Layered mantle structure beneath the western Guyana Shield, Venezuela: Evidence from diamonds and xenocrysts in Guaniamo kimberlites     

Daniel J. Schulze  Dante Canil  Felix V. Kaminsky 《Geochimica et cosmochimica acta》2006,70(1):192-205

Mantle xenoliths and xenocrysts from Guaniamo, Venezuela kimberlites record equilibration conditions corresponding to a limited range of sampling in the lithosphere (100-150 km). Within this small range, however, compositions vary considerably, but regularly, defining a strongly layered mantle sequence. Major and trace element compositions suggest the following lithologic sequence: highly depleted lherzolite from 100 to 115 km, mixed ultra-depleted harzburgite and lherzolite from 115 to 120 km, relatively fertile lherzolite from 120 to 135 km, and mixed depleted harzburgite and relatively fertile lherzolite from 135 to 150 km. Based on comparison with well-documented mantle peridotites and xenocrysts from elsewhere, we conclude that the Meso-proterozoic Cuchivero Province (host to the Guaniamo kimberlites) is underlain by depleted and ultra-depleted shallow Archean mantle that was underplated, and uplifted, by Proterozoic subduction, perhaps more than once. These Proterozoic subduction events introduced less-depleted oceanic lithosphere beneath the Archean section, which remains there and is the source of the abundant Guaniamo eclogite-suite diamonds that have ocean-floor geochemical signatures. Although diamond-indicative low-Ca Cr-pyrope garnets are abundant, they are derived primarily from the shallow depleted layer within the field of graphite stability, and the rare peridotite-suite diamonds are either metastably preserved at these shallow depths, or were derived from the small amount of depleted lithosphere sampled by these kimberlites that remains within the diamond stability field (the mixture of Archean and Proterozoic mantle in the depth range 135-150 km).  相似文献   

Economic assessment of production of flour from Prosopis alba and P. pallida pods for human food applications.     

Peter Felker  Nora Grados  Gaston Cruz  Dante Prokopiuk 《Journal of Arid Environments》2003,53(4):517-528

This paper presents a detailed cost accounting of the processes involved in the production of flours from the mesocarps of the fruits of Prosopis alba and P. pallida to be used in human foods. The flours from both species are similar and contain 7–8% protein, 0·8–2% fat, 26–32% total dietary fiber and 48–59% sucrose. The data were based on actual production rates in use at the Universidad de Piura pilot plant using simple machinery. Machinery hourly charges were based on equivalent rental costs in order to avoid interest charge calculations. As opposed to other analyses which only included processing costs delivered to the plant, our analysis ascribed value to the owner of the trees in order to provide incentives to plant and care for the trees. The sensitivity analyses showed that the most economically important factor was the conversion efficiency of pods into flour. When a 40% conversion efficiency, such as that which has been obtained in both Peru and Argentina was obtained, and by-product credits for high fiber containing fraction were assumed, the wholesale selling price with a 5% marketing cost and a 40% profit direct costs was estimated to be $0·66 kg⁻¹ for Peru (using a $0·40 h⁻¹ labor rate ) and $1·76 kg⁻¹ for Argentina (using a $1·5 h⁻¹ labor rate).  相似文献   

Accretion, dispersal, and reaccumulation of the Bishunpur (LL3.1) brecciated chondrite: Evidence from troilite-silicate-metal inclusions and chondrule rims     

Tomoko Kojima  Dante S. Lauretta 《Geochimica et cosmochimica acta》2003,67(16):3065-3078

A set of troilite-silicate-metal (TSM) inclusions and chondrule rims in the Bishunpur (LL3.1) chondrite provide information regarding impact brecciation of small bodies in the early solar system. The TSM inclusions and chondrule rims consist of numerous angular to subrounded silicate grains that are individually enclosed by fine networks of troilite. FeNi metal also occurs in the troilite matrix. The silicates include olivine (Fo_55-98), low-Ca pyroxene (En_78-98), and high-Ca pyroxene (En_48-68Wo_11-32). Al- and Si-rich glass coexists with the silicates. Relatively coarse silicate grains are apparently fragments of chondrules typical of petrologic type-3 chondrites. Troilite fills all available cracks and pores in the silicate grains. Some of the TSM inclusions and rims are themselves surrounded by fine-grained silicate-rich rims (FGR).The TSM inclusions and rims texturally resemble the troilite-rich regions in the Smyer H-chondrite breccia. They probably formed by shock-induced mobilization of troilite during an impact event on a primitive asteroidal body. Because silicates in the TSM inclusions and rims have highly unequilibrated compositions, their precursor was presumably type-3 chondritic material like Bishunpur itself. The TSM inclusions and the chondrules with the TSM rims were fragmented and dispersed after the impact-induced compaction, then reaccreted onto the Bishunpur parent body. FGR probably formed around the TSM inclusions and rims, as well as around some chondrules, during the reaccumulation process. Components of most type-2 and 3 chondrites probably experienced similar processing, i.e., dispersal of unconsolidated materials and subsequent reaccumulation.  相似文献   

