I. Ultramafic rocks - Peridotite—gabbro—basalt complex from the equatorial Mid-Atlantic Ridge

1971 ◽  
Vol 268 (1192) ◽  
pp. 385-402 ◽  
Keyword(s):  
Upper Mantle ◽  
Early Stage ◽  
Ultramafic Rocks ◽  
Metamorphic Rocks ◽  
Fracture Zones ◽  
Equatorial Atlantic ◽  
Isotopic Data ◽  
The World ◽  
Mid Atlantic Ridge ◽  
Liquid Fractionation

Rocks were dredged where the Mid-Atlantic Ridge is intersected by the Chain, Romanche, St Paul and Vema Fracture Zones, and from unfractured portions of the Ridge between 6 and 8° N. Peridotites are common at the fracture zones, but were found also in unfractured sections of the Ridge; harzburgites prevail, but lherzolites, dunites and plagioclase peridotites are also present. A variety of gabbros was recovered, generally above the peridotites, including norites, troctolites, quartz gabbros and theralites. The chemistry of these gabbros indicates a marked crystal-liquid fractionation, following both a ‘tholeiitic’ and an ‘alkali’ trend. The basalts show also both trends, but less markedly. Metamorphic rocks ranging from ‘greenschist’ to ‘amphibolite’ facies are found throughout the sections. Strontium isotopic data suggest that the peridotites (excluding St Peter-Paul rocks) are not related genetically to the associated gabbro-basalt, in a situation similar to that of alpine complexes on the continents. The peridotites are probably residual and were depleted of lithophile elements at some early stage of their history, before the opening of the Atlantic rift. It is postulated that in the upper mantle below the equatorial Atlantic a zone exists of residual, alpine-type peridotite, while the lower crust consists of a mixture of ultramafics and intrusive gabbros. The data indicate strong similarities between the Mid-Atlantic Ridge and alpine complexes from various parts of the world.

Serpentinization at the Rainbow and Saldanha sites, Mid-Atlantic Ridge: Mineralogical, geochemical, and isotopic features

2019 ◽  
Vol 57 (5) ◽  
pp. 677-706
Author(s):  
Isabel Ribeiro da Costa ◽  
Frederick Joseph Wicks ◽  
Fernando J.A.S. Barriga
Keyword(s):  
Upper Mantle ◽  
Hydrothermal Activity ◽  
Isotopic Data ◽  
Geochemical Characterization ◽  
Textural Evolution ◽  
Mantle Peridotites ◽  
Carbonate Deposition ◽  
Mid Atlantic Ridge ◽  
Ree Patterns

Abstract The Rainbow hydrothermal field (36°14′N) and the Saldanha seamount (36°34′N), in the Mid-Atlantic Ridge (MAR), are tectonic exposures of serpentinized upper mantle peridotites, both associated with significant hydrothermal activity. On the basis of detailed mineralogical and geochemical characterization of serpentinites from both sites, several serpentinization-related issues are discussed in the present work. As expected in oceanic environments, most of the sampled rocks are lizardite-chrysotile serpentinites exhibiting a variety of pseudomorphic through non-pseudomorphic textures, such textural evolution probably being related to changing water/rock ratios during this retrograde process. Oxygen isotope temperatures indicate that the serpentinization took place at 300–200 °C; on the other hand, isotopic data suggest that replacement of early pseudomorphic lizardite by lizardite ± chrysotile non-pseudomorphic textures requires that temperatures and/or water/rock ratios are high enough to promote the necessary dissolution–recrystallization processes. Mass-balance calculations for olivine-serpentine and orthopyroxene-serpentine pairs provided a basis for establishing serpentinization reactions likely to have produced the present rocks. Moreover, these calculations also showed that, notwithstanding some noticeable loss of MgO from olivine and of SiO2 from orthopyroxene, serpentinization of both minerals implies volume increases on the order of 26–27%, therefore potentially promoting the overall expansion of the rock. The geochemical and isotopic features of the studied rocks indicate that unmodified seawater was responsible for the serpentinization of the MAR peridotites. However, the mineralogy and REE patterns of some of these serpentinites indicate occasional subsequent interaction of the serpentinized rocks with seawater at much lower temperatures (seafloor alteration, characterized by carbonate deposition and negative Ce anomalies), or with high-temperature ore-forming hydrothermal fluids (ore-forming alteration, characterized by sulfide precipitation and steep positive Eu anomalies).

