| 1. |
-
- 2019
-
Tidskriftsartikel (refereegranskat)
|
|
| 2. |
- Burchardt, Steffi, et al.
(författare)
-
Ardnamurchan 3D cone-sheet architecture explained by a single elongate magma chamber
- 2013
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 3, s. 2891-
-
Tidskriftsartikel (refereegranskat)abstract
- The Palaeogene Ardnamurchan central igneous complex, NW Scotland, was a defining place for the development of the classic concepts of cone-sheet and ring-dyke emplacement and has thus fundamentally influenced our thinking on subvolcanic structures. We have used the available structural information on Ardnamurchan to project the underlying three-dimensional (3D) cone-sheet structure. Here we show that a single elongate magma chamber likely acted as the source of the cone-sheet swarm(s) instead of the traditionally accepted model of three successive centres. This proposal is supported by the ridge-like morphology of the Ardnamurchan volcano and is consistent with the depth and elongation of the gravity anomaly underlying the peninsula. Our model challenges the traditional model of cone-sheet emplacement at Ardnamurchan that involves successive but independent centres in favour of a more dynamical one that involves a single, but elongate and progressively evolving magma chamber system.
|
|
| 3. |
- Cheraghi, Saeid, et al.
(författare)
-
Seismic imaging across fault systems in the Abitibi greenstone belt : an analysis of pre- and post-stack migration approaches in the Chibougamau area, Quebec, Canada
- 2021
-
Ingår i: Solid Earth. - : Copernicus Publications. - 1869-9510 .- 1869-9529. ; 12:5, s. 1143-1164
-
Tidskriftsartikel (refereegranskat)abstract
- Two high-resolution seismic reflection profiles acquired north and south of Chibougamau, located in the northeast of the Abitibi subprovince of Canada, help understand historic volcanically hosted massive sulfide (VMS) deposits and hydrothermal Cu-Au mineralization found there. Major faults crossed by the profiles include the Barlow fault in the north and the Doda fault and the Guercheville fault in the south, all targets of this study that seeks to determine spatial relationships with a known metal endowment in the area. Common-offset DMO corrections and common-offset pre-stack time migrations (PSTMs) were considered. Irregularities of the trace midpoint distribution resulting from the crooked geometry of both profiles and their relative contribution to the DMO and PSTM methods and seismic illumination were assessed in the context of the complex subsurface architecture of the area. To scrutinize this contribution, seismic images were generated for offset ranges of 0-9 km using increments of 3 km. Migration of out-of-plane reflections used cross-dip element analysis to accurately estimate the fault dip. The seismic imaging shows the thickening of the upper-crustal rocks near the fault zones along both profiles. In the northern seismic reflection section, the key geological structures identified include the Barlow fault and two diffraction sets imaged within the fault zone that represent potential targets for future exploration. The south seismic reflection section shows rather a complicated geometry of two fault systems. The Guercheville fault observed as a subhorizontal reflector connects to a steeply dipping reflector. The Doda fault dips subvertical in the shallow crust but as a steeply dipping reflection set at depth. Nearby gold showings suggest that these faults may help channel and concentrate mineralizing fluids.
|
|
| 4. |
- Gaborit, Mathieu
(författare)
-
Modelling strategies for thin imperfect interfaces and layers
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The global trend towards quieter environments has been one of the key topics of acoustics research for years. The recent tightening of the regulations on noise exposure as well as the many reports on the impact of noise on human health confirm this situation and stress ever more the need for innovative mitigation strategies. Numerous efforts from many teams allowed to refine existing solutions and explore new approaches towards a lower noise level ultimately leading to a number of promising concepts. Central to this field, the use of poroelastic media and the development of realistic meta-materials are paving the way to tackle the problem. In the meantime, a great part of the most widely adopted systems to mitigate noise, such as acoustics panels for instance, resort to thin resistive screens placed on the surface to protect the bulk and control the properties. Despite often being one of the thinnest components of the systems, they have a non-negligible impact on the overall response and are subject to a number of uncertainties.The approach chosen in this thesis differs from the global trend of designing new solutions and conversely relies on investigating the effect of uncertainties inherent to all these sound proofing systems. More precisely, the work performed focuses on modelling the impact of uncertain interfaces and uncertain parameters in the thin layers used as protective, tuning or aesthetic elements. These acoustic films, and to a certain extent the thin interface zones resulting from the assembly process, are notably challenging to characterise with precision. The main goal of this thesis is then to propose strategies to account for uncertainties on the parameters of the films and interfaces and predict their impact on the overall response of the systems.Three different scientific contributions are presented in this thesis. Together they discuss modelling aspects related to the films, propose possible simplifications and demonstrate the effect of parameter uncertainties. Finally they introduce numerical strategies to efficiently account for uncertainties in computations within the context of poroelastic and meta-poroelastic media.
|
|
| 5. |
- Mathieu, Lucie, et al.
