Constraints on the nature of the subvolcanic reservoir at South Sister volcano,Oregon from U-series dating combined with sub-crystal trace-element analysis of plagioclase and zircon     

Mark E. Stelten  Kari M. Cooper 《Earth and Planetary Science Letters》2012

We present sub-crystal-scale ²³⁸U–²³⁰Th zircon ages and ²³⁸U–²³⁰Th–²²⁶Ra plagioclase ages of bulk mineral separates from the Holocene (2.0–2.3 ka) eruptions of the Rock Mesa (RM) and Devil's Hills (DH) rhyolites at South Sister volcano, Oregon. We link these age data with sub-crystal trace-element analyses of zircon and plagioclase to provide insight into the subvolcanic system at South Sister, as an example of a small-volume continental arc volcano. Our results document the presence of coeval yet physically-distinct regions within the magma reservoir and constrain the timescales over which these heterogeneities existed. Zircons from the RM and DH dominantly record ages from 20 to 80 ka, with some grains recording ages > 350 ka, whereas plagioclase records ²³⁰Th–²²⁶Ra ages of 2.3–6.8 ka (RM) and 4.0–9.6 ka (DH-3) and a ²³⁸U–²³⁰Th age of 10 ± 34 ka (DH-3). We interpret zircons with ages < 350 ka as antecrysts inherited from a longer lived upper-crustal magma reservoir from which the rhyolites were generated, based on crystallization ages coeval with earlier periods of silicic volcanism at South Sister, the undersaturated nature of the RM and DH magmas with respect to zircon, and Ti-in-zircon temperatures consistent with low-temperature (< 815 °C) crystallization. In contrast, plagioclase ages are near the eruption age and dominantly preserve information about the recent (< 10 ka), higher-temperature evolution of the host magmas. Although zircon and plagioclase record different crystallization ages, each phase crystallized over the same time period in the RM compared to DH rhyolites. Linking these crystal age data with sub-crystal trace-element analyses demonstrates that zircon and plagioclase have distinct trace-element characteristics between eruptions, which require that the RM and DH crystals (and therefore magmas) were derived from distinct regions that had evolved independently for > 50 ka within a heterogeneous magmatic system and coexisted as physically-distinct, dominantly-liquid bodies prior to eruption. Thus, we favor a model where rhyolites are generated in independent batches by accumulation of evolved liquids in a heterogeneous, largely crystalline reservoir. Similarities in crystal age and chemical data to that at other young silicic systems (e.g., Mount St. Helens, Okataina Caldera Complex) suggest that this model may be more generally applicable to silicic magmas.  相似文献   

Dual sensor streamer technology used in Sleipner CO2 injection monitoring     

Anne‐Kari Furre  Ola Eiken 《Geophysical Prospecting》2014,62(5):1075-1088

CO₂ has been injected into the saline aquifer Utsira Fm at the Sleipner field since 1996. In order to monitor the movement of the CO₂ in the sub‐surface, the seventh seismic monitor survey was acquired in 2010, with dual sensor streamers which enabled optimal towing depths compared to previous surveys. We here report both on the time‐lapse observations and on the improved resolution compared to the conventional streamer surveys. This study shows that the CO₂ is still contained in the subsurface, with no indications of leakage. The time‐lapse repeatability of the dual sensor streamer data versus conventional data is sufficient for interpreting the time‐lapse effects of the CO₂ at Sleipner, and the higher resolution of the 2010 survey has enabled a refinement of the interpretation of nine CO₂ saturated layers with improved thickness estimates of the layers. In particular we have estimated the thickness of the uppermost CO₂ layer based on an analysis of amplitude strength together with time‐separation of top and base of this layer and found the maximum thickness to be 11 m. This refined interpretation gives a good base line for future time‐lapse surveys at the Sleipner CO₂ injection site.  相似文献   

A GIS-based method for the selection of the location of residence     

Xavier ALBACETE  Kari PASANEN  Mikko KOLEHMAINEN 《地球空间信息科学学报》2012,15(1)

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Theoretical interpretation of photometric properties of the Martian surface and atmosphere     

