Geolunch seminar @ UiB

Eirik Wiese, Felix Halpaap, Ronny Tømmerbakke, Sebastian Wolf
2016-11-02 12:00 - 13:00 (Europe/Oslo) | Glassburet, Allegaten 41, Bergen, Norway
Raiders of the Lost Arc
by Eirik Wiese, Felix Halpaap, Ronny Tømmerbakke, Sebastian Wolf
Abstract: In this more or less scientific geolunch, we present geological and some sociocultural revelations from our field trip to the Brasilia belt in southern Minas Gerais state in Brazil in September. In the frame of an educational collaboration between the Universities of Bergen, Rio de Janeiro and Saõ Paulo, we (four students and Indiana Fossen) participated in this 5th summer school of the “Integrated Orogen – Sedimentary Basin Studies” series. We introduce you to the large-scale geodynamic setting of southeastern Brazil and show features and lessons that we learned along three transects in the field. The geological setting of old orogens like the Brasilia belt and the passive margin along Brazil’s east is similar to the setting we find in Norway. We can thus discuss similarities and differences related to e.g. exhumation of subducted rocks, topography evolution and many more. This talk will be full of images, so bring your lunch, enjoy the journey and help us answer the geological questions that we brought back together with several kilograms of coffee!

Gang Lu
2016-10-26 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Potential temperature and margin width control melt volume at rifted margins
Gang Lu and Ritske S. Huismans

Passive continental margins may have a wide variety of structural and magmatim styles, but the controlling factors of magmatism remain controversial. Common explanations attribute the variation of magmatism to the change of mantle temperature, and associate volcanic margins to high temperature mantle plumes. However, this interpretation has been challenged due to the lack of evidences of plume tracks at some volcanic margins. Furthermore, anomalously low mantle temperature is required for non-volcanic margins, which is too low to produce normal oceanic crust. Here we use numerical models to investigate melt generation for margins with realistic rifting styles. Our results demonstrate a surprising correlation of enhanced magmatism with wide margin. This relationship is explained by the dynamic process of differential rifting, in which the lithospheric mantle ruptures earlier than the crust. On the basis of differential rifting, we derive an analytical prediction of melt volume over margin width, which is in agreement with both numerical results and nature observations. The new mechanism proposed here provides an alternative interpretation for enhanced magmatism, and suggests that mantle temperature at wide volcanic margins was probably over-estimated.

Hamed Khani
2016-10-19 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Pre-Mesozoic structural configuration in the northern North Sea rift basin; as a result of Devonian orogenic collapse in the Scandinavian-Scottish Caledonides
The northern North Sea rift basin is a product of multiple rifting phases during the Mesozoic time, developed on the heterogeneous crust comprising preexisting structures inherited from the Caledonian Orogeny and the Devonian post orogenic collapse. Pre-Mesozoic structural configuration and the basement rock distribution in the northern North Sea area has been investigated by an integration of more than 200,000 km² two dimensional regional seismic reflection data and more than 75 basement wells. Four main seismic facies has been described below the top acoustic basement surface and has been utilized to consistently map the seismic reflection patterns in the study area. Thick (500-1000 ms) high amplitude dipping reflection packages interpreted as offshore extensional shear zones that has been linked to the northwest and west dipping (towards the hinterland) onshore shear zones in the southwestern Norway including the Nord-Sogn Detachment Zone (NSDZ), Bergen Arc, Hardangerfjord, Karmøy and Stavanger Shear Zones (BASZ, HSZ, KSZ and SSZ respectively). However, several east and west dipping structures has also been mapped in the Måløy Slope, East Shetland Basin, East Shetland Platform and around the Utsira High and Åsta Graben. These structures shows the development of both foreland and hinterland dipping shear zones in the northern North Sea area, while towards the margin of the orogenic belt in the SW Norway and NE offshore Scotland only hinterland dipping structures have been developed. These pre-rifting structures seem to exert a first order control on the geometry and the development of the northern North Sea rift basin.

Christian Haug Eide
2016-10-12 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Tana – a very old river: Linking an Early Triassic delta to antecedent topography

The Fennoscandian Barents Sea Margin has been subject to little tectonic activity since the Carboniferous, and large portions have eluded significant Quaternary glacial erosion. Published fission track data indicate little denudation since the late Permian-Early Triassic. It may therefore be one of the most geologically stable margins on Earth, and it is therefore likely that catchments in the region could contain elements inherited from ancient catchments.

