Amphibole pyroxenite xenoliths: Cumulate or replacement phenomena from the upper mantle,Nunivak Island,Alaska     

Donald M. Francis 《Contributions to Mineralogy and Petrology》1976,58(1):51-61

Interstitial to poikilitic amphibole found in garnet pyroxenite xenoliths has been interpreted, in the past, to represent a critically silica undersaturated, residual intercumulus melt trapped by its cumulate assemblage of anhydrous phases. The textural features of such amphibole in pyroxenite xenoliths from Nunivak Island, Alaska, however, are more compatible with an origin by replacement of the anhydrous phases of the pyroxenite, following a period of cooling and sub-solidus recrystallization in the upper mantle. The reaction of amphibole and olivine to give orthopyroxene, observed in two specimens, requires that the associated fluid phase was not critically silica undersaturated. The amphibole is therefore thought to reflect the interaction of an alkali-bearing, migratory, aqueous fluid and an upper mantle consisting of spinel lherzolite cut by veins of spinel and garnet pyroxenite.  相似文献   

Some trace element relationships among liquid and solid phases in the course of the fractional crystallization of magmas     

Francis Albarede 《Geochimica et cosmochimica acta》1976,40(6):667-673

The classical equations relating the trace element concentrations of the liquid and solid phases coexisting in the simple fractional crystallization of a parental magma have been put in a simple graphical form, which allows rapid analysis of the possible genetic relationships in a given rock suite. The effects of an incomplete separation between the two phases are taken into account. The approach does not require the use of otherwise estimated partition coefficients. Trace element data concerning the minerals of cumulates, where available, may provide an independent estimation of the effective mineral-liquid partition coefficients. With reasonable assumptions, this approach may even be applied to plutonic rocks. Interpretation of the published rare earth element data from the Southern California Batholith by this procedure suggests that a tonalitic parental magma could generate a granodioritic liquid by crystallizing 40–50 wt % of a solid residue of gabbroic composition, in agreement with Larsen's (Mem. Geol. Soc. Amer. 29, 1948) calculations. The calculated mineral-liquid partition coefficients for the REE fall in the range of published phenocryst-groundmass values for acidic volcanic rocks.  相似文献   

Implications of continental drift to the earth sciences. 1 : D.H. Tarling and S.K. Runcorn (editors). Academic Press, 1973, 620 pp., £13.80     

Peter Francis 《Tectonophysics》1974,22(1-2)

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Land-sea warming contrast: the role of the horizontal energy transport     

Olivier Geoffroy  David Saint-Martin  Aurore Voldoire 《Climate Dynamics》2015,45(11-12):3493-3511

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Biogeochemical impact of a model western iron source in the Pacific Equatorial Undercurrent     

Lia Slemons  Thomas Gorgues  Olivier Aumont  Christophe Menkes  James W. Murray 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(12):2115-2128

Trace element distributions in the source waters of the Pacific Equatorial Undercurrent (EUC) show the existence of elevated total acid-soluble iron concentrations. This region has been suggested to contribute enough bioavailable iron to regulate interannual and interglacial variability in biological productivity downstream in the high-nitrate low-chlorophyll upwelling zone of the eastern equatorial Pacific. We investigated the advection and first-order biogeochemical impact of an imposed, data-based iron maximum in the western Pacific EUC using an ecosystem model forced by a global dynamical model. We imposed two source profiles of iron constrained by total acid-soluble iron measurements. Though the data for total acid-soluble iron included both dissolved and acid-soluble particulate iron species, we treated all of the total acid-soluble iron as if it was dissolved and bioavailable. A deeper (270 m) source was centered in the density horizon of the observed iron maximum and a shallower (180 m) source was located in the core of our model's EUC, where a dissolved iron maximum has been frequently postulated. These source runs were compared with a control run that contained no specific source of iron associated with the EUC. In the source runs elevated iron concentrations were simulated in the EUC across its entire zonal span, evident as a subsurface plume of dissolved iron slightly below the core of the EUC. In the control run there was no iron maximum associated with the EUC. Upwelling of iron-replete water in the central and eastern equatorial Pacific increased integrated primary productivity in the Wyrtki box (180°W:90°W, 5°S:5°N, 0:200 m) by 41% and 66% for the deeper and shallower iron perturbation, respectively. The source runs increased the realism of the zonal extent of HNLC conditions and the meridional distributions of biological productivity, relative to the control run. However, in the source simulations surface chlorophyll concentrations were too high by a factor of two and maximum surface nitrate concentrations were too low, relative to climatologies. The relative abundance of diatoms roughly doubled upon the input of additional iron, exceeding field observations. Though biogeochemical data are limited and we did not adjust parameters to optimize the model fits to observations, these results suggest that acid-soluble particulate iron supplied to the EUC in the western equatorial Pacific is unlikely to be entirely bioavailable.  相似文献   

