Entrained Macrocryst Minerals as a Key to the Source Region of Olivine Nephelinites: Humberg, Kaiserstuhl, Germany

Olivine nephelinites commonly contain macrocrysts of olivineand clinopyroxene. Some of these macrocrysts might representfragments of the source region of the host magma transportedto the Earth's surface. If this hypothesis is correct thesefragments can be used to characterize the composition of thesource region and to put constraints on the magma generationprocess. In this study, we investigate the origin of macrocrystsand mineral aggregates from an olivine nephelinite from theKaiserstuhl, Germany. We focus on clinopyroxenes (Cpx), whichcan be divided into three groups. Cpx I is relict Cpx from aggregateswith deformed olivine that is depleted in Ca and characterizedby strong light rare earth element (LREE) fractionation, lowTi/Eu and negative high field strength element (HFSE) anomalies.Its geochemical signature is consistent with formation by carbonatitemetasomatism and with equilibration in the presence of orthopyroxene.Cpx II is Ca-rich Cpx, forming both aggregates with deformedolivine and individual macrocrysts. The LREE, as for Cpx I,are strongly fractionated. Convex REE patterns may be present.The depletion in HFSE is less pronounced. Cpx III is oscillatoryzoned Cpx phenocrysts showing enrichment in Ca, convex REE patternsand no HFSE anomalies. The transition in the trace element abundancesbetween the Cpx of the three groups is gradual. However, CpxI and II did not crystallize from the host magma, as demonstratedby the presence of kink-bands and undulose extinction in theassociated olivine and by the composition of alkali aluminosilicateglass inclusions in Cpx II. Based on the Cpx relationships,we interpret the studied suite of macrocrysts and mineral aggregatesas a mixture of disintegrated fragments of the source regionof the host olivine nephelinite. The process of melt generationwas multi-stage. A primary carbonatite melt ascending from deeperlevels in the mantle, probably from the dolomite–garnetperidotite stability field, reacted with mantle peridotite alongthe solidus ledge in the system lherzolite–CO₂ (< 20–22kbar) and started to crystallize carbonate minerals. Becauseof its low solidus temperature, the resulting carbonate-wehrliteassemblage melted incongruently with the formation of additionalclinopyroxene. The carbonatite melt evolved during crystallizationof carbonate minerals and concomitant incongruent melting ofthe carbonate-wehrlite, accompanied by the segregation of incipientalkali aluminosilicate melts. As a consequence of fast reactionrates in the presence of a carbonatite melt, this process probablytook place under disequilibrium conditions. Further meltingof the assemblage wehrlite + alkali aluminosilicate melt ledto the generation of the olivine nephelinite magma. It entrainedfragments of the wehrlite and brought them to the surface. KEY WORDS: carbonatite; metasomatism; source region; clinopyroxene macrocrysts; wehrlite; olivine nephelinite; Kaiserstuhl     

Seismicityof the Novaya Zemlya archipelago: relocated event catalog from 1974 to 2014

We have relocated seismic events registered in the area of the Novaya Zemlya Archipelago, which are not identified as nuclear explosions but are probably of tectonic nature. For the relocation, we collected all available seismic bulletins and waveform data. The location was performed by applying a modified method of generalized beamforming. Verification of the modified method and selection of the travel time model were performed using data on two Novaya Zemlya nuclear explosions that occurred on 02.11.1974 and 24.10.1990. The modified method and the BARENTS travel time model provide sufficient accuracy for event location in the region. The relocation procedure was applied for 9 seismic events registered in the area of the Novaya Zemlya Archipelago. As a result, the new coordinates of the five events turned out to be significantly different from those that were defined previously.     

Woolly rhino discovery in the lower Kolyma River

A nearly complete frozen mummy of a woolly rhinoceros (Coelodonta antiquitatis Blum., 1799) was discovered in a gold mine on the lower reaches of the Kolyma River, north–eastern Siberia. This is the first find of the whole body of woolly rhino in permafrost. A large part of the mummified body was preserved, including the left part of the body, covered by skin, including skin of the head and ear, fore and hind legs. The skull with 2 horns and the lower jaw were also preserved. Most of the internal organs were lost, except the intestines, stomach, and their contents. A rib fragment from this individual was dated by AMS-radiocarbon method to 39,140 ± 390 years BP (OxA-18755). Spore and pollen analyses of the stomach contents indicate that grasses and sagebrushes formed the main part of the diet of C. antiquitatis in this region of Arctic Siberia.     

