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P. Lira R. A. Johnson A. Lawrence R. Cid Fernandes 《Monthly notices of the Royal Astronomical Society》2007,382(4):1552-1590
We present optical and infrared broad-band images, radio maps, and optical spectroscopy for the nuclear region of a sample of nearby galaxies. The galaxies have been drawn from a complete volume-limited sample for which we have already presented X-ray imaging. We modelled the stellar component of the spectroscopic observations to determine the star formation history of our targets. Diagnostic diagrams were used to classify the emission-line spectra and determine the ionizing mechanism driving the nuclear regions. All those sources classified as active galactic nuclei present small Eddington ratios (∼10−3 –10−6 ) , implying a very slow growth rate of their black holes. We finally investigate the relative numbers of active and normal nuclei as a function of host galaxy luminosity and find that the fraction of active galaxies slowly rises as a function of host absolute magnitude in the M B ∼−12 to −22 range. 相似文献
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Roberto Ventura Santos Edilton J. dos Santos João Adauto de Souza Neto Luis Christian Montreuil Carmona Alcides Nóbrega Sial Luis Henrique Mancini Lauro Cézar Montefalco de Lira Santos Gilzênia Henrique do Nascimento Lucas UpaDafubigin Santos Mendes Emerson Marcello Ferreira Anastácio 《Gondwana Research》2013,23(1):380-389
Strongly-deformed marbles may be easily confused with linear and elongated carbonatite intrusions. Both rocks may present similar texture and foliation to the host rock, or even cross cutting field relationships, which could be interpreted either as igneous or high-grade metamorphosed marble. Diagnostic criteria are even more complex when there is evidence of melting of the metasedimentary carbonate rock, such as has been described in the Himalayas and in the Eastern Ghats, India.In the Alto Moxotó Terrane, a high-grade gneissic domain of the Borborema Province, Northeastern Brazil, there are metacarbonates associated with banded gneisses and different metaplutonic rocks. Field evidence indicates the absence of other metasedimentary rocks associated with these marbles, thus suggesting that these carbonates were separated from other siliciclastic metasedimentary rocks. The presence of marble also suggests that it may represent the initial stage of a crustal carbon recycling into the mantle. These marbles present many field similarities to carbonatites (e.g., fluid-flow structure) and, together with metagranites and metamafic intrusions, may represent a major collisional tectonic suture.A detailed study of the carbon, oxygen and strontium isotopic composition of these marbles is presented. This study aims to identify the origin of the different isotopic components. It is argued that these rocks were subjected to temperature and pressure conditions that were sufficiently high to have melted them. The isotopic data presented here support this interpretation and indicate the mixing of two components: (i) one characterized by radiogenic Sr isotopes and mantle-like carbon isotopes, which is associated with the gneissic and mafic rocks, and (ii) another characterized by low 87Sr/86Sr ratios and highly positive δ13C values. Available geochemical data for the upper Paleoproterozoic indicate that the 87Sr/86Sr ratio of ocean water, varying between 0.7050 (2.25 ± 0.25 Ga) and 0.7047 (1.91 Ga), falls within the lower range of the samples from Itatuba and thus reinforces the interpretation that these marbles are sedimentary-derived and were partially contaminated by interaction with the host gneissic and mafic rocks. 相似文献
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Michael J. Dorais Raul Lira Yadong Chen David Tingey 《Contributions to Mineralogy and Petrology》1997,130(1):31-46
The Achala batholith of Argentina contains very unusual layered enclaves containing up to 30% apatite and 50% biotite in
some layers. This modal mineralogy produces bulk-rock compositions that cannot represent liquids, having as little as 29%
SiO2 and up to 8% P2O5. Nor can the enclaves represent metasedimentary xenoliths because: (1) none of the Precambrian wall rocks has these compositions;
(2) none of the metasedimentary xenoliths present within the batholith shows any degree of transition to the mica-apatite-rich
enclaves; (3) the compositions and textures in the enclaves are inconsistent with metasediments; (4) a geochronological study
of zircon from an enclave gives an age of 368 ± 2 Ma, the exact age of zircons in the granitic host rocks. For these reasons,
we conclude that the enclaves are neither xenoliths of Precambrian wall rocks nor restite of a Precambrian source. The identical
age of the enclave and the host granites, coupled with textural, mineralogical, and bulk-rock characteristics of the enclaves,
indicates that the enclaves are magmatic segregations, i.e., cumulates. The F-rich nature of the stubby-shaped apatites and
biotites indicates a high F content of the magma parental to the enclaves. We infer that the viscosity of the melt was lowered
sufficiently to allow cumulates to form in spite of the granitic composition of the melt.
