Getting over continent ocean boundaries

Eagles, Graeme; Pérez-Díaz, Lucía; Scarselli, Nicola

doi:10.1016/j.earscirev.2015.10.009

Cited by 86 publications

(77 citation statements)

References 178 publications

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“…The definition of the Continent-Ocean Boundaries have been made by hand by following "at best" both prominent features in the first derivative of the map of the Earth gravity field model (GRACE GGM02, [10]) and the second derivative in the magnetic anomaly map EMAG2 [11]. The result is however not fundamentally different from other publications as reported by Eagles et al [12], and does not significantly affect the statistical outcomes provided below.…”

Section: /54contrasting

confidence: 32%

Statistics of the Earth’s Topography

Vérard¹

2017

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The so-called "typical" values for the Earth's topography are often used in the literature, such as the mean continental altitude (MCA), the Moho depth for "normal" continental crust, or "typical" depth of mid-oceanic ridges. However, the statistical relevance of those values is hardly discussed. Focussed on data for the global topography, this paper presents statistical analyses regarding various environments. It is shown in particular that the definition of the mid-oceanic ridge is not straightforward, and varies considerably according to what is actually considered: the ridge "inner-rift", the ridge "crest", or the "virtual ridge" at spreading centre. This definition is also a function of the spreading rate and has strong implications for the rationale on the age-depth relationship of the sea-floor. In addition, the latter relationship is highly dependent on how the topographic data are corrected from sediment load. The correction itself implies numerous aspects that relies on the precision and associated uncertainties of, in particular, the sediment thickness, sediment porosity, and the mantle, water and sediment densities. In this respect, the analysis carried out here favours a plate cooling model (PCM) for the agedepth dependence of the sea-floor. The topographic elevation at trench proves also to be related to the age of the sea-floor through a different PCM equation. Away from the trench, the oceanic lithosphere is affected by flexuration, for which equations can be defined assuming that the end-load position is not located at trench. On the other hand, the elevation of magmatic arc does not appear to be related to sea-floor age or spreading rate. However, the correlation between the arc-trench distance and the topographic elevation of arc for continental crust seems to be an indicator of slab dip and therefore the existence of slab roll-back processes. Along intra-oceanic magmatic arc, a periodicity in topographic elevation suggests a periodicity in the occurrence of magma chambers, and therefore magmatic processes that need to be further studied. At passive margin, the transition between continental and oceanic crust seems to be relatively sharp in average. Subdivision of the datasets according to the age of the continent-ocean boundary (COB) indicates that rift and passive margin shoulders are found within a couple of degree away from the COB and for ages younger than ca. 20 Ma. Finally, the statistical analysis

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Section: /54contrasting

confidence: 32%

Statistics of the Earth’s Topography

Vérard¹

2017

OALib

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“…Hence, the LaLOC and ECC, independently of the quality of the mapping, cannot be used as markers for plate kinematic restorations. Eagles et al () showed, for instance, that the LaLOCs can never be superposed. Transfer faults cutting the thinned and exhumed mantle domains provide the direction of motion during a stage of deformation, but they do not provide time indications.…”

Section: Hyperextended Rifted Margins: a Kinematic Descriptionmentioning

confidence: 99%

Kinematic Evolution of the Southern North Atlantic: Implications for the Formation of Hyperextended Rift Systems

et al. 2018

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We focus on the southern North Atlantic rifted margins to investigate the partitioning and propagation of deformation in hyperextended rift systems using plate kinematic modeling. The kinematic evolution of this area is well determined by oceanic magnetic anomalies after the Cretaceous normal polarity superchron. However, the rift and early seafloor spreading evolution (200–83 Ma) remains highly disputed due to contentious interpretations of the J magnetic anomaly on the Iberia‐Newfoundland conjugate margins. Recent studies highlight that the J anomaly is probably polygenic, related to polyphased magmatic events, and therefore does not correspond to an isochron. We present a new palinspastic restoration without using the J magnetic anomaly as the chron M0. We combine 3‐D gravity inversion results with local structural, stratigraphic, and geochronological constraints on the rift deformation history. The restoration of the southern North Atlantic itself is not the primary aim of the study but rather is used as a method to investigate the spatiotemporal evolution of hyperextended rift systems. We include continental microblocks that enable the partitioning of the deformation between different rift segments, which is of particular importance for the evolution of the Iberia‐Eurasia plate boundary. Our modeling highlights the following: (1) the segmentation of the Iberia‐Newfoundland rift system during continental crust thinning, (2) the northward V‐shape propagation of mantle exhumation and seafloor spreading, (3) the complex partitioning of deformation along the Iberia‐Eurasia plate boundary, and (4) a three‐plate propagation model which implies transtension.

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“…The onset of oceanic, or thick oceanic crust of Icelandic type in case of the Walvis Ridge, is at approximately the same distance from shore for all profiles. Besides the disagreement on the location of a COB, Eagles et al (2015) recently challenged the concept of COBs in general. The large uncertainties involved in defining the COB makes it of little use in plate kinematic reconstructions even though the COB is still invoked (Eagles et al, 2015).…”

Section: The Crustal Composition Of the Eastern Walvis Ridgementioning

confidence: 99%

The onset of Walvis Ridge: Plume influence at the continental margin

et al. 2017

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The opening of the South Atlantic is a classical example for a plume related continental breakup. Flood basalts are present on both conjugate margins as well as aseismic ridges connecting them with the current plume location at Tristan da Cunha. To determine the effect of the proposed plume head on the continental crust, we acquired wide-angle seismic data at the junction of the Walvis Ridge with the African continent and modelled the Pwave velocity structure in a forward approach. The profile extends 430 km along the ridge and continues onshore to a length of 720 km. Crustal velocities beneath the Walvis Ridge vary between 5.5 km/s and 7.0 km/s, a typical range for oceanic crust. The crustal thickness of 22 km, however, is approximately three times larger than of normal oceanic crust. The continent-ocean transition is characterized by 30 km thick crust with strong lateral velocity variations in the upper crust and a high-velocity lower crust (HVLC), where velocities reach up to 7.5 km/s. The HVLC is 100 to 130 km wider at the Walvis Ridge than it is farther south, and impinges onto the continental crust of the Kaoko fold belt. Such high seismic velocities indicate Mg-rich igneous material intruded into the continental crust during the initial rifting stage. However, the remaining continental crust seems unaffected by intrusions and the root of the 40 km-thick crust of the Kaoko belt is not thermally abraded. We conclude that the plume head did not modify the continental crust on a large scale, but caused rather local effects. Thus, it seems unlikely that a plume drove or initiated the breakup process. We further propose that the plume already existed underneath the continent prior to the breakup, and ponded melt erupted at emerging rift structures providing the magma for continental flood basalts.

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Getting over continent ocean boundaries

Cited by 86 publications

References 178 publications

Statistics of the Earth’s Topography

Statistics of the Earth’s Topography

Kinematic Evolution of the Southern North Atlantic: Implications for the Formation of Hyperextended Rift Systems

The onset of Walvis Ridge: Plume influence at the continental margin

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