Petrologic and experimental evidence for the movement and heating of the pre-eruptive Minoan rhyodacite (Santorini, Greece)   总被引：1，自引：1，他引：0  

Elizabeth Cottrell  James E. Gardner  Malcolm J. Rutherford 《Contributions to Mineralogy and Petrology》1999,135(4):315-331

Hydrothermal experiments combined with petrologic observations form the basis for a new two-stage model for the evolution of the pre-eruption Minoan magma chamber at Santorini, Greece. Ninety-nine percent of the erupted volume is two-pyroxene, rhyodacitic magma that had been stored at a temperature of ∼885 °C, based on magnetite-ilmenite and QUILF geothermometry. The rest of the volume is basaltic to andesitic magma, which occurs as <10 cm scoria clasts and as small inclusions in rhyodacite pumices. Petrologic observations show that these magmas mixed at different scales and at different times (i.e., multiple batches of mafic magma). Hydrothermal experiments were carried out on samples of rhyodacite and a mafic scoria in order to determine magma storage conditions and the mixing history of the two magmas. At 885 °C, the rhyodacite must have been stored at water-saturated pressures of ∼50 MPa, based on its phase assemblage, matrix-glass composition, and crystal content. However, glass inclusions inside rhyodacitic plagioclase phenocrysts contain more than 6 wt% H₂O, indicating they formed at pressures >200 MPa. In addition, the composition of the plagioclase hosts (An_{56 ± 6}) of the inclusions require temperatures of 825 ± 25 °C at pressures >200 MPa. This demonstrates that the Minoan rhyodacitic magma underwent a two-stage evolution, first crystallizing at ∼825^∘C and >200 MPa, and then rinsing to a shallow ∼50 MPa storage region with a concomitant rise in temperature to ∼885 °C. We suggest that the episodic intrusion of mafic magmas provided the necessary heat and perhaps contributed to the ascent of the magma to shallow crustal depths where it reequilibrated before the cataclysmic eruption. Phase equilibria suggest that much of the heating of the rhyodacite occurred in the shallow storage region. Thermal budget calculations suggest that the rhyodacite magma could have been heated by intrusions of basalt rising at reasonable upwelling rates and injected into the storage zone over several hundred years. Preservation of amphibole in the mafic scoria indicate that injection of mafic magma continued up until days before the cataclysmic eruption, perhaps triggering the event. Received: 30 September 1997 / Accepted: 5 October 1998  相似文献   

Spatial and temporal variability in the responses of Arctic terrestrial ecosystems to environmental change     

Terry V. Callaghan  Malcolm C. Press  John A. Lee  David L. Robinson  Clive W. Anderson 《Polar research》1999,18(2):191-197

This paper compares the responses of two contrasting Arctic ecosystems to climate change simulations: a polar semi-desert (in Svalbard) and a dwarf shrub heath (at Abisko, northern Sweden). These ecosystems are located close to the northern-and southernmost extremes of the Arctic region, respectively. Inmacts of simulated climatic changes were determined through factorial perturbation experiments, where growing season temperature, nutrient availability and water supply were manipulated. The results are compared with the impact of interannual variation in climate on the growth of a keystone moss species, Hylocomium splendens , from the wider circumpolar area. The perturbation studies revealed that current interannual variability in temperature and the temperate tolerance of many species may exceed predicted changes in mean summer temperature over the next century. Arctic ecosystems differed in their responses to environmental manipulations, with the structure of the dwarf shrub health being affected through shifts in competitive hierarchy, potentially leading to lower biodiversity, and the polar semi-desert being affected through invasion, potentially leading to higher diversity. H. splendens showed negative responses to perturbation at the sub-Arctic site, in contrast to the positive relationship between temperature and growth observed in the natural environment. This apparent discrepancy may result from: (i) artefacts arising from the perturbations, such as lower atmospheric relative humidity; (ii) non-equilibrium responses during the relatively short-term perturbation studies and/or (iii) ecotypic variation in the moss population. Thus, caution should be employed when extrapolating from perturbations studies to both longer time-scales and different ecosystems within the Arctic.  相似文献   

Ascent and eruption of a lunar high-titanium magma as inferred from the petrology of the 74001/2 drill core     

Catherine M. WEITZ  Malcolm J. RUTHERFORD  James W. HEAD III  David S. McKAY 《Meteoritics & planetary science》1999,34(4):527-540

Abstract— An analysis of the orange glasses and crystallized beads from the 68 cm deep 74001/2 core has been conducted to understand the processes occurring during ascent and eruption of the Apollo 17 orange glass magma. Equilibrium between melt and metal blebs (Fe₈₅Ni₁₄Co₁) within the core, along with Cr contents in olivine phenocrysts, suggest there was an oxidation of C and a reduction of the melt at an O fugacity of IW-1.3 and 1320 °C to form CO gas at 200 bars or ～4 km depth. This was followed by development of more oxidized conditions during ascent. Also during ascent, there was formation of euhedral, homogeneous Fo₈₁ olivine crystals and spinel crystals with higher Al and Mg contents than the smaller spinels in the crystallized beads. Both the metal blebs and Al-rich spinels were trapped inside the Fo₈₁ olivine phenocrysts as they grew prior to eruption. The composition of the orange glasses are homogeneous throughout the core, except for a few distinct glasses at the top that appear to have been mixed in by micrometeorite reworking. A few glassy melt inclusions of orange glass composition trapped in the Fo₈₁ phenocrysts contain 600 ± 100 ppm S and ～50 ppm Cl compared to the 200 ppm S and 50 ppm Cl in the orange glass melt when quenched. These inclusions therefore document the addition of 400 ppm S to the CO-rich volcanic gas during the eruption. The size and distribution of different volcanic beads in the Apollo 17 deposit indicate a mode of eruption in which the orange glasses and partially crystallized beads formed further away from the volcanic vent where cooling rates were faster. Progressively larger and more numerous crystals in the black beads reflect slower cooling rates at higher optical densities in the volcanic plume. The development of a brown texture in the orange glasses at the bottom of the core, where the black beads dominate, is interpreted to result from devitrification by subsolidus heating either as the orange glasses fell back through the hot plume or after deposition on the surface. The change from domination by orange glasses to black beads in the core probably reflects a decrease in gas content over time, which consequently would increase the plume optical density and favor slower cooling rates.  相似文献   

