A simple model of hillslope response for overland flow generation

This paper deals with the derivation of the hydrological response of a hillslope on the assumption of quick runoff by surface runoff generation. By using the simple non‐linear storage based model, first proposed by Horton, an analytical solution of the overland flow equations over a plane hillslope was derived. This solution establishes a generalization for different flow regimes of Horton's original solution, which is valid for the transitional flow regime only. The solution proposed was compared successfully with that of Horton and, for the turbulent flow regime, to the one derived from kinematic wave theory. This solution can be applied easily to both stationary and non‐stationary rainfall excess events. An analytical solution for the instantaneous response function (IRF) was also derived. Finally, simple expressions to compute peak and time to peak of IRF are proposed. Copyright © 2001 John Wiley & Sons, Ltd.     

Models of natural and human dynamics in forest landscapes: Cross-site and cross-cultural synthesis

We synthesize the study of coupled natural and human systems across sites and cultures through a process of simplification and abstraction based on multiple dimensions of human-nature connectedness: satisfaction of basic needs, psycho-cultural connectedness and regulation of use of natural resources. We thus provide both a place-based and general understanding of value-driven anthropogenic environmental change and response. Two questions guide this research: what are the crucial stakeholder values that drive land use decisions and thus land cover change? And how can knowledge of these values be used to make decisions and policies that sustain both the human and natural systems in a place? To explore these questions we build simulation models of four study sites, two in the State of Texas, United States, and two in Venezuela. All include protected areas, though they differ in the specifics of vegetation and land use. In the Texas sites, relatively affluent individuals are legally converting forests to residential, commercial, and industrial uses, while in Venezuela landless settlers are extra-legally converting forests for purposes of subsistence agriculture. Contemporary modeling techniques now facilitate simulations of stakeholder and ecosystem dynamics revealing emergent patterns. Such coupled human and natural systems are currently recognized as a form of biocomplexity. Our modeling framework is flexible enough to allow adaptation to each of the study sites, capturing the essential features of the respective natural and anthropogenic land use changes and stakeholder reactions. The interactions between human stakeholders are simulated using multi-agent models that act on forest landscape models, and receive feedback of the effects of these actions on ecological habitats and hydrological response. The multi-agent models employ a formal logic-based method for the Venezuelan sites and a decision analysis approach using multi-attribute utility functions for the Texas sites, differing more in style and emphasis than in substance. Our natural-systems models are generic and can be tailored according to site-specific conditions. Similar models of tree growth and patch transitions are used for all the study sites and the differing responses to environmental variables are specified for each local species and terrain conditions.     

Dynamics and Variability of Terra Nova Bay Polynya

Abstract. We present a process study on the dynamics and variability of the Terra Nova Bay polynya in the western sector of the Ross Sea. The air-sea heat exchange is known to be particularly large in polynya during the winter, when differences between air and sea temperatures are large. We apply a 1-D model (Pease, 1987; Van Woert, 1999a, 1999b), which is modified in the latent heat parameterisation in order to account for time-dependent relative humidity and cloud coverage. Furthermore, the Ice Collection Depth is correlated linearly with a variable wind speed. The model is forced with two different meteorological data sets: the operational analysis of the European Center for Medium Range Weather Forecasts atmospheric data set and the meteorological parameters measured by an Automatic Weather Station located on the coast of Terra Nova Bay. The results are compared in terms of polynya extension, ice, and High Salinity Shelf Water production. According to the two different wind velocities, the results obtained from the different data sets clearly differ. Qualitatively, however, the results are in good agreement.     

Pressure-Dependence of Rare Earth Element Distribution in Amphibolite- and Granulite- Grade Garnets. A LA-ICP-MS Study

