Pressure sensitivity of olivine slip systems: first-principle calculations of generalised stacking faults

We have used a first-principle approach based on the calculation of generalised stacking faults (GSF) to study the influence of pressure on the mechanical properties of forsterite. Six cases corresponding to [100] glide over (010), (021) and (001), and [001] glide over (100), (010) and (110) have been considered. The relaxed energy barriers associated with plastic shear have been calculated by constraining the Si atoms to move perpendicular to the fault plane and allowing Mg and O atoms to move in every direction. These conditions, which preserve dilations as a relaxation process, introduce Si–O tetrahedral tilting as an additional relaxation mechanism. Relaxed GSF show little plastic anisotropy of [100] glide over different planes and confirms that [001] glide is intrinsically easier than [100] glide. The GSF are affected by the application of a 10 GPa confining pressure with a different response for each slip system that cannot be explained by sole elastic effect. In particular, [100](010) is found to harden significantly under pressure compared to [001](010). Our results give the first theoretical framework to understand the pressure-induced change of dominant slip systems observed by Couvy et al. (in Eur J Mineral 16(6):877–889, 2004) and P. Raterron et al. (in GRL, submitted). It appears necessary to account for the influence of pressure on the mechanical properties of silicates in the context of the deep Earth.     

金龙——丘岭金矿床成矿流体的储运规律及区域找金方向

金龙山——丘岭金矿区含金矿源为层上泥盆统南羊山组和下石炭统袁家沟组。组成含金矿源层岩石为高频互层的细碎屑岩-碳酸盐岩，其中细砂岩、粉砂岩、碳酸盐岩含成矿流体物性较好．页岩、板岩含成矿流体物性较差，构成屏蔽层。金鸡岭Ⅰ级复式向斜控制着金、砷、锑等异常范围；松枣Ⅱ级复式背斜控制着金的矿化带；金龙山-丘岭金矿Ⅲ级背斜控制着金的矿（化）体；镇安——板岩镇断裂的次级断裂是金矿化体的容矿有利位置。在成矿过程中，构造变形与成矿流体的形成、运移及储集密切相关。其规律是：①原生构造导致成矿流体的初次聚集。②第一期构造变形导致成矿流体的聚集。③第二期构造变形导致成矿流体运移及金矿床形成。此期变形是金的主要成矿期。④第三期构造变形使成矿流体进一步聚集和金矿体的富集。⑤第四期构造变形是石英方解石脉的形成时期。总结出矿床形成模式。据此提出了在4种不同的构造部位找金的方向。     

Intraplate deformation and 3D rheological structure of the Rhine Rift System and adjacent areas of the northern Alpine foreland

The lithosphere of the Northern Alpine foreland has undergone a polyphase evolution during which interacting stress-induced intraplate deformation and upper mantle thermal perturbations controlled folding of the thermally weakened lithosphere. In this paper we address relationships among deeper lithospheric processes, neotectonics and surface processes in the Northern Alpine foreland with special emphasis on tectonically induced topography. We focus on lithosphere memory and neotectonics, paying special attention to the thermo-mechanical structure of the Rhine Graben System and adjacent areas of the northern Alpine foreland lithosphere. We discuss implications for mechanisms of large-scale intraplate deformation and links with surface processes and topography evolution.     

Validating the ability of the discontinuous deformation analysis method to model normal P‐wave propagation across rock fractures

The effects of fractures on wave propagation problems are increasingly abstracting the attention of scholars and engineers in rock engineering field. This study aims to fully validate the ability of discontinuous deformation analysis (DDA) to model normal P‐wave propagation across rock fractures. The effects of a single fracture and multiple parallel fractures are all tested. The results indicate that DDA can accurately reflect the fracture effects, including the fractures stiffness, the fracture spacing and the fracture number, and the effects of incident wave frequency on one‐dimensional P‐wave propagation problems. Thus, DDA is able to deal well with normal incident P‐wave propagation problems. Copyright © 2017 John Wiley & Sons, Ltd.     

联合GPS和GRACE数据分析陕甘宁地区地表垂直形变

采用甘肃省CORS网和中国大陆构造环境监测网络中共48个台站的GPS观测数据，解算得到观测台站的垂直位移，并与GRACE时变重力场Mascon模型解CSR RL05M数据计算得到的垂直形变进行比较，分析区域地表垂直形变特征。结果表明，研究区内台站垂直形变存在局部特征，甘肃庆阳和平凉地区垂直形变与其他地区存在明显差异，相关系数、均方根减少量和周年信号减少量均高于其他地区；扣除趋势项后，观测台站GPS垂直位移与GRACE垂直形变时间序列相关系数均值为0.72，GPS和GRACE周年信号振幅均值分别为6.00 mm和3.70 mm，周年信号减少量和均方根误差减少量均值分别为0.51和0.29；研究区内GPS垂直位移和GRACE垂直形变时间序列一致性较强，GRACE垂直形变能有效解释50%以上的GPS垂直位移周年信号，GPS垂直位移时间序列包含的非构造形变中平均约29%来源于环境负载变化所引起的负荷形变。     

On the pore‐scale mechanisms leading to brittle and ductile deformation behavior of crystalline rocks