The catchment of the Tana River has long been interpreted to show features indicating that it was developed prior to present-day topography (Fig. 1A). A large delta-system that prograded from the present-day mouth of the Tana River during the Early Triassic, is visible in seismic data from the Finnmark Platform. In this study, we demonstrate that the present day Tana River Catchment shows several geomorphic evidence of having survived since the Earliest Triassic, that the studied Triassic delta was sourced from the present-day mouth of the Tana catchment, and that the post-Triassic modification of this catchment has been relatively small. We thus make the case that the present-day Tana catchment was formed close to the Permian-Triassic boundary.

This is important for explorationists because it demonstrates that reservoir properties in the Triassic of the Barents Sea are strongly influenced by catchment properties and sediment transport networks. Source-to-sink techniques can thus be instrumental in predicting extent and quality of subsurface reservoirs. Triassic strata in the Barents Sea generally show more favorable reservoir properties close to the Fennoscandian shield. This is because the majority of the basin fill was supplied through a vast fluvial system from the Uralian Orogen, and these sediments make up the bulk of the Triassic sedimentary package. Smaller catchments along the Fennoscandian margin supplied more mature shield-derived sediment to the basin margins only. Understanding these ancient catchments will help inform and constrain the amount of high-quality sand supplied from the shield to the basin through time.

Wenlu Zhu (UMD)
2016-10-05 13:00 - 14:00
Title: Reaction-induced cracking during mineral carbonation: Evidence from time-resolved microtomography

Laurent Montési (UMD)
2016-10-05 12:00 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Melt extraction processes and speed at mid-ocean ridges

Jhon Munoz-Barrera
2016-09-28 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Subsurface characterization of structural traps in the outer Nunchia foothills, Colombia.
The foothills have been focus of several researches because (1) in their sediments are recorded the uplift history of the mountain belts, (2) these areas accommodate the regional shortening, and (3) these zones are highly prospective for hydrocarbon exploration. Usually in these areas the structural models are generated based on surface geology, 2D seismic and exploratory wells. After a discovery, the models are updated using 3D seismic, development wells and production history.
The Eastern foothill of the Eastern Cordillera of Colombia is highly explored by its hydrocarbon potential. Based on some transverse zones and changes in structural styles it have been divided in three zones (Bayona et al., 2008; Cortés et al., 2006 and Cortés et al., 2009) Northern, Central and Southern Llanos Foothills (Figures 1 and 2). The Central Llanos Foothill is the most prospective zone with more than 3000MMOB of original reserves tested. Eight oil fields are situated in this zone; in the south: Cusiana, Cupiagua, Pauto Complex (Pauto, Floreña, Volcanera and Dele) and Huron oil fields and in the north the Capachos oil field. Between these two areas a region of 130km has been explored without success. Informally this region is composed by the Nunchia and Zamaricote foothills (figure 1). Two important geological features can be highlighted in this region, first the Eastern Cordillera changes its direction from N30E to N-S and second, the presence of new thrust salient that keeps the N30E direction and is composed by the Piedemonte fault system. The area have been interpreted as thin-skinned (Rochat et al. 2003) to thick-skinned (Teson et al, 2013) with some variations between them (Cediel et al; Munoz 2015). Rochat et al. (2003) divided the Nunchia foothills in two main regions, internal and external structure (Figure 2).
This work used 533.5Km2 of an exploratory 3D seismic acquired with sparse design, 511Km of 2D seismic, two exploratory wells and surficial geological information located in the Nunchia outer foothills (Figure 1) to (1) recognize the geometry of the structures, (2) identify the variability of the structures along strike, (3) identify which structures involve the reservoir rocks, and (4) define the structural style.
This research presents the first 3D exploratory structural model of the Nunchía outer Foothills. An integration of surface geology, 2D and 3D seismic and well information in ArcGis and Petrel software allowed the surface analysis, seismic interpretation and well correlation. Additionally, the interpretation was exported to Move software to build the structural model and generate the displacement analysis. This tool allowed the identification of interpretation problems. The model was created in time domain because the study area had only two exploratory well separated 3.4km in the dip direction.
The end-member of the Nunchia Foothills can be classified as active-roof duplex, characterized by a thin-skinned structural style. In this zone, the shortening is accommodated in a series of imbricate to duplex structures with different detachment levels. Therefore, this area can be divided in three zones: 1) basal structures, defined as structures that have the lower detachment in the Gachetá Formation; 2) intermediate structures, with detachment in both C-8 (Lower Carbonera Formation) and C-6 (Middle Carbonera Formation), and; 3) upper to surface structures with detachment level in C-2 (Upper Carbonera Formation). Along strike the Nunchía outer foothill become deeper to the north and the distance between the inner antiformal stack and outer imbricate region widens. The well correlation between the foreland and foothills sequence allowed interpreting that the Carbonera, León and Guayabo formations are syn-deformation deposits, with lateral thickness variation, increasing to the west and to the north.
Only the basal structures involve the reservoir rocks. Two structures were identified. The southern structure, Tangara, is a water bearing structure and the northern structure is untested with remain oil prospectivity.

