The polar regions of the Arctic and Antarctica face a similar problem with most areas covered by ice and/or sea water. But both polar regions attract international attention due to the ongoing climate change. While the Arctic realm hosts vast extended continental shelves bordering old land masses, one of the largest submarine Large Igneous Provinces (LIPs) -the Alpha-Mendeleev Ridge - of Mesozoic age, and the slowest mid-ocean spreading ridge (the Gakkel Ridge) on the globe; West Antarctica has been, tectonically, the active margin between the cratonic East Antarctica and the Pacific Ocean for ~500 Ma, recording several episodes of magmatism, fragmentation and continental growth. Both regions have a complex geological history and comprise crustal blocks of disparate tectonic origins. In this regard, applied and theoretical research in sedimentology, tectonics, geophysics, and geochemistry to investigate the tectonic evolution and dynamics of the polar regions is desired. This session provides a forum for discussions of a variety of problems linked to the Circum-Arctic geodynamics as well as evolution of West Antarctica, and aims to bring together a diversity of sub-disciplines including plate tectonics, mantle tomography, seismology, geodynamic modelling, igneous and structural geology, geophysical imaging, sedimentology, and geochemistry.
vPICO presentations: Mon, 26 Apr
West Antarctica developed as the tectonically active margin separating East Antarctica and the Pacific Ocean for almost half a billion years. Its dynamic history of magmatism, continental growth and fragmentation are recorded in sparse outcrops, and revealed by regional geophysical patterns. Compared with East Antarctica, West Antarctica is younger, more tectonically active and has a lower average elevation. We identify three broad physiographic provinces within West Antarctica and present their overlapping and interconnected tectonic and geological history as a framework for future study: 1/ The Weddell Sea region, which lay furthest from the subducting margin, but was most impacted by the Jurassic initiation of Gondwana break-up. 2/ Marie Byrd Land and the West Antarctic rift system which developed as a broad Cretaceous to Cenozoic continental rift system, reworking a former convergent margin. 3/ The Antarctic Peninsula and Thurston Island which preserve an almost complete magmatic arc system. We conclude by briefly discussing the evolution of the West Antarctic system as a whole, and the key questions which need to be addressed in future. One such question is whether West Antarctica is best conceived as an accreted collection of rigid microcontinental blocks (as commonly depicted) or as a plastically deforming and constantly growing melange of continental fragments and juvenile magmatic regions. This distinction is fundamental to understanding the tectonic evolution of young continental lithosphere. Defining the underlying geological template of West Antarctica and constraining its linkages to the dynamics of the overlying ice sheet, which is vulnerable to change due to human activity, is of critical importance.
How to cite: Jordan, T., Riley, T., and Siddoway, C.: Overview of West Antarctic tectonic evolution from ~500 Ma to the present, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8265, https://doi.org/10.5194/egusphere-egu21-8265, 2021.
Antarctica has traditionally been considered continental inside the coastline of ice and bedrock since Press and Dewart (1959). Sixty years later, we reconsider the conventional extent of this sixth continent (Artemieva and Thybo, Earth-Science Reviews, 2020, https://doi.org/10.1016/j.earscirev.2020.103106).
Geochemical observations show that subduction was active along the whole western coast of West Antarctica until the mid-Cretaceous after which it gradually ceased towards the tip of the Antarctic Peninsula. We propose that the entire West Antarctica formed as a back-arc basin system flanked by a volcanic arc, similar to e.g. the Japan Sea, instead of a continental rift system as conventionally interpreted and tagged in the literature as “West Antarctica Rift System”.
Globally, the fundamental difference between oceanic and continental lithosphere is reflected in hypsometry, largely controlled by lithosphere buoyancy. The equivalent (corrected for ice and water) hypsometry in West Antarctica (−580 ± 335 m on average, extending down to −1580 m) is much deeper than in any continent, since even continental shelves do not extend deeper than −200 m in equivalent hypsometry. However, an unusually deep equivalent hypsometry in West Antarctica corresponds to back-arc basins (with average values of equivalent hypsometry between ca −3000 m and −300 m) and oceans proper. This first order observation questions the conventional interpretation of West Antarctica as continental.
