Subsurface geometry and structural evolution of La Gomera island based on gravity data

The hyper-extended Porcupine Basin, offshore southwest Ireland, is a component of the Eastern North Atlantic rifted continental margin. The basin developed following multiple rifting phases with different extension directions between the Late-Palaeozoic and the Cenozoic. The present-day north-south trend of the Porcupine Basin developed during the main Middle-Jurassic to Lower-Cretaceous rifting phase, which is interpreted to have overprinted earlier extension directions. In this study, we outline the tectono-stratigraphic architecture and the kinematics of the Porcupine Basin derived from seismic interpretation and fault analysis of multiple 2D and 3D seismic datasets.Our ongoing work identifies different fault networks with distinctive orientations and ages, confirming multiple rifting phases of the basin. The older faults identified strike NE/SW and offset the top of the Jurassic basement and the oldest syn-tectonic sequences. The younger faults strike N/S, offset the whole syn-tectonic stratigraphic sequence and bound the present-day tilted blocks of thinned continental crust. Interactions between these two main generations of faults created strong lateral variability in the geometry of the fault-bounded blocks. In addition, our interpretations highlight strong segmentation along the axis of the basin, evidenced by changes in the structural architecture of the faults along the flanks of the basin, and by rapid changes in the depth to the Jurassic basement from one segment to another. This segmentation occurs across several lineaments that are orthogonal to the main N-S direction of the tilted blocks observed along the flanks of the basin, and that are also observed in the central parts of the basin with gravity data and by the compartmentalisation of sedimentary depocenters. We interpret these lineaments as transfer zones that can be related to the kinematics of the basin. These zones may have accommodated either temporal or spatial changes in the directions of extension, or a stepped variation in E-W extension along the axis of the basin.Our results help to better understand the controls on the geometry and kinematics of fault systems within the Porcupine Basin, and to better evaluate the structural evolution of the Porcupine Basin and its significance in the broader context of the North Atlantic rifting.

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Constraining the geometry at depth of La Maladeta and Andorra-Mont Louis granites (Central Pyrenees) through gravity modelling

10.5194/egusphere-egu2020-5688 ◽

2020 ◽

Author(s):

Conxi Ayala ◽

Pilar Clariana ◽

Ruth Soto ◽

Joan Martí ◽

Aina Margalef ◽

...

Keyword(s):

Gravity Anomaly ◽

Cross Sections ◽

Gravity Data ◽

Gravity Modelling ◽

The North ◽

Geological Surveys ◽

Residual Gravity Anomaly ◽

Paleozoic Rocks ◽

Subsurface Geometry ◽

Central Pyrenees

In the Central Pyrenees, where density contrast between the Paleozoic rocks and the intruded granitic bodies is measurable, geological cross-sections constrained with gravity data help to unravel the subsurface geometry of the granites.With this goal in mind, during 2018 and 2019 several gravimetric surveys were carried out in the Central Pyrenees to improve the existent spatial resolution of the gravity data from the databases of the Spanish and Catalan Geological Surveys, especially in La Maladeta and Andorra Mont-Louis granites&#8217; area. After the gravity reductions, we obtained the Bouguer gravity anomaly from which we calculated the residual gravity anomaly by subtracting a third degree polynomial which represents the regional anomaly in agreement with the geometry of the crust in this region.The gravimetric response over La Maladeta and Andorra Mont-Louis granites is markedly dissimilar pointing out differences in the composition and geometry at depth of the two granites. La Maladeta granite shows a gravimetric zonation with small variations in its amplitude from one zone to the next, consistent with small lateral changes in its composition, predominantly granodioritic. By contrast, the Andorra Mont-Louis pluton is characterized by a relative minimum suggesting a more granitic composition.With respect to the inferred geometry at depth, the results obtained from gravity modelling show that the La Maladeta granite displays a laccolithic shape with its basal contact deeping to the North whereas the Andorra Mont-Louis granite has a more batholitic shape. Although the emplacement age of both granites is similar (Late Carboniferous &#8211; Early Permian), their different geometry at depth suggests that either (1) their emplacement mechanisms were different or (2) the subsequent Alpine orogeny affected both granites in different ways better preserving the original geometry of the Andorra Mont-Louis granite.

