The Mid-Atlantic Ridge near 45° N. XII. Coercivity, secondary magnetization, polarity, and thermal stability of dredge samples

1970 ◽  
Vol 7 (6) ◽  
pp. 1499-1514 ◽  
Author(s):  
J. K. Park ◽  
E. Irving
Keyword(s):  
Coercive Force ◽  
Empirical Relationship ◽  
Blocking Temperature ◽  
Lower Intensity ◽  
Volcanic Zone ◽  
Rock Types ◽  
Mid Atlantic Ridge ◽  
The Mean ◽  
Force Range ◽  
Thermal Stability Of

The mean coercivities of natural (n.r.m.), anhysteretic (a.r.m.), and isothermal (i.r.m.) remanent magnetization in 34 samples of submarine basalt from the Mid-Atlantic Ridge are 270, 250, and 370 oersteds respectively, showing their magnetization to be stable. The spectra of coercive force of n.r.m. and a.r.m. of these basalts are similar, although, because of small secondary components, there are small differences in the low coercive force range (0 to 100 Oe). The magnitude and sign of these differences are used to derive an empirical relationship between coercivity and the magnitude of secondary components, and to infer the polarity of primary components. The inferred polarities of samples from within the Median Valley of the Ridge are all normal, whereas both normal and reversed polarities are found from the adjacent mountains and plateaus. Experiments show that warming specimens from the Median Valley to 100 °C for 90 h causes the production of a new component with a lower intensity, and higher blocking temperature, but with the same direction as the original natural remanence. Similar effects may occur in the axial volcanic zone, and may have caused the decrease in intensity with distance from the axis. The magnetic properties of various other rock types from the Mid-Atlantic Ridge are also described.

scholarly journals Five-Year Enhanced Natural Attenuation of Historically Coal-Tar-Contaminated Soil: Analysis of Polycyclic Aromatic Hydrocarbon and Phenol Contents

2021 ◽  
Vol 18 (5) ◽  
pp. 2265
Author(s):  
Arkadiusz Telesiński ◽  
Anna Kiepas-Kokot
Keyword(s):  
Aromatic Hydrocarbons ◽  
Natural Attenuation ◽  
Soil Analysis ◽  
Coal Tar ◽  
Soil Samples ◽  
Lower Intensity ◽  
Sampling Points ◽  
Polycyclic Aromatic ◽  
Monoaromatic Hydrocarbons ◽  
The Mean

The objective of this study was to assess the soil pollution on an industrial wasteland, where coal-tar was processed in the period between 1880 and 1997, and subsequent to assess the decline in the content of phenols and polycyclic aromatic hydrocarbons (PAHs) during enhanced natural attenuation. The soil of the investigated area was formed from a layer of uncompacted fill. Twelve sampling points were established in the investigated area for collecting soil samples. A study conducted in 2015 did not reveal any increase in the content of heavy metals, monoaromatic hydrocarbons (BTEX), and cyanides. However, the content of PAHs and phenols was higher than the content permitted by Polish norms in force until 2016. In the case of PAHs, it was observed for individual compounds and their total contents. Among the various methods, enhanced natural attenuation was chosen for the remediation of investigated area. Repeated analyses of the contents of phenols and PAHs were conducted in 2020. The results of the analyses showed that enhanced natural attenuation has led to efficient degradation of the simplest substances—phenol and naphthalene. The content of these compounds in 2020 was not elevated compared to the standards for industrial wastelands. The three- and four-ring hydrocarbons were degraded at a lower intensity. Based on the mean decrease in content after 5-year enhanced natural attenuation, the compounds can be arranged in the following order: phenols > naphthalene > phenanthrene > fluoranthene > benzo(a)anthracene > chrysene > anthracene.

