Displays

Between August and October 2017, the German research vessel Maria S. Merian acquired geophysical data along the Northeast Greenland continental margin during its cruise MSM-67. This included seismic reflection and wide-angle/refraction data as well as potential field data. In comparison to the conjugate mid-Norwegian margins, the Northeast Greenland continental margin is less well studied. Hence, one of the key objectives of the expedition was to improve the understanding of the opening of the Northeast Atlantic Ocean and the evolution of the conjugate margin pair. One particular goal of the experiment was the mapping of the lateral extent of magmatism associated with the opening and how this relates to margin segmentation.

Seismic refraction line BGR17-2R2 runs on the shelf and parallel to the coast of NE Greenland. It crosses the landward extension of the West Jan Mayen Fracture Zone that separates the seafloor spreading along the Mohn’s Ridge in the north from the Kolbeinsey Ridge in the south. A total of 29 ocean bottom seismometers (OBS) equipped with a hydrophone and three-component geophones were deployed along the 235-km-long line. The seismic source was a G-gun array with a total volume of 4840 cubic inches (79.3 L) fired every 60 s. In the central and northern part of the line, two older seismic refraction profiles are crossed (lines AWI2003-500 and 400, respectively), which run perpendicular to the margin and can be used for lateral correlation of the crustal structure.

For the initial analysis, a velocity model was developed by forward and inverse modeling of travel times using the program RAYINVR. Later, a travel time tomography was carried out employing the code Tomo2D and performing a Monte Carlo analysis with 100 inversions from which an average model was calculated. The models show a 1-to 3-km-thick sedimentary column with velocities ranging from 1.6 to 4.0 km/s. In the central and northern part, a 1-km-thick layer with velocities around 4.6 km/s is underlying the sediments and is interpreted to consist of volcanic material. Below and extending along the entire length of the line, velocities of 5.6 km/s are observed in a layer that is ~2 km thick. The crystalline basement has a depth around 5 km with higher velocities in the north (6.5 km/s) than in the south (6.3 km/s). High lower crustal velocities (>7.2 km/s) are observed along the entire line and either indicate magmatic underplating or lower crustal sill intrusions. The Moho depth is seismically constrained along the central part of the line where it is 30 km. Gravity modeling suggest a depth of 35 and 27 km at the southern and northern limit of the profile, respectively. Within the zone of the landward extension of the West Jan Mayen Fracture Zone, a decrease in mid-crustal velocities by 0.2 km/s is observed. Slightly to the north of the fracture zone, a 50-km-wide zone with increased mid-and lower crustal velocities may indicate an igneous center in an area where the upper volcanic layer is shallowest.

How to cite: Funck, T., Madsen, A. S., Berndt, C., Dannowski, A., Franke, D., Geissler, W., Schnabel, M., and Thorwart, M.: The crustal structure of the Northeast Greenland continental shelf across the extension of the West Jan Mayen Fracture Zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2296, https://doi.org/10.5194/egusphere-egu2020-2296, 2020.

Gas hydrates are potential energy resources which can be formed at low temperature and high pressure. The number of recoverable gas hydrates are limited due to the specific temperature, pressure conditions and technical limitations of gas production. Various production methods have been studied around the world to overcome these technical limitations. Gas production methods from gas hydrates are divided into methods of dissociating gas hydrates and non-dissociating gas hydrates. The dissociation methods including depressurization method, thermal injection method, and chemical inhibitor injection method can decrease in effective stress of the ground due to phase conversion. On the other hand, CH₄-CO₂ replacement method is geomechanically stable because it does not dissociate gas hydrates. Also, CH₄-CO₂ replacement method has the advantage of sequestering carbon dioxide while producing methane. However, CH₄-CO₂ replacement method has the disadvantage such as low production efficiency and understanding kinetics of gas production. In this study, soaking, gas permeability of gas hydrate layer and hydrate saturation are considered in order to promote the production efficiency of CH₄-CO₂ replacement method. Results show that production efficiency increases with the number of soaking process, the higher gas permeability and hydrate saturation. According to the experimental results in this study, the production efficiency can be increased by considering the soaking time, procedure and selecting the proper gas hydrates site.

