Maps as geomedial action spaces: considering the shift from logocentric to egocentric engagements

This paper considers some significant questions in geography and cognate fields about the roles of maps in the information age. Most maps are now digital products, offering immersive environments for user involvement. The increasingly networked digital distribution of geographic information in consumer-orientated cartographic representations leads to substantial changes how people individually and collaboratively experience and produce space and place. This article focuses on the ongoing metamorphosis arising through geobrowsing, the media-based flexible production of geographic knowledge through interactive maps. Drawing on work in media studies influenced by the so-called spatial turn—the rediscovering of geography-related questions in the social sciences and humanities, after modernism’s claimed prioritization of time and history (Soja in Postmodern Geographies. The reassertion of space in critical social theory, London, 1989; Jameson in Postmodernism, or, the cultural logic of late capitalism, Duke University Press, Durham, 1991)—this paper develops a theoretical framework built on the dynamic networked geomedial action spaces concept to understand the changing roles of information age maps as imagined materialist spaces for the experience and production of space—ultimately a medial turn. Following this concept, maps change from offering static and non-interactive frames of geographic reference for the production of space and place and as geomedia support a veritable infinity of interactive and map-based activities. Geobrowsing facilitates some new modes of geographic interactions that move from logocentric engagements with static maps to egocentric dynamic interactions with code-based elements of geomedial action spaces. Google Earth and similar geomedia facilitate maps that become intrinsic to a growing number of social action spaces and alter the experience and production of space and place.     

Virtualizing Los Angeles: Pierre Levy, <Emphasis Type="Italic">The Shield</Emphasis>, and http://theshieldrap.proboards45.com/

I explore how Pierre Levy’s virtualization works between actual places, television, and the Internet by referencing the real landscapes of Los Angeles, the visualized landscapes of the FX network television show The Shield, and the cyberscapes of . Unlike current Deleuzean-based theories of visualization that privilege the passage from the virtual to the actual, Levy focuses instead on how virtualization moves back from the real/actual toward the virtual. I argue that this philosophical reversal illustrates the way in which the virtual constitutes the viewer/consumer and thus functions to resituate the virtual within the body through the use of digital landscapes. I further argue, using The Shield as the modality, that the virtual is necessarily an element of the very body which it serves to constitute because the virtual is indeed an essential part of the determination of the geographies of every concrete biocultural body. My example of The Shield becomes the means by which we can bring the force of the virtual, in the form of web-based landscapes, to bear on our experience. I use the show and its Internet counterpart as the catalyst for an expansion of the margin of indetermination constitutive of our technically-facilitated embodiment. By further relating the TV show to our seemingly playful interactions with the digital landscape, I explore how this interaction crosses multiple scales and multiple viewing modalities and further blurs the borders of experiential reality and the visualization of fantasized landscapes. The Shield’s representations of the Los Angeles landscape become embodied experiences for viewers of the show and by virtualizing the real landscapes of Los Angeles and their televisual counterparts, allows consumers to know the spaces of the city through their virtual experience of place as imagined by the website and its members. Thus, I show how Levy’s virtualization theories can be used to specify the virtual dimension constitutive of human experience.     

The evolving narrative of the Darfur conflict as represented in <Emphasis Type="Italic">The New York Times</Emphasis> and <Emphasis Type="Italic">The Washington Post</Emphasis>, 2003–2009

News media influence local to global interactions between people, societies, and governments by producing place images. Representations of Africa in Western news media are heavily imbued with colonialist notions of cultural geography. In particular, Western news media have represented conflicts in Africa as ‘tribal’, a trope that erases geographic and historical context, and discourages actions that could prevent or reduce violent conflict. To determine if ‘tribalism’ remains important in coverage of African conflict, we use framing analysis to evaluate news on Sudan’s Darfur region in The New York Times and The Washington Post during 2003–2009. We find that these newspapers predictably relied on stereotypes related to tribalism to simplify Darfur’s geography and make the conflict meaningful to intended readers. Tribal portrayal of African war is inherently political, and, problematically, neither newspaper recognized that their use of the tribal narrative was parallel to the views of both the Sudanese government and external observers that challenged the actions of the Sudanese government. However, we also found that stereotypical representations became less prominent over time, apparently because reporters found that the initial, simplistic framing of the conflict did not match their encounters with geographic reality. We emphasize the decline in stereotypical tropes, because this suggests behind-the-scenes negotiation about representations in these news organizations. Recognizing voices that challenge stereotypical portrayals is necessary to developing place images that are geographically more accurate.     