Risk Assessment based on the Mathematical Model of Diffuse Exogenous Geological Processes

The estimation of the risk caused by hazardous geological processes is a common problem. The aim of this paper is to present a method for solving problems involving a wide spectrum of diffuse exogenous geological processes, based on the mathematical morphology of landscapes. Diffuse processes develop as random rounded sites within certain areas and include karstification, subsidence, thermo-karstification and aeolian processes. Model assumptions take into consideration spatial and temporal randomness of occurrence, independent growth under occasional conditions, and cessation of growth given a ‘stop factor’, with transformation into degenerate sites. Based on these model assumptions, the following probabilities of impact by diffuse exogenous geological processes are solved for analytically. Firstly, the probability of impact on engineering constructions of round shape given the size of the diffuse processes and the known average impact risk; secondly, the probability of impact on small engineering constructions (points); and lastly, the probability of impact on linear engineering constructions of specified length. The computed impact probabilities are verified in various areas within Western Siberia.     

Discovery of an albite gneiss from the Ile de Groix (Armorican Massif, France): geochemistry and LA-ICP-MS U–Pb geochronology of its Ordovician protolith

For the first time, an albite orthogneiss has been recognised and dated within the HP–LT blueschist facies metabasites and metapelites of the Ile de Groix. It is characterised by a peraluminous composition, high LILE, Th and U contents, MORB-like HREE abundances and moderate Nb and Y values. A U–Pb age of 480.8?±?4.8?Ma was obtained by LA-ICP-MS dating of zircon and titanite. It is interpreted as the age of the magmatic emplacement during the Early Ordovician. Morphologically different zircon grains yield late Neoproterozoic ages of 546.6–647.4?Ma. Zircon and titanite U–Pb ages indicate that the felsic magmatism from the Ile de Groix is contemporaneous with the acid, pre-orogenic magmatism widely recognised in the internal zones of the Variscan belt, related to the Cambro-Ordovician continental rifting. The magmatic protolith probably inherited a specific chemical composition from a combination of orogenic, back-arc and anorogenic signatures because of partial melting of the Cadomian basement during magma emplacement. Besides, the late Devonian U–Pb age of 366?±?33?Ma obtained for titanite from a blueschist facies metapelite corresponds to the age of the HP–LT peak metamorphism.     

How well do coupled models replicate ocean energetics relevant to ENSO?

Accurate replication of the processes associated with the energetics of the tropical ocean is necessary if coupled GCMs are to simulate the physics of ENSO correctly, including the transfer of energy from the winds to the ocean thermocline and energy dissipation during the ENSO cycle. Here, we analyze ocean energetics in coupled GCMs in terms of two integral parameters describing net energy loss in the system using the approach recently proposed by Brown and Fedorov (J Clim 23:1563?C1580, 2010a) and Fedorov (J Clim 20:1108?C1117, 2007). These parameters are (1) the efficiency ?? of the conversion of wind power into the buoyancy power that controls the rate of change of the available potential energy (APE) in the ocean and (2) the e-folding rate ?? that characterizes the damping of APE by turbulent diffusion and other processes. Estimating these two parameters for coupled models reveals potential deficiencies (and large differences) in how state-of-the-art coupled GCMs reproduce the ocean energetics as compared to ocean-only models and data assimilating models. The majority of the coupled models we analyzed show a lower efficiency (values of ?? in the range of 10?C50% versus 50?C60% for ocean-only simulations or reanalysis) and a relatively strong energy damping (values of ??^?1 in the range 0.4?C1?years versus 0.9?C1.2?years). These differences in the model energetics appear to reflect differences in the simulated thermal structure of the tropical ocean, the structure of ocean equatorial currents, and deficiencies in the way coupled models simulate ENSO.