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

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.

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

Solid Earth ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 1515-1547
Author(s):  
Puy Ayarza ◽  
José Ramón Martínez Catalán ◽  
Ana Martínez García ◽  
Juan Alcalde ◽  
Juvenal Andrés ◽  
...  
Keyword(s):  
Lower Crust ◽  
Normal Incidence ◽  
Crustal Thickness ◽  
P Wave ◽  
Iberian Massif ◽  
Velocity Increase ◽  
P Wave Velocity ◽  
Asymptotic Geometry ◽  
Surface Geology ◽  
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, along with surface geology, unraveling their evolution. In this paper we present the most complete transect, to date, 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 the data 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 the 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 into the evolution of the orogen (i.e., of the magnitude of compression and the effects and extent of later-Variscan gravitational collapse). Moreover, the limited thickness of the lower crust below, in central and northwestern Iberia, might have constrained the response of the Iberian microplate to Alpine shortening. Here, this discontinuity, featuring a Vp (P-wave velocity) increase, is observed as an orogen-scale boundary with characteristics compatible with those of the globally debated Conrad discontinuity.

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

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.

Petroleum Systems Analysis of The Tungkal PSC Area, South Sumatra – A Means of Adding New Life to A Mature Area

2020 ◽  
Author(s):  
A. Livsey
Keyword(s):  
Seismic Data ◽  
Systems Analysis ◽  
Generation Model ◽  
Hydrocarbon Accumulation ◽  
Petroleum Systems ◽  
Oil Generation ◽  
Exploration Risk ◽  
Exploration Area ◽  
Hydrocarbon Charge ◽  
Surface Geology

South Sumatra is considered a mature exploration area, with over 2500MMbbls of oil and 9.5TCF of gas produced. However a recent large gas discovery in the Kali Berau Dalam-2 well in this basin, highlights that significant new reserve additions can still be made in these areas by the re-evaluation of the regional petroleum systems, both by identification of new plays or extension of plays to unexplored areas. In many mature areas the exploration and concession award history often results in successively more focused exploration programmes in smaller areas. This can lead to an increased emphasis on reservoir and trap delineation without further evaluation of the regional petroleum systems and, in particular, the hydrocarbon charge component. The Tungkal PSC area is a good example of an area that has undergone a long exploration history involving numerous operators with successive focus on block scale petroleum geology at the expense of the more regional controls on hydrocarbon prospectivity. An improved understanding of hydrocarbon accumulation in the Tungkal PSC required both using regional petroleum systems analysis and hydrocarbon charge modelling. While the Tungkal PSC operators had acquired high quality seismic data and drilled a number of wells, these were mainly focused on improving production from the existing field (Mengoepeh). More recent exploration-driven work highlighted the need for a new look at the hydrocarbon charge history but it was clear that little work had been done in the past few year to better understand exploration risk. This paper summarises the methodology employed and the results obtained, from a study, carried out in 2014-15, to better understand hydrocarbon accumulation within the current Tungkal PSC area. It has involved integration of available well and seismic data from the current and historical PSC area with published regional paleogeographic models, regional surface geology and structure maps, together with a regional oil generation model. This approach has allowed a better understanding of the genesis of the discovered hydrocarbons and identification of areas for future exploration interest.

scholarly journals Two-step obduction of the Porvenir serpentinites: A cryptic Devonian suture in SW Iberian Massif (Ossa-Morena Complex)

2021 ◽  
Author(s):  
Rubén Díez Fernández ◽  
Jerónimo Matas ◽  
Ricardo Arenas ◽  
Luis Miguel Martín-Parra ◽  
Sonia Sánchez Martínez ◽  
...  
Keyword(s):  
Continental Crust ◽  
Upper Mantle ◽  
Suture Zone ◽  
Lower Plate ◽  
Late Devonian ◽  
Iberian Massif ◽  
Step Process ◽  
Nw Iberia ◽  
Thrust System ◽  
Tectonic Slice