Effect of Sorption Heterogeneity on Moments of Solute Residence Time in Convergent Flows

In this paper, we analyze the impact of physical and chemical heterogeneity on solute travel time to a pumping well. We consider a solute undergoing reversible linear instantaneous equilibrium sorption. Both the distribution coefficient, K _d , and the transmissivity field, T, are considered spatially variable, and are modeled as partially correlated spatial random functions. Groundwater flow and solute transport are then solved within the context of a numerical Monte Carlo framework. The results are analyzed on the basis of dimensional analysis techniques. Simple and compact expressions characterizing the dependence of the target travel time moments on relevant dimensionless groups are proposed. The functional form of these expressions is inspired by, and is consistent with, the previous works of Sanchez-Vila and Rubin (Water Resour. Res. 39(4):1086, 2003) and Riva et al. (J. Contam. Hydrol. 82:23–43, 2006) A key result is that the effects of the chemical and physical heterogeneities on the mean travel time can be decoupled consistently with existing analytical results. The relative role of physical and geochemical heterogeneities in travel time variance is more complex, and such a decoupling is not observed. Potential uses of this work include the assessment of aquifer reclamation time by means of a single pumping well.     

Grain growth in partially molten olivine aggregates

Grain growth rates in partially molten olivine aggregates were determined experimentally at a pressure of 1 GPa. The aim of the experiments with fine-grained starting material (solution–gelation derived Fo₉₀ olivine with a grain size of ∼1 μm with 2 and 4 wt.% added basaltic glass) was to determine growth rates during steady-state grain growth. A series of experiments was conducted at a fixed temperature of 1,350°C for durations from 2 to 700 h, and a second series at fixed duration (168 h) at temperatures from 1,250 to 1,450°C. The resulting activation energy (E=390 kJ/mol) and growth exponent (n=4.3) are comparable to melt-free results (Nichols and Mackwell 1991). The observed grain size distributions are broader than those predicted for normal grain growth or Ostwald ripening and most similar to the Log-normal distribution. The observed melt distribution is influenced by the continuous rearrangement of neighboring grains during growth. The relatively large growth exponent observed in this study and by Nichols and Mackwell (1991) where secondary phases are present suggests that grain growth in the upper mantle is slower than predicted by Karato (1989).     

Response to “Comment on ‘Otolith Microchemistry Reveals Substantial Use of Freshwater by Southern Flounder in the Northern Gulf of Mexico’” by Pedro Morais

Lowe et al. (Estuar Coast 34:630–639, 2011) used Sr/Ca in the otoliths of juvenile southern flounder (Paralichthys lethostigma) to demonstrate the importance of low-salinity habitats in the northern Gulf of Mexico during early life. While otolith cores indicated that most southern flounder originated in high-salinity environments (elevated Sr/Ca in otolith core) and moved into lower salinity habitats (decreased Sr/Ca outside of the otolith core), approximately one third of the sampled individuals had otolith core chemistry that indicated spawning or hatching in or near freshwater habitats (low Sr/Ca throughout the otolith). Morais (Estuar Coast 34:630–639, 2012) proposes a different interpretation: he suggests that the high Sr/Ca found in 68 % of juvenile otolith cores (and low Sr/Ca just outside of the core region) may be due to females hydrating their eggs in offshore (high-salinity) waters, with spawning, hatching, and egg/larval development all actually occurring in low-salinity environments (his “sea-run mother” hypothesis). While there is ample literature supporting the importance of maternal contributions to otolith microchemistry during vitellogenesis, it is our contention that such contributions ultimately depend on the ecology and reproductive physiology of each species. Further, a mass inshore migration of adult southern flounder during their spawning season is counter to the well-documented life history patterns for this species throughout its range. While we appreciate Morais' perspective, we continue to stand by the conclusion of our original paper.     