scholarly journals Uppermost Mantle Velocity beneath the Mid-Atlantic Ridge and Transform Faults in the Equatorial Atlantic Ocean

2020 ◽  
Author(s):  
Guilherme W. S. de Melo ◽  
Ross Parnell-Turner ◽  
Robert P. Dziak ◽  
Deborah K. Smith ◽  
Marcia Maia ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Upper Mantle ◽  
Equatorial Atlantic ◽  
Uppermost Mantle ◽  
Transform Faults ◽  
Equatorial Atlantic Ocean ◽  
Mid Atlantic Ridge ◽  
Mantle Velocity ◽  
Ray Paths

ABSTRACT Seismic rays traveling just below the Moho provide insights into the thermal and compositional properties of the upper mantle and can be detected as Pn phases from regional earthquakes. Such phases are routinely identified in the continents, but in the oceans, detection of Pn phases is limited by a lack of long-term instrument deployments. We present estimates of upper-mantle velocity in the equatorial Atlantic Ocean from Pn arrivals beneath, and flanking, the Mid-Atlantic Ridge and across several transform faults. We analyzed waveforms from 50 earthquakes with magnitude Mw>3.5, recorded over 12 months in 2012–2013 by five autonomous hydrophones and a broadband seismograph located on the St. Peter and St. Paul archipelago. The resulting catalog of 152 ray paths allows us to resolve spatial variations in upper-mantle velocities, which are consistent with estimates from nearby wide-angle seismic experiments. We find relatively high velocities near the St. Paul transform system (∼8.4  km s−1), compared with lower ridge-parallel velocities (∼7.7  km s−1). Hence, this method is able to resolve ridge-transform scale velocity variations. Ray paths in the lithosphere younger than 10 Ma have mean velocities of 7.9±0.5  km s−1, which is slightly lower than those sampled in the lithosphere older than 20 Ma (8.1  km±0.3  s−1). There is no apparent systematic relationship between velocity and ray azimuth, which could be due to a thickened lithosphere or complex mantle upwelling, although uncertainties in our velocity estimates may obscure such patterns. We also do not find any correlation between Pn velocity and shear-wave speeds from the global SL2013sv model at depths <150  km. Our results demonstrate that data from long-term deployments of autonomous hydrophones can be used to obtain rare and insightful estimates of uppermost mantle velocities over hundreds of kilometers in otherwise inaccessible parts of the deep oceans.

The Mid-Atlantic Ridge Near 45 °N. XVI. Serpentinized Ultramafic Intrusions

1971 ◽  
Vol 8 (6) ◽  
pp. 631-663 ◽  
Author(s):  
F. Aumento ◽  
H. Loubat
Keyword(s):  
Solid State ◽  
Hydrostatic Pressure ◽  
Upper Mantle ◽  
Sea Water ◽  
Mechanical Deformation ◽  
Ultramafic Rocks ◽  
Physical Conditions ◽  
Mid Atlantic Ridge ◽  
Directional Component ◽  
Solid State Recrystallization

Detailed descriptions of the mineralogy, petrography, geochemistry, and physical properties of serpentinized ultramafic rocks dredged from the Mid-Atlantic Ridge at 45° N support an interpretation of the events which affected these rocks after their original crystallization. Crystallization apparently took place in lopoliths emplaced at the Crust/Upper Mantle interface beneath the axis of the ridge under conditions quiet enough to permit gravity crystal differentiation and layering. The rocks were then fractured without hydration under high hydrostatic pressure, with a feeble directional component, possibly under conditions favoring solid-state recrystallization of interstitial minerals. Hydration (amphibolization) began during the last phases of intimate mechanical deformation and the commencement of rodingitic metasomatism. Further hydration resulted in multiple overlapping periods of serpentinization dependent on varying physical conditions. Hydrating fluids may have been derived both from juvenile waters and from sea water.

