Crustal structure of the ocean‐continent transition at Flemish Cap: Seismic refraction results

Funck, Thomas; Hopper, John R.; Larsen, Hans Christian; Louden, K. E.; Tucholke, Brian E.; Holbrook, W. S.

doi:10.1029/2003jb002434

Cited by 155 publications

(263 citation statements)

References 59 publications

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“…Both our gravity inversion and the seismic study of Watts et al interpret this thin crust to be thin oceanic crust (thinning factor 1 in the gravity inversion). The geometry of this thin crust is similar to that reported by Funck et al (2003) and Hopper et al (2007) for the SCREECH 1 line on the NE Newfoundland margin, which is a magmapoor margin on which mantle exhumation has been identified. Outboard of the thin crust, the crustal basement thickens to normal, or slightly greater than normal, oceanic values (Figs 3 & 7).…”

Section: South American Sectionsupporting

confidence: 80%

Crustal structure of the conjugate Equatorial Atlantic Margins, derived by gravity anomaly inversion

Kusznir

Roberts²,

Alvey³

2018

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The crustal structure of the Equatorial Atlantic conjugate margins (South America and West Africa) has been investigated using 3D gravity anomaly inversion, which allows for (1) the elevated geothermal gradient of the lithosphere following rifting and break-up and (2) magmatic addition to the crust during rifting and break-up. It is therefore particularly suitable for the analysis of rifted margins and their associated ocean basins. Maps of crustal thickness and conjugate-margin stretching, derived from gravity anomaly inversion, are used to illustrate how the Equatorial Atlantic opened as a set of stepped rift-transform segments, rather than as a simple orthogonal rifted margin. The influence of the transform faults and associated oceanic fracture zones is particularly clear when the results of the gravity anomaly inversion are combined with a shaded-relief display of the free-air gravity anomaly. A set of crustal cross-sections has been extracted from the results of the gravity inversion along both equatorial margins. These illustrate the crustal structure of both rifted-margin segments and transform-margin segments. The maps and cross-sections are used to delineate crustal type on the margins as (1) inboard, entirely continental, (2) outboard, entirely oceanic and (3) the ocean-continent transition in between where mixed continental and magmatic crust is likely to be present. For a given parameterization of melt generation the amount of magmatic addition within the ocean-continent transition is predicted by the gravity inversion. One of the strengths of the gravity-inversion technique is that these predictions can be made in the absence of any other directly acquired data. On both margins anomalously thick crust is resolved close to a number of oceanic fracture zones. On the South American margin we believe that this thick crust is probably the result of post-break-up magmatism within what was originally normal-thickness oceanic crust. On the West African margin, however, three possible origins are discussed: (1) continental crust extended oceanwards along the fracture zones; (2) oceanic crust magmatically thickened at the fracture zones; and (3) oceanic crust thickened by transpression along the fracture zones. Gravity inversion alone cannot discriminate between these possibilities. The cross-sections also show that, while 'normal thickness' oceanic crust (c. 7 km) predominates regionally, local areas of thinner (c. 5 km) and thicker (c. 10 km) oceanic crust are also present along both margins. Finally, using maps of crustal thickness and thinning factor as input to plate reconstructions, the regional palaeogeography of the Equatorial Atlantic during and after break-up is displayed at 10 Ma increments.Supplementary material: Detailed illustrations of the crustal-thickness mapping, the crustal cross-sections and the plate reconstructions are available at: https://doi

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Section: South American Sectionsupporting

confidence: 80%

Crustal structure of the conjugate Equatorial Atlantic Margins, derived by gravity anomaly inversion