Sedimentology,palaeoecology and geochronology of Marine Isotope Stage 5 deposits on the Shetland Islands,Scotland

New stratigraphical, palynological and dating evidence is presented for pre‐Late Devensian/Weichselian sediments at Fugla Ness and Sel Ayre, Shetland. The Fugla Ness Peat rests on till and formed during an interglacial that saw the development of maritime heaths, with scattered trees and shrubs, including Pinus and possibly Ilex. A decline into stadial conditions is marked by overlying periglacial breccia and till. The Sel Ayre Organic Sands and Gravels lie between periglacial breccias and beneath till and appear to record a changing interstadial environment in which trees were absent and the vegetation comprised largely heaths, with Bruckenthalia, and grasslands. The Fugla Ness Peat is dated to 110+40/?35 ka by uranium series disequilibrium, suggesting that it formed during the Ipswichian/Eemian Interglacial (Marine Isotope Substage 5e). Luminescence ages of ca. 98–105 ka on intercalated sands within the Sel Ayre Organic Sands and Gravels place these deposits in Marine Isotope Substage 5c (Brørup Interstadial). The two sites provide the first detailed record of Marine Isotope Stage 5 environments on Shetland. Copyright © 2002 John Wiley & Sons, Ltd.     

What’s Hiding Behind Ontogenetic δ<Superscript>13</Superscript>C Variations in Mollusk Shells? New Insights from the Great Scallop (<Emphasis Type="Italic">Pecten maximus</Emphasis>)

Mollusk shells contain geochemical information about environmental conditions that prevailed at the time of formation. We investigated ontogenetic and seasonal variations of δ¹³C in calcitic shells of Pecten maximus. Ontogenetic variations of δ¹³C_shell in three large specimens collected in Norway, France, and Spain exhibited a similar linear decrease with increasing shell height. We removed this linear drift (detrending). These three residual time series displayed variations that could be linked to environmental fluctuations. To check it, we reanalyzed the isotopic datasets of Lorrain et al. (Journal of Experimental Marine Biology and Ecology 275:47–61, 2002, Geochimica et Cosmochimica Acta 68:3509–3519, 2004), who worked on three scallops harvested in 2000 in the bay of Brest (France), a well-monitored ecosystem. Lowest values of δ¹³C_{shell detrended} were recorded in all shells in late spring–early summer, most likely reflecting corresponding variations in food availability. Our results indicate that ontogenetic and seasonal variations of δ¹³C_shell cannot be used as a proxy for past δ¹³C_DIC variations but should be considered as promising tools for ecophysiological studies.     

Learning from (small) disasters

In this article, disasters are understood as processes that have different impacts on social routines in terms of scale, scope and duration. The extent of adaptive processes in society can provide the ground for a rough classification of disaster types. Such classification has, on the one hand, practical and analytical advantages. On the other hand, they harbour the danger of overlooking transitions of scale and discourage comprehensive scale-related learning forms. Based on the disaster scale by Fischer (Int J Mass Emerg Disasters 1:91–107, 2003), flash floods in mountain rivers and torrents are described as extreme emergencies or small-town disasters. Three given examples will clearly show that learning rarely takes place within an institutional setting that is subjected to small disasters, because the stakeholder’s focus remains on only one level. Therefore, we propose to implement a system of self-organised and scale-independent learning, so called deutero learning, within the political subsystem. Following a damaging event, participative processes that involve all levels should be initialised. Their task would be to assess the combination of causes and draw conclusions for mitigation measures. An aggregation of these assessments would help the responsible political subsystems to adapt the current natural disasters policy to the changing environmental conditions.     