Some Guidance for Hull Form Selection for SWATH Ships

1988 ◽  
Vol 25 (04) ◽  
pp. 239-252
Author(s):  
G. Robed Lamb
Keyword(s):  
High Speed ◽  
Early Stage ◽  
The United States ◽  
Practical Application ◽  
Hull Form ◽  
Stage Design ◽  
Seakeeping Performance ◽  
The World ◽  
Selection For ◽  
Early Stage Design

Even though in 1987 there were only a dozen SWATH (smali-waterplane-area twin-hull) craft and ships afloat around the world, word of their markedly superior seakeeping performance is spreading rapidly. The number of SWATH vessels is likely to double within five years. As in many other areas of technology, the United States and Japan are the acknowledged leaders in the development and practical application of the SWATH concept. This paper reviews the characteristics of existing SWATH craft and ships from the standpoint of the stated seakeeping objective. Hull form differences between four SWATH craft and ships, including the Navy's SSP Kairnalino, are analyzed and interpreted. Important considerations for the early-stage design of a SWATH ship are discussed. Differences in the range of feasible hull form geometries for coastal areas and unrestricted ocean operations, and for low-speed versus moderately high-speed applications, are pointed out.

A Multicultural Approach at the Early Stage of Teaching a Foreign language

2021 ◽  
pp. 34-40
Author(s):  
Nadezhda Kantysheva ◽  
Alfiya Rahmatullina
Keyword(s):  
Foreign Language ◽  
Novice Teacher ◽  
Early Stage ◽  
Language Teachers ◽  
Future Teacher ◽  
Cultural Identification ◽  
Foreign Language Teachers ◽  
The World ◽  
Elective Course ◽  
Technological Competencies

The article presents the experience of developing an elective course program for future foreign language teachers studying at Tyumen State University. The content of the course is based on the principles of communication and variability and is focused on the development of the communicative, psychological, pedagogical and technological competencies of the future teacher. The creation by the teacher of favorable pedagogical conditions for a positive cultural identification of the student’s personality allows the child to become aware of the multicultural space of the world. The professional portfolio of a novice teacher includes techniques, methods and technologies that can be used for further pedagogical modeling.

Transverse isotropy of the upper mantle in the vicinity of Pacific fracture zones

1969 ◽  
Vol 59 (1) ◽  
pp. 59-72
Author(s):  
Robert S. Crosson ◽  
Nikolas I. Christensen
Keyword(s):  
Upper Mantle ◽  
Symmetry Axis ◽  
Transverse Isotropy ◽  
Transversely Isotropic ◽  
Seismic Wave Propagation ◽  
Fracture Zones ◽  
Mantle Material ◽  
Transversely Isotropic Media ◽  
Horizontal Symmetry ◽  
Isotropic Media

Abstract Several recent investigations suggest that portions of the Earth's upper mantle behave anisotropically to seismic wave propagation. Since several types of anisotropy can produce azimuthal variations in Pn velocities, it is of particular geophysical interest to provide a framework for the recognition of the form or forms of anisotropy most likely to be manifest in the upper mantle. In this paper upper mantle material is assumed to possess the elastic properties of transversely isotropic media. Equations are presented which relate azimuthal variations in Pn velocities to the direction and angle of tilt of the symmetry axis of a transversely isotropic upper mantle. It is shown that the velocity data of Raitt and Shor taken near the Mendocino and Molokai fracture zones can be adequately explained by the assumption of transverse isotropy with a nearly horizontal symmetry axis.