DENSITIES OF METAMORPHIC ROCKS

Geophysics ◽  
1971 ◽  
Vol 36 (4) ◽  
pp. 690-694 ◽  
Author(s):  
Scott B. Smithson
Keyword(s):  
Metamorphic Rock ◽  
Granite Gneiss ◽  
Biotite Granite ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
Rock Density ◽  
Rock Types ◽  
Crystalline Crust ◽  
The Mean ◽  
Few Data

Although metamorphic rocks comprise a large part of the crystalline crust, relatively few data concerning metamorphic rock densities are available. In this paper, we present rock densities from seven different metamorphic terrains. Mean densities for rock types range from [Formula: see text] for biotite granite gneiss to [Formula: see text] for diopside granofels. Mean rock densities for metamorphic terrains range from 2.70 to [Formula: see text]. Rock density may decrease in the lower part of the upper crust. Most mean rock densities for metamorphic terrains fall between 2.70 and [Formula: see text]; the mean density of [Formula: see text] commonly used for the upper crystalline crust is too low.

scholarly journals Return migration patterns of porbeagle shark (Lamna nasus) in the Northeast Atlantic: implications for stock range and structure

2017 ◽  
Vol 74 (5) ◽  
pp. 1268-1276 ◽  
Author(s):  
Gérard Biais ◽  
Yann Coupeau ◽  
Bernard Séret ◽  
Beatriz Calmettes ◽  
Rémy Lopez ◽  
...  
Keyword(s):  
General Pattern ◽  
Late Summer ◽  
The Arctic ◽  
Bay Of Biscay ◽  
Migration Patterns ◽  
Northeast Atlantic ◽  
Archival Tags ◽  
Mid Atlantic Ridge ◽  
The Common ◽  
The Mean

During two surveys in 2011 and 2013, we deployed pop-up satellite archival tags (PSATs) on subadult or adult porbeagles at the Bay of Biscay shelf break. We collected data that enabled the reconstruction of nine migrations (eight females, one male) that uncover the large spatial extent of these sharks in the Northeast Atlantic. The mean duration of each deployment was 292 d, with four reaching 365 d. The reconstructions show that, after migrations that extended up to 2000 km away from the point of release, the tagged porbeagles returned to their location of tagging. All the reconstructed migrations followed the same general pattern of a migration away from the Bay of Biscay in late summer, and a return in spring the following year. The total distance of the migrations was estimated at 5000–13 000 km for PSATs deployed for a full year (n = 4), with examples of migration to the Arctic Circle, southward to Madeira and westward to the mid-Atlantic Ridge. The observed site fidelity to the Bay of Biscay and the common migration pattern of all females provide evidence of complex spatial structure and dynamics that encompasses both the open ocean and heavily fished coastal areas, and highlights the challenge of assessing and managing the porbeagle stock in this area.

Enhanced Thermal Stability and Mechanical Properties of Ultrafine-Grained Aluminum Alloy

2010 ◽  
Vol 667-669 ◽  
pp. 331-336 ◽  
Author(s):  
Rinat K. Islamgaliev ◽  
Marina A. Nikitina ◽  
Aidar F. Kamalov
Keyword(s):  
Thermal Stability ◽  
Aluminum Alloy ◽  
Volume Fraction ◽  
High Pressure Torsion ◽  
Coarse Grained ◽  
Dynamic Precipitation ◽  
Ultrafine Grained ◽  
The Mean ◽  
Fatigue Endurance ◽  
Thermal Stability Of

The paper reports on microstructure, strength and fatigue of ultrafine-grained (UFG) samples of the Al-Cu-Mg-Si aluminum alloy processed by high pressure torsion (HPT) at various temperatures. Application of the HPT treatment led to strong grain refinement, as well as to a raise of the mean-root square strains and dynamic precipitation. In case of optimal HPT treatment the UFG samples have demonstrated the enhanced thermal stability, an increase in ultimate tensile strength in 2.5 times and enhancement in fatigue endurance limit by 20 % in comparison with coarse-grained alloy subjected to standard treatment. It is shown that the regime of the HPT treatment governs the volume fraction of precipitates and segregations, thereby affecting a grain size and thermal stability of ultrafine-grained structure.

scholarly journals Excitation Class of Nebulae as an Evolution Criterion

1993 ◽  
Vol 155 ◽  
pp. 481-481
Author(s):  
G.A. Gurzadyan ◽  
A.G. Egikyan
Keyword(s):  
Empirical Relationship ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
Independent Parameter ◽  
The Mean ◽  
Evolutionary Interpretation

A principally new, quantitative system of the classification of spectra of planetary nebulae is proposed. The excitation class of a nebula, p, is determined according to the relative intensities of emission lines, N1+N2/4686 HeII and N1+N2/Hβ. The excitation classes are obtained for 177 PN with known distances and sizes of all classes – low (p=1–3), middle (p=4–8) and high (p=9–12+). An empirical relationship between the excitation class p and the mean radius of the nebulae Rn is discovered – the largest sizes occur for highly excited nebulae, and the smallest for low excitation ones. This relationship as well as excitation class p, as an independent parameter admit an evolutionary interpretation (Gurzadyan, Egikyan 1991).

