Field and flume comparisons of the modified and standard (savonius-rotor) Aanderaa self-recording current meters     

Thomas M. Hammond  Charitha B. Pattiaratchi  Michael J. Osborne  Michael Collins 《Ocean Dynamics》1986,39(2):41-63

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Secondary circulations near sand banks and in coastal embayments     

Anthony D. Heathershaw  Francis D. C. Hammond 《Ocean Dynamics》1980,33(4):135-151

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Denitrification in anoxic sediments supported by biological nitrate transport     

M.G. Prokopenko  D.M. Sigman  D.E. Hammond  L. Chong 《Geochimica et cosmochimica acta》2011,75(22):7180-7199

Biologically available nitrogen (fixed N) is removed from the oceans by metabolic conversion of inorganic N forms (nitrate and ammonium) to N₂ gas. Much of this removal occurs in marine sediments, where reaction rates are thought to be limited by diffusion. We measured the concentration and isotopic composition of major dissolved nitrogen species in anoxic sediments off the coast of California. At depths below the diffusive penetration of nitrate, we found evidence of a large nitrate pool transported into the sediments by motile microorganisms. A ∼20‰ enrichment in ¹⁵N and ¹⁸O of this biologically transported nitrate over bottom water values and elevated [N₂] and δ¹⁵N-N₂ at depth indicate that this nitrate is consumed by enzymatic redox reactions with the production of N₂ as the end product. Elevated N₂O concentrations in pore waters below the nitrate diffusion depth confirm that these reactions include the denitrification pathway. A data-constrained model shows that at least 31% of the total N₂ production in anoxic sediments is linked to nitrate bio-transport. Under suboxic/anoxic regimes, this nitrate bio-transport augments diffusive transport, thus increasing benthic fixed nitrogen losses and the reducing burial efficiency of sedimentary organic matter.  相似文献   

Geophysical evidence for post-Miocene rotation of the island of Viti Levu,Fiji, and its relationship to the tectonic development of the North Fiji Basin     

Alexander Malahoff  Stephen R. Hammond  John J. Naughton  David L. Keeling  Ronald N. Richmond 《Earth and Planetary Science Letters》1982,57(2):398-414

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Spinelloid phases in the nickel gallosilicate system     

R. Hammond  J. Barbier 《Physics and Chemistry of Minerals》1991,18(3):184-190

The phase diagram of the NiO-Ga₂O₃- SiO₂ system has been investigated at high temperatures (up to 1550° C) and 1 atm. pressure. The only ternary phases observed in this system are the spinelloid phases I, II, and V, forming on the NiGa₂O₄-Ni₂SiO₄ pseudo-binary join at temperatures above 1400° C. Our results show that phase V is stable at higher temperature than phase I, while phase II may be metastable. The stability of phases I and V has been confirmed by the successful growth of single crystals from a silica-rich flux. Phases I, II, and V have been characterized by powder X-ray diffraction and transmission electron microscopy. The dimensions of their orthorhombic unit-cells are: (I) a= 5.7741(5), b=11.712(1), c=8.2387(9) Å; (II) a= 5.765(1), b= 17.619(3), c= 8.238(2) Å; (V) a= 5.7914(4), b=8.7809(7), c=8.2346(6) Å. High resolution electron microscopy has also revealed the formation of microscopic intergrowths similar to those previously observed for the spinelloid phases of the NiO-Al₂O₃-SiO₂ system.  相似文献   

Paleomagnetic evidence of northward movement of the Pacific plate in deep-sea cores from the Central Pacific Basin     

S.R. Hammond  F. Theyer  G.H. Sutton 《Earth and Planetary Science Letters》1974,22(1):22-28

Seven deep-sea sediment cores recovered in the central equatorial Pacific collectively span a magneto- and biostratigraphically determined age interval ranging from about 0.1 to 21 m.y. B.P. Measured values of paleomagnetic inclination and their systematic variation with depth in these cores denote relative motion between the central Pacific lithosphere and the magnetic field of the earth. Assuming that the position of the earth's dipole field remained essentially parallel to the present spin axis during the interval, the data provide evidence of a marked decrease in the northward rate of plate motion from about 11 cm/yr to about 6 cm/yr at approximately 12 m.y. B.P. This date of change of motion as well as the northward direction and overall average rate of about 8 cm/yr throughout the last 21 m.y., agree reasonably well with results of other studies of the tectonic history of the Pacific plate and ridge system. More significantly, however, these preliminary results demonstrate the usefulness of the paleomagnetic record in deep-sea sediment cores spanning sufficiently long intervals of time as an aid in reconstructing plate motions.  相似文献   

Voronoi Meshing to Accurately Capture Geological Structure in Subsurface Simulations     

LaForce  Tara  Ebeida  Mohamed  Jordan  Spencer  Miller  Terry A.  Stauffer  Philip H.  Park  Heeho  Leone  Rosie  Hammond  Glenn 《Mathematical Geosciences》2023,55(2):129-161

