Opaque minerals in primitive stony meteorites     

Dante S. Lauretta 《Meteoritics & planetary science》2002,37(4):475-476

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Policy and practice in the live reef fish for food trade: A case study from Palawan,Philippines     

Michael Fabinyi  Dante Dalabajan 《Marine Policy》2011

The live reef fish for food trade is a highly significant fishery that provides income for many coastal communities in the Asia-Pacific region but faces challenges relating to sustainability. This paper draws attention to the large gaps that exist between policy and practice in the live reef fish for food trade in Palawan, Philippines. While many policies have been introduced over many years, effective implementation remains a challenge. We show how the implementation of successive sets of policies has been hindered by three broadly inter-related features of the local social landscape: the capacity of government institutions and legal frameworks to implement regulations, the distinctive culture of fisheries governance in the Philippines, and the perspectives and practices of local fishers themselves. By focusing on the gaps between policy and practice, we highlight the ongoing need to examine more explicitly the ways in which local contexts shape the effectiveness of implementation, enforcement and policy more generally.  相似文献   

The physical structure of a cold filament in a Chilean upwelling zone (Península de Mejillones, Chile, 23°S)     

Marcus Sobarzo  Dante Figueroa 《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(12)

Cold filaments associated with Eastern Boundary Currents are typically narrower than 100 km but can be several hundred kilometers long, extending from the coast to the open ocean in upwelling areas. One such structure, observed off Península de Mejillones (23°S, Chile), was studied with both satellite images and two 5-days hydrographic cruises carried out during January 1997. The study used a coastal grid of 31 stations in an area of 165 ×155 km², approximately. The spatial distribution of the filament and its change between cruises are described from the horizontal distributions of dynamic height, temperature, salinity and dissolved oxygen. The filament was a shallow feature (thickness <100 m) and extended at least 165 km toward the open ocean. A meandering northward current flowed at the borders of the filament, separating oceanic and coastal waters of different physical properties. Comparisons of cross sections of the filament near the coast and in the oceanic zone show the ascent of the shallow salinity minimum (SSM), and its extension toward the ocean, bound to the filament. It is concluded that Subantarctic Water ((SAAW) distinguish by low salinity, high dissolved oxygen) and Equatorial Subsurface Water ((ESSW) high salinity, low dissolved oxygen, high nutrient content) form this filament, and that their relative proportions depend on the strength of the coastal upwelling. Thus, the knowledge of the dynamics of these structures is fundamental to better understanding of the spatial distribution of important biological variables, such as nutrients and chlorophyll, in the coastal ecosystem.  相似文献   

A search for planets transiting the M-dwarf debris disc host, AU Microscopii     

Leslie Hebb  Larry Petro  Holland C. Ford  David R. Ardila  Ignacio Toledo  Dante Minniti  David A. Golimowski  Mark Clampin 《Monthly notices of the Royal Astronomical Society》2007,379(1):63-72

We present high-cadence, high-precision multiband photometry of the young, M1Ve, debris disc star, AU Microscopii. The data were obtained in three continuum filters spanning a wavelength range from 4500 to 6600 Å, plus Hα, over 28 nights in 2005. The light curves show intrinsic stellar variability due to star-spots with an amplitude in the blue band of 0.051 mag and a period of 4.847 d. In addition, three large flares were detected in the data which all occur near the minimum brightness of the star. We remove the intrinsic stellar variability and combine the light curves of all the filters in order to search for transits by possible planetary companions orbiting in the plane of the nearly edge-on debris disc. The combined final light curve has a sampling of 0.35 min and a standard deviation of 6.8 mmag. We performed Monte Carlo simulations by adding fake transits to the observed light curve and find with 95 per cent significance that there are no Jupiter mass planets orbiting in the plane of the debris disc on circular orbits with periods,   P ≤ 5  d. In addition, there are no young Neptune like planets (with radii 2.5 times smaller than the young Jupiter) on circular orbits with periods,   P ≤ 3  d.  相似文献   

An experimental study of the formation of cubanite (CuFe2S3) in primitive meteorites          下载免费PDF全文

Eve L. Berger  Lindsay P. Keller  Dante S. Lauretta 《Meteoritics & planetary science》2015,50(1):1-14

