Magmatic Conditions and Magma Ascent as Indicated by Hornblende Phase Equilibria and Reactions in the 1995-2002 Soufriere Hills Magma

A study of amphiboles and associated minerals in samples ofSoufrière Hills andesite erupted from 1995 to 2002 showssignificant compositional variations within hornblende phenocrysts,a separate set of small pargasitic crystals in the groundmass,and two types of reaction rims on the phenocrysts. The compositionof the amphiboles and coexisting phases defines the thermalhistory of the erupting magma. As many as seven zones (<200µm wide) in the hornblende phenocrysts begin with a sharpincrease in Mg and Si, and then change gradually to a more Fe-and Al-rich hornblende, a transition that is consistent witha temperature rise. Analyses of the hornblende phenocrysts andassociated Fe–Ti oxides verify previous conclusions thatthe pre-eruption magma was at 130 MPa and 830 ± 10°C,but was variably heated before eruption. The heating occurredwithin     

A Mainly Crustal Origin for Tonalitic Granitoid Rocks, Superior Province, Canada: Implications for Late Archean Tectonomagmatic Processes

The central Wabigoon subprovince of the Superior Province, likemost plutonic domains within Archean cratons, is dominated bygranitoid rocks of the tonalite–trondhjemite–granodiorite(TTG) series. Heterogeneous <2·83–2·74Ga tonalite gneisses and foliated tonalite to granodiorite units,emplaced at 2·722–2·709 Ga, exhibit initial     

CORRECTION FACTORS IN THE DETERMINATION OF MEAN VELOCITY OF OVERLAND FLOW

The velocity of overland flow has been conventionally measured using tracers, but it is difficult to measure the mean flow velocity directly because the centroid of the tracer plume is not easily identified. Consequently, previous investigators have measured the velocity of the leading edge of the plume and multiplied it by a correction factor α to obtain an estimate of mean velocity. An alternative method is to measure the velocity of the peak concentration in the tracer plume and multiply this velocity by another correction factor β to estimate mean velocity. To investigate the controls of α and β and develop predictive models for these correction factors, 40 experiments were performed in a flume with a mobile sand bed. Multiple regression analyses reveal that both α and β vary inversely with slope and directly with Reynolds number. The derived regression equations may be used to calculate the mean velocity of other shallow overland flows, at least within the range of slope and Reynolds number for which the equations were developed. In the experiments, slope ranged from 2.7;° to 10° and Reynolds number from 1900 to 12 600.     

Breeding biology of dark-bellied brent geese Branta b. bernicla in Taimyr in 1990 in the absence of arctic foxes and under favourable weather conditions

In combination with observations in spring staging and wintering grounds in western Europe, a detailed etho-ecological study of nesting dark-bellied brent geese Branta b. bernicla in western Taimyr, Krasnoyarsk, Russia, was made in 1990. Most brent geese arrived on the breeding grounds from 14–19 June and started nesting within a few days. In the study area 264 nests of breeding brent geese were found, mainly on islands but also along small rivers on the mainland. The mean clutch size was 3.0 and 80% of the eggs hatched. Time budget studies showed that incubating females spent on average 138 minutes per 24 hours on feeding. Despite favourable weather conditions and a low density of arctic foxes, only about one-third of the mature birds in the study area bred. In the autumn an intermediate breeding success of 20% juveniles was recorded in the wintering areas. This was probably due to the relatively poor condition in which the brent geese left their spring staging areas.     

A guide to pollen analysis

P. D. Moore & J. A. Webb: An Illustrated Guide to Pollen Analysis , Hodder & Stoughton, London-Sydney-Auckland-Toronto.     

NOBLE GAS ANOMALIES AND SYNTHESIS OF THE CHEMICAL ELEMENTS

There are two types of planetary noble gases: One, containing isotopically “anomalous” argon, krypton and xenon but isotopically “normal” helium and neon, was derived from outer stellar regions. The other, consisting almost entirely of isotopically “normal” argon, krypton and xenon, with little or no helium or neon, was derived from inner stellar regions. Mixing of nucleosynthesis products from different regions of a supernova is responsible for the observed correlations between elemental and isotopic ratios of planetary noble gases in different classes of meteorites. The solar system condensed directly from the chemically and isotopically heterogeneous debris of a single supernova. There is no convincing evidence, however, of separate nucleogenetic components in neon. Fractionation and spallation can account for all previously identified components of trapped meteoritic neon, Ne-A, Ne-B, Ne-C, Ne-D, Ne-E, Ne-Al, Ne-A2, Ne-E(L), Ne-E(H) and Ne-O, and this same mechanism also explains differences between the isotopic compositions of meteoritic, atmospheric, and solar wind neon. Variations in the abundance pattern of planetary noble gases are primarily the result of stellar fusion reactions and physical adsorption, rather than gas solubility.     

Temporal Evolution of Magmatism in the Northern Volcanic Zone of the Andes: The Geology and Petrology of Cayambe Volcanic Complex (Ecuador)

In the Northern Volcanic Zone of the Andes, the Cayambe VolcanicComplex consists of: (1) a basal, mostly effusive volcano, theViejo Cayambe, whose lavas (andesites and subordinate dacitesand rhyolites) are typically calc-alkaline; and (2) a younger,essentially dacitic, composite edifice, the Nevado Cayambe,characterized by lavas with adakitic signatures and explosiveeruptive styles. The construction of Viejo Cayambe began >1·1Myr ago and ended at 1·0 Ma. The young and still activeNevado Cayambe grew after a period of quiescence of about 0·6Myr, from 0·4 Ma to Holocene. Its complex history isdivided into at least three large construction phases (Angurealcone, Main Summit cone and Secondary Summit cone) and compriseslarge pyroclastic events, debris avalanches, as well as periodsof dome activity. Geochemical data indicate that fractionalcrystallization and crustal assimilation processes have a limitedrole in the genesis of each suite. On the contrary, field observations,and mineralogical and geochemical data show the increasing importanceof magma mixing during the evolution of the volcanic complex.The adakitic signature of Nevado Cayambe magmas is related topartial melting of a basaltic source, which could be the lowercrust or the subducted slab. However, reliable geophysical andgeochemical evidence indicates that the source of adakitic componentis the subducted slab. Thus, the Viejo Cayambe magmas are inferredto come from a mantle wedge source metasomatized by slab-derivedmelts (adakites), whereas the Nevado Cayambe magmas indicatea greater involvement of adakitic melts in their petrogenesis.This temporal evolution can be related to the presence of thesubducted Carnegie Ridge, modifying the geothermal gradientalong the Wadati–Benioff zone and favouring slab partialmelting. KEY WORDS: adakites; ⁴⁰Ar/³⁹Ar dating; Cayambe volcano; Ecuador; mantle metasomatism; Andes     

Modelling the response of an alluvial aquifer to anthropogenic and recharge stresses in the United States Southern Great Plains

This paper uses Visual MODFLOW to simulate potential impacts of anthropogenic pumping and recharge variability on an alluvial aquifer in semi-arid northwestern Oklahoma. Groundwater withdrawal from the aquifer is projected to increase by more than 50% (relative to 1990) by the year 2050. In contrast, climate projections indicate declining regional precipitation over the next several decades, creating a potential problem of demand and supply. The following scenarios were simulated: (1) projected groundwater withdrawal, (2) a severe drought, (3) a prolonged wet period, and (4) a human adjustment scenario, which assumes future improvements in water conservation measures. Results indicate that the combined impacts of anthropogenic pumping and droughts would create drawdown of greater than 12 m in the aquifer. Spatially, however, areas of severe drawdown will be localized around large-capacity well clusters. The worst impacts of both pumping and droughts will be on stream–aquifer interaction. For example, the projected aquifer pumpage would lead to a total streamflow loss of 40%, creating losing stream system regionally. Similarly, a severe drought would lead to a total streamflow loss of >80%. A post-audit of the model was also carried out to evaluate model performance. By simulating various stress scenarios on the alluvial aquifer, this study provides important information for evaluating management options for alluvial aquifers.     

Dynamic models for Icelandic meteorological data sets

Dynamic models are derived from pairs of time series of daily surface and 500 hPa height observations in the Icelandic region in order to interpret these data. The models describe the motion of data points in the phase plane spanned by a pair of variables. For each pair, a regression model of first order (R-model) is derived, which assumes linear motion in the phase plane. The coefficients of the corresponding Fokker–Planck equation (FP) are also derived from the data. This equation describes changes of the probability density distribution of the data pair and takes nonlinear aspects into account. The data are interpreted in the light of both models. The R-model yields a mean rotation and convergence which characterize the basic type of motion inherent in a data set. It is found in all cases that the timescale of contraction is shorter than the "dynamic" timescale linked to the rotation. The FP equation yields a mean motion which resembles quite often that in the R-model as well as a diffusive part. The R-model is not satisfactory in some cases which involve the meridional surface winds. For example, southerlies (northerlies) and temperature rotate clockwise (anticlockwise). Meridional and zonal surface winds rotate anticlockwise in a southerly flow, but clockwise in a northerly one. Therefore, new aspects of the Icelandic meteorology can be extracted form the data by use of the FP equation.     

http://www.sciencedirect.com/science/article/pii/S1674987114000036

The paper evaluates sensitivity of various spaceborne digital elevation models （DEMs）, viz., Advanced Spaceborne Thermal Emission and Reflection Radiometer （ASTER）, Shuttle Radar Topography Mapping Mission （SRTM） and Global Multi-resolution Terrain Elevation Data 2010 （GMTED）, in comparison with the DEM （TOPO） derived from contour data of 20 m interval of Survey of India topographic sheets of 1 ： 50,000 scale. Several topographic attributes, such as elevation （above mean sea level）, relative relief, slope, aspect, curvature, slope-length and -steepness （LS） factor, terrain ruggedness index （TRI）, topo- graphic wetness index （TWI）, hypsometric integral （lhyp） and drainage network attributes （stream number and stream length） of two tropical mountain river basins, viz. Muthirapuzha River Basin and Pambar River Basin are compared to evaluate the variations. Though the basins are comparable in extent, they differ in respect of terrain characteristics and climate. The result.,; suggest that ASTER and SRTM provide equally reliable representation of topography portrayed by TOP（） and the topographic attributes extracted from the spaceborne DEMs are in agreement with those derived from TOPO. Despite the coarser resolution, SRTM shows relatively higher vertical accuracy （RMSE -- 23 and 20 m respectively in MRB and PRB） compared to ASTER （RMSE - 33 and 24 m） and GMTED （RMSE - 59 and 48 m）. Vertical accuracy of all the spaceborne DEMs is influenced by relief of the terrain as well as type of vegetation. Further, GMTED shows significant deviation for most of the attributes, indicating its inability for mountain-river-basin-scale studies.