Using an excimer (KrF) laser ablation ICP-MS system, we studied the distribution of REE in garnets from metapelites and metabasites from Ivrea-Verbano (Western Alps, Italy) and from the Peña Negra Anatectic Complex (Central Iberia), finding systematic variations that correlate well with the metamorphic grade. Chondrite-normalized REE patterns of garnets from amphibolite-grade metapelites have lower-than-chondrite levels from La to Sm, a very small or no Eu anomaly, and a steep rise in the abundance of heavy REE as the atomic number increases. Metapelitic garnets from the amphibolite-granulite transition have a marked Eu negative anomaly and are enriched in MREE such that Sm is 10-15 times chondrite and the pattern is almost flat from Dy to Yb-Lu. In garnets from granulite-grade metapelites, the intensity of the Eu anomaly and the relative concentration of Nd, Sm, Gd and Tb increase, with almost flat chondrite-normalized patterns from Sm to Lu. Garnets from mafic granulites are remarkably similar to those of metapelitic garnets equilibrated at the same pressure, except for the Eu anomaly. The apparent paradox of enhanced uptake of larger REE ions with increasing pressure is attributed to the 3M²⁺ 2REE³⁺+ vacancy substitution, which produces a net decrease in the dimensions of the unit-cell of garnet. Variations in REE patterns depend essentially on the pressure and have little dependence on either temperature, bulk-composition of garnet, or REE whole-rock composition, so they could represent a new approach for geobarometric studies. The best numerical parameter to express pressure-related variations of REE distribution in garnets is the Gd/Dy ratio which does not seem perceptibly affected by disequilibrium partitioning. The regression equation between GASP pressure and the average Gd/Dy^garnet is P = 3.6 + 5.6 Gd/Dy. This equation seems to be reliable for garnets: (1)equilibrated within a pressure range of 4-9 kbar, (2) coexisting with modal monazite; and (3) with unit-cell dimensions under 11.46 Å.     

The seismic strength of the earth

Summary The seismic strength (resistance to sudden failure) of the seismically active regions of the crust and upper mantle is estimated and is found to be maximum at depths of 50 to 125 km. The pattern of strength versus depth can be explained in terms of lithospheric plate sinking beneath an ocean trench. The lack of earthquakes at depths larger than 700 km is probably due to decreasing shear stress rather than vanishing seismic strength.

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Résumé Dans cette communication on évalue la résistance à la rupture séismique des matériaux constituant l'écorce et le manteau supérieur de la Terre. Les résultats indiquent la présence d'un maximum à la profondeur de 50–125 km. La distribution de la résistance avec la profondeur peut être expliquée par la résorption de la lithosphère au-dessous d'un fossé océanique. L'absence de séismes dans les zones plus profondes (z>700 km) n'est pas due à la réduction de la résistance séismique, mais très probablement à l'insuffisance des tensions internes dans les matériaux.

     

Platinum-group minerals in chromitites from the ojen lherzolite massif (Serrania de Ronda,Betic Cordillera,Southern Spain)

Summary Chromitites (Cr ores) of the Ojen lherzolite massif (Serranía de Ronda, Betic Cordillera, Southern Spain) were found to contain platinum-group minerals (PGM) as discrete inclusions in the chromite and in the associated silicates. The PGM mineralogy consists of sulfides [laurite, erlichmanite, malanite, unnamed (Ni-Fe-Cu)₂ (Ir, Rh) S₃, unidentified Pd-S], sulfarsenides (irarsite, hollingworthite, ruarsite, and osarsite), arsenides [sperrylite, unidentified (Pd, Ni)-As], one unidentified Pd-Bi compound, and native platinum group elements (PGE) consisting of Ru and Pt-Fe alloys. Textural considerations suggest that the PGE chalcogenides with S and As were formed in the high-temperature magmatic stages, as part of the chromite precipitation event (primary PGM), in contrast with the native PGE, which originated during the low-temperature serpentinization of the ultramafic host of the chromitites (secondary PGM).The primary PGM inclusions in the Ojen chromite are unusual compared with PGM inclusions in chromitites from tectonitic upper-mantle of ophiolites and other alpine-type complexes in that i) they display a great variety of mineral species sulfides, sulfarsenides and arsenides, and ii) comprise specific phases of all six PGE. The singularity of the primary PGM mineralization probably reflects high activities of both S and As during chromite precipitation at Serrania de Ronda to be related with particular physico-chemical conditions during uplifting of sub-continental, astenospheric mantle.The nature, composition, and paragenetic association of secondary PGM at Ojen confirm the relatively-high mobility of the PGE at low temperature, and indicate that remobilization can be selective under appropriate redox conditions causing separation and redistribution of the PGE in the rocks as a result of the alteration process.

