Crustal thickness beneath Atlas region from gravity, topographic, sediment and seismic data

<p>In past years, a good understanding of the structure and tectonics of the Flemish Cap and the Goban Spur margin has been obtained based on seismic data, potential field data, and borehole data. However, due to limited data coverage and quality, the rift-related domains along the margin pair have remained poorly defined and their architecture has been primarily delineated on the basis of a small number of co-located 2-D seismic profiles. In addition, according to previous studies, the geophysical characteristics (e.g. velocity structure, crustal thickness, seismic patterns, etc.) across both the margins are strikingly different. Furthermore, from restored models of the southern North Atlantic, some scholars argue against the linkage of the Goban Spur and the Flemish Cap, questioning the widely-accepted &#8220;conjugate&#8221; relationship of the two margins. However, these restored models are mainly dependent on potential field data analysis, lacking seismic constraints, particularly for the Irish Atlantic Margin.</p><p>In this study, new long offset 2D multichannel seismic data, acquired in 2013 and 2014 by Eni Ireland for the Department of Communications, Climate Action & Environment of Ireland, cover the shelf, slope, and deepwater regions of the offshore Irish Altlantic margin. Combining these with seismic reflection data at the NE Flemish Cap, seismic refraction data, DSDP drilling sites, gravity and magnetic maps, crustal thickness maps, and oceanic isochrones, we integrate all constraints together to characterize the structure and evolution of both margins. These geophysical data reveal significant along-strike structural variations along both margins, and aid to delimit five distinct crustal zones related to different rifting stages and their regional extents. The geometries of each crustal domain are variable along the margin strike, probably suggestive of different extension rates during the evolution of the margin and/or inherited variations in crustal composition and rheology. Particularly, the along-strike exhumed serpentinized mantle domain of the Goban Spur margin spans a much wider (~ 42 - 60 km) area while it is much narrower (~25 km) at the NE Flemish Cap margin. In the exhumed domain, only peridotite ridges are observed at the Flemish Cap, while both peridotite ridges and a wide region of exhumed mantle with deeper basement are observed at the Goban Spur, indicative of a more complex evolutionary model than previously thought for both margins. Plate reconstruction of the Goban Spur and the Flemish Cap using GPlates reveals asymmetry in their crustal architectures, likely due to rift evolution involving more 3-D complexity than can be explained by simple 2-D extensional kinematics. In spite of uncertainties, the crustal architecture comparison between the two margins provides 3D seismic evidence related to the temporal and spatial rifting evolution on both sides.</p>

Download Full-text

Evolution of the Iberian Massif as deduced from its crustal thickness and geometry of a mid-crustal (Conrad) discontinuity

10.5194/se-2020-158 ◽

2020 ◽

Author(s):

Puy Ayarza ◽

José Ramón Martínez Catalán ◽

Ana Martínez García ◽

Juan Alcalde ◽

Juvenal Andrés ◽

...

Keyword(s):

Seismic Data ◽

Lower Crust ◽

Normal Incidence ◽

Crustal Thickness ◽

Iberian Massif ◽

Nw Iberia ◽

Asymptotic Geometry ◽

Surface Geology ◽

Internal Architecture ◽

European Variscides

Abstract. Normal incidence seismic data provide the best images of the crust and lithosphere. When properly designed and continuous, these sections greatly contribute to understanding the geometry of orogens and, together with surface geology, to unravel their evolution. In this paper we present an almost complete transect of the Iberian Massif, the westernmost exposure of the European Variscides. Despite the heterogeneity of the dataset, acquired during the last 30 years, the images resulting from reprocessing with a homogeneous workflow allow us to clearly define the crustal thickness and its internal architecture. The Iberian Massif crust, formed by the amalgamation of continental pieces belonging to Gondwana and Laurussia (Avalonian margin) is well structured in upper and lower crust. A conspicuous mid-crustal discontinuity is clearly defined by the top of the reflective lower crust and by the asymptotic geometry of reflections that merge into it, suggesting that it has often acted as a detachment. The geometry and position of this discontinuity can give us insights on the evolution of the orogen, i.e. of the effects and extent of the late Variscan gravitational collapse. Also, its position and the limited thickness of the lower crust in central and NW Iberia constraints the response of the Iberian microplate to Alpine shortening. This discontinuity is here observed as an orogeny-scale feature with characteristics compatible with those of the worldwide, Conrad discontinuity.