Melanie Siegburg (U. of Southampton)
2016-09-14 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Geological Evolution of Boset-Bericha Volcanic Complex, Ethiopia, northern East African Rift
Continental rifting and break up is accompanied by tectonism and magmatism that varies over time in the Main Ethiopian Rift (MER) at the northern part of the East African rift. The Boset-Bericha volcanic complex (BBVC) is one of the largest stratovolcano complex in the MER, but little is known about the eruptive history, despite the fact that 4 million people live within 100 km of the volcano. The BBVC consists of the Gudda Volcano and the younger Bericha Volcano, two silicic eruption centres along the rift axis. The main volcanic activity of the BBVC is estimated to have occurred over the last ~2 Ma. Here I present a detailed
relative eruption chronology for the BBVC from morphometric analyses and mapping using high resolution LiDAR data. Petrographical and whole rock analyses provide new constrains on magmatic evolution at the BBVC.
The formation of the BBVC can be differentiated into 5 main eruption stages, subdivided in at least 12 phases with in total 128 mapped lava flows. Cross-cutting relationships of lava flows and eruption phases provide a relative chronology of the eruption history of the BBVC, starting with pre-BBVC rift basalts, pre-caldera and caldera activity and two post-caldera phases at
the Gudda Volcano. The Bericha Volcano formed during two main phases, followed by another post-caldera phase at Gudda Volcano. At least four fissure eruption phases recurred on the rift axis temporally in between the main eruptions phases. Morphometric analyses indicate a total corrected volume of eruptive material at the BBVC of ~36 km3, of which 68 % is
felsic, in particular erupted by the pre- and first post-caldera phase of the Gudda Volcano, 25 % is basaltic and 7 % has an intermediate composition. The total area of the BBVC is ~870 km2, of which ~62 % are rift basalts. Magma evolution is spatially and temporally complex shown by a bimodal distribution of rift floor basalts as well as peralkaline trachytic and rhyolitic lavas for the Gudda and Bericha Volcano, respectively, with rare intermediate lavas from fissure eruptions. Main compositional correlations indicate that fractional crystallisation may have played a major role in the development of magmas at the BBVC. Different FeO, MnO and Al2O3 contents at the Gudda and Bericha lavas may suggest different parental magmas
and/or a separate feldspar crystallisation due to changed conditions in the magma chamber of the Gudda volcano. Detailed differentiation of processes for magmatic evolution will be investigated by trace element and isotopic analyses. The composition and morphometry of lava flows changed over relative time from mafic rift floor basalts covered a large area, to explosive large – volume activity at silicic centres, which demonstrates a complex development of the BBVC.

Johannes Wiest
2016-09-07 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Constraints from the Lyderhorn Gneiss on the tectonomagmatic evolution of the Øygarden Complex, SW Norway

The Øygarden Complex and the Bergen Arc System are enigmatic large-scale structures in the SW Norwegian Caledonides. So far, the lack of published U-Pb zircon ages from the Øygarden Complex limits clear interpretations. Located in the poorly studied eastern part of the Øygarden Complex, the Lyderhorn Gneiss forms the core of the Bergen Arc System. Detailed field mapping was conducted and seven samples were dated by SIMS U-Pb zircon geochronology.
Igneous protoliths formed during the Gothian-Telemarkian (1504 Ma) and Sveconorwegian (1041 Ma; 1026 – 1022 Ma) orogenic periods. Metamict zircons were reset by an Early Ordovician (483 Ma) thermal event and sustained elevated temperatures annealed previous radiation damage. Caledonian regional metamorphism left no measurable effect on the U–Pb system.
The structure of the Lyderhorn Gneiss is characterized by lineation-parallel, recumbent folds that record constrictional strain. Consistently oriented, top-to-ENE shearing prevailed during deformation from amphibolite facies conditions to the brittle-plastic transition. Fluid-assisted strain weakening formed E-dipping, phyllonitic detachments.
Mesoproterozoic protolith ages correlate the Lyderhorn Gneiss (and Øygarden Complex) with the Telemarkia domain of the Baltican basement and show a relation with the Sirdal Magmatic Belt. Our results suggest a continuous NNW-trend of Sveconorwegian domain boundaries and contradict widespread Sveconorwegian high-T metamorphism.
The structure of the Lyderhorn Gneiss is inconsistent with the current tectonic model of the Bergen area, however, it is well explained by an alternative model that considers core complex exhumation of the Øygarden Complex. The discussed model reconciles the interpretation of basement culminations along the entire Norwegian margin and enhances onshore-offshore correlations.

