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11.
Claude Robin Philippe Mossand Guy Camus Jean-Marie Cantagrel Alain Gourgaud Pierre M. Vincent 《Journal of Volcanology and Geothermal Research》1987,31(1-2)
The evolution of the Colima volcanic complex can be divided into successive periods characterized by different dynamic and magmatic processes: emission of andesitic to dacitic lava flows, acid-ash and pumice-flow deposits, fallback nuées ardentes leading to pyroclastic flows with heterogeneous magma, plinian air-fall deposits, scoriae cones of alkaline and calc-alkaline nature. Four caldera-forming events, resulting either from major ignimbrite outbursts or Mount St. Helens-type eruptions, separate the main stages of development of the complex from the building of an ancient shield volcano (25 × 30 km wide) up to two summit cones, Nevado and Fuego.The oldest caldera, C1 (7–8 km wide), related to the pouring out of dacitic ash flows, marks the transition between two periods of activity in the primitive edifice called Nevado I: the first one, which is at least 0.6 m.y. old, was mainly andesitic and effusive, whereas the second one was characterized by extrusion of domes and related pyroclastic products. A small summit caldera, C2 (3–3.5 km wide), ended the evolution of Nevado I.Two modern volcanoes then began to grow. The building of the Nevado II started about 200,000 y. ago. It settled into the C2 caldera and partially overflowed it. The other volcano, here called Paleofuego, was progressively built on the southern side of the former Nevado I. Some of its flows are 50,000 y. old, but the age of its first outbursts is not known. However, it is younger than Nevado II. These two modern volcanoes had similar evolutions. Each of them was affected by a huge Mount St. Helens-type (or Bezymianny-type) event, 10,000 y. ago for the Paleofuego, and hardly older for the Nevado II. The landslides were responsible for two horseshoe-shaped avalanche calderas, C3 (Nevado) and C4 (Paleofuego), each 4–5 km wide, opening towards the east and the south. In both cases, the activity following these events was highly explosive and produced thick air-fall deposits around the summit craters.The Nevado III, formed by thick andesitic flows, is located close to the southwestern rim of the C3 caldera. It was a small and short-lived cone. Volcan de Fuego, located at the center of the C4 caldera, is nearly 1500 m high. Its activity is characterized by an alternation of long stages of growth by flows and short destructive episodes related to violent outbursts producing pyroclastic flows with heterogeneous magma and plinian air falls.The evolution of the primitive volcano followed a similar pattern leading to formation of C1 and then C2. The analogy between the evolutions of the two modern volcanoes (Nevado II–III; Paleofuego-Fuego) is described. Their vicinity and their contemporaneous growth pose the problem of the existence of a single reservoir, or two independent magmatic chambers, after the evolution of a common structure represented by the primitive volcano. 相似文献
12.
13.
PRELIMINARY STUDY ON THE DISSOLVED AND COLLOIDAL ORGANIC CARBON IN THE ZHUJIANG RIVER ESTUARY 总被引:3,自引:0,他引:3
INTRODUCTIONEstuariescompriseamajorbiogeochemicalinterfaceconnectingthelandandthesea (Man toura,1 987) .Thebehaviorandfateofaparticularriver bornesubstanceintroducedintoanestuaryisdeterminedtoalargeextentbythebiogeochemicalpropertiesofthesubstanceaswellasp… 相似文献
14.
15.
The Tillaberi stone fell in April 1970 in Republic of Niger. In the 157 g piece sent to Paris, a centimeter wide lithic inclusion is found. Contrary to previous assumptions, the stone is an L6 chondrite in which few chondrules can be distinguished; olivine is Fa 25 ± 0.4 percent with minor amounts of Ca, Cr, Ti; orthopyroxene is Fs 21.6 ± 1.2 percent with a rather large scatter of the amounts of minor elements. The feldspar, well developed, contains 10 to 11 percent An, 84 to 85 percent Ab, five percent Or, and 0.77 ± 0.09 percent FeO. The lithic inclusion contains much feldspar which corresponds to 14 to 17 percent An, 75 to 79 percent Ab, four to five percent Or without almost any FeO. This inclusion contains also rounded grains of olivine and minute crystals of chromite. It has a frothy microdoleritic texture with a frozen border against the chondritic material. As the nickel rich grains are either martensite or acicular plessite and the silicates are undeformed, a quick cooling after a short but intense heating is postulated to account for the mineralogical characteristics. 相似文献
16.
Characterization of Compass M-1 signals 总被引:7,自引:4,他引:3
André Hauschild Oliver Montenbruck Jean-Marie Sleewaegen Lennard Huisman Peter J. G. Teunissen 《GPS Solutions》2012,16(1):117-126
An analysis of observations from China’s first medium earth orbit satellite Compass M-1 is presented, with main focus on the
first orbit and clock solution for this satellite. The orbit is computed from laser ranging measurements. Based on this orbit
solution, the apparent clock offset is estimated using measurements from two GNSS receivers, which allow Compass tracking.
The analysis of the clock solutions reveals unexpectedly high dynamics in the pseudorange and carrier-phase observations.