Received: 12 December 1996 / Accepted: 11 August 1997 相似文献
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P. Lira M. J. Ward A. Zezas S. S. Murray 《Monthly notices of the Royal Astronomical Society》2002,333(3):709-714
We present high spatial resolution X-ray Chandra HRC and HST WFPC2 H α observations of the prototypical infrared-luminous galaxy NGC 6240. The central region of this system shows a remarkably complex morphology, with filaments and loops observed in the optical and X-rays. The total X-ray luminosity is dominated by the extended emission. Both nuclei are clearly detected in the HRC image and both appear to be extended. The energetics of the nuclei imply that the southern nucleus is the more plausible counterpart to the obscured active galactic nucleus. The overall spectral energy distribution of the galaxy is in good agreement with a blend of starburst and AGN components that have similar bolometric luminosities, L bol ∼5×1045 erg s-1 , with the starburst dominating the observed continuum in the near-infrared ( K band), optical and soft X-ray bands. 相似文献
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This study provides evidence for the existence of halite and sylvite solid inclusions in igneous quartz and feldspars, the first to be reported in intrusive rocks, and to partially constrain the physicochemical environment that lets halides crystallize under magmatic conditions.Halite and sylvite solid inclusions were found included in quartz and feldspars from a micrographic–granophyric assemblage in a miarolitic aplite and, rarer, in alkali-feldspar from a miarolitic monzogranite. Monzogranite and aplite represent I-type, K-enriched postcollisional rocks of the Late Cambrian–Early Ordovician Sierra Norte–Ambargasta batholith in the Eastern Sierras Pampeanas. Both granitoids fall among the most evolved felsic rocks of the batholith, with aplite approaching haplogranitic compositions. Halite is far more common than sylvite and the presence and distribution of one or both halides are erratic within the felsic intrusive bodies. Halides occur as small skeletal grains, commonly in cross-shaped aggregates of less than 50 μm. No K or Na was found at the detection limits of EDS in either halite or sylvite respectively. Textural relationships suggest that the alkali-chlorides separated from the melt near the minima along the quartz–feldspar cotectics of PH2O > 160 < 200 MPa in a silica-, and potassium-rich magmatic system at approximately 750–700 °C, prior to the H2O-vapor saturated miarole-forming stage.Computed ratios for the magmatic volatile phase (MVP) coexisting with melt at the early stage of aplite crystallization are: NaCl/HCl = 0.11–0.97 and KCl/HCl = 0.24–1.62, being the highest range of values (0.79–0.97 and 1.45–1.62, respectively) found in those alkali-chloride-bearing samples. Maximum HCl/ΣCl(MVP) (0.28 to 0.31) indicates higher total Cl concentration in the MVP of alkali-chloride-bearing aplites, which is much higher in the halite-free aplite samples (HCl/ΣCl(MVP) = 0.59 to 0.74). One miarolitic monzogranite sample, where halite solid inclusions are present, also yielded the highest ratios for NaCl/HCl(MVP) (0.91) and KCl/HCl(MVP) (1.46), and the HCl/ΣCl(MVP) is 0.30. A high HCl concentration in the fluid phase is suggested by the log f(HF)/f(H2O) = − 4.75 to − 4.95, log f(HCl)/f(H2O) = − 3.73 to − 3.86, and log f(HF)/f(HCl) = − 0.88 to − 1.22, computed at 750 °C after biotite composition. The Cl concentrations at 800 °C, computed with a Dv/lCl = 0.84 + 26.6P (P at 200 MPa), yielded values within the range of 70 to 700 ppm Cl in the melt and 4000 to 40 000 ppm Cl in the coexisting MVP. The preferential partitioning of Cl in the vapor phase is controlled by the Dv/lCl; however, the low concentration of Cl in the melt suggests that high concentrations of Cl are not necessary to saturate the melt in NaCl or KCl.Cl-saturation of the melt and coexisting MVP might have been produced by a drop in Cl solubility due to the near-haplogranitic composition of the granitoids after extreme fractionation, probably enhanced by fluctuating reductions of the emplacement pressure in the brittle monzogranite host. Liquid immiscibility, based in the differential viscosity and density among alkali-chloride saturated hydrosaline melt, aluminosilicate felsic melt, and H2O-rich volatiles is likely to have crystallized halite and sylvite from exsolved hydrosaline melt. High degrees of undercooling might have been important at the time of alkali-chloride exsolution. The effectiveness of alkali-chloride separation from the melt at magmatic temperatures is in line with the interpretation of “halite subtraction” as a necessary process to understand the origin of the “halite trend” in highly saline fluid inclusions from porphyry copper and other hydrothermal mineralizations, despite the absence of the latter in the Cerro Baritina aplites, where this process preceded the exsolution of halite-undersaturated fluids.Pervasive alteration of the monzogranite country rock as alkali-metasomatic mineral assemblages, the mineral chemistry of some species, and the association of weak molybdenite mineralization are compatible with the activity of alkaline hypersaline fluids, most likely exsolved during the earliest stages of aplite consolidation. 相似文献