Gino De Gelder (IPGP)
2016-08-31 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Flexural normal faulting in Corinth and an uplifting Hellenic fore-arc (S-Greece): tectonic changes in the Plio-Quaternary

Michael Gazley (CSIRO)
2016-08-24 12:15 | 4C12a, CGB seminar room 4th floor
High resolution characterisation of gold mineralisation
Microcharacterisation techniques are becoming increasingly advanced, with speed of data collection and detection limits continually improving. As micro-scale variation can be key to understanding the large-scale variations in a mineral system, these developments are enhancing the geologist’s ability to resolve mineral systems complexity
This talk will summarise some of the research currently being undertaken in the Mineral Resources program of Australia’s Commonwealth Scientific Industrial Research Organisation (CSIRO). This talk will highlight applications of advanced resource characterisation to a variety of settings including samples from orogenic and epithermal systems. Techniques discussed will include scanning electron microscopy, electron back scatter diffraction, synchrotron X-ray fluorescence mapping, high-resolution X-ray computed tomography, and atom probe, as applied to understanding the elements and minerals that are associated with gold and the micro-nano-structure of the gold itself.

Joint seminar with GeoBio

Sarah Schröder (GFZ)
2016-08-23 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Calibration of Surface Evolution Codes (SECs) Using a DEM as Initial Topography: A case Study for the Pamir

Casey Nixon
2016-08-17 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: A network approach to characterising normal faults

Tristan Salles (USyd)
2016-06-16 12:00 - 13:00 | Auditorium 5, 3rd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Continental-Scale Landscape Dynamic

Over the last year, within the ARC Basin Genesis Hub, I have started the development of a new numerical framework to better quantify the fundamental feedbacks between mantle flow, geodynamics, landscape dynamics and associated sediment transport at continental scale. The approach relies on Badlands (a finite volume code which simulated geomorphological evolution and stratigraphic records under various climatic and tectonic forcing). Here I present how this new framework can be used to quantify the impact of dynamic topography on Australian landscape evolution over the last 150 Ma.

Based on a mantle convection model (CITCOMS), a dynamic topography evolution since the Late Jurassic has been reconstructed.
We use these predictions as forcing conditions within Badlands in addition to a history of varying climate and sea-level and predefined sedimentary materials derived from paleo- environment maps. The model simulates the time dependence of erosion and deposition as well as the evolution of catchment dynamics, drainages capture and flow network reorganisation. The model shows that the motion of Australian plate has resulted in significant changes in river drainage, intercontinental erosion and sedimentation. In particular, we show how the model is able to reproduce today’s main features of Australia Great Dividing Range. The model outputs have been compared in terms of denudation rates, paleo-drainage and river profiles.

Despite limitations, this first- order coupling approach between the mantle convection model and the surface process one shows promising results and reflects on the fundamental link between dynamic uplift, fluvial erosion and depositional pulses in basins distal to passive margin highlands.

Flyer

Annie Jerkins
2016-06-08 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Seismic Modeling for Geothermal Reservoir Characterization
The world’s energy demand is increasing, and there is a need for alternative energy sources to replace depleting fossil fuels. Geothermal energy could be an important part of these new sources of energy. For efficient and reliable geothermal energy production, characterization of geothermal reservoirs is needed. Characterization of reservoir properties is for a large part obtained using geophysical methods. In this thesis I develop a new seismic modeling method that can be used in geothermal reservoir characterization.
In passive seismics the amount of seismic data obtained at a geothermal reservoir can be quite large. For example, at The Geysers in California, over a period of about 30 years, hundreds of thousands of microseismic events have been recorded by about a hundred receivers. Efficient seismic modeling using, for example ray tracing, is therefore essential. In this thesis the main focus was on ray tracing. The goal was to develop a ray tracing algorithm, that is both fast and accurate. Ray tracing was implemented using three different numerical methods: Euler’s method, the midpoint method and fourth order Runge-Kutta. From a systematic comparison for realistic geothermal reservoir models and their overburdens, it was found that the midpoint method with a small time step is the preferred numerical method.
When performing ray tracing for e.g. source characterization it is essential to have reliable seismic velocity models. In this thesis an overview of velocity models at 15 enhanced geothermal systems was made. 1D velocity models exist at almost all the geothermal reservoirs. However, 3D velocity models, which tends to be much more accurate, only exist for half of these reservoirs. In this thesis the ray tracing algorithms were used for efficient waveform modeling, using both 1D and 3D velocity models, in order to check trade-offs in terms of travel times, amplitudes and wave- forms. The velocity models used were a 1D velocity model of the The Geysers as given in the literature. The 3D model consisted of this 1D model on which were superimposed 3D perturbations. The modeling was done using two different seismic sources: a double couple source and a non-double couple source. The results showed that there were significant differences between the 1D and 3D modeling. The most significant deviations were differences in amplitudes and amplitude polarities for the calculated synthetic seismograms. Also, it was found that the results depend upon the seismic source, where there were large differences between the double couple and
non-double couple source. Thus, the use of 1D velocity models for geothermal reser- voir characterization, can lead to wrong results about permeability of fractures. It is recommended that 3D seismic velocity models are used, and if necessary developed, when studying microseismicity and especially when inverting for source mechanisms.