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Le filtrage des anomalies gravimetriques; une cle pour la comprehension des structures tectoniques du Boulonnais et de l'Artois (France)

BSGF - Earth Sciences Bulletin ◽

10.2113/172.3.267 ◽

2001 ◽

Vol 172 (3) ◽

pp. 267-274 ◽

Cited By ~ 28

Author(s):

Michel Everaerts ◽

Jean-Louis Mansy

Keyword(s):

Gravity Data ◽

Structural Evolution ◽

Spectral Domain ◽

Fault System ◽

Horizontal Gradient ◽

Published Data ◽

Vertical Derivative ◽

Transfer Zones ◽

New Interpretation ◽

First Vertical Derivative

Abstract The geology of the Boulonnais has been well studied since the early part of the last century [Gosselet and Bertaut, 1873; Olry, 1904; Pruvost and Delepine, 1921]. Extensive coal exploration added substantially to the general understanding of the geology of the region but as outcrop is poor, many questions remain. Gravity methods used in the analysis of geological structures have had a long and successful history in helping to study the earth's crust for scientific and applied objectives. Regional gravity data are particularly useful in mapping geographic distribution and configuration of density contrast of rocks. Previous gravity research shows the main trends of the structure. In most cases the regional Bouguer gravity hides the relationship between the geology and the shape of the anomaly caused by the perturbing body. New information can be obtained by filtering the maps. The purpose of filtering a map is to remove unwanted characteristics and enhance desirable characteristics that are diagnostic for the geology. Because of their simple mathematical forms, most potential field filters are in the spectral domain. It is advisable to transform the original unfiltered field to the spectral domain, apply the filter, then transform the filtered map back to the spatial domain for use in the interpretation. Several spectrally filtered versions of the original gravity map are used in this regional interpretation. In the case of the Boulonnais the most useful filters have been the horizontal component and the first vertical derivative. In the first instance computing the horizontal gradients of the gravity field permits us to localise the limit of the blocks and then the fault positions. The gravimetric field above a vertical contact of rock with different density shows a low on the side of the low density rocks and a high on the side of the high density rocks. The inflection point is located just on the contact of the two types of rocks. This contact can be outlined by locating the maxima of the horizontal gradient. In the case of a low dipping contact maxima stay close to the contact, but are displaced down dip. In the second instance the first vertical derivative acts as a booster for the short wavelength; this attenuates or destroys the effect of the regional field. The resulting map shows a better structure because in complex areas they give a better definition of the different bodies by separating their effects. In the case of the Boulonnais the first vertical derivative allows us to distinguish the depressed region from the uplifted one. The structural evolution of the Boulonnais-Artois area includes two main extensional events in the late Palaeozoic-early Cretaceous interval and an inversion in mid-late Palaeocene time. The new gravity data in combination with recent field and published data have provided a new insight into the structure of the Boulonnais-Artois area and a new interpretation is proposed. -- Fault patterns are oriented 110N and 040N in the Boulonnais and 140N in Artois areas. -- The linkage between the faults shows a relay geometry with transfer zones [cf. Morley et al., 1990 and Pea-cock and Sanderson, 1994]. The best example is located between Sangatte (near the tunnel) and Landrethun faults where overlapping synthetic faults with a relay ramp are imaged. -- There is no major continuous fault zone but a complex en echelon fault system. -- Linkage between Boulonnais and Artois fault is not well constrained. An important discontinuity between the two regions is apparent. This model underlines the importance of overlapping fault tips with the generation of transfer zones. These structures are also known in the Wessex and Weald basins [Stoneley, 1982; Chadwick, 1993] where heritage and inversion are significant.

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Microstructure and reactivity of small metal particles: The role of Ce additives

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100121995 ◽

1992 ◽

Vol 50 (1) ◽

pp. 318-319

Author(s):

L.D. Schmidt ◽

K. R. Krause ◽

J. M. Schwartz ◽

X. Chu

Keyword(s):

Atmospheric Pressure ◽

Noble Metals ◽

Mixed Oxides ◽

Catalytic Properties ◽

Chemical Shifts ◽

Catalytic Converter ◽

Structural Evolution ◽

Single Particles ◽

Small Metal Particles

The evolution of microstructures of 10- to 100-Å diameter particles of Rh and Pt on SiO2 and Al2O3 following treatment in reducing, oxidizing, and reacting conditions have been characterized by TEM. We are able to transfer particles repeatedly between microscope and a reactor furnace so that the structural evolution of single particles can be examined following treatments in gases at atmospheric pressure. We are especially interested in the role of Ce additives on noble metals such as Pt and Rh. These systems are crucial in the automotive catalytic converter, and rare earths can significantly modify catalytic properties in many reactions. In particular, we are concerned with the oxidation state of Ce and its role in formation of mixed oxides with metals or with the support. For this we employ EELS in TEM, a technique uniquely suited to detect chemical shifts with ∼30Å resolution.

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The Structural Evolution of Morality

10.1017/cbo9780511550997 ◽

2007 ◽

Cited By ~ 59

Author(s):

J. McKenzie Alexander

Keyword(s):

Structural Evolution ◽

Evolution Of Morality

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Electrodeposition of Strained-Layer Superlattices

MRS Proceedings ◽

10.1557/proc-451-413 ◽

1996 ◽

Vol 451 ◽

Cited By ~ 8

Author(s):

T. P. Moffat

Keyword(s):

Charge Transfer ◽

Mass Transport ◽

Structural Evolution ◽

Iron Group ◽

Morphological Instability ◽

Group Metal ◽

Iron Group Metal ◽

Transport Control ◽

Strained Layer Superlattices ◽

Interfacial Charge

ABSTRACTA variety of Cu/(Ni, Co) multilayers have been grown on Cu single crystals by pulse plating from an alloy electroplating bath. Copper is deposited under mass transport control while the iron group metal is deposited under interfacial charge transfer control. The structural evolution of these films is influenced by the morphological instability of the mass transport limited copper deposition reaction and the development of growth twins during iron-group metal deposition. Specular films have been obtained for growth on Cu(100) while rough, defective films were typically obtained for growth on Cu(111) and Cu(110).

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Pattern Formation in Thin Polymer Films: A New Morphology

MRS Proceedings ◽

10.1557/proc-629-ff1.2 ◽

2000 ◽

Vol 629 ◽

Author(s):

Jean-Loup Masson ◽

Peter F. Green

Keyword(s):

Growth Rate ◽

Pattern Formation ◽

Early Stage ◽

Structural Evolution ◽

Distinct Form ◽

Thin Polymer Films ◽

Intermediate Morphology ◽

Thin Polymer ◽

Nonwetting Liquid ◽

Cylindrical Holes

ABSTRACTResearchers have shown that thin, nonwetting, liquid homopolymer films dewet substrates, forming patterns that reflect fluctuations in the local film thickness. These patterns have been shown to be either discrete cylindrical holes or bicontinuous “spinodal-like” patterns. In this paper we show the existence of a new morphology. During the early stage of dewetting, discrete highly asymmetric holes appear spontaneously throughout the film. The nucleation rate of these holes is faster than their growth rate. The morphology of the late stage of evolution, after 18 days, is characterized by a bicontinuous pattern, distinct form conventional spinodal dewetting patterns. This morphology has been observed for a range of film thicknesses between 7.5 and 21nm. The structural evolution of this intermediate morphology is discussed.

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