Aridity indices to assess desertification susceptibility: a methodological approach using gridded climate data and cartographic modeling

Natural Hazards - Desertification is a land degradation phenomenon with dire and irreversible consequences, affecting different regions of the world. Assessment of spatial climate susceptibility to...     

A FORM-based approach for probabilistic analysis in geotechnics: Application to a reinforced concrete drainage culvert

As numerical models are increasingly used as a design tool in geotechnical engineering, it is highly desirable if geotechnical reliability analysis can be conducted based on numeral models. Currently, the practical use of geotechnical reliability analysis-based numerical models is still quite limited. In this study, an easy to access method is derived to conduct geotechnical reliability analysis based on numerical models. To facilitate its application, a procedure is outlined to implement the suggested method such that geotechnical reliability analysis can be automated using existing geotechnical numerical packages. The procedure is illustrated in detail with an example, and the source codes provided can be easily adapted to analyze other similar problems. The method described in this paper is used to study the reliability of a deteriorating reinforced concrete drainage culvert in Shanghai, China. The suggested method provides a convenient means for reliability analysis of complex geotechnical problems.     

Low temperature alteration of magmatic Ni-Cu-PGE sulfides as a source for hydrothermal Ni and PGE ores: A quantitative approach using automated mineralogy

Magmatic Ni-Cu-PGE sulfide assemblages are almost ubiquitously comprised of pyrrhotite-pentlandite-chalcopyrite(-pyrite). Sulfide alteration is common during syn- or post-magmatic fluid interaction, usually replacing sulfides with amphiboles or serpentine. However, some are altered to a low temperature (<200 °C) hydrothermal assemblage of pyrite-millerite-chalcopyrite (PMC). An example is the Ni-Cu-PGE mineralisation in the Grasvally-Norite-Pyroxenite-Anorthosite (GNPA) Member, northern Bushveld Complex, which displays a continuum of mineralogical styles formed through progressive alteration: Style 1 primary pyrrhotite-pentlandite-chalcopyrite; which is altered to Style 2 pyrrhotite-pyrite-pentlandite-chalcopyrite; Style 3 pyrite-pentlandite-chalcopyrite; Style 4 pyrite-pentlandite-millerite-chalcopyrite; and Style 5 pyrite-millerite-chalcopyrite-cubanite. Modelling using CHILLER confirms this mineralogical sequence is thermodynamically possible at ∼200 °C. Quantitative characterisation using automated Energy-Dispersive X-ray spectroscopy mapping alongside in situ laser ablation analyses determined mineral proportions, major and trace element concentrations and deportments in each style. The early loss of pyrrhotite removes over half of the bulk Fe and S during the initial stages of PMC alteration, increasing Cu, Ni and PGE tenors of the remaining sulfides significantly. As water–rock interaction progresses, pyrrhotite is replaced by pyrite and pentlandite by millerite, with concurrent losses in Fe, S and Ni. Copper is lost throughout the alteration, and is most pronounced in the more advanced stages. The fluids responsible were most likely acidic and oxidised, with metals mobilised as chloride complexes. Using Rh as an immobile normalising element, the overall mass loss in the most altered samples is calculated to be up to 90%, consistent with textural relationships that indicate 40–90% volume loss from Styles 2–5, with sulfides replaced by secondary silicates, including phlogopite, quartz, chlorite, pyroxenes and minor amphiboles. Magnetite is not a significant alteration product and thus Fe is mobilised, or incorporated into silicates. Most trace elements present in the magmatic sulfide (the IPGE, Rh and Bi) remain in the sulfide phases, and are effectively transferred to pyrite during PMC alteration, except Pd, which remains in pentlandite, and is liberated from the sulfide assemblage when pentlandite disappears. Selenium tenors increase slightly with alteration, demonstrating that alteration decreases S/Se ratios. The significant mobilisation of Ni, Cu and Pd during PMC alteration produces fluids enriched in these elements that may represent a metal source for a number of enigmatic hydrothermal Ni deposits such as Avebury, Enterprise and Talvivaara, whose metal sources remain speculative. The PMC alteration of the GNPA Member may be specifically a source for the nearby Waterberg hydrothermal Pt deposit. Furthermore, this study has implications not only for magmatic ore deposits, but also for the general implications of sulfide transformation and metal transfer in ore systems in general.     

