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81.
François Risacher Bertrand Fritz Arturo Hauser 《Journal of South American Earth Sciences》2011,31(1):153-170
Thermal waters of northern (18°–27°S) and southern (37°–45°S) Chile occur in two very different climatic, geologic and hydrologic environments: arid closed basins with abundant evaporites in the north; humid climate and well drained valleys in the south. The origin and behavior of the main components of the two groups of waters are examined and compared to each other. The modeling of the alteration of volcanic rocks leads to water compositions very different from those observed both in the north and south. In addition to hydrothermal alteration and deep emanations, the Cl/Br ratio reveals a major contribution of saline waters to the two groups: infiltrating brines from salt lakes in the north; seawater in the south.In the north, concentrations of Cl, Br, Na, K, Ca, SO4, Li, B, Si result from the mixing of alteration waters with recycled brines. Hydrothermal alteration is obscured by this massive saline input, except for Mg. δ34S values are consistent with an origin of sulfate from salar brines, which are themselves derived from deep Tertiary gypsum. In the south, two processes account for the composition of thermal waters: mixing of alteration waters with seawater and deep magmatic contribution. The mixing process controls the concentration of Cl, Br, Na, Alk, Si, K, Ca, Mg. Magmatic inputs are detectable for SO4, Li and B. δ34S suggests that sulfate stems from the mixing of alteration waters with either marine SO4 in coastal waters or with deep SO2 in inland waters. In both the north and south, the Mg concentration is drastically lowered (<1 μmol/L) by the probable formation of a chlorite-type mineral. In the south, very small amounts of seawater (<1% in volume) are sufficient to imprint a clear signature on thermal waters. Not only coastal springs are affected by seawater mixing, but also remote inland springs, as far as 150 km from the sea. Subduction of marine sediments in the accretive margin could be the source of the marine imprint in thermal waters of southern Chile. Seawater may be expelled from the subducted lithosphere and incorporated into the mantle source. 相似文献
82.
It has been proposed that erosional unloading by focused incision can be accommodated by flexural rebound, which in turn, potentially exerts a positive feedback on erosion. This paper presents morphometric data from the La Paz drainage basin in the Bolivian Andes to illustrate the effects of such a feedback mechanism between erosion and crustal bending. The Rio La Paz is a prominent system with the headwaters on the Altiplano and a trunk stream segment that cuts across the Cordillera Real thereby connecting large portions of the Altiplano with the Amazon Basin. The flexural feedback model explains why all drainages beyond the watershed disperse their waters to the Altiplano. It also provides an explanation for the presence of the highest peaks just next to the location where the La Paz River cuts into the bedrock across the Cordillera Real. 相似文献
83.
Jrg Fritz Natalia Artemieva Ansgar Greshake 《Meteoritics & planetary science》2005,40(9-10):1393-1411
Abstract— We investigated the transfer of meteorites from Mars to Earth with a combined mineralogical and numerical approach. We used quantitative shock pressure barometry and thermodynamic calculations of post‐shock temperatures to constrain the pressure/temperature conditions for the ejection of Martian meteorites. The results show that shock pressures allowing the ejection of Martian meteorites range from 5 to 55 GPa, with corresponding post‐shock temperature elevations of 10 to about 1000 °C. With respect to shock pressures and post‐shock temperatures, an ejection of potentially viable organisms in Martian surface rocks seems possible. A calculation of the cooling time in space for the most highly shocked Martian meteorite Allan Hills (ALH) 77005 was performed and yielded a best‐fit for a post‐shock temperature of 1000 °C and a meteoroid size of 0.4 to 0.6 m. The final burial depths of the sub‐volcanic to volcanic Martian rocks as indicated by textures and mineral compositions of meteorites are in good agreement with the postulated size of the potential source region for Martian meteorites during the impact of a small projectile (200 m), as defined by numerical modeling (Artemieva and Ivanov 2004). A comparison of shock pressures and ejection and terrestrial ages indicates that, on average, highly shocked fragments reach Earth‐crossing orbits faster than weakly shocked fragments. If climatic changes on Mars have a significant influence on the atmospheric pressure, they could account for the increase of recorded ejection events of Martian meteorites in the last 5 Ma. 相似文献
84.
Observations of Comet 9P/Tempel 1 around the Deep Impact event by the OSIRIS cameras onboard Rosetta
Horst Uwe Keller Sonia Fornasier Stubbe F. Hviid Jörg Knollenberg Miriam Rengel Gabriele Cremonese Detlef Koschny Ekkehard Kührt Holger Sierks Cesare Barbieri Hans Rickman Michael F. A'Hearn Maria-Antonella Barucci Vania da Deppo Björn J.R. Davidsson Stefano Debei Fritz Gliem José J. Lopez Moreno Giampiero Naletto Angel Sanz Andrés 《Icarus》2007,187(1):87-103
The OSIRIS cameras on the Rosetta spacecraft observed Comet 9P/Tempel 1 from 5 days before to 10 days after it was hit by the Deep Impact projectile. The Narrow Angle Camera (NAC) monitored the cometary dust in 5 different filters. The Wide Angle Camera (WAC) observed through filters sensitive to emissions from OH, CN, Na, and OI together with the associated continuum. Before and after the impact the comet showed regular variations in intensity. The period of the brightness changes is consistent with the rotation period of Tempel 1. The overall brightness of Tempel 1 decreased by about 10% during the OSIRIS observations. The analysis of the impact ejecta shows that no new permanent coma structures were created by the impact. Most of the material moved with . Much of it left the comet in the form of icy grains which sublimated and fragmented within the first hour after the impact. The light curve of the comet after the impact and the amount of material leaving the comet ( of water ice and a presumably larger amount of dust) suggest that the impact ejecta were quickly accelerated by collisions with gas molecules. Therefore, the motion of the bulk of the ejecta cannot be described by ballistic trajectories, and the validity of determinations of the density and tensile strength of the nucleus of Tempel 1 with models using ballistic ejection of particles is uncertain. 相似文献
85.
