Mapping ambivalence: Exploring the geographies of community change and rails-to-trails development using photo-based Q method and PPGIS

As the literature on trail development suggests, recreational trail projects can generate conflicts and controversies, particularly when built on abandoned rail corridors through developed areas. These conflicts are often understood as “not in my back yard” (NIMBY) reactions, suggesting a spatial proximity to conflict which increases as one draws closer to the proposed trail. This research seeks to understand local residents’ perceptions and reactions to recreational trail development in the City of Delaware (Ohio, USA). It addresses two spatially infused questions: Does the potential for conflict related to trail development increase as people live closer to a potential trail (the NIMBY factor)? Can important qualitative factors about favorable and unfavorable land uses including potential recreational trail sites be defined using a participatory methodology and then represented in GIS? The study used a mixed-method approach to collect and analyze qualitative data from a group of local residents. Each participant was interviewed and asked to sort 19 pictures related to trail development. After each of the sorts, participants were asked to explain why they ranked the pictures the way they did. Results of the picture sorts were then analyzed using Q method and mapped with GIS. The results show that spatial proximity matters in the context of trail development and potential NIMBY reactions to trails. Significant differences were found in the picture sorts that reveal the importance of proximity and location, although in a manner contrary to the assumptions in the writings on rails-to-trails. Through combining qualitative methods, Q analysis and PPGIS analysis, the research shows that qualitative place-based studies are capable of generating insights about the complexities of situated geographic change such as recreational trail development.     

Origin of Fe-Ti Oxide Ores in Mafic Intrusions: Evidence from the Panzhihua Intrusion, SW China

Economic concentrations of Fe–Ti oxides occur as massive,conformable lenses or layers in the lower part of the Panzhihuaintrusion, Emeishan Large Igneous Province, SW China. Mineralchemistry, textures and QUILF equilibria indicate that oxidesin rocks of the intrusion were subjected to extensive subsolidusre-equilibration and exsolution. The primary oxide, reconstructedfrom compositions of titanomagnetite in the ores and associatedintergrowths, is an aluminous titanomagnetite (Usp₄₀) with 40wt % FeO, 34 wt % Fe₂O₃, 16·5 wt % TiO₂, 5·3 wt% Al₂O₃, 3·5 wt % MgO and 0·5 wt % MnO. This compositionis similar to the bulk composition of the oxide ore, as inferredfrom whole-rock data. This similarity strongly suggests thatthe ores formed from accumulation of titanomagnetite crystals,not from immiscible oxide melt as proposed in earlier studies.The occurrence of oxide ores in the lower parts of the Panzhihuaintrusion is best explained by settling and sorting of densetitanomagnetite in the ferrogabbroic parental magma. This magmamust have crystallized Fe–Ti oxides relatively early andabundantly, and is likely to have been enriched in Fe and Tibut poor in SiO₂. These features are consistent with fractionationof mantle-derived melts under relatively high pressures (10kbar), followed by emplacement of the residual magma at 5 kbar.This study provides definitive field and geochemical evidencethat Fe–Ti oxide ores can form by accumulation in ferrogabbro.We suggest that many other massive Fe–Ti oxide depositsmay have formed in a similar fashion and that high concentrationsof phosphorus or carbon, or periodic fluctuation of fO₂ in themagma, are of secondary importance in ore formation. KEY WORDS: ELIP; Fe–Ti oxide ore; layered intrusion; Panzhihua; QUILF     

Trace Element Partitioning and Accessory Phase Saturation during H2O-Saturated Melting of Basalt with Implications for Subduction Zone Chemical Fluxes