Pengelly's legacy reconsidered: a GIS approach to spatial analysis of palaeontological and archaeological collections from Kents Cavern, England

Tens of thousands of palaeontological and archaeological remains were collected by William Pengelly during 19th century excavations of Kents Cavern, but are now widely dispersed between museums. This has previously precluded spatial analysis. We have now assembled available museum records into a single database, and, using our previously-reconstructed Pengelly excavation map as a base, we have been able to exploit the unique Pengelly location code to set up a GIS mapping system. This allows, for the first time, the analysis of spatial patterns. In addition, the GIS serves to highlight potential problems of recording or curation in the original data. Here we report on the construction of the GIS system and its first use in the analysis of spatial distribution of bear remains. The maps demonstrate that Ursus deningeri entered the cave through a now-sealed High Level Chamber entrance at the back of the cave in the middle Pleistocene, whereas Ursus arctos accessed the cave in the late Pleistocene through the now-sealed Northeast Gallery entrance. The denning areas are reconstructed as Labyrinth/Bear's Den for U. deningeri and Vestibule/Great Chamber for U. arctos. Considerable post-mortem re-distribution of the remains of both species is indicated.     

利用微裂隙内流体包裹体面研究构造运动——以苏北盆地富民、花庄油田为例

流体包裹体面（FIP）研究是当前的热点研究对象之一,已经取得了较为丰硕的成果,但利用FIP研究构造运动的文献为数不多。以苏北盆地富民、花庄油田为例,利用FIP研究了该油田的构造活动。结果表明：研究区至少经历了4次主要构造运动,主要发育3种类型的FIP。结合构造演化史、埋藏史及热史,确定了构造运动与油气成藏的时间与期次。     

Dating metamorphic reactions and fluid flow: application to exhumation of high-P granulites in a crustal-scale shear zone, western Canadian Shield

The Legs Lake shear zone is a crustal‐scale thrust fault system in the western Canadian Shield that juxtaposes high‐pressure (1.0+ GPa) granulite facies rocks against shallow crustal (< 0.5 GPa) amphibolite facies rocks. Hangingwall decompression is characterized by breakdown of the peak assemblage Grt + Sil + Kfs + Pl + Qtz into the assemblage Grt + Crd + Bt ± Sil + Pl + Qtz. Similar felsic granulite occurs throughout the region, but retrograde cordierite is restricted to the immediate hangingwall of the shear zone. Textural observations, petrological analysis using P–T/P–M_H2O phase diagram sections, and in situ electron microprobe monazite geochronology suggest that decompression from peak conditions of 1.1 GPa, c. 800 °C involved several distinct stages under first dry and then hydrated conditions. Retrograde re‐equilibration occurred at 0.5–0.4 GPa, 550–650 °C. Morphology, X‐ray maps, and microprobe dates indicate several distinct monazite generations. Populations 1 and 2 are relatively high yttrium (Y) monazite that grew at 2.55–2.50 Ga and correspond to an early granulite facies event. Population 3 represents episodic growth of low Y monazite between 2.50 and 2.15 Ga whose general significance is still unclear. Population 4 reflects low Y monazite growth at 1.9 Ga, which corresponds to the youngest period of high‐pressure metamorphism. Finally, population 5 is restricted to the hydrous retrograded granulite and represents high Y monazite growth at 1.85 Ga that is linked directly to the synkinematic garnet‐consuming hydration reaction (KFMASH): Grt + Kfs + H₂O = Bt + Sil + Qtz. Two samples yield weighted mean microprobe dates for this population of 1853 ± 15 and 1851 ± 9 Ma, respectively. Subsequent xenotime growth correlates with the reaction: Grt + Sil + Qtz + H₂O = Crd. We suggest that the shear zone acted as a channel for fluid produced by dehydration of metasediments in the underthrust domain.     

地球化学场精细结构解析方案与应用

为满足勘查地球化学对化探数据处理越来越精细的要求,把人工神经网络和统计分析结合起来形成地球化学场精细结构解析方案。该方案包括对地球化学样品的分类和对各类样品性质的详细研究,目的在于提供便捷的数学和计算机软件工具,以提取化探数据中的深层信息。可以用于:①研究各组样品中元素含量水平和组合特征以解释可能的矿种;②研究元素组合特征与指示元素的关联和区别以揭示可能的成矿作用过程;③研究异常样品的空间组合属性以揭示地球化学场的精细结构;④研究异常样品之间的差异性以缩小找矿靶区;⑤综合分析以确定剥蚀深度和找矿前景。该方案也适用于环境地球化学及矿产资源预测研究。     

Resource recovery and remediation of highly alkaline residues: A political-industrial ecology approach to building a circular economy

Highly alkaline industrial residues (e.g., steel slag, bauxite processing residue (red mud) and ash from coal combustion) have been identified as stocks of potentially valuable metals. Technological change has created demand for metals, such as vanadium and certain rare earth elements, in electronics associated with renewable energy generation and storage. Current raw material and circular economy policy initiatives in the EU and industrial ecology research all promote resource recovery from residues, with research so far primarily from an environmental science perspective. This paper begins to address the deficit of research into the governance of resource recovery from a novel situation where re-use involves extraction of a component from a bulk residue that itself represents a risk to the environment. Taking a political industrial ecology approach, we briefly present emerging techniques for recovery and consider their regulatory implications in the light of potential environmental impacts. The paper draws on EU and UK regulatory framework for these residues along with semi-structured interviews with industry and regulatory bodies. A complex picture emerges of entwined ownerships and responsibilities for residues, with past practice and policy having a lasting impact on current possibilities for resource recovery.     

致密砂岩储层脆性测井评价方法研究及应用——以鄂尔多斯盆地渭北油田为例

致密砂岩储层具有非均质性强、物性差、勘探开发难度大等特点,为了寻找渭北油田致密砂岩储层的高脆性段进行储层的压裂改造,针对现有横波测井资料匮乏以及当前脆性预测方法在渭北油田致密砂岩储层是否适用等问题,提出了基于ANN(artificial neural network)模型的横波预测方法,预测值与实测值高度吻合,进而通过弹性参数法计算出研究区每口井的脆性指数。为了校正该方法预测脆性指数的准确性,通过对研究区较少井的X射线衍射全岩分析研究,明确了石英和碳酸盐类矿物为研究区延长组的主要脆性矿物,利用“(石英+碳酸盐)含量/矿物总量计算岩石脆性指数去校正弹性参数法预测的脆性指数,这种矿物组分法和弹性参数法相互制约而又相互依存的方法,不但提高了预测精度,而且弥补了阵列声波测井和全岩分析资料不足的问题。利用该方法对渭北油田WB2井区延长组致密砂岩储层进行了测井脆性评价,为WB52和WB49井高脆性有利压裂目的层段识别及增产方案设计提供了依据。所提出的方法和流程具有较强的应用价值和推广价值。     

Interpolation by regularized spline with tension: II. Application to terrain modeling and surface geometry analysis

A general approach to the computation of basic topographic parameters independent of the spatial distribution of given elevation data is developed. The approach is based on an interpolation function with regular first and second order derivatives and on application of basic principles of differential geometry. General equations for computation of profile, plan, and tangential curvatures are derived. A new algorithm for construction of slope curves is developed using a combined grid and vector approach. Resulting slope curves better fulfill the condition of orthogonality to contours than standard grid algorithms. Presented methods are applied to topographic analysis of a watershed in central Illinois.     

The hydrochemical facies and anomalous fluoride content in the Serra Geral aquifer system,southern Brazil: a GIS approach with tectonic and principal component analysis

Groundwater with high fluoride content and water mixture patterns were studied in Serra Geral aquifer system (SGAS) using three aspects, principal component analysis (PCA), tectonic scenery and hydrochemical interpretation from 309 groundwater chemical data information from deep wells. A four-component model is suggested and explains 81% of total variance in the PCA. Six hydrochemical facies were identified. These facies suggest two different fluoride sources. Tectonic approach shows the relationship between defined hydrochemical facies and regional fracture control. The applied methodology reveals a minimum level to understand hydrochemical mixtures. The fluoride enrichment mechanisms into the groundwater are comprised in advance to guide the future uses of SGAS to the public supply.     

Miocene andesitic lavas of Sierra de Angangueo: a petrological,geochemical, and geochronological approach to arc magmatism in Central Mexico

ABSTRACT

The early and middle Miocene andesitic lavas of the Sierra de Angangueo (MALSA) represent one of the most prominent landforms of intermediate magmatism in Central Mexico. In this paper, we present new petrological, geochemical, thermobarometric, and geochronological data in order to discuss the conditions of MALSA’s emplacement in the lithosphere.

MALSA comprises a voluminous eroded early Miocene andesitic structure, emplaced on a Mesozoic basement. MALSA shows a wide variety of textures, from glassy and aphanitic to porphyritic, mainly composed of plagioclase (An_10-55), clinopyroxene (Wo_60-65; En_35-40), amphibole (Mg-hornblende/edenite), and rarely olivine (Fo_75–86) or orthopyroxene (En_72-80). Major and trace elements plots follow a typical calc-alkaline trend with relatively increasing fractionation.

The ⁸⁷Sr/⁸⁶Sr isotopic signatures range between 0.703343 and 0.704459 and εNd values from +1.37 to +4.84; apparently without a significant contribution of an old, thick, or highly radiogenic continental crust. Lead isotope values ²⁰⁶Pb/²⁰⁴Pb vary between 18.68 and 18.83, ²⁰⁷Pb/²⁰⁴Pb from 15.57 to 15.65, and ²⁰⁸Pb/²⁰⁴Pb from 38.39 to 38.67, suggesting contamination of magmas by juvenile crust. Thermodynamic calculations indicate equilibrium conditions at ≤900°C and ~2 kbar and an average log ?O₂ ≈ ?10.

Ar–Ar and K–Ar dating carried out on whole rock, matrix, amphibole, and plagioclase phenocrysts yielded ages between 13.0 ± 0.5 and 23.9 ± 0.3 Ma. These dates indicate a series of pulses with maximum magmatic activity between 24 and 18 Ma.

The geochemical and petrologic data suggest partial melting processes in the lower or middle crust associated with possible magma mixing during its ascent; such a mechanism could explain a hybrid mantle-lower crust origin of this large volume of andesites. The MALSA, as well as the early to middle Miocene magmatism from Western Mexico, could represent two coeval and independent magmatic arcs prior to the present Trans-Mexican Volcanic Belt (TMVB) in Central Mexico.     

一维到三维密度分布函数及其可视化在大数据分析中的应用——以苦橄质玄武岩等为例

提出不同维度的密度分布函数的计算方法和可视化方案,以解决不同数量级和不同测量误差的岩石样本数据分析对比困难的问题。通过SiO_2、全碱和MgO指标的三维密度分布函数和t-分布随机邻域嵌入可视化方法对GEOROC和PETDB数据库进行发掘,发现大洋岩(oceanite)和富辉橄玄岩(ankaramite)与苦橄质玄武岩(basalt, picritic)成分相近,而铁质苦橄岩(picrite,ferro)与侵入的橄榄辉长岩和苦橄岩(picrite)成分相似。利用二维密度分布函数和可视化技术,对比分析了不同岩石在TAS图解和硅镁图上的数据分布状态和数据集中核心区域。发现总体分布上,更富镁的苦橄岩的SiO_2含量高于苦橄质玄武岩,超基性的苦橄岩(picrate)核心区域主要分布在TAS图解的B区,这与以SiO_2=45%划分基性岩和超基性岩界线的观点矛盾。     

Determining the equivalent permeability tensor for fractured rock masses using a stochastic REV approach: Method and application to the field data from Sellafield,UK

A numerical procedure to determine the equivalent permeability tensor of a fractured rock is presented, using a stochastic REV (Representative Elementary Volume) concept that uses multiple realizations of stochastic DFN (Discrete Fracture Network) models. Ten square DFN models are generated using the Monte Carlo simulations of the fracture system based on the data obtained from a site characterization program at Sellafield, Cumbria, UK. Smaller models with varying sizes of from 0.25 m×0.25 m to 10 m×10 m are extracted from the generated DFN models and are used as two-dimensional geometrical models for calculation of equivalent permeability tensor. The DFN models are also rotated in 30º intervals to evaluate the tensor characteristics of calculated directional permeability. Results show that the variance of the calculated permeability values decreases significantly as the side lengths of the DFN models increase, which justifies the existence of a REV. The REV side length found in this analysis is about 5 m and 8 m with 20% and 10% acceptable variations, respectively. The calculated directional permeability values at the REV size have tensor characteristic that is confirmed by a close approximation of an ellipse in a polar plot of the reciprocal of square roots of the directional permeability.

A virtual voyage through 3D structures generated by chaotic mixing of magmas and numerical simulations: a new approach for understanding spatial and temporal complexity of magma dynamics

In this contribution, we present a virtual voyage through 3D structures generated by chaotic mixing of magmas and numerical simulations with the aim to highlight the power of 3D representations in the understanding of this geological phenomenon. In particular, samples of mixed juveniles from Salina island (Southern Italy) are reconstructed in 3D by serial lapping and digital montage and numerical simulations are performed by using a 3D chaotic dynamical system. Natural and simulated magma mixing structures are visualized by using several multimedia tools including animations and “virtual reality” models. It is shown that magma interaction processes can generate large spatial and temporal compositional heterogeneities in magmatic systems. The same topological structures are observed in both 3D reconstructed rock samples and chaotic numerical simulations, indicating that the mixing of magmas is governed by chaotic dynamics. The use of 3D multimedia models gives the opportunity to penetrate into magma mixing structures and to understand their significance in the context of magma dynamics. Such an approach is very powerful since multimedia tools can strongly capture the attention of the reader bringing him/her into an interactive and memorable geological experience. Electronic supplementary material  enclosed:     

