scholarly journals Geochemical segmentation of the Mid-Atlantic Ridge north of Iceland and ridge-hot spot interaction in the North Atlantic

2005 ◽  
Vol 6 (1) ◽  
pp. n/a-n/a ◽  
Author(s):  
Janne Blichert-Toft ◽  
Arnaud Agranier ◽  
Magdalena Andres ◽  
Richard Kingsley ◽  
Jean-Guy Schilling ◽  
...  
Keyword(s):  
North Atlantic ◽  
Hot Spot ◽  
The North ◽  
Mid Atlantic Ridge ◽  
The North Atlantic

scholarly journals Kinematic sequence stratigraphy of the European Cenozoic Rift System and Alpine Foreland Basin: correlation with Mediterranean and Atlantic plate-boundary events

2006 ◽  
Vol 85 (2) ◽  
pp. 77-129 ◽  
Author(s):  
W. Sissingh
Keyword(s):  
North Atlantic ◽  
Plate Boundary ◽  
Foreland Basin ◽  
Rift System ◽  
The North ◽  
Mid Atlantic Ridge ◽  
Alpine Foreland ◽  
Alpine Foreland Basin ◽  
The North Atlantic ◽  
Plate Kinematics

AbstractA review of the sequence stratigraphic development of the Tertiary basins of the North and West Alpine Foreland domains shows that their structural and depositional history was episodically affected by brief tectonic phases. These were associated with intermittent deformation events induced by the collisional convergence and compressional coupling of the Apulian and Iberian microplates with the European Plate. The plate kinematics-related episodicity was essentially isochronously recorded in the basin fills of the Alpine Foreland region. These are generally correlative with changes in eustatic sea level. The ensuing correlative successions of so-called Cenozoic Rift and Foredeep (CRF) sequences and phases can be traced throughout the European Cenozoic Rift System and Alpine Foreland Basin. Their temporal correlation indicates that, apparently, the changes in the plate collision-related stress regime of the Alpine Foreland were repeatedly accompanied by coeval changes in eustatic sea level. To test and substantiate the validity of this inferred causal relationship between intraplate deposition, plate kinematics and eustacy, the tectono-sedimentary evolution of the basins of the Mediterranean plate-boundary zone has been analysed in conjunction with a review of the plate-boundary events in the North Atlantic. Within the uncertainty range of available datings, synchroneity could thus be demonstrated for the punctuated tectonostratigraphic development of basins of the western Mediterranean (comprising the Liguro-Provençal Basin, Valencia Trough, Sardinia Rift and Tyrrhenian Basin), the Apenninic-Calabrian Arc, the Betic domain (including the Alboran Basin) and the North and West Alpine Foreland regions. Similar temporal correlations of plate tectonicsrelated events near the Mid-Atlantic Ridge in the North Atlantic and tectonostratigraphic sequences and phases of the Alpino-Pyrenean Foreland basins are further evidence of a common causal mechanism. The driving mechanisms appear to have been the northward drift of Africa and the resulting mechanical coupling of Apulia and Iberia with the southern passive margin of Europe, as well as the stepwise opening of the North Atlantic and accompanying episodic plate re-organisations of the Mid-Atlantic Ridge.

Halogens in the mantle beneath the North Atlantic

1980 ◽  
Vol 297 (1431) ◽  
pp. 147-178 ◽  
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Partial Melting ◽  
North Atlantic ◽  
Low Pressure ◽  
The North ◽  
Mid Atlantic Ridge ◽  
Ionic Size ◽  
The North Atlantic ◽  
Incompatible Trace Elements

F, Cl and Br contents of tholeiitic volcanic glasses dredged along the Mid-Atlantic Ridge from 53° to 28° N, including the transect over the Azores Plateau, are reported. The halogen variations parallel those of 87 Sr/ 86 Sr, La/Sm or other incompatible elements of varying volatility. The latitudinal halogen variation pattern is not obliterated if only Mg-rich lavas are considered. Variations in extent of low-pressure fractional crystallization or partial melting conditions do not appear to be the primary cause of the halogen variations. Instead, mantle-derived heterogeneities in halogens, with major enrichments in the mantle beneath the Azores, are suggested. The Azores platform is not only a ‘hotspot’ but also a ‘wetspot’, which may explain the unusually intense Azores volcanic activity. The magnitude of the halogen and incompatible element enrichments beneath the Azores appear strongly dependent on the size of these anions and cations, but independent of relative volatility at low pressure. The large anions Cl and Br behave similarly to large cations Rb, Cs and Ba, and the smaller anion F similarly to Sr and P. Processes involving crystal and liquid (fluid and/or melt), CO 2 rather than H 2 O dominated, seem to have produced these largescale mantle heterogeneities. Geochemical ‘anomalies’ beneath the Azores are no longer apparent for coherent element pair ratios of similar ionic size. Values of such ‘unfractionated’ coherent trace element ratios provide an indication of the mantle composition and its nature before fractionation event (s) which produced the inferred isotopic and trace element heterogeneities apparently present beneath the North Atlantic. The relative trace element composition of this precursor mantle does not resemble that of carbonaceous chondrites except for refractory trace element pairs of similar ionic size. It is strongly depleted in halogens, and to a lesser extent in large alkali ions Rb and Cs relative to refractory Ba. These relative depletions are comparable within a factor of 5 to Ganapathy & Anders’s estimates for the bulk Earth, with the exception of Cs. There is also evidence for removal of phosphorus into the iron core during its formation. With the exception of San Miguel, alkali basalts from the Azores Islands appear to have been derived from the same mantle source as tholeiitic basalts from the ridge transect over the Azores Platform but by half as much degree of partial melting. The Azores subaerial basalts seem to have been partly degassed in Cl, Br and F, in decreasing order of intensity. A working model involving metasomatism from release of fluids at phase transformation during convective mantle overturns is proposed to explain the formation of mantle plumes or diapirs enriched in larger relative to smaller halogen and other incompatible trace elements. The model is ad hoc and needs testing. However, any other dynamical model accounting for the 400 -1000 km long gradients in incompatible trace elements, halogens and radiogenic isotopes along the Mid-Atlantic Ridge should, at some stage, require either (1) some variable extent of mixing or (2) differential migration of liquid relative to crystals followed by re-equilibration (or both), as a diffusion controlled mechanism over such large distances is clearly ruled out, given the age of the Earth.

scholarly journals Demosponges from the Northern Mid-Atlantic Ridge shed more light on the diversity and biogeography of North Atlantic deep-sea sponges

2015 ◽  
Vol 95 (7) ◽  
pp. 1475-1516 ◽  
Author(s):  
Paco Cárdenas ◽  
Hans Tore Rapp
Keyword(s):  
North Atlantic ◽  
Fracture Zone ◽  
Deep Sea ◽  
The North ◽  
Mid Atlantic Ridge ◽  
The North Atlantic

In July–August 2004, the Mid-Atlantic Ridge Ecosystems (MAR-Eco) expedition collected Demospongiae (Porifera) from the Northern Mid-Atlantic Ridge (MAR) north of the Azores, between 41°N and 61°N. Demosponges were found at 10 stations, at depths ranging from 753 to 3046 m. Twenty-two species were identified: 17 Tetractinellida, one Polymastiida, one Suberitida, two Poecilosclerida and one Dendroceratida. The study of this material is an opportunity to revise the taxonomy and the North Atlantic distribution of each of these deep-sea species. Some species are particularly rare and poorly known (Tetilla longipilis, Tetilla sandalina, Craniella azorica, Polymastia corticata) and two are new to science:Forcepia(Forcepia)toxaferasp. nov. andIotroata paravaridenssp. nov. This study suggests that the MAR is not a longitudinal barrier for the dispersal of deep-sea demosponges while on the contrary, the Charlie-Gibbs Fracture Zone (CGFZ) may be a latitudinal border for the dispersal of deep-sea demosponges, due to great depths and currents.

scholarly journals Interannual Variability in the Pathways of the North Atlantic Current over the Mid-Atlantic Ridge and the Impact of Topography

2008 ◽  
Vol 38 (1) ◽  
pp. 104-120 ◽  
Author(s):  
Amy S. Bower ◽  
Wilken-Jon von Appen
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
Fracture Zone ◽  
Subpolar Gyre ◽  
North Atlantic Current ◽  
The North ◽  
Mid Atlantic Ridge ◽  
The North Atlantic ◽  
The Impact ◽  
Atlantic Current

Abstract Recent studies have indicated that the North Atlantic Ocean subpolar gyre circulation undergoes significant interannual-to-decadal changes in response to variability in atmospheric forcing. There are also observations, however, suggesting that the southern limb of the subpolar gyre, namely, the eastward-flowing North Atlantic Current (NAC), may be quasi-locked to particular latitudes in the central North Atlantic by fracture zones (gaps) in the Mid-Atlantic Ridge. This could constrain the current’s ability to respond to variability in forcing. In the present study, subsurface float trajectories at 100–1000 m collected during 1997–99 and satellite-derived surface geostrophic velocities from 1992 to 2006 are used to provide an improved description of the detailed pathways of the NAC over the ridge and their relationship to bathymetry. Both the float and satellite observations indicate that in 1997–99, the northern branch of the NAC was split into two branches as it crossed the ridge, one quasi-locked to the Charlie–Gibbs Fracture Zone (CGFZ; 52°–53°N) and the other to the Faraday Fracture Zone (50°–51°N). The longer satellite time series shows, however, that this pattern did not persist outside the float sampling period and that other branching modes persisted for one or more years, including an approximately 12-month time period in 2002–03 when the strongest eastward flow over the ridge was at ∼49°N. Schott et al. showed how northward excursions of the NAC can temporarily block the westward flow of the Iceland–Scotland Overflow Water through the CGFZ. From the 13-yr time series of surface geostrophic velocity, it is estimated that such blocking may occur on average 6% of the time, although estimates for any given 12-month period range from 0% to 35%.

Mid-Atlantic Ridge hydrothermal events recorded by deep-sea corals

1999 ◽  
Vol 36 (4) ◽  
pp. 511-517 ◽  
Author(s):  
Jodie E Smith ◽  
Uwe Brand ◽  
Michael J Risk ◽  
Henry P Schwarcz
Keyword(s):  
North Atlantic ◽  
Discharge Zone ◽  
Coral Skeletons ◽  
The North ◽  
Oceanic Spreading ◽  
History Of ◽  
Mid Atlantic Ridge ◽  
Tectonic Settings ◽  
The North Atlantic ◽  
Isotope Analyses

Trace-element and stable-isotope analyses were performed on azooxanthellate corals from the North Atlantic, at two different tectonic settings. One set was from Orphan Knoll, near Newfoundland (1700 m depth, 50°25.57'N, 46°22.05'W), the other from the Mid-Atlantic Ridge (1200 m depth, 45°14.12'N, 28°34.12'W). The Mid-Atlantic Ridge corals contain significantly greater quantities of Fe, Mn, Cu, Ni, and Zn within their skeletons than the Orphan Knoll corals. The metal concentrations are not homogeneous within the Mid-Atlantic Ridge coral skeletons, but occur as episodic pulses during a decade or two of each coral's lifetime. We believe these metals originated in a hydrothermal discharge zone associated with the Mid-Atlantic spreading centre. If so, it is evidence that the duration of an individual hydrothermal event is from a decade up to 30 years or so. With more specimens of known ages, it may be possible to reconstruct the history of a particular segment of an oceanic spreading centre.

The Mid-Atlantic Ridge Near 45° N. XVII. Magnetic Anomalies and Ocean Floor Spreading

1971 ◽  
Vol 8 (8) ◽  
pp. 883-898 ◽  
Author(s):  
B. D. Loncarevic ◽  
R. L. Parker
Keyword(s):  
North Atlantic ◽  
Magnetic Anomalies ◽  
Ocean Floor ◽  
The North ◽  
Ocean Floor Spreading ◽  
Magnetic Model ◽  
Mid Atlantic Ridge ◽  
The North Atlantic

In the North Atlantic it is difficult to correlate single magnetic profiles with the spreading ocean floor magnetic models. Within the area of intensive surveys at 45° N, it is possible to average the observations in the direction of the trend of the magnetic anomalies. The profile of averaged anomalies for all data between 45° N and 45.5° N correlates well with a magnetic model spreading (with respect to the ridge axes) westwards at 1.28 cm/y and eastwards at 1.10 cm/y, if the trend of the anomalies is assumed to be 015° East of North.

scholarly journals Centromedon zoe (Crustacea: Amphipoda: Lysianassoidea: Uristidae), a new deep-water scavenger species from the North Atlantic, with a key to the genus Centromedon

Zootaxa ◽  
2011 ◽  
Vol 2869 (1) ◽  
pp. 54 ◽  
Author(s):  
TAMMY HORTON ◽  
MICHAEL THURSTON
Keyword(s):  
New Species ◽  
North Atlantic ◽  
Deep Water ◽  
The North ◽  
Baited Traps ◽  
Mid Atlantic Ridge ◽  
The North Atlantic ◽  
A New Species

A new species of Centromedon Sars, 1891 is described based on abundant material collected in baited traps at 2500 m on the Mid-Atlantic Ridge. The species can be distinguished from the most closely allied species, Centromedon typhlops (Sars, 1879), Centromedon mediator (Barnard, 1962) comb. nov. and Centromedon laevis (Bonnier, 1896) comb. nov., by the form of the gnathopods, and characters of the mouthparts. A key to the eight species in the genus is provided. The differences between the closely allied genera Uristes Dana, 1849 and Centromedon are discussed.

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