Determination of predevelopment denudation rates of an agricultural watershed (Cayaguás River, Puerto Rico) using in-situ-produced Be in river-borne quartz

Accurate estimates of watershed denudation absent anthropogenic effects are required to develop strategies for mitigating accelerated physical erosion resulting from human activities, to model global geochemical cycles, and to examine interactions among climate, weathering, and uplift. We present a simple approach to estimate predevelopment denudation rates using in-situ-produced cosmogenic ¹⁰Be in fluvial sediments. Denudation processes in an agricultural watershed (Cayaguás River Basin, Puerto Rico) and a matched undisturbed watershed (Icacos River Basin) were compared using ¹⁰Be concentrations in quartz for various size fractions of bed material. The coarse fractions in both watersheds bear the imprint of long subsurface residence times. Fine material from old shallow soils contributes little, however, to the present-day sediment output of the Cayaguás. This confirms the recent and presumably anthropogenic origin of the modern high denudation rate in the Cayaguás Basin and suggests that pre-agricultural erosional conditions were comparable to those of the present-day Icacos.     

Landslide detection and susceptibility mapping using LiDAR and an artificial neural network approach: a case study in the Cuyahoga Valley National Park,Ohio

The purpose of this study was to detect shallow landslides using hillshade maps derived from light detection and ranging (LiDAR)-based digital elevation model (DEM) derivatives. The landslide susceptibility mapping used an artificial neural network (ANN) approach and backpropagation method that was tested in the northern portion of the Cuyahoga Valley National Park (CVNP) located in northeast Ohio. The relationship between landslides and predictor attributes, which describe landform classes using slope, profile and plan curvatures, upslope drainage area, annual solar radiation, and wetness index, was extracted from LiDAR-based DEM using geographic information system (GIS). The approach presented in this paper required a training study area for the development of the susceptibility model and a validation study area to test the model. The results from the validation showed that within the very high susceptibility class, a total of 42.6 % of known landslides that were associated with 1.56 % of total area were correctly predicted. In contrast, the very low susceptibility class that represented 82.68 % of the total area was associated with 1.20 % of known landslides. The results suggest that the majority of the known landslides occur within a small portion of the study area, consistent with field investigation and other studies. Sample probabilistic maps of landslide susceptibility potential and other products from this approach are summarized and presented for visualization to help park officials in effective management and planning.     

New constraints on UHT metamorphism in the Eastern Ghats Province through the application of phase equilibria modelling and in situ geochronology

High Mg–Al granulites from the Sunki locality in the central portion of the Eastern Ghats Province record evidence for the high-temperature peak and retrograde evolution. Peak metamorphic phase assemblages from two samples are garnet + orthopyroxene + quartz + ilmenite + melt and orthopyroxene + spinel + sillimanite + melt, respectively. Isochemical phase diagrams (pseudosections) based on bulk rock compositions calculated in the chemical system Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–Fe₂O₃ (NCKFMASHTO) and Al contents in orthopyroxene indicate peak UHT metamorphic conditions in excess of 960 °C and 9.7 kbar. Microstructures and the presence of cordierite interpreted to record the post-peak evolution show that the rocks underwent decompression and minor cooling from conditions of peak UHT metamorphism to conditions of ~ 900 °C at ~ 7.5 kbar. In situ U–Pb isotope analyses of monazite associated with garnet and cordierite using the Sensitive High Resolution Ion Microprobe (SHRIMP) yield a weighted mean ²⁰⁷Pb/²³⁵U age of ca. 980 Ma, which is interpreted to broadly constrain the timing of high-temperature monazite growth during decompression and melt crystallization at ~ 900–890 °C and 7.5 kbar. However, the range of ²⁰⁷Pb/²³⁵U monazite ages (from ca. 1014 Ma to 959 Ma for one sample and ca. 1043 Ma to 922 Ma for the second sample) suggest protracted monazite growth during the high-temperature retrograde evolution, and possibly diffusive lead loss during slow cooling after decompression. The results of the integrated petrologic and geochronologic approach presented here are inconsistent with a long time gap between peak conditions and the formation of cordierite-bearing assemblages at lower pressure, as proposed in previous studies, but are consistent with a simple evolution of a UHT peak followed by decompression and cooling.     

