The magnesiowüstite: iron equilibrium and its implications for the activity-composition relations of (Mg,Fe)<Subscript>2</Subscript>SiO<Subscript>4</Subscript> olivine solid solutions     

Hugh?St. C.?O'NeillEmail author  Mark?I.?Pownceby  Catherine?A.?McCammon 《Contributions to Mineralogy and Petrology》2003,146(3):308-325

The chemical potential of oxygen (µO₂) in equilibrium with magnesiowüstite solid solution (Mg, Fe)O and metallic Fe has been determined by gas-mixing experiments at 1,473 K supplemented by solid-cell EMF experiments at lower temperatures. The results give:where IW refers to the Fe-"FeO" equilibrium. The previous work of Srecec et al. (1987) and Wiser and Wood (1991) agree well with this equation, as does that of Hahn and Muan (1962) when their reported compositions are corrected to a new calibration curve for lattice parameter vs. composition. The amount of Fe³⁺ in the magnesiowüstite solid solution in equilibrium with Fe metal was determined by Mössbauer spectroscopy on selected samples. These data were combined with literature data from gravimetric studies and fitted to a semi-empirical equation:These results were then used to reassess the activity-composition relations in (Mg, Fe)₂SiO₄ olivine solid solutions at 1,400 K, from the partitioning of Mg and Fe²⁺ between olivine and magnesiowüstite in equilibrium with metallic Fe experimentally determined by Wiser and Wood (1991). The olivine solid solution is constrained to be nearly symmetric with , with a probable uncertainty of less than ±0.5 kJ/mol (one standard deviation). The results also provide a useful constraint on the free energy of formation of Mg₂SiO₄.Editorial responsibility: B. Collins  相似文献   

Searching for the earliest record of life on Earth     

Hugh Rollinson 《Geology Today》2001,17(5):180-185

Are the remains of the Earth's earliest life now to be found in the hostile wilderness of Greenland?  相似文献   

A Farey story: the pioneer geologist John Farey (1766–1826)     

Trevor D. Ford  Hugh S. Torrens† 《Geology Today》2001,17(2):59-68

John Farey was a pioneer British geologist whose work has been too long overlooked. His only major geological publication was concealed in what appears to be a local report on the agriculture and minerals of Derbyshire, commissioned by the Board of Agriculture and published in three volumes between 1811 and 1817. Farey also published an extraordinary amount in periodicals and prepared a remarkable series of geological maps and cross-sections which were never published, although a number of hand-drawn copies circulated and undoubtedly influenced the rise of stratigraphical geology.  相似文献   

Quartz silt in mudrocks as a key to sequence stratigraphy (Kimmeridge Clay Formation, Late Jurassic, Wessex Basin, UK)     

Carolyn J. Williams  Stephen P. Hesselbo  Hugh C. Jenkyns  & Helen S. Morgans-Bell 《地学学报》2001,13(6):449-455

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Carbon monoxide in low-mass dwarf stars     

Hugh R. A. Jones  Yakiv Pavlenko  Serena Viti  R. J. Barber  Larisa A. Yakovina  David Pinfield  Jonathan Tennyson 《Monthly notices of the Royal Astronomical Society》2005,358(1):105-112

We compare high-resolution infrared observations of the CO 2–0 bands in the 2.297–2.310 μm region of M dwarfs and one L dwarf with theoretical expectations. We find a good match between the observational and synthetic spectra throughout the 2000–3500 K temperature regime investigated. None the less, for the 2500–3500 K temperature range, the temperatures that we derive from synthetic spectral fits are higher than expected from more empirical methods by several hundred kelvin. In order to reconcile our findings with the empirical temperature scale, it is necessary to invoke warming of the model atmosphere used to construct the synthetic spectra. We consider that the most likely reason for the back-warming is missing high-temperature opacity due to water vapour. We compare the water vapour opacity of the Partridge–Schwenke line list used for the model atmosphere with the output from a preliminary calculation by Barber & Tennyson. While the Partridge–Schwenke line list is a reasonable spectroscopic match for the new line list at 2000 K, by 4000 K it is missing around 25 per cent of the water vapour opacity. We thus consider that the offset between empirical and synthetic temperature scales is explained by the lack of hot water vapour used for computation of the synthetic spectra. For our coolest objects with temperatures below 2500 K, we find best fits when using synthetic spectra which include dust emission. Our spectra also allow us to constrain the rotational velocities of our sources, and these velocities are consistent with the broad trend of rotational velocities increasing from M to L.  相似文献   

