Calculated greenschist facies mineral equilibria in the system CaO−FeO−MgO−Al2O3−SiO2−CO2−H2O

The kinetic problems associated with the experimental determination of reactions among complex solidsolution phases at low temperatures have hindered our understanding of the phase relations in greenschist facies rocks. In the absence of reliable experimental data, we have used the new, expanded internally-consistent thermodynamic dataset of Holland and Powell (1990), to present calculated phase equilibria for the system CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–CO₂ (CaFMASCH) with quartz in eccess, in the range 400°–500°C at low to intermediate pressures, involving the minerals amphibole, chlorite, anorthite, clinozoisite, dolomite, chloritoid, garnet, margarite, andalusite, and calcite. By solving independent sets of non-linear equations formed from equilibrium relationships, we calculate not only the loci of reactions in pressuretemperature-x(CO₂) space, but also the compositions of coexisting minerals in terms of the substitutions, FeMg_-1 and (Fe,Mg)SiAl_-1Al_-1. Invariant, univariant and divariant equilibria are calculated and discussed in relation to naturally-occurring greenschist facies metabasic and siliceous dolomitic mineral assemblages. We thus avoid the use of activity-corrected curves so commonly presented in the literature as a substitute for genuine univariant phase diagram boundaries.     

A time varying AR coefficient model for modelling and simulating earthquake ground motion

A smoothness priors-time varying autoregressive (AR) coefficient model method for the modelling of earthquake ground motion is shown. The method yields the instantaneous smoothed values of the AR coefficients and the instantaneous smoothed values of the innovations variance. These results in turn yield estimates of the instantaneous spectral density, the time varying covariance function and a simulation model for the ground motion data. An example of the application of the method to the analysis of an accelogram from the February 1971 San Fernando, California earthquake is shown.     

Stratigraphic and structural controls on groundwater salinity variations in the Poso Creek Oil Field,Kern County,California, USA

Hydrogeology Journal - Groundwater total dissolved solids (TDS) distribution was mapped with a three-dimensional (3D) model, and it was found that TDS variability is largely controlled by...     

Deep learning for dune pattern mapping with the AW3D30 global surface model

In this paper we present a deep learning (U-Net)-based workflow for classifying linear dune landforms based on the discrete Laplacian convolution of a new global elevation dataset, the AW3D30 digital surface model. Crest vectors were then derived for landscape pattern analysis. The U-Net crest classification model was trained and evaluated on sample data from dunefields across the Australian continent. The resulting crest vectors and dune defect placement were then evaluated in typical semi-arid and arid dune landscapes in eastern central Australia where high-resolution (5 m horizontal) digital elevation models are available (for three out of our four study sites) as a reference dataset. The method was applied to quantify dune pattern metrics for the entire Simpson Desert dunefield, Australia. The U-Net does a very good job of segmenting dune crests, even where dunes are less clear in the Laplacian map (intersection over union score ≈ 0.68). When crest vectors and dune defects (network nodes) were derived, the defect predictions were typically correct (0.4 to 0.79 correctness) but incomplete (0.02 to 0.64 completeness). Much of the residual error was traced to the resolution of the input data. Through the application to the Simpson Desert, we nevertheless demonstrated that our method can effectively be used for regional-scale dune pattern analysis. Furthermore, we suggest that the combination of morphological filtering and a convolutional neural network could readily be adapted to target other geomorphic features, such as channel networks or geological lineaments. © 2020 John Wiley & Sons, Ltd.     

Understanding the spatial distribution and physical attributes of upland swamps in the Sydney Basin as a template for their conservation and management

Temperate Highland Peat Swamps on Sandstone (THPSS) and Coastal Upland Swamps in the Sydney Basin (CUSSB) are listed as endangered ecological communities under Australia's national and state legislation. They are threatened by a range of human and climate impacts. Across the region there are 3208 individual, valley-bottom, elongate-shaped, upland swamps that drain first- or second-order drainage lines and small catchment areas (mean?=?0.25?km²). They occur at a median distance of 57?km from the coast in areas with an average annual rainfall of 1505?mm/year and average annual temperature of 15°C. Those closer to the coast occur on elevations as low as 160?m a.s.l., and those further from the coast, on plateau country, occur up to 1172?m a.s.l. (median 634?m a.s.l.). The valleys that contain these swamps terminate downstream at a valley constriction or bedrock step, behind which alluvial materials have accumulated, and peat has formed to produce relatively steep swamps (median slope 6.2 per cent). Understanding the spatial distribution and physical attributes of these systems, and having the accompanying maps as a resource, is critical for development of sound, well-informed conservation, rehabilitation and monitoring programs, and for analysing the ecosystem services they provide.     