We present a suite of geophysical observations that supports our geodynamic interpretation:
- a linear belt of seismicity sub-parallel to the volcanic arc along the Pacific margin of West Antarctica;
- a pattern of free air gravity anomalies typical of subduction systems;
- and extremely thin crystalline crust typical of back-arc basins.
We calculate lithosphere density for two end-member scenarios to fit the calculated mantle residual gravity anomalies and seismic data on crustal thickness and demonstrate that it requires the presence of:
- (1) a thick sedimentary sequence of up to ca. 50% of the total crustal thickness, or
- (2) extremely low density mantle below the deep basins of West Antarctica and, possibly, the Wilkes Basin in East Antarctica.
Case (1) implies that for 25 ±6 km of the total crustal thickness, the crystalline basement is only 12-15 km thick, and such values are not observed in continental crust. Case (2) requires the presence of anomalously hot mantle below the entire West Antarctica with a size much larger than around continental rifts.
These results favor the presence of oceanic or transitional crust in most of West Antarctica and possibly beneath the Ronne Ice Shelf. Our model predicts that a granitic crustal layer with a high radiogenic heat production is almost absent in most of West Antarctica, which may affect heat flux at the base of the ice with potential important implications for models of ice melting. We propose, by analogy with back-arc basins in the Western Pacific, the existence of rotated back-arc basins caused by differential slab roll-back during subduction of the Phoenix plate under the West Antarctica margin.
Our finding reduces the continental lithosphere in Antarctica to 2/3 of its traditional area. It has significant implications for global models of lithosphere-mantle dynamics and models of the ice sheet evolution.
How to cite: Artemieva, I. M. and Thybo, H.: One third of Antarctica is not continental: Geophysical evidence for West Antarctica as a backarc system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9259, https://doi.org/10.5194/egusphere-egu21-9259, 2021.
Yelcho Station is set on Doumer Island located in the southernmost section of Gerlache Strait between Anvers and Wienke Islands at the northwestern region of Antarctic Peninsula. This area is dominated by plutonic and volcanic deposits associated with the active margin developed during the Mesozoic and Cenozoic in the Antarctic Peninsula (e.g. Leat et al., 1995). Although Yelcho Station has been intensively visited since a few decades, the outcropping rocks have not been studied in detail. Furthermore, this location has hosted relevant contributions in the environmental and ecological sciences. We will present a detailed map (1:500) of the geological units outcropping in Yelcho Station based in fieldwork observations, which will be combined with drone and satellite images. Additionally, remote sensing spectral studies will be developed to support the geological mapping. This work will help to establish a geological baseline, which may serve for future studies in the area of Yelcho Station. This contribution will be a detailed geological study in the Antarctic Peninsula, which will also enhance our understanding of the geological units outcropping in Gerlache Strait. This material will also serve as an educational and outreach information for the polar community.
Leat et al. (1995). Geological Magazine 132 (4), 399-412 (DOI: 10.1017/S0016756800021464).
How to cite: Jara, W., Bastias, J., Jaña, R., and Leppe, M.: The geology of Yelcho Station: a new high-resolution geological map at northwestern Antarctic Peninsula, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12707, https://doi.org/10.5194/egusphere-egu21-12707, 2021.
King George Island is the largest one of the South Shetland Islands group distributed parallel to and separated by the Bransfield Strait of the northern tip of Antarctic Peninsula. The archipelago of the South Shetlands is mainly composed of the products of the active margin developed as a result of the subduction of the Phoenix Plate beneath the continental crust of the Antarctic Peninsula (e.g. Barker, 1982; Bastias et al., 2019). The lithologies are largely dominated by Mesozoic and Cenozoic sedimentary and volcanic successions that are cut by a few hypabyssal plutons. While some authors have suggested a southwest to northeast trend along the archipelago from older to younger magmatic activity (e.g. Haase et al., 2012), others have indicated that some of the magmatic events may have been recorded along the entire archipelago (e.g. Valanginian arc rocks; Bastias et al., 2019). Regardless, King George Island hosts an exceptional stratigraphical record of the Cenozoic period. Moreover, this island is mostly covered by an ice cap at the present day, which is commonly terminated with ice cliffs around much of the island. The southern edge of the island host Mesozoic and Paleogene successions, these rocks are dominated by volcanic and volcaniclastic units. The rocks in King George Island are generally young to the east and to the north ends. Cape Melville, the southeast extreme of the island, hosts the youngest sedimentary rocks known on the island: the Moby Dick Group (Birkenmajer, 1985).