Seismic liquefaction analysis of a reservoir dam foundation in the South–North Water Diversion project in China. Part I: Liquefaction potential assessment

In this paper, the dynamic characteristics of a liquefiable silt substratum within the foundation soil of a reservoir dam in the Tianjin area are investigated by means of standard penetration resistance and dynamic triaxial tests. Properties including N-values, factors influencing liquefaction as a cyclic stress, consolidation pressure, structure, and particle composition are considered in this research. Parameters used to evaluate liquefaction potential are obtained through testing. A comprehensive program based on the Chinese code and standard for geological investigation (Ministry of Water Resources of China 1999a; Ministry of Construction of China 2001a) and Seed’s simplified method (Seed and Idriss 1971; in J Geotech Eng Div ASCE 109(3): 458–482, 1983) was carried out to evaluate the potential of liquefaction within the reservoir dam foundation. Liquefaction potentials were also assessed in response to the Chinese codes for seismic design (Hydropower Research Institute of China 2000; Ministry of Construction of China 2001b). The evaluation shows that saturated surface silt in the reservoir dam foundations is vulnerable to liquefaction at seismic intensities of VII and above. The two assessment methods are in good agreement with each other, and the research results can provide useful information for the safe construction and normal operation of the reservoir.     

An integrated model simulating the initiation and motion of earthquake and rain induced rapid landslides and its application to the 2006 Leyte landslide

A gigantic rapid landslide claiming over 1,000 fatalities was triggered by rainfalls and a small nearby earthquake in the Leyte Island, Philippines in 2006. The disaster presented the necessity of a new modeling technology for disaster risk preparedness which simulates initiation and motion. This paper presents a new computer simulation integrating the initiation process triggered by rainfalls and/or earthquakes and the development process to a rapid motion due to strength reduction and the entrainment of deposits in the runout path. This simulation model LS-RAPID was developed from the geotechnical model for the motion of landslides (Sassa 1988) and its improved simulation model (Sassa et al. 2004b) and new knowledge obtained from a new dynamic loading ring shear apparatus (Sassa et al. 2004a). The examination of performance of each process in a simple imaginary slope addressed that the simulation model well simulated the process of progressive failure, and development to a rapid landslide. The initiation process was compared to conventional limit equilibrium stability analyses by changing pore pressure ratio. The simulation model started to move in a smaller pore pressure ratio than the limit equilibrium stability analyses because of progressive failure. However, when a larger shear deformation is set as the threshold for the start of strength reduction, the onset of landslide motion by the simulation agrees with the cases where the factor of safety estimated by the limit equilibrium stability analyses equals to a unity. The field investigation and the undrained dynamic loading ring shear tests on the 2006 Leyte landslide suggested that this landslide was triggered by the combined effect of pore water pressure due to rains and a very small earthquake. The application of this simulation model could well reproduce the initiation and the rapid long runout motion of the Leyte landslide.     

Computation of influence functions for automatic mining subsidence prediction

This paper presents a computer tool that automatically predicts mining subsidence using the generalized n-k-g influence function detailed in (González Nicieza et al. Int J Rock Mech Min Sci 42(3):372–387, 2005). This function depends on two physical concepts: the first is gravity, which characterizes the forces acting on the ground, and the second, the convergence of the roof and floor of the mine workings due to the stress state of the ground. The developed tool also allows other influence functions to be used to predict subsidence, namely the spatial influence function (Ramírez Oyanguren et al. 2000) and the normal-type classical (Knothe, Arch Gór Hut 1, 1952) and modified (González Nicieza et al. Bull Eng Geol Environ 66(3):319–329, 2007) time functions. Moreover, the inputting and periodic updating of data from subsidence monitoring surveys is controlled by one of the tool’s modules using a method that minimizes errors resulting from time discontinuities in landmarks measurements. In addition, when actual landmarks measurements exist, the developed tool allows calibration of the subsidence parameters, minimizing the errors between actual measurements and those obtained by prediction. The tool includes a viewer, developed using OpenGL, which enables the results of the calculations carried out to be viewed, allowing the point of view to be varied. It also includes the option of viewing and saving the results of the calculations carried out over the original topographic plane defined in the AutoCAD DXF data file format. The efficacy of the tool is demonstrated via its application to a real case of mining work carried out in a village in the Principality of Asturias, Spain.     

