Volcanological and petrological evolution of Marsili Seamount (southern Tyrrhenian Sea)     

Teresa Trua  Giancarlo Serri  Michael Marani  Alberto Renzulli  Fabiano Gamberi 《Journal of Volcanology and Geothermal Research》2002,114(3-4)

A swath bathymetric survey was conducted on Marsili Volcano, the biggest seamount in the Tyrrhenian Sea. It stands 3000 m above the surrounding oceanic crust of the 3500 m-deep Marsili back-arc basin and is axially located within the basin. The seamount has an elongated shape and presents distinctive morphology, with narrow (<1000 m) ridges, made up of several elongated cones, on the summit zone and extensive cone fields on its lower flanks. A dredging campaign carried out at water depths varying between 3400 and 600 m indicates that most of Marsili Seamount is composed of medium-K calc-alkaline basalts. Evolved high-K andesites were only recovered from the small cones on the summit axis zone. Petrological and geochemical characteristics of the least differentiated basalts reveal that at least two varieties of magmas have been erupted on the Marsili Volcano. Group 1 basalts have plagioclase and olivine as dominant phases and show lower Al, Ca, K, Ba, Rb and Sr, and higher Fe, Na, Ti and Zr with respect to a second type of basaltic magma. Group 2 basalts reveal the presence of clinopyroxene as an additional phenocryst phase. In addition, the two basaltic magmas have different original pre-eruptive H₂O content (group 1, H₂O-poor and group 2, H₂O-rich). Moreover, comparison of the compositional trends and mineralogical compositions obtained from MELTS [Ghiorso, M.S., Sack, R.O., Contrib. Mineral. Petrol. 119 (1995) 197–212] fractional crystallization calculations reveal that the evolved andesites can only exclusively be derived from a low-pressure (0.3 kbar) fractionation of magmas compositionally similar to the least evolved group 2 basalts. Finally, we suggest that the high vesicularity of the basalts sampled at relatively great depths (>2400 m) on the edifice is governed by H₂O and, probably, CO₂ exsolution and is not a feature indicative of shallow water depth eruption.  相似文献   

Predicting average annual groundwater levels from climatic variables: an empirical model   总被引：8，自引：0，他引：8  

Zhuoheng Chen  Stephen E. Grasby  Kirk G. Osadetz 《Journal of Hydrology》2002,260(1-4):102-117

On the basis of one-dimensional theoretical water flow model, we demonstrate that the groundwater level variation follows a pattern similar to recharge fluctuation, with a time delay that depends on the characteristics of aquifer, recharge pattern as well as the distance between the recharge and observation locations. On the basis of a water budget model and the groundwater flow model, we propose an empirical model that links climatic variables to groundwater level. The empirical model is tested using a partial data set from historical records of water levels from more than 80 wells in a monitoring network for the carbonate rock aquifer, southern Manitoba, Canada. The testing results show that the predicted groundwater levels are very close to the observed ones in most cases. The overall average correlation coefficient between the predicted and observed water levels is 0.92. This proposed empirical statistical model could be used to predict variations in groundwater level in response to different climate scenarios in a climate change impact assessment.  相似文献   

Evaluating Earthquake-Triggered Landslide Hazard at the Basin Scale Through Gis in the Upper Sele River Valley   总被引：6，自引：0，他引：6  

Domenico Capolongo  Alberto Refice  Joseph Mankelow 《Surveys in Geophysics》2002,23(6):595-625

To evaluate techniques for assessing earthquake-triggeredlandslide hazard in the Southern Apennines (Italy), a GIS-based analysis was used to modelseismically induced slope deformations. Geological, geotechnical, geomorphological and seismologicaldata were integrated into a standard earthquake slope stability model. The model assessed thelandslide potential that existed during the 1980 Irpinian earthquake in the Upper Sele river Valley.The standard Newmark displacement analysis, widely used for predicting the location of shallowunstable slopes, does not take into account errors and/or uncertainties in the input parameters.Therefore, a probabilistic Newmark displacement analysis technique has been used. Probabilistictechniques allow, e.g., an estimation of the probability that a slope will exceed a certain criticalvalue of Newmark displacement. In our probabilistic method, a Monte-Carlo based simulation modelis used in conjunction with a GIS. The random variability of geotechnical data is modelled by probabilitydensity functions (pdfs), while for the seismic input three different regression laws wereconsidered. Input probability distributions are sampled and the resulting values input into empiricalrelations for estimating Newmark displacement. The outcome is a map in which to each siteis related a spatial probability distribution for the expected displacement in response to seismic loading.Results of the experiments show a high grade of uncertainty in the application of the Newmarkanalysis both for the deterministic and probabilistic approach in a complex geological setting suchas the high Sele valley, quite common in the Southern Apennines. They show a strong dependence onthe reliability of the spatial data used in input, so that, when the model is used at basin scale,results are strongly influenced by local environmental condition (e.g., topography, lithology, groundwatercondition) and decrease the model performance.  相似文献   

Gravity evidence for a larger Limpopo Belt in southern Africa and geodynamic implications   总被引：2，自引：0，他引：2  

R. T. Ranganai  A. B. Kampunzu  E. A. Atekwana  B. K. Paya  J. G. King  D. I. Koosimile  E. H. Stettler 《Geophysical Journal International》2002,149(3):F9-F14

  相似文献   

Enrichissement en uranium authigène dans les sédiments glaciaires de l'océan AustralEnrichments in authigenic uranium in glacial sediments of the Southern Ocean     

Laurent Dezileau  Gilles Bareille  Jean-Louis Reyss 《Comptes Rendus Geoscience》2002,334(14):1039-1046