Authorship in IPCC AR5 and its implications for content: climate change and Indigenous populations in WGII

This essay examines the extent to which we can expect Indigenous Knowledge, understanding, and voices on climate change (??Indigenous content??) to be captured in WGII of the IPCC Fifth Assessment Report (AR5), based on an analysis of chapter authorship. Reviewing the publishing history of 309 chapter authors (CAs) to WGII, we document 9 (2.9%) to have published on climate change and Indigenous populations and involved as authors in 6/30 chapters. Drawing upon recent scholarship highlighting how authorship affect structure and content of assessment reports, we argue that, unaddressed, this will affect the extent to which Indigenous content is examined and assessed. While it is too late to alter the structure of AR5, there are opportunities to prioritize the recruitment of contributing authors and reviewers with expertise on Indigenous issues, raise awareness among CAs on the characteristics of impacts, adaptation, and vulnerability faced by Indigenous peoples, and highlight how Indigenous perspectives can help broaden our understanding of climate change and policy interventions.     

Phase relations in the greenschist-blueschist-amphibolite-eclogite facies in the system Na2O-CaO-FeO-MgO-Al2O3-SiO2-H2O (NCFMASH), with application to metamorphic rocks from Samos, Greece

Calculated phase equilibria among the minerals sodic amphibole, calcic amphibole, garnet, chloritoid, talc, chlorite, paragonite, margarite, omphacite, plagioclase, carpholite, zoisite/clinozoisite, lawsonite, pyrophyllite, kyanite, sillimanite, quartz and H₂O are presented for the model system Na₂O-CaO-FeO-MgO-Al₂O₃-SiO₂-H₂O (NCFMASH), which is relevant for many greenschist, blueschist, amphibolite and eclogite facies rocks. Using the activity-composition relationships for multicomponent amphiboles constrained by Will and Powell (1992), equilibria containing coexisting calcic and sodic amphiboles could be determined. The blueschist–greenschist transition reaction in the NCFMASH system, for example, is defined by the univariant reaction sodic amphibole + zoisite = calcic amphibole + chlorite + paragonite + plagioclase (+ quartz + H₂O) occurring between approximately 420 and 450 °C at 9.5 to 10 kbar. The calculated petrogenetic grid is a valuable tool for reconstructing the PT-evolution of metabasic rocks. This is shown for rocks from the island of Samos, Greece. On the basis of mineral and whole rock analyses, PT-pseudosections were calculated and, together with the observed mineral assemblages and reaction textures, are used to reconstruct PT-paths. For rocks from northern Samos, pseudomorphs after lawsonite preserved in garnet, the assemblage sodic amphibole-garnet-paragonite-chlorite-zoisite-quartz and the retrograde appearance of albitic plagioclase and the formation of calcic amphibole around sodic amphibole constrain a clockwise PT-path that reaches its thermal maximum at some 520 °C and 19 kbar. The derived PT-trajectory indicates cooling during exhumation of the rocks and is similar to paths for rocks from the western part of the Attic-Cycladic crystalline complex. Rocks from eastern Samos indicate lower pressures and are probably related to high-pressure rocks from the Menderes Massif in western Turkey. Received: 8 July 1997 / Accepted: 11 February 1998     

An evaluation of the use of renewable energy to pump water in Sacala las Lomas,Guatemala

An evaluation has been conducted to establish if using renewable energy is technically and economically feasible to pump water in Sacala las Lomas, Guatemala. A deep groundwater well has been proposed and a multi-stage pump system is being considered to distribute groundwater to users’ homes. A weather station was erected in Sacala to collect site-specific data. Wind velocity, wind direction, solar insolation, temperature, precipitation, and barometric pressure data were collected over a 1-year study period. The analysis of the data indicated that the potential power generated by a photovoltaic array or wind turbine would be insufficient to economically pump water to the village under current conditions. Although there may be reasons other than economics that make the potential renewable energy applications attractive, the space and maintenance required to install and operate a sufficient off-grid system outweigh the benefits. A grid-intertie system would allow any number of solar panels to be used in the system while still providing the electricity demand using grid-power.