Prediction of the thermodynamic properties of metal–arsenate and metal–arsenite aqueous complexes to high temperatures and pressures and some geological consequences

The standard thermodynamic properties at 25°C, 1 bar (ΔG _f^o, ΔH _f^o, S ^o, C _P^o, V ^o, ω) and the coefficients of the revised Helgeson–Kirkham–Flowers equations of state were evaluated for several aqueous complexes formed by dissolved metals and either arsenate or arsenite ions. The guidelines of Shock and Helgeson (Geochim Cosmochim Acta 52:2009–2036, 1988) and Sverjensky et al. (Geochim Cosmochim Acta 61:1359–1412, 1997) were followed and corroborated with alternative approaches, whenever possible. The SUPCRT92 computer code was used to generate the log K of the destruction reactions of these metal–arsenate and metal–arsenite aqueous complexes at pressures and temperatures required by the EQ3/6 software package, version 7.2b. Apart from the AlAsO₄^o and FeAsO₄^o complexes, our log K at 25°C, 1 bar are in fair agreement with those of Whiting (MS Thesis, Colorado School of Mines, Golden, CO, 1992). Moreover, the equilibrium constants evaluated in this study are in good to fair agreement with those determined experimentally for the Ca–dihydroarsenate and Ca–hydroarsenate complexes at 40°C (Mironov et al., Russ J Inorg Chem 40:1690, 1995) and for Fe(III)–hydroarsenate complex at 25°C (Raposo et al., J Sol Chem 35:79–94, 2006), whereas the disagreement with the log K measured for the Ca–arsenate complex at 40°C (Mironov et al., Russ J Inorg Chem 40:1690, 1995) might be due to uncertainties in this measured value. The implications of aqueous complexing between dissolved metals and arsenate/arsenite ions were investigated for seawater, high-temperature geothermal liquids and acid mine drainage and aqueous solutions deriving from mixing of acid mine waters and surface waters. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.     

On the Use of Skempton’s Compression Index Equation

In this study, an alternate approach to establish the e-log p relationships for clayey soils within a vertical pressure range of 10–1,000 kPa is discussed. Skempton’s compression index equation correlating the liquid limit, w _L, and the compression index, C _c, and the reported equation correlating the void ratio at liquid limit, e _L, and the void ratio at a vertical pressure of 100 kPa, e ₁₀₀, by Burland (1990), were used to establish the e-log p relationships for several reconstituted normally consolidated clayey soils. Consolidation test results of 13 clayey soils covering a sufficiently wide range of liquid limit were selected from the literature. Also, consolidation tests were carried out on two highly expansive soils in this study. A comparison of the experimental consolidation test results with the calculated e-log p relationships in the current study indicated that in general, the agreements between the calculated relationships and the experimental results are good. The agreements were found to be slightly better for soils with liquid limits less than about 70%. A comparison of the calculated e-log p relationships in the current study with that determined following methods suggested by Nagaraj and Srinivasa Murthy (1983) and Burland (1990) showed that all the three methods yielded very similar results for soils with liquid limit less than 70%. For soils with liquid limits greater than 70%, the difference between the e-log p relationships calculated in this study and that following Burland (1990)’s method was insignificant, whereas Nagaraj and Srinivasa Murthy (1983)’s method slightly over-predicted the void ratios at larger vertical stresses.     