Deformation mechanisms at the pore scale are responsible for producing large strains in porous rocks. They include cataclastic flow, dislocation creep, dynamic recrystallization, diffusive mass transfer, and grain boundary sliding, among others. In this paper, we focus on two dominant pore‐scale mechanisms resulting from purely mechanical, isothermal loading: crystal plasticity and crofracturing. We examine the contributions of each mechanism to the overall behavior at a scale larger than the grains but smaller than the specimen, which is commonly referred to as the mesoscale. Crystal plasticity is assumed to occur as dislocations along the many crystallographic slip planes, whereas microfracturing entails slip and frictional sliding on microcracks. It is observed that under combined shear and tensile loading, microfracturing generates a softer response compared with crystal plasticity alone, which is attributed to slip weakening where the shear stress drops to a residual level determined by the frictional strength. For compressive loading, however, microfracturing produces a stiffer response than crystal plasticity because of the presence of frictional resistance on the slip surface. Behaviors under tensile, compressive, and shear loading invariably show that porosity plays a critical role in the initiation of the deformation mechanisms. Both crystal plasticity and microfracturing are observed to initiate at the peripheries of the pores, consistent with results of experimental studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Displacement analytical prediction of shallow tunnel based on unified displacement function under slope boundary

For slope condition of ground surface, the asymmetrical deformation about the vertical center line and the horizontal center line of the tunnel cross section can be formed. A unified displacement function expressed by the Fourier series is presented to express the asymmetrical deformation of the tunnel cross section. Five basic deformation modes corresponding to the expansion order 2 are a complete deformation mode to reflect deformation behaviors of the tunnel cross section under slope boundary. Such this complete displacement mode is implemented into the complex variable solution for analytically predicting tunneling-induced ground deformation under slope boundary. All of these analytical solutions are verified by good agreements of the comparison between the analytical solutions and finite element method results. A parameter study is carried out to investigate the influence of deformation modes of the tunnel cross section, geometrical conditions of the tunnel and the slope angle, and “Buoyancy effect” on the displacement field. Finally, the proposed method is consistent with measured data of the Hejie tunnel in China qualitatively. The presented solution can provide a simplified indication for evaluating the ground deformation under slope condition of ground surface.     

临震前地壳变形不动点现象与机制研究

在综合分析国内外地形变前兆研究现状的基础上,结合汶川8.0级地震前GPS、应变、重力等研究结果,提出临震前震源区域可能出现变形不动点现象。地壳变形过程中的不动点现象是临震前区域应力场进入临界状态的重要标志,是地震潜在危险区域划定的重要依据。借助不动点理论,给出汶川地震前变形不动点集合的演化,结合大区域地震活动空区与远场显著形变异常分布,探讨变形不动点现象发生的动力学背景,验证了汶川地震前地壳变形的不动点现象是大区域应力场有序运动的结果。     

Complex hydraulic interactions between compartmentalized carbonate aquifers and heterogeneous siliciclastic successions: a case study in southern Italy

The sedimentary sequences containing lithologic units with low permeability represent hydrogeologic systems, which, as of now, have been little studied despite their diffusion worldwide. A hydrogeologic study, aimed to assess the main factors controlling the groundwater flow dynamics in such systems and their hydraulic interactions with nearby carbonate aquifers, has been carried out in Longano (Isernia, Southern Italy). The analysis of the hydraulic heads, combined with the regimes of the springs and the electric conductivity of the groundwater, mainly reflect vertical and lateral heterogeneities of the media in terms of hydraulic properties. In particular, the flow system is controlled by lateral heterogeneities, which characterize a surficial horizon made up of clayey colluviums and talus deposits, separated from the deeper saturated, fissured bedrock. One‐to‐ten relationships in hydraulic heads, monitored in piezometers crossing the fissured media, further uphold the crucial role played by the lateral contrasts of permeability in controlling the flow dynamics. On the whole, significant interactions with the nearby carbonate hydrostructure take place. Nevertheless, the heterogeneities of the siliciclastic succession and surficial horizon, coupled with the compartmentalization of the carbonate system, lead to a complex hydrogeological scenario. In a wider perspective, this study gives information of utmost importance in order to improve the implementation of mathematical models and configuration of tapping works within these heterogeneous and complex settings. Copyright © 2015 John Wiley & Sons, Ltd.     

Upper Cretaceous marine‐continental transition (Leonese Area,NW Spain) defined from integrated outcrop and seismic stratigraphy

The Upper Cretaceous succession of the Leonese Area (NW Spain) comprises mixed clastic and carbonate sediments. This succession is divided into two lithostratigraphic units, the Voznuevo Member and the Boñar Formation, which represent fluvial, shoreface, intertidal, subtidal and open‐shelf sedimentary environments. Regional seismic interpretation and sequence stratigraphic analysis have allowed the study of lateral and vertical changes in the sedimentary record and the definition of third‐order levels of stratigraphic cyclicity. On the basis of these data, the succession can be divided into two second‐order depositional sequences (DS‐1 and DS‐2), incorporating three system tracts in a lowstand to transgressive to highstand system tract succession (LST–TST–HST). These sequences are composed of fluvial systems at the base with palaeocurrents that flowed westward and south‐westward. The upper part of DS‐1 (Late Albian–Middle Turonian) shows evidence of intertidal to subtidal and offshore deposits. DS‐2 (Late Turonian–Campanian) comprises intertidal to subtidal, tidal flat, shallow marine and lacustrine deposits and interbedded fluvial deposits. Two regressive–transgressive cycles occurred in the area related to eustatic controls. The evolution of the basin can be explained by base‐level changes and associated shifts in depositional trends of successive retrogradational episodes. By using isobath and isopach maps, the main palaeogeographic features of DS‐1 and DS‐2 were constrained, namely coastline positions, the existence and orientation of corridors through which fluvial networks were channelled and the location of the main depocentres of the basin. Sedimentation on the Upper Cretaceous marine platform was mainly controlled by (i) oscillations of sea level and (ii) the orientation of Mesozoic faults, which induced sedimentation along depocentres. Copyright © 2013 John Wiley & Sons, Ltd.