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31.
An APL Program for a Leslie matrix population projection is developed and applied to analysis of a Canadian polar bear population. Hunting specified with respect to sex ratio within a total quota may be included in the projections. Application to the lower central arctic islands' polar bear population of 1100 animals indicates a growth to 1560 animals during ten years without hunting. Projection with two males taken for each female indicates that 54 animals may be taken from the population each year. However, the same sized hunt, but with a one-to-one sex ratio, caused a significant depression of the population. 相似文献
32.
The phase relationships of three peralkaline rhyolites fromthe Kenya Rift have been established at 150 and 50 MPa, at oxygenfugacities of NNO - 1·6 and NNO + 3·6 (log fO2relative to the NiNiO solid buffer), between 800 and660°C and for melt H2O contents ranging between saturationand nominally anhydrous. The stability fields of fayalite, sodicamphiboles, chevkinite and fluorite in natural hydrous silicicmagmas are established. Additional phases include quartz, alkalifeldspar, ferrohedenbergite, biotite, aegirine, titanite, montdoriteand oxides. Ferrohedenbergite crystallization is restrictedto the least peralkaline rock, together with fayalite; it isreplaced at low melt water contents by ferrorichterite. Riebeckitearfvedsoniteappears only in the more peralkaline rocks, at temperaturesbelow 750°C (dry) and below 670°C at H2O saturation.Under oxidizing conditions, it breaks down to aegirine. In themore peralkaline rocks, biotite is restricted to temperaturesbelow 700°C and conditions close to H2O saturation. At 50MPa, the tectosilicate liquidus temperatures are raised by 5060°C,and that of amphibole by 30°C. Riebeckitearfvedsonitestability extends down nearly to atmospheric pressure, as aresult of its F-rich character. The solidi of all three rocksare depressed by 40100°C compared with the solidusof the metaluminous granite system, as a result of the abundanceof F and Cl. Low fO2 lowers solidus temperatures by at least30°C. Comparison with studies of metaluminous and peraluminousfelsic magmas shows that plagioclase crystallization is suppressedas soon as the melt becomes peralkaline, whatever its CaO orvolatile contents. In contrast, at 100 MPa and H2O saturation,the liquidus temperatures of quartz and alkali feldspar arenot significantly affected by changes in rock peralkalinity,showing that the incorporation of water in peralkaline meltsdiminishes the depression of liquidus temperatures in dry peralkalinesilicic melts compared with dry metaluminous or peraluminousvarieties. At 150 MPa, pre-eruptive melt H2O contents rangefrom 4 wt % in the least peralkaline rock to nearly 6 wt % inthe two more peralkaline compositions, in broad agreement withprevious melt inclusion data. The experimental results implymagmatic fO2 at or below the fayalitequartzmagnetitesolid buffer, temperatures between 740 and 660°C, and meltevolution under near H2O saturation conditions. KEY WORDS: peralkaline; rhyolite; phase equilibria 相似文献
33.
A trace-gas climatology above Zotino, central Siberia 总被引:1,自引:1,他引:1
34.
35.
SANTANU ACHARJEE JYOTISANKAR RAY PAYEL DEY DEBAPRIYA BHATTACHARYYA MOUSUMI BANERJEE BASAB CHATTOPADHYAY SHYAMAL SENGUPTA A K BHATT D CHOWDHURY A K DWIVEDI SANJOY MAHATO ARKA RANJAN JANA P B MAITHANI P V RAMESH BABU 《Journal of Earth System Science》2016,125(8):1681-1696
The area of investigation at and around Mashak Pahar, Bankura district, West Bengal, India comprises a number of rock types namely: granite gneiss, migmatized quartz tourmaline gneiss, quartz pebble conglomerate, ferruginous quartzite, quartz tourmaline veins (as veins) and graphite schists. Interestingly, the study area lies in the region extending South Purulia Shear Zone (~Tamar–Porapahar Shear Zone) which marks the boundary between two contrasting tectonic blocks of eastern India, namely, the Chhotanagpur Gneissic Terrane (CGC) to the north and Singhbhum Group of rocks to the south. The rocks of the study area are poly-phasedly deformed by three phases of folding, namely, F1, F2 and F3. All the tourmalines are classified to be of ‘Alkali Group’. Chemistry of tourmalines from migmatized quartz tourmaline gneiss and those from quartz tourmaline veins are in conformity with their relation to (earthquake induced) shear system evolution in this terrain. In general, the compositional evolution of tourmaline during prograde metamorphism (~400°–730°C) has been supported by both petrographic and chemical evidences. Assessment of mineral–chemical data of constituent tourmaline grains clearly suggests compositional variations across zonal boundaries within tourmaline that was controlled by changing metamorphic milieu in this terrane. Field and petrographic evidences clearly indicate activation of earlier and later shears in this region accompanied by infiltration of boron and formation of zoned tourmaline crystals. 相似文献
36.