Experimental phase equilibrium and trace element partitioningdata are reported for H₂O-saturated mid-ocean ridge basalt at2·5 GPa, 750–900°C and oxygen fugacities atthe nickel–nickel oxide buffer. Garnet, omphacite andrutile are present at all temperatures. Amphibole and epidotedisappear as residual phases above 800°C; allanite appearsabove 750°C. The Na–Al-rich silicate glass presentin all run products is likely to have quenched from a supercriticalliquid. Trace element analyses of glasses demonstrate the importantcontrol exerted by residual minerals on liquid chemistry. Inaddition to garnet, which controls heavy rare earth elements(HREE) and Sc, and rutile, which controls Ti, Nb and Ta, allanitebuffers the light REE (LREE; La–Sm) contents of liquidsto relatively low levels and preferentially holds back Th relativeto U. In agreement with previous experimental and metamorphicstudies we propose that residual allanite plays a key role inselectively retaining trace elements in the slab during subduction.Experimental data and analyses of allanite-bearing volcanicrocks are used to derive a model for allanite solubility inliquids as a function of pressure, temperature, anhydrous liquidcomposition and LREE content. The large temperature dependenceof allanite solubility is very similar to that previously determinedfor monazite. Our model, fitted to 48 datapoints, retrievesLREE solubility (in ppm) to within a factor of 1· 40over a pressure range of 0–4 GPa, temperature range of700–1200°C and for liquids with anhydrous SiO₂ contentsof 50–84 wt %. This uncertainty in LREE content is equivalentto a temperature uncertainty of only ± 27°C at 1000K, indicating the potential of allanite as a geothermometer.Silicic liquids from either basaltic or sedimentary protolithswill be saturated in allanite except for Ca-poor protolithsor at very high temperatures. For conventional subduction geothermsthe low solubility of LREE (+ Th) in liquids raises questionsabout the mechanism of LREE + Th transport from slab to wedge.It is suggested either that, locally, temperatures experiencedby the slab are high enough to eliminate allanite in the residueor that substantial volumes of H₂O-rich fluids must pass throughthe mantle wedge prior to melting. The solubility of accessoryphases in fluids derived from subducted rocks can provide importantconstraints on subduction zone thermal structure. KEY WORDS: subduction; experimental petrology; allanite; solubility; supercritical liquid; eclogite     

Origin of the Oceanic Lithosphere

In a global examination of mid-ocean ridge basalt (MORB) glasscompositions, we find that Na₈–Fe₈–depth variationsdo not support modeling of MORBs as aggregates of melt compositionsgenerated over a large range of temperature and pressure. However,the Na₈–Fe₈ variations are consistent with the compositionalsystematics of solidus melts in the plagioclase–spinellherzolite transition in the CaO–MgO–Al₂O₃–SiO₂–Na₂O–FeO(CMASNF) system. For natural compositions, the P–T rangefor melt extraction is estimated to be 1·2–1·5GPa and 1250–1280°C. This P–T range is a closematch with the maximum P–T conditions for explosive pressure-releasevaporization of carbonate-bearing melts. It is proposed thatfracturing of the lithosphere induces explosive formation andescape of CO₂ vapor. This provides the vehicle for extractionof MORBs at a relatively uniform T and P. The upper portionof the CO₂-bearing and slightly melted seismic low-velocityzone flows toward the ridge, rises at the ridge axis to lower-lithospheredepths, melts much more extensively during this rise, and releasesMORB melts to the surface driven by explosively escaping CO₂vapor. The residue and overlying crust produced by this meltingthen migrate away from the ridge axis as new oceanic lithosphere.The entire process of oceanic lithosphere creation involvesonly the upper 140 km. When lithospheric stresses shift fractureformation to other localities, escape of CO₂ ceases, the vehiclefor transporting melt to the surface disappears, and ridgesdie. Inverse correlations of Na₈ vs Fe₈ for MORB glasses areexplained by mantle heterogeneity, and positive variations superimposedon the inverse variations are consistent with progressive extractionof melts from short, ascending melting columns. The uniformlylow temperatures of MORB extraction are not consistent withthe existence of hot plumes on or close to ocean ridges. Inthis modeling, the southern Atlantic mantle from Bouvet to about26°N is relatively homogeneous, whereas the Atlantic mantlenorth of about 26°N shows significant long-range heterogeneity.The mantle between the Charlie Gibbs and Jan Mayen fracturezones is strongly enriched in FeO/MgO, perhaps by a trappedfragment of basaltic crust. Iceland is explained as the productof this enrichment, not a hot plume. The East Pacific Rise,Galapagos Ridge, Gorda Ridge, and Juan de Fuca Ridge samplemantle that is heterogeneous over short distances. The mantlebeneath the Red Sea is enriched in FeO/MgO relative to the mantlebeneath the northern Indian Ocean.     