The low‐temperature form of CuFe₂S₃, cubanite, has been identified in the CI chondrite and NASA Stardust mission collections. The presence of this mineral constrains the maximum temperature to 210 °C since the time of its formation. However, until now, the conditions under which cubanite forms were less well constrained. In order to refine the history of the time‐varying, low‐temperature fluids which existed on the CI‐chondrite parent body and Comet 81P/Wild 2 (Wild 2), we synthesized cubanite. The experimental synthesis of this mineral was achieved, for the first time, under low‐temperature aqueous conditions relevant to the CI‐chondrite parent body. Using a variant of in situ hydrothermal recrystallization, cubanite formed in aqueous experiments starting with temperatures of 150 and 200 °C, pH approximately 9, and oxygen fugacities corresponding to the iron‐magnetite buffer. The composition and structure of the cubanite were determined using electron microprobe and transmission electron microscopy techniques, respectively. The combined compositional, crystallographic, and experimental data allow us to place limits on the conditions under which the formation of cubanite is feasible, which in turn constrains the nature of the fluid phase on the CI‐chondrite parent body and Wild 2 when cubanite was forming.  相似文献   

Experimental constraints on the mobility of Rhenium in silicate liquids     

Jason M. MacKenzie  Dante Canil 《Geochimica et cosmochimica acta》2006,70(20):5236-5245

The volatization of Rhenium (Re) from melts of natural basalt, dacite and a synthetic composition in the CaO-MgO-Al₂O₃-SiO₂ system has been investigated at 0.1 MPa and 1250-1350 °C over a range of fO₂ conditions from log fO₂ = −10 to −0.68. Experiments were conducted using open top Pt crucibles doped with Re and Yb. Analysis of quenched glasses by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) normal to the melt/gas interface showed concentration profiles for Re, to which a semi-infinite one-dimensional diffusion model could be applied to extract diffusion coefficients (D). The results show Re diffusivity in basalt at 1300 °C in air is log D_Re = −7.2 ± 0.3 cm²/s and increases to log D_Re = −6.6 ± 0.3 cm²/s when trace amounts of Cl were added to the starting material. At fO₂ conditions below the nickel-nickel oxide (NNO) buffer Re diffusivity decreases to and to in dacitic melt. In the CMAS composition, . The diffusivity of Re is comparable to Ar and CO₂ in basalt at 500 MPa favoring its release as a volatile. Our results support the contention that subaerial degassing is the cause of lower Re concentrations in arc-type and ocean island basalts compared to mid-ocean ridge basalts.  相似文献   

Thermodynamic constraints on the formation conditions of winonaites and silicate-bearing IAB irons     

Gretchen K. Benedix  Dante S. Lauretta 《Geochimica et cosmochimica acta》2005,69(21):5123-5131

Silicate inclusions in IAB irons and related winonaite meteorites have textures, mineralogies and mineral chemistries that indicate a complex formation history of heating, followed by brecciation and metamorphism. Using olivine-orthopyroxene-chromite assemblages in five IAB iron silicate inclusions (Caddo County, Campo del Cielo, Copiapo, Lueders, and Udei Station) and one winonaite (Winona), we calculated closure temperatures and oxygen fugacities for these meteorites. Calculated olivine-chromite Fe-Mg exchange temperatures are compared to two-pyroxene temperatures. Olivine-chromite closure temperatures range from ∼590°C to ∼700°C, while two-pyroxene temperatures range from ∼900°C to ∼1200°C. Oxygen fugacities of these meteorites, determined for the first time in this study, range from 2.3 to 3.2 log units below the Fe-FeO buffer and define a line between the Fe-FeO and Cr-Cr₂O₃ buffers. Highly variable temperatures were experienced by these rocks on the hand sample, and sometimes even the thin section, scale consistent with the idea that the winonaite-IAB iron parent body experienced collisional fragmentation and reassembly after peak temperatures were reached. Although modest reduction likely occurred during cooling, the oxygen fugacities and mineral compositions recorded at peak metamorphic temperatures suggest that the chondritic precursor for this parent body was initially more reduced than ordinary chondrites.  相似文献   

Imaging shallow structure with active-source surface wave signal recorded by distributed acoustic sensing arrays          下载免费PDF全文

Zhenghong Song  Xiangfang Zeng  Clifford H. Thurber  Hebert F. Wang  Dante Fratta 《地震科学（英文版）》2018,31(4):208-214