Geophysical inversion with a neighbourhood algorithm—I. Searching a parameter space     

Malcolm Sambridge 《Geophysical Journal International》1999,138(2):479-494

This paper presents a new derivative-free search method for finding models of acceptable data fit in a multidimensional parameter space. It falls into the same class of method as simulated annealing and genetic algorithms, which are commonly used for global optimization problems. The objective here is to find an ensemble of models that preferentially sample the good data-fitting regions of parameter space, rather than seeking a single optimal model. (A related paper deals with the quantitative appraisal of the ensemble.)
  The new search algorithm makes use of the geometrical constructs known as Voronoi cells to derive the search in parameter space. These are nearest neighbour regions defined under a suitable distance norm. The algorithm is conceptually simple, requires just two 'tuning parameters', and makes use of only the rank of a data fit criterion rather than the numerical value. In this way all difficulties associated with the scaling of a data misfit function are avoided, and any combination of data fit criteria can be used. It is also shown how Voronoi cells can be used to enhance any existing direct search algorithm, by intermittently replacing the forward modelling calculations with nearest neighbour calculations.
  The new direct search algorithm is illustrated with an application to a synthetic problem involving the inversion of receiver functions for crustal seismic structure. This is known to be a non-linear problem, where linearized inversion techniques suffer from a strong dependence on the starting solution. It is shown that the new algorithm produces a sophisticated type of 'self-adaptive' search behaviour, which to our knowledge has not been demonstrated in any previous technique of this kind.  相似文献   

Geophysical inversion with a neighbourhood algorithmII. Appraising the ensemble     

Malcolm Sambridge 《Geophysical Journal International》1999,138(3):727-746

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Development of a unified oil droplet size distribution model with application to surface breaking waves and subsea blowout releases considering dispersant effects     

Zhengkai Li  Malcolm Spaulding  Deborah French McCay  Deborah Crowley  James R. Payne 《Marine pollution bulletin》2017,114(1):247-257

An oil droplet size model was developed for a variety of turbulent conditions based on non-dimensional analysis of disruptive and restorative forces, which is applicable to oil droplet formation under both surface breaking-wave and subsurface-blowout conditions, with or without dispersant application. This new model was calibrated and successfully validated with droplet size data obtained from controlled laboratory studies of dispersant-treated and non-treated oil in subsea dispersant tank tests and field surveys, including the Deep Spill experimental release and the Deepwater Horizon blowout oil spill. This model is an advancement over prior models, as it explicitly addresses the effects of the dispersed phase viscosity, resulting from dispersant application and constrains the maximum stable droplet size based on Rayleigh-Taylor instability that is invoked for a release from a large aperture.  相似文献   

The Value of Wastewater Derived Struvite as a Source of Phosphorus Fertilizer          下载免费PDF全文

Chirag M. Mehta  Malcolm N. Hunter  Gaius Leong  Damien J. Batstone 《洁净——土壤、空气、水》2018,46(7)

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Isotope hydrology of the Allt a' Mharcaidh catchment,Cairngorms, Scotland: implications for hydrological pathways and residence times     

C. Soulsby  R. Malcolm  R. Helliwell  R. C. Ferrier  A. Jenkins 《水文研究》2000,14(4):747-762

The hydrology of oxygen‐18 (¹⁸O) isotopes was monitored between 1995 and 1998 in the Allt a' Mharcaidh catchment in the Cairngorm Mountains, Scotland. Precipitation (mean δ¹⁸O=−7·69‰) exhibited strong seasonal variation in δ¹⁸O values over the study period, ranging from −2·47‰ in the summer to −20·93‰ in the winter months. As expected, such variation was substantially damped in stream waters, which had a mean and range of δ¹⁸O of −9·56‰ and −8·45 to −10·44‰, respectively. Despite this, oxygen‐18 proved a useful tracer and streamwater δ¹⁸O variations could be explained in terms of a two‐component mixing model, involving a seasonally variable δ¹⁸O signature in storm runoff, mixing with groundwater characterized by relatively stable δ¹⁸O levels. Variations in soil water δ¹⁸O implied the routing of depleted spring snowmelt and enriched summer rainfall into streamwaters, probably by near‐surface hydrological pathways in peaty soils. The relatively stable isotope composition of baseflows is consistent with effective mixing processes in shallow aquifers at the catchment scale. Examination of the seasonal variation in δ¹⁸O levels in various catchment waters provided a first approximation of mean residence times in the major hydrological stores. Preliminary estimates are 0·2–0·8 years for near‐surface soil water that contributes to storm runoff and 2 and >5 years for shallow and deeper groundwater, respectively. These ¹⁸O data sets provide further evidence that the influence of groundwater on the hydrology and hydrochemistry of upland catchments has been underestimated. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献