Kari Lumme  Leonard J. Martin  William A. Baum 《Icarus》1981,45(2):379-397

Earth-based UBV photometry, high-quality photographs from the Lowell Observatory collection, and Mariner 9 data have been combined with a new radiative transfer theory to derive physical parameters for the Martian surface and atmosphere, both before and during the 1971 dust storm. We find that the dust particles of the storm had a single-scattering albedo of 0.84 ± 0.02 and an asymmetry factor of 0.35 ± 0.10 in green (V) light. The geometric albedo of Mars was 0.15 and the phase integral 1.83, which yield 0.27 for the Bond albedo. The mean optical thickness of the “clear” atmosphere averaged over the whole planet was 0.15 ± 0.05 and was not detectably dependent on wavelength. Geometric albedos for the surface are 0.25 (light areas) and 0.17 (dark areas) in V, 0.095 in B (both areas), and 0.060 in U (both areas). The soil particles are moderately backward scattering with an asymmetry factor of ?0.20, indicating them to be rather opaque. The mean surface roughness, on a scale larger than that of individual dust particles and therefore large compared with the wavelength, is 0.57. This represents the depth/radius ratio of an average hole and it is only one-half as large as values typical for the Moon and asteroids.  相似文献   

Kinetic control of oxidation state at thermodynamically buffered potentials in subsurface waters     

John W. Washington  Dinku M. Endale  Kari E. Chappell 《Geochimica et cosmochimica acta》2004,68(23):4831-4842

Dissolved oxygen (DO) and organic carbon (C_org) are among the highest- and lowest-potential reactants, respectively, of redox couples in natural waters. When DO and C_org are present in subsurface settings, other couples are drawn toward potentials imposed by them, generating a bimodal clustering of calculated redox potentials. Which cluster a couple is drawn toward is determined by whether the couple’s oxidant or reductant is more concentrated. Generally, reactants >10^-6M are near equilibrium with their dominant complementary reactant and in a cluster, whereas reactants <10^-6M are relatively slow to react and diverge from the clusters. These observations suggest that reactions of higher-potential oxidants with lower-potential reductants commonly proceed simultaneously, regardless of the presence of other potential reactants, with the rates of reaction being determined more by concentration than relative potentials. As DO or C_org decreases, the potential gap separating couples diminishes. In waters having quantifiable concentrations of higher potential oxidants O₂ and NO₃^-, [H₂] was not diagnostic of their presence. In the water we analyzed having no quantifiable O₂ or NO₃^-, redox potential calculated with [H₂] was similar to potentials calculated for SO₄^2- reduction and methanogenesis. Composite reactions, NO₃^-→N₂ and O₂→H₂O, are best characterized in multiple steps due to slow reaction of low-concentration intermediates. The [CO] data we report, among the first for groundwater, are high compared to water equilibrated with the atmosphere.  相似文献   

Palaeomagnetic results from the Palaeozoic basement of the southern Drummond Basin, central Queensland, Australia   总被引：1，自引：0，他引：1  

Kari L. Anderson  Mark A. Lackie  David A. Clark 《Geophysical Journal International》2004,159(2):473-485

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Superstructures in calcian ankerites     

Kari Reksten 《Physics and Chemistry of Minerals》1990,17(3):266-270

Electron diffraction patterns from low-temperature calcian ankerites reveal weak c- and d-type superstructure reflections. The reflections arise in small local domains within the host crystal. A model for the c-domain superstructure is proposed, having space group P2/ c and the composition CaFe(CO₃)₂. The formation of such domains is possibly favoured in dolomites with excess Ca, implying that the solid solubility of Fe may be more restricted in calcian dolomites than in dolomites with stoichiometric Ca contents.  相似文献   

A case study of airborne and satellite remote sensing of a spring bloom event in the Gulf of Finland     

Sampsa Koponen  Jenni Attila  Jouni Pulliainen  Kari Kallio  Timo Pyhälahti  Antti Lindfors  Kai Rasmus  Martti Hallikainen 《Continental Shelf Research》2007

The concentrations of chlorophyll-a (chl-a), total suspended solids (TSS) and the absorption coefficient of colored dissolved organic matter (a_CDOM(400)) are estimated in Case II waters using medium resolution imaging spectrometer (MERIS) satellite (full resolution [FR] level 1b, 300 m resolution) and AISA airborne spectrometer data acquired during a spring bloom in the Gulf of Finland, Baltic Sea on April 27, 2004. The accuracy of the estimation is analyzed using empirical band-ratio algorithms together with in situ observations that include water samples analyzed in a laboratory (variation ranges: 22–130 μg/l, 2.9–20 mg/l, and 1.29–2.61 m⁻¹ for chl-a, TSS and a_CDOM(400), respectively). Additional in situ estimates (transects) on these characteristics are available through absorption and scattering coefficients measured with an ac-9 absorption and attenuation meter installed in a flow-through system. The retrieval accuracy (R²) of all three water quality characteristics with MERIS data is close to or above 0.9, while the RMSE is 7.8 μg/l (22%), 0.74 mg/l (16%) and 0.08 m⁻¹ (5%), for chl-a, TSS and a_CDOM(400), respectively. The validity of the chl-a algorithm is tested using nine additional data points. The BIAS-error for these points is 5.2 μg/l and the RMSE is 10.6 μg/l. The effects of changes in the atmospheric characteristics on band-ratio algorithms in cases where no concurrent in situ reference data are available are analyzed using the MODerate spectral resolution atmospheric TRANSmittance algorithm and computer model (MODTRAN). The additional error due to these changes is estimated to be below 20% for the applied ratio algorithms. The water quality data available in the level 2 MERIS-product distributed by the European Space Agency did not include valid results for the date investigated here.  相似文献   

