Decoding a protracted zircon geochronological record in ultrahigh temperature granulite,and persistence of partial melting in the crust,Rogaland, Norway

This contribution evaluates the relation between protracted zircon geochronological signal and protracted crustal melting in the course of polyphase high to ultrahigh temperature (UHT; T?>?900 °C) granulite facies metamorphism. New U–Pb, oxygen isotope, trace element, ion imaging and cathodoluminescence (CL) imaging data in zircon are reported from five samples from Rogaland, South Norway. The data reveal that the spread of apparent age captured by zircon, between 1040 and 930 Ma, results both from open-system growth and closed-system post-crystallization disturbance. Post-crystallization disturbance is evidenced by inverse age zoning induced by solid-state recrystallization of metamict cores that received an alpha dose above 35 × 10¹⁷ α  g^?1. Zircon neocrystallization is documented by CL-dark domains displaying O isotope open-system behaviour. In UHT samples, O isotopic ratios are homogenous (δ¹⁸O = 8.91?±?0.08‰), pointing to high-temperature diffusion. Scanning ion imaging of these CL-dark domains did not reveal unsupported radiogenic Pb. The continuous geochronological signal retrieved from the CL-dark zircon in UHT samples is similar to that of monazite for the two recognized metamorphic phases (M1: 1040–990 Ma; M2: 940–930 Ma). A specific zircon-forming event is identified in the orthopyroxene and UHT zone with a probability peak at ca. 975 Ma, lasting until ca. 955 Ma. Coupling U–Pb geochronology and Ti-in-zircon thermometry provides firm evidence of protracted melting lasting up to 110 My (1040–930 Ma) in the UHT zone, 85 My (ca. 1040–955 Ma) in the orthopyroxene zone and some 40 My (ca. 1040–1000 Ma) in the regional basement. These results demonstrate the persistence of melt over long timescales in the crust, punctuated by two UHT incursions.     

Construction,management and maintenance of embankments used for road and rail infrastructure: implications of weather induced pore water pressures

Understanding the age and construction quality of embankments used for road and rail infrastructure is critical in the effective management and maintenance of our transport networks, worth £billions to the UK economy. This paper presents for the first time results from full-scale, carefully controlled experiments on a unique model embankment conducted over the 4-year period between 2008 and 2011. It combines point location and spatially distributed measurements of pore water pressures and water content with outputs from hydrological modelling to draw conclusions of significance to both ongoing research in this field and to the asset management practices of infrastructure owners. For researchers, the paper highlights the crucial importance of transient permeability and soil water retention behaviour of fill materials in controlling the magnitude and distribution of pore water pressure in response to climate and weather events. For practitioners, the work demonstrates that there are significant differences in pore water pressure behaviour across the embankment, which is influenced by construction-related issues such as compaction level, aspect and presence of a granular capping material. Permeability was also observed to vary across the embankment both spatially and with depth, being dependent on degree of saturation and macroscale effects, particularly within a ‘near surface zone’. It is proposed that this ‘near surface zone’ has a critical effect on embankment stability and should be the focus of both ongoing scientific research and inspection and monitoring as encompassed by asset management regimes.     

A global landslide catalog for hazard applications: method,results, and limitations

A systematic inventory of landslide events over the globe is valuable for estimating human and economic losses, quantifying the relationship between landslide occurrences and climate variations and for evaluating emerging global landslide prediction efforts based on remote sensing data. This study compiles a landslide catalog for rainfall-triggered events for several years, drawing upon news reports, scholarly articles, and other hazard databases to provide a landslide catalog at the global scale. While this database may only represent a subset of rainfall-triggered landslides globally, due to lack of reports, it presents a lower boundary on the number of events globally and provides initial insight into the spatiotemporal statistical trends in landslide distribution and impact. This article develops a methodology for landslide event compilation that can be used in evaluating global landslide forecasting initiatives and assessing patterns in landslide distribution and frequency worldwide.     

Resolving the source and mixing proportions of modern leakage to the Memphis aquifer in a municipal well field using geochemical and 3H/3He data, Memphis, Tennessee, USA

The Memphis aquifer in southwestern Tennessee is a confined to semi-confined unconsolidated sand aquifer and is the primary municipal water source for the Memphis metropolitan area. Leakage of modern water from shallow unconfined aquifers through the upper Claiborne confining unit locally degrades water quality in the Memphis aquifer and makes the aquifer more vulnerable to contamination. Major solute chemistry, tritium, and ³H/³He data were used to investigate the source and mixing proportions of modern water in the Memphis aquifer in the Davis well field, Memphis, Tennessee. Water quality in several production wells in the Davis well field has declined over the past 30 years, mainly through increased total dissolved solids, iron, alkalinity, and hardness. Trends in chemical data, tritium, and other hydrogeologic data support a source for the leakage from the Mississippi River Valley Alluvial aquifer. Mixing proportions of alluvial water in production well water obtained by inverse chemical modeling with PHREEQCi range from 7 to 45%. For two of the production wells, MLGW 414 and 432, ³H/³He data yield mixing ratios similar to those obtained from PHREEQCi in three of four cases; the dissimilar ratio is likely due to a poor solution from the PHREEQCi inverse modeling. Modeling of the age distribution obtained from MLGW 414 and 432 using an exponential-piston flow model (EPM) with an inverse solution computer code yielded mixed results. The EPM solution obtained for MLGW 414 converged with difficulty only for a 5-year transit time in the shallow aquifer and is consistent with a source from the Mississippi River Valley Alluvial aquifer; however, the modeled age of the water is greater than that observed. In comparison, the EPM solution for MLGW 432 converged for the 5- and 7-year transit periods in the shallow aquifer and yielded model ages consistent with observed ³H/³He ages; however, the extent of the maximum radii for infiltration source is not consistent with a Mississippi River Valley Alluvial aquifer source. Other potential sources for leakage to MLGW 432 include water from the Fluvial-terrace aquifer migrating along a fault east of the well field or infiltration of water from a lake south of the well field.     

