Origin, timing, and temperature of secondary calcite-silica mineral formation at Yucca Mountain, Nevada

The origin of secondary calcite-silica minerals in primary and secondary porosity of the host Miocene tuffs at Yucca Mountain has been hotly debated during the last decade. Proponents of a high-level nuclear waste repository beneath Yucca Mountain have interpreted the secondary minerals to have formed from cool, descending meteoric fluids in the vadose zone; critics, citing the presence of two-phase fluid inclusions, argued that the minerals could only have formed in the phreatic zone from ascending hydrothermal fluids. Understanding the origin, temperature, and timing of these minerals is critical in characterizing geologically recent fluid flux at the site, and has significant implications to whether waste should be stored at Yucca Mountain.Petrographic and paragenetic studies of 155 samples collected from the Exploratory Studies Facility (ESF) and repository block cross drift (ECRB) tunnels indicate that heterogeneously distributed calcite with lesser chalcedony, quartz, opal, and fluorite comprise the oldest secondary minerals. These are typically overgrown by intermediate-aged calcite, often exhibiting distinctive bladed habits. The youngest event recorded across the site is the deposition of Mg-enriched (up to ∼1 wt%) and depleted, growth-zoned calcite intergrown with U-enriched opal. The cyclical variation in Mg enrichment and depletion is probably related to climate changes that have occurred during the last few million years. The distribution of secondary minerals is consistent with precipitation in the vadose zone.Fluid inclusion petrography of sections from the 155 samples determined that 96% of the fluid inclusion assemblages (FIAs) contained liquid-only inclusions that formed at ambient temperatures (<35°C). However, 50% of the samples (n = 78) contained relatively rare FIA that contain both liquid-only and liquid plus vapor inclusions (herein termed two-phase FIAs) that formed at temperatures above 35°C. Virtually all of these two-phase FIAs occur in paragenetically old calcite; rare two-phase inclusion assemblages were also observed in early fluorite and quartz, and early-intermediate calcite. Homogenization temperatures (≡ trapping temperatures) across Yucca Mountain are generally 45 to 60°C, but higher temperatures reaching 83°C were recorded in calcite from the north portal and ramp of the ESF. Cooler temperatures of ∼35 to 45°C were recorded in the intensely fractured zone. Multiple populations of two-phase FIAs from lithophysal cavities in the ESF and ECRB cross drift indicate early fluid cooling with time from temperatures >45°C in early calcite, to <35 to 45°C in paragenetically younger calcite. Freezing point depressions range from −0.2 to −1.6°C, indicating trapping of a low salinity fluid. The majority of intermediate calcite and all outermost Mg-enriched calcite contains rare all-liquid inclusions and formed from ambient temperature (<35°C) fluids.Carbon and oxygen isotope data reveal a consistent trend of decreasing δ¹³C (from 9.5 to −8.5‰) and increasing δ¹⁸O (from 5.2 to 22.1‰) values from paragenetically early calcite to Mg-enriched growth-zoned calcite. Depleted δD values (−131 to −90‰) of inclusion fluids from intermediate and the youngest Mg-enriched calcite indicate derivation from surface meteoric fluids. Recalculation of δ¹⁸O_H2O values of −12 to −10‰ is consistent with derivation from paleometeoric fluids.Results of integrated U-Pb dating (opal and chalcedony) and fluid inclusion microthermometry indicate that two-phase FIAs that trapped fluids of >50°C are older than 6.29 ± 0.30 Ma. Two-phase FIAs in paragenetically later calcite, which formed from fluids of 35 to 45°C, are older than 5.32 ± 0.02 Ma. There is no evidence for trapping of fluids with elevated temperatures during the past 5.32 my. The youngest Mg-enriched calcite intergrown with opal began to precipitate between about 1.9 to 2.9 Ma and has continued to precipitate within the past half million years. The presence of liquid-only inclusions and the consistent occurrence of Mg-enriched calcite and opal as the youngest event indicate a minor, but chemically distinct, ambient temperature (<35°C) fluid flux during the past 2 to 3 my.     

The July 2007 rock and ice avalanches at Mount Steele, St. Elias Mountains, Yukon, Canada

A large rock and ice avalanche occurred on the north face of Mount Steele, southwest Yukon Territory, Canada, on July 24, 2007. In the days and weeks preceding the landslide, several smaller avalanches initiated from the same slope. The ice and rock debris traveled a maximum horizontal distance 5.76 km with a maximum vertical descent of 2,160 m, leaving a deposit 3.66 km² in area on Steele Glacier. The seismic magnitude estimated from long-period surface waves (M _s) is 5.2. Modeling of the waveforms suggests an estimated duration of approximately 100 s and an average velocity of between 35 and 65 m/s. This landslide is one of 18 large rock avalanches known to have occurred since 1899 on slopes adjacent to glaciers in western Canada. We describe the setting, reconstruct the event chronology and present a preliminary characterization of the Mount Steele ice and rock avalanches based on field reconnaissance, analysis of seismic records and an airborne LiDAR survey. We also present the results of a successful dynamic simulation for the July 24 event.     