C. Vignali F. Pozzi J. Fritz A. Comastri C. Gruppioni E. Bellocchi F. Fiore M. Brusa R. Maiolino M. Mignoli F. La Franca L. Pozzetti G. Zamorani A. Merloni 《Monthly notices of the Royal Astronomical Society》2009,395(4):2189-2195
We present multiwavelength observations (from optical to submillimetre, including Spitzer and Submillimetre Common-User Bolometer Array) of H2XMMJ 003357.2−120038 (also GD 158_19), an X-ray selected, luminous narrow-line (type 2) quasar at z = 1.957 selected from the HELLAS2XMM survey. Its broad-band properties can be reasonably well modelled assuming three components: a stellar component to account for the optical and near-infrared (IR) emission; an active galactic nucleus (AGN) component (i.e. dust heated by an accreting active nucleus), dominant in the mid-IR, with an optical depth at 9.7 along the line of sight (close to the equatorial plane of the obscuring matter) of τ(9.7) = 1 and a full covering angle of the reprocessing matter (torus) of 140° and a far-IR starburst component (i.e. dust heated by star formation) to reproduce the wide bump observed longward of 70 .
The derived star formation rate is ≈1500 M⊙ yr−1 . The overall modelling indicates that GD 158_19 is a high-redshift X-ray luminous, obscured quasar with coeval powerful AGN activity and intense star formation. It is probably caught before the process of expelling the obscuring gas has started, thus quenching the star formation. 相似文献
The derived star formation rate is ≈1500 M
86.
We present a model which, for the first time, accounts for nucleation, growth and/or resorption of particles of variable composition in aqueous solutions (AS). Devised for describing the precipitation of binary solid solutions, it yields the time evolution of all ion activities in the AS, together with the particle population characteristics: number, size and composition profile of particles as a function of time and of their time of nucleation. We apply this numerical approach to the prototypical case of (Ba,Sr)CO3 solid solution precipitation. We demonstrate the great sensitivity of the composition profiles and particle sizes to the initial conditions under which the AS is prepared, and thus illustrate the possibility of engineering the particle characteristics into a chosen state. Finally, by comparing the precipitation of two solid solutions (Ba,Sr)CO3 and (Ba,Sr)SO4, we evidence the sensitivity of the particle composition profiles to the ratio of the end-member solubility products, which leads to the formation of core-shell particles in the case of (Ba,Sr)SO4. 相似文献
87.
The Paleozoic of Graz is an isolated nappe complex of about 1,500 km2 size and belongs to the Austroalpine units of the eastern European Alps. Despite more than 500 publications on stratigraphy,
paleontology and local structure, many aspects of the internal geometry of this complex as a whole remained unclear. In this
contribution, we present integrated geological profiles through the entire nappe complex. Based on these profiles, we present
(1) a simplified lithological subdivision into 13 rock associations, (2) a modified tectonostratigraphy where we consider
only two major tectonic units: an upper and a lower nappe system and in which we abandon the traditionally used facies nappe
concept, and (3) a modified paleogeography for the whole complex. Finally, we discuss whether the internal deformation of
the Paleozoic of Graz is of Variscan or Eo-Alpine age and which of the published models best explain the tectonic evolution
of the Paleozoic of Graz. 相似文献
88.
Damian Steffen Fritz Schlunegger Frank Preusser 《International Journal of Earth Sciences》2010,99(8):1975-1989
This study investigates the connection between sediment aggradation, erosion and climate in a desert environment of the Majes
valley, southern Peru. Luminescence dating of terraces and fans shows that sediment aggradation correlates with wet time intervals
on the Altiplano, suggesting a climatic influence on the aggradation–degradation cycles. Major periods of aggradation occurred
between ~110–100, ~60–50 and 12–8 ka. More precipitation in the Majes catchment resulted in increased erosion and transportation
of sediment from the hillslopes into the trunk river. As a result, the sediment loads exceeded the transport capacity of the
Majes River and aggradation started in the lower reaches where the river gradient is less. Depletion of the hillslope sediment
reservoirs caused a relative increase in the capacity of the trunk river to entrain and transport sediment, resulting in erosion
of the previously deposited sediment. Consequently, although climate change may initiate a phase of sediment accumulation,
degradation can be triggered by an autocyclic negative feedback and does not have to be driven by climatic change. 相似文献
89.
Fritz Nipkow 《Aquatic Sciences - Research Across Boundaries》1962,24(1):1-43
Ohne Zusammenfassung 相似文献
90.