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71.
Settling particles from duplicate free-drifting sediment traps were collected at 150 m depth in May and July at a landward and a seaward site in the 350 m deep Laurentian Trough. The total organic carbon (TOC) fluxes were high (95–454 mg/m2/d), comparable to those reported for Dabob Bay (a similar moderately productive deep coastal environment) and for the highly productive Peru upwelling region. The TOC (26–67 mg C/g) consisted of lipids (17–37%), carbohydrates (7.9–16%), hydrolysable amino acids (8.4–16%), labile proteins (0.3–2.6%), and a non-characterized fraction (40–64%). Amino acids, proteins and uncharacterized compounds accounted for 24–42, 1–10 and 58–76%, respectively, of total nitrogen (2.3–7.7 mg N/g). The pigment fraction was largely dominated by pheopigments (0.06-1.15 mg/g vs 0.004–0.15 mg/g for chlorophyll a). C/N and C/pigment ratios indicated that on average, about half of the carbon flux was of terrigenous origin. Marine sources included a dominant zooplanktonic contribution, indicated by the abundance of fecal pellets, lipids and pheopigments, and a smaller contribution from fresh algae. Cluster and correlation analyses confirmed the decoupling of pigment and TOC fluxes and the strong zooplanktonic influence of the trap material. Despite large day-to-day and inter-trap variability, clear differences were observed in the fluxes, TOC content and composition at both sampling sites and months. Such trends are attributed to the relative contribution from terrestrial and marine sources and seasonal patterns of primary production. 相似文献
72.
Alexander Wittig Camilla Colombo Roberto Armellin 《Celestial Mechanics and Dynamical Astronomy》2017,128(4):435-452
This paper introduces and combines for the first time two techniques to allow long-term density propagation in astrodynamics. First, we introduce an efficient method for the propagation of phase space densities based on differential algebra (DA) techniques. Second, this DA density propagator is used in combination with a DA implementation of the averaged orbital dynamics through semi-analytical methods. This approach combines the power of orbit averaging with the efficiency of DA techniques. While the DA-based method for the propagation of densities introduced in this paper is independent of the dynamical system under consideration, the particular combination of DA techniques with averaged equations of motion yields a fast and accurate technique to propagate large clouds of initial conditions and their associated probability density functions very efficiently for long time. This enables the study of the long-term behavior of particles subjected to the given dynamics. To demonstrate the effectiveness of the proposed approach, the evolution of a cloud of high area-to-mass objects in Medium Earth Orbit is reproduced considering the effects of solar radiation pressure, the Earth’s oblateness and luni-solar perturbations. The method can propagate 10,000 random fragments and their density for 1 year within a few seconds on a common desktop PC. 相似文献
73.
International Journal of Earth Sciences - Channel-levee deposits that occur in some large sand-dominated fluvial systems are commonly elevated above the surrounding floodplain. However, the... 相似文献
74.
Carolina?P.?N.?MoretoEmail author Lena?V.?S.?Monteiro Roberto?P.?Xavier Robert?A.?Creaser S.?Andrew?DuFrane Gustavo?H.?C.?Melo Marco?A.?Delinardo da Silva Colombo?C.?G.?Tassinari Kei?Sato 《Mineralium Deposita》2015,50(5):517-546
The Southern Copper Belt, Carajás Province, Brazil, hosts several iron oxide–copper–gold (IOCG) deposits, including Sossego, Cristalino, Alvo 118, Bacuri, Bacaba, Castanha, and Visconde. Mapping and U–Pb sensitive high-resolution ion microprobe (SHRIMP) IIe zircon geochronology allowed the characterization of the host rocks, situated within regional WNW–ESE shear zones. They encompass Mesoarchean (3.08–2.85 Ga) TTG orthogneiss, granites, and remains of greenstone belts, Neoarchean (ca. 2.74 Ga) granite, shallow-emplaced porphyries, and granophyric granite coeval with gabbro, and Paleoproterozoic (1.88 Ga) porphyry dykes. Extensive hydrothermal zones include albite–scapolite, biotite–scapolite–tourmaline–magnetite alteration, and proximal potassium feldspar, chlorite–epidote and chalcopyrite formation. U–Pb laser ablation multicollector inductively coupled mass spectrometry (LA-MC-ICP-MS) analysis of ore-related monazite and Re–Os NTIMS analysis of molybdenite suggest multiple Neoarchean (2.76 and 2.72–2.68 Ga) and Paleoproterozoic (2.06 Ga) hydrothermal events at the Bacaba and Bacuri deposits. These results, combined with available geochronological data from the literature, indicate recurrence of hydrothermal systems in the Southern Copper Belt, including 1.90–1.88-Ga ore formation in the Sossego–Curral ore bodies and the Alvo 118 deposit. Although early hydrothermal evolution at 2.76 Ga points to fluid migration coeval with the Carajás Basin formation, the main episode of IOCG genesis (2.72–2.68 Ga) is related to basin inversion coupled with Neoarchean (ca. 2.7 Ga) felsic magmatism. The data suggest that the IOCG deposits in the Southern Copper Belt and those in the Northern Copper Belt (2.57-Ga Salobo and Igarapé Bahia–Alemão deposits) do not share a common metallogenic evolution. Therefore, the association of all IOCG deposits of the Carajás Province with a single extensive hydrothermal system is precluded. 相似文献
75.
