The evolution of a global magma ocean with olivine flotation     

Siegfried Franck  Michael Riedel 《Earth, Moon, and Planets》1991,54(1):59-65

We investigate the thermal evolution of a global magma ocean divided by a dunite septum into a shallow and a lower part with help of simple stability estimations and cooling time calculations. It comes out that the septum is not stable against thermal convection so that this mechanism for a separated chemical evolution of the two mantle regions does not work.  相似文献   

Evaluation of the possible presence of clathrate hydrates in Europa's icy shell or seafloor     

Olga Prieto-Ballesteros  Jeffrey S. Kargel  Franck Selsis  Eduardo Sebastián Martínez 《Icarus》2005,177(2):491-505

Several substances besides water ice have been detected on the surface of Europa by spectroscopic sensors, including CO₂, SO₂, and H₂S. These substances might occur as pure crystalline ices, as vitreous mixtures, or as clathrate hydrate phases, depending on the system conditions and the history of the material. Clathrate hydrates are crystalline compounds in which an expanded water ice lattice forms cages that contain gas molecules. The molecular gases that may constitute Europan clathrate hydrates may have two possible ultimate origins: they might be primordial condensates from the interstellar medium, solar nebula, or jovian subnebula, or they might be secondary products generated as a consequence of the geological evolution and complex chemical processing of the satellite. Primordial ices and volatile-bearing compounds would be difficult to preserve in pristine form in Europa without further processing because of its active geological history. But dissociated volatiles derived from differentiation of a chondritic rock or cometary precursor may have produced secondary clathrates that may be present now. We have evaluated the current stability of several types of clathrate hydrates in the crust and the ocean of Europa. The depth at which the clathrates of SO₂, CO₂, H₂S, and CH₄ are stable have been obtained using both the temperatures observed in the surface [Spencer, J.R., Tamppari, L.K., Martin, T.Z., Travis, L.D., 1999. Temperatures on Europa from Galileo photopolarimeter-radiometer: Nighttime thermal anomalies. Science 284, 1514-1516] and thermal models for the crust. In addition, their densities have been calculated in order to determine their buoyancy in the ocean, obtaining different results depending upon the salinity of the ocean and type of clathrate. For instance, assuming a eutectic composition of the system MgSO₄H₂O for the ocean, CO₂, H₂S, and CH₄ clathrates would float but SO₂ clathrate would sink to the seafloor; an ocean of much lower salinity would allow all these clathrates to sink, except that CH₄ clathrate would still float. Many geological processes may be driven or affected by the formation, presence, and destruction of clathrates in Europa such as explosive cryomagmatic activity [Stevenson, D.J., 1982. Volcanism and igneous processes in small icy satellites. Nature 298, 142-144], partial differentiation of the crust driven by its clathration, or the local retention of heat within or beneath clathrate-rich layers because of the low thermal conductivity of clathrate hydrates [Ross, R.G., Kargel, J.S., 1998. Thermal conductivity of Solar System ices, with special reference to martian polar caps. In: Schmitt, B., De Berg, C., Festou, M. (Eds.), Solar System Ices. Kluwer Academic, Dordrecht, pp. 33-62]. On the surface, destabilization of these minerals and compounds, triggered by fracture decompression or heating could result in formation of chaotic terrain morphologies, a mechanism that also has been proposed for some martian chaotic terrains [Tanaka, K.L., Kargel, J.S., MacKinnon, D.J., Hare, T.M., Hoffman, N., 2002. Catastrophic erosion of Hellas basin rim on Mars induced by magmatic intrusion into volatile-rich rocks. Geophys. Res. Lett. 29 (8); Kargel, J.S., Prieto-Ballesteros, O., Tanaka K.L., 2003. Is clathrate hydrate dissociation responsible for chaotic terrains on Earth, Mars, Europa, and Triton? Geophys. Res. 5. Abstract 14252]. Models of the evolution of the ice shell of Europa might take into account the presence of clathrate hydrates because if gases are vented from the silicate interior to the water ocean, they first would dissolve in the ocean and then, if the gas concentrations are sufficient, may crystallize. If any methane releases occur in Europa by hydrothermal or biological activity, they also might form clathrates. Then, from both geological and astrobiological perspectives, future missions to Europa should carry instrumentation capable of clathrate hydrate detection.  相似文献   

Observations of Normal Modes from 84 Recordings of the Alaskan Earthquake of 1964 March 28-II. Further Remarks based on new Spheroidal Overtone Data     

A. M. Dziewonski  F. Gilbert 《Geophysical Journal International》1973,35(4):401-437

  相似文献   

Announcement Internatioal Society for Diatom Research and Nederlands-Vlaamse Kring van Diatomisten     

Gaston Mialaret  Gilbert Landsheere  Dieter Mahr  Marcel Postic  A. Harry Passow  et al. 《Journal of Paleolimnology》1991,6(2):171-172

Announcement Internatioal Society for Diatom Research and Nederlands-Vlaamse Kring van Diatomisten  相似文献   

A search for a nonbiological explanation of the Viking Labeled Release life detection experiment     

Gilbert V. Levin  Patricia A. Straat 《Icarus》1981,45(2):494-516

The Viking Labeled Release (LR) data obtained on Mars satisfy the criteria established for a biological response. The importance of the issue, especially when viewed against the harsh environment on Mars, requires careful consideration of possible nonbiological reactions that may have produced false positive results. A $\text{3}\text{1}\text{2}\text{-}\text{year}$ laboratory effort to investigate possible chemical, physical, and physicochemical agents or mechanisms has been concluded. Among nonbiological possibilities, hydrogen peroxide, putatively on Mars, emerged as the principal candidate. When placed on analog Mars soils prepared to match the Viking inorganic analysis of the Mars surface material, hydrogen peroxide did not duplicate the LR Mars data. When other materials were used as substrate, hydrogen peroxide could be made to evoke the type of responses obtained by the LR Mars experiment. However, essential criteria concerning the formation, accuumulation, and preservation of hydrogen peroxide to qualify it as the active agent on Mars have not been met and new data show it to be essentially absent from the Mars atmosphere. The presence of a biological agent on Mars must still be considered. This interpretation of the LR results is strengthened by a recent report that the Viking organic analysis instrument (GCMS) failed to detect organics in an Antarctic soil in which the LR instrument had demonstrated the presence of microorganisms.  相似文献   

Wave Propagation and a Secular Theory of Calculation Based on Hamilton-Jacobi Theory     

Barry Block  Freeman Gilbert 《Geophysical Journal International》1972,30(3):343-352

  相似文献   

Research directions for information and communication technology and society in Geography     

Melissa R. Gilbert 《Geoforum》2005,36(3):277-279

  相似文献   

Examining tendencies of in-plane rupture to migrate to material interfaces     

Gilbert B. Brietzke  Yehuda Ben-Zion 《Geophysical Journal International》2006,167(2):807-819

  相似文献   

Understanding the occurrences of fault and landslide in the region of West-Cameroon using remote sensing and GIS techniques     

Aretouyap  Zakari  Kemgang  Franck Eitel G  Domra  Janvier K  Bisso  Dieudonne  Njandjock  Philippe N 《Natural Hazards》2021,109(2):1589-1602

Natural Hazards - Remote sensing was used to visualize the West region with the purpose of investigating recent natural hazards observed in this area. Various approaches used based on...  相似文献   

The use of ballistic trajectory and granular flow models in predicting rockfall propagation     

Franck Bourrier  Luuk Dorren  Oldrich Hungr 《地球表面变化过程与地形》2013,38(4):435-440

The term rockfall is often used ambiguously to describe various mass movement processes. Here we propose more precise terminology based on the physical nature of the moving mass, differentiating between two distinct types of rockfall: fragmental rockfall and rock mass fall. For both rockfall types, the current knowledge of the mechanisms controlling propagation of the mass movement are described, showing how these mechanisms can be simulated with different modelling approaches. However, we point out that almost no development has been realized concerning dynamic behaviour of the transitional processes between these two end‐member rockfall types. Some simplified means of dealing with these complications are suggested, but we emphasize that a considerable amount of fundamental methodological development remains necessary. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献