While several authors have presented local studies in the King George Island over the last three decades, an integrated assessment of the outcropping units in the entire island remains unexplored. A new geological map for King George Island will allow to update the current understanding of the stratigraphy of the South Shetland Islands, which will help to support not only the geological studies but also those focused on the environmental and paleontological record.
Barker, 1982. Journal of the Geological Society 19, 787-801. (DOI: 10.1144/gsjgs.139.6.0787)
Bastias et al. (2019). International Geology Review 62 (11), 1467-1484. (DOI: 10.1080/00206814.2019.1655669)
Birkenmajer (1985). Bulletin Polish Academic Earth Sciences 33:15-23.
Haase et al. (2012). Contributions to Mineralogy and Petrology 163, 1103-1119. (DOI: 10.1007/s00410-012-0719-7).
How to cite: Lopez, B., Bastias, J., Matus, D., Jaña, R., and Leppe, M.: The geology of King George Island, South Shetland Islands: uniting local geological maps and stratigraphical columns, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13145, https://doi.org/10.5194/egusphere-egu21-13145, 2021.
Northern Victoria Land constitutes the Pacific terminus of the Transantarctic Mountains (TAM) on the western shoulder of the Cenozoic West Antarctic Rift System. It is characterised by a distinct morphological transition from an elevated peneplain that dominates throughout most of the TAM to a strongly undulating relief with prominent narrow crests and alpine peaks. This contrast is associated with a lithological change from high-grade metamorphics and granitoids to low-grade metasedimentary rocks that contain only few scattered igneous bodies.
New high-resolution thermochronological data (fission-track and (U-Th-Sm)/He) from more than 60 locations in the Southern Cross Mountains and Mountaineer Range of northern Victoria Land provide the basis for studying regional exhumation and uplift with particular focus on the establishment of landscape contrasts. In an integrated approach, differences in topography are examined with respect to regional and local controls including tectonics, lithology and climate to identify differential trends and quantify the morphological evolution of the TAM and West Antarctic Rift System.
Two coastal profiles covering 2 to 3 km in elevation reveal apatite fission track ages from 23 to 45 Ma with mean track lengths of 13.3 – 14.7 μm. Corresponding (U-Th-Sm)/He apatite and zircon data range between 19 – 32 Ma and 24 – 27 Ma, respectively. The dates show distinctive spatial trends of increasing ages from north to south and at greater distance to the coast whereby younger cooling ages correlate with stronger terrain segmentation and higher topographic relief.
Thermal history modelling of the combined data indicates that accelerated cooling commencing at 35 Ma proceeded at progressively higher rates reaching >25°C/Ma in late stages. This cooling episode continued until at least 20 Ma and refers to exhumation from burial depths of more than 5 km, clearly exceeding the calculated overburden on adjacent crustal blocks to the south. Although rapid upper lithospheric cooling is a generic feature of northern Victoria Land, the current data demonstrates that Cenozoic exhumation dynamics were highly differential. Understanding these patterns requires thorough balancing of structural against isostatic factors, lithological against climate parameters and focussed local incision against large-scale denudation and levelling processes.
How to cite: Roehnert, D., Lisker, F., Balestrieri, M. L., Grewe, L., Balbi, E., Läufer, A., Crispini, L., and Spiegel, C.: Thermochronology as a key to deciphering controls on landscape evolution in northern Victoria Land (Transantarctic Mountains) , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12982, https://doi.org/10.5194/egusphere-egu21-12982, 2021.
The Rennick Geodynamic Belt (RGB, East Antarctica) is a regionally sized, ca N-S trending, deformation zone (length > 100 km) where a dense fault network separates tectonic units of northern the Victoria Land, to the W from the East Antarctic Craton, to the E.
The RGB is long known to have been active since Cambrian-Ordovician times up to recent, but its framework and geodynamic evolution is still debated and partially investigated. The long-lived tectonic activity led to a great structural complexity, due to the superposition and polyphasic reactivation of regional faults. Such complexity is reflected by the numerous (in some cases contrasting) tectonic reconstructions of the RGB area.
