Li abundances in eclogite minerals: a clue to a crustal or mantle origin?

The mineral phases of 33 eclogite and garnet clinopyroxenite samples from various tectonic settings were analysed for Li by secondary ion mass spectrometry (SIMS). In all samples, Li is preferentially incorporated into clinopyroxene (0.4 to 80 µg/g), whereas co-existing garnet contains only minor amounts of Li (0.01 to 3.7 µg/g). When present, glaucophane shows Li abundances which are similar to those of clinopyroxene, but phengite contains significantly less Li than clinopyroxene. Additional phases, such as amphibole, quartz, clinozoisite and kyanite, have low Li concentrations (<1 µg/g). No correlation is apparent between the Li contents and major-element compositions of clinopyroxene or garnet. On the basis of both measured Li concentrations in clinopyroxene and estimated Li abundances in the whole rocks, the investigated samples can be subdivided into high-Li and low-Li groups. These groups coincide with the mode of origin of the rocks. Metabasaltic (metagabbroic) eclogites from high-pressure terranes belong to the high-Li group whereas, except for one eclogite, all kimberlite- and basanite-hosted xenoliths have low Li contents. Samples from eclogites and garnet clinopyroxenites associated with orogenic peridotites fall into both groups. It is suggested that the high-Li eclogites originated from basaltic oceanic crust whereby the notable Li enrichment of some samples was probably caused by low-temperature hydrothermal alteration prior to subduction. Furthermore, the low-Li eclogites and garnet clinopyroxenites may represent high-pressure cumulates from mafic melts percolating through the mantle.     

Age constraints on faulting and fault reactivation: a multi-chronological approach

Movement within the Earth’s upper crust is commonly accommodated by faults or shear zones, ranging in scale from micro-displacements to regional tectonic lineaments. Since faults are active on different time scales and can be repeatedly reactivated, their displacement chronology is difficult to reconstruct. This study represents a multi-geochronological approach to unravel the evolution of an intracontinental fault zone locality along the Danube Fault, central Europe. At the investigated fault locality, ancient motion has produced a cataclastic deformation zone in which the cataclastic material was subjected to hydrothermal alteration and K-feldspar was almost completely replaced by illite and other phyllosilicates. Five different geochronological techniques (zircon Pb-evaporation, K–Ar and Rb–Sr illite, apatite fission track and fluorite (U-Th)/He) have been applied to explore the temporal fault activity. The upper time limit for initiation of faulting is constrained by the crystallization age of the primary rock type (known as “Kristallgranit”) at 325 ± 7 Ma, whereas the K–Ar and Rb–Sr ages of two illite fractions <2 μm (266–255 Ma) are interpreted to date fluid infiltration events during the final stage of the cataclastic deformation period. During this time, the “Kristallgranit” was already at or near the Earth’s surface as indicated by the sedimentary record and thermal modelling results of apatite fission track data. (U–Th)/He thermochronology of two single fluorite grains from a fluorite–quartz vein within the fault zone yield Cretaceous ages that clearly postdate their Late-Variscan mineralization age. We propose that later reactivation of the fault caused loss of helium in the fluorites. This assertion is supported by geological evidence, i.e. offsets of Jurassic and Cretaceous sediments along the fault and apatite fission track thermal modelling results are consistent with the prevalence of elevated temperatures (50–80°C) in the fault zone during the Cretaceous.     

Integrated geophysical and geological methods to investigate the inner and outer structures of the Quaternary Mýtina maar (W-Bohemia,Czech Republic)

The Mýtina maar is the first known Quaternary maar in the Bohemian Massif. Based on the results of Mrlina et al. (J Volcanol Geother Res 182:97–112, 2009), a multiparametric geophysical (electrical resistivity tomography, gravimetry, magnetometry, seismics) and geological/petrochemical research study had been carried out. The interpretation of the data has provided new information about the inner structure of the volcanic complex: (1) specification of the depth of post-volcanic sedimentary fill (up to ~100 m) and (2) magnetic and resistivity signs of one (or two) hidden volcanic structures interpreted as intrusions or remains of a scoria cone. The findings at the outer structure of the maar incorporate the (1) evidence of circular fracture zones outside the maar, (2) detection and distribution of volcanic ejecta and tephra-fall deposits at the surface, and (3) indications from electrical resistivity tomography and gravity data in the area between the Mýtina maar and ?elezná h?rka scoria cone, interpreted as a palaeovalley, filled by volcaniclastic rocks, and aligned along the strike line (NW–SE) of the Tachov fault zone. These findings are valuable contributions to extend the knowledge about structure of maar volcanoes in general. Because of ongoing active magmatic processes in the north-east part of the Cheb Basin (ca. 15–30 km north of the investigation area), the Mýtina maar-diatreme volcano and surroundings is a suitable key area for research directed to reconstruction of the palaeovolcanic evolution and assessment of possible future hazard potential in the Bohemian Massif.     