Acknowledgement

This work is supported by the Korea Agency for Infrastructure Technology Advancement(KAIA) grant funded by the Ministry of Land, Infrastructure and Transport (Grant 20CTAP-C152100-02). Also, it is supported by partial funding from NPRP grant # NPRP8-594-2-244 from the Qatar national research fund (a member of Qatar Foundation) and  the Ministry of Trade, Industry, and Energy (MOTIE) through the Project “Gas Hydrate Exploration and Production Study (20-1143)” under the management of the Gas Hydrate Research and Development Organization (GHDO) of Korea and the Korea Institute of Geoscience and Mineral Resources (KIGAM).

How to cite: Jung, J., Ryou, J., Lee, J. Y., AI-Raoush, R. I., Alshibli, K., Shin, S. W., and Han, J. H.: Soaking effects on CH4-CO2 replacement efficiency in gas hydrates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2581, https://doi.org/10.5194/egusphere-egu2020-2581, 2020.

Conventional plate tectonics envisages simple continental breakup with clean splitting of supercontinents and subsequent orderly widening of oceans by seafloor spreading about a central ridge. No sooner was this paradigm proposed when the clear, first-order misfit of intraplate and large-volume volcanism was highlighted. That was quickly accommodated by adding an additional degree of freedom into the theory of Earth dynamics, i.e., ad hoc mantle plumes. Although this simple picture was adequate in the early years of plate tectonics, the subsequent rapid accumulation of vast datasets of ever-more-precise observations has rendered a theory of such simplicity no longer tenable. Simple plate tectonics can now serve only as a basic canvas on which the complexities of the real world must be painted. There is no better region for illustrating this than the Northeast Atlantic Realm which illustrates the full range of complexities. After a history of tectonic unrest spanning several 100 Myr true continental breakup, involving fracture of the entire lithosphere and ocean widening via sea-floor spreading, finally proceeded. However, geological complications are on at least an equal level to features arguably amenable to description by simple plate tectonics. Spreading ridges developed by propagation through continental lithosphere comprising a collage of cratons separated by orogenic belts. Where these propagators met insurmountable barriers the extension demanded by local kinematics could only be accommodated by diffuse continental extension. Continual changes occurred in the direction of regional extension and these resulted in local tectonic instabilities manifest in lateral ridge migrations, jumps, and parallel-ridge-pair extension. Extreme, magma-assisted continental extension, together with intense volcanism, formed lava-capped transitional crust. As a consequence the true extent of continental crust under the oceans is unclear. The geophysical characteristics of transitional crust are ambiguous in terms of physical properties. This presents a challenge to mapping continental material in the oceans, a problem that can be mitigated by joint interpretation with gravity, heatflow and geochemical data. Known continental blocks in the ocean include the array of blocks west of the British continental shelf (the Hatton-, George Bligh-, Lousy-, Bill Bailey’s- and Faroe Bank Highs, and Wyville-Thompson- and Fugløy Ridges), the Jan Mayen Microplate Complex, the Greenland-Iceland-Faroe Ridge and likely others that remain to be found. All of the above complexities in the solid Earth have profoundly affected the natural environment in the region, especially the oceans and the biosphere, and must be taken into account in predictions of future evolution of the natural environment.

How to cite: Foulger, G.: Beyond Plate Tectonics: The Northeast Atlantic Realm, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3624, https://doi.org/10.5194/egusphere-egu2020-3624, 2020.