Investigation of effect of near-fault motions on substandard bridge structures

The objective of this study was to investigate the effects of near-fault ground motions on substandard bridge columns and piers. To accomplish these goals, several large scale reinforced concrete models were constructed and tested on a shake table using near- and far-field ground motion records. Because the input earthquakes for the test models had different characteristics, three different measures were used to evaluate the effect of the input earthquake. These measures are peak shake table acceleration, spectral acceleration at the fundamental period of the test specimens, and the specimen drift ratios. For each measure, force-displacement relationships, strains, curvatures, drift ratios, and visual damage were evaluated. Results showed that regardless of the measure of input or response, the near-fault record generally led to larger strains, curvatures, and drift ratios. Furthermore, residual displacements were small compared to those for columns meeting current seismic code requirements.     

Phase equilibrium and calorimetric study of the transition of MnTiO3 from the ilmenite to the lithium niobate structure and implications for the stability field of perovskite

The phase boundary between MnTiO₃ I (ilmenite structure) and MnTiO₃ II (lithium niobate structure) has been determined by analysis of quench products from reversal experiments in a cubic anvil apparatus at 1073–1673 K and 43–75 kbar using mixtures of MnTiO₃ I and II as starting materials. Tight brackets of the boundary give P(kbar)=121.2−0.045 T(K). Thermodynamic analysis of this boundary gives ΔH^o=5300±1000 J·mol⁻¹, ΔS^o = 1.98 ±1J·K⁻¹· mol⁻¹. The enthalpy of transformation obtained directly by transposed-temperature-drop calorimetry is 8359 ±2575 J·mol⁻¹. Possible topologies of the phase relations among the ilmenite, lithium niobate, and perovskite polymorphs are constrained using the above data and the observed (reversible with hysteresis) transformation of II to III at 298 K and 20–30 kbar (Ross et al. 1989). The observed II–III transition is likely to lie on a metastable extension of the II–III boundary into the ilmenite field. However the reversed I–II boundary, with its negative dP/ dT does represent stable equilibrium between ilmenite and lithium niobate, as opposed to the lithium niobate being a quench product of perovskite. We suggest a topology in which the perovskite occurs stably at low T and high P with a triple point (I, II, III) at or below 1073 K near 70 kbar. The I–II boundary would have a negative P-T slope while the II–III and I–III boundaries would be positive, implying that entropy decreases in the order lithium niobate, ilmenite, perovskite. The inferred positive slope of the ilmenite-perovskite transition in MnTiO₃ is different from the negative slopes in silicates and germanates. These thermochemical parameters are discussed in terms of crystal structure and lattice vibrations.     

Updating the Phase 1 habitat map of Wales, UK, using satellite sensor data

The Phase 1 Survey is the most comprehensive and widely used national level map of semi-natural habitats in Wales. However, the survey was based largely on field survey and was conducted over several decades, before being completed in 1997. Given that resources for a repeat survey were limited, this study has used an object-orientated rule-based classification implemented within eCognition of multi-temporal satellite sensor data acquired between 2003 and 2006 to map semi-natural habitats and agricultural land across Wales, thereby allowing a progressive update of the Phase 1 Survey. The classification of objects to Phase 1 habitat classes was undertaken in two steps; firstly the landscape of Wales was divided into objects using orthorectified SPOT-5 High Resolution Geometric (HRG) reflectance data (10 m spatial resolution) and Land Parcel Information System (LPIS) boundaries. A rule-base was then developed to progressively discriminate and map the distribution of 105 sub-habitats across Wales based on time-series of SPOT HRG, Terra-1 Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Indian Remote Sensing Satellite (IRS) LISS-3 data, derived datasets (e.g., vegetation indices, fractional images) and ancillary information (e.g., topography). The rules coupled knowledge of ecology and the information content of these remote sensing data using a combination of thresholds, Boolean operations and fuzzy membership functions. A second rule-base was then developed to translate the more detailed sub-habitat classification to Phase 1 habitat classes. Indicative accuracies of the revised Phase 1 mapping, based on comparisons with the later Phase 2 survey (for selected habitats), were >80% overall and typically between 70% and 90% for many classes. Through this exercise, Wales has become the first country in Europe to produce a national map of habitats (as opposed to land cover) through object-orientated classification of satellite sensor data. Furthermore, the approach can be adapted to allow continual monitoring of the extent and condition of habitats and agricultural land.     