Kusznir

Roberts²,

Alvey³

2018

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“…Bulk densities are also reported from studies where the authors combined gravity and seismic data to determine crustal density. References are (1) Funck et al (2008), (2) Grobys et al (2007), (3) Cooper et al (1981), (4) Grobys et al (2009), (5) Borissova et al (2003), (6) Klingelhoefer et al (2007), (7) Funck (2003), (8) Gerlings et al (2011), (9) Fowler et al (1989), (10) Breivik et al (2012), (11) Lebedeva-Ivanova et al (2006), (12) Morewood et al (2005), (13) Vogt et al (1998), and (14) Collier et al (2009 In the geological record, large volumes of crustal accretion are carried out by the collision of composite terranes or continental fragments onto continents (Vink et al, 1984). In North America, the amalgamation of the Wrangellia and Stikinia terranes resulted in a ribbon continent (SABIYA) that was ∼ 8000 km long and ∼ 500 km wide (Johnston, 2001).…”

Section: Composite Terranesmentioning

confidence: 99%

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

Tetreault

Buiter

2014

Solid Earth

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Abstract. Allochthonous accreted terranes are exotic geologic units that originated from anomalous crustal regions on a subducting oceanic plate and were transferred to the overriding plate by accretionary processes during subduction. The geographical regions that eventually become accreted allochthonous terranes include island arcs, oceanic plateaus, submarine ridges, seamounts, continental fragments, and microcontinents. These future allochthonous terranes (FATs) contribute to continental crustal growth, subduction dynamics, and crustal recycling in the mantle. We present a review of modern FATs and their accreted counterparts based on available geological, seismic, and gravity studies and discuss their crustal structure, geological origin, and bulk crustal density. Island arcs have an average crustal thickness of 26 km, average bulk crustal density of 2.79 g cm −3 , and three distinct crustal units overlying a crust-mantle transition zone. Oceanic plateaus and submarine ridges have an average crustal thickness of 21 km and average bulk crustal density of 2.84 g cm −3 . Continental fragments presently on the ocean floor have an average crustal thickness of 25 km and bulk crustal density of 2.81 g cm −3 . Accreted allochthonous terranes can be compared to these crustal compilations to better understand which units of crust are accreted or subducted. In general, most accreted terranes are thin crustal units sheared off of FATs and added onto the accretionary prism, with thicknesses on the order of hundreds of meters to a few kilometers. However, many island arcs, oceanic plateaus, and submarine ridges were sheared off in the subduction interface and underplated onto the overlying continent. Other times we find evidence of terrane-continent collision leaving behind accreted terranes 25-40 km thick. We posit that rheologically weak crustal layers or shear zones that were formed when the FATs were produced can be activated as detachments during subduction, allowing parts of the FAT crust to accrete and others to subduct. In many modern FATs on the ocean floor, a sub-crustal layer of high seismic velocities, interpreted as ultramafic material, could serve as a detachment or delaminate during subduction.

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“…Only the eastern WL and western DML sectors as well as some isolated areas such as Bruce Rise of the EL sector and the Adélie Rift Block in the WL sector show well-observed magmatic characteristics that are explained by syn-rift mantle plumes or other smaller-scale magmatic events. Most other margins seem to have been formed by processes similar to those proposed for other nonvolcanic margins, such as the IberianNewfoundland conjugate margins (e.g., Sibuet et al, 2007) and the Nova Scotia margin (e.g., Funck et al, 2003), which exhibit widely extended, thinned, and block-faulted continental crust. Whether any updoming of lower continental crust is a possible process, as Gaina et al (2007) suggest for the Enderby Land margin, is difficult to assess because of a lack of drill information.…”

Section: Geodynamic and Plate-tectonic Implications And Complicationsmentioning

confidence: 99%

Antarctica‘s continent-ocean transitions: consequences for tectonic reconstructions

Gohl¹

2007

Open-File Report

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Crustal structure of the ocean‐continent transition at Flemish Cap: Seismic refraction results

Cited by 155 publications

References 59 publications

Crustal structure of the conjugate Equatorial Atlantic Margins, derived by gravity anomaly inversion

Crustal structure of the conjugate Equatorial Atlantic Margins, derived by gravity anomaly inversion

Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments

Antarctica‘s continent-ocean transitions: consequences for tectonic reconstructions

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