scholarly journals A near-bottom magnetic survey of the Mid-Atlantic Ridge axis at 26°N: Implications for the tectonic evolution of the TAG segment

2003 ◽  
Vol 108 (B5) ◽  
Author(s):  
Maurice A. Tivey ◽  
Hans Schouten ◽  
Martin C. Kleinrock
Keyword(s):  
Tectonic Evolution ◽  
Magnetic Survey ◽  
Ridge Axis ◽  
Mid Atlantic Ridge

Tectonic evolution and trace element composition of basement rocks of the Mid-Atlantic Ridge: 8° S

1971 ◽  
Vol 268 (1192) ◽  
pp. 661-661
Keyword(s):  
Tectonic Evolution ◽  
Regional Metamorphism ◽  
Trace Element Composition ◽  
Element Composition ◽  
Laboratory Measurements ◽  
Refraction Seismology ◽  
Basement Rocks ◽  
Mid Atlantic Ridge ◽  
Temperature And Pressure ◽  
Geomagnetic Anomaly

Rapidly growing information regarding the rocks of the Mid-Atlantic Ridge has led Melson & Thompson to postulate a basement consisting of an upper layer of oceanic tholeiites with subsidiary hydrothermal metabasalts, and a lower plutonic layer of peridotites, serpentinites and gabbros. These layers may correspond to the second and third layers of refraction seismology. The same data permit the assumption that the oceanic tholeiites are underlain by an intermediate layer of metabasalts resulting from iso-chemical regional metamorphism under increased temperature and pressure. Laboratory measurements of magnetic properties have shown that the Koningsberger ratio of oceanic metabasalts is generally less than unity. Thus, such a regional metamorphic layer would place a floor under the zone responsible for the observed geomagnetic anomaly patterns.

The Mid-Atlantic Ridge Near 45 °N. XIX. An Electron Microscope Investigation of the Magnetic Minerals in Basalt Samples

1972 ◽  
Vol 9 (6) ◽  
pp. 671-678 ◽  
Author(s):  
M. E. Evans ◽  
M. L. Wayman
Keyword(s):  
Electron Microscopy ◽  
Fine Structure ◽  
Single Domain ◽  
Dominant Factor ◽  
Dispersed Phase ◽  
Magnetic Minerals ◽  
Ridge Axis ◽  
Electron Microscope Investigation ◽  
Mid Atlantic Ridge ◽  
Domain Models

Basalt samples from the vicinity of the Mid-Atlantic Ridge near 45 °N have been examined by electron microscopy, since many of the magnetic properties could be due to the fine structure of the titanomagnetites present. The observed remanence of axial material cannot be accounted for by multidomain or pseudo-single domain models. Furthermore, an explanation in terms of submicroscopic unmixing of titanomagnetite grains is shown to be untenable. However, electron microscopy did reveal the presence in all samples of a finely dispersed phase believed to be single-domain titanomagnetite grains. These will inevitably contribute to the remanence and may well be the dominant factor. The decay in remanence with distance from the ridge axis, which could similarly be associated with fine structure, is also discussed.

scholarly journals 3-D P-wave velocity structure of oceanic core complexes at 13°N on the Mid-Atlantic Ridge

2020 ◽  
Vol 221 (3) ◽  
pp. 1555-1579 ◽  
Author(s):  
N M Simão ◽  
C Peirce ◽  
M J Funnell ◽  
A H Robinson ◽  
R C Searle ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Velocity Structure ◽  
P Wave ◽  
Ocean Bottom ◽  
Uppermost Mantle ◽  
Ridge Axis ◽  
Magma Supply ◽  
P Wave Velocity ◽  
Mid Atlantic Ridge ◽  
Detachment Faulting

SUMMARY The Mid-Atlantic Ridge at 13°N is regarded as a type locality for oceanic core complexes (OCCs), as it contains, within ∼70 km along the spreading axis, four that are at different stages of their life cycle. The wealth of existing seabed observations and sampling makes this an ideal target to resolve contradictions between the existing models of OCC development. Here we describe the results of P-wave seismic tomographic modelling within a 60 × 60 km footprint, containing several OCCs, the ridge axis and both flanks, which determines OCC crustal structure, detachment geometry and OCC interconnectivity along axis. A grid of wide-angle seismic refraction data was acquired along a series of 17 transects within which a network of 46 ocean-bottom seismographs was deployed. Approximately 130 000 first arrival traveltimes, together with sparse Moho reflections, have been modelled, constraining the crust and uppermost mantle to a depth of ∼10 km below sea level. Depth slices through this 3-D model reveal several independent structures each with a higher P-wave velocity (Vp) than its surrounds. At the seafloor, these features correspond to the OCCs adjacent to the axial valley walls at 13°20′N and 13°30′N, and off axis at 13°25′N. These high-Vp features display dipping trends into the deeper crust, consistent with the surface expression of each OCC's detachment, implying that rocks of the mid-to-lower crust and uppermost mantle within the footwall are juxtaposed against lower Vp material in the hangingwall. The neovolcanic zone of the ridge axis has systematically lower Vp than the surrounding crust at all depths, and is wider between OCCs. On average, throughout the 13°N region, the crust is ∼6 km-thick. However, beneath a deep lava-floored basin between axial OCCs the crust is thinner and is more characteristically oceanic in layering and velocity–depth structure. Thicker crust at the ridge axis suggests a more magmatic phase of current crustal formation, while modelling of the sparse Moho reflections suggests the crust–mantle boundary is a transition zone throughout most of the 13°N segment. Our results support a model in which OCCs are bounded by independent detachment faults whose dip increases with depth and is variable with azimuth around each OCC, suggesting a geometry and mechanism of faulting that is more complicated than previously thought. The steepness of the northern flank of the 13°20′N detachment suggests that it represents a transfer zone between different faulting regimes to the south and north. We propose that individual detachments may not be linked along-axis, and that OCCs act as transfer zones linking areas of normal spreading and detachment faulting. Along ridge variation in magma supply influences the nature of this detachment faulting. Consequently, not only does magma supply control how detachments rotate and migrate off axis before finally becoming inactive, but also how, when and where new OCCs are created.

scholarly journals Tectonic evolution of 200 km of Mid-Atlantic Ridge over 10 million years: Interplay of volcanism and faulting

2015 ◽  
Vol 16 (7) ◽  
pp. 2303-2321 ◽  
Author(s):  
Johnson R. Cann ◽  
Deborah K. Smith ◽  
Javier Escartin ◽  
Hans Schouten
Keyword(s):  
Tectonic Evolution ◽  
Mid Atlantic Ridge

Extensive volcaniclastic deposits at the Mid-Atlantic Ridge axis: results of deep-water basaltic explosive volcanic activity?

Terra Nova ◽  
1998 ◽  
Vol 10 (5) ◽  
pp. 280-286 ◽  
Author(s):  
Fouquet ◽  
Eissen ◽  
Ondreas ◽  
Barriga ◽  
Batiza ◽  
...  
Keyword(s):  
Deep Water ◽  
Volcanic Activity ◽  
Ridge Axis ◽  
Mid Atlantic Ridge ◽  
Volcaniclastic Deposits
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