Alternative cooling and warming have occurred many times in the history of Earth since its formation. In the meantime, active and quiescent periods of geological activity have also alternatively occurred in this same planet. When Earth became hotter, it shows widespread geological activities, such as LIPs, whereas during the colder stage, it became relatively quiet without too much magma activities. Although various models have been used to explain the trigger for each of these activities, there is no consensus about the fundamental relationships between the thermal cycles and episodically geological processes. The major energy sources for Earth after ~3.8 Ga include primordial heat left from the accretion, differentiation, and the radioactive decay of heat-producing elements. Surface tectonics and magmatism control the transport of heat from the interior to the surface and most surface tectonic features of Earth are the expression of their interior dynamics. Supercontinental breakup and aggregation have occurred for many times in the Earth history, accompanied by episodic cooling and warming on the Earth surface. This breakup and aggregation regime is known as plate tectonics and is characterized by high average surface heat flow fluctuations. Based on the thermodynamic principle, a thermodynamic equilibrium equation describing the earth’s thermal cycles is established. We realized that this thermal cycle may drive Earth itself to evolve, and is the fundamental reason for the periodicity or rhythmicity of geological events such as tectonic movements, orogenies, glacial periods and biological extinctions. Following this principle, we then introduced a project of Wall Chat to compile global data or evidences using a variety of literatures in Geology of early investigations of geological events to explore the relationship between geological events and Earth’s thermal cycles. The data includes the supercontinent cycle, tectonic movement, plate tectonics, extremely hot event, extremely cold event, evaporite, marine red bed, biological evolution and extinction, sea level fluctuation, etc. The Wall Chat reveals that most of the geological events have their relation to the Earth’s thermal cycles. We found that there may exist a good correlation between the occurrence of evaporites and marine red beds and the higher temperature periods, which then provides a new perspective to understand the triggering of these events. The Wall Chat also raises an interest and important question on why are the two Great Oxidation Events (GOE) both related to the two snowball events? We have several clear objectives for the future. First, we are currently cooperating with some of the related institutes of geology to obtain additional evidence data to fill in many of the gaps in the chat; targeted areas include Paleontology, Glaciology, evaporite and red beds. Second, to understand fully the relationship between thermal cycles and, at least, most of the great geological events. Such studies, when sufficiently constrained by event data, should lead to a greatly improved understanding of the earth evolution.

How to cite: Gong, B., Tang, C., Chen, T., Qin, Z., and Zhang, H.: Earth’s thermal cycles and geological events, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7912, https://doi.org/10.5194/egusphere-egu2020-7912, 2020.

The Northeast Atlantic area presents new fundamental challenges in geodynamics, making it a superb international laboratory to develop new models and concepts that can be tested elsewhere. Among the most exciting challenges in this area is characterization of the different types of crust that may be encountered in oceanic realms. Viewing this area objectively, it appears that the classical distinction between oceanic and continental lithosphere is no longer adequate to interpret contemporary observations. This is a direct consequence of the huge input of magma into the lithosphere that has occurred at different stages of its evolution. Notably, we do not fully understand the true nature of the crust beneath Iceland and along the nearby continental margins and aseismic ridges (e.g., the GIFR). In particular, the classical distinctions made from linear magnetic anomalies (LMA) to distinguish oceanic and continental lithosphere is proven to not work. Massive magmatic-type accretion may occur together with continental thinning and stretching to generate symmetrical LMA over wide continental domains and give rise to erroneous interpretations as oceanic-type lithosphere. If part of the crust is inherited from former, albeit transformed, continental crust, this must also apply to the underlying mantle lithosphere. For example, old slabs may be trapped and reworked in the lithosphere and play major roles in its evolution. These new considerations have fundamental economic, political and scientific implications. It is now urgent to target and investigate the true nature of the crust in the NE-Atlantic, in particular seeking clues to the existence of continental material in specific areas. In my presentation I will make specific proposals.

How to cite: Geoffroy, L.: The NE-Atlantic challenge: where should we core and where should we conduct a wide-angle seismic survey? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10090, https://doi.org/10.5194/egusphere-egu2020-10090, 2020.