Download Full-text

Crustal thickness under the Gulf of St. Lawrence, northern Appalachians, from gravity and deep seismic data

Canadian Journal of Earth Sciences ◽

10.1139/e89-130 ◽

1989 ◽

Vol 26 (8) ◽

pp. 1517-1532 ◽

Cited By ~ 36

Author(s):

F. Marillier ◽

J. Verhoef

Keyword(s):

Seismic Data ◽

Bouguer Anomaly ◽

Crustal Thickness ◽

Moho Depth ◽

Crustal Layer ◽

Reflection Seismic ◽

Middle Paleozoic ◽

Lateral Extent ◽

Well Data ◽

Lower Crustal

We have determined crustal thickness in the Gulf of St. Lawrence, an area that corresponds to an offset of the main northern Appalachians units. A "complete" Bouguer anomaly was calculated from recent depth-to-basement compilations and sediment densities from well data. The Moho surface was obtained by inverting the Bouguer anomaly, assuming a single density contrast at depth, and using an average depth provided by deep reflection seismic data. The resulting crustal model shows a Moho depth of 42–44 km beneath the Grenville Craton, north of the Appalachian deformation front. South of this front, the depth to Moho displays a pronounced thinning of the crust beneath the Carboniferous Magdalen Basin. This is in striking contrast to the deep seismic data, which give a Moho depth of about 43 km. The modelling of the Bouguer anomaly in the Magdalen Basin, taking into account the seismic reflection and refraction data, reconciles these different results and suggests that a 43 km deep Moho beneath the basin is associated with a lower crustal layer about 13 km thick, with high velocity (7.35 km/s) and density (3.05 g/cm3). The Bouguer anomaly suggests that the lateral extent of this high-density layer is confined roughly to the Magdalen Basin. We suggest that this layer is due to mantle underplating of the crust as a result of the Carboniferous-age formation of the Magdalen Basin, and that it is not a feature related to the early to middle Paleozoic development of the Appalachian Orogen.

Download Full-text

Crustal thickness and velocity structure across the Moroccan Atlas from long offset wide-angle reflection seismic data: The SIMA experiment

Geochemistry Geophysics Geosystems ◽

10.1002/2013gc005164 ◽

2014 ◽

Vol 15 (5) ◽

pp. 1698-1717 ◽

Cited By ~ 25

Author(s):

P. Ayarza ◽

R. Carbonell ◽

A. Teixell ◽

I. Palomeras ◽

D. Martí ◽

...

Keyword(s):

Seismic Data ◽

Velocity Structure ◽

Crustal Thickness ◽

Wide Angle ◽

Reflection Seismic ◽

Long Offset

Download Full-text

Lateral variations of lunar crustal thickness from the Apollo seismic data set

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2005.12.017 ◽

2006 ◽

Vol 243 (1-2) ◽

pp. 1-14 ◽

Cited By ~ 62

Author(s):

H CHENET ◽

P LOGNONNE ◽

M WIECZOREK ◽

H MIZUTANI

Keyword(s):

Seismic Data ◽

Crustal Thickness ◽

Data Set ◽

Lateral Variations

Download Full-text

Crustal structure of the Volgo-Uralian subcraton revealed by inverse and forward gravity modeling

10.5194/se-2021-98 ◽

2021 ◽

Author(s):

Igor Ognev ◽

Jörg Ebbing ◽

Peter Haas

Keyword(s):

Crustal Structure ◽

Seismic Data ◽

Lower Crust ◽

Crustal Thickness ◽

Moho Depth ◽

Gravity Modeling ◽

Gravity Inversion ◽

Ural Mountains ◽

Satellite Gravity ◽

Crustal Model

Abstract. Volgo-Uralia is a Neoarchean easternmost part of the East European craton. Recent seismic studies of the Volgo-Uralian region provided new insights into the crustal structure of this area. In this study, we combine satellite gravity and seismic data in a common workflow to perform a complex study of Volgo-Uralian crustal structure which is useful for further basin analysis of the area. In this light, a new crustal model of the Volgo-Uralian subcraton is presented from a step-wise approach: (1) inverse gravity modeling followed by (2) 3D forward gravity modeling. First, inversion of satellite gravity gradient data was applied to determine the Moho depth for the area. Density contrasts between crust and mantle were varied laterally according to the tectonic units present in the region, and the model is constrained by the available active seismic data. The Moho discontinuity obtained from the gravity inversion was consequently modified and complemented in order to define a complete 3D crustal model by adding information on the sedimentary cover, upper crust, lower crust, and lithospheric mantle layers in the process of forward gravity modeling where both seismic and gravity constraints were respected. The obtained model shows crustal thickness variations from 32 to more than 55 km in certain areas. The thinnest crust with a thickness below 40 km is found beneath the Pericaspian basin, which is covered by a thick sedimentary layer. The thickest crust is located underneath the Ural Mountains as well as in the center of the Volga-Uralian subcraton. In both areas the crustal thickness exceeds 50 km. At the same time, initial forward gravity modeling has shown a gravity misfit of ca. 95 mGal between the measured Bouguer gravity anomaly and the forward calculated gravity field in the central area of the Volga-Uralian subcraton. This misfit was interpreted and modeled as a high-density lower crust which possibly represents underplated material. Our preferred crustal model of the Volga-Uralian subcraton respects the gravity and seismic constraints and reflects the main geological features of the region with Moho thickening in the cratons and under the Ural Mountains and thinning along the Paleoproterozoic rifts, Pericaspian sedimentary basin, and Pre-Urals foredeep.

Download Full-text