In this contribution we explore the present-day tectonic framework of the RGB, investigating the stress field that possibly characterised the last geodynamic events in the area. We base on selected datasets of fault-slip data and fractures density (collected by the Authors in various PNRA Italian Antarctic expeditions) and combine fault-slip data inversion with the azimuthal orientation of faults and the spatial distribution of fractures intensity across the RGB.
To obtain a more robust portrait of the RGB geodynamic evolution, two different software based on different fault-inversion methods were used in this study: DAISY (Windows, version 3.5) and FSA (MAC, version 36.5x7i). The software DAISY implements the multiple Monte Carlo convergent method and provides the best orientation of the principal paleostresses with an estimate of the error quantified by the factor MAD (Mean Angular Deviation, corresponding to the average angular deviation between the measured pitch of the kinematic vector on the fault plane and the predicted one by applying to the fault the computed paleostress). At each step, faults are uniquely associated to the stress tensor that provides the lowest MAD. Differently, the FSA software combines a random grid search of the stress tensors following a Monte Carlo approach, under the univocal condition of fulfilment of the frictional constraint (i.e. the fault plane must form with an orientation that satisfies the Mohr-Coulomb yield criterion, i.e. t/sn = tgf with t = shear stress, sn = normal stress and f = angle of internal friction). Additionally, this software allows a direct examination of the reduced Mohr circle of the calculated stress tensors, so that we can select the one with the largest number of faults showing a high t/sn ratio.
The paleostress tensors were computed from 373 fault-slip data collected in 34 structural stations on site. Results from this multi methodological approach revealed:
(i) the existence of two, N-S oriented geotectonic provinces (namely the Bowers Mts province to the W and Usarp Mts to the E) characterized by the different spatial distribution of brittle deformation, more intense in the Bower Mts domain.
(ii) The superposition of two recent (Meso-Cenozoic) major tectonic events, with prevalent strike-slip kinematics and characterized by faults reactivation with right-lateral movement overprinting a previous left-lateral one.
How to cite: Locatelli, M., Cianfarra, P., Crispini, L., and Federico, L.: Multiple reactivation of the Rennick Geodynamic Belt (northern Victoria Land, Antarctica): insights from inversion of fault slip data , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11675, https://doi.org/10.5194/egusphere-egu21-11675, 2021.
The Mesozoic Karoo-Maud and Kerguelen plumes had a significant influence on Gondwana and the oceanic lithosphere. Jurassic magmatism, formed under the influence of a huge Karoo plume at 184–178 Ma ago, covered large areas of the Dronning Maud Land in East Antarctica. Later, 130 – 0 m.y. ago, under the influence of the Kerguelen plume, magmatism formed in the area of the Lambert glacier, and the Gaussberg volcano (Quaternary time) appeared, located on the coast opposite the Kerguelen archipelago. We assume that the Karoo mantle plume initiated the formation of a “mega-apophyses” from the main plume manifestation area within the Karoo province in the southeastern African continet (ca. 2000 km in diameter). These mega-apophyses are represented by the Ferrar Igneous Province (ca. 3000 km long area of intrusive activity along the Transantarctic Mountains) and a supposed igneous province (ca. 1500 km long) covering the East Antarctic coast between the Lazarev and Cosmonauts Seas. Based on petrological and geochemical studies, the characteristic features of magmas of the Karoo, Dronning Maud Land, and Ferrar igneous provinces have been determined, which indicate that for all magmas associated with Karoo and Kerguelen plumes, the main source of melt enrichment is a mantle source with characteristics of the EM-II component (most typically for magmas of the Ferrar Province). It reflects the properties of an enriched, fluid-rich, ancient continental mantle, metasomatized at the early stages of the tectonic development of the region and involved in the melting process. A rarer admixture of the ancient lithospheric component (EM-I, with 206Pb/204Pb = 16.5 and 143Nd/144Nd = 0.5122) was revealed in both plumes. The existence of mantle plumes in the Southern Hemisphere and their long-term development had a significant impact on the structure and evolution of the East Antarctica.
How to cite: Sushchevskaya, N., Leitchenkov, G., and Belyatsky, B.: Tectono-magmatic evolution of the Karoo and Kerguelen plumes and their impact onto magmatism of the East Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5128, https://doi.org/10.5194/egusphere-egu21-5128, 2021.
