Multiple Enrichment Processes and their Relationships in the Subcrustal Lithosphere Beneath the Eifel (Germany)

Three types of enrichment processes may be distinguished inspinel peridotite mantle xenoliths from the West Eifel (Germany):

1. Enrichmentof light rare earth elements (LREE) occurs in wholerocks andclinopyroxenes in conjunction with the formation ofTi-pooramphiboles (<0•5%) in a low-tempetature suite(900C).
2. Enrichment in high field strength elements (HFSE; Ti and Hf)is associated with strong zoning of TiO₂ in amphibole adjacentto mica hornblendite veins. A reheating from 900 to 1050C associatedwith this vein formation is reflected by the zoning profilesin orthopyroxenes with Ca, Al, and Cr increasing from core torim.
3. Moderate enrichment of LREE without amphibole formationin ahigh-temperature suite (1125C) is observed at the contactofperidotites to pyroxenite veins yielding the same temperature.
4. Based on geochemical and isotopic evidence, enrichment process(1) is inferred to be due to interaction of peridotites fromthe subcrustal lithosphere with low-density fluids. Process(2) represents a subsequent interaction of amphibole-bearingperidotites formed during the first process with basic meltsmoving through a system of cross-cutting dykes and veins. Processes(2) and (3) are linked to the Quaternary West Eifel volcanism.Geothermobarometry of the xenoliths shows that these processesare related to different depth regimes of the lower lithosphere.

     

Effects of forest roads on the hydrological response of a small‐scale mountain watershed in Greece

The effects of land use changes on the ecology and hydrology of natural watersheds have long been debated. However, less attention has been given to the hydrological effects of forest roads. Although less studied, several researchers have claimed that streamflow changes related to forest roads can cause a persistent and pervasive effect on hillslope hydrology and the functioning of the channel system. The main potential direct effects of forest roads on natural watersheds hydrologic response are runoff production on roads surfaces due to reduced infiltration rates, interruption of subsurface flow by road cutslopes and rapid transfer of the produced runoff to the stream network through roadside ditches. The aforementioned effects may significantly modify the total volume and timing of the hillslope flow to the stream network. This study uses detailed field data, spatial data, hydro‐meteorological records, as well as numerical simulation to investigate the effects of forest roads on the hydrological response of a small‐scale mountain experimental watershed, which is situated in the east side of Penteli Mountain, Attica, Greece. The results of this study highlight the possible effects of forest roads on the watersheds hydrological response that may significantly influence direct runoff depths and peak flow rates. It is demonstrated that these effects can be very important in permeable watersheds and that more emphasis should be given on the impact of roads on the watersheds hydrological response. Copyright © 2014 John Wiley & Sons, Ltd.     

Analytical models of contaminant transport in coastal aquifers

The Henry formulation, which couples subsurface flow and salt transport via a variable-density flow formulation, can be used to evaluate the extent of sea water intrusion into coastal aquifers. The coupling gives rise to nontrivial flow patterns that are very different from those observed in inland aquifers. We investigate the influence of these flow patterns on the transport of conservative contaminants in a coastal aquifer. The flow is characterized by two dimensionless parameters: the Péclet number, which compares the relative effects of advective and dispersive transport mechanisms, and a coupling parameter, which describes the importance of the salt water boundary on the flow. We focus our attention on two regimes – low and intermediate Péclet number flows. Two transport scenarios are solved analytically by means of a perturbation analysis. The first, a natural attenuation scenario, describes the flushing of a contaminant from a coastal aquifer by clean fresh water, while the second, a contaminant spill scenario, considers an isolated point source.     

SEPARATION OF REGIONAL AND RESIDUAL ANOMALIES BY LEAST-SQUARES ORTHOGONAL POLYNOMIAL AND RELAXATION TECHNIQUES: A PERFORMANCE EVALUATION1

The performances of least-squares orthogonal polynomial and relaxation techniques in the separation of regional and residual anomalies have been evaluated with a view to minimizing personal biasing. The advantage of orthogonal over nonorthogonal polynomials is their ability to estimate an optimum order of polynomial to represent the predominant regional trend in the data using an approximate 2D difference table, the Z-matrix. The correlation coefficients between residuals of two consecutive orders also give the same result. In the relaxation technique, a linear trend is assumed within each cell of the mesh of a square grid. A set of such linear segments can approximate any complicated regional trend. The performances of these two techniques have been evaluated using simulated gravity anomalies produced by 2D and 3D complex regional structures superimposed on residual fields due to cylinders and prismatic bodies, as well as three field examples taken from the published literature. The analyses have revealed that the relaxation technique produces excellent results when an optimum polynomial order rather than an arbitrary fixed one is used for computing the boundary conditions along the periphery of the map. Analyses have revealed that such boundary conditions provide minimum distortion near the two ends of the profile.     

