Rates and Processes of Potassic Magma Evolution beneath Sangeang Api Volcano, East Sunda Arc, Indonesia

U-series isotopes can provide unique insights into the physicalprocesses of magma evolution by constraining the time scalesover which they operate. This, however, requires rock suitesthat provide a clear and complete record of the liquid lineof descent. Sangeang Api volcano, in the east Sunda arc, providessuch an opportunity because it erupts potassic lavas (SiO₂     

Heating experiments simulating atmospheric entry heating of micrometeorites: Clues to their parent body sources

Abstract— Depending on their velocity, entry angle and mass, extraterrestrial dust particles suffer certain degrees of heating during entry into Earth's atmosphere, and the mineralogy and chemical composition of these dust particles are significantly changed. In the present study, pulse-heating experiments simulating the atmospheric entry heating of micrometeoroids were carried out in order to understand the mineralogical and chemical changes quantitatively as well as to estimate the peak temperature experienced by the particles during entry heating. Fragments of the CI chondrites Orgueil and Alais as well as pyrrhotites from Orgueil were used as analogue material. The experiments show that the volatile elements S, Zn, Ga, Ge, and Se can be lost from 50 to 100 μm sized CI meteorite fragments at temperatures and heating times applicable to the entry heating of similar sized cosmic dust particles. It is concluded that depletions of these elements relative to CI as observed in micrometeorites are mainly caused by atmospheric entry heating. Besides explaining the element abundances in micrometeorites, the experimentally obtained release patterns can also be used as indicators to estimate the peak heating of dust particles during entry. Using the abundances of Zn and Ge and assuming their original concentrations close to CI, a maximum heating of 1100–1200 °C is obtained for previously analyzed Antarctic micrometeroites. Thermal alteration also strongly influenced the mineralogy of the meteorite fragments. While the unheated samples mainly consisted of phyllosilicates, these phases almost completely transformed into olivine and pyroxene in the fragments heated to ≥800 °C. Therefore, dust particles that still contain hydrous minerals were probably never heated to temperatures ≥800 °C in the atmosphere. During continued heating, the grain size of the newly formed silicates increased and the composition of the olivines equilibrated. Applying these results quantitatively to Antarctic micrometeorites, typical peak temperatures in the range of 1100–1200 °C during atmospheric entry heating are deduced. This temperature range corresponds to the one obtained from the volatile element concentrations measured in these micrometeorites and points to an asteroidal origin of the particles.     

Abundance and Partitioning of OH in a High-pressure Magmatic System: Megacrysts from the Monastery Kimberlite, South Africa

Concentrations of OH, and major and trace elements were determinedin a suite of mantle-derived megacrysts that represent the crystallizationproducts of a kimberlite-like magma at     

On the Origin of Crystal-poor Rhyolites: Extracted from Batholithic Crystal Mushes

The largest accumulations of rhyolitic melt in the upper crustoccur in voluminous silicic crystal mushes, which sometimeserupt as unzoned, crystal-rich ignimbrites, but are most frequentlypreserved as granodioritic batholiths. After approximately 40–50%crystallization, magmas of intermediate composition (andesite–dacite)typically contain high-SiO₂ interstitial melt, similar to crystal-poorrhyolites commonly erupted in mature arc and continental settings.This paper analyzes the feasibility of system-wide extractionof this melt from the mush, a mechanism that can rationalizea number of observations in both the plutonic and volcanic record,such as: (1) abrupt compositional gaps in ignimbrites; (2) thepresence of chemically highly evolved bodies at the roof ofsubvolcanic batholiths; (3) the observed range of ages (up to200–300 ka) recorded by zircons in silicic magmas; (4)extensive zones of low P-wave velocity in the shallow crustunder active silicic calderas. We argue that crystal–meltsegregation occurs by a combination of several processes (hinderedsettling, micro-settling, compaction) once convection is hamperedas the rheological locking point of the crystal–melt mixture(     

Early Weichselian dust storm layer at Achenheim in Alsace, France

The cause of the rapid transition from lush grasslands and woodlands of the Early Glacial interstadiul to Pleniglacial barrens in Europe is still a mystery. In the loess sections of Bohemia and Austria this transition is associated with thin layers of fine-grained airborne dust known as 'markers', believed to be deposited by major contineiital-scale dust storms. Here we present evidence that a similar. sharply delimited layer with a minimum TL age of 64.9 ± 6.9 ka separates the autochthonous humus steppe soils from abiogenic sediments of the Achenheim 1 pedocomplex in France. The soil complex has been previously correlated on pedostratigraphic grounds with marine oxygen isotope stage (MIS) 5. Given its age and stratigraphic position, the dust layer correlates with the PKII marker in Bohemia. The rccogiiition of a marker in Achenheim suggests that the development of the Early Glacial steppe soils ended abruptly not only in central Europe, but also in Alsace, France, prior to 65 ka, possibly as a result of a single continental-scale dust storm.     

The pelagic distribution of marine birds in a heterogeneous environment

In this paper I review recent, small-scale, process-oriented studies of the pelagic distribution of marine birds. I examine the roles played by a variety of hydrographic features, including steep flow gradients (fronts) and water column stratification, in determining the abundance or availability of avian prey. The ice edge/marginal ice zone is a frontal area of particular interest in polar regions. In most oceanic systems we have examples of avian use of a feature, hut only poor information on the importance of the feature for supporting the population as a whole. I review recent studies of the spatial and numerical concordance of marine birds and their prey, and find that these studies have yielded mixed results, with correlations stronger for piscivorous birds, particularly murres foraging on capelin, than for planktivores. Review of investigations of multispecies interactions during foraging shows that flock foraging has both beneficial and negative aspects. Interspecific facilitation of foraging occurs in numerous interactions involving both other species of birds and marine mammals. However, co-occurrence of predators may occur because both seek the same prey, and caution must be used in assessing mutualistic interactions between predatory species.     

Hollow Australite Button with Flange,Hordern Vale,Otway Peninsula,Western Victoria

Abstract A relatively thin walled hollow australite button recently discovered in an unbroken condition on the surface of a shallow sand pit in the Otway Ranges, Victoria, contains a double internal cavity with a total calculated volume of approximately four cubic centimeters. A little over half of a well developed circumferential flange is still attached to the hollow core of the specimen, the missing portion having been removed by terrestrial erosion. The front surface reveals a well preserved aerodynamic sculpture pattern such that the orientation of the specimen during hypersonic atmospheric transit can be accurately determined to show its aerodynamically stable flight position. Such double bubbles are unique among Australian tektites, whether in the fractured or well preserved state, and it is equally as uncommon to find an unbroken hollow australite core with remnants of still attached circumferential flange.