(författare)
-
Dykes, cups, saucers and sills : analogue experiments on magma intrusion into brittle rocks
- 2008
-
Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 271:1-4, s. 1-13
-
Tidskriftsartikel (refereegranskat)abstract
- Magma is transported in the crust by blade-like intrusions such as dykes, sills, saucers, and also collects in thicker laccoliths, lopoliths and plutons. Recently, the importance and great number of shallow (< ;5 km) saucer-shaped intrusions has been recognized. Lopoliths and cup-shaped intrusions have also been reported in many geological contexts. Our field observations indicate that many intrusions, especially those emplaced into breccias or fractured rocks, have bulging, lobate margins and have shear faults at their bulbous terminations. Such features suggest that magma can propagate along a self-induced shear fault rather than a hydraulic tension-fracture. To investigate this we use analogue models to explore intrusion propagation in a brittle country rock. The models consist of the injection of analogue magma (honey or Golden syrup) in a granular material (sand or sieved ignimbrite) that is a good analogue for brittle or brecciated rocks. These models have the advantage (over other models that use gelatin) to well represent the properties of brittle materials by allowing both shear-faults and tension fractures to be produced at suitable stresses. In our experiments we mainly obtain vertical dykes and inverted-cone like structures that we call cup-shaped intrusions. Dykes bifurcate into cup-shaped intrusions at depths depending on their viscosity. All cup-shaped intrusions uplift a central block. By injecting against a vertical glass plate we obtain detailed observations of the intrusion propagation style. We observe that dykes commonly split and produce cup-shaped intrusions near the surface and that shear zone-related intrusions develop at the dyke tip. We conclude that many dykes propagate as a viscous indenter resulting from shear failure of host rock rather than tensional hydraulic fracturing of host rocks. The shear propagation model provides an explanation for the shape and formation of cup-shaped intrusions, saucer-sills and lopoliths.
|
|
| 6. |
- Mathieu, Lucie, et al.
(författare)
-
Geological constraints on the dynamic emplacement of cone-sheets - The Ardnamurchan cone-sheet swarm, NW Scotland
- 2015
-
Ingår i: Journal of Structural Geology. - : Elsevier BV. - 0191-8141 .- 1873-1201. ; 80, s. 133-141
-
Tidskriftsartikel (refereegranskat)abstract
- Cone-sheets are a significant constituent of many central volcanoes, where they contribute to volcano growth by intrusion and through flank eruptions, although the exact emplacement mechanisms are still controversially discussed. In particular, it is not yet fully resolved whether cone-sheets propagate as magma-driven, opening-mode fractures or as shear fractures, and to what extent pre-existing host-rock structures and different stress fields influence cone-sheet emplacement. To shed further light on the role of these parameters in cone-sheet emplacement, we use detailed field and remote sensing data of the classic Ardnamurchan cone-sheet swarm in NW-Scotland, and we show that the cone-sheets primarily propagated as opening-mode fractures in the sigma(1)-sigma(2) plane of the volcanic stress field. In addition, more than one third of the Ardnamurchan cone-sheet segments are parallel to lineaments that form a conjugate set of NNW and WNW striking fractures and probably reflect the regional NW SE orientation of sigma(1) during emplacement in the Palaeogene. Cone-sheets exploit these lineaments within the NE and SW sectors of the Ardnamurchan central complex, which indicates that the local volcanic stress field dominated during sheet propagation and only allowed exploitation of host-rock discontinuities that were approximately parallel to the sheet propagation path. In addition, outcrop-scale deflections of cone-sheets into sills and back into cone-sheets (also referred to as "staircase" geometry) are explained by the interaction of stresses at the propagating sheet tip with variations in host-rock strength, as well as the influence of sheet-induced strain. As a consequence, cone-sheets associated with sill-like segments propagate as mixed-mode I/II fractures. Hence, cone-sheet emplacement requires a dynamic model that takes into account stress fields at various scales and the way propagating magma interacts with the host rock and its inherent variations in rock strength.
|
|
| 7. |
- Mathieu, Lucie, et al.