The structure and tectonostratigraphic development of the mid-Norwegian volcanic passive margin have been extensively studied over last 30 years. However, an understanding of its crustal architecture and basin evolution remains incomplete and debated. A main point of a debate concerns the crustal and basin structure of the yet underexplored outer parts of the Møre and Vøring basins which are significantly covered by breakup-related volcanics. This discussion generally resides on the origin of the high-velocity (7+km/s) lower crustal body which alternatively interpreted either as a wide zone of exhumed/serpentinized mantle assuming direct structural similarities with the magma-poor Iberian margin or instead inherited high-grade Caledonian crust later intruded by breakup-related magmatic intrusions. Another important point of contention is whether the Møre and Vøring basins developed through either several discrete extensional events, or alternatively a single phase of continuous extension from Late Jurassic-Early Cretaceous necking to lithospheric breakup in the late Paleocene-early Eocene.

Recently, a new generation of high-quality 2D and 3D seismic data acquired in the outer parts of the mid-Norwegian margin allowed a better imaging of deep Vøring and Møre basins and sub-basalt domains. Also new well data allowed a better regional seismostratigraphic control. An integrated 3D/4D interpretation of new seismic data calibrated with published refraction data and tested by potential field and forward basin modelling helped to better reveal the crustal and basin architecture of the Møre and Vøring basins.

Our results support the crustal nature of the controversial high-velocity and high-density lower crustal body and associated deep reflections, which we interpret as an old exhumed high-grade Caledonian crust later mixed with breakup-related mafic and ultra-mafic magmatic material. Our seismic interpretation shows that the basins were subjected to discrete and localized Cretaceous-Paleocene rifting events which sequentially migrated laterally and towards the future breakup axis and were separated by intermediate cooling/subsidence phases. We explain this migration of the rift axes by a strain hardening due to lithospheric cooling with possible enhancement from lateral lower crustal flow.

We suggest that the outer portion of the Vøring and Møre basins represents distal “marginal plateaus” that likely formed an elevated crustal domain bounded to the east by a failed and cooling inner rift system and to the west by Cenozoic volcanic margins. The presence of such a marginal plateau may better explain (1) the observed structural styles and 3D geometries of the sedimentary successions in the outer basins (e.g. shallowing of the Base Cretaceous Unconformity), (2) the long-time lag (˃80-100 Myr) between the mid-Mesozoic necking and the final (off axis) lithospheric breakup, (3) the subaerial and shallow marine emplacement of breakup-related lavas, (4) the signatures of upper crustal contamination in breakup-related flows, and (5) the relatively low magnetization of the basement in the outer basins. Our interpretations do not support the magma-poor Iberian margin model which were recently extrapolated and applied to the pre-breakup development and structural environment of the mid-Norwegian volcanic passive margin.

How to cite: Zastrozhnov, D., Gernigon, L., Abdelmalak, M. M., Planke, S., Faleide, J. I., and Myklebust, R.: Marginal plateaus and pre-breakup development of the mid-Norwegian volcanic passive margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10558, https://doi.org/10.5194/egusphere-egu2020-10558, 2020.

How to cite: Nummelin, A., Straume, E. O., Gaina, C., LaCasce, J. H., and Nisancioglu, K. H.: Eocene - Oligocene paleobathymetry of the Atlantic - Arctic Oceanic Gateways: Influence on ocean circulation and climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11303, https://doi.org/10.5194/egusphere-egu2020-11303, 2020.

Deglaciation, volcanism and seismicity: the Icelandic record in the northern Atlantic during the Eemian and the Holocene

Van Vliet-Lanoë Brigitte ⁽¹⁾, Guillou Hervé ⁽²⁾, Bergerat Françoise⁽³), Chazot Gilles⁽¹⁾, Innocent Christophe ⁽⁴⁾,  Nonotte Philippe⁽¹⁾ , Liorzou Céline⁽¹⁾

• 1) Bretagne Occidentale, CNRS UMR 6538 Géosciences Océan 29280 Plouzané, France. brigitte.vanvlietlanoe@univ-brest.fr; gilles.chazot@univ-brest.fr, philippe.nonnote@univ-brest.fr, celine.liorzou@univ-brest.fr
• 2) CNRS-CEA, UMR 8212 LSCE. Gif /Yvette, France. guillou@lsce.ipsl.fr
• 3) Sorbonne Université, CNRS, Institut des Sciences de la Terre de Paris (ISTeP), UMR 7193, 4 place Jussieu 75005 Paris, France, bergerat@sorbonne-universite.fr
• 4) BRGM – LAB/ISO, Orléans cedex 2- France - innocent@brgm.fr