Recognising early Archaean mantle: a reappraisal

This paper examines 3.8 Ga peridotites from Greenland and Labrador to test claims that these samples are unmodified early Archaean mantle. Geochemical criteria were applied in which samples were compared to the mantle array in Mg/Si versus Al/Si (wt%) space, their REE patterns were compared to those of different mantle types and their chromite compositions were compared to mantle chromite compositions as expressed by their cr# and fe#. Geochemical data were used from the previously published works of Friend et al. (2002) and Bennett et al. (2002). Only two samples, from the region south of Isua satisfied all criteria, indicating that the area south of the Isua Greenstone Belt in west Greenland is a suitable place to search for early Archaean mantle. This study also confirms the observation by Friend et al. (2002) that early Archaean mantle from south of Isua is of a different character from Archaean mantle from the subcontinental lithosphere. Calculations presented here show that some mantle fragments from south of Isua experienced a lower degree of melt extraction and were probably more oxidising than early Archaean mantle preserved in the subcontinental lithosphere. Elemental concentrations of Os in early Archaean mantle are lower than the new estimate for the primitive upper mantle of Becker et al. (2006). Peridotites from the Isua greenstone belt are not mantle, but have an affinity with the layered intrusions found south of Isua.     

Determination of Coefficient of Radial Consolidation Using Steepest Tangent Fitting Method

Barron (Trans ASCE 113:718–724, 1948) theoretical relationship between degree of consolidation (U _r ) and time factor (T _r ) is generally used to determine the coefficient of radial consolidation c _r . Several researchers have proposed different laboratory techniques for obtaining the value of c _r . However, the usual approach is to compare some salient features of the theoretical U _r –T _r relationship with the compression, δ and time, t based on the laboratory data. In this paper, rapid consolidation test procedure originally proposed by Su (J Soil Mech Found Div Am Soc Civ Eng No. 95: Proc. Pap. 1729 (1–9), 1958) to determine the coefficient of vertical consolidation (c _v ) is extended to evaluate Barron’s coefficient of radial consolidation c _r for the case of equal strain. The characteristic feature of the proposed method is the identification of the steepest tangent from the δ–log t plot. The slope of steepest tangent is independent of the drain spacing ratio (n) with a value of 0.847. This approach is rapid, and it predicts more reliable values of c _r as it is less influenced by the secondary compression. In addition, this method is more versatile and can be applied for consolidation trends which do not always exhibit the typical S-shape.     

Comment on: ‘High-temperature dehydration melting and decompressive P–T path in a granulite complex from the Eastern Ghats India’ by S. Bhattacharya and R. Kar

Thermodynamic and chemographic modelling of complex reaction textures observed in Mg-Al-rich pelitic granulites is an important tool to unravel the P–T evolutionary history of high-grade rocks. In the Eastern Ghats Belt, India, several studies have been carried out on these fascinating aluminous granulites, and the results of these studies have revealed complex P–T–t histories (Dasgupta and Sengupta 1995; Sengupta et al. 1999; Rickers et al. 2001a, 2001b; Gupta et al. 1999; Dobmeier and Simmat 2002; Dobmeier and Raith 2003). In recent communication, Bhattacharya and Kar (2002) reported reaction textures from a suite of Mg-Al granulites from the Paderu area of the Eastern Ghats Belt. Combining the textural relations and thermodynamic calibration of some construed reactions, the authors have put forward a single phase metamorphic evolution of the area along a clockwise pressure–temperature trajectory. Combining the petrological features from the Paderu area with those reported from the Chilka Lake complex, the authors proposed a general tectonic model for the entire Eastern Ghats Belt. Incidentally, the rocks in and around Paderu have been studied in some detail by several other workers (Lal et al. 1987; Mohan et al. 1997; Sengupta et al. 1997). The purpose of this comment is to demonstrate that the conclusions made in the paper are inconsistent with the petrological features described in the text. Further, the thermodynamic treatment used in the paper has serious errors in many places, and hence, is often in complete disagreement with the existing experimental data and theoretical analyses on the Mg-Al-rich assemblages. There are also significant problems arising from the poor quality of the analytical database. Unfortunately, the authors cite only a few published works (mostly their own) ignoring many other relevant studies from this belt (cited above). Our observations are organised according to the sections of the paper.Editorial responsibility: T.L. Grove     

Experimental Validation of an Method for In Situ Estimation of Hydraulic Conductivity of Water Treatment Granular Materials