Oxygen Isotope Evidence for Chemical Interaction of Ki lauea Historical Magmas with Basement Rocks

Klauea historical summit lavas have a wide range in matrix ¹⁸O_VSMOWvalues (4·9–5·6) with lower values in rockserupted following a major summit collapse or eruptive hiatus.In contrast, ¹⁸O values for olivines in most of these lavasare nearly constant (5·1 ± 0·1). The disequilibriumbetween matrix and olivine ¹⁸O values in many samples indicatesthat the lower matrix values were acquired by the magma afterolivine growth, probably just before or during eruption. BothMauna Loa and Klauea basement rocks are the likely sources ofthe contamination, based on O, Pb and Sr isotope data. However,the extent of crustal contamination of Klauea historical magmasis probably minor (< 12%, depending on the assumed contaminant)and it is superimposed on a longer-term, cyclic geochemicalvariation that reflects source heterogeneity. Klauea's heterogeneoussource, which is well represented by the historical summit lavas,probably has magma ¹⁸O values within the normal mid-ocean ridgebasalt mantle range (5·4–5·8) based on thenew olivine ¹⁸O values. KEY WORDS: Hawaii; Klauea; basalt; oxygen isotopes; crustal contamination     

Phase Relations and Melting of Anhydrous K-bearing Eclogite from 1200 to 1600{degrees}C and 3 to 5 GPa

To investigate eclogite melting under mantle conditions, wehave performed a series of piston-cylinder experiments usinga homogeneous synthetic starting material (GA2) that is representativeof altered mid-ocean ridge basalt. Experiments were conductedat pressures of 3·0, 4·0 and 5·0 GPa andover a temperature range of 1200–1600°C. The subsolidusmineralogy of GA2 consists of garnet and clinopyroxene withminor quartz–coesite, rutile and feldspar. Solidus temperaturesare located at 1230°C at 3·0 GPa and 1300°C at5·0 GPa, giving a steep solidus slope of 30–40°C/GPa.Melting intervals are in excess of 200°C and increase withpressure up to 5·0 GPa. At 3·0 GPa feldspar, rutileand quartz are residual phases up to 40°C above the solidus,whereas at higher pressures feldspar and rutile are rapidlymelted out above the solidus. Garnet and clinopyroxene are theonly residual phases once melt fractions exceed 20% and garnetis the sole liquidus phase over the investigated pressure range.With increasing melt fraction garnet and clinopyroxene becomeprogressively more Mg-rich, whereas coexisting melts vary fromK-rich dacites at low degrees of melting to basaltic andesitesat high melt fractions. Increasing pressure tends to increasethe jadeite and Ca-eskolaite components in clinopyroxene andenhance the modal proportion of garnet at low melt fractions,which effects a marked reduction in the Al₂O₃ and Na₂O contentof the melt with pressure. In contrast, the TiO₂ and K₂O contentsof the low-degree melts increase with increasing pressure; thusNa₂O and K₂O behave in a contrasted manner as a function ofpressure. Altered oceanic basalt is an important component ofcrust returned to the mantle via plate subduction, so GA2 maybe representative of one of many different mafic lithologiespresent in the upper mantle. During upwelling of heterogeneousmantle domains, these mafic rock-types may undergo extensivemelting at great depths, because of their low solidus temperaturescompared with mantle peridotite. Melt batches may be highlyvariable in composition depending on the composition and degreeof melting of the source, the depth of melting, and the degreeof magma mixing. Some of the eclogite-derived melts may alsoreact with and refertilize surrounding peridotite, which itselfmay partially melt with further upwelling. Such complex magma-genesisconditions may partly explain the wide spectrum of primitivemagma compositions found within oceanic basalt suites. KEY WORDS: eclogite; experimental petrology; mafic magmatism; mantle melting; oceanic basalts     

