The role of heterogeneous strain in the development and preservation of a polymetamorphic record in high-P granulites, western Canadian Shield

Mafic rocks in the Chipman domain of the Athabasca granulite terrane, western Canadian Shield, provide the first well‐documented record of two distinct high‐P granulite facies events in the same domain in this region. Textural relations and the results of petrological modelling (NCFMASHT system) of mafic granulites are interpreted in terms of a three‐stage tectonometamorphic history. Stage 1 involved development of the assemblage Grt + Cpx + Qtz ± Pl (M₁) from a primary Opx‐bearing igneous precursor at conditions of 1.3 GPa, 850–900 °C. Field and microstructural observations suggest that M₁ developed synchronously with an early S₁ gneissic fabric. Stage 2 is characterized by heterogeneous deformation (D₂) and synkinematic partial retrogression of the peak assemblage to an amphibole‐bearing assemblage (M₂). Stage 3 involved a third phase of deformation and a return to granulite facies conditions marked by the prograde breakdown of amphibole (Amph₂) to produce matrix garnet (Grt_3a) and the coronitic assemblage Cpx_3b + Opx_3b + Ilm_3b + Pl_3b (M_3b) at 1.0 GPa, 800–900 °C. M₁ and M_3b are correlated with 2.55 and 1.9 Ga metamorphic generations of zircon, respectively, which were dated in a separate study. Heterogeneous strain played a crucial role in both the development and preservation of these rare examples of multiple granulite facies events within single samples. Without this fortuitous set of circumstances, the apparent reaction history could have incorrectly led to an interpretation involving a single‐cycle high‐grade event. The detailed P–T–t–D history constructed for these rocks provides the best evidence to date that much of the east Lake Athabasca region experienced long‐term lower crustal residence from 2.55 to 1.9 Ga, and thus the region represents a rare window into the reactivation and ultimate stabilization processes of cratonic lithosphere.     

Relations between hydrology and velocity of a continuously moving landslide—evidence of pore-pressure feedback regulating landslide motion?

We measured displacement, pore-water pressure, and climatic conditions for 3 years at the continuously moving Slumgullion landslide in Colorado, USA. The landslide accelerated when pore-water pressure increased within the landslide body, but this occurred as pore-water pressure decreased along the landslide margin. The decrease probably occurred in response to shear-induced soil dilation at rates greater than pore-pressure diffusion and likely increased resistance to shear displacement and resulted in landslide deceleration. This dilative strengthening has been experimentally observed and explained theoretically, but not previously identified during field studies. Although landslide displacement should have exceeded that required to achieve critical-state density of shear boundaries, observed relocation of these boundaries indicates that shearing is episodic at fixed locations, so it permits renewed dilative strengthening when “fresh” soil is sheared. Thus, dilatant strengthening may be a considerable mechanism controlling landslide velocity, even for landslides that have continuously moved great distances.     

The Latnenskoe refractory clay deposit (Central Russia)

This paper reports the results of our recent studies and generalizes previously known data on the geology, mineralogy, geochemistry, and genesis of the Russia’s largest Latnenskoe refractory clay deposit. It is shown that conditions of its localization were defined by regional and local factors. The regional factors controlled the distribution of the clay raw material in the region, while the local factors were responsible for the genesis and composition of refractory clays of the Latnenskoe deposit. Our studies showed that the formation of refractory clays is not only related to terrigenous but also to authigenic processes of sedimentation. The terrigenous component of clays was formed by the erosion of kaolin weathering crusts of the Voronezh anteclise crystalline basement and Paleozoic sedimentary hydromica–kaolinite rocks. Authigenic processes were significantly contributed by organic matter, which determined the environmental pH and Eh parameters. It is established that the mineral matter of clays of the deposit is represented by three morphological modifications (crystalline, amorphous, and biomorphic), which were formed subsequently and (or) simultaneously and could be transformed into each other. Application of a complex of modern precision methods allowed us to reveal a previously unknown biomorphic modification of kaolinite, the major rock-forming mineral, as well as mixed-layer kaolinite-smectite in the clays. It is shown that the distribution of major and trace elements and the sulfur isotope composition in different technological types of clay depend mainly on the facies conditions of their formation. Technological properties of clay raw material are considered.     