Jeff Prancevic
2016-05-18 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title:
Sediment transport in steep channels and the transition to landsliding

by Jeff Prancevic (ETH Zürich)

Abstract:
The mobility of sediment in steep mountain rivers controls the denudation rate and height of mountain ranges worldwide. Sediment movement within the steepest terrain often occurs as catastrophic shallow landsliding, posing significant hazards to those living downstream. Despite the importance of steep channels, our observations of sediment transport are mostly limited to rivers with slopes of less than 2°. This prevents us from predicting the runoff required to transport sediment throughout most of the drainage network and from knowing the mode of transport that should dominate (dilute river transport vs. landsliding). I performed a series of laboratory experiments in an artificial river with an adjustable slope to test the flow depths required to transport sediment on slopes up to the dry angle of repose. Counterintuitively, sediment becomes harder to move on steeper slopes by dilute river processes. Laboratory observations of flow hydraulics and field observations of cobble stability reveal that this reduced mobility is a hydraulic effect resulting from the shallow flows that are inherent to steep channels. In experiments that were conducted at slopes steeper than half of the dry angle of repose, sediment was more easily transported by shallow landsliding than dilute river processes. Within this landsliding regime, sediment was again observed to be more stable than predicted by traditional theory. Documentation of these experimental failures with high-speed video revealed that failures occur with a characteristic length scale that is shorter than predicted, and that these short failures experience a strong buttressing force at their downstream margin. These results suggest that landslide length scales consistently with width, and also provides new expectations for the saturation level required to initiate failures. Ultimately, these experiments provide us with expectations of the flow depth required to transport sediment throughout the entire drainage network, and also allow us to partition the drainage network into river-dominated and landslide-dominated regimes.

EGU prep talks
2016-04-13 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
12:15 – Guillaume Duclaux: “Preferential development of extension-orthogonal basins in oblique continental rifts”
12:30 – Thomas Theunissen: “Long-term coupling and feedbacks between surface processes and tectonics during rifting”
12:45 – Romain Beucher: “Morphotectonic evolution of passive margins undergoing active surface processes: Insights from large-scale numerical models”

– break –

13:15 – Gang Lu: “Magmatism at passive margins: Effects of depth-dependent rifting and lithospheric counterflow”
13:30 – Vivi Pedersen: “Isostatic and dynamic support of high topography on a North Atlantic passive margin”
13:45 – Katrin Spieker: “Evidence for magmatic underplating under the Azores Islands from P-wave receiver functions”

Gang Lu
2016-03-30 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Magmatism at passive margins: Effect of depth-dependent rifting and depleted continental lithospheric counterflow

Some passive margins exhibit complex depth-dependent rifting that are not explained by the classical uniform-extension model. Typical examples are found at the Iberia-Newfoundland conjugate margins (Type I) with earlier breakup of crust, and at some ultra-wide South Atlantic margins (Type II) with wide thin crust beneath which the continental mantle lithosphere has been removed. Moreover, the southern segment of South Atlantic margins are volcanic, while margins of the central segment are contrastingly non-volcanic, although they are both wide margins. The dynamics of such structural styles and magmatism activities are not fully understood.
In this study, we perform 2-D thermo-mechanical numerical experiments to investigate magmatism at various passive margins. End-member models with strong (Model I) or weak (Model II) crust are designed to account for depth-dependent rifting. In addition, lithospheric counterflow are investigated by models with thick depleted mantle lithosphere (C models), compared with normal lithosphere (A models).
Results show that depth-dependent rifting and lithospheric counterflow strongly affect magmatism during rifting. Strong crust (model I-A) results in the formation of narrow margins and early establishment of seafloor spreading, while weak crust (model II-A) forms wide margin with early magmatism but late establishment of seafloor spreading. Thick (>20 km) igneous crust may form in the continent-ocean transition.
The presence of lithospheric lithosphere strongly delays the onset of magmatism. It results in large traction of exhumed continental mantle with limited magmatism in model I-C, and forms non-volcanic wide margin in model II-C.
We illustrate that model I-A and I-C are comparable with the Gulf of Aden conjugate margins and the Iberia-Newfoundland non-volcanic margins, respectively. Model II-C is consistent with central South Atlantic non-volcanic margins while model II-A likely contributes to the formation of extrusive igneous rocks at southern South Atlantic volcanic margins.

Felix Halpaap
2016-03-16 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Sub, Intra, Supra: Intermediate Depth Earthquakes all around the Hellenic slab
Abstract: We are conducting an earthquake relocation study in connection with 3-D traveltime tomography in the Western Hellenic subduction zone. This subduction system is a natural laboratory for comparing different subduction environments regarding the occurrence of intermediate depth seismicity and connected petrology variations. The systems suitability for such a comparison stems from the combination of both continental and oceanic subduction in a spatially compact domain in Western Greece. We want to interpret the locations of intermediate depth earthquakes in conjunction with high-resolution structural slab information from receiver function studies. Our first robust results suggest that the WHSZ hosts sub-, intra-, and supra-slab earthquakes in the Southern, continental subduction part, while the Northern part is nearly quiet. We present newest P-velocity and Vp/Vs-ratio images of the 3-D traveltime tomography study of the area which reveals additional 3-D structure. Afterwards, we invite everyone to discuss conflicting models and ideas of the intermediate depth seismicity and slab structure in the WHSZ.

Rosie Smithells
2016-03-09 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Source-to-Sink and Landscape Evolution Modeling of Extensional Basins: A Case Study of the Gulf of Corinth, Greece.

Anneleen Geurts
2016-03-02 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Transient landscape development in the central Italian Apennines: Assessment of controlling factors using surface process modelling

Kristian Jensen
2016-02-24 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Modelling and processing of flexural ice waves
Abstract: One of the most common problems with seismic data obtained in Arctic environments is the presence of so-called flexural ice wave noise on the seismic raw data. Flexural wave noise occurs on seismic data acquired on ice sheets in the transition zone between the shoreline and a water depth of approximately 5.5 meters. As the flexural waves are highly dispersive they are manifested as a broad fan of noise on the seismic data, often having an order of magnitude 40-60 dB higher than reflected signals. In addition, the frequency spectrum of flexural ice waves frequently overlaps with reflected signals, and due to the low velocities of flexural waves, spatial aliasing commonly occurs. Thus, flexural waves are difficult to remove using conventional seismic processing.
This study aims to outline how flexural waves may be modelled synthetically, as well as how effective various processing techniques are in removing the flexural waves while keeping reflected signals intact. Through investigating how parameters such as ice temperature and ice thickness affect the modelled flexural waves insight into the dispersion relation of the flexural waves may be obtained. Further, by comparing various processing approaches, knowledge about which parameters should be taken into account when setting up a processing work flow may be acquired. Results of the analysis indicates that conventional f-k filtering works well when dense receiver spacing is used to lessen spatial aliasing. Further, when the flexural wave velocities are separated from wave velocities in the subsurface layers, Tau-p filtering provides a good approach for effectively muting flexural wave noise. When these criteria are not met, however, more unconventional approaches, or a combination of various approaches, are required.

Vivi Pedersen
2016-02-17 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Isostatic and dynamic support of high passive margin topography in southern Scandinavia

Abstract: Substantial controversy surrounds the origin and recent evolution of high topography along passive continental margins in the North Atlantic, with suggested age of formation ranging from early Paleozoic Caledonian orogenesis to Neogene uplift of a Mesozoic peneplain. Here we focus on the well-documented high passive margin in southwestern Scandinavia, and quantify the relative contributions of crustal isostasy and dynamic topography in controlling the present topography. We find that most topography is compensated by the crustal structure, suggesting a topographic age related to ~400 Myr old Caledonian orogenesis. In addition, we infer that dynamic uplift (~300 m) has rejuvenated existing topography locally in coastal region within the last ~10 Myr due to mantle convection. Such uplift has, in combination with a general eustatic sea-level fall and concurrent erosion-driven isostatic rock-column uplift, the potential to increase erosion of coastal-near regions and explain observations that have traditionally been interpreted in favor of the peneplain uplift model. We conclude that high topography along the Scandinavian margin cannot represent remnants of a peneplain uplifted within the last ~20 Myr. Topography must have been high since the Caledonian orogeny.