ABSTRACT The Porvenir serpentinites are an ∼600-m-thick body of meta-peridotites exposed in SW Iberia (Variscan Orogen). The serpentinites occur as a horse within a Carboniferous, out-of-sequence thrust system (Espiel thrust). This thrust juxtaposes the serpentinites and peri-Gondwanan strata onto younger peri-Gondwanan strata, with the serpentinites occupying an intermediate position. Reconstruction of the pre-Espiel thrust structure results in a vertical juxtaposition of terranes: Cambrian strata below, Porvenir serpentinites in the middle, and the strata at the footwall to the Espiel thrust culminating the tectonic pile. The reconstructed tectonic pile accounts for yet another major thrusting event, since a section of upper mantle (Porvenir serpentinites) was sandwiched between two tectonic slices of continental crust (a suture zone sensu lato). The primary lower plate to the suture is now overlying the upper plate due to the Espiel thrust. Lochkovian strata in the upper plate and the Devonian, NE-verging folds in the lower plate suggest SW-directed accretion of the lower plate during the Devonian, i.e., Laurussia-directed underthrusting for the closure of a Devonian intra-Gondwana basin. Obduction of the Porvenir serpentinites was a two-step process: one connected to the development of a Devonian suture zone, and another related to out-of-sequence thrusting that cut the suture zone and brought upward a tectonic slice of upper mantle rocks hosted in that suture. The primary Laurussia-dipping geometry inferred for this partially obducted suture zone fits the geometry, kinematics, and timing of the Late Devonian suture zone exposed in NW Iberia and may represent the continuation of such suture into SW Iberia.

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

2020 ◽  
Vol 11 (1) ◽  
pp. 18-30
Author(s):  
Franck Eitel Kemgang Ghomsi ◽  
Robert Tenzer ◽  
Sévérin Nguiya ◽  
Animesh Mandal ◽  
Robert Nouayou
Keyword(s):  
Seismic Data ◽  
Crustal Thickness

Global Crustal Thickness and Velocity Structure From Geostatistical Analysis of Seismic Data

2019 ◽  
Vol 124 (2) ◽  
pp. 1626-1652 ◽  
Author(s):  
Wolfgang Szwillus ◽  
Juan Carlos Afonso ◽  
Jörg Ebbing ◽  
Walter D. Mooney
Keyword(s):  
Seismic Data ◽  
Velocity Structure ◽  
Crustal Thickness ◽  
Geostatistical Analysis

RELATION OF SEISMIC CORRECTIONS TO SURFACE GEOLOGY

Geophysics ◽  
1952 ◽  
Vol 17 (2) ◽  
pp. 218-228 ◽  
Author(s):  
H. M. Thralls ◽  
R. W. Mossman
Keyword(s):  
Seismic Data ◽  
Reference Plane ◽  
Illinois Basin ◽  
Low Velocity ◽  
Near Surface ◽  
Low Velocity Layer ◽  
Surface Geology ◽  
Velocity Layer ◽  
Layer Problem

The arbitrary application of any set type of near‐surface corrections to seismic data can lead to erroneous results. The determination of the type of correction to be used must be based, in part, on the type of formations present in the near‐surface. Case studies are offered to illustrate conditions arising in areas of youthful and mature topography. Specifically, they deal with a complex low velocity layer problem in a river valley, a pre‐glacial topography in the Illinois Basin, a problem arising in a mature topography in Kansas, and a youthful topography in central Wyoming. In such cases, the use of a “floating” elevation reference plane is advocated for the “Correction Zone” lying immediately below the surface.

Features of the crust-mantle structure of Himalayas-Tibet: a comparison with seismic traverses of Alpine, Pyrenean and Variscan orogenic belts

1988 ◽  
Vol 326 (1589) ◽  
pp. 17-32 ◽  
Keyword(s):  
High Resolution ◽  
Crustal Structure ◽  
Upper Mantle ◽  
Seismic Data ◽  
Lower Crust ◽  
Mantle Structure ◽  
Tectonic Features ◽  
Orogenic Belts

Seismic data able to resolve the crustal structure are limited in quantity and quality with respect to the size and complexity of Tibet—Himalayas. They may be interpreted as indicating a strong heterogeneity: lack of continuity of even major interfaces across strike, defining different crustal blocks, but also lack of continuity of surface tectonic features down through the whole lithosphere. A thickening by imbrication of both the upper crustal and the lower crust-upper mantle levels is suggested. Indications from recent high-resolution surveys in other domains of thickened crust are also of a less smooth geometry of structures and depth than intuitively considered.

The variation of crustal thickness across the Swiss Alps based on gravity and explosion seismic data

1976 ◽  
Vol 114 (3) ◽  
pp. 479-494 ◽  
Author(s):  
H. G. Kahle ◽  
E. Klingele ◽  
St. Mueller ◽  
R. Egloff
Keyword(s):  
Seismic Data ◽  
Crustal Thickness ◽  
Swiss Alps
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