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901.
The volcano-tectonic evolution of Concepción,Nicaragua 总被引:1,自引:1,他引:0
We describe the evolution of Concepción volcano by integrating regional geology, eruptive activity, morphology, stratigraphy,
petrology, structure and active deformation data. This Nicaraguan volcano is set close to the back limb of the northwest-trending
Tertiary Rivas anticline, a regional structure that bounds the southwest side of Lake Nicaragua. Concepción rises 1,600 m
above a 1-km-thick sequence of Quaternary lacustrine mud-stones. There is no record of volcanism in the lake prior to Concepción.
In addition, the only nearby volcano, Maderas volcano, has not deposited material on Concepción because of the trade winds.
Thus, Concepción (and Made ras, too) can be considered as pristine volcanic environments, unaffected by other centres. A topographic
rise forms an annulus 20 km in diameter around the cone. The rise is created by thrust-related folds at the western base,
where the trade winds have accumulated a thick sequence of tephra, and by mud diapirs at the eastern base where only lake
mudstones are present. Four magmatic-eruptive episodes exist in the stratigraphic record. The first begins with primitive
low-alumina basalt and subsequently evolves to dacitic compositions. The following three episodes begin with high-alumina
basalts and evolve only to silicic andesites. The occurrence of the high-alumina basalt after the first episode is indicative
of crystal fractionation at lower crustal depths. The first episode may be associated with a compressive phase of volcano
evolution. In this phase, the edifice load compresses substrata, allowing a longer magma residence time and differentiation
in a shallow reservoir (possibly located at the density contrast between the lake sediments and the Tertiary flysch). During
the next three episodes the weak sediments below the volcano started to rupture and yield under its increasing load, beginning
a thrusting/diapiring phase of volcano evolution. Because of outward thrusting, vertical and horizontal stresses above the
chamber were reduced, allowing magma to erupt more easily and to reach a lesser degree of evolution. If we consider the future
evolution of Concepción, the differentiation in the shallow reservoir has probably generated a cumulitic complex, which eventually
will start to deform and spread, beginning another, this time plutonic, spreading phase. This phase, which may be beginning
now, could allow less evolved magmas to be erupted again. Four components influence the phases of volcano evolution: (1) the
regional geology that is the boundary condition of the environment, (2) the substrata rheology that controls deformation,
(3) the load of the volcanic edifice and (4) the magma, which provides the input of mass and energy. Our model of volcanic
evolution suggests that Concepción is a complex geologic environment. The volcanic activity, tectonics and hazards can only
be constrained through a complete knowledge of the many components of this environment.
Published online: 20 February 2003
Editorial responsibility: R. Cioni 相似文献
902.
Marion GS Dunbar RB Mucciarone DA Kremer JN Lansing JS Arthawiguna A 《Marine pollution bulletin》2005,50(9):931-944
This study introduces a new method of tracing the history of nutrient loading in coastal oceans via delta(15)N analysis of organic nitrogen preserved in the skeleton of the massive Porites coral. Four coral cores were collected in Bali, Indonesia, from reefs exposed to high levels of fertilizers in agricultural run-off, from lagoonal corals impacted by sewage, and from a reef located 30 km offshore. Skeletal delta(15)N in the agriculturally exposed coral declined from 10.7+/-0.4 per thousand in 1970-1971, when synthetic fertilizers (-0.8 per thousand+/-0.2 per thousand) were introduced to Bali, to a depleted "anthropogenic" baseline of 3.5 per thousand+/-0.4% in the mid-1990s. delta(15)N values were negatively correlated with rainfall, suggesting that marine delta(15)N lowers during flood-bourn influxes of waste fertilizers. Reef cores exposed to untreated sewage in terrestrial discharge were enriched (7.8 and 7.3+/-0.4 per thousand), while the offshore core reflected background oceanic signals (6.2+/-0.4 per thousand). delta(15)N, N concentration, and C:N systematics indicate that the N isotopic composition of skeletal organic matter was generally well preserved over 30 years. We suggest that skeletal organic delta(15)N can serve as a recorder of past nitrogen sources. In Bali, this tracer suggests that the intensification of Western style agricultural practices since 1970 are contributing to the degradation of coastal coral reefs. 相似文献
903.
Paleogeography of the Upper Rhine Graben (URG) and the Swiss Molasse Basin (SMB) from Eocene to Pliocene 总被引:1,自引:1,他引:0
Jean-Pierre Berger Bettina Reichenbacher Damien Becker Matthias Grimm Kirsten Grimm Laurent Picot Andrea Storni Claudius Pirkenseer Christian Derer Andreas Schaefer 《International Journal of Earth Sciences》2005,94(4):697-710
Twenty paleogeographic maps are presented for Middle Eocene (Lutetian) to Late Pliocene times according to the stratigraphical data given in the companion paper by Berger et al. this volume. Following a first lacustrine-continental sedimentation during the Middle Eocene, two and locally three Rupelian transgressive events were identified with the first corresponding with the Early Rupelian Middle Pechelbronn beds and the second and third with the Late Rupelian Serie Grise (Fischschiefer and equivalents). During the Early Rupelian (Middle Pechelbronn beds), a connection between North Sea and URG is clearly demonstrated, but a general connection between North Sea, URG and Paratethys, via the Alpine sea, is proposed, but not proved, during the late Rupelian. Whereas in the southern URG, a major hiatus spans Early Aquitanian to Pliocene times, Early and Middle Miocene marine, brackish and freshwater facies occur in the northern URG and in the Molasse Basin (OMM, OSM); however, no marine connections between these basins could be demonstrated during this time. After the deposition of the molasse series, a very complex drainage pattern developed during the Late Miocene and Pliocene, with a clear connection to the Bresse Graben during the Piacenzian (Sundgau gravels). During the Late Miocene, Pliocene and Quaternary sedimentation persisted in the northern URG with hardly any interruptions. The present drainage pattern of the Rhine river (from Alpine area to the lower Rhine Embayment) was not established before the Early Pleistocene. 相似文献
904.