Comparison of arsenic concentrations in simultaneously-collected groundwater and aquifer particles from Bangladesh,India, Vietnam,and Nepal

One of the reasons the processes resulting in As release to groundwater in southern Asia remain poorly understood is the high degree of spatial variability of physical and chemical properties in shallow aquifers. In an attempt to overcome this difficulty, a simple device that collects groundwater and sediment as a slurry from precisely the same interval was developed in Bangladesh. Recently published results from Bangladesh and India relying on the needle-sampler are augmented here with new data from 37 intervals of grey aquifer material of likely Holocene age in Vietnam and Nepal. A total of 145 samples of filtered groundwater ranging in depth from 3 to 36 m that were analyzed for As (1–1000 μg/L), Fe (0.01–40 mg/L), Mn (0.2–4 mg/L) and S (0.04–14 mg/L) are compared. The P-extractable (0.01–36 mg/kg) and HCl-extractable As (0.04–36 mg/kg) content of the particulate phase was determined in the same suite of samples, in addition to Fe(II)/Fe ratios (0.2–1.0) in the acid-leachable fraction of the particulate phase. Needle-sampler data from Bangladesh indicated a relationship between dissolved As in groundwater and P-extractable As in the particulate phase that was interpreted as an indication of adsorptive equilibrium, under sufficiently reducing conditions, across 3 orders of magnitude in concentrations according to a distribution coefficient of 4 mL/g. The more recent observations from India, Vietnam and Nepal show groundwater As concentrations that are often an order of magnitude lower at a given level of P-extractable As compared to Bangladesh, even if only the subset of particularly reducing intervals characterized by leachable Fe(II)/Fe >0.5 and dissolved Fe >0.2 mg/L are considered. Without attempting to explain why As appears to be particularly mobile in reducing aquifers of Bangladesh compared to the other regions, the consequences of increasing the distribution coefficient for As between the particulate and dissolved phase to 40 mL/g for the flushing of shallow aquifers of their initial As content are explored.     

Characterization and cycling of atmospheric mercury along the central US Gulf Coast

Concentrations of atmospheric Hg species, elemental Hg (Hg^°), reactive gaseous Hg (RGM), and fine particulate Hg (Hg-PM_2.5) were measured at a coastal site near Weeks Bay, Alabama from April to August, 2005 and January to May, 2006. Mean concentrations of the species were 1.6 ± 0.3 ng m⁻³, 4.0 ± 7.5 pg m⁻³ and 2.7 ± 3.4 pg m⁻³, respectively. A strong diel pattern was observed for RGM (midday maximum concentrations were up to 92.7 pg m⁻³), but not for Hg^° or Hg-PM_2.5. Elevated RGM concentrations (>25 pg m⁻³) in April and May of 2005 correlated with elevated average daytime O₃ concentrations (>55 ppbv) and high light intensity (>500 W m⁻²). These conditions generally corresponded with mixed continental-Gulf and exclusively continental air mass trajectories. Generally lower, but still elevated, RGM peaks observed in August, 2005 and January–March, 2006 correlated significantly (p < 0.05) with peaks in SO₂ concentration and corresponded to periods of high light intensity and lower average daytime O₃ concentrations. During these times air masses were dominated by trajectories that originated over the continent. Elevated RGM concentrations likely resulted from photochemical oxidation of Hg^° by atmospheric oxidants. This process may have been enhanced in and by the near-shore environment relative to inland sites. The marine boundary layer itself was not found to be a significant source of RGM.