Neoproterozoic Volhynia-Brest magmatic province in the western East European craton: Within-plate magmatism in an ancient suture zone

The reasons for the isotopic and geochemical heterogeneity of magmatism of the Neoproterozoic large Volhynia-Brest igneous province (VBP) are considered. The province was formed at 550 Ma in response to the break up of the Rodinia supercontinent and extends along the western margin of the East European craton, being discordant to the Paleoproterozoic mobile zone that separates Sarmatia and Fennoscandia and the Mesoproterozoic Volhynia-Orsha aulacogen. The basalts of VBP show prominent spatiotemporal geochemical zoning. Based on petrographic, mineralogical, geochemical, and isotopic data, the following types of basalts can be distinguished: olivine-normative subalkaline basalts consisting of low-Ti (sLT, < 1.10–2.0 wt % TiO₂; ε_Nd(550) from ?6.6 to ?2.7) and medium-Ti (sMT, 2.0–3.0 wt % TiO₂, occasionally up to 3.6 wt % TiO₂; ε_Nd(550) from ?3.55 to + 0.6) varieties; normal quartz-normative basalts (tholeiites) including low-Ti (tLT, < 1.75–2.0 wt % TiO₂) and medium-to-high-Ti (tHT1, 2.0–3.6 wt % TiO₂, ε_Nd(550) from ?1.3 to + 1.0) varieties. The hypabyssal bodies are made up of subalkaline low-Ti olivine dolerites (LT, 1.2–1.5 wt % TiO₂; ε_Nd(550) = ?5.8) and subalkaline high-Ti olivine gabbrodolerites (HT2, 3.0–4.5 wt % TiO₂; ε_Nd(550) = ?2.5). Felsic rocks of VBP are classed as volcanic rocks of normal (andesidacites, dacites, and rhyodacites) and subalkaline (trachyrhyodacites) series with TiO₂ 0.72–0.77 wt% and ε_Nd(550) of ?12. The central part of VBP is underlain by a Paleoproterozoic domain formed by continent-arc accretion and contains widespread sills of HT2 dolerites and lavas of LT basalts; the northern part of the province is underlain by the juvenile Paleoproterozoic crust dominated by MT and HT1 basalts. MT and LT basalts underwent significant AFC-style upper crustal contamination. During their long residence in the upper crustal magmatic chambers, the basaltic melts fractionated and caused notable heating of the wall rocks and, correspondingly, nonmodal melting of the upper crustal protolith containing high-Rb phase (biotite), thus producing the most felsic rocks of the province. The basalts of VBP were derived from geochemically different sources: probably, the lithosphere and a deep-seated plume (PREMA type). The HT2 dolerites were generated mainly from a lithospheric source: by 3–4% melting of the geochemically enriched garnet lherzolite mantle. LT dolerites were obtained by partial melting of the modally metasomatized mantle containing volatile-bearing phases. The concepts of VBP formation were summarized in the model of three-stage plume-lithosphere interaction.     

Weibull statistical analysis of granite bending strength

Summary  This paper describes and discusses the adequacy of Weibull statistical analysis to analyse the bending strength of granite. The experimental results show that strength variability is related with a specific origin of failure. This conclusion is based on analysing the influence of the surface condition (extrinsic defects) on the bending strength results treated by the Weibull statistics. The conclusions drawn from this study have been validated by analysing the results of the critical flaw dimension estimated by applying the linear elastic fracture mechanics (LEFM) formulae. Results obtained from fractographic examination also have been used to describe the location of the origin of the fracture and understand the distribution of defects; i.e., there is a unimodal distribution of defects (intrinsic defects), despite the fact that some outlier values are normally observed in the fractured surfaces. Correspndence: P. M. Amaral, Department of Materials Engineering, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal     

Chemical composition,volatile components,and trace elements in melts of the Karymskii volcanic center,Kamchatka, and Golovnina volcano,Kunashir Island: Evidence from inclusions in minerals

Melt inclusions were examined in phenocrysts in basalt, andesite, dacite, and rhyodacite from the Karymskii volcanic center in Kamchatka and dacite form Golovnina volcano in Kunashir Island, Kuriles. The inclusions were examined by homogenization and by analyzing glasses in more than 80 inclusions on an electron microscope and ion microprobe. The SiO₂ concentrations in the melt inclusions in plagioclase phenocrysts from basalts from the Karymskii volcanic center vary from 47.4 to 57.1 wt %, these values for inclusions in plagioclase phenocrysts from andesites are 55.7–67.1 wt %, in plagioclase phenocrysts from the dacites and rhyodacites are 65.9–73.1 wt %, and those in quartz in the rhyodacites are 72.2–75.7 wt %. The SiO₂ concentrations in melt inclusions in quartz from dacites from Golovnina volcano range from 70.2 to 77.0 wt %. The basaltic melts are characterized by usual concentrations of major components (wt %): TiO₂ = 0.7–1.3, FeO = 6.8–11.4, MgO = 2.3–6.1, CaO = 6.7–10.8, and K₂O = 0.4–1.7; but these rocks are notably enriched in Na₂O (2.9–7.4 wt % at an average of 5.1 wt %, with the highest Na₂O concentration detected in the most basic melts: SiO₂ = 47.4–52.0 wt %. The concentrations of volatiles in the basic melts are 1.6 wt % for H₂O, 0.14 wt % for S, 0.09 wt % for Cl, and 50 ppm for F. The andesite melts are characterized by high concentrations (wt %) of FeO (6.5 on average), CaO (5.2), and Cl (0.26) at usual concentrations of Na₂O (4.5), K₂O (2.1), and S (0.07). High water concentrations were determined in the dacite and rhyodacite melts: from 0.9 to 7.3 wt % (average of 15 analyses equals 4.5 wt %). The Cl concentration in these melts is 0.15 wt %, and those of F and S are 0.06 and 0.01 wt %, respectively. Melt inclusions in quartz from the dacites of Golovnina volcano are also rich in water: they contain from 5.0 to 6.7 wt % (average 5.6 wt %). The comparison of melt compositions from the Karymskii volcanic center and previously studied melts from Bezymyannyi and Shiveluch volcanoes revealed their significant differences. The former are more basic, are enriched in Ti, Fe, Mg, Ca, Na, and P but significantly depleted in K. The melts of the Karymskii volcanic center are most probably less differentiated than the melts of Bezymyannyi and Shiveluch volcanoes. The concentrations of water and 20 trace elements were measured in the glasses of 22 melt inclusions in plagioclase and quartz from our samples. Unusually high values were obtained for Li concentrations (along with high Na concentrations) in the basaltic melts from the Karymskii volcanic center: from 118 to 1750 ppm, whereas the dacite and rhyolite melts contain 25 ppm Li on average. The rhyolite melts of Golovnina volcano are much poorer in Li: 1.4 ppm on average. The melts of the Karymskii volcanic center are characterized by relative minima at Nb and Ti and maxima at B and K, as is typical of arc magmas.     

Quantitative sinkhole hazard assessment. A case study from the Ebro Valley evaporite alluvial karst (NE Spain)

Quantitative sinkhole hazard assessments in karst areas allow calculation of the potential sinkhole risk and the performance of cost-benefit analyses. These estimations are of practical interest for planning, engineering, and insurance purposes. The sinkhole hazard assessments should include two components: the probability of occurrence of sinkholes (sinkholes/km² year) and the severity of the sinkholes, which mainly refers to the subsidence mechanisms (progressive passive bending or catastrophic collapse) and the size of the sinkholes at the time of formation; a critical engineering design parameter. This requires the compilation of an exhaustive database on recent sinkholes, including information on the: (1) location, (2) chronology (precise date or age range), (3) size, and (4) subsidence mechanisms and rate. This work presents a hazard assessment from an alluvial evaporite karst area (0.81 km²) located in the periphery of the city of Zaragoza (Ebro River valley, NE Spain). Five sinkholes and four locations with features attributable to karstic subsidence where identified in an initial investigation phase providing a preliminary probability of occurrence of 0.14 sinkholes/km² year (11.34% in annual probability). A trenching program conducted in a subsequent investigation phase allowed us to rule out the four probable sinkholes, reducing the probability of occurrence to 0.079 sinkholes/km² year (6.4% in annual probability). The information on the severity indicates that collapse sinkholes 10–15 m in diameter may occur in the area. A detailed study of the deposits and deformational structures exposed by trenching in one of the sinkholes allowed us to infer a modern collapse sinkhole approximately 12 m in diameter and with a vertical throw of 8 m. This collapse structure is superimposed on a subsidence sinkhole around 80 m across that records at least 1.7 m of synsedimentary subsidence. Trenching, in combination with dating techniques, is proposed as a useful methodology to elucidate the origin of depressions with uncertain diagnosis and to gather practical information with predictive utility about particular sinkholes in alluvial karst settings: precise location, subsidence mechanisms and magnitude, and timing and rate of the subsidence episodes.     

Drought and institutional adaptation in the Great Plains of Alberta and Saskatchewan, 1914–1939

Agriculture in the southern Great Plains of Canada has been particularly vulnerable to prolonged episodes of drought. Using climate data and a precipitation minus potential evapotranspiration index, the extent of the region’s exposure to drought is examined. Between 1914 and 1917, the Dry Belt was particularly vulnerable to drought, whereas after 1928, a much larger region known as the Palliser Triangle covering most of southern Alberta and Saskatchewan was much more exposed to drought. These droughts provoked major institutional adaptation, in particular the establishment of the Special Areas Board by the Government of Alberta, and the creation of the Prairie Farm Rehabilitation Administration by the Government of Canada. Both organizations have proved to be relatively permanent public adaptations to the natural hazard of drought in the region. Moreover, these earlier experiences with prolonged drought as well as institution-building may be of value in helping the residents of the Palliser Triangle adapt to predicted climate changes in the future as well as anticipate some of the barriers to effective institutional adaptation.     

Tidal inundation mapping under enhanced land subsidence in Semarang,Central Java Indonesia

Tidal inundation by high tide under enhanced land subsidence is a damaging phenomenon and a major threat to the Semarang urban area in Indonesia. It impacts on economic activities, as well as the cost of an emergency program and causes interruption of pubic services, danger of infectious diseases and injury to human lives. This study examines a spatial analysis tool on the GIS-raster system for the tidal inundation mapping based on the subsidence-benchmark data and modified detail digital elevation model. Neighborhood operation and iteration model as a spatial analysis tool have been applied in order to calculate the encroachment of the tidal inundation on the coastal area. The resulting map shows that the tidal flood spreads to the lowland area and causes the inundation of coastal settlement, infrastructure, as well as productive agricultural land, i.e., the fish-pond area. The monitoring of the vulnerable area due to the tidal inundation under the scenario of extended land subsidence plays an important role in long-term coastal zone management in Semarang.     

Deep-seated gravitational slope deformations and their influence on consequent mass movements (case studies from the highest part of the Czech Carpathians)

Gravitational spreading of mountain ridges displays primary disequilibrium of flysch mountain areas of the Czech Carpathians. The progression of various types of mass movements is a product of long-term ridge disintegration and is predisposed by the geological structure of the area and the upper Tertiary-Quaternary morphogenesis of the mountain area. Deep-seated slope deformations are spatially interconnected by the occurrence of some other types of slope deformations (e.g. debris flows, debris slides, slumps, rock avalanches, etc.), which pose a considerable risk for the existence of human society. An important causative factor in these dynamically developing hazardous processes is, among other factors, the way in which land has been used in the last three centuries. Therefore, the occurrence of various types of slope deformations is studied in terms of their relation to deep-seated gravitational deformations and in terms of other limiting factors (structural geological, morphological and climatic factors, manmade impacts, etc.). The paper presents several case studies of slope deformations (Velká Čantoryje Mt, Lysá hora Mt, Ropice Mt and Smrk Mt) in the area of the Outer Carpathians within the territory of the Czech Republic and also adverts to some consequences in terms of the socioeconomic structure of the landscape.     

The state of land subsidence and prediction approaches due to groundwater withdrawal in China

This article gives a general introduction to land subsidence with the prediction approaches due to withdrawal of groundwater in three subsided/subsiding regions in China: the deltaic plain of Yangtse River (YRDP), North China Plain (NCP), and Fenwei Plain (FP). On YRDP, Shanghai is the typical subsided/subsiding city; on NCP Tianjin is the typical subsided/subsiding city, and on FP Taiyuan is the typical subsided/subsiding city. The subsided area with subsidence over 200 mm on YRDP is about 10,000 km² and the maximum subsided value reached 2.9 m at Shanghai; on NCP the subsided area reached 60,000 km² with the maximum subsidence of 3.9 m at Tianjing; on FP the subsided area is relatively smaller than that on the other two plains and is about 1,135 km² with maximum subsidence of 3.7 m at Taiyuan city. In order to protect the civil and industrial facilities, it is necessary to predict the future development of land subsidence based on present state. Many researchers proposed several approaches to predict the land subsidence due to groundwater withdrawal according to different geological conditions and groundwater withdrawal practice. This article classifies these approaches into five categories: (i) statistical methods; (ii) 1D numerical method; (iii) quasi-3D seepage model; (iv) 3D seepage model; (v) fully coupled 3D model. In China, the former four categories are presently employed in the prediction practice and their merits and demerits are discussed. According to the prediction practice, 3D seepage model is the best method presently.