Sebastián M. Jovic Diego M. Guido Isidoro B. Schalamuk Francisco J. Ríos Colombo C. G. Tassinari Clemente Recio 《Mineralium Deposita》2011,46(3):257-271
The Pingüino deposit, located in the low sulfidation epithermal metallogenetical province of the Deseado Massif, Patagonia,
Argentina, represents a distinct deposit type in the region. It evolved through two different mineralization events: an early
In-bearing polymetallic event that introduced In, Zn, Pb, Ag, Cd, Au, As, Cu, Sn, W and Bi represented by complex sulfide
mineralogy, and a late Ag–Au quartz-rich vein type that crosscut and overprints the early polymetallic mineralization. The
indium-bearing polymetallic mineralization developed in three stages: an early Cu–Au–In–As–Sn–W–Bi stage (Ps1), a Zn–Pb–Ag–In–Cd–Sb stage (Ps2) and a late Zn–In–Cd (Ps3). Indium concentrations in the polymetallic veins show a wide range (3.4 to 1,184 ppm In). The highest indium values (up
to 1,184 ppm) relate to the Ps2 mineralization stage, and are associated with Fe-rich sphalerites, although significant In enrichment (up to 159 ppm) is
also present in the Ps1 paragenesis associated with Sn-minerals (ferrokesterite and cassiterite). The hydrothermal alteration associated with the
polymetallic mineralization is characterized by advanced argillic alteration within the immediate vein zone, and sericitic
alteration enveloping the vein zone. Fluid inclusion studies indicate homogenisation temperatures of 308.2–327°C for Ps1 and 255–312.4°C for Ps2, and low to moderate salinities (2 to 5 eq.wt.% NaCl and 4 to 9 eq.wt.% NaCl, respectively). δ34S values of sulfide minerals (+0.76‰ to +3.61‰) indicate a possible magmatic source for the sulfur in the polymetallic mineralization
while Pb isotope ratios for the sulfides and magmatic rocks (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 17.379 to 18.502; 15.588 to 15.730 and 38.234 to 38.756, respectively) are consistent with the possibility that
the Pb reservoirs for both had the same crustal source. Spatial relationships, hydrothermal alteration styles, S and Pb isotopic
data suggest a probable genetic relation between the polymetallic mineralization and dioritic intrusions that could have been
the source of metals and hydrothermal fluids. Mineralization paragenesis, alteration mineralogy, geochemical signatures, fluid
inclusion data and isotopic data, confirm that the In-bearing polymetallic mineralization from Pingüino deposit is a distinct
type, in comparison with the well-known epithermal low sulfidation mineralization from the Deseado Massif. 相似文献
76.
77.
J.F. Albacete Colombo †‡ N.I. Morrell †§¶ V.S. Niemela † M.F. Corcoran 《Monthly notices of the Royal Astronomical Society》2001,326(1):78-84
Optical spectroscopy of CPD −59° 2635, one of the O-type stars in the open cluster Trumpler 16 in the Carina Nebula, reveals this star to be a double-lined binary system. We have obtained the first radial velocity orbit for this system, consisting of a circular solution with a period of 2.2999 d and semi-amplitudes of 208 and 273 km s−1 . This results in minimum masses of 15 and 11 M⊙ for the binary components of CPD −59° 2635, which we classified as O8V and O9.5V, although spectral type variations of the order of 1 subclass, which we identify as the Struve–Sahade effect , seem to be present in both components. From ROSAT HRI observations of CPD −59° 2635 we determine a luminosity ratio log( L x / L bol )≈−7 , which is similar to that observed for other O-type stars in the Carina Nebula region. No evidence of light variations is present in the available optical or X-ray data sets. 相似文献
78.