Diet of Haplognathia ruberrima (Gnathostomulida) in a Caribbean marine mangrove          下载免费PDF全文

Pierre‐Yves Pascal  Claude Bellemare  Wolfgang Sterrer  Henricus T. S. Boschker  Silvina Gonzalez‐Rizzo  Olivier Gros 《Marine Ecology》2015,36(2):246-257

Haplognathia ruberrima is a cosmopolitan gnathostomulid species found in sulfur bacterial mats in mangroves in Guadeloupe (French West Indies). Haplognathia ruberrima presents a δ¹³C value lower than all measured meiofaunal grazers and lower than the available measured food sources of this environment. This low δ¹³C value can not be due to specific ingestion of ¹³C‐depleted methanogenic bacteria because abundances of those bacteria are reduced in surficial and deep sediments as revealed by δ¹³C of bacterial fatty acid. According to scanning electron microscope observations, no bacterial ectosymbionts were observed at the surface of the gnathostomulids, and transmission electron microscope views revealed the absence of bacterial endosymbionts. Energy‐dispersive X‐ray spectroscopy analysis detected low levels of sulfur (0.32%±0.8) in biological tissues of H. ruberrima, confirming the absence of thioautotrophic bacterial symbionts in these animals. Consequently, the low δ¹³C value of H. ruberrima can not be due to the presence of sulfur‐oxidizing symbionts but more probably to the selective and exclusive consumption of free‐living, sulfur‐oxidizing bacteria.  相似文献   

Integrative taxonomic description of Plakina kanaky,a new polychromatic sponge species from New Caledonia (Porifera: Homoscleromorpha)          下载免费PDF全文

César Ruiz  Julijana Ivanišević  Pierre Chevaldonné  Alexander V. Ereskovsky  Nicole Boury‐Esnault  Jean Vacelet  Olivier P. Thomas  Thierry Pérez 《Marine Ecology》2015,36(4):1129-1143

Four similar sponges of different colors, all unknown to science, were collected in submarine caves of New Caledonia. We aimed at determining whether the four chromotypes represented different species or phenotypic variations of a unique new species. We used an integrative taxonomic approach combining morphologic, molecular and metabolomic analyses. The main traits that define these specimens are a skeleton made of monolophose, trilophose and tetralophose calthrops only, high chemical diversity and a high abundance and diversity of prokaryotic symbionts. The symbiotic community includes two unique prokaryote morphotypes, which are described for the first time in Homoscleromorpha, and appeared to be vertically transmitted. Although several features slightly differ among chromotypes, the most parsimonious conclusion was to propose a single new species Plakina kanaky sp. nov. Our phylogenetic analysis indicated the paraphyly of the Plakina genus, with P. kanaky sp. nov. belonging to a clade that includes Plakina jani and Plakina trilopha. The present work demonstrates that integrative taxonomy should be used in order to revise the entire Plakinidae family and especially the non‐monophyletic genus Plakina.  相似文献   

Stability of methane clathrate hydrates under pressure: Influence on outgassing processes of methane on Titan     