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Platingruppen-Minerale in chromititen aus dem ojen-lherzolithmassiv (Serranía de Ronda, Betische Kordillere, Süd-Spanien)

Zusammenfassung Platingruppen-Minerale in Chromititen aus dem Ojen-Lherzolithmassiv (Serranía de Ronda, Betische Kordillere, Süd-Spanien) In den Chromititen (Cr-Erzen) aus dem Ojen-Lherzolithmassiv (Serranía de Ronda, Betische Kordillere, Süd-Spanien) warden Platingruppen-Minerale (PGM) als einzelne Einschlüsse im Chromit and in den begleitenden Silikaten gefunden. Die Mineralogie der PGM setzt sich aus Sulfiden [Laurit, Erlichmanit, Malanit, einem unbenannten (Ni-Fe-Cu)₂ (Ir, Rh)S₃ und einem nicht identifizierten Pd-S], Sulfarseniden (Irarsit, Hollingworthit, Ruarsit und Osarsit), Arseniden [Sperrylit, einem nicht identifizierten (Pd, Ni)-As], einer nicht identifizierten Pd-Bi-Verbindung sowie gediegenen Platingruppen-Elementen (PGE) bestchend aus Ru and Pt-Fe-Legierungen, zusammen. Texturelle Untersuchungen haben ergeben, daß die PGE-Chalkogenide mit S und As im Zuge der Chromitfällung (primäre PGM) in den hochtemperierten, magmatischen Stadien gebildet warden, während die gediegenen PGE während der niedriggradigen Serpentini sierung des ultramafischen Nebengesteins der Chromitite (sekundäre PGM) gebildet warden.Die primären PGM-Einschlüsse in den Ojen-Chromiten sind im Vergleich zu PGM-Einschlüssen in Chromititen aus dem tektonisierten oberen Mantel in Ophiolithen und anderen alpinotypen Komplexen ungewöhnlich: i) Einerseits zeigen sie eine große Vielfalt an Mineralarten aus der Gruppe der Sulfide, Sulfarsenide und Arsenide. ii) Andererseits enthalten sie spezifische Phasen aller sechs PGE. Die Einzigartigkeit der primären PGM-Mineralisation könnte hohe Aktivitäten von S and As während der Chromit-Fällung in Serranía de Ronda widerspiegeln, die mit besonderen physiko-chemischen Bedingungen während der Hebung des subkontinentalen, asthenosphärischen Mantels zusammenhängen.Die Art, die Zusammensetzung and die paragenetische Vergesellschaftung von sekundären PGM in Ojen bestätigen die relativ hohe Mobilität der PGE bei niedriger Temperatur und zeigen, daß die Remobilisierung unter geeigneten Redox-Bedingungen selektiv wirken kann, wodurch eine Trennung und Neuverteilung der PGE in den Gesteinen als Ergebnis des Alterationsprozesses bewirkt wird.

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With 7 Figures     

Late Quaternary deformation on the island on Pantelleria: New constraints for the recent tectonic evolution of the Sicily Channel Rift (southern Italy)

Structural observations carried out on the volcanic Island of Pantelleria show that the tectonic setting is dominated by NNE trending normal faults and by NW-striking right-lateral strike-slip faults with normal component of motion controlled by a ≈N 100°E oriented extension. This mode of deformation also controls the development of the eruptive fissures, dykes and eruptive centres along NNE–SSW belts that may thus represent the surface response to crustal cracking with associated magma intrusions. Magmatic intrusions are also responsible for the impressive vertical deformations that affect during the Late Quaternary the south-eastern segment of the island and producing a large dome within the Pantelleria caldera complex. The results of the structural analysis carried out on the Island of Pantelleria also improves the general knowledge on the Late Quaternary tectonics of the entire Sicily Channel. ESE–WNW directed extension, responsible for both the tectonic and volcano-tectonic features of the Pantelleria Island, also characterizes, at a greater scale, the entire channel as shown by available geodetic and seismological data. This mode of extension reactivates the older NW–SE trending fault segments bounding the tectonic troughs of the Channel as right-lateral strike-slip faults and produces new NNE trending pure extensional features (normal faulting and cracking) that preferentially develop at the tip of the major strike-slip fault zones. We thus relate the Late Quaternary volcanism of the Pelagian Block magmatism to dilatational strain on the NNE-striking extensional features that develop on the pre-existing stretched area and propagate throughout the entire continental crust linking the already up-welled mantle with the surface.     

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.     

Geologic remote sensing (Ninth Thematic Conference)

Geologic remote sensing (Ninth Thematic Conference)