Mode of formation of the Nile Gorge in northern Egypt: a study by DEM‐SRTM data and GIS analysis

This is an overview of the mode of formation of the Nile Gorge in northern Egypt. It is based on the interpretation of the Shuttle Radar Topography Mission (SRTM) data along with detailed analysis of landsat image, geological map and seismic data. The results show that the current course of the Nile was caused by a differential uplift of two plateaus: Ma'aza, to the east, and Western Desert plateau, to the west of the river. This uplift is caused by dynamic forces resulting from subsurface convection processes. It also contributed to the formation of several drainage systems, basins and structural features. Abundant faults and fractures that are parallel to the Nile Valley on both flanks that are associated with uplift are proven to be contemporaneous with formation of the river. We conclude that understanding of the uplift is crucial to visualizing the Nile course and its geodynamic formation. The information derived from the SRTM data reveals invaluable knowledge in support of the presented remotely sensed geological features. The paper clearly explains the stages of formation of the Nile segments in space and time and structural controls on the path of the Nile River in Egypt. Copyright © 2015 John Wiley & Sons, Ltd.     

基于Ansys的三维地应力场及洞室围岩稳定分析--以宜兴抽水蓄能电站为例

根据宜兴抽水蓄能站的地应力资料以及厂房区的地质构造条件,通过边界位移的大量调整,模拟出构造应力以及厂房区的三维地应力场,运用Ansys软件单元的生与死,模拟洞室开挖效应引起的围岩稳定性,然后运用等效概化原理,考虑锚杆的作用,对围岩进行加固,结果表明锚固作用明显。     

Landslide risk analysis in the area North of Lisbon (Portugal): evaluation of direct and indirect costs resulting from a motorway disruption by slope movements

A risk analysis is developed for a test site located in the area north of Lisbon using a scenario of a temporary interruption of the motorway A9 due to a landslide of rotational or translational type. Landslide susceptibility is assessed at the regional scale independently for rotational and translational slides, comparing the landslide distribution with a set of assumed independent landslide predisposing factors. Susceptibility models are validated and classified through the computation of prediction rate curves based on the temporal partition of the landslide data sets. Landslide hazard maps are based on a scenario of future landslide occurrence for the next 27 years. These maps allow the definition of two critical areas on the motorway A9 with regards to landslide susceptibility. Direct costs associated with both critical spots are assessed taking into account the probable affected area of the motorway, and the reconstruction costs. Indirect costs derived from the traffic interruption are evaluated considering the alternatives paths to the motorway, and include costs resulting from: (1) additional fuel consumption; (2) decrease in tollgate income; and (3) loss of productive time. Results show that indirect costs may be 24 to 43 times higher than direct costs, assuming a temporary interruption of the motorway for 6 months.     

Local to regional scale structural controls on mineralisation and the importance of a major lineament in the eastern Mount Isa Inlier, Australia: Review and analysis with autocorrelation and weights of evidence

Although major crustal lineaments may play an important role in mineralisation, the relationship between lineaments and mineral deposits can be quite cryptic, and structural controls may vary as a function of scale along lineaments. Major lineaments alone may be of limited use for detailed target generation. The Cloncurry Lineament in the Eastern part of the Mount Isa Inlier is a crustal scale structure defined by potential field-derived ‘worms’. Weights-of-evidence quantifies the association between mineral occurrences and this lineament. Autocorrelation is used to recognise structural controls on mineralisation at different scales, by progressively limiting the lengths of the vectors between mineral occurrence points in the autocorrelation plot. The weights-of-evidence analysis shows that Au, Au–Cu, Cu–Au and Cu deposits have a positive spatial correlation to the Cloncurry Lineament, which suggests it that acted as a primary crustal scale control on the localisation of Cu and Au through focussing mineralisation systems on a broad scale. However, autocorrelation defines a variety of local structural controls, which can be interpreted as shear zones, variably oriented fault sets, en echelon fault arrays, and potentially the orientation of bedding and/or iron formations which localise fluid flow and mineral deposition at finer scales. The results suggest that major lineaments defined by geophysical contrasts can be used in conjunction with techniques of spatial analysis for targeting structurally controlled mineralisation in areas under thin cover adjacent to mineralised terrains such as the Mt Isa Inlier.