Along-axis variations in oceanic crustal density and their contribution to gravity anomalies at slow-spreading ridges

1996 ◽  
Vol 23 (8) ◽  
pp. 849-852 ◽  
Author(s):  
T. A. Minshull
Keyword(s):  
Gravity Anomalies ◽  
Spreading Ridges ◽  
Slow Spreading ◽  
Crustal Density

scholarly journals Fast and slow spreading ridges: Structure and hydrothermal activity, ultramafic topographic highs, and CH4output

1993 ◽  
Vol 98 (B6) ◽  
pp. 9643 ◽  
Author(s):  
Henri Bougault ◽  
Jean-Luc Charlou ◽  
Yves Fouquet ◽  
Hubert D. Needham ◽  
Nathalie Vaslet ◽  
...  
Keyword(s):  
Hydrothermal Activity ◽  
Spreading Ridges ◽  
Slow Spreading

Seismic controls on the progress of serpentinization at ultra-slow spreading ridges

2020 ◽  
Author(s):  
Claire Aupart ◽  
Vera Schlindwein ◽  
Yehuda Ben-Zion ◽  
François Renard ◽  
Bjorn Jamtveit
Keyword(s):  
Spreading Ridges ◽  
Slow Spreading

An analysis of the crust–mantle boundary in Hudson Bay from gravity and seismic observations

1968 ◽  
Vol 5 (5) ◽  
pp. 1297-1303 ◽  
Author(s):  
J. R. Weber ◽  
A. K. Goodacre
Keyword(s):  
Gravity Anomaly ◽  
Gravity Anomalies ◽  
Gravitational Effect ◽  
Compressional Wave ◽  
Seismic Survey ◽  
Hudson Bay ◽  
Mantle Boundary ◽  
Crustal Velocity ◽  
Velocity Variations ◽  
Crustal Density

A study of the results of the gravity and seismic surveys in Hudson Bay in 1965 has shown that the gravitational effect of a two-layer model based on the seismically determined depths has no correlation with the observed gravity anomalies. On the profile from Churchill to Povungnituk the gravity and seismic observations can be reconciled by postulating lateral variations of the acoustic compressional wave velocity within the crust. A crustal model has been calculated—using the same time-terms and the same mean crustal velocity—whose gravitational effect fits the observed gravity. The velocity varies from 6.15 to 6.56 km/s and the postulated depths are almost entirely within the confidence limits of the original model.In order to test the hypothesis, the postulated velocity variations have been compared with the lower refractor velocities of the shallow seismic survey, based on the assumption that the crustal velocities ought to be systematically higher than the crystalline surface velocities and that there may be a correlation between variations in crustal and surface velocities. The test is inconclusive because bottom refractor velocities are higher than crustal velocities in two areas where volcanic flows and high-velocity sediments may be present.The case of linearly related velocity (V) and density (ρ) variations has been analyzed and it is shown that the gravitational effect of the crust–mantle boundary undulations may be completely masked or even overbalanced by density changes in the crust if [Formula: see text]. The crust can be characterized by having dominant velocity variations (in which case the gravity anomaly reflects the undulations of the crust–mantle boundary) or dominant density variations (in which case the gravity anomaly inversely reflects the crust–mantle boundary undulations) depending on the relationship between average crustal density and average crustal velocity.

scholarly journals Mantle rock exposures at oceanic core complexes along mid-ocean ridges

Geologos ◽  
2015 ◽  
Vol 21 (4) ◽  
pp. 207-231 ◽  
Author(s):  
Jakub Ciazela ◽  
Juergen Koepke ◽  
Henry J.B. Dick ◽  
Andrzej Muszynski
Keyword(s):  
Partial Melting ◽  
Geophysical Methods ◽  
Ex Situ ◽  
Crustal Rocks ◽  
New Class ◽  
Ocean Ridges ◽  
Common Structure ◽  
Spreading Ridges ◽  
Slow Spreading ◽  
Lower Crustal

Abstract The mantle is the most voluminous part of the Earth. However, mantle petrologists usually have to rely on indirect geophysical methods or on material found ex situ. In this review paper, we point out the in-situ existence of oceanic core complexes (OCCs), which provide large exposures of mantle and lower crustal rocks on the seafloor on detachment fault footwalls at slow-spreading ridges. OCCs are a common structure in oceanic crust architecture of slow-spreading ridges. At least 172 OCCs have been identified so far and we can expect to discover hundreds of new OCCs as more detailed mapping takes place. Thirty-two of the thirty-nine OCCs that have been sampled to date contain peridotites. Moreover, peridotites dominate in the plutonic footwall of 77% of OCCs. Massive OCC peridotites come from the very top of the melting column beneath ocean ridges. They are typically spinel harzburgites and show 11.3–18.3% partial melting, generally representing a maximum degree of melting along a segment. Another key feature is the lower frequency of plagioclase-bearing peridotites in the mantle rocks and the lower abundance of plagioclase in the plagioclase-bearing peridotites in comparison to transform peridotites. The presence of plagioclase is usually linked to impregnation with late-stage melt. Based on the above, OCC peridotites away from segment ends and transforms can be treated as a new class of abyssal peridotites that differ from transform peridotites by a higher degree of partial melting and lower interaction with subsequent transient melt.

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