DOWNES HILARY; MACDONALD RAY; UPTON BRIAN G. J.; COX KEITH G.; BODINIER JEAN-LOUIS; MASON PAUL R. D.; JAMES DODIE; HILL PETER G.; HEARN B. CARTER JR 《Journal of Petrology》2004,45(8):1631-1662
Ultramafic xenoliths in Eocene minettes of the Bearpaw Mountainsvolcanic field (Montana, USA), derived from the lower lithosphereof the Wyoming craton, can be divided based on textural criteriainto tectonite and cumulate groups. The tectonites consist ofstrongly depleted spinel lherzolites, harzburgites and dunites.Although their mineralogical compositions are generally similarto those of spinel peridotites in off-craton settings, somecontain pyroxenes and spinels that have unusually low Al2O3contents more akin to those found in cratonic spinel peridotites.Furthermore, the tectonite peridotites have whole-rock majorelement compositions that tend to be significantly more depletedthan non-cratonic mantle spinel peridotites (high MgO, low CaO,Al2O3 and TiO2) and resemble those of cratonic mantle. Thesecompositions could have been generated by up to 30% partialmelting of an undepleted mantle source. Petrographic evidencesuggests that the mantle beneath the Wyoming craton was re-enrichedin three ways: (1) by silicate melts that formed mica websteriteand clinopyroxenite veins; (2) by growth of phlogopite fromK-rich hydrous fluids; (3) by interaction with aqueous fluidsto form orthopyroxene porphyroblasts and orthopyroxenite veins.In contrast to their depleted major element compositions, thetectonite peridotites are mostly light rare earth element (LREE)-enrichedand show enrichment in fluid-mobile elements such as Cs, Rb,U and Pb on mantle-normalized diagrams. Lack of enrichment inhigh field strength elements (HFSE; e.g. Nb, Ta, Zr and Hf)suggests that the tectonite peridotites have been metasomatizedby a subduction-related fluid. Clinopyroxenes from the tectoniteperidotites have distinct U-shaped REE patterns with strongLREE enrichment. They have 143Nd/144Nd values that range from0·5121 (close to the host minette values) to 0·5107,similar to those of xenoliths from the nearby Highwood Mountains.Foliated mica websterites also have low 143Nd/144Nd values (0·5113)and extremely high 87Sr/86Sr ratios in their constituent phlogopite,indicating an ancient (probably mid-Proterozoic) enrichment.This enriched mantle lithosphere later contributed to the formationof the high-K Eocene host magmas. The cumulate group rangesfrom clinopyroxene-rich mica peridotites (including abundantmica wehrlites) to mica clinopyroxenites. Most contain >30%phlogopite. Their mineral compositions are similar to thoseof phenocrysts in the host minettes. Their whole-rock compositionsare generally poorer in MgO but richer in incompatible traceelements than those of the tectonite peridotites. Whole-rocktrace element patterns are enriched in large ion lithophileelements (LILE; Rb, Cs, U and Pb) and depleted in HFSE (Nb,Ta Zr and Hf) as in the host minettes, and their SrNdisotopic compositions are also identical to those of the minettes.Their clinopyroxenes are LREE-enriched and formed in equilibriumwith a LREE-enriched melt closely resembling the minettes. Thecumulates therefore represent a much younger magmatic event,related to crystallization at mantle depths of minette magmasin Eocene times, that caused further metasomatic enrichmentof the lithosphere. KEY WORDS: ultramafic xenoliths; Montana; Wyoming craton; metasomatism; cumulates; minette 相似文献
37.