A numerical Round Robin on tunnels under seismic actions

Although the seismic behaviour of shallow circular tunnels in soft ground is generally safer than aboveground structures, some tunnels were recently damaged during earthquakes. In some cases, damage was associated with strong ground shaking and site amplification, which increased the stress level in the tunnel lining. Pseudo-static and simplified dynamic analyses enable to assess transient changes in internal forces during shaking. Nevertheless, experimental evidences of permanent changes in internal loads in the tunnel lining would suggest that a full dynamic analysis including plastic soil behaviour should be performed when modelling the dynamic interaction between the tunnel and the ground. While sophisticated numerical methods can be used to predict seismic internal forces on tunnel structures during earthquakes, the accuracy of their predictions should be validated against field measurements, but the latter are seldom available. A series of centrifuge tests were therefore carried out at the University of Cambridge (UK) on tunnel models in sand, in the framework of a research project funded by the Italian Civil Protection Department. A numerical Round Robin on Tunnel Tests was later promoted among some research groups to predict the observed behaviour by means of numerical modelling. In this paper, the main results of five selected numerical predictions are summarized and compared with the experimental results.     

IUPA: a tool for the evaluation of the general usefulness of practices for adaptation to climate change and variability

A prototype multi-purpose index is proposed for use in the evaluation of practices for adaptation to climate variability and change. The Index of Usefulness of Practices for Adaptation (IUPA) allows the user to assign weights and scores to a set of user-defined evaluation criteria. Individual criterion scores are aggregated into a final index value. Both the final value and the individual parameter scores provide useful information for improved decision making in the context of climate change. An innovative aspect of IUPA is that guidance is given to the user through the inclusion of recommendations on evaluation criteria and criterion-specific weight factors. These have been defined by a panel of experts from the Latin-American and Caribbean Region (LAC). Application of the index is demonstrated for an existing adaptation practice from the Coquimbo Region, Chile. The IUPA tool is recommended for use in the evaluation of adaptation practices in their design, implementation and post-implementation phase. It is practical for a quick first assessment or when limited financial resources are available, making the tool especially useful for practitioners in the developing world. The index is flexible both from the perspective of its construction and use. Additional expert opinions can easily be included in the future versions of the tool.     

Magnetism of natural pyrrhotite,haematite and ilmenite

Summary The paper deals with the magnetic properties of the natural minerals haematite, ilmenite and pyrrhotite. The natural remanent magnetization J_n, the volume susceptibility , the specific magnetization of saturation _so, the Curie temperature , the A.C. demagnetization of natural remanent magnetization, the thermal demagnetization J_n, the temperature dependence of the specific magnetization of saturation, and several other parameters were determined for the individual sets of minerals. Since natural minerals can and do contain various heterogeneous and isomorphic admixtures, their magnetic properties may change depending on the content and type of these admixtures. Therefore, all the investigations of the magnetic properties described in this paper were carried out with extensive sets of minerals, representing various Czechoslovak and world localities. A number of interesting results were obtained from the executed experiments, e.g., the different stability of the natural remanent magnetization of haematite with respect to A.C. demagnetization, the presence and type of heterogeneous inclusions in ilmenite, the phase changes connected with the -transition in natural pyrrhotites, etc. The types of distributions of the investigated values of the magnetic properties were also determined.     