Structural and other contributions to the third-law entropies of silicates

The true third-law entropies of many minerals are frequently quite different from those values derived from calorimetric measurements. The discrepancy can usually be attributed to neglected residual or unextracted entropies related either to site-mixing and molecular disorders or to the lack of significant magnetic ordering at those temperatures reached by the heat capacity measurements. A literature review indicates that many silicates present site-mixing and vacancies in one or several of their crystallographic sites. The effect on entropy is well known in feldspars, but residual entropies of similar or greater magnitudes are also present in many amphiboles, micas, chlorites, zeolites, scapolites, feldspathoids, and other silicates. Less conspicuously, disorder in water molecules or hydrogen bonding may be responsible for yet another frequently overlooked entropy contribution. Unextracted entropy results from limited heat capacity measurements so that magnetic ordering effects to be expected in minerals with transition metals are either not registered or only incompletely recorded. In some cases, significant magnetic ordering probably only takes place at temperatures well below 15 K.The discussion in this paper centers on the causes resulting in discrepancies between calorimetric and third-law entropies. A set of tables reproduces the crystallographic information for most important rock-forming silicates and indicates the entropy contribution arising from site-mixing and vacancies, and possible magnetic ordering in those substances with transition metals. In addition, most elements appear in several isotopic forms, and it is this effect that gives rise to isotopic site-mixing and thus to another configurational entropy. It can on the whole be neglected. A discussion centered on the system fayalite-iron oxides (wüstite, hematite, magnetite) indicates the uncertainties involved in deriving third-law entropies from either equilibrium data or calorimetric investigations, which is especially relevant when dealing with substances presenting vacancies (wüstite), transition metals, and the possibility of magnetic ordering. The published entropies of many minerals are probably only approximations to true third-law values and should be checked against structural and magnetic information.     

Penumbral velocity oscillations

Doppler velocity variations of four sunspot penumbrae were observed in November 1988 at the Observatorio del Teide, Tenerife, using the spectral line Fe i 5576 Å. All of the penumbrae show local power maxima in the five-minute range, while no power is found around three minutes. This indicates that the five-minute oscillations are still present in the penumbrae, but the direction of the velocities might be tilted by the magnetic field. On the other hand, the maxima of the power and of the Evershed flow do not always occur at the same locations.The Gregory-Coudé telescope is operated by the Universitäts-Sternwarte Göttingen in cooperation with the Kiepenheuer-Institut für Sonnenphysik in Freiburg and the Institut für Astronomie und Astrophysik der Universität Würzburg.     

The influence of pick-up ion-induced wave pressures on the dynamics of the mass-loaded solar wind

The solar wind at larger distances is known to be a multicomponent plasma. The different components, solar ions, pick-up ions, and anomalous ions, are without collisional coupling but they are all coupled to the intrinsic wave turbulences by nonlinear wave-particle interactions. Since quite a long time it is not understood why dynamical processes associated with the loading of the primary solar wind by secondary pick-up ions neither lead to a recognizable heating nor to a deceleration of the solar wind at larger distances. While the inefficient heating seems to be explained by the fact that pick-up ions do not assimilate quickly enough to the solar wind distribution function, the unobservable deceleration of the distant solar wind always remained mysterious. Different from all theoretical approaches up to now, here we intend to show that the wave-induced pick-up ion pressure has to be introduced into the equations of motion in an adequate non-polytropic form to correctly describe the multicomponent plasma dynamics. If this is done it becomes clear that the deceleration of the solar wind is considerably reduced or even vanishing.     

Geochemical pattern classification of recent volcanic products from Mt. Etna, Italy, based on Kohonen maps and fuzzy clustering

We present the application of a classification method based on Kohonen maps and fuzzy clustering to geochemical analyses of volcanic products erupted on Mt. Etna from 1995 to 2005. Based on 13 major and trace elements, the classification allows a new way to visualize distinct compositional features of magma both considering long period as well as single eruptive events, such as in 2001 and 2002–03 flank eruptions. Products of the various vents do not necessarily form homogeneous groups, but show clear trends of chemical evolution with time. Using a convenient color code, the graphical visualization of the results in just a single picture allows the rapid identification of the compositional features of each sample and their comparison with all the products analyzed in the 10-year-long time span. This single picture accounts for the mutual interactions of the 13 components avoiding shortcomings of classical low-dimensional plots where components relevant for the discrimination have to be found in a priori study of many diagrams. On the basis of the synoptic information provided by pattern classification, we identify links between the products of different eruptive vents which deliver a reliable picture of a multifaceted plumbing system, in agreement with geochemical and geophysical evidence reported in literature. The analysis of the 13-dimensional data set using the Kohonen maps and fuzzy clustering simultaneously turned out to be straightforward and easy. Accordingly, the results of this application will be useful also as a contextual data set for new data in future ongoing eruptive episodes.     

Close correlation between Sr/Ca ratios in bulk sediments from the southern Cape Basin and the SPECMAP record

High-resolution records of Ca and Sr were obtained from shipboard XRF analyses of bulk sediments in five gravity cores from the southern Cape Basin, South Atlantic Ocean. Sr/Ca ratios display regular glacial/interglacial variations of 14–40% and reveal a close correlation with the SPECMAP record, minimum Sr/Ca ratios appearing during glacial (¹⁸ O) maxima, distinct increases during periods of deglaciation, and highest ratios in interstadials. Shifts in carbonate-producing phytoplankton and/or zooplankton assemblages over glacial/interglacial cycles are suggested to be the main cause for the observed variations in Sr/Ca patterns. Quick assessment of the relationship between Sr/Ca ratios and the SPECMAP record made it possible to easily transfer an age model to the newly collected cores already during the cruise.     

An impact model of Newton’s law of gravitation

The far-reaching gravitational force—in the approximation of Newton’s law of gravitation—is described by a heuristic model with hypothetical massless particles propagating at the speed of light in vacuum and transferring momentum and energy between physical entities through interactions on a local basis. The model has some similarities with the impact theory presented by Nicolas Fatio de Duillier to the Royal Society in 1690. Objections raised against this idea are dispelled by invoking the Special Theory of Relativity, considering non-local interactions, and replacing the shielding concept by a secular mass increase of massive bodies. Some consequences and applications of the model are discussed.