Evaluating the effect of the global ionospheric map on aiding retrieval of radio occultation electron density profiles

Radio occultation (RO) has been proven to be a powerful technique for ionospheric electron density profile (EDP) retrieval. The Abel inversion currently used in RO EDP retrieval has degraded performance in regions with large horizontal gradients because of an assumption of spherical symmetry as indicated by many studies. Some alternative methods have been proposed in the past; the global ionospheric map (GIM)-aided Abel inversion is most frequently studied. Since the number of RO observations will likely increase rapidly in the near future, it is worthwhile to continue to improve retrieval method. In this study, both the simulations and the real data test have been done to evaluate the GIM-aided Abel inversion method. It is found that the GIM-aided Abel inversion can significantly improve upon the standard Abel inversion in either the F or the E region if an accurate GIM is available. However, the current IGS GIM does not appear accurate enough to improve retrieval results significantly, because of the spherical symmetry assumption and sparse global navigation satellite system (GNSS) stations used in its creation. Generating accurate GIM based on dense GNSS network to aid the Abel inversion might be an alternative method.     

Significance of ancient sulfide PGE and Re–Os signatures in the mantle beneath Calatrava,Central Spain

Spinel lherzolite and wehrlite xenoliths from the Cenozoic Calatrava volcanic field carry the geochemical imprint of metasomatic agents that have affected the subcontinental lithospheric mantle beneath Central Iberia. Some xenoliths (mainly wehrlites) were enriched in REE, Sr, P, and CO₂ by silicic-carbonate-rich metasomatic melts/fluids, while others record the effects of subduction-related hydrous silicate fluids that have precipitated amphibole and induced high Ti/Eu in primary clinopyroxene. The petrographic observations and geochemical data suggest that interstitial glass in the xenoliths represent the quenched products of Si-rich melts that infiltrated the mantle peridotite shortly before the entrainment of the xenoliths in the host magmas that erupted ca 2 million years ago. During their infiltration, the metasomatic melts reacted with peridotite, resulting in silica enrichment, while remobilizing grains of iron-rich monosulfide solid solution (Fe-rich Mss) initially enclosed in, or intergranular to, primary olivine and pyroxenes. In situ laser ablation inductively coupled plasma-mass spectrometry analysis of single sulfide grains reveals that the Fe-rich Mss in glass shows platinum-group element (PGE) patterns and ¹⁸⁷Os/¹⁸⁸Os compositions identical to the Fe-rich Mss occurring as inclusions in, or at grain boundaries of primary silicates. Moreover, independent of its microstructural position, Fe-rich Mss exhibits PGE and ¹⁸⁷Os/¹⁸⁸Os signatures typical of Mss either residual after partial melting or crystallized directly from sulfide melts. Our findings reveal that young metasomatic melt(s)/fluid(s) may carry remobilized sulfides with PGE and Os-isotopic signatures identical to those of texturally older sulfides in the peridotite xenolith. These sulfides thus still provide useful information about the timing and nature of older magmatic events in the subcontinental mantle.     

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.     

Electronic environments in carrollite, CuCo2S4, determined by soft X-ray photoelectron and absorption spectroscopy

Fracture surfaces of a natural carrollite specimen have been characterised by synchrotron and conventional X-ray photoelectron spectroscopy and near-edge X-ray absorption spectroscopy. For the synchrotron X-ray measurements, the mineral surfaces were prepared under clean ultra high vacuum and were unoxidised. The characterisation was undertaken primarily to establish unequivocally the oxidation state of the Cu in the mineral, but also to obtain information on the electronic environments of the Co and S, and on the surface species. Experimental and simulated Cu L_2,3-edge absorption spectra confirmed an oxidation state of Cu^I, while Co 2p photoelectron and Co L_2,3 absorption spectra were largely consistent with the Co^III established previously by nuclear magnetic resonance spectroscopy. S 2p photoelectron spectra provided no evidence for S to be present in the bulk in more than one state, and were consistent with an oxidation state slightly less negative than S^-II. Therefore it was concluded that carrollite can be best represented by Cu^ICo^III₂(S₄)^-VII. The Cu^I oxidation state is in agreement with that expected for Cu tetrahedrally coordinated by S, but is in disagreement with the Cu^II deduced previously from some magnetic, magnetic resonance and Cu L-edge X-ray absorption spectroscopic measurements. A significant concentration of S species with core electron binding energies both lower and higher than the bulk value were formed at fracture surfaces, and these entities were assigned to monomeric and oligomeric surface S species. The density of Cu d states calculated for carrollite differed from that previously reported but was consistent with the observed Cu L₃ X-ray absorption spectrum. The initial oxidation of carrollite in air under ambient conditions was confirmed to be congruent, unlike the incongruent reaction undergone by a number of non-thiospinel sulfide minerals.     