A complex tectonic history and global climate change has influenced the land masses bordering the Arctic ocean. On land tectonic movement affects runoff patterns, local hydology such as increased precipitation and local surface elevation, which again affects landform development, coastline distribution, discharge routing and vegetation distribution. Land- atmosphere- biosphere links and feedback loop with the ocean are continuously refined for use in earth system models for the youngest part of geological history. With access to large data sets, improved technology and new knowledge and methodologies it is now increasingly possible to also reconstruct direct surface response to tectonic movement in deep time.
The Paleogene Central Tertiary Basin, Svalbard, Norway formed in response to the complex opening and collision at the entrance to the Arctic Ocean, causing uplift in the west and basin formation and fill in the Central Spitsbergen area. Well exposed outcrops and extensive work in the area for decades provides a framework of palaeogeographic change within the basin. The basin deposits range from continental to deep marine with changing coastline positions largely caused by tectonic activity. The timing of the basin development coincides with the time period immediately before and after the PETM and thus provides an example of a terrestrial system in a warm Arctic. Syndepositional volcanic eruptions in the Arctic area are reflected in tephra layers, which also provide opportunity for correlation and absolute time estimates (Jones et al. 2017).
We use data from two formations deposited within the basin as a field laboratory for surface response to tectonic and climate change in the Arctic. The Paleocene Firkanten Fm, is deposited during the early stages of basin formation and pre-PETM. The Eocene Aspelintoppen Formation, is deposited during late stages of basin filling and is post-PETM. Both formations are characterized by continental to paralic deposits and contain traces of palaeovegetation such as coal seams, palaeosols and fossil leaves. A large amount of exploration drill holes through the Firkanten Fm provide a unique insight into the palaeotopography and depositional trends relative to topography during deposition (Marshall et al., submitted). The presence of coal seams allows for direct reconstruction of vegetation (peat bogs) and interaction between hydrology and deposition. The Aspelintoppen Formation comprises a thick succession of channel and floodplain deposits and reflects a balance between sediment supply and accommodation. We use virtual outcrops to provide 3D architecture from inaccessible mountain sides to improve the possibilities for quantification of precipitation and discharge parameters from the basin.
Jones, M.T., Augland, L.E.,, Shephard, G.E., Burgess, S.D., Eliassen, G.T., Jochmann, M.M., Friis, B., Jerram, D.A., Planke, S. & Svensen, H.H., 2017: Constraining shifts in North Atlantic plate motions during the Palaeocene by U-Pb dating of Svalbard tephra layers. Nature Scientific Reports 7: 6822 DOI:10.1038/s41598-017-06170-7
Marshall, C., Jochmann, M., Jensen, M., Spiro, B.F., Olaussen, S., Large, D.J.: Time, hydrologic landscape and the long-term storage of peatland carbon in sedimentary basins. Submitted to Journal of Geophysical Research - Earth Surface
How to cite: Jensen, M. A., Jochmann, M., Marshall, C., and Bøgh Mannerfelt, A.: How does increased palaeosurface reconstruction contribute to understanding of the Arctic? - Developing a deep time palaeoclimate field laboratory in Svalbard., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16340, https://doi.org/10.5194/egusphere-egu21-16340, 2021.
Prior to break up of Greenland and Svalbard, the Wandel sea basin with Carboniferous to Cenozoic deposits formed in eastern North Greenland. These deposits were affected by the last major period of Arctic tectonism, the Eocene Eurekan deformation. Vitrinite reflectance data from late Cretaceous rocks long the east coast of North Greenland indicate unusual high thermal maturity in association with a swarm of quartz veins, which exceeds the thermal maturity associated with the Eurekan deformation further inland. This pattern is also observed in Cenozoic sediments further to the north as well as along the conjugated North Atlantic margin, in western Svalbard. However, cause and origin of the elevated heat flow indicated by thermal maturity values are not known so far and the timing is not well constrained. We test the hypothesis whether this pattern was established coevally along both margins of the North Atlantic and marks a post-Eurekan thermal event. Vitrinite reflectance data indicate temperatures high enough to reset low temperature chronometers, therefore we used apatite fission track (AFT) and (U-Th-Sm)/He (AHe) thermochronology to determine the age of the high thermal maturation and associated quartz veins formation.