Large estuarine and lacustrine deposits in South, S-W, North and NE (Van Vliet-Lanoë et al., 2007, 2010, 2018), Iceland allow a fair record of the history of the deglaciation at MIS 3/2, 2/1, late 1 and MIS 6/5e, late 5e periods, consolidated with dating (Guillou et al. 2010, 2019, VVL et al. 2018). Pulsed deglaciations are all under control of orbital forcing and DO events, in association with a modification in the path of the Irminger current. In both systems, the history of the volcanic activity for Grἰmsvötn, Bárðarbunga, Askja and Hekla volcanoes are very similar, in connection with glacial unloading history. Tectonic activity and seismicity increased temporarily during deglaciation events leading to the discrete activity of inland SDR (Bourgeois et al., 2005, Bergerat & Plateau, 2012). Large earthquakes are restricted to full interglacial conditions (VVL et al., 2005, - on line). Hyaloclastite ridges are ice margin features related to long partial unloading events. The extent of these patterns to full glacial conditions revealed very unstable ice sheets under control of DO events and the associated gravitational spreading, leading to the formation of temporary ice shelves or grounded glacier margins.  

Bergerat, F., Plateaux, R. 2012. C.R. Geoscience, 344, 3-4, 191-204. doi : 10.1016/j.crte.2011.12.005,

Bourgeois O, Dauteuil O., Hallot E.   2005. Geodyn. Acta 18/1, 1-22.

Guillou, H., Scao, V., Nomade, S., Van Vliet-Lanoë, B., Liorzou, C., Guðmundsson, Á., 2019. 40. Quater.Sci. Rev., 209, 52-62.

Guillou, H., Van Vliet-Lanoë, B., Gudmundsson, A., Nomade, S., 2010. Quater. Geochr. 5 (1), 10-19.

Van Vliet-Lanoë B., Bourgeois O., Dauteuil O., Embry J.C., Guillou H., Schneider J.L. 2005. Geodyn Acta  18, 81-100.

Van Vliet-Lanoë, B., Bergerat, F., Allemand, P., Innocent, D, C., Guillou, H., Cavailhes, T., Liorzou C, Grandjean,  P. Passot, S. On line Quater. Res., 1-27. DOI:10.1017/QUA.2019.68

Van Vliet-Lanoë, B., Guðmundsson, A., Guillou, H., Duncan, R.A., Genty, D., Gassem, B., Gouy, S., Récourt, P., Scaillet, S. 2007 CRAS Géosciences 339, 1-12.

Van Vliet-Lanoë, B., Guðmundsson, Á., Guillou, H., Van Loon, A.J., De Vleeschouwer, F. Geologos 16(4), p.201–223. 2010.

How to cite: van Vliet-Lanoe, B.: Deglaciation, volcanism and seismicity: the Icelandic record in the northern Atlantic during the Eemian and the Holocene, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11329, https://doi.org/10.5194/egusphere-egu2020-11329, 2020.

Understanding the evolution and dynamics of polar ice sheets is of the utmost importance for reconstructing the climatic development in the past and estimating the future global climate changes. The Cenozoic climatic evolution has been characterized by repeated fluctuations between somewhat warmer and colder conditions. While the first appearance of continental-scale polar ice sheets on Antarctica is widely inferred and well constrained (Eocene‐Oligocene Transition, EOT; Miller et al., 2009; Cramer et al., 2012), the onset of the glaciation in the Northern Hemisphere remains much more enigmatic and controversial. It is commonly accepted that small ice sheets have been present on Greenland since late Miocene (Larsen et al., 1994) with an intensification of the glaciation and development of extensive polar ice sheets in the late Pliocene (Bailey et al., 2013). Although glacier ice was likely to be present on Greenland at the EOT (Moran et al., 2006; Tripati et al., 2005, 2008) it is still debated if it derived from scattered coastal outlet glaciers or from an actual ice sheet.