Christian Eide
2016-02-10 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Title: Seismic-scale architecture of deep-seated igneous intrusions in a sedimentary basin: Jameson Land, East Greenland
Abstract: Igneous sills are common components in rifted sedimentary basins globally. Much work has focussed on intrusions emplaced at relatively shallow paleodepths (0-1.5 km). However, due to constraints of reflection-seismic imaging and limited field-exposures, intrusions emplaced at deeper paleodepths (1.5-4 km) within sedimentary basins are as not well-understood in regard to their emplacement-mechanisms and host-rock interactions. Results from a world-class, seismic-scale outcrop of intruded Jurassic sedimentary rocks in East Greenland are presented here. Volcanic intrusions and host-rock have been studied in the field and utilising a 22 km long “virtual outcrop” acquired using helicopter-mounted lidar. The results show how the geometry of deeply emplaced (c. 3 km) sills are controlled by host-rock lithology, sedimentology and cementation state. Sills exploit even small mudstone horizons, even exploiting mudstone-draped dune foreset in otherwise homogeneous sandstones. Sills in poorly cemented intervals show clear ductile structures, in contrast to sills in cemented units which show brittle emplacement-structures. The host-rock is remarkably undeformed despite intrusion. Volumetric expansion caused by the intrusions is almost exclusively accommodated by vertical jack-up of large host-rock blocks, on a 1:1 ratio, implying that intrusions may play a significant role in uplift of a basin if emplaced at deep basinal levels.

Claudio Mora
2016-02-03 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
TITLE: From orogen to rifted passive margin formation in Brazil: numerical geodynamic modeling considering structural inheritance, rheology and lithospheric structure
ABSTRACT: Structural inheritance is related to mechanical weaknesses in the lithosphere due to previous tectonic events, e.g. rifting, subduction and collision. The North and South Atlantic rifted passive margins that formed during the breakup of Western Gondwana, are parallel to the older Caledonide and the Brasiliano-Pan-African orogenic belts. In the South Atlantic, ‘old’ mantle lithospheric fabric resulting from crystallographic preferred orientation of olivine is suggested to play a role during rifted margin formation (Tommasi and Vauchez, 2001). Magnetometric and gravimetric mapping of onshore structures in the Camamu and Almada basins suggest that extensional faults are controlled by two different directions of inherited older Brasiliano structures in the upper lithosphere (Ferreira et al., 2009). In the South Atlantic Campos Basin, 3D seismic data indicate that inherited basement structures provide a first order control on basin structure (Fetter, 2009).
Here we investigate the role of structural inheritance on the formation of rifted passive margins with high-resolution 2D thermo-mechanical numerical experiments. The numerical domain is 1200 km long and 600 km deep and represents the lithosphere and the sublithospheric mantle. Model experiments were carried out by creating self-consistent orogenic inheritance where a first phase of orogen formation is followed by extension. We focus in particular on the role of varying amount of orogenic shortening, crustal rheology, contrasting styles of orogen formation on rifted margin style, and the time delay between orogeny and subsequent rifted passive formation. Model results are compared to contrasting structural styles of rifted passive margin formation as observed in the South Atlantic.

Rifting and passive margin workshop
2016-01-27 10:00 - 14:15
We have visitors in the Geodynamics group so we will be running a small workshop on rifting from 10.00 to 14.30 in the PhD lunchroom (3rd floor).

You can find the tentative program below.

10.00-10.45: Jan Inge Faleide (UiO): North Atlantic Rifted Margin formation
10.45-11.30: Magdalena Scheck Wenderoth (GFZ): Effective mechanisms of heat transport in sedimentary basins at different scales
11.30-12.00: Ritske Huismans: Styles of rifted margin formation
12.00-: Lunch break / seminar
13.15-13.45: Guillaume Duclaux: 3D modelling of oblique rifting
13.45-14.05: Thomas Theunissen: Linking surface processes and lithosphere extension

Thomas Theunissen
2015-12-09 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Long-term coupling and feedbacks between surface processes and tectonics during rifting
Thomas Theunissen, Ritske Huismans
University of Bergen, Department of Earth Science , Allegaten, 41 5020 Bergen
Whereas significant efforts have been made to understand the relationship between mountain building and surfaces processes, limited research has been done on the relationship between surface processes and extensional tectonics. Here we present high-resolution 2-D coupled tectonic-surface processes modeling of extensional basin formation. The main aim is to find out how erosion and deposition affect the deformation in extensional systems. We test sensitivity of the rift mode to the combined effects of crustal rheology and varying surface process efficiency (erodibility, sea level). The results show that both erosion of rift flank areas and basin deposition enhance localization of crustal deformation. Frictional-plastic extensional shear zones accumulate more deformation during a longer period of time, and time of lithospheric rupture is delayed when fluvial erosion, transport and deposition are efficient. We show that removal of mass from rift flanks and sedimentary loading in the basin area are the main cause of the feedbacks providing a first order control on the style of extensional basin formation. Variation of strain localization in natural rift systems correlates with the observed behavior and suggests similar feedbacks as demonstrated by the forward numerical models.