14C content of ten meteorites measured by tandem accelerator mass spectrometry

¹⁴C has been measured in three North American and seven Antarctic meteorites with the Chalk River MP tandem accelerator. In most cases cosmogenic¹⁴C, which is tightly bound, was separated from absorbed atmospheric radiocarbon by stepwise heating extractions. Terrestrial ages obtained by comparing cosmogenic¹⁴C in the meteorite to that in Bruderheim are (7.2 ± 0.6) × 10³ years for Yamato 7304, (11.6 ± 0.4) × 10³ years for Estacado, and range from (32.7 ± 0.5) × 10³ to (41.0 ± 0.8) × 10³ years for six meteorites recovered at Allan Hills and its vicinity. The present upper limit to age determination by the accelerator method varies from 50 × 10³ to 70 × 10³ years depending upon mass and carbon content of the sample. The natural limit caused by cosmic ray production of¹⁴C in silicate rocks at 2000 m elevation is estimated to be (55 ± 5) × 10³ years. “Weathering ages” were estimated for the Antarctic meteorites from the specific activity of loosely-bound CO₂ considered to be absorbed from the terrestrial atmosphere on weathering. The accelerator measurements are in accordance with previous low-level counting measurements but have higher precision and sensitivity.     

Low temperature,low pressure deformation and metamorphism of the Vangorda massive sulphide orebody,Yukon, Canada

The Vangorda orebody is a small stratiform massive sulphide orebody located in Anvil District, Yukon, Canada. The orebody consists of fineto medium-grained semi-massive and massive sulphides with a common sulphide mineralogy of pyrite, pyrrhotite, sphalerite, galena, and minor chalcopyrite. The host rocks and the sulphide lithofacies have been complexly deformed during two phases of deformation (D₁ and D₂) and associated metamorphism (M₁ and M₂). The effects of d₁ and M₁ are penetratively overprinted by D₂ and M₂. D₂ and M₂ resulted in tight to isoclinal F₂ folding of the orebody, remobilisation of the sulphides, recrystallisation and development of shear zones along the limbs of the F₂ folds. Chlorite thermometry and sulphide thermobarometry have been carried out on the host phyllites and on the sulphides. Chlorite was analysed from the S₁ and S₂ foliations in the phyllites to determine M₁ and M₂ temperatures, respectively. However, no difference was found between chlorite compositions in these foliations and a mean temperature of 363 °C was calculated from the tetrahedral A1_IV occupancy. Arsenopyrite thermometry yielded a comparable mean temperature of 336 °C. Sphalerite inclusions in M₂ pyrite porphyroblasts from D₂ shear zones were analysed for pressure using the sphalerite + hexagonal pyrrhotite + pyrite barometer. Inclusions were analysed in an attempt to determine if relic m₁ sphalerite, and hence pressure signature, was preserved. Inclusion compositions appear to reflect only M₂ conditions and yielded a mean pressure of 4.0 kb. Sphalerite + hexagonal pyrrhotite assemblages were analysed from D₂ shear zones to determine the M₂ pressure using the sphalerite + hexagonal pyrrhotite barometer. These calculations yielded a mean pressure of 6.1 kb. The M₂ temperatures and pressures calculated using these calibrations are in good agreement with those estimated from petrogenetic relationships.