Microearthquake Studies Using Sonobuoys: Preliminary Results from the Gulf of California     

I. Reid  M. Reichle  J. Brune  H. Bradner 《Geophysical Journal International》1973,34(3):365-379

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Epithermal gold veins in a caldera setting: Banská Hodruša, Slovakia     

Peter Koděra  Jaroslav Lexa  Andrew Hugh Rankin  Anthony Edward Fallick 《Mineralium Deposita》2005,39(8):921-943

The central zone of the large Miocene tiavnica stratovolcano in the Western Carpathians hosts epithermal Au mineralization of intermediate-sulfidation type, located at deep levels of the historic Rozália base-metal mine at Banská Hodrua. The Au mineralization occurs as subhorizontal veins at the base of pre-caldera andesites, close to the roof of a subvolcanic granodiorite intrusion. The veins are dismembered by a set of quartz–diorite porphyry sills and displaced by the younger, steeply dipping, Rozália base-metal vein, and parallel structures. The base-metal vein structures are related to resurgent horst uplift in the caldera center. The Au mineralization formed during two stages. Based on fluid inclusion evidence, both stages formed from fluids of low salinity (0–3 wt% NaCl eq.), which underwent extensive boiling at moderate temperatures (280–330°C). Variable pressure conditions (39–95 bars, neglecting the effect of CO₂) indicate continual opening of the system and a transition from suprahydrostatic towards hydrodynamic conditions at shallow depths (~550 m). The fluid inclusions of the Rozália base-metal vein show homogenization temperature peaks at ~285 and 187°C and salinities between 1 and 4 wt% NaCl eq. Precipitation of Au is considered to be the result of prolonged boiling of fluids and associated decrease in Au solubility. Oxygen and hydrogen isotope data for quartz and carbonate from the Au veins show a relatively homogeneous fluid composition (–2.7 to 1.1¹⁸O, –78 to –62D). The combined ¹⁸O_fluid and D_fluid values suggest a mixed character of fluids, falling between the fields of typical magmatic and meteoric water influenced by ¹⁸O_fluid shift due to fluid–rock isotopic exchange. End stages of open-system boiling and fractionation could have been reached, at least locally. Significantly lower isotopic composition of meteoric fluids associated with Au mineralization compared to those associated with the intrusion-related mineralizations could have resulted from changing paleoclimate and/or analytical problems of extraction of water from fluid inclusions. The proposed genetic model for the Au deposit at Rozália mine highlights the importance of hydrothermal activity during the early stage of caldera collapse. Caldera subsidence established new, convective, fluid-flow paths along marginal caldera faults, which acted as infiltration zones. Major metal precipitation occurred within subhorizontal structures that formed as the result of a collapse-related stress field. A shallow, differentiated magma chamber at the base of the volcano was the likely source of heat and magmatic components for the mineralizing fluids.Editorial handling: S. Nicolescu  相似文献   

Albian high-resolution biostratigraphy and isotope stratigraphy: The Coppa della Nuvola pelagic succession of the Gargano Promontory (Southern Italy)   总被引：1，自引：0，他引：1  

Valeria Luciani  Miriam Cobianchi  Hugh C. Jenkyns 《Eclogae Geologicae Helvetiae》2004,97(1):77-92

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The case for Archaean boninites     

R.?Hugh.?SmithiesEmail author  David?C.?Champion  Shen-Su?Sun 《Contributions to Mineralogy and Petrology》2004,147(6):705-721