Our data reveals a more complex thermal history than hypothesized:
For the eastern North Greenland margin thermal history modelling of the combined AFT and AHe ages indicates a pre-Eurekan phase of elevated heat flow between 72 Ma and 66 Ma causing the high vitrinite reflectance and the formation of the quartz veins in the late Cretaceous rocks. Additional petrographic and electron microprobe analysis reveals the growth of feldspar, hematite, amphibole, and tourmaline within the quartz veins. According to most paleogeographic reconstructions, northern Greenland was located to the south of Svalbard close to a volcanic province near Bear Island. Heating may thus be associated with incipient igneous activity of that area, related to initial North Atlantic opening. A second phase of elevated heat flow between 58 Ma and 52 Ma is indicated by thermal history modelling of the AFT and AHe ages from the Cenozoic rocks further north. This frames the timing of the initiation of the dextral displacement between Greenland and Svalbard and might be associated with heat transfer along the transform fault from the active spreading centres in the North Atlantic and the Arctic Ocean.
Contrasting to the results of North Greenland, thermal history modelling of AFT and AHe ages from the Cenozoic rocks of western Svalbard reveals heating throughout the Eocene and onset of cooling only during the early Oligocene for the Svalbard margin. Thus, even though we cannot exclude a similar thermal history during the Paleocene to early Eocene, the eastern North Greenland and western Svalbard margins are characterized by a differential thermal evolution during the ~middle Eocene to Oligocene.
In conclusion, our data show that the thermal history of the conjugated continental margins along the northern North Atlantic is characterized by episodic heat flow variations predominantly controlled by oceanic plate tectonic processes.
How to cite: Meier, K., O'Sullivan, P., Jochmann, M., Monien, P., Piepjohn, K., Lisker, F., and Spiegel, C.: Thermal imprints along conjugated continental margins in response to the opening of the northern North Atlantic - case studies from eastern North Greenland and western Svalbard, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15213, https://doi.org/10.5194/egusphere-egu21-15213, 2021.
Sub-surface sampling of marine sediments allows investigation of paleo-depositional conditions and subsequent modification by post-depositional geochemical processes. This sedimentary record can encompass many thousands of years and record discrete events where proximal and distal material is incorporated into the pelagic sediment column. The Arctic Ocean is the world’s smallest ocean, however evidence from sedimentary records show it has a pivotal role in the regulation of many oceanographic and physiographic processes. Despite this, there are only limited studies on the distribution and geochemical behaviour of metals within sub-surface marine sediments of the Arctic Ocean basin. This study presents a detailed geochemical investigation for two sediment piston cores to a maximum of 5.7 metres depth and spanning at least 44,000 years BP, from two seamounts bordering the western flanks of the Molloy Hole in the Fram Strait.
Comparison to other studies of sub-surface ridge sediments below 60oS on the Mid-Atlantic Ridge reveals these piston cores contain elevated metal concentrations, particularly for Mn, Co, and Ni. Distinct variability is observed within, and between the cores; particularly the interplay between Fe and Mn, the two most common authigenic elements in marine pelagic sediments. Within the Molloy Ridge neovolcanic zone, in the upper half of the easternmost core (PC127/79), Fe and Mn are decoupled and metal distribution is controlled by redox front migration. Decoupling occurs as Mn is more readily dissolved compared to Fe, and Fe in solution is more reactive and precipitates quicker during remobilisation. In PC127/79, Mn is strongly associated with other redox-sensitive metals (e.g., Co, Ni, Mo, U) likely in Mn-oxide dominated horizons, and Fe is strongly associated with V and As. Towards the base of the core, Fe and Mn are coupled, but are not associated with a distinct discrete metalliferous signature of Co, Ni, Cd and Ti. These metals are also negatively associated with major rock-forming elements such as Si, Al, Mg, and Ca. In the western core (PC127/80), Fe and Mn are coupled, are positively associated with the majority of metals and the major rock forming elements, and negatively correlated with common clay-derived components.