(författare)
-
The interaction between volcanoes and strike-slip, transtensional and transpressional fault zones : Analogue models and natural examples
- 2011
-
Ingår i: Journal of Structural Geology. - : Elsevier BV. - 0191-8141 .- 1873-1201. ; 33:5, s. 898-906
-
Tidskriftsartikel (refereegranskat)abstract
- Regional strike-slip faulting can control magma movements, deform volcanoes and may destabilise their flanks. The aim of this study is to address this problem by comparing two natural examples, Basse Terre Island volcanoes, Lesser Antilles and Maderas volcano, Nicaragua, with analogue experiments. The field and remote sensing analyses of their structures reveal that Guadeloupe volcanoes, which developed in a 145 degrees-striking sinistral transtensional fault zone, are dominantly fractured in a 090 degrees-120 degrees direction, which is parallel to the maximum principal horizontal stress and to the elongation direction of the summit graben of analogue models. This graben is bordered by the Sigmoid-I fault, or Y shear structure, and has facilitated the formation of the Beaugendre and Vieux-Habitants valleys by faulting, erosion or collapse. This structure has also influenced the injection of dykes and the transport of hydrothermal fluids. The comparison of Maderas volcano with the analogue models confirms that the volcano has developed parallel to a 135 degrees-striking dextral transtensional fault zone and is also gravitationally spreading over a weak substratum. This study illustrates how regional strike-slip faulting and gravitational loading combine to produce a clear set of structures within volcanic edifices, which control the location of intrusive zones, hydrothermal activity and collapse directions.
|
|
| 8. |
- Mathieu, Lucie, et al.
(författare)
-
The structure and morphology of the Basse Terre Island, Lesser Antilles volcanic arc
- 2013
-
Ingår i: Bulletin of Volcanology. - : Springer Science and Business Media LLC. - 0258-8900 .- 1432-0819. ; 75:3, s. 700-
-
Tidskriftsartikel (refereegranskat)abstract
- Basse Terre Island is made up of a cluster of composite volcanoes that are part of the Lesser Antilles volcanic arc. The morphology of these volcanoes and the onshore continuation of the grabens and strike-slip faults that surround the island are poorly documented due to erosion and rainforest cover. Therefore, we conducted a morphological analysis of the island using Digital Elevation Model (DEM) data integrated with field observations to document erosional, constructional, and deformational processes. A DEM-based analysis of 1,249 lineaments and field structural measurements of 16 normal faults, 3,741 veins and fractures, and 46 dykes was also carried to document the structures that predominate in sub-surface rocks. The results indicate that the over 1-My-old and elongated Northern Chain volcano, which makes up the northern half of the island, was built by high eruption rates and/or a low viscosity magma injected along the N-S to NNW-SSE-striking extensional structures formed by the flexure of the lithosphere by the overall subduction regime. After 1 Ma, the southern half of the island was shaped by an alignment of conical volcanoes, likely built by a more viscous magma type that was guided by the NW-SE-striking Montserrat-Bouillante strike-slip fault system. These N to NNW and NW structural directions are however poorly expressed onshore, possibly due to slow slip motion. The sub-surface rocks mostly contain E-W-striking structures, which have likely guided the many flank instabilities documented in the studied area, and guide hydrothermal fluids and shallow magmatic intrusions. These structures are possibly part of the E-W-striking Marie-Gallante offshore graben.
|
|
| 9. |
- Rosser, Neil, et al.
(författare)
-
Hybrid speciation driven by multilocus introgression of ecological traits
- 2024
-
Ingår i: Nature. - 0028-0836. ; 628, s. 811-817
-
Tidskriftsartikel (refereegranskat)abstract
- Hybridization allows adaptations to be shared among lineages and may trigger the evolution of new species1,2. However, convincing examples of homoploid hybrid speciation remain rare because it is challenging to demonstrate that hybridization was crucial in generating reproductive isolation3. Here we combine population genomic analysis with quantitative trait locus mapping of species-specific traits to examine a case of hybrid speciation in Heliconius butterflies. We show that Heliconius elevatus is a hybrid species that is sympatric with both parents and has persisted as an independently evolving lineage for at least 180,000 years. This is despite pervasive and ongoing gene flow with one parent, Heliconius pardalinus, which homogenizes 99% of their genomes. The remaining 1% introgressed from the other parent, Heliconius melpomene, and is scattered widely across the H. elevatus genome in islands of divergence from H. pardalinus. These islands contain multiple traits that are under disruptive selection, including colour pattern, wing shape, host plant preference, sex pheromones and mate choice. Collectively, these traits place H. elevatus on its own adaptive peak and permit coexistence with both parents. Our results show that speciation was driven by introgression of ecological traits, and that speciation with gene flow is possible with a multilocus genetic architecture.
|
|