RAY Durbar BANERJEE Ranadip MAZUMDER Anin PAROPKARI Anil L. MUKHOPADHYAY Subir BALAKRISHNAN Srinivasan 《海洋学报(英文版)》2018,37(4):22-33
Polymetallic sulfides from two hydrothermal chimneys and talus deposit from the Vienna Woods field of Manus Basin were studied for mineralogy, elemental composition, and S-isotope ratio to understand their evolution. The factors including the nature of source fluid, mineral paragenesis, and related geochemical processes have been discussed. Mineralogy and elemental concentration of Cu and Fe-rich large chimney at the central part of this hydrothermal field was completely different from the smaller Zn-rich peripheral chimney and Fe-rich talus deposit, suggesting the variable degree of alterations generate physico-chemically different source fluids responsible for these hydrothermal structures. Similarly, S-isotope ratios also indicate chemically diverse fluids and different modes of precipitation were involved in their evolution. Distinct mineral zonings and associated elemental and isotopic compositions within individual deposit confirm paragenetic shifts were involved during their growth process. 相似文献
38.
JYOTISANKAR RAY ABHISHEK SAHA SOHINI GANGULY V BALARAM A KESHAV KRISHNA SAMPA HAZRA 《Journal of Earth System Science》2011,120(3):459-473
The Mylliem granitoids of the Meghalaya Plateau, northeastern India, represent one of the disharmonic Neoproterozoic igneous
plutons, which are intrusive into low-grade Shillong Group of metasediments. Field studies indicate that the Mylliem granitoids
cover an area of about 40 km2 and is characterized by development of variable attitude of primary foliations mostly marked along the margin of the pluton.
Xenoliths of both Shillong Group of metasediments and mafic rocks have been found to occur within Mylliem granitoids. Structural
study of the primary foliation is suggestive of funnel-shaped intrusion of Mylliem granitoids with no appreciable evidence
of shearing. Petrographically, Mylliem granitoids are characterized by pink to white phenocrysts of prismatic microcline/perthite
and lath-shaped plagioclase (An20–An29). Groundmass material is characterized by quartz, microcline, plagioclase, muscovite and biotite. Sphene and apatite occur
as accessory minerals. Petrographically Mylliem granitoids have been discriminated as granite and granodiorite according to
IUGS system of classification. 相似文献
39.
Serpentinites from the inside corner high(6°38.5′S/68°19.34′E)from the Northern Central Indian Ridge(NCIR)are comprised mainly of high Mg-rich lizardite and chrysotile pseudomorphs with varying morphologies.‘Mesh rim',‘window',‘hourglass' and‘bastite' are the most common textures displayed by both chrysotile and lizardite.Numerous chrysotile veins in association with cross cutting magnetite veins indicate an advanced stage of serpentinisation.The relatively high abundance of chrysotile and lizardite suggest their close association and formation at a temperature below 250℃. Abundant‘mesh rim'and‘bastite'texture and variegated matrix reveal that the present serpentinites might have formed due to the interaction of harzburgite and seawater.Positive Eu anomaly(Eu/Eu~* up to 3.38),higher La/Sm(up to 4.40)and Nb/La(up to 6.34)ratios suggest substantial hydrothermal influence during the formation of the serpentinites. 相似文献
40.
Noble gases and nitrogen were measured in two adjacent samples each from the Raghunathpura (IIAB) and the Nyaung (IIIAB) iron meteorite falls. Light noble gases in both the meteorites were of pure cosmogenic origin. Using (3He/4He)c ratios and the production systematic of Ammon et al. ( 2009 ), we estimated the sample depth and meteoroid size for Nyaung (~8 cm depth in a ~15 cm radius object) and Raghunathpura (~12–14 cm depth in a ~25 cm object). We derived cosmic ray exposure ages of 1710 ± 256 Ma (for Nyaung, the highest reported so far for the IIIAB group) and 224 ± 34 Ma (for Raghunathpura). Variable amounts of trapped Kr and Xe were found in both meteorites. The phase Q‐like elemental ratio (84Kr/132Xe) suggests that the trapped component is of indigenous origin, and most likely hosted in the heterogeneously distributed micro‐inclusions of troilite/schreibersite. Trapped phase Q component is being reported for the first time, for a IIAB iron meteorite. Both meteorites showed light isotopic composition for nitrogen, and need at least two N components to explain the observed N isotopic systematic. Variable amounts of trapped noble gases and the presence of more than one N component suggest that the magmatic process that formed the parent body of these meteorites either could not completely homogenize or completely degas all the phases. 相似文献