Distributed acoustic sensing (DAS) is one recently developed seismic acquisition technique that is based on fiber-optic sensing. DAS provides dense spatial spacing that is useful to image shallow structure with surface waves. To test the feasibility of DAS in shallow structure imaging, the PoroTomo team conducted a DAS experiment with the vibroseis truck T-Rex in Brady’s Hot Springs, Nevada, USA. The Rayleigh waves excited by the vertical mode of the vibroseis truck were analyzed with the Multichannel Analysis of Surface Waves (MASW) method. Phase velocities between 5 and 20 Hz were successfully extracted for one segment of cable and were employed to build a shear-wave velocity model for the top 50 meters. The dispersion curves obtained with DAS agree well with the ones extracted from co-located geophones data and from the passive source Noise Correlation Functions (NCF). Comparing to the co-located geophone array, the higher sensor density that DAS arrays provides help reducing aliasing in dispersion analysis, and separating different surface wave modes. This study demonstrates the feasibility and advantage of DAS in imaging shallow structure with surface waves.  相似文献   

Opaque minerals in chondrules and fine‐grained chondrule rims in the Bishunpur (LL3.1) chondrite     

Dante S. Lauretta  Peter R. Buseck 《Meteoritics & planetary science》2003,38(1):59-79

Abstract— We present a detailed petrographic and electron microprobe study of metal grains and related opaque minerals in the chondrule interiors and rims of the Bishunpur (LL3.1) ordinary chondrite. There are distinct differences between metal grains that are completely encased in chondrule interiors and those that have some portion of their surface exposed outside of the chondrule boundary, even though the two types of metal grains can be separated by only a few microns. Metal grains in chondrule interiors exhibit minor alteration in the form of oxidized P‐, Cr‐, and Si‐bearing minerals. Metal grains at chondrule boundaries and in chondrule rims are extensively altered into troilite and fayalite. The results of this study suggest that many metal grains in Bishunpur reacted with a type‐I chondrule melt and incorporated significant amounts of P, Cr, and Si. As the system cooled, some metal oxidation occurred in the chondrule interior, producing metal‐associated phosphate, chromite, and silica. Metal that migrated to chondrule boundaries experienced extensive corrosion as a result of exposure to the external atmosphere present during chondrule formation. It appears that chondrule‐derived metal and its corrosion products were incorporated into the fine‐grained rims that surround many type‐I chondrules, contributing to their Fe‐rich compositions. We propose that these fine‐grained rims formed by a combination of corrosion of metal expelled from the chondrule interior and accretion of fine‐grained mineral fragments and microchondrules.  相似文献   

Petrography,stable isotope compositions,microRaman spectroscopy,and presolar components of Roberts Massif 04133: A reduced CV3 carbonaceous chondrite     

Jemma Davidson  Devin L. Schrader  Conel M. O'D. Alexander  Dante S. Lauretta  Henner Busemann  Ian A. Franchi  Richard C. Greenwood  Harold C. Connolly Jr.  Kenneth J. Domanik  Alexander Verchovsky 《Meteoritics & planetary science》2014,49(12):2133-2151

Here, we report the mineralogy, petrography, C‐N‐O‐stable isotope compositions, degree of disorder of organic matter, and abundances of presolar components of the chondrite Roberts Massif (RBT) 04133 using a coordinated, multitechnique approach. The results of this study are inconsistent with its initial classification as a Renazzo‐like carbonaceous chondrite, and strongly support RBT 04133 being a brecciated, reduced petrologic type >3.3 Vigarano‐like carbonaceous (CV) chondrite. RBT 04133 shows no evidence for aqueous alteration. However, it is mildly thermally altered (up to approximately 440 °C); which is apparent in its whole‐rock C and N isotopic compositions, the degree of disorder of C in insoluble organic matter, low presolar grain abundances, minor element compositions of Fe,Ni metal, chromite compositions and morphologies, and the presence of unequilibrated silicates. Sulfides within type I chondrules from RBT 04133 appear to be pre‐accretionary (i.e., did not form via aqueous alteration), providing further evidence that some sulfide minerals formed prior to accretion of the CV chondrite parent body. The thin section studied contains two reduced CV3 lithologies, one of which appears to be more thermally metamorphosed, indicating that RBT 04133, like several other CV chondrites, is a breccia and thus experienced impact processing. Linear foliation of chondrules was not observed implying that RBT 04133 did not experience high velocity impacts that could lead to extensive thermal metamorphism. Presolar silicates are still present in RBT 04133, although presolar SiC grain abundances are very low, indicating that the progressive destruction or modification of presolar SiC grains begins before presolar silicate grains are completely unidentifiable.  相似文献