Characteristics of tide-water calving at Glaciar San Rafael, Chile

1995 ◽  
Vol 41 (138) ◽  
pp. 273-289 ◽  
Author(s):  
Charles R. Warren ◽  
Neil F. Glasser ◽  
Stephan Harrison ◽  
Vanessa Winchester ◽  
Andrew R. Kerr ◽  
...  
Keyword(s):  
Water Depth ◽  
Environmental Variables ◽  
Empirical Relationship ◽  
Glacier Surface ◽  
Frequency Distributions ◽  
Low Salinity ◽  
The Mean ◽  
Oceanographic Data ◽  
San Rafael ◽  
Tidal Stage

AbstractGlacial calving is a poorly understood process. This study tests the influence of local environmental variables on the magnitude and frequency distributions of calving behaviour at Glaciar San Rafael, Chile. Near the terminus of the glacier, surface speeds average 17 m d −1 in summer and calving is profuse and continual. The size, location and characteristics of over 7000 calving events were recorded during 32d in 1991 and 1992, together with meteorological, bathymetric and oceanographic data. Mean daily calving exceeds 400 events per day and the mean calving flux is more than 2 Mm3d1. Mean annual calving speed and calving flux are about 4500 m a −1 and 2.0 km3 a−1, respectively. This calving speed is higher than that predicted by the established empirical relationship between tide-water calving speed and water depth. This is surprising, given the low salinity of Laguna San Rafael and that fresh-water calving speeds are commonly much lower than those in ride water. Daily patterns of calving frequency and flux correlate poorly or not at all with meteorological variables, but tidal stage may have some control over the timing of large submarine calving events. Submarine calving produced the largest bergs. However, the relatively small total flux recorded from the submerged pars of the ice cliff may imply unusually rapid melt rates.

Production Estimates for Scotian Shelf Copepods Based on Mass Specific P/B Ratios

1983 ◽  
Vol 40 (6) ◽  
pp. 749-753 ◽  
Author(s):  
M. John Tremblay ◽  
John C. Roff
Keyword(s):  
Body Mass ◽  
Secondary Production ◽  
Empirical Relationship ◽  
Copepod Species ◽  
Scotian Shelf ◽  
Adult Body Mass ◽  
Adult Body ◽  
The Mean ◽  
First Time ◽  
Good Agreement

We estimated annual secondary production by copepod species on the Emerald Bank, Scotian Shelf, for the first time. We tentatively ranked copepod species in order of importance based on production to biomass (P/B) ratios calculated from adult body mass using an empirical relationship. The significance of assessing species in terms of production rather than population biomass is demonstrated. The mean estimate of total copepod production (530 kJ∙m−2) is in good agreement with previous estimates of secondary production on the Scotian Shelf.

Unravelling rift development: a key study from the Northern Volcanic Zone of Iceland

2020 ◽  
Author(s):  
Elena Russo ◽  
Alessandro Tibaldi ◽  
Fabio Luca Bonali ◽  
Federico Pasquarè Mariotto ◽  
Páll Einarsson ◽  
...  
Keyword(s):  
Normal Faults ◽  
Volcanic Zone ◽  
The North ◽  
Rift Propagation ◽  
Extensive Field ◽  
Northern Volcanic Zone ◽  
Regional Tectonic ◽  
Aerial Vehicle ◽  
Mid Atlantic Ridge ◽  
Plate Separation