Middle Weichselian environments on western Yamal Peninsula, Kara Sea based on pollen records

Pollen data from two sections from a coastal cliff on the western Yamal Peninsula (69°43.27′N, 66°48.80′E) document the environmental history during the Karginsky (Middle Weichselian) interstadial. Low pollen concentrations, high amounts of redeposited pollen, and relatively high presence of Artemisia pollen characterize sediments deposited at about 33,000 ¹⁴C yr B.P. Grass-sedge plant associations with few other herbs occupied the area during the late Karginsky interstadial. Artemisia pollen may indicate rather xerophytic vegetation and disturbed soils in the area. The dominance of redeposited pollen reflects scarce (disturbed) vegetation cover and low pollen productivity. The climate was relatively cold and dry. Sediments dated to 32,400 ¹⁴C yr B.P. contain fewer redeposited pollen and concentration of non-redeposited pollen is significantly higher. Pollen contents indicate the dominance of tundra-like grass-sedge vegetation and more humid conditions. Pollen records dated between 30,100 and 25,100 ¹⁴C yr B.P. also reflect scarce tundra-like vegetation during this interval. The presence of Betula nana and Salix pollen may reflect limited presence of shrub communities. This suggests that the climate was somewhat warmer during the latter part of the interstadial. However, generally the pollen records show that harsh environmental conditions prevailed on the Yamal Peninsula during the Karginsky interstadial.     

The Proterozoic evolution of northern Siberian Craton margin: a comparison of U–Pb–Hf signatures from sedimentary units of the Taimyr orogenic belt and the Siberian platform

Identifying the cratonic affinity of Neoproterozoic crust that surrounds the northern margin of the Siberian Craton (SC) is critical for determining its tectonic evolution and placing the Craton in Neoproterozoic supercontinental reconstructions. Integration of new U–Pb–Hf detrital zircon data with regional geological constraints indicates that distinct Neoproterozoic arc-related magmatic belts can be identified within the Taimyr orogen. Sedimentary rocks derived from 970 to 800 Ma arc-related suites reveal abundant Archean and Paleoproterozoic detritus, characteristic of the SC. The 720–600 Ma arc-related zircon population from the younger Cambrian sedimentary rocks is also complemented by an exotic juvenile Mesoproterozoic zircon population and erosional products of older arc-related suites. Nonetheless, numerous evidences imply that both arcs broadly reworked Siberian basement components. We suggest that the early Neoproterozoic (ca. 970–800 Ma) arc system of the Taimyr orogen evolved on the active margin of the SC and probably extended along the periphery of Rodinia into Valhalla orogen of NE Laurentia. We also suggest the late Neoproterozoic (750–550 Ma) arc system could have been part of the Timanian orogen, which linked Siberia and Baltica at the Precambrian/Phanerozoic transition.     

Probabilistic seismic hazard assessment for some parts of the Indo-Gangetic plains,India

Natural Hazards - Indo-Gangetic plains are seismically most vulnerable due to the proximity of adjacent great Himalayan earthquakes and thick alluvium deposits of the Ganga River system. As the...     

Ground Movement and Strains from Airphoto Measurements in Avonside Caused by 2010 Darfield Earthquake

In this work ground failure following the 2010 Darfield earthquake in Canterbury, NZ was studied. Lateral spreading and horizontal ground strains were analyzed in an area near the Central Business District of Christchurch city. The Avon river runs through the middle of the study area and includes natural, filled and artificially cut stream bed stretches. Lateral displacement vectors from photogrammetric data were interpolated and used to produce ground strains. Large compressive and tensile strains were identified. Natural point bars were found to correlate closely with tensile strains. Natural stream bed (filled and existing) was found to closely correlate with compressive strains. Vector magnitude values of lateral displacements were found to correlate with water supply pipe repair rates (R² = 0.42). However, ground strains did not correlate with lateral displacements, water supply pipe repair rates or settlements from the photogrammetric data. Therefore, it may be concluded that ground strains have limited use in the indication of potential repair rates and do not directly predict settlement. However, ground strains were observed as useful in identifying paleo-geomorphology of the area in general and changing soil density profiles in particular.     

Magmatic and hydrothermal inclusions in carbonatite of the Magnet Cove Complex,Arkansas

The carbonatite at Magnet Cove, Arkansas, USA contains a great variety and abundance of magmatic and hydrothermal inclusions that provide an informative, though fragmentary, record of the original carbonatite melt and of late hydrothermal solutions which permeated the complex in postmagmatic time. These inclusions were studied by optical and scanning electron microscopy. Primary magmatic inclusions in monticellite indicate that the original carbonatite melt contained approximately 49.7 wt% CaO, 16.7% CO₂, 15.7% SiO₂, 11.4% H₂O, 4.4% FeO+Fe₂O₃, 1.1% P₂O₅ and 1.0% MgO. The melt was richer in SiO₂ and iron oxides than the carbonatite as now exposed; this is attributed to crystal settling and relative enrichment of calcite at shallower levels. The density of the carbonatite melt as revealed by the magmatic inclusions was approximately 2.2–2.3 g/cc. Such a light melt should separate rapidly from any denser parent material and could be driven forcibly into overlying crustal rocks by buoyant forces alone. Fluid inclusions in apatite suggest that a separate (immiscible) phase composed of supercritical CO₂ fluid of low density coexisted with the carbonatite magma, but the inclusion record in this mineral is inconclusive with respect to the nature of any other coexisting fluids. Maximum total pressure during CO₂ entrapment was about 450 bars, suggesting depths of 1.5 km or less for apatite crystallization and supporting earlier proposals of a shallow, subvolcanic setting for the complex. Numerous secondary inclusions in the Magnet Cove calcite contain an intriguing variety of daughter minerals including some 19 alkali, alkaline earth and rare earth carbonates, sulfates and chlorides few of which are known as macroscopic phases in the complex. The exotic fluids from which the daughter minerals formed are inferred to have cooled and diluted through time by progressive mixing with local groundwaters. These fluids may be responsible for certain late veins and elemental enrichments associated with the complex.