James E. Cloern Andrea E. Alpine Brian E. Cole Raymond L.J. Wong James F. Arthur Melvin D. Ball 《Estuarine, Coastal and Shelf Science》1983,16(4):415-429
Phytoplankton dynamics in the upper reach of the northern San Francisco Bay estuary are usually characterized by low biomass dominated by microflagellates or freshwater diatoms in winter, and high biomass dominated by neritic diatoms in summer. During two successive years of very low river discharge (the drought of 1976-77), the summer diatom bloom was absent. This is consistent with the hypothesis that formation of the diatom population maximum is a consequence of the same physical mechanisms that create local maxima of suspended sediments in partially-mixed estuaries: density-selective retention of particles within an estuarine circulation cell. Because the estuary is turbid, calculated phytoplankton growth rates are small in the central deep channel but are relatively large in lateral shallow embayments where light limination is less severe. When river discharge falls within a critical range (100–350 m3 s?1) that positions the suspended particulate maximum adjacent to the productive shallow bays, the population of neritic diatoms increases. However, during periods of high discharge (winter) or during periods of very low discharge (drought), the suspended particulate maximum is less well-defined and is uncoupled (positioned downstream or upstream) from the shallow bays of the upper estuary, and the population of neritic diatoms declines. Hence, the biomass and community composition of phytoplankton in this estuary are controlled by river discharge. 相似文献
905.
906.
907.
Giovanni B. Valsecchi Andrea Milani Giovanni F. Gronchi Steven R. Chesley 《Celestial Mechanics and Dynamical Astronomy》2000,78(1-4):83-91
Öpiks theory of close encounters allows us to deduce an analytic expression for the distribution of energy perturbations at close encounters between small bodies and planets. The derivation of this expression highlights a simple geometric structure in the plane containing the planet and perpendicular to the unperturbed planetocentric velocity vector. The analytic formulation reproduces well the results of the numerical integrations that first pointed out the asymmetries in the distribution of energy perturbations. 相似文献
908.
Andrea Donnellan John Rundle Geoffrey Fox Dennis McLeod Lisa Grant Terry Tullis Marlon Pierce Jay Parker Greg Lyzenga Robert Granat Margaret Glasscoe 《Pure and Applied Geophysics》2006,163(11-12):2263-2279
We are developing simulation and analysis tools in order to develop a solid Earth Science framework for understanding and studying active tectonic and earthquake processes. The goal of QuakeSim and its extension, the Solid Earth Research Virtual Observatory (SERVO), is to study the physics of earthquakes using state-of-the-art modeling, data manipulation, and pattern recognition technologies. We are developing clearly defined accessible data formats and code protocols as inputs to simulations, which are adapted to high-performance computers. The solid Earth system is extremely complex and nonlinear, resulting in computationally intensive problems with millions of unknowns. With these tools it will be possible to construct the more complex models and simulations necessary to develop hazard assessment systems critical for reducing future losses from major earthquakes. We are using Web (Grid) service technology to demonstrate the assimilation of multiple distributed data sources (a typical data grid problem) into a major parallel high-performance computing earthquake forecasting code. Such a linkage of Geoinformatics with Geocomplexity demonstrates the value of the Solid Earth Research Virtual Observatory (SERVO) Grid concept, and advances Grid technology by building the first real-time large-scale data assimilation grid. 相似文献
909.
Mehmet Aktas Galip Aydin Andrea Donnellan Geoffrey Fox Robert Granat Lisa Grant Greg Lyzenga Dennis McLeod Shrideep Pallickara Jay Parker Marlon Pierce John Rundle Ahmet Sayar Terry Tullis 《Pure and Applied Geophysics》2006,163(11-12):2281-2296
We describe the goals and initial implementation of the International Solid Earth Virtual Observatory (iSERVO). This system is built using a Web Services approach to Grid computing infrastructure and is accessed via a component-based Web portal user interface. We describe our implementations of services used by this system, including Geographical Information System (GIS)-based data grid services for accessing remote data repositories and job management services for controlling multiple execution steps. iSERVO is an example of a larger trend to build globally scalable scientific computing infrastructures using the Service Oriented Architecture approach. Adoption of this approach raises a number of research challenges in millisecond-latency message systems suitable for internet-enabled scientific applications. We review our research in these areas. 相似文献
910.
Within the scope of the further development of geochemical transport models the consideration of the influence of the heterogeneous structures of the geological layers plays an important role. For the verification and parameter estimation of such models it is necessary to measure the heterogeneous transport and sorption processes inside the samples. Tomographic radiotracer methods (positron emission tomography (PET)) enable nondestructive spatially resolved observations of the transport processes in these layers. A special quantitative evaluation system for geoscientific PET studies was developed. Investigations of the water flow distribution in a drill core of a lignite mining dump and of the migration of Cu ions in a horizontal soil column illustrate the potential of this method. Spatial distribution functions of the flow velocity, the specific mass flow and the longitudinal dispersivity were determined on the basis of PET investigations. 相似文献