<p>Unravelling the kinematics, development and origin of the structures along a volcano-tectonic rift is of paramount importance for understanding plate separation, seismicity, volcanic activity and the associated hazards. Here, we focus on an extremely detailed survey of the Holocene deformation field along the Northern Volcanic Zone of Iceland, the northernmost point of emergence of the Mid-Atlantic Ridge. The study of this extremely dynamic rift is also useful for a better comprehension of how mid-oceanic ridges work. The study is based on extensive field and unmanned aerial vehicle surveys performed over the last four years, completed by about 6000 measures collected at 1633 sites on fault strike, dip and offset, and fracture strike, dip, dilation direction and dilation amount. The rift, named Theistareykir Fissure Swarm, is composed of N-S to NNE-SSW-striking normal faults and extension fractures affecting an area 8 km-wide and 34 km-long. The computed overall spreading direction is N111° averaged during Holocene times, with values of N125° to the north and N106° to the south. The kinematics is characterised by the presence of complex components of right-lateral and left-lateral strike-slip motions, with a strong predominance of right-lateral components along structures parallel and coeval to the rift zone. The surveyed 33 Holocene faults (696 sites of measurement) along the central part of the rift show two opposite directions of fault/rift propagation, based on fault slip profile analyses. We discuss the possible causes of these characteristics and analyse in detail the interaction of both faults and extension fractures with the WNW-ESE transform Tjornes Fracture Zone, and in particular with the parallel right-lateral Husavik-Flatey Fault in the central part of the rift, and the Grimsey Lineament to the north. We also assess the role of: i) repeated dyke intrusions from the magma chamber outward along the plate margin, ii) regional tectonic stresses, iii) mechanical interaction of faults, and iv) changes in the rheological characteristics of rocks.</p>

The Mid-Atlantic Ridge Near 45 °N. XXII. Sedimentary Deposition and Lithogenesis on Mid-Atlantic Ridge Mountain Tops

1974 ◽  
Vol 11 (8) ◽  
pp. 1157-1167 ◽  
Author(s):  
Charles T. Schafer
Keyword(s):  
Surface Sediments ◽  
Bottom Current ◽  
Current Direction ◽  
Sediment Distribution ◽  
Rock Types ◽  
Rock Cores ◽  
Rapid Changes ◽  
Unconsolidated Sediment ◽  
Mid Atlantic Ridge ◽  
Coralline Limestone

Bottom photographs and drilled rock cores collected on several mountain tops along the crest of the Mid-Atlantic Ridge near 45°N describe the sediment distribution, sediment dynamics and shallow stratigraphy of these sites. Lag pebble deposits and pebble waves indicate rapid changes in bottom current direction and velocities that may approach 100 cm/s (>2 knots) one meter above the bottom so that surface sediments are often not indicative of sediment and rock types sampled using shallow drilling techniques. Absolute dates (14C) of coralline limestone, which underlies coarse unconsolidated sediment at most drilling sites, suggest deposition and initial lithification of these deposits during a middle Wisconsin interstadial period.

scholarly journals Paleomagnetism of Siluro-Devonian rocks from eastern Maine

1980 ◽  
Vol 17 (12) ◽  
pp. 1653-1665 ◽  
Author(s):  
Dennis V. Kent ◽  
Neil D. Opdyke
Keyword(s):  
Reasonable Agreement ◽  
Lower Devonian ◽  
Northeastern North America ◽  
Rock Types ◽  
Magnetic Carriers ◽  
Paleomagnetic Study ◽  
Intrusive Rocks ◽  
The Mean ◽  
Upper Silurian ◽  
Accurate Record

A diverse suite of rocks was collected for paleomagnetic study from two formations in the Eastport area of northeastern Maine: 18 sites (103 samples) from redbeds and diabase sills of the Hersey Formation (uppermost Silurian to Lower Devonian) and 14 sites (74 samples) from lavas, redbeds, and calcareous nodules of the Eastport Formation (Lower Devonian; Rb/Sr age 412 Ma). Characteristic magnetizations based on AF and thermal demagnetization analyses give mean directions, after simple correction for bedding tilt, of D = 163.6°, I = 41.3°, α95 = 6.3°, for N = 16 sites in the Hersey, and D = 179.3°, I = 38.0°, α95 = 9.4°, for N = 14 sites in the Eastport Formation. Baked contact relations, the presence of opposite polarities, and the similarity in directions over different rock types and magnetic carriers point to an acquisition of magnetization near to the time of rock formation. The mean directions correspond to (south) paleopole positions at 19.8°S lat., 308.8°E long. (δp, δm = 4.7°, 7.7°) for the Hersey and 23.7°S lat., 293.7°E long. (δp, δm = 6.6°, 11.1°) for the Eastport Formation.These paleopoles are removed from the Upper Silurian Bloomsburg Formation pole, but are in reasonable agreement with similar age results from central Newfoundland, suggesting that the Acadia displaced terrain encompassed these areas. Siluro-Devonian paleopoles from intrusive rocks in northeastern North America are generally widely divergent and these may not be providing an accurate record of paleomagnetic field in all cases.

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