Four sediment cores from the Polar frontal zone and the Antarctic zone in the Indian sector of the Southern Ocean present an increase of authigenic uranium during glacial periods. We show that this increase in uranium is due to a combination of (i) an increase in the lateral transport of organic matter, (ii) a decrease in the oxygen in deep waters, and (iii) a process of diagenesis. It appears that uranium concentration cannot be used as a proxy of palaeoproductivity in the Southern Ocean, as previously suggested by Kumar et al. in 1995. To cite this article: L. Dezileau et al., C. R. Geoscience 334 (2002) 1039–1046.  相似文献   

The geography of water conflict and cooperation: internal pressures and international manifestations   总被引：2，自引：0，他引：2  

Meredith Giordano  Mark Giordano  & Aaron Wolf 《The Geographical journal》2002,168(4):293-312

Studies on transboundary water conflict and cooperation generally consider interstate relations over shared water resources as distinct from intrastate relations. While connections have been made between international water relations and regional relationships in general, it is conceivable that international water conflict and cooperation may also be influenced by domestic water events and vice versa. This paper seeks to investigate the dynamics of water interactions across geographic scale and their relationship to broader international affairs. The research approach involves the creation of an analytical framework for assessing possible linkages between external and internal interactions over freshwater resources. The framework is applied to three case studies – the Middle East, South Asia and Southern Africa – utilizing 'event data'. To validate the findings from the quantitative analyses, the results are compared with conventional qualitative understandings of water and overall relations in the three regions. The comparison demonstrates not only the efficacy of the analytical framework in general, but also highlights, at least in terms of the specific case studies selected, the disparate water dynamics across geographic regions and the importance of considering water events, both national and international, within larger political and historical contexts.  相似文献   

Infiltration on mountain slopes: a comparison of three environments     

Carol P. Harden  P. Delmas Scruggs 《Geomorphology》2003,55(1-4):5

Water is well established as a major driver of the geomorphic change that eventually reduces mountains to lower relief landscapes. Nonetheless, within the altitudinal limits of continuous vegetation in humid climates, water is also an essential factor in slope stability. In this paper, we present results from field experiments to determine infiltration rates at forested sites in the Andes Mountains (Ecuador), the southern Appalachian Mountains (USA), and the Luquillo Mountains (Puerto Rico). Using a portable rainfall simulator–infiltrometer (all three areas), and a single ring infiltrometer (Andes), we determined infiltration rates, even on steep slopes. Based on these results, we examine the spatial variability of infiltration, the relationship of rainfall runoff and infiltration to landscape position, the influence of vegetation on infiltration rates on slopes, and the implications of this research for better understanding erosional processes and landscape change.Infiltration rates ranged from 6 to 206 mm/h on lower slopes of the Andes, 16 to 117 mm/h in the southern Appalachians, and 0 to 106 mm/h in the Luquillo Mountains. These rates exceed those of most natural rain events, confirming that surface runoff is rare in montane forests with deep soil/regolith mantles. On well-drained forested slopes and ridges, apparent steady-state infiltration may be controlled by the near-surface downslope movement of infiltrated water rather than by characteristics of the full vertical soil profile. With only two exceptions, the local variability of infiltration rates at the scale of 10° m overpowered other expected spatial relationships between infiltration, vegetation type, slope position, and soil factors. One exception was the significant difference between infiltration rates on alluvial versus upland soils in the Andean study area. The other exception was the significant difference between infiltration rates in topographic coves compared to other slope positions in the tabonuco forest of one watershed in the Luquillo Mountains. Our research provides additional evidence of the ability of forests and forest soils to preserve geomorphic features from denudation by surface erosion, documents the importance of subsurface flow in mountain forests, and supports the need for caution in extrapolating infiltration rates.  相似文献   

BELGIAN SETTLEMENT AND SOCIETY IN THE INDIANA RUST BELT*     

SUSAN E. HUME 《Geographical review》2003,93(1):30-50

ABSTRACT. At first glance the industrial city of Mishawaka, near the northern border of Indiana, appears to be ethnically homogeneous. Closer examination, however, reveals the rich ethnic heritage of Mishawaka, as it does in so many other Rust Belt cities from Pittsburgh to Chicago. One of the most fascinating of these immigrant stories is the rise of Belgian Town, on Mishawaka's southwest side. This study examines residential, commercial, and social patterns of this evolving ethnic community during the first three decades of the twentieth century. Although industrial jobs attracted immigrants to the city, creation of a Flemish Catholic church provided the foundation on which to build a tightly knit Belgian community.  相似文献   

南天山西段古生代火山岩Ar-Ar年龄新资料   总被引：7，自引：0，他引：7  

龚福华  李曰俊  王清华  胡世玲  黄智斌  罗俊成 《高校地质学报》2003,9(3):494-498

根据新近采自中国南天山西段志留-泥盆系乌帕塔尔坎群中的安山岩样品和石炭-二叠纪康克林组上部英安岩角砾样品的全岩Ar-Ar定年测试,乌帕塔尔坎群安山岩的坪年龄为427.70±0.60 Ma,等时年龄为426.96±4.57 Ma; 康克林组上部的英安岩角砾的坪年龄为288.16±0.40 Ma,等时年龄为289.18±2.02 Ma.测试结果为研究中国南天山(西段)古生代造山带的构造体系提供了新的依据.  相似文献   

云南腾冲-潞西金成矿带地质特征与成矿预测   总被引：1，自引：0，他引：1  

普传杰  秦德先 《矿产与地质》2003,17(4):523-525

腾冲-潞西金成矿带是云南省重要金成矿带之一。通过分析其地质特征，解剖矿带内典型金矿床，讨论矿带成矿模式及找矿方向，进而提出了矿带内两个重要矿化集中区(段)。  相似文献