Mathematical Geosciences - Mesh generation lies at the interface of geological modeling and reservoir simulation. Highly skewed or very small grid cells may be necessary to accurately capture the...  相似文献   

Geochemistry and chronology of the Bunburra Rockhole ungrouped achondrite          下载免费PDF全文

Lev J. Spivak‐Birndorf  Audrey Bouvier  Gretchen K. Benedix  Samantha Hammond  Gregory A. Brennecka  Kieren Howard  Nick Rogers  Meenakshi Wadhwa  Philip A. Bland  Pavel Spurný  Martin C. Towner 《Meteoritics & planetary science》2015,50(5):958-975

Bunburra Rockhole is a unique basaltic achondrite that has many mineralogical and petrographic characteristics in common with the noncumulate eucrites, but differs in its oxygen isotope composition. Here, we report a study of the mineralogy, petrology, geochemistry, and chronology of Bunburra Rockhole to better understand the petrogenesis of this meteorite and compare it to the eucrites. The geochemistry of bulk samples and of pyroxene, plagioclase, and Ca‐phosphate in Bunburra Rockhole is similar to that of typical noncumulate eucrites. Chronological data for Bunburra Rockhole indicate early formation, followed by slow cooling and perhaps multiple subsequent heating events, which is also similar to some noncumulate eucrites. The ²⁶Al‐²⁶Mg extinct radionuclide chronometer was reset in Bunburra Rockhole after the complete decay of ²⁶Al, but a slight excess in the radiogenic ²⁶Mg in a bulk sample allows the determination of a model ²⁶Al‐²⁶Mg age that suggests formation of the parent melt for this meteorite from its source magma within the first ~3 Ma of the beginning of the solar system. The ²⁰⁷Pb‐²⁰⁶Pb absolute chronometer is also disturbed in Bunburra Rockhole minerals, but a whole‐rock isochron provides a re‐equilibration age of ~4.1 Ga, most likely caused by impact heating. The mineralogy, geochemistry, and chronology of Bunburra Rockhole demonstrate the similarities of this achondrite to the eucrites, and suggest that it formed from a parent melt with a composition similar to that for noncumulate eucrites and subsequently experienced a thermal history and evolution comparable to that of eucritic basalts. This implies the formation of multiple differentiated parent bodies in the early solar system that had nearly identical bulk elemental compositions and petrogenetic histories, but different oxygen isotope compositions inherited from the solar nebula.  相似文献   

Fluorine and chlorine in mantle minerals and the halogen budget of the Earth’s mantle     

B.?M.?UrannEmail author  V.?Le?Roux  K.?Hammond  H.?R.?Marschall  C.-T.?A.?Lee  B.?D.?Monteleone 《Contributions to Mineralogy and Petrology》2017,172(7):51

The fluorine (F) and chlorine (Cl) contents of arc magmas have been used to track the composition of subducted components, and the F and Cl contents of MORB have been used to estimate the halogen content of depleted MORB mantle (DMM). Yet, the F and Cl budget of the Earth’s upper mantle and their distribution in peridotite minerals remain to be constrained. Here, we developed a method to measure low concentrations of halogens (≥0.4 µg/g F and ≥0.3 µg/g Cl) in minerals by secondary ion mass spectroscopy. We present a comprehensive study of F and Cl in co-existing natural olivine, orthopyroxene, clinopyroxene, and amphibole in seventeen samples from different tectonic settings. We support the hypothesis that F in olivine is controlled by melt polymerization, and that F in pyroxene is controlled by their Na and Al contents, with some effect of melt polymerization. We infer that Cl compatibility ranks as follows: amphibole > clinopyroxene > olivine ~ orthopyroxene, while F compatibility ranks as follows: amphibole > clinopyroxene > orthopyroxene ≥ olivine, depending on the tectonic context. In addition, we show that F, Cl, Be and B are correlated in pyroxenes and amphibole. F and Cl variations suggest that interaction with slab melts and fluids can significantly alter the halogen content of mantle minerals. In particular, F in oceanic peridotites is mostly hosted in pyroxenes, and proportionally increases in olivine in subduction-related peridotites. The mantle wedge is likely enriched in F compared to un-metasomatized mantle, while Cl is always low (<1 µg/g) in all tectonic settings studied here. The bulk anhydrous peridotite mantle contains 1.4–31 µg/g F and 0.14–0.38 µg/g Cl. The bulk F content of oceanic-like peridotites (2.1–9.4 µg/g) is lower than DMM estimates, consistent with F-rich eclogite in the source of MORB. Furthermore, the bulk Cl budget of all anhydrous peridotites studied here is lower than previous DMM estimates. Our results indicate that nearly all MORB may be somewhat contaminated by seawater-rich material and that the Cl content of DMM could be overestimated. With this study, we demonstrate that the halogen contents of natural peridotite minerals are a unique tool to understand the cycling of halogens, from ridge settings to subduction zones.  相似文献