Insight into the nature of the ocean-continent transition off West Iberia from a deep multichannel seismic reflection profile

Pickup, S. L. B.; Whitmarsh, R. B.; Fowler, C. M. R.; Reston, T. J.

doi:10.1130/0091-7613(1996)024<1079:iitnot>2.3.co;2

Cited by 168 publications

(240 citation statements)

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“…An alternative interpretation is that the basement in the ocr is primarily serpentinized upper mantle peridotites [Boillot et al, 1989;Pickup et al, 1996]. Conversion of seismic velocity to degree of serpentinization in Figure 12 is made using laboratory measurements on ophiolite samples [Christensen, 1966] and on samples from the Mid-Atlantic Ridge [Christensen, 1972] Approximately at the position of line CAM132, the basement depths and velocity models suggest further changes in basement structure from east to west.…”

Section: Density Of the Water Layer Ismentioning

confidence: 99%

Deep structure of the ocean‐continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: Ocean Drilling Program (Legs 149 and 173) transect

Chian¹,

Louden²,

Minshull³

et al. 1999

J. Geophys. Res.

174

195

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Abstract. We present a wide-angle seismic refraction study of an 80x40 km region of the southern Iberia Abyssal Plain, south of Galicia Bank. An intersecting grid of two E-W and four N-S wide-angle reflection/refraction profiles is used to define variations of the basement velocity blocks immediately south of Galicia Bank. This crust is underlain by a high-velocity layer (7.3-7.9 km/s) of weakly serpentinized (i.e., 0-25%) peridotite, which exists throughout the eastern part of the survey area. Basement within the OCT appears to consist dominantly of a broad region of exposed upper mantle that has been serpentinized heterogeneously both vertically and horizontally. In the southeast sector of our survey where basement topography deepens and becomes subdued, continental fault blocks are absent; instead, basement contains an upper layer of more pervasively serpentinized (i.e., 25-45%) peridotite that is ~2 km thick. This layer is characterized by low velocity at the top of basement (4.2 km/s) that increases rapidly with depth, and it probably corresponds to a seismically unreflective layer, previously identified in reflection profiles to the south of our survey. In the western section of our survey, beneath a series of elevated basement ridges, velocities are reduced within both the upper •asement layer (3.5-6.0 km/s) and lower layer (6.4-7.5 km/s). These changes suggest that both upper and lower layers have become more highly serpentinized (with values of 60-100% in the upper layer and 25-45% in the lower layer) probably during the last stages of rifting and immediately before formation of oceanic crust. A normal or slow spreading oceanic crustal structure is not found within the survey region. Thus it appears that the onset of seafloor spreading occurs in the region west of the peridotite ridge sampled at ODP Site 897 and east of the J magnetic anomaly.

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Section: Density Of the Water Layer Ismentioning

confidence: 99%

Deep structure of the ocean‐continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: Ocean Drilling Program (Legs 149 and 173) transect

Chian¹,

Louden²,

Minshull³

et al. 1999

J. Geophys. Res.

174

195

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“…Sloping mostly continentward, sometimes oceanward, they appear also on many seismic lines recorded on oceanic lithosphere adjacent to non-volcanic passive margins. For example, clear images of such reflectors were recorded in the Iberia Abyssal Plain off the Portugal passive margin (Pickup et al 1996;Fig. 9), and in the Biscay Abyssal Plain bounding the Goban Spur (Masson et al 1985).…”

Section: Dipping Reflectors and Shear Zones In Oceanic Lithospherementioning

confidence: 99%

Non-volcanic rifted margins, continental break-up and the onset of sea-floor spreading: some outstanding questions

Boillot

Froitzheim

2001

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During the last 20 years, regional studies on the West Iberia margin and on the former margins of the Tethys have considerably advanced the understanding of processes related to continental break-up and the onset of sea-floor spreading. However, some questions remain outstanding. To tentatively answer these, a coherent interpretation of available data is proposed, based on the detachment fault concept applied to the continental as well as the oceanic lithosphere, and on the hypothesis of a multi-staged rifting process. The interpretation addresses the nature of the lower crust beneath non-volcanic passive margins, the origin of ophicalcites, the probable time gap between syn-or post-rift crystallization of gabbros and extrusion of basalts on the sea floor, and the significance of dipping reflectors within oceanic lithosphere adjacent to non-volcanic passive margins. The interpretation also considers the symmetry v. asymmetry of continental rifting and break-up, the location of the ocean-continent boundary, and the possible association of magnetic quiet zones with ultramafic sea floor (serpentinized peridotite) bordering non-volcanic passive margins.

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“…Carlson and Miller, 1997;Chian et al, 1999;Whitmarsh et al, 1996;Pickup et al, 1996]. If the upper basement layer is thin (<7 km) [Skelton et al, 2005], serpentinization can be achieved by hydrothermally driven water influx, possibly aided by circulation along deep faults.…”

Section: Crustal Structure Of the Accommodation Zonementioning

confidence: 99%

“…Dean et al, 2000;Pickup et al, 1996] which is attributed to the extensive serpentinization of brecciated upper mantle peridotite, reducing the seismic velocity [Miller and Christensen, 1997] and hence the impedance contrast to the overlying sediments. The highly reflective and rotated fault-block signature of the upper basement layer near OBS B7 (Figure 6b) contradicts with these observations.…”

Section: Crustal Structure Of the Accommodation Zonementioning

confidence: 99%

East Greenland Ridge in the North Atlantic Ocean: An integrated geophysical study of a continental sliver in a boundary transform fault setting

et al. 2008

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The combined Greenland‐Senja Fracture Zones (GSFZ) represent a first‐order plate tectonic feature in the North Atlantic Ocean. The GSFZ defines an abrupt change in the character of magnetic anomalies with well‐defined seafloor spreading anomalies in the Greenland and Norwegian basins to the south but ambiguous and weak magnetic anomalies in the Boreas Basin to the north. Substantial uncertainty exists concerning the plate tectonic evolution of the latter area, including the role of the East Greenland Ridge, which is situated along the Greenland Fracture Zone. In 2002, a combined ocean‐bottom seismometer and multichannel seismic (MCS) survey acquired two intersecting wide‐angle reflection and coincident MCS profiles across and along the East Greenland Ridge. We present the results of integrated reflection seismic interpretation, first‐arrival tomography, 2D kinematic raytracing, full‐wave amplitude modeling, and gravity modeling of the intersecting profiles. The results show that (1) the Greenland Basin is characterized by a normal oceanic crustal velocity structure, (2) the velocity structure of the East Greenland Ridge is of overall continental type, and (3) a major faulted basin province above highly extended continental crust exists to the NE of the ridge. The results further suggest that a zone of extremely thin and faulted continental crust above partially serpentinized mantle peridotite defines the NW edge of the East Greenland Ridge and the transition to the NE Greenland margin.

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Insight into the nature of the ocean-continent transition off West Iberia from a deep multichannel seismic reflection profile

Cited by 168 publications

References 0 publications

Deep structure of the ocean‐continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: Ocean Drilling Program (Legs 149 and 173) transect

Deep structure of the ocean‐continent transition in the southern Iberia Abyssal Plain from seismic refraction profiles: Ocean Drilling Program (Legs 149 and 173) transect

Non-volcanic rifted margins, continental break-up and the onset of sea-floor spreading: some outstanding questions

East Greenland Ridge in the North Atlantic Ocean: An integrated geophysical study of a continental sliver in a boundary transform fault setting

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