Rare Archaean light rare earth element (LREE)-enriched mafic rocks derived from a strongly refractory mantle source show a range of features in common with modern boninites. These Archaean second-stage melts are divided into at least two distinct groups—Whundo-type and Whitney-type. Whundo-type rocks are most like modern boninites in terms of their composition and association with tholeiitic to calc-alkaline mafic to intermediate volcanics. Small compositional differences compared to modern boninites, including higher Al₂O₃ and heavy REE (HREE), probably reflect secular changes in mantle temperatures and a more garnet-rich residual source. Whundo-type rocks are known from 3.12 and 2.8 Ga assemblages and are true Archaean analogues of modern boninites. Whitney-type rocks occur throughout the Archaean, as far back as ca. 3.8 Ga, and are closely associated with ultramafic magmatism including komatiites, in an affiliation unlike that of modern subduction zones. They are characterised by very high Al₂O₃ and HREE concentrations, and their extremely depleted compositions require a source which at some stage was more garnet-rich than the source for either modern boninites or Whundo-type second-stage melts. Low La/Yb and La/Gd ratios compared to Whundo-type rocks and modern boninites either reflect very weak subduction-related metasomatism of the mantle source or very limited crustal assimilation by a refractory-mantle derived melt. Regardless, the petrogenesis of the Whitney-type rocks appears either directly or indirectly related to plume magmatism. If Whitney-type rocks have a boninitic petrogenesis then a plume related model similar to that proposed for the modern Tongan high-Ca boninites might apply, but with uniquely Archaean source compositions and source enrichment processes. Second-stage melts from Barberton (S. Africa –3.5 Ga) and ca. 3.0 Ga rocks from the central Pilbara (Australia) have features in common with both Whundo- and Whitney-types, but appear more closely related to the Whitney-type. Subduction zone processes essentially the same as those that produce modern boninites have operated since at least ~3.12 Ga, while a uniquely Archaean boninite-forming process, involving more buoyant oceanic plates and very inefficient mantle-source enrichment, may have occurred before then.  相似文献   

Effect and timing of increased freshwater runoff into sheltered harbor environments around Auckland City, New Zeland     

Bruce W. Hayward  Hugh R. Grenfell  Ashwaq T. Sabaa  Margaret S. Morley  Mark Horrocks 《Estuaries and Coasts》2006,29(2):165-182

Two short cores of late Holocene, low tidal, estuarine sediment from the sheltered fringes of the Auckland's Waitemata Harbor, New Zealand, record the following changes through time since human colonization: an abrupt decline and disappearance of marine molluscs, a major decline and virtual disappearance of ostracods, an abrupt decline in calcareous foraminifera (mostlyAmmonia spp.), a rapid increase, in abundance of agglutinated foraminifera, large diatoms, and freshwater thecamoebians, and an increase in sedimentation rate, but no consistent trend in change of grain size. The up-core foraminiferal changes mimic their present day up-estuary zonation, which correlates strongly with decreasing salinity and pH. In both localities the faunal changes can be correlated with the documented local land-use history and increased freshwater runoff over time. At the head of the Waitemata Harbor, in Lucas Creek estuary, three phases of foraminiferal faunal change occurred: minor changes during initial Polynesian forest clearance (1500–1800 AD), a major change in early European times (1840–1870 AD) with clearance of most of the remaining native forest, and another small change in very, recent times (∼1990s) with urbanization in the Lucas Creek catchment. On the eastern, seaward fringes of the Waitemata Harbor, in the smaller Tamaki Estuary, no faunal changes occurred in association with complete forest clearance and establishment of pastoral farming in Polynesian and early European times (before 1950s). Major foraminiferal and other faunal changes occurred in the late European period (1960s–1970s) coincident with the onset of major urbanization spreading throughout the Tamaki catchment. Our results suggest increased freshwater runoff is the major culprit for many of the observed biotic changes in the urbanized estuaries of New Zealand.  相似文献