Investigation of pelagic versus hydrothermal component indices indicate that the distinct metalliferous signature towards the base of PC127/79 may have a hydrothermal origin. Hydrothermal activity associated with ultramafic oceanic core complexes is known on superslow-spreading ridges to the north and south of the Molloy Ridge, however contributions of metals from ice-rafted debris or past mass wasting events off the Spitsbergen margin cannot be ruled out.
How to cite: Grant, H., Lockwood-Ireland, C., Howe, J., and Stewart, H.: Controls on the distribution and behaviour of metals in sub-surface metalliferous seamount sediments from the Molloy Ridge system, Arctic Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10154, https://doi.org/10.5194/egusphere-egu21-10154, 2021.
The High Arctic Large Igneous Province (HALIP) represents extensive Cretaceous magmatism throughout the circum-Arctic borderlands and within the Arctic Ocean (e.g., the Alpha-Mendeleev Ridge). Recent aeromagnetic data shows anomalies that extend from the Alpha Ridge onto the northern coast of Ellesmere Island, Nunavut, Canada. To test this linkage we present new bulk rock major and trace element geochemistry, and mineral compositions for clinopyroxene, plagioclase, and olivine of basaltic dykes and sheets and rhyolitic lavas for the stratotype section at Hansen Point, which coincides geographically with the magnetic anomaly at northern Ellesmere Island. New U-Pb chronology is also presented.
The basaltic and basaltic-andesite dykes and sheets at Hansen Point are all evolved with 5.5–2.5 wt% MgO, 48.3–57.0 wt% SiO2, and have light rare-earth element enriched patterns. They classify as tholeiites and in Th/Yb vs. Nb/Yb space they define a trend extending from the mantle array toward upper continental crust. This trend, also including a rhyolite lava, can be modeled successfully by assimilation and fractional crystallization. The U-Pb data for a dacite sample, that is cut by basaltic dykes at Hansen Point, yields a crystallization age of 95.5 ± 1.0 Ma, and also shows crustal inheritance. The chronology and the geochemistry of the Hansen Point samples are correlative with the basaltic lavas, sills, and dykes of the Strand Fiord Formation on Axel Heiberg Island, Nunavut, Canada. In contrast, a new U-Pb age for an alkaline syenite at Audhild Bay is significantly younger at 79.5 ± 0.5 Ma, and correlative to alkaline basalts and rhyo- lites from other locations of northern Ellesmere Island (Audhild Bay, Philips Inlet, and Yelverton Bay West; 83–73 Ma). We propose these volcanic occurrences be referred to collectively as the Audhild Bay alkaline suite (ABAS). In this revised nomenclature, the rocks of Hansen Point stratotype and other tholeiitic rocks are ascribed to the Hansen Point tholeiitic suite (HPTS) that was emplaced at 97–93 Ma. We suggest this subdivision into suites replace the collective term Hansen Point volcanic complex.
The few dredge samples of alkali basalt available from the top of the Alpha Ridge are akin to ABAS in terms of geochemistry. Our revised dates also suggest that the HPTS and Strand Fiord Formation volcanic rocks may be the hypothesized subaerial large igneous province eruption that drove the Cretaceous Ocean Anoxic Event 2.
How to cite: Naber, T. V., Grasby, S. E., Cuthbertson, J. P., Rayner, N., and Tegner, C.: New constraints on the age, geochemistry and environmental impact of High Arctic Large Igneous Province magmatism: Tracing the extension of the Alpha Ridge onto Ellesmere Island, Canada, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16329, https://doi.org/10.5194/egusphere-egu21-16329, 2021.
Located along the Canadian polar continental margin, the Sverdrup Basin is an elongated, intracontinental sedimentary basin that originated during Carboniferous-Early Permian rifting. Starting in the Early Cretaceous, volcanic complexes (VC) were emplaced throughout the basin, which are associated with the High Arctic Large Igneous Province (HALIP). Geochronological and geochemical data on HALIP rocks exposed on Axel Heiberg Island and northern Ellesmere Island suggest several discrete stages of emplacement; (1) voluminous mafic intrusive activity of tholeiitic character accompanied by minor extrusive volcanism at ca. 125-110 Ma (VC1a); the eruption of tholeiitic flood basalts on Axel Heiberg Island at ca. 100-90 Ma (VC1b); the emplacement of mildly alkaline lava flows, sills and dykes on Ellesmere Island at ca. 100-90 Ma (VC2); and the eruption of a suite of alkaline lava flows from central volcanoes at ca. 85-75 Ma (VC3). Each magmatic episode is characterized by a distinctive eruptive style and coherent geochemical signature regardless of the mode of emplacement. In this context, onshore manifestations of the HALIP can be viewed as time-markers in the evolution of the adjacent polar continental margin.
