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A developmental model of olivine morphology as a function of the cooling rate and the degree of undercooling 总被引:3,自引:2,他引:1
Faure François Trolliard Gilles Nicollet Christian Montel Jean-Marc 《Contributions to Mineralogy and Petrology》2003,145(2):251-263
We performed dynamic crystallization experiments in the CMAS system at 1 atm to investigate the evolution of the morphology of forsterite crystals as a function of cooling rate and degree of undercooling. In sections parallel to the (010) plane, we observed the evolution of the forsterite morphology from tablets to hopper (skeletal) crystals, and then to swallowtail shapes (dendritic morphology) for increased degree of undercooling. The other shapes described in the literature can be interpreted as particular sections of those three shapes. The onset of dendritic growth is due to a competition between the growth of the faces of the initial hopper crystal and dendrite overgrowths. The forsterite dendrites are formed by a succession of units which look like hopper shapes. This result has been tested by an additional set of experiments. 相似文献
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525.
Fabienne?GiraudEmail author Davide?Olivero Fran?ois?Baudin Stéphane?Reboulet Bernard?Pittet Olivier?Proux 《International Journal of Earth Sciences》2003,92(2):267-284
The latest Albian sediments deposited in the Vocontian basin in south-eastern France record the oceanic anoxic event (OAE) 1d, locally named the Breistroffer interval. They are represented by argillaceous marls and marls, containing organic matter (total organic carbon varying from 0.8 to 1%). Changes in calcareous nannofossil abundance and assemblage composition as well as macrofauna abundance, ichnofossil assemblage, and bioturbation intensity were analysed in order to evaluate the main palaeoenvironmental factors controlling the deposition of the OAE 1d sediments in this area. The pelagic carbonate production is limited and the carbonate fraction is predominantly of nektonic/benthic, and of allochthonous origin from carbonate platforms. The enrichment in organic carbon within the Breistroffer interval is weak and not associated with high surface-water productivity. The organic matter is mainly terrigenous. Its record is due to (1) a good preservation under dysoxic conditions within the sediments, and (2) a weak input of allochthonous carbonates. Eustatic fluctuations strongly influenced the variations of nannofossil and macrofauna abundances. Distinctive patterns in nannofossil assemblages and macrofauna abundances within the Breistroffer interval are also recognized, reflecting changes from mesotrophic to more oligotrophic conditions which are probably controlled by climate. 相似文献
526.
Observing stellar oscillations provides a powerful probe for studying stellarinteriors. The frequencies of these modes depend on the properties of the star and give strong constraints on stellar models and evolution theories. The five-minute oscillations in the Sun, induced by stochastic excitation of its convective zone, have provided a wealth of information about the solar interior and has led to significant revisions to solar models. Until recently, the Sun was the only star in which solar-like oscillations were clearly established and characterized. The most important difficulty lies in the extremely small amplitude of the acoustic modes. Thanks in great part to high precision ground based Doppler measurements, solar-like oscillations have been now clearly detected in a growing list of main sequence and subgiant stars (Procyon, Hyi, Her A, Cen A, Eri and Boo). In some of them, p-modes were identified and characterized. New results and prospects in this field are presented. 相似文献
527.
Françoise Praderie Eduardo Simonneau Theodore P. Snow Jr. 《Astrophysics and Space Science》1975,38(2):337-343
The wings of Lα in α Lyr (A0 V), observed by theCopernicus satellite, cannot be interpreted if one assumes a classical LTE model photosphere. We argue that the electron temperature must increase outwards over the surface value reached in radiative equilibrium. 相似文献
528.
A plot of spin rate versus orientation when Hyperion is at the pericenter of its orbit (surface of section) reveals a large chaotic zone surrounding the synchronous spin-orbit state of Hyperion, if the satellite is assumed to be rotating about a principal axis which is normal to its orbit plane. This means that Hyperion's rotation in this zone exhibits large, essentially random variations on a short time scale. The chaotic zone is so large that it surrounds the ½ and 2 states, and libration in the 3/2 state is not possible. Stability analysis shows that for libration in the synchronous and ½ states, the orientation of the spin axis normal to the orbit plane is unstable, whereas rotation in the 2 state is attitude stable. Rotation in the chaotic zone is also attitude unstable. A small deviation of the principal axis from the orbit normal leads to motion through all angles in both the chaotic zone and the attitude unstable libration regions. Measures of the exponential rate of separation of nearby trajectories in phase space (Lyapunov characteristic exponents) for these three-dimensional motions indicate the the tumbling is chaotic and not just a regular motion through large angles. As tidal dissipation drives Hyperion's spin toward a nearly synchronous value, Hyperion necessarily enters the large chaotic zone. At this point Hyperion becomes attitude unstable and begins to tumble. Capture from the chaotic state into the synchronous or ½ state is impossible since they are also attitude unstable. The 3/2 state does not exist. Capture into the stable 2 state is possible, but improbable. It is expected that Hyperion will be found tumbling chaotically. 相似文献
529.
Summary A large-scale relict domain of granulite facies deformation fabrics has been identified within the Blansky les granulite body.
The granulite facies mylonitic fabric is discordant to the dominant amphibolite facies structures of the surrounding retrograde
granulite. The complex geometry of retrograde amphibolite facies fabric indicates a large-scale fold-like structure, which
is interpreted to be a result of either crustal-scale buckling of an already exhumed granulite sheet or active rotation of
a rigid granulite facies ellipsoidal domain in kinematic continuity with the regional amphibolite facies deformation. We argue
that both concepts allow similar restoration of the original granulite facies fabrics prior to the amphibolite facies deformation
and “folding”. The geometry of the granulite facies foliations coincides with the earliest fabrics in the nearby mid-crustal
units suggesting complete mechanical coupling between the deep lower crust and the mid-crustal levels during the vertical
movements of crustal materials. Microstructures indicate grain-size sensitive flow enhanced by the presence of silicate melts
at deep crustal levels and a beginning of an exhumation process of low viscosity granulites through a vertical channel. The
amphibolite facies fabrics developed at middle crustal levels and their microstructures indicate significant hardening of
feldspar-made rigid skeleton of the retrograde granulite. Increase in the strength of the granulite allowed an active buckling
or a rigid body rotation of the granulite sheet, which acted as a strong layer inside the weaker metasediments. 相似文献
530.
, and ratios have been measured on the same samples for carbonatite complexes. The results show that besides the ‘carbonatite box’ of Tayloret al. (1967) there exist higher δ18O and δ13C values than can be explained by late magmatic or deuteric processes. These processes correspond to high concentrations of CO2 and lead to big enrichments in 18O and 13C as well as in some ‘volatile’ elements. Strontium results are consistent with a model of selective contamination of deep-seated material by highly radiogenic strontium. The whole study leads to the opinion that parent magmas of carbonatites differentiated in a crustal environment with or without significant contamination. 相似文献