The intensity of the earth's magnetic field in the past derived from the archaeomagnetic data

a n¶rt;u¶rt; amuu amua uuu anmuaum n a n¶rt;u 8500 m nm um au aam m uuu m naama. ¶rt;u u ¶rt;a ¶rt; u ¶rt; m¶rt; mumu auu nau nuu aau mama [1–3] (Puc. 1.B). nma aau auau (Puc.2) mnaua m m m¶rt;a, ¶rt; au n¶rt; amu u, m n¶rt;u 2- ma m, mmu naa auu nu¶rt; n¶rt;a 1000 m u 350 m, au a aumu, mmm 80%- mmu. am au ¶rt;a u anmu ¶rt; m¶rt; mumu (mum) naa auu u¶rt; ma u ¶rt; m naama[5] (Puc. 3). uma a mam nma aaua naaa auu nu¶rt; n¶rt;a 750 m, 200 m u a — 300 m. (Puc. 4.) nmu u ¶rt;a nma amua an¶rt;u n¶rt;u n u ma m (au) auumu m ¶rt;m m (Puc. 5). aa a m¶rt;m nu naamaum n aam ¶rt;uu mu au, anum¶rt;a m uua nm m¶rt;a.

---

---

Dedicated to Academician Alois Zátopek on His 65th Birthday     

Towards a classification of organic enrichment in marine sediments based on biogeochemical indicators

A nomogram is developed to show that pH, redox potentials (Eh_NHE) and measures of dissolved sulfides (H₂S + HS⁻ + S²⁻)(total free S²⁻) can be used to classify organic enrichment impacts in marine sediments. The biogeochemical cycle of sulfur in marine sediments is described to show that changes in macrobenthic infauna community structure associated with high levels of organic matter supply result from stress due to oxygen deficiency (hypoxia and anoxia) and toxic effects of S²⁻. The changes reflect enhancement of microbial sulfate reduction under conditions of high organic matter sedimentation and the progressive formation of hypoxic–anoxic conditions measured by decreased Eh_NHE and increased concentrations of S²⁻. The nomogram provides a basis for classification of the oxic status of marine sediments based on changes in inter-related biological and biogeochemical variables along an organic enrichment gradient.     

Climate induced temperature effects on growth performance, fecundity and recruitment in marine fish: developing a hypothesis for cause and effect relationships in Atlantic cod (Gadus morhua) and common eelpout (Zoarces viviparus)

Effects of global warming on animal distribution and performance become visible in many marine ecosystems. The present study was designed to develop a concept for a cause and effect understanding with respect to temperature changes and to explain ecological findings based on physiological processes. The concept is based on a wide comparison of invertebrate and fish species with a special focus on recent data obtained in two model species of fish. These fish species are both characterized by northern and southern distribution limits in the North Atlantic: eelpout (Zoarces viviparus), as a typical non-migrating inhabitant of the coastal zone and the cod (Gadus morhua), as a typical inhabitant of the continental shelf with a high importance for fisheries.Mathematical modelling demonstrates a clear significant correlation between climate induced temperature fluctuations and the recruitment of cod stocks. Growth performance in cod is optimal at temperatures close to 10°C, regardless of the population investigated in a latitudinal cline. However, temperature specific growth rates decrease at higher latitudes. Also, fecundity is less in White Sea than in North and Baltic Sea cod or eelpout populations. These findings suggest that a cold-induced shift in energy budget occurs which is unfavorable for growth performance and fecundity. Thermal tolerance limits shift depending on latitude and are characterized by oxygen limitation at both low or high temperatures. Oxygen supply to tissues is optimized at low temperature by a shift in hemoglobin isoforms and oxygen binding properties to lower affinities and higher unloading potential. Protective stimulation of heat shock protein synthesis was not observed.According to a recent model of thermal tolerance the downward shift of tolerance limits during cold adaptation is associated with rising mitochondrial densities and, thus, aerobic capacity and performance in the cold, especially in eurythermal species. At the same time the costs of mitochondrial maintenance reflected by mitochondrial proton leakage should rise leaving a lower energy fraction for growth and reproduction. The preliminary conclusion can be drawn that warming will cause a northern shift of distribution limits for both species with a rise in growth performance and fecundity larger than expected from the Q₁₀ effect in the north and lower growth or even extinction of the species in the south. Such a shift may heavily affect fishing activities in the North Sea.