Appropriate Uses and Practical Limitations of 2D Numerical Analysis of Tunnels and Tunnel Support Response

In spite of the gradual development of three-dimensional analysis packages utilizing finite element models or finite difference algorithms for stress–strain calculations, two-dimensional (2D) analysis is still used as the primary engineering tool for practical analysis of tunnel behavior and tunnel support performance for design—particularly at the preliminary stage of a project. The applicability of 2D finite element analysis or analytical convergence confinement solutions to staged support installation depend on the application of an assumed or validated longitudinal displacement profile. Convergence in commonly applied 2D staged models is controlled by boundary displacement or internal pressure relaxation. While there have been developments to improve this methodology, this often assumes independence between the ground reaction curve and the support resistance, independence between the longitudinal displacement profile to support application, and the assumption that non-isotropic stresses and non-circular geometries can be handled in the same way as circular tunnels in isotropic conditions. This paper examines the validity of these assumptions and the error inherent in these extensions to 2D tunnel analysis. Anisotropic stresses and lagged (staged) excavation present a particular problem. Practical solutions are proposed for support longitudinal displacement LDPs in simplified conditions.     

Fred’s Flow (Canada) and Murphy Well (Australia): thick komatiitic lava flows with contrasting compositions,emplacement mechanisms and water contents

Two Archaean komatiitic flows, Fred’s Flow in Canada and the Murphy Well Flow in Australia, have similar thicknesses (120 and 160 m) but very different compositions and internal structures. Their contrasting differentiation profiles are keys to determine the cooling and crystallization mechanisms that operated during the eruption of Archaean ultramafic lavas. Fred’s Flow is the type example of a thick komatiitic basalt flow. It is strongly differentiated and consists of a succession of layers with contrasting textures and compositions. The layering is readily explained by the accumulation of olivine and pyroxene in a lower cumulate layer and by evolution of the liquid composition during downward growth of spinifex-textured rocks within the upper crust. The magmas that erupted to form Fred’s Flow had variable compositions, ranging from 12 to 20 wt% MgO, and phenocryst contents from 0 to 20 vol%. The flow was emplaced by two pulses. A first ~20-m-thick pulse was followed by another more voluminous but less magnesian pulse that inflated the flow to its present 120 m thickness. Following the second pulse, the flow crystallized in a closed system and differentiated into cumulates containing 30–38 wt% MgO and a residual gabbroic layer with only 6 wt% MgO. The Murphy Well Flow, in contrast, has a remarkably uniform composition throughout. It comprises a 20-m-thick upper layer of fine-grained dendritic olivine and 2–5 vol% amygdales, a 110–120 m intermediate layer of olivine porphyry and a 20–30 m basal layer of olivine orthocumulate. Throughout the flow, MgO contents vary little, from only 30 to 33 wt%, except for the slightly more magnesian basal layer (38–40 wt%). The uniform composition of the flow and dendritic olivine habits in the upper 20 m point to rapid cooling of a highly magnesian liquid with a composition like that of the bulk of the flow. Under equilibrium conditions, this liquid should have crystallized olivine with the composition Fo94.9, but the most magnesian composition measured by electron microprobe in samples from the flow is Fo92.9. To explain these features, we propose that the parental liquid contained around 32 wt% MgO and 3 wt% H₂O. This liquid degassed during the eruption, creating a supercooled liquid that solidified quickly and crystallized olivine with non-equilibrium textures and compositions.     

Noble gas and isotope geochemistry in western Canadian Arctic watersheds: tracing groundwater recharge in permafrost terrain

In Canada’s western Arctic, perennial discharge from permafrost watersheds is the surface manifestation of active groundwater flow systems with features including the occurrence of year-round open water and the formation of icings, yet understanding the mechanisms of groundwater recharge and flow in periglacial environments remains enigmatic. Stable isotopes (δ¹⁸O, δD, δ¹³C_DIC), and noble gases have proved useful to study groundwater recharge and flow of groundwater which discharges along rivers in Canada’s western Arctic. In these studies of six catchments, groundwater recharge was determined to be a mix of snowmelt and precipitation. All systems investigated show that groundwater has recharged through organic soils with elevated P_CO2, which suggests that recharge occurs largely during summer when biological activity is high. Noble gas concentrations show that the recharge temperature was between 0 and 5 °C, which when considered in the context of discharge temperatures, suggests that there is no significant imbalance of energy flux into the subsurface. Groundwater circulation times were found to be up to 31 years for non-thermal waters using the ³?H-³He method.     

Earthquakes in Switzerland and surrounding regions during 2010

This report of the Swiss Seismological Service summarizes the seismic activity in Switzerland and surrounding regions during 2010. During this period, 407 earthquakes and 85 quarry blasts were detected and located in the region under consideration. With a total of only 19 events with M_L ≥ 2.5, the seismic activity in the year 2010 was below the average over the previous 35 years. The two most noteworthy earthquakes were the M_L 3.4 Barrhorn event near Sankt Niklaus (VS) and the M_L 3.0 event of Feldkirch, both of which produced shaking of intensity IV.     

Systemic geopolitical modeling. Part 2: subjectivity in prediction of geopolitical events

This paper studies subjective priorities for the data amounts in the processing of geopolitical data accoding to Mazis I. Th., theoretical paradigm of Systemic Geopolitical Analysis. After defining geopolitical plans and geopolitical focus sets, they are introduced geopolitical preferences and geopolitical management capacities. The geopolitical rational choice is studied, as well as the geopolitical preference-capacity distributions. Then, they are investigated geopolitical contrasts of subjective priorities by several geopolitical operators, and it is shown that there are cores and equilibriums of geopolitical contrasts, the study of which may provide useful information.     

The Relationship between Wellbeing and Indigenous Land,Language and Culture in Australia

A consistent finding in the literature on Indigenous peoples is the importance of the sustainability of land, language and culture. All three are related, with the maintenance of one helping to protect the others. This paper uses a nationally representative, cross-sectional survey of the Indigenous Australian population to look at the factors associated with individual measures of sustainability. Geography matters for those in remote areas who are much more likely to have participated in hunting, fishing and gathering than those in non-remote areas and somewhat more likely to be learning an Indigenous language. However, those in remote areas are somewhat less likely to have participated in Indigenous cultural production. Participation in the mainstream economy is not necessarily a barrier to these aspects of wellbeing as those with high levels of formal education were more likely to speak, understand or be learning an Indigenous language. While important in their own right, such aspects of sustainability also have the potential to directly contribute to narrower measures of social and emotional wellbeing. A positive relationship was found between the sustainability of Indigenous land, language and culture and an Indigenous person's subjective emotional wellbeing.     

An individual-component approximation to quadratic stress for flow-decomposition analysis

An individual-component approximation (ICA) to the one-dimensional quadratic stress is presented for analysis of hydrodynamic systems that contain multiple-frequency fluid motion such as tidal current and nearshore currents. Criteria governing development of the approximation are accuracy, symmetry, and preservation of contributions (magnitude and direction) of individual and coupled velocity components. Preservation of directionality is required to isolate functioning of individual terms for flow-decomposition analysis. The ICA is compared with the small-amplitude approximation analytically and through numerical examination for two velocity components. The two approximations differ at second order within the range of validity of the small-amplitude approximation. The ICA is exact in the limits of components with large magnitudes and components of equal magnitudes. Based on calculations comparing the exact numerical solution for velocity components with a wide range of relative magnitudes, relative periods, and phase differences, the ICA is accurate except in restricted regions of small-magnitude quadratic velocity. The ICA is generalized to multiple components without restriction on magnitude, period, or phase, and example calculations are given for flows comprised of three components and six components. The method is applied to velocity tidal constituents for Galveston Bay, Texas, and Tampa Bay, Florida.     

The marine prochlorophyte Prochlorococcus contributes significantly to phytoplankton biomass and primary production in the Sargasso Sea

The newly-discovered prochlorophyte Prochlorococcus marinus is often numerically dominant in the euphotic zone of the tropical and subtropical ocean; however, its contribution to phytoplankton biomass and primary production is largely unknown. Using its unique pigment divinyl-chlorophyll a (Chl a₂) as a chemosystematic marker, we show that Prochlorococcus is present at a station in the Sargasso Sea throughout most of the year. Whereas it is only found at depth during the early summer, it can be found throughout the euphotic zone during the rest of the year. Averaged over the year Prochlorococcus pigment-biomass constitutes about 30% of the total. Its growth rate, estimated from the incorporation of ¹⁴C into Chl a₂ ranged from values of 0.3 day⁻¹ in the surface layer to values less than 0.1 day⁻¹ at the bottom of the euphotic zone. Averaged over the seasons, approximately 25% of the total productivity was due to Prochlorococcus. Prochlorococcus clearly is an important component of the ecosystem in the Sargasso Sea, and perhaps the world ocean.