In this work we present detrital apatite fission-tracks analysis (AFT) on offshore deposits in order to reconstruct the sediment provenance. In detrital samples, grain-age distributions can be decomposed by statistical means into different main grain-age components or peaks (e.g. Galbraith and Green 1990) thus discerning the provenance of the sediments eroded at the time. Age peaks trends throughout the section also provide information about the exhumation rate and tectonic evolution of the source rock.

We collected detrital apatites from some sites of ODP Leg 152 and ODP Leg 162, conveniently located near the East Greenland coast (southern and central East Greenland, respectively), in order to obtain a continuous record from Eocene to middle Oligocene and from middle Miocene to present. The age peaks inferred for the offshore samples have been compared with the thermochronological data available onshore to find the potential sources. Our results point out a common provenance (at least since late Miocene) for both central and southern East Greenland offshore sediments, despite the distance of >1200 km between the two locations. Moreover, both samples display a mutually consistent trend of increasingly older AFT ages moving up the section, indicative of provenance changes. Such trend seems compatible with ice-rafting from icebergs calved from the Scoresby Sound outlet glaciers and drifting along the East Greenland Current that, should this be the case, would be active with the same modalities as now since the late Miocene. We tentatively argue that the “older ages upwards” trend is determined by climate variations, specifically by the expansion/thickening of the ice sheet. Any change due to tectonic events, if present, cannot be resolved. Conversely, the Eocene to middle Oligocene record displays a younging upwards trend with decreasing lagtime typical of an eroding continental margin.

How to cite: Cattò, S., Olivetti, V., and Zattin, M.: Provenance of Cenozoic glaciomarine sediments of East Greenland: constraints to the cryosphere evolution and continental margin erosion, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18992, https://doi.org/10.5194/egusphere-egu2020-18992, 2020.

A radical model for the North Atlantic and the Greenland-Iceland-Faroes Ridge

Christian Schiffer, Gillian Foulger, Kenni Petersen and Laurent Geoffroy

christian.schiffer@geo.uu.se

Analysis of teleseismic data from a seismological experiment in the East Greenland Caledonides reveals an east-dipping sub-crustal high velocity structure. The observations are consistent with a dipping eclogite layer underlying hydrated serpentinised mantle. The structure is therefore interpreted as a fossil subduction complex and may have radical implications for our understanding of the North Atlantic. 
Comparison with the very similar and well-known “Flannan reflector” in northern Scotland suggests that these two structures were once connected and now separated by the North Atlantic Ocean. Spatial correlation with geodynamic and magmatic events as well as structural peculiarities in the North Atlantic suggests an important control of this pre-existing structure on the plate tectonic evolution. For example, the Greenland-Faroe-Iceland Ridge formed where the North Atlantic rift crossed the proposed structure. The Jan Mayen Microplate formed exactly to the north of this intersection[CS1] .
We propose a new model for the formation of the North Atlantic that involves mainly plate tectonic processes and structural inheritance. The model involves delamination of dense orogenic crustal root and lithosphere triggering lower mantle upwelling and formation of a Large Igneous Province (LIP). Crustal flow and/or exhumation of the initially very thick (e.g. Tibet-like) continental lower-crust beneath extrusives could explain part of the anomalous thickness of the Greenland-Iceland-Faroes Ridge.

Our model explains several features of the North Atlantic, including microplate formation, enhanced magmatism and LIP formation, the formation of magma-rich and magma-poor continental margins, high-velocity lower crustal bodies, rift migration and formation of the Greenland-Faroe-Iceland Ridge.

How to cite: Schiffer, C., Petersen, K., Foulger, G., and Geoffroy, L.: A radical model for the North Atlantic and the Greenland-Iceland-Faroes Ridge, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22628, https://doi.org/10.5194/egusphere-egu2020-22628, 2020.