Rebecca Bell
2015-12-02 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Did the Earth move for you? From tsunami earthquakes to slow slip
By Rebecca Bell
Faculty of Engineering, Department of Earth Science & Engineering, Imperial College, London, UK
ABSTRACT:
Over the last couple of decades we have learned that a whole spectrum of different fault slip behaviour takes place on subduction megathrust faults from stick-slip earthquakes to slow slip and stable sliding. Geophysical data, including seismic reflection data, can be used to characterise margins and fault zones that undergo different modes of slip. In this presentation we will focus on the Hikurangi margin, New Zealand, which exhibits marked along-strike changes in seismic behaviour and margin characteristics. Campaign and continuous GPS measurements reveal deep interseismic coupling and deep slow slip events (~30-60 km) at the southern Hikurangi margin. The northern margin, in contrast, experiences aseismic slip and shallow (<10-15 km) slow slip events (SSE) every 18-24 months with equivalent moment magnitudes of MW 6.5-6.8. Updip of the SSE region two unusual megathrust earthquakes occurred in March and May 1947 with characteristics typical of tsunami earthquakes.
Using 2D seismic reflection, magnetic anomaly and geodetic data we observe in the source areas of the 1947 tsunami earthquakes i) low amplitude interface reflectivity, ii) shallower interface relief, iii) bathymetric ridges, iv) magnetic anomaly highs and in the case of the March 1947 earthquake v) stronger geodetic coupling. We suggest that this is due to the subduction of seamounts, similar in dimensions to seamounts observed on the incoming Pacific plate, to depths of <10 km. We propose a source model for the 1947 tsunami earthquakes based on geophysical data and find that extremely low rupture velocities (c. 300 m/s) are required to model the observed large tsunami run-up heights (Bell et al. 2014, EPSL). Our study suggests that subducted topography can cause the nucleation of moderate earthquakes with complex, low velocity rupture scenarios that enhance tsunami waves, and the role of subducted rough topography in seismic hazard should not be under-estimated.

David Peacock
2015-11-25 12:15 - 13:15 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
Fault interactions and associated damage
D.C.P. Peacock1, C.W. Nixon1, A. Rotevatn1 & D.J. Sanderson2
1 Department of Earth Science, University of Bergen, Allégaten 41, 5007 Bergen, Norway
2 Engineering and the Environment, University of Southampton, Highfield, Southampton, SO17 1BJ, UK.

The way that faults interact with each other will control fault geometries, displacements and strains, which in turn affects fluid flow and mineralisation. This is important as faults rarely occur individually but as networks of numerous faults. The arrangement of these faults (i.e. the topology) and their development can produce a variety of different fault interactions, including but not limited to fault splays, abutments, relay zones and cross-cutting relationships. What are the characteristics of these different interactions? How do we interpret them? What are their implications for fault behaviour? To answer these questions, we describe and analyse different fault interactions, focussing on improving our understanding of their development and the resulting fault damage.
Fault interactions can occur between two or more faults of any orientation or relative age. They are defined by the geometric and kinematic relationships that form between the interacting faults. For example the faults may or may not be geometrically coupled, when fault planes share an intersection line (or branch line); and/or kinematically coupled, where the displacements, stresses and strain of one fault influences those of the other. Thus fault interactions are analysed in terms of the following: 1) Geometry and topology – describing the arrangement of the faults and whether the faults share an intersection line or not. The topology describes the geometric relationships between the faults and can be linked to connectivity. 2) Kinematics – describing the displacement distributions of the interacting faults and whether the slip directions are parallel, perpendicular or oblique to the intersection line, and if the faults have the same or opposite slip directions. 3) Stress and strain – whether extension or contraction dominates in the acute bisector between the faults. 4) Chronology – the relative ages of the faults.
We explore a variety of fault interactions that illustrate the use of this classification scheme in understanding fault-related structures, discussing the implications for the analysis of damage zones. We introduce the terms intersection damage zone for structures created around the intersection line of geometrically coupled faults, and approaching damage zone for the zone between geometrically uncoupled faults.

Kathrin Spieker
2015-11-18 12:15 - 13:00 | The usual place, Room 2G16c, 2nd floor, Realfabyyget, 41 Allégaten, Bergen, 5007, Norway
TITLE: Moho depth variations beneath the Azores Islands