A suite of alkali basalts and gabbros associated with the Hare Bay Allochthon of western Newfoundland

1977 ◽  
Vol 14 (3) ◽  
pp. 346-356 ◽  
Author(s):  
R. A. Jamieson
Keyword(s):  
Oceanic Crust ◽  
Continental Margin ◽  
Upper Mantle ◽  
Ultramafic Rocks ◽  
Alkali Basalts ◽  
Crust And Upper Mantle ◽  
Bay Area ◽  
Close Proximity ◽  
Thrust Sheets

The Hare Bay Allochthon of northwestern Newfoundland consists of a series of sedimentary, volcanic, metamorphic, and ultramafic rocks which was emplaced over a Cambro-Ordovician continental margin as several thrust sheets. It probably represents a continental margin sequence overridden by oceanic crust and upper mantle. The Partridge Point gabbro, Cape Onion volcanics, and Ireland Point Volcanics, which now occur in the Maiden Point, Cape Onion, and St. Anthony tectonic slices respectively, appear to be closely related on petrographic and chemical grounds. Olivine, titanaugite, kaersutite, and plagioclase indicate that these rocks formed as a single suite of hydrous alkali basalts, possibly as part of a seamount near a continental margin. This relationship provides a link between the lower sedimentary and the upper igneous-metamorphic structural slices of the allochthon and implies that most of the transported rocks in the Hare Bay area evolved in close proximity to each other.

Nd isotopic characteristics of metamorphic and plutonic rocks of the Coast Mountains near Prince Rupert, British Columbia

1998 ◽  
Vol 35 (5) ◽  
pp. 556-561 ◽  
Author(s):  
P J Patchett ◽  
G E Gehrels ◽  
C E Isachsen
Keyword(s):  
British Columbia ◽  
Volcanic Rocks ◽  
Metamorphic Rocks ◽  
Published Data ◽  
Isotopic Data ◽  
Crustal Component ◽  
Coast Mountains ◽  
Crustal Rocks ◽  
Metasedimentary Rocks ◽  
Plutonic Rocks

Nd isotopic data are presented for a suite of metamorphic and plutonic rocks from a traverse across the Coast Mountains between Terrace and Prince Rupert, British Columbia, and for three contrasting batholiths in the Omineca Belt of southern Yukon. A presumed metamorphic equivalent of Jurassic volcanic rocks of the Stikine terrane gives epsilon Nd = +6, and a number of other metaigneous and metasedimentary rocks in the core of the Coast Mountains give epsilon Nd values from +3 to +7. A single metasedimentary rock approximately 3 km east of the Work Channel shear zone gives a epsilon Nd value of -9. Coast Belt plutons in the traverse yield epsilon Nd from -1 to +2. The Omineca Belt plutons give epsilon Nd from -10 to -17. All results are consistent with published data in demonstrating that (i) juvenile origins for both igneous and metamorphic rocks are common in the Coast Belt; (ii) representatives of a continental-margin sedimentary sequence with Precambrian crustal Nd are tectonically interleaved in the Coast Mountains; (iii) Coast Mountains plutons can be interpreted as derived from a blend of metamorphic rocks like those seen at the surface, or as arc-type melts contaminated with the older crustal component; and (iv) Omineca Belt plutons are dominated by remelted Precambrian crustal rocks.

scholarly journals Are people excessively pessimistic about the risk of coronavirus infection?

2020 ◽  
Author(s):  
Jocelyn Raude ◽  
Marion Debin ◽  
Cécile Souty ◽  
Caroline Guerrisi ◽  
Clement Turbelin ◽  
...  
Keyword(s):  
Social Psychology ◽  
Early Stage ◽  
Risk Of Infection ◽  
Health Threat ◽  
Recent Emergence ◽  
The World ◽  
The Future ◽  
Coronavirus Infection ◽  
Future Consequences ◽  
Large Survey

The recent emergence of the SARS-CoV-2 in China has raised the spectre of a novel, potentially catastrophic pandemic in both scientific and lay communities throughout the world. In this particular context, people have been accused of being excessively pessimistic regarding the future consequences of this emerging health threat. However, consistent with previous research in social psychology, a large survey conducted in Europe in the early stage of the COVID-19 epidemic shows that the majority of respondents was actually overly optimistic about the risk of infection.

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