造岩片。阿索构造混杂岩带所包含的蛇绿岩主要岩性单位有：蛇纹岩、辉石岩、英云闪长岩、似层状花斑岩和辉长岩、粒玄岩、辉长辉绿岩、枕状玄武岩、角斑岩、硅质岩、含铁锰粉砂岩、薄层灰岩、浊积岩等，属弧后盆地扩张一消减产物。根据硅质岩中放射虫、复理石岩片中孢粉时代及构造片岩中同位素年龄等资料，该弧后盆地扩张于晚侏罗世、闭合于早白垩世早期。空间上将狮泉河、永珠湖一纳木湖蛇绿岩带相连。     

Common-ray tracing and dynamic ray tracing for S waves in a smooth elastic anisotropic medium

Anisotropic common S-wave rays are traced using the averaged Hamiltonian of both S-wave polarizations. They represent very practical reference rays for calculating S waves by means of the coupling ray theory. They eliminate problems with anisotropic-ray-theory ray tracing through some S-wave slowness-surface singularities and also considerably simplify the numerical algorithm of the coupling ray theory for S waves. The equations required for anisotropic-common-ray tracing for S waves in a smooth elastic anisotropic medium, and for corresponding dynamic ray tracing in Cartesian or ray-centred coordinates, are presented. The equations, for the most part generally known, are summarized in a form which represents a complete algorithm suitable for coding and numerical applications.