Resilience and seismic risk perception at school: a geoethical experiment in Aiello Calabro,southern Italy     

De Pascale  Francesco  Bernardo  Marcello  Muto  Francesco  Di Matteo  Dante  Dattilo  Valeria 《Natural Hazards》2016,86(2):569-586

The last few years have seen the debate on the geoethics of environmental and climatic protection growing to include resilience as a central idea within this new discipline, which holds many similarities with geography. Resilience analysis often looks at the capacity to re-establish conditions of equilibrium within a system which has been hit by a serious shock, e.g. a natural or man-made disaster. Geoethics works, in tandem with geological analyses and the geography of risk, to inform a population and develop integrated risk management in such a way as to strengthen a community’s resilience. The aim of this work is to study some people’s capacity to overcome what was potentially a disastrous event and, through a process of reconstruction, turn it into an occasion for growth. The experiment, carried out in the primary and middle schools in Aiello Calabro (Calabria, southern Italy), was conducted on the basis of the belief that there is a close relationship between a population’s having a realistic understanding of the risk of such an event, e.g. an earthquake, and high levels of resilience. We also tried to gain an insight into the relationship that may exist between resilience in primary and secondary school children and methods of coping which give an appropriate management of seismic risk. To be more precise, we try to discover whether there is a link between good/appropriate resilience and good/appropriate risk management.

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Distribution of benthic flora in the lower course of the Valdivia River,Chile     

Carlos Ramírez  Heriberto Figueroa  Enrique Hauenstein  Domingo Contreras 《Estuaries and Coasts》1989,12(2):111-118

The Valdivia River (Lake Region, Chile) originates in Riñihue Lake and flows into the sea at Corral Bay (39°52′S latitude), changing names several times along its course. The aquatic benthic flora (algae and aquatic plants) of the Valdivia River was characterized, based on 22 sites sampled and 124 plant species collected. Four benthic vegetation zones were established using presence-absence data: a freshwater zone and a marine zone were found at the extremes of the transect; an estuarine zone and a discontinuity zone were detected in the middle of this transect. The freshwater zone was characterized by a relatively diverse assemblage of vascular plants, the marine zone was dominated by algae and was rich in species. By contrast the estuarine zone was inhabited by only a few species but in great abundance, while the discontinuity zone was poor, in species and low in cover vegetation.  相似文献   

EJECTION–COLLISION ORBITS AND INVARIANT PUNCTURED TORI IN A RESTRICTED FOUR‐BODY PROBLEM     

Dante L. Maranhão  Jaume Llibre 《Celestial Mechanics and Dynamical Astronomy》1998,71(1):1-14

We study the motion of an infinitesimal mass point under the gravitational action of three mass points of masses μ, 1–2μ and μ moving under Newton's gravitational law in circular periodic orbits around their center of masses. The three point masses form at any time a collinear central configuration. The body of mass 1–2μ is located at the center of mass. The paper has two main goals. First, to prove the existence of four transversal ejection–collision orbits, and second to show the existence of an uncountable number of invariant punctured tori. Both results are for a given large value of the Jacobi constant and for an arbitrary value of the mass parameter 0<μ≤1/2. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Spatial and temporal variations in aboveground and belowground biomass of Spartina maritima (small cordgrass) in created and natural marshes     

Jesús M. Castillo  Pablo Leira-Doce  Alfredo E. Rubio-Casal  Enrique Figueroa 《Estuarine, Coastal and Shelf Science》2008,78(4):819-826

Spartina species are commonly used for salt marsh manipulative projects, where aboveground and belowground biomasses are functional traits that play important roles, showing high spatial and temporal variations. This work analyses variations in AGB and BGB of Spartina maritima and abiotic environmental parameters along a chronosequence of six marshes created from 1997 to 2003 with disparate sediment dynamics, and adjacent natural marshes and unvegetated tidal flats. S. maritima behaved as an autogenic engineer, as its colonization of bare sediments yielded abiotic environmental changes: specifically, bed level rise accompanied by higher oxygenation and salinity. These modifications of the environment were site-specific, depending mainly on sedimentary dynamics. At the same time, abiotic environmental changes determined biomass production rates of S. maritima that were higher in more-accreting marshes; however, AGB was kept constant from early in its development (2 years). The increase in BGB with elevation seemed to be related to the inhibition of subsurface tissue development in anoxic sediments. Biomass accumulation and production varied markedly, depending on the spatial scale, indicating the relevance of the plot size chosen for the analysis of biomass of cordgrasses. Our results show that managers of salt marshes should consider sedimentary dynamics carefully when setting realistic expectations for success criteria of created and restored wetlands.  相似文献   

Environmental limitations on recruitment from seed in invasive Spartina densiflora on a southern European salt marsh     

Enrique Mateos-Naranjo  Susana Redondo-Gmez  Carlos J. Luque  Eloy M. Castellanos  Anthony J. Davy  M. Enrique Figueroa 《Estuarine, Coastal and Shelf Science》2008,79(4):727-732

The South American cordgrass, Spartina densiflora, has invaded a range of different habitats that can support different native species assemblages on salt marshes in the Gulf of Cadiz, Spain. Little is known about the mechanisms of invasion. We examined the potential for seed germination and recruitment in a field transplant experiment, representing a wide range of environments, on elevational gradients across marshes with muddy and sandy sediments. The biotic resistance of native, perennial vegetation (where present) to recruitment of the alien was also investigated. Spartina densiflora seeds were able to germinate over a greater than 2-m range of elevation in the tidal frame. Germination success on unvegetated muddy sediments was related to sediment redox potential, with poor germination at strongly negative redox potentials on the lower sites. On sandy, well-drained sediments, germination was apparently constrained by water availability at the highest elevations. Comparison of vegetated and cleared plots on the upper marsh showed that there was a negative relationship between the presence of Atriplex portulacoides and germination on the muddy sediments. Recruitment (survival of seedlings for 12 weeks) was seen only on unvegetated muddy sediments at the highest elevation. Hence the invasive success and wide elevational tolerance of S. densiflora on the marshes of the Gulf of Cadiz are not reflected in its short-term ability to become established from its prolific seed production. Colonization of sub-optimal habitats may be largely by vegetative propagules and clonal growth.  相似文献   

Sulfide‐rich metallic impact melts from chondritic parent bodies     

Devin L. SCHRADER  Dante S. LAURETTA  Harold C. CONNOLLY jr.  Yulia S. GOREVA  Dolores H. HILL  Ken J. DOMANIK  Eve L. BERGER  Hexiong YANG  Robert T. DOWNS 《Meteoritics & planetary science》2010,45(5):743-758

Abstract– Sacramento Wash 005 (SaW) 005, Meteorite Hills 00428 (MET) 00428, and Mount Howe 88403 (HOW) 88403 are S‐rich Fe,Ni‐rich metal meteorites with fine metal structures and homogeneous troilite. We compare them with the H‐metal meteorite, Lewis Cliff 88432. Phase diagram analyses suggest that SaW 005, MET 00428, and HOW 88403 were liquids at temperatures above 1350 °C. Tridymite in HOW 88403 constrains formation to a high‐temperature and low‐pressure environment. The morphology of their metal‐troilite structures may suggest that MET 00428 cooled the slowest, SaW 005 cooled faster, and HOW 88403 cooled the quickest. SaW 005 and MET 00428 contain H‐chondrite like silicates, and SaW 005 contains a chondrule‐bearing inclusion that is texturally and compositionally similar to H4 chondrites. The compositional and morphological similarities of SaW 005 and MET 00428 suggest that they are likely the result of impact processing on the H‐chondrite parent body. SaW 005 and MET 00428 are the first recognized iron‐ and sulfide‐rich meteorites, which formed by impact on the H‐chondrite parent body, which are distinct from the IIE‐iron meteorite group. The morphological and chemical differences of HOW 88403 suggest that it is not from the H‐chondrite body, although it likely formed during an impact on a chondritic parent body.  相似文献   

The role of amphibole in the evolution of arc magmas and crust: the case from the Jurassic Bonanza arc section, Vancouver Island, Canada   总被引：6，自引：4，他引：2  

Jeff Larocque  Dante Canil 《Contributions to Mineralogy and Petrology》2010,159(4):475-492

The Jurassic Bonanza arc, on Vancouver Island, British Columbia, represents an exhumed island arc crustal section of broadly diorite composition. We studied bodies of mafic and ultramafic cumulates within deeper levels of the arc to constrain the conditions and fractionation pathways leading from high-Mg basalt to andesite and dacite. Major element trends coupled with textural information show the intercumulus crystallization of amphibole, as large oikocrysts enclosing olivine in primitive cumulates controls the compositions of liquids until the onset of plagioclase crystallization. This process is cryptic, occurring only in the plutonic section, and explains the paucity of amphibole in mafic arc volcanics and the change in the Dy/Yb ratios in many arc suites with differentiation. The correlation of octahedral Al in hornblende with pressure in liquidus experiments on high-Mg basalts is applied as an empirical barometer to hornblendes from the Bonanza arc. It shows that crystallization took place at 470–880 MPa in H₂O-saturated primitive basaltic magmas. There are no magmatic equivalents to bulk continental crust in the Bonanza arc; no amount of delamination of ultramafic cumulates will shift the bulk arc composition to the high-Mg# andesite composition of bulk continental crust. Garnet removal from wet magmas appears to be the key factor in producing continental crust, requiring high pressures and thick crust. Because oceanic island arcs are built on thinner crust, the long-term process generating the bulk continental crust is the accretion of island arcs to continental margins with attendant tectonic thickening.  相似文献