Influence of calibration methodology on ground water flow predictions

We constructed a numerical model of transient ground water flow and solute transport for a portion of the Biscayne Aquifer in Florida, and calibrated the model with three different combinations of data from a 193-day period: head (h) data alone, data on h and ground water discharge to a canal (q), and data on h, q, and ground water chloride concentration (C). We used each of the three calibrated models to predict h and q during a 182-day test period separate from the calibration period. All three calibrated models predicted h equally well during the test period (r = 0.95, where r = 1 indicates perfect agreement between measured and simulated values), though the model calibrated on h alone had significantly different parameter values than the other two models. Predictions of q during the test period depended on calibration methodology; models calibrated with multiple targets simulated q more accurately than the model calibrated on h alone (r = 0.79 compared to r = 0.49). Based on the results of these simulations, we conclude: (1) Post-calibration prediction is important in assessing the value of different data types in automated calibration; (2) inverse-solution uniqueness is not a requirement for accurate h predictions; (3) relatively simple models can predict with reasonable accuracy transient ground water flow in a complex aquifer, and parameters governing this prediction can be estimated by nonlinear regression methods that incorporate both h and q data; (4) addition of C data to the calibration did not improve model predictive capacity because the information in the C data was similar to that in the q data, from the perspective of model calibration (the subsurface chemical signal in question was controlled mainly by seepage of high-chloride canal water into the low-chloride ground water system).     

陕西省略阳县杨家坝多金属矿区成矿作用地球化学示踪

本文以陕西省略阳县杨家坝多金属矿区为例,通过对该矿区岩(矿)石和各类脉体的岩相学、稀土和微量元素及流体包裹体地球化学示踪发现,多金属中重晶石的形成及硅化、碳酸盐化、滑石化、纤闪石化、绢云母化和绿泥石化和透闪石岩的含氟浅闪石及隐晶硅质玻璃和微晶硅质,这表明与成矿蚀变有关的热液流体是一种不同于一般地壳流体的富硅、钛、铁、碱质和挥发份,并具备熔体性质的成矿流体。各类样品的稀土元素配分模式明显富集LREE,在Ce、Eu、Yb异常的组合上也各具特征。LREE富集是地幔流体作用的显著特征之一;矿石和脉体的负Ce、正Eu和负Yb异常以及流体包裹体中H2O-C6H6成分,是高温还原地幔流体的重要标志;正Ce和负Eu异常的出现,以及Ce、Eu、Yb异常的减弱和消失则是壳幔混染叠加改造的显示。综合研究表明:矿区成矿过程可能统一受制于秦岭地区碰撞造山背景下具高温还原性质的地幔流体作用,且由此引发壳幔强烈混染的叠加改造作用在成矿过程中发挥了重要作用。     

EQUATIONS D'ONDE ET MODELES *

The method of finite differences is applied to the computation of multi-dimensional synthetic seismograms. This paper gives a study of the mathematical and numerical formulations of the problem, the boundary conditions, the convergence conditions and how to simulate the source in both one solid or a liquid. It is shown that the numerical formulation chosen is valid both for direct and inverse problems (i.e. for modeling and migration). This formulation makes it possible to use the normal incidence reflection coefficients for P and S waves, whether they travel horizontally or vertically. The examples shown have been chosen on purpose in order to be easily interpreted. They do not give a full idea of the possibilities of the algorithm which allows to consider non-planar interfaces, except close to the vertical axis.     

A NOTE ON THE INTERPRETATION OF MAGNETIC ANOMALIES OF INFINITE THIN SHEETS BY USING RELATION FIGURES*

The concept of relation figures is utilized in the case of a thin infinite sheet for identification and determination of the causative source geometry, and its various parameters. The plot of ?T versus ?V is a conic, the plots between the respective symmetric components and the respective asymmetric components are straight lines, and the resulting diagram between the first horizontal versus the first vertical derivative of either ?T or ?V is a cardioid. The authors are grateful to Shri V. Babu Rao and Dr R. K. Verma for their encouragement. They would like to thank the Director of the N. G. R. I. for permission to publish this paper. The neat drawing of Sri P. Sundara Rao is appreciated.     

The Working World of the Paladar: The Production of Contradictory Space during Cuba's Period of Fragmentation*

This article examines the social spaces of self‐employment in Havana, Cuba, to uncover the deeply conflicting and contradictory values that comprise the dialectics of state–society relations. These spaces and the many actors who traverse them provide important insight into the complexity surrounding contemporary Cuba. Through detailed research into one form of self‐employment, paladares (small in‐home restaurants), this article examines how paladares have come to reflect the struggle for society and state to mediate the multitude of external and internal pressures amongst the current geopolitical climate. Using interviews conducted during several visits in 1999 and 2000, we demonstrate that paladares do not necessarily represent a capitalist transition. Rather, they embody the struggle to mediate contradictory spaces through the assertion of the self in the discourse of change.