Domestic wastewater-treatment system is today a widely held technique. In order to evaluate the efficiency of these systems, it is necessary to determinate the in situ hydraulic conductivity of the water-treatment granular materials constituting them. The in situ measurement of the hydraulic conductivity of soils has proven to be imprecise, take a long time. Empirical equations based on the physical properties of soil have been proposed to overcome these difficulties. In this context, the originality of this paper is to propose an in situ method to obtain reliable input parameters for the predictive equations of Chapuis (Can Geotech J 41(5): 787–795, 2004) and Carrier (J Geotech Geoenviron Eng 129(11): 1054–1056, 2003) by using both a penetrometer and a geoendoscope. This method is described in the first part of this paper. Then, the validation of the method based on laboratory tests performed under controlled conditions for three kinds of soils is presented. Hydraulic conductivity obtained when applying the method is compared to that measured by a Darcy permeameter. The difference between these two hydraulic conductivities is less than 25%. Finally, the precision of the results is discussed.     

Stochastic methods for safety assessment of the flood defense system in the Scheldt Estuary of the Netherlands

In this study, we address the effective method to apply a novel reliability method integrated with finite element models to the safety assessment of pilot site Scheldt in the Netherlands. This site was considered as one of the three main pilot sites in Europe to assess the application of newly suggested techniques in order to reduce and manage the flood risk in the Floodsite project. , 2004–2009). The novel method of dynamic bounds (DB) is applied to this site after a successful experience in (Rajabalinejad in Reliability methods for finite element models, 1 edn. IOS Press, Amsterdam, 2009). In this study, the bi-functional response of the finite element model is considered, and the dimensional uncertainty is defined presenting the expected uncertainty for a certain dimension in the DB method. The uncertainty is used as a judgment tool to choose the dimension for the DB method for the desired accuracy. The results obtained by applying this technique are presented in this paper.     

Coupling of oceanic and continental crust during Eocene eclogite-facies metamorphism: evidence from the Monte Rosa nappe,western Alps

High precision U–Pb geochronology of rutile from quartz–carbonate–white mica–rutile veins that are hosted within eclogite and schist of the Monte Rosa nappe, western Alps, Italy, indicate that the Monte Rosa nappe was at eclogite-facies metamorphic conditions at 42.6 ± 0.6 Ma. The sample area [Indren glacier, Furgg zone; Dal Piaz (2001) Geology of the Monte Rosa massif: historical review and personal comments. SMPM] consists of eclogite boudins that are exposed inside a south-plunging overturned synform within micaceous schist. Associated with the eclogite and schist are quartz–carbonate–white mica–rutile veins that formed in tension cracks in the eclogite and along the contact between eclogite and surrounding schist. Intrusion of the veins at about 42.6 Ma occurred at eclogite-facies metamorphic conditions (480–570°C, >1.3–1.4 GPa) based on textural relations, oxygen isotope thermometry, and geothermobarometry. The timing of eclogite-facies metamorphism in the Monte Rosa nappe determined in this study is identical to that of the Gran Paradiso nappe [Meffan-Main et al. (2004) J Metamorphic Geol 22:261–281], confirming that these two units have shared the same Alpine metamorphic history. Furthermore, the Gran Paradiso and Monte Rosa nappes underwent eclogite-facies metamorphism within the same time interval as the structurally overlying Zermatt-Saas ophiolite [∼50–40 Ma; e.g., Amato et al. (1999) Earth Planet Sci Lett 171:425–438; Mayer et al. (1999) Eur Union Geosci 10:809 (abstract); Lapen et al. (2003) Earth Planet Sci Lett 215:57–72]. The nearly identical P–T–t histories of the Gran Paradiso, Monte Rosa, and Zermatt-Saas units suggest that these units shared a common Alpine tectonic and metamorphic history. The close spatial and temporal associations between high pressure (HP) ophiolite and continental crust during Alpine orogeny indicates that the HP internal basement nappes in the western Alps may have played a key role in exhumation and preservation of the ophiolitic rocks through buoyancy-driven uplift. Coupling of oceanic and continental crust may therefore be critical in preventing permanent loss of oceanic crust to the mantle.