Polyorogenic reworking of ore‐controlling shear zones at the South Range of the Sudbury impact structure: A telltale story from in situ U–Pb titanite geochronology

The post‐impact orogenic evolution of the world class Ni–Cu–PGE Sudbury mining camp in Ontario remains poorly understood. New temporal constraints from ore‐controlling, epidote–amphibolite facies shear zones in the heavily mineralised Creighton Mine (Sudbury, South Range) illuminate the complex orogenic history of the Sudbury structure. In situ U–Pb dating of shear‐hosted titanite grains by LA‐ICP‐MS reveals new evidence for shear zone reworking during the Yavapai (ca. 1.77–1.7 Ga), Mazatzalian–Labradorian (1.7–1.6 Ga) and Chieflakian–Pinwarian (1.5–1.4 Ga) accretionary events. The new age data show that the effects of the Penokean orogeny (1.9–1.8 Ga) on the structural architecture of the Sudbury structure have been overestimated. At a regional scale, the new titanite age populations corroborate that the Southern Province of the Canadian Shield documents the same tectonothermal episodes that are recorded along orogenic strike within the accretionary provinces of the Southwestern United States.     

The global martian volcanic evolutionary history

Viking mission image data revealed the total spatial extent of preserved volcanic surface on Mars. One of the dominating surface expressions is Olympus Mons and the surrounding volcanic province Tharsis. Earlier studies of the global volcanic sequence of events based on stratigraphic relationships and crater count statistics were limited to the image resolution of the Viking orbiter camera. Here, a global investigation based on high-resolution image data gathered by the High-Resolution Stereo Camera (HRSC) during the first years of Mars Express orbiting around Mars is presented. Additionally, Mars Orbiter Camera (MOC) and Thermal Emission Imaging System (THEMIS) images were used for more detailed and complementary information. The results reveal global volcanism during the Noachian period (>3.7 Ga) followed by more focused vent volcanism in three (Tharsis, Elysium, and Circum-Hellas) and later two (Tharsis and Elysium) volcanic provinces. Finally, the volcanic activity became localized to the Tharsis region (about 1.6 Ga ago), where volcanism was active until very recently (200-100 Ma). These age results were expected from radiometric dating of martian meteorites but now verified for extended geological units, mainly found in the Tharsis Montes surroundings, showing prolonged volcanism for more than 3.5 billions years. The volcanic activity on Mars appears episodic, but decaying in intensity and localizing in space. The spatial and temporal extent of martian volcanism based on crater count statistics now provides a much better database for modelling the thermodynamic evolution of Mars.     

The shape of Fraught – urban – rural – the nation-state: tensions and dynamics

I argue that the tension between cities and nation states go through the countryside, or rural areas, at least in the U.S. Further, cities are decidedly constrained in their abilities to effectuate many of the changes associated with them: addressing climate change, economic inequality and more. What is missing is the way in which rural alienation from economic prosperity plays out politically.     

A Review of “Urban Climate Change Crossroads”

This article examines the former location-based social medium Brightkite, over its three-year life span, based on the concept of natural cities. The term natural cities refers to spatially clustered geographic events, such as the agglomerated patches aggregated from individual social media users’ locations. We applied the head/tail division rule to derive natural cities, based on the fact that there are far more low-density areas than high-density areas on the Earth's surface. More specifically, we generated a triangulated irregular network, made up of individual unique user locations, and then categorized small triangles (smaller than an average) as natural cities for the United States (mainland) on a monthly basis. The concept of natural cities provides a powerful means to develop new insights into the evolution of real cities, because there are virtually no data available to track the history of cities across their entire life spans and at very fine spatial and temporal scales. Therefore, natural cities can act as a good proxy of real cities, in the sense of understanding underlying interactions, at a global level, rather than of predicting cities, at an individual level. Apart from the data produced and the contributed methods, we established new insights into the structure and dynamics of natural cities; for example, the idea that natural cities evolve in nonlinear manners at both spatial and temporal dimensions.     

The Kuroshio Extension and its recirculation gyres

This paper reports on the strength and structure of the Kuroshio Extension and its recirculation gyres. In the time average, quasi-permanent recirculation gyres are found to the north and south of the Kuroshio Extension jet. The characteristics of these recirculations gyres are determined from the combined observations from the Kuroshio Extension System Study (KESS) field program (June 2004–June 2006) and include current meters, pressure and current recording inverted echo sounders, and subsurface floats. The position and strength of the recirculation gyres simulated by a high-resolution numerical model are found to be consistent with the observations. The circulation pattern that is revealed is of a complex system of multiple recirculation gyres that are embedded in the crests and troughs of the quasi-permanent meanders of the Kuroshio Extension. At the location of the KESS array, the Kuroshio Extension jet and its recirculation gyres transport of about 114 Sv. This represents a 2.7-fold increase in the transport of the current compared to the Kuroshio's transport at Cape Ashizuri before it separates from the coast and flows eastward into the open ocean. This enhancement in the current's transport comes from the development of the flanking recirculation gyres. Estimates from an array of inverted echo sounders and a high-resolution ocean general circulation model are of similar magnitude.