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M.S. O&#x;Leary R. Lira M.J. Dorais C.C.G. Tassinari 《Journal of South American Earth Sciences》2009,28(3):277-287
Over 20 lamprophyre dykes, varying in width between a few centimeters and several meters, have been identified in central Sierra Norte – Eastern Pampean Ranges, Córdoba, Argentina. Their mineralogy and chemistry indicate that they are part of the calc-alkaline lamprophyres clan (CAL). They contain phenocrysts of magnesiohornblende ± augite set in a groundmass of magnesiohornblende, calcic-plagioclase, alkali feldspar, and opaque minerals, which designate them as spessartite-type lamprophyres. Alteration products include chlorite, calcite and iron oxides after mafic phenocrysts, though some are partially replaced by actinolite. Feldspars are replaced by carbonate and clay minerals.The dykes are relatively primitive, and show restricted major element variation (SiO2 51.1–55.3 wt.%, Al2O3 12–16.6 wt.%, total alkalies 1.5–4.7 wt.%), high Mg# (55–77), high Cr contents (27–988 ppm) and moderate to high Ni contents (60–190 ppm). Lamprophyre LILE (e.g. Rb averages 110 ppm, Sr 211–387 ppm, Ba 203–452 ppm) are high relative to HFSE (e.g., Ta 0.2–1.6 ppm, Nb 4–11 ppm, Y 17–21 ppm), and are enriched in LREE (30–70 times chondrite). They are characterized by relatively high 208Pb/204Pb (38.8–39.9), 207Pb/204Pb (15.7), and 206Pb/204Pb (18.7–20.1), combined with low (epsilon)εNd (−4.69 to −1.52) and a relative moderately high (87Sr/86Sr)i of 0.7055–0.7074. The Rb–Sr whole rock isochron indicates an Early Ordovician age of 485 ± 25 Ma. The calculated TDM (1.7 Ga) suggests that these rocks appear to have originated from a reservoir that was created during a mantle metasomatism event related to the Pampean orogeny.The Sierra Norte lamprophyres show affinities with a subduction-related magma in an active continental margin. Their geochemical and isotopic features suggest a multicomponent source, composed of enriched mantle material variably contaminated by crustal components. The lamprophyric suite emplacement occurred at the dawning stage of the Pampean orogeny, in a regional post-collisional extensional setting developed in the Sierra Norte-Ambargasta batholith (SNAB) in Early Ordovician times. 相似文献
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REE (rare-earth-element) and Th mineralization at the Rodeo de Los Molles deposit occurs within an elliptical body of hydrothermally altered rocks (fenite) located in a biotite monzogranite of the Las Chacras batholith. Ore assemblages are found as isolated patches of intergrown britholite, allanite, apatite, bastnaesite, fluorite, sphene, quartz, and aegirine-augite, as well as nodules of uranothorite and late-stage veins of calcite, fluorite, and bastnaesite. Composition-volume computations suggest that the fenite was produced by alteration of the biotite monzogranite by addition of K and Na, and loss of Ca and Sr. Petrographic evaluations indicate that microcline and plagioclase have been replaced by perthite, and biotite was converted to aggregates of clinochlore, anatase, kaolinite, and hematite. Relict biotite is characterized by lower Fe/(Fe+Mg) and Ti values with progressive alteration. Fluorine-rich phlogopite is present in mineralized areas, but textural evidence suggests that it was not produced via biotite alteration. Mass-balance constraints also show that Ca and Mg in ore zones may result from redistribution, rather than their being a result of external derivation. The 18O values of quartz (8.6–11.1) and feldspar (7.8–10.6) suggest that feldspar continued to exchange oxygen isotopes with a fluid to lower temperatures than did quartz. Feldspars equilibrated with a fluid of 18O8 at a fluid/rock ratio less than 1. The 18O values of quartz and aegirine-augite that crystallized during REE mineralization also suggest equilibration with a fluid of 18O8. The D values of biotite (-83 to-120) are relatively low for igneous rocks and are thought to have resulted from exsolution of a D-enriched magmatic vapor. The D values of both mineralized and barren fenites are consistent with equilibration with fluid of magmatic origin. Meteoric water was involved in the production of calcite and clinochlore alteration, and late-stage calcite-fluorite-bastnaesite veins. The 13C values of calcite and bastnaesite (-7.8 to-13.5%) suggest that carbon was derived by leaching of carbon from igneous and/or enclosing metamorphic rock types, and that a majority of carbon ultimately was derived from sedimentary organic meterial. 相似文献