Colombo Celso Gaeta Tassinari Fabio Diaz Pinzon Juaquin Buena Ventura 《Ore Geology Reviews》2008,33(3-4):505-518
Epigenetic gold mineralization occurs in the Marmato mining district, within the Calima Terrain of the Setentrional Andes, Colombia. Regional rocks associated with this mineralization include: graphite- and chlorite-schists of the Arquia Complex; metamorphosed during the Cretaceous, Miocene sandstones, shales and conglomerates of the Amagá Formation; as well as pyroclastic rocks (clasts of basalt, andesites and mafic lavas) and subvolcanic andesitic/dacitic bodies of the Combia Formation (9 to 6 Ma). The subvolcanic Marmato stock hosts mesothermal and epithermal low-sulfidation Au–Ag ores in the form of distensional veins, stockwork, and quartz veinlets within brecciated zones. Ore minerals are pyrite, sphalerite and galena with subordinate chalcopyrite, arsenopyrite, pyrrhotite, argentite and native gold/electrum.Sericitized plagioclase from a porphyry dacite yielded a K–Ar age of 5.6 ± 0.6 Ma, interpreted as the age of ore deposition. This is in close agreement with the age of reactivation of the Cauca–Romeral Fault System (5.6 ± 0.4 Ma), which bounds the Calima Terrain. A porphyry andesite–dacite (6.7 ± 0.1 Ma), hosting the Au–Ag veins, shows a measured 87Sr/86Sr between 0.70440 and 0.70460, εNd between + 2.2 and + 3.2 and 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 18.964 to 19.028; 15.561 to 15.570; and 38.640 to 38.745, respectively. The 87Sr/86Sr and εNd values of rocks from the Arquia Group range from 0.70431 to 0.73511 and − 12.91 to + 10.0, respectively, whereas the corresponding Pb isotopic ratios (206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb) range from 18.948 to 19.652; 15.564 to 15.702; and 38.640 to 38.885, respectively. 87Sr/86Sr and εNd values obtained on sulfides from the gold quartz veins, which occur at shallow and intermediate levels, range from 0.70500 to 0.71210 and from − 1.11 to + 2.40. In the deepest veins, εNd values lie between + 1.25 and + 3.28 and the 87Sr/86Sr of calcite and pyrite fall between 0.70444 and 0.70930. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of all mineralization are in the ranges 18.970 to 19.258; 15.605 to 15.726 and 38.813 to 39.208, respectively. Carbonates have an average 87Sr/86Sr ratio of 0.70445, which is within the range of values measured in the host dacite. The Sr isotopic data indicate that carbonic fluids have a restricted hydrothermal circulation within the host igneous body, while the Sr, Pb and Nd isotopic compositions of the sulfides suggest that the fluids not only circulated within the Marmato stock, but also throughout the Arquia Complex, inferring that these rocks offer a potential target for mineral exploration. Based on geological and geochronological evidence, the epizonal Marmato gold ores formed during the Miocene to Pliocene, as a result of cooling of the Marmato stock and reactivation along a crustal-scale fault zone related to thermal processes in an accretionary oceanic–continental plate orogen. 相似文献
79.
80.
An accurate measurement of the gravitational field of the Sun, needed for the verification of the theories of gravitation, requires the use of a geodesic test body. To eliminate the effect of non-gravitational forces (mainly the solar radiation pressure) we propose to use two twin space probes, whose surface has identical geometrical and optical properties, but with different mass. Their differential motion leads to the determination of the motion of an ideal geodesic point. We discuss in detail the various conditions which are needed to ensure the required degree of identity and submit as a possible solution two cylindrical probes, whose sides are covered by cavities to make them absorbing, rotating at a fast rate around an axis orthogonal to the ecliptic plane. We discuss briefly also the accuracy in the determination of the parameters of the metric field of the Sun obtainable from range measurements.Work done at the European Space Research Institute, Frascati, Italy 相似文献