Seismic Stratigraphy in a Transverse Ridge, Atlantis II Fracture Zone

Swift, Stephen A.; Hoskins, Hartley; Stephen, Ralph A.

doi:10.2973/odp.proc.sr.118.141.1991

Cited by 10 publications

(13 citation statements)

References 24 publications

(32 reference statements)

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“…For oceanic core complexes, regions of predominantly peridotite at shallow depths are unlikely to have avoided significant serpentinization and as such their seismic velocity will be relatively low,

\leq 5

km/s. Conversely, the presence of high velocities,

\geq 6

km/s, at shallow depths can be taken as indicator of a predominantly gabbroic rocks rather than as a region of moderately, 20–40%, serpentinized peridotite of similar velocity [ Canales et al ., ; Xu et al ., ; Henig et al ., ], an association supported by the velocity ties to recovered gabbro at Hole U1309D and at Hole 735B on Atlantis Bank [ Swift et al ., ]. From these heuristics and supporting field data, Canales et al .…”

Section: Discussionmentioning

confidence: 99%

Velocity structure near IODP Hole U1309D, Atlantis Massif, from waveform inversion of streamer data and borehole measurements

Harding

Arnulf

Blackman

2016

Geochem Geophys Geosyst

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Seismic full waveform inversion (FWI) is a promising method for determining the detailed velocity structure of the igneous oceanic crust, especially for locations such as the Mid‐Atlantic Ridge with significant lateral heterogeneity and seafloor topography. We examine the accuracy of FWI by inverting, after downward continuation to datum just above the seafloor, a multichannel seismic (MCS) profile from Atlantis Massif oceanic core complex at 30°N that passes close to Integrated Ocean Drilling Program (IODP) Hole U1309D and comparing the results against borehole measurements and existing on‐bottom refraction data. The comparisons include the results of IODP Expedition 340T, which extended the sonic logging and vertical seismic profiling to the bottom of the borehole at 1400 m below seafloor. Compared to travel time tomography, the refinement in velocity and velocity gradient produced by FWI significantly improves the overall match to the borehole measurements, and allows the multilevel pattern of deformation and alteration of the detachment footwall seen in Hole U1309D to be extrapolated across the Central Dome. Prestack depth migration of the profile using the FWI velocities reveals the top and edges of the high‐velocity, gabbroic core of the massif. It also indicates that the comparatively uniform gabbroic rocks drilled at Hole U1309D extend to ∼2.5 km below seafloor but overlie an extended, ∼2 km thick, mantle transition zone.

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\leq 5

km/s. Conversely, the presence of high velocities,

\geq 6

Section: Discussionmentioning

confidence: 99%

Velocity structure near IODP Hole U1309D, Atlantis Massif, from waveform inversion of streamer data and borehole measurements

Harding

Arnulf

Blackman

2016

Geochem Geophys Geosyst

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“…al., 1999), is responsible for the reflector identified during Leg 118 at this depth (Swift et al, 1991). In general, V P gradients increase with depth ( Fig.…”

Section: Gj Iturrino Et Al Velocity Structure Of the Lower Oceanicmentioning

confidence: 80%

Velocity structure of the lower oceanic crust: results from Hole 735B, Atlantis II Fracture Zone

Iturrino¹,

Ildefonse²,

Boitnott³

2002

Proceedings of the Ocean Drilling Program

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Laboratory compressional wave (V P) and shear wave (V S) velocities were measured as a function of confining pressure for the gabbros from Hole 735B and compared to results from Leg 118. The upper 500 m of the hole has a V P mean value of 6895 m/s measured at 200 MPa, and at 500 meters below seafloor (mbsf), V P measurements show a mean value of 7036 m/s. V S mean values in the same intervals are 3840 m/s and 3857 m/s, respectively. The mean V P and V S values obtained from log data in the upper 600 m are 6520 and 3518 m/s, respectively. These results show a general increase in velocity with depth and the velocity gradients estimate an upper mantle depth of 3.32 km. This value agrees with previous work based on dredged samples and inversion of rare element concentrations in basalts dredged from the conjugate site to the north of the Atlantis Bank. Laboratory measurements show V P anisotropy ranging between 0.4% and 8.8%, with the majority of the samples having values less than 3.8%. Measurements of velocity anisotropy seem to be associated with zones of high crystal-plastic deformation with predominant preferred mineral orientations of plagioclase, amphiboles, and pyroxenes. These findings are consistent with results on gabbros from the Hess Deep area and suggest that plastic deformation may play an important role in the seismic properties of the lower oceanic crust. In contrast to ophiolite studies, many of the olivine gabbros show a small degree of anisotropy. Log derived V S anisotropy shows an average of 5.8% for the upper 600 m of Hole 735B and tends to decrease with depth where the overburden pressure and the age of the crustal section suggests closure of cracks and infilling of fractures by alteration

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“…Stabilization of the sea level during the last 6.5 kyr has led to the formation of a sedimentary wedge on the shelf over the deposits of the previous transgressive sedimentary environments and the establishment of the present coastal environment (Swift et al 1991). The deposition of fine-grained sediments controlled by the shelf morphology and seasonal circulation patterns gave rise to the formation of the mud depocentres previously mentioned (Dias et al 2002a, b).…”

Section: Pleistocene -Holocene Evolution and Climate Cyclesmentioning

confidence: 88%

Chapter 8 The NW Iberian continental shelf

Rey

Álvarez-Iglesias

Araújo

et al. 2014

Memoirs

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The continental shelf of NW Iberia is of particular interest due to the complex North Atlantic rifting tectonics and modern oceanographic processes that led to its current geomorphological configuration and sediment dynamics. The shelf forms a narrow slow-dipping north-bearing geomorphological structure with a well-defined shelf break located at water depths of 160-180 m. It is a continental margin with sedimentation rates of about 1.5 + 2.0 mm a 21 (the highest values in recent bottom sediments of the ría) subjected to a highly energetic seasonal regime of waves and tides, seasonal upwelling and coast-parallel currents, significantly modulated by the North Atlantic Oscillation. Sediment provenance is dominated by inputs of continental sediments via runoff and riverine discharges and, to a lesser extent, by an upwelling-enhanced bioclastic input. Present-day sedimentation in the area occurs closely associated with two geomorphologically distinct sedimentary environments: the rías inner shelf sedimentary systems and the open continental shelf, and their subsequent evolution since the last glacial.

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Seismic Stratigraphy in a Transverse Ridge, Atlantis II Fracture Zone

Cited by 10 publications

References 24 publications

Velocity structure near IODP Hole U1309D, Atlantis Massif, from waveform inversion of streamer data and borehole measurements

Velocity structure near IODP Hole U1309D, Atlantis Massif, from waveform inversion of streamer data and borehole measurements

Velocity structure of the lower oceanic crust: results from Hole 735B, Atlantis II Fracture Zone

Chapter 8 The NW Iberian continental shelf

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