Melt/harzburgite reaction in the petrogenesis of tholeiitic magma from Kilauea volcano, Hawaii

We use the results of elevated pressure melting experiments to constrain the role of melt/mantle reaction in the formation of tholeiitic magma from Kilauea volcano, Hawaii. Trace element abundance data is commonly interpreted as evidence that Kilauea tholeiite is produced by partial melting of garnet lherzolite. We experimentally determine the liquidus relations of a tightly constrained estimate of primary tholeiite composition, and find that it is not in equilibrium on its liquidus with a garnet lherzolite assemblage at any pressure. The composition is, however, cosaturated on its liquidus with olivine and orthopyroxene at 1.4 GPa and 1425 °C, from which we infer that primary tholeiite is in equilibrium with harzburgite at lithospheric depths beneath Kilauea. These results are consistent with our observation that tholeiite primary magmas have higher normative silica contents than experimentally produced melts of garnet lherzolite. A model is presented whereby primary tholeiite forms via a two-stage process. In the first stage, magmas are generated by melting of garnet lherzolite in a mantle plume. In the second stage, the ascent and decompression of magmas causes them to react with harzburgite in the mantle by assimilating orthopyroxene and crystallizing olivine. This reaction can produce typical tholeiite primary magmas from significantly less siliceous garnet lherzolite melts, and is consistent with the shift in liquidus boundaries that accompanies decompression of an ascending magma. We determine the proportion of reactants by major element mass balance. The ratio of mass assimilated to mass crystallized (M_a/M_c) varies from 2.7 to 1.4, depending on the primary magma composition. We use an AFC calculation to model the effect of melt/harzburgite reaction on melt rare earth and high field strength element abundances, and find that reaction dilutes, but does not significantly fractionate, the abundances of these elements. Assuming olivine and orthopyroxene have similar heats of fusion, the M_a/M_c ratio indicates that reaction is endothermic. The additional thermal energy is supplied by the melt, which becomes superheated during adiabatic ascent and can provide more thermal energy than required. Melt/harzburgite reaction likely occurs over a range of depths, and we infer a mean depth of 42 km from our experimental results. This depth is well within the lithosphere beneath Kilauea. Since geochemical evidence indicates that melt/harzburgite reaction likely occurs in the top of the Hawaiian plume, the plume must be able to thin a significant portion of the lithosphere. Received: 4 February 1997 / Accepted: 27 August 1997     

Groundbased Doas UV/visible measurements at Kiruna (Sweden) during the sesame winters 1993/94 and 1994/95.

Zenith sky observations of O3, NO2, OClO and BrO are reported, which were performed at Kiruna (67.9°N, 21.1°E) within the SESAME winters 1993/1994 and 1994/95. For both winters large total amounts of OClO were observed inside the polar vortex at twilight, indicating the degree and the temporal variation of the halogen activation of the polar stratosphere. Occasionally OClO could also be observed outside the polar vortex, most likely due to export of halogen activated vortex air masses into the ambient stratosphere. BrO could also be detected in winter 1994/95, with the largest slant column amounts (5·1014/cm2) occuring in the polar vortex in mid-winter. Similar abundances of stratospheric BrO were observed at dusk and dawn, for both, air masses inside and outside the vortex. This observation is in reasonable agreement with previous studies on stratospheric BrO (observations and models) of Wahner et al. (1992), Arpag et al. (1994), Krug et al. (1996), and Lary et al. (1996a,b), but partly in disagreement with those of Solomon et al. (1989), Fish et al. (1995), and Sessler et al. (1996).     

Fission track ages of North American tektites

Fission track ages of North American tektites from Texas, Georgia and Martha's vineyard range widely between 0.8 my and 34.2 my with the tektites from Georgia giving the lowest ages. Size studies of the fission track etch pits reveal the thermal history of each individual tektite resulting in the partial loss of tracks. Therefore, the measured fission track ages can be understood as thermally lowered.

Based on annealing experiments, correction factors for the thermally lowered fission track ages are found. The weighted mean of the corrected fission track ages is 34.9 my for the bediasites and the Martha's Vineyard tektite. On the other hand, the corrected fission track ages of the Georgia tektites are much lower resulting from a more complex thermal history.

It may now be stated that North American tektites and Libyan Desert glasses cannot have had a simultaneous origin.     

15th order resonance terms using the decaying orbit of TETR-3

The orbit of TETR-3 (1971-83B), inclination: 33°, passed through resonance with 15th order geopotential terms in February 1972. The resonance caused the orbit inclination to increase by 0.015°. Analysis of 48 sets of mean Kepler elements for this satellite in 1971–1972 (across the resonance) has established the following strong constraint for high degree, 15th order gravitational terms (normalized):

$\text{10}{}^9\text{(}\text{C, S}\text{)}{}_{15}\text{= (28.3 ± 3.0, 7.4 ± 3.0) =}\text{0.001(}\text{C, S}\text{)}{}_{\mathrm{15,15}}\text{?0.015(}\text{C, S}\text{)}{}_{\mathrm{17,15}}\text{+0.073(}\text{C, S}\text{)}{}_{\mathrm{19,15}}\text{?0.219(}\text{C, S}\text{)}{}_{\mathrm{21,15}}\text{+0.477(}\text{C, S}\text{)}{}_{\mathrm{23,15}}\text{?0.781(}\text{C, S}\text{)}{}_{\mathrm{25,15}}\text{+1.000(}\text{C, S}\text{)}{}_{\mathrm{27,15}}\text{?0.0963(}\text{C, S}\text{)}{}_{\mathrm{29,15}}\text{+0.622(}\text{C, S}\text{)}{}_{\mathrm{31,15}}\text{?0.119(}\text{C, S}\text{)}{}_{\mathrm{33,15}}\text{?0.290(}\text{C, S}\text{)}{}_{\mathrm{35,15}}\text{+0.403(}\text{C, S}\text{)}{}_{\mathrm{37,15}}\text{?0.223(}\text{C, S}\text{)}{}_{\mathrm{39,15}}\text{?0.058(}\text{C, S}\text{)}{}_{\mathrm{41,15}}\text{+…}$

This result combined with previous results on high inclination 15th order and other resonant orbits suggests that the coefficients of the gravity field beyond the 15th degree are smaller than Kaula's rule ($\text{10}{}^{\mathrm{?5}}\text{l}{}^2$).     

Current interruption by density depression

Using a one-dimensional electrostatic particle code, we examine processes associated with current interruption in a collisionless plasma when a density depression is present along the current channel. Current interruption due to double layers was suggested by Alfvén and Carlqvist (1967) as a cause of solar flares. At a local density depression, plasma instabilities caused by an electron current flow are accentuated, leading to current disruption. Our simulation study encompasses a wide range of the parameters in such a way that under appropriate conditions, both the Alfvén and Carlqvist (1967) regime and the Smith and Priest (1972) regime take place. In the latter regime the density depression decays into a stationary structure (ion-acoustic layer) which spawns a series of ion-acoustic solitons and ion phase space holes travelling upstream. A large inductance of the current circuit tends to enhance the plasma instabilities.     

Tektonik und Landschaft im Karstgebiet

Ohne Zusammenfassung     

Pfingstsitzung des „Damnu“ in Göttingen

Ohne Zusammenfassung     

Die Geologie im Schulunterrichte

Ohne Zusammenfassung     

The Black Sea Ecosystem Changes Related to the Introduction of New Mollusc Species

Abstract. The unintentional introduction of the new mollusc species Rupunu rhomasiuna, Mya arenaria , and Scuphurcu inaequivulvis has become a significant reason for modern transformations of certain bottom biocoenoses in the Black Sea. These molluscs have been passed across natural barriers in fouling of ships or in ship seawater ballast and have successfully acclimatized in the new region, forming communities with a high density and biomass. The resulting changes in the structure of the bottom biocoenoses after these introductions are in many cases comparable with or exceed the consequences of other episodic environmental events and other kinds of anthropogenic activity. The intense spreading of the introduced species in the new area is the result of their high adaptive capability and the instability of the Black Sea ecosystem, the latter being due to its few species, low level of competitive interactions, and constant growth of diverse anthropogenic loads.     

Refractivity estimation using multiple elevation angles

Estimation of the atmospheric refractivity is important for the prediction of radar performance. Surface or elevated trapping layers formed by the outflow of relatively dry and warm air over a cooler body of water often result in the refractive structure-supporting-convergence-zone-like behavior and multimodal effects. The propagation under such conditions can be very sensitive to even small changes in the vertical and horizontal structure of refractivity. Obtaining in situ measurements of sufficient fidelity to estimate where intensifications in the electromagnetic field will occur is difficult. The authors previously have demonstrated the ability to infer refractivity parameters from grazing-incidence radar sea-clutter data. The radar system was the 2.8-GHz space range radar that overlooks the Atlantic Ocean in the vicinity of Wallops Island, VA. The forward modeling consisted of the mapping of an 11-parameter environmental model via an electromagnetic propagation model into the space of the radar clutter observations. A genetic algorithm was employed to optimize the objective function. Ground truth data were atmospheric soundings obtained by a helicopter flying a saw-tooth pattern. The overall result was that the ability to estimate the propagation within the duct itself was comparable to that of in situ measurements. However, the ability to characterize the region above the duct was quite poor. Modern three-dimensional radars, however, have relatively narrow beams. Using these narrow beams at multiple elevations might resolve the ambiguity leading to the poor characterization in the region above the duct. Using radar data from the SPANDAR radar, it is demonstrated that such an approach is feasible and that more-robust estimates can be obtained by using two elevation angles and/or by constraining the solution to contain realistic refractivity profiles.