Mathieu Choukroun  Olivier Grasset 《Icarus》2010,205(2):581-10437

We have conducted high-pressure experiments in the H₂O-CH₄ and H₂O-CH₄-NH₃ systems in order to investigate the stability of methane clathrate hydrates, with an optical sapphire-anvil cell coupled to a Raman spectrometer for sample characterization. The results obtained confirm that three factors determine the stability of methane clathrate hydrates: (1) the bulk methane content of the samples; (2) the presence of additional gas compounds such as nitrogen; (3) the concentration of ammonia in the aqueous solution. We show that ammonia has a strong effect on the stability of methane clathrates. For example, a 10 wt.% NH₃ solution decreases the dissociation temperature of methane clathrates by 14-25 K at pressures above 5 MPa. Then, we apply these new results to Titan’s conditions. Dissociation of methane clathrate hydrates and subsequent outgassing can only occur in Titan’s icy crust, in presence of locally large amounts of ammonia and in a warm context. We propose a model of cryomagma chamber within the crust that provides the required conditions for methane outgassing: emplacement of an ice plume triggers the melting (if solid) or heating (if liquid) of large ammonia-water pockets trapped at shallow depth, and the generated cryomagmas dissociate surrounding methane clathrate hydrates. We show that this model may allow for the outgassing of significant amounts of methane, which would be sufficient to maintain the presence of methane in Titan’s atmosphere for several tens of thousands of years after a large cryovolcanic event.  相似文献   

Mercury surface composition: Integrating petrologic modeling and remote sensing data to place constraints on FeO abundance     

Miriam A. Riner  Francis M. McCubbin  G. Jeffrey Talyor 《Icarus》2010,209(2):301-313

A significant opaque component in Mercury’s crust is inferred based on albedo and spectral observations. Previous workers have favored iron-titanium bearing oxide minerals as the spectrally neutral opaque. A consequence of this hypothesis is that Mercury’s surface would have a high FeO content. An array of remote sensing techniques have not provided definitive constraints on the FeO content of Mercury’s surface. However, spectral observations have not detected a diagnostic 1 μm absorption band and have thus limited the FeO in coexisting silicates to <2 wt.% FeO. In this paper, we assess equilibrium among oxide and silicate minerals to constrain the distribution of iron between opaque oxides and silicates under a variety of environmental conditions. Equilibrium modeling is favored here because the geologic process that produced Mercury’s low-albedo intermediate terrain must have occurred globally, which favors a common widespread igneous process. Based on our modeling, we find that iron-rich ilmenite cannot occur with silicates that do not display a 1 μm absorption feature unless plagioclase abundances are high. However, such high plagioclase abundances are precluded by Mercury’s low albedo. Incorporating equilibrium crystallization modeling with spectral and albedo constraints we find the iron abundance of Mercury’s intermediate terrain is ?10 wt.% FeO. This intermediate iron composition matches constraints provided by visible albedo and total neutron absorption observed by MESSENGER. In fact, the total neutron absorption of mixtures of oxide, plagioclase, olivine and pyroxene for the oxide abundances estimated for Mercury, favor Mg-rich members of the ilmenite-geikielite solid-solution series. This work offers compositional constraints for Fe, Ti, and Mg that will be testable by various MESSENGER instrument data sets after it begins its orbital mission.  相似文献   

Letters to the editor     

Malcolm Haddon  Robert C. Francis 《新西兰海洋与淡水研究杂志》2013,47(4):447-449

A preliminary scuba survey of oligotrophic Lake Rotoma in 1972 revealed a vegetation mainly composed of native hydrophytes in which exotics were at an early stage of colonisation. In 1973 the presence of species was recorded in 5708 quadrats (625 cm²) at 1 m intervals along a total of 50 line transects placed systematically around the lake. Water depth was measured, and quadrat cover and substrate type were subjectively estimated. Species frequency calculations showed that the dominant vegetation pattern was a characean meadow of Chara fibrosa f. acanthopitys (A.Br.) R.D.W., Nitella leptostachys var. leonhardii (R.D.W.) R.D.W., and N. pseudoflabellata var. mucosa (Nordst.) Bailey. The charophytes extended over a depth range of 1–17.5 m on a wide variety of substrates and gradients. Native vascular plants were absent from many transects, and had a depth range only from 0 to 4.5 m, with most occurring above 3.5 m. The Low Mixed Community, found in shallow water less than 1.25 m in depth at the northeast end of the lake, provided this area with a high species diversity. Exotic hydrophytes had established in many areas around the lake. The distribution of Lagarosiphon major (Ridley) Moss and Elodea canadensis Michx. appeared to coincide with boating access and fallen submerged trees over a depth range of 0–6.0 m, although much of the available habitat had not yet been exploited. Emergent species were most abundant within the southwest inlet and also in the lagoons surrounding the lake where sheltered conditions and shallow gradients prevail.  相似文献