We use digital plate tectonic models, constructed via the GPlates software, to explore the parallel development of the Sverdrup Basin and proto-Arctic Ocean (Amerasia Basin) during the Early Cretaceous, and the transition from a sedimentary to volcanic Sverdrup Basin. Plate reconstructions of the Amerasia Basin at ca. 125 Ma suggest two zones of extension; one within the Canada Basin, which may include seafloor spreading, (Zone 1, more distal to the Sverdrup Basin) and the second further northwards in the Alpha-Mendeleev Ridge and Makarov Basin domains offshore northern Ellesmere Island (Zone 2, proximal to the northeastern portion of the Sverdrup Basin). The potential for enhanced melting caused by mantle flow (possibly related to the arrival of a mantle plume) towards the Sverdrup Basin depocentre could explain widespread magmatism of tholeiitic character from ca. 125-90 Ma (VC1). The transition to mildly alkaline (VC2) and alkaline magmatism (VC3) at ca. 100 Ma may have signaled the end of extension in Zone 1. The persistence of localized extension in Zone 2 could explain the shift in magmatic style and compositional diversity of igneous rocks emplaced at intrusive complexes (VC2) vs constructional volcanic edifices (VC3). In addition, greater depth to Moho along the northeastern Sverdrup Basin may have contributed to restricted mantle flow in Zone 2. We propose that the spatio-temporal evolution of HALIP magmatism in the Sverdrup Basin during the Cretaceous relates to (1) different styles of tectonic extension (distal vs proximal, protracted vs discrete, widespread vs narrow, seafloor spreading vs hyper-extensional rifting), and (2) the presence of hot, thin lithosphere close to the basin depocentre vs cold and thick lithosphere in the northeastern part of the basin.
How to cite: Williamson, M.-C., Shephard, G. E., and Kellett, D. A.: Contrasting styles of magmatism and rifting in the High Arctic LIP, Sverdrup Basin, Canadian Arctic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12230, https://doi.org/10.5194/egusphere-egu21-12230, 2021.
During Late Cretaceous times the Sverdrup Basin, Arctic Canada, received considerable air-fall volcanic material. This is manifested as numerous centimetre- to decimetre-thick diagenetically altered volcanic ash layers (bentonites) that occur interbedded with mudstones of the Kanguk Formation. Previous research on bentonite samples from an outcrop section in the east of the basin (Sawtooth Range, Ellesmere Island) revealed two distinct volcanic sources for the bentonites: most of the bentonites analysed (n=9) are relatively thick (0.1 to 5 m), were originally alkaline felsic ashes, and were likely sourced from local volcanic centres on northern Ellesmere Island or the Alpha Ridge that were associated with the High Arctic Large Igneous Province (HALIP). Two thinner (<5 cm) bentonites with contrasting subalkaline geochemistry were also identified. These were inferred to have been derived from further afield, from volcanic centres within the Okhotsk-Chukotka Volcanic Belt, Russia.
To better understand volcanism within the vicinity of the Sverdrup Basin during Late Cretaceous times, and further test the above interpretations, a larger suite of bentonite samples was investigated, drawing on samples from outcrop sections in the central and eastern Sverdrup Basin. Whole-rock geochemical analyses and combined zircon U-Pb age and Hf isotope analyses were undertaken. The vast majority of bentonites analysed to date have alkaline geochemistry and were likely sourced from proximal volcanic centres related to the HALIP. The combined U-Pb and Hf isotope data from these bentonites show a progression from evolved (-2 to 0) to moderately juvenile (+9 to +10) εHf(t) values between late Cenomanian and early Campanian times (c. 97–81 Ma). This is interpreted to record compositional change through time within the local HALIP magmatic system.
How to cite: Pointon, M., Flowerdew, M., Hülse, P., Schneider, S., Millar, I., and Whitehouse, M.: Tracking compositional changes within the High Arctic Large Igneous Province using zircon Hf isotopