Petrology of the Northern East Greenland Tertiary Flood Basalts: Evidence from Hold with Hope and Wollaston Forland

Predominantly silica-oversaturated tholeiitic basalts spreadwidely across the northern East Greenland continental margin(73–76° N) at the onset of Tertiary magmatism. Thesehave been studied in two of the principal outcrop areas: Holdwith Hope and Wollaston Forland. In Hold with Hope very minoreruption of nephelinitic magma preceded the tholeiitic phase.The early tholeiites of northern East Greenland tend to be moresiliceous and aluminous and less iron and titanium rich thantheir more voluminous counterparts in the main East Greenlandprovince south of 70° N. Some, notably those of WollastonForland, approach ‘enriched MORB’ compositions.The early flood basalts (distinguished in the Hold with Hoperegion as the Lower Plateau Lava Series, LPLS) show limitedcompositional range. Such variation as is shown is attributedto low-pressure plagioclase—olivine—augite fractionation.Intrusion of quartz dolerite sills within and beneath the LPLSmay have constituted a separate but closely allied magmaticevent. The sills are slightly more enriched in incompatibleelements, have higher initial Sr isotopic ratios and show morepronounced Fe-enrichment trends. Conformably overlying the LPLS in the Hold with Hope area isa succession of incompatible element enriched basalts composingthe Upper Plateau Lava Series (UPLS). The more extremely enrichedlavas (anomalous UPLS) tend to define the base of the UPLS andrange from olivine tholeiites to analcime basanites. Togetherwith the more normal UPLS, these range from nearly aphyric tostrongly porphyritic varieties; the latter include highly magnesianoceanites and ankaramites. The normal UPLS ranges from picriticolivine tholeiites to quartz tholeiites. While orthopyroxenephenocrysts occur among the more differentiated basalts, pigeoniteappears wholly absent from the UPLS. Compositional variationamong the normal UPLS is ascribed to olivine + spinel fractionationjoined by clinopyroxene in compositions with less than 8 percent MgO. The UPLS basalts have incompatible element levelsand elemental ratios (e.g. Zr/Nb, Zr/Y, La/Y and Ti/V) thatdistinguish them from the earlier, more depleted tholeiites.Initial Sr isotope ratios vary widely, with high values indicativeof crustal interaction. A genetic model is proposed whereby the more depleted tholeiites,as exemplified by those of Wollaston Forland and the earliervolcanic products on Hold with Hope, arose from large-scalemelting of relatively infertile asthenosphere prior to the initiationof the Mohn's Ridge and continental separation, while the UPLSof the Hold with Hope region and isolated inland occurrencesof nephelinitic and basanitic magmatism were produced by meltingof K–Ti–P enriched facies of the heterogeneous mantlepresumed to have formed the lower part of the sub-Greenlandcontinental lithosphere. Basalts of the Vøring Plateauon the Norwegian continental shelf, may represent analoguesof the UPLS on the eastern Atlantic margins.     

Normalized 87Sr86Sr by multiple collection and comparison to a standard

A system for precisely determining normalized ${}^{87}\text{Sr}{}^{86}\text{Sr}$ by comparing unknown to standard in a solid-source quadruple-collector mass spectrometer is outlined. This is made possible by a mathematical approximation in the data-reduction process.     

Measurements of solar occulation: the error in a naive retrieval if the constituent's concentration changes

The stratospheric concentrations of many minor constituents change rapidly at sunrise or sunset. If this happens, there is an inherent error when retrieving the vertical profiles of the constituents from measurements of their absorption of sunlight. For retrievals of NO at sunset the error can be estimated from in-situ measurements alone, without appeal to a model of stratospheric photochemistry. Below 20 km this error can approach 100% so that the retrieved NO is zero. But at 40 km, and at 25 km when the absorption is strong and Lorentzian, it can be less than 20%. Precise calculations of the error, even if small, require model calculations of the sunset and sunrise changes. With a model, we have calculated the error for NO, NO₂, OH and ClO.     

The Askervein Hill Project: Wind-tunnel simulations at three length scales

Wind-tunnel simulations of neutrally-stable atmospheric boundary-layer flow over an isolated, low hill (Askervein) have been carried out at three different length scales in two wind-tunnel facilities. The objectives of these simulations were to assess the reliability with which changes in mean wind and turbulence structure induced by the prototype hill on boundary-layer flow can be reproduced in the wind tunnel, and to determine the relative impact of certain modelling approaches (surface roughness, model scale, measurement techniques, etc.) on the quality of the simulations. The wind-tunnel results are compared with each other and with full-scale data and are shown in general to model the prototype flow very well. The effects of relaxing the criterion of aerodynamic roughness of the model surface were limited to certain regions in the lee of the hill and were linked to separation phenomena.     

IMPROVED PHASE-ELLIPSE METHOD FOR IN SITU GEOPHONE CALIBRATION*

For amplitude and phase response calibration of moving-coil electromagnetic geophones two parameters are needed, namely, the geophone natural frequency, f₀, and the geophone upper resonance frequency f_u. The phase-ellipse method is commonly used for the in situ determination of these parameters. For a given signal-to-noise ratio, the precision of the measurement off₀ andf_u depends on the phase sensitivity, f(δφ/δf) For some commercial geophones f(δφ/δf) atf_u can be an order of magnitude less than the sensitivity atf₀. In this paper we present an improved phase-ellipse method with increased precision. Compared to measurements made with the existing phase-ellipse methods, our method shows a 6- and 3-fold improvement in the precision, respectively, on measurements of f₀ andf_u on a commercial geophone.     

Explosive magma-water interactions: Thermodynamics,explosion mechanisms,and field studies

Physical analysis of explosive, magma-water interaction is complicated by several important controls: (1) the initial geometry and location of the contact between magma and water; (2) the process by which thermal energy is transferred from the magma to the water; (3) the degree to and manner by which the magma and water become intermingled prior to eruption; (4) the thermodynamic equation of state for mixtures of magma fragments and water; (5) the dynamic metastability of superheated water; and (6) the propagation of shock waves through the system. All of these controls can be analyzed while addressing aspects of tephra emplacement from the eruptive column by fallout, surge, and flow processes. An ideal thermodynamic treatment, in which the magma and external water are allowed to come to thermal equilibrium before explosive expansion, shows that the maximum system pressure and entropy are determined by the mass ratio of water and magma interacting. Explosive (thermodynamic) efficiency, measured by the ratio of maximum work potential to thermal energy of the magma, depends upon heat transfer from the pyroclasts to the vapor during the expansion stage. The adiabatic case, in which steam immediately separates from the tephra during ejection, produces lower efficiencies than does the isothermal case, in which heat is continually transferred from tephra to steam as it expands. Mechanisms by which thermal equilibrium between water and magma can be obtained require intimate mixing of the two. Interface instabilities of the Landau and Taylor type have been documented by experiments to cause fine-scale mixing prior to vapor explosion. In these cases, water is heated rapidly to a metastable state of superheat where vapor explosion occurs by spontaneous nucleation when a temperature limit is exceeded. Mixing may also be promoted by shock wave propagation. If the shock is of sufficient strength to break the magma into small pieces, thermal equilibrium and vapor production in its wake may drive the shock as a thermal detonation. Because these mechanisms of magma fragmentation allow calculation of grain size, vapor temperature and pressure, and pressure rise times, detailed emplacement models can be developed by critical field and laboratory analysis of the resulting tephra deposits. Deposits left by dense flows of tephra and wet steam as opposed to those left by dilute flows of dry steam and tephra show contrasts in median grain size, dispersal area, grain shape, grain surface chemistry, and bed form.     

Zur Bemessung unterirdischer Enteisenungsanlagen Teil 1: Chemisch-analytische Methoden der Erkundung und Bemessung

In underground deferrization processes there exists a dynamic cation exchange euquilibrium for Fe-II to the solid phase of the underground when an Fe-II containing ground water is delivered. Methods of investigation for the estimation of the initial oxygen demand and of the Fe-II content of the aquifer are tested and described in detail. At dynamic filtering tests and within the framework of technically simpler batch-tests the oxygen demand was higher than expected according to the stoichiometric Fe-II share. A relatively good agreement was obtained between the results of both procedures. Fe-II bound to solid matter is measured by a developed Fe-III difference method. Fe-II can be extracted and determined also directly with 1,10-phenanthroline. Moreover, the determination method of the distribution coefficient with its influencing factors is described. Finally, the results of regression relations are explained.