Volcanic facies architecture of an intra-arc strike-slip basin, Santa Rita Mountains, Southern Arizona     

Cathy J. Busby  Kari N. Bassett 《Bulletin of Volcanology》2007,70(1):85-103

The three-dimensional arrangement of volcanic deposits in strike-slip basins is not only the product of volcanic processes, but also of tectonic processes. We use a strike-slip basin within the Jurassic arc of southern Arizona (Santa Rita Glance Conglomerate) to construct a facies model for a strike-slip basin dominated by volcanism. This model is applicable to releasing-bend strike-slip basins, bounded on one side by a curved and dipping strike-slip fault, and on the other by curved normal faults. Numerous, very deep unconformities are formed during localized uplift in the basin as it passes through smaller restraining bends along the strike-slip fault. In our facies model, the basin fill thins and volcanism decreases markedly away from the master strike-slip fault (“deep” end), where subsidence is greatest, toward the basin-bounding normal faults (“shallow” end). Talus cone-alluvial fan deposits are largely restricted to the master fault-proximal (deep) end of the basin. Volcanic centers are sited along the master fault and along splays of it within the master fault-proximal (deep) end of the basin. To a lesser degree, volcanic centers also form along the curved faults that form structural highs between sub-basins and those that bound the distal ends of the basin. Abundant volcanism along the master fault and its splays kept the deep (master fault-proximal) end of the basin overfilled, so that it could not provide accommodation for reworked tuffs and extrabasinally-sourced ignimbrites that dominate the shallow (underfilled) end of the basin. This pattern of basin fill contrasts markedly with that of nonvolcanic strike-slip basins on transform margins, where clastic sedimentation commonly cannot keep pace with subsidence in the master fault-proximal end. Volcanic and subvolcanic rocks in the strike-slip basin largely record polygenetic (explosive and effusive) small-volume eruptions from many vents in the complexly faulted basin, referred to here as multi-vent complexes. Multi-vent complexes like these reflect proximity to a continuously active fault zone, where numerous strands of the fault frequently plumb small batches of magma to the surface. Releasing-bend extension promotes small, multivent styles of volcanism in preference to caldera collapse, which is more likely to form at releasing step-overs along a strike-slip fault. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Diversity of murtoos and murtoo-related subglacial landforms in the Finnish area of the Fennoscandian Ice Sheet     

Antti E. K. Ojala  Joni Mäkinen  Elina Ahokangas  Kari Kajuutti  Markus Valkama  Aleksi Tuunainen  Jukka-Pekka Palmu 《Boreas: An International Journal of Quaternary Research》2021,50(4):1095-1115

Murtoos are recently discovered triangular-shaped subglacial landforms that form under warm-based ice and in association with significant subglacial meltwater flow. They appear in distinct fields and commonly occur in the area that was covered by the Fennoscandian Ice Sheet during glacial periods. Murtoos potentially represent a transition form from non-channelized to channelized subglacial drainage networks. In the present study, we analyse and classify murtoos and murtoo-related landforms in the Finnish area of the Fennoscandian Ice Sheet based on their characteristics and appearance in LiDAR-based digital elevations models. Combined with morphometric analyses, the observations suggest that five types of murtoos and murtoo-related landforms are common and widespread in Finland: (i) triangle-type murtoos (TTMs), (ii) chevron-type murtoos (CTMs), (iii) lobate-type murtoos (LTMs), (iv) murtoo-related ridges and escarpments (MREs), and (v) other murtoo-related polymorphous landforms (PMRs) that look like small mounds and ridges. The morphometric characteristics of the different types are described here in detail, and it is shown that they are spatially and geomorphologically related. In addition, we provide examples of murtoos other than the TTMs to demonstrate that different murtoo types and murtoo-related landforms are composed of similar sediments and architectural characteristics. The diversity of murtoo landforms and the transition between distinct murtoo types indicate rapid and complicated variations in the configuration of subglacial hydrology at different spatial and temporal scales. This study emphasizes the essential role of subglacial meltwater in the shaping of glacial landscapes and the redistribution of large volumes of sediments during the deglaciation of the Fennoscandian Ice Sheet.  相似文献