Furthermore, carrier-to-noise density ratio, pseudorange noise, and multipath are analyzed and compared to GPS and GIOVE.
The results of the clock analysis motivate further research on the signals of the geostationary satellites of the Compass
constellation. 相似文献
17.
Recent studies have shown the capabilities of Global Positioning System (GPS) carrier phases for frequency transfer based
on the observations from geodetic GPS receivers driven by stable atomic clocks. This kind of receiver configuration is the
kind primarily used within the framework of the International GPS Service (IGS). The International GPS Service/Bureau International
des Poids et Mesures (IGS/BIPM) pilot project aims at taking advantage of these GPS receivers to enlarge the network of Time
Laboratories contributing to the realization of the International Atomic Time (TAI).
In this article, we outline the theory necessary to describe the abilities and limitations of time and frequency transfer
using the GPS code and carrier phase observations. We report on several onsite tests and evaluate the present setup of our
12-channel IGS receiver (BRUS), which uses a hydrogen maser as an external frequency reference, to contribute to the IGS/BIPM
pilot project.
In the initial experimental setup, the receivers had a common external frequency reference; in the second setup, separate
external frequency references were used. Independent external clock monitoring provided the necessary information to validate
the results. Using two receivers with a common frequency reference and connected to the same antenna, a zero baseline, we
were able to use the carrier phase data to derive a frequency stability of 6 × 10−16 for averaging times of one day. The main limitation in the technique originates from small ambient temperature variations
of a few degrees Celsius. While these temperature variations have no effect on the functioning of the GPS receiver within
the IGS network, they reduce the capacities of the frequency transfer results based on the carrier phase data. We demonstrate
that the synchronization offset at the initial measurement epoch can be estimated from a combined use of the code and carrier
phase observations. In our test, the discontinuity between two consecutive days was about 140 ps. ? 1999 John Wiley & Sons,
Inc. 相似文献
18.
Correction of inertial oscillations by assimilation of HF radar data in a model of the Ligurian Sea 总被引:1,自引:1,他引:0
This article aims at analyzing if high-frequency radar observations of surface currents allow to improve model forecasts in the Ligurian Sea, where inertial oscillations are a dominant feature. An ensemble of ROMS models covering the Ligurian Sea, and nested in the Mediterranean Forecasting System, is coupled with two WERA high-frequency radars. A sensitivity study allows to determine optimal parameters for the ensemble filter. By assimilating observations in a single point, the obtained correction shows that the forecast error covariance matrix represents the inertial oscillations, as well as large- and meso-scale processes. Furthermore, it is shown that the velocity observations can correct the phase and amplitude of the inertial oscillations. Observations are shown to have a strong effect during approximately half a day, which confirms the importance of using a high temporal observation frequency. In general, data assimilation of HF radar observations leads to a skill score of about 30% for the forecasts of surface velocity. 相似文献
19.
The ecohydrodynamics of the Gibraltar Strait and the Western Alboran Sea is investigated using a 3-D, two-way nested, coupled
hydrodynamic/plankton ecosystem model, exploiting the MEDATLAS climatological database. A high-resolution model (~1 km) of
the Gibraltar/Western Alboran region embedded within a coarse-resolution model of the West Mediterranean (~5 km) is implemented.
The model seasonal climatology of the 3-D circulation and the flow characteristics at the Gibraltar Strait and the Alboran
Sea are discussed, and their impact on the plankton ecosystem evolution is explored. An important ecohydrodynamic feature
produced by the model is a permanent upwelling zone in the northwestern part of the Alboran Sea in agreement with observations.
Model results show that both horizontal and vertical current intensity of the Atlantic Jet increases progressively at the
strait to obtain maximum values in the northeastern Mediterranean entrance, inducing an upward displacement of the nitracline.
The nutrient-rich water transport through the strait along with the generation of cyclonic vorticity in the northwestern Alboran
Sea result in the accumulation of nutrients there and thus induce a permanent fertilisation of this area. 相似文献
20.
Jean-Marie Auzende Daniel Bideau Enrico Bonatti Mathilde Cannat José Honnorez Yves Lagabrielle Jacques Malavieille Vassilios Mamaloukas-Frangoulis Catherine Mével 《地学学报》1990,2(1):68-73
One of the two objectives of the Vemanaute cruise of the French deep submersible Nautile, was the geological study of the eastern intersection area between the Mid-Atlantic Ridge (MAR) and the Vema Fracture Zone in the equatorial Atlantic. Fourteen dives were conducted that allowed detailed geological survey and sampling of the main morphostructural units of this area: the northern and southern walls of the fracture zone, the median ridge, the northern and southern troughs and the nodal basin. In situ observations of recent tectonic features such as furrows, ridges and circular depressions, concentrated within the southern trough, allowed us to establish the location and the size of the present-day displacement zone. Geological investigations have shown that the nodal basin is entirely floored by basalts thus contrasting with other equivalent areas such as the Kane and Oceanographer fracture zone-MAR eastern intersections. Finally, this study stresses the great opposition between the relatively old and tectonically inactive northern part of the fracture, and the southern part which shows active tectonics and recent volcanic activity. 相似文献