An experimental study on the effects of phenocrysts on convection in magmas

The effect of phenocrysts on convection in magma chambers is investigated experimentally using small heavy particles in convecting fluids. The particles are initially uniformly distributed in a fluid which is either heated from below or cooled from above. The system is allowed to evolve, and temperature and particle concentration profiles are measured as functions of time. When the concentration of particles is sufficiently small, convection is basically unaffected by their presence. When the concentration is above a critical value, however, the convective motion is considerably altered. The effect of particles on the subsequent fluid behaviour is different in the cases of heating from below and cooling from above. In the former case, there are strong convective motions confined to a sedimentary layer of decreasing thickness beneath a clear layer which displays rather weak convective motions. With time, the destabilizing increase of temperature in the lower layer overcomes the stabilizing contribution to the bulk density due to the particles and the layer overturns quite suddenly. In the situation of cooling from above, a critical condition separates a case of continual overturn from a case of no overturn at all, with the sedimentary layer falling unimpeded to the bottom. Theoretical analysis suggests that the critical value is determined primarily by the ratio of the contribution to the bulk density of the suspension due to particles to the change in fluid density due to the thermal effect. The size distribution of the particles can also modify the fluid behaviour. Applying our general results to geological situations, we suggest that the presence of relatively small concentrations of phenocrysts can critically influence the mode of convection in magmas.     

First record of Karydomys (Rodentia, Mammalia) from the German part of the North Alpine Foreland Basin

Karydomys, a rare genus of cricetid rodents from the Middle Miocene of central Europe, had previously been reported only from the Swiss part of the North Alpine Foreland basin; documented evidence from the German part was lacking. This paper describes several new specimens of Karydomys from the German localities Höll and Laimering 3. A correlation of both localities to the Bavarian local biostratigraphic scale OSM F is proposed. Taxonomically, the fossils are most probably linked to K. wigharti from Hambach 6C (north-west Germany), and thus assigned to K. cf. wigharti. In spite of the scarcity of Karydomys fossils in the Upper Freshwatermolasse, the taxon is an important biostratigraphical marker because of its short stratigraphical range.     

Partitioning of Ca and Al between forsterite and silicate melt in dynamic systems with implications for the origin of Ca,Al‐rich forsterites in primitive meteorites

Abstract— We report the results of dynamic crystallization experiments that were specifically designed to study the dependence of Ca and Al partitioning between forsterite and melt in rapidly cooling Caand Al‐rich melts. The partitioning of Ca between olivine and silicate melt is found to be independent of the cooling rate within the range of 1.5 to 1000°C/hr and at CaO contents of up to 25 wt%. Within analytical uncertainty, our data plot on the equilibrium partitioning curve obtained by Libourel (1999). The partitioning behavior of Al at high cooling rates is more complex. Aluminum is much more heterogenously distributed in the olivine and the co‐existing melt than Ca. But, no systematic trend of Al partition coefficient with cooling rate is observed. We apply the results of the experiments to the formation of meteoritic forsterites with relatively high contents of Ca and Al. Although these forsterites are found frequently inside chondrules, the Ca contents of their host chondrules are far too low to crystallize these high Ca‐forsterites. This is also true for very rapid cooling of chondrule melts. The parental melt of these forsterites requires CaO contents above 20 wt%.     

Radium isotopes in sub-Arctic waters

Measurements of the²²⁸Ra/²²⁶Ra activity ratio in the waters of the Greenland, Norwegian and Labrador Seas and Baffin Bay reveal strong horizontal gradients in the surface waters. The coastal waters are dominated by²²⁸Ra injection from nearshore sediments. There is an inverse correlation between the²²⁸Ra/²²⁶Ra activity ratio and salinity in the 30–36‰ salinity range. Vertical profiles indicate that the²²⁸Ra/²²⁶Ra activity ratio is also strongly coupled toσ_θ except for some regions where²²⁸Ra is being injected into higher density water as these isopycnals intersect coastal areas. We use these measurements in the area of formation of North Atlantic Deep Water to estimate that this water mass forms with a²²⁸Ra/²²⁶Ra activity ratio of 0.10.     

Computing a design flood in the absence of historical records

Summary A design flood for a Venezuelan river is computed in the absence of rainfall and stream-flow data of more than a few years. From synoptic studies of an area embracing northern South America and the Caribbean, the type of disturbance producing the abundant rains of the area is determined. A disturbance of this type is maximized on the basis of the ratio of energy dissipated through friction to released latent energy represented by rainfall — in other words, theefficiency of the system is given its highest reasonable value. The synthetic disturbance is moved over the river basin in a manner most favorable for heavy rain. Certain data available from other rivers are used as a cross-check on the resultant flood values.     

Kinetic rate laws derived from order parameter theory III: Al,Si ordering in sanidine

The time dependence of the ordering and disordering of Al and Si in sanidine is described within the framework of the kinetic rate laws developed in papers I and II of this series. It was found that the relevant order parameter Q _t is homogeneous and non-conserved. The rate law is:

The local invariants under rotations about an axis and their applications

The three possible scalar products formed from the position-speed state vector lead to Stumpff's local invariants. The assumption of a distinguished axis (001) gives rise to the axial local invariantsz and under the rotations about this axis.-If a satellite moves in the field of a rotationally symmetric central body, then there will be an appropriate set of invariants for which a regular, non-linear system of differential equations holds. It can be used to derive recurrence relations for time series expansions and special perturbation methods, which are characterised by the occurrence of the scalar products of the perturbational acceleration with the position and speed vectors and (001).Presented at the Conference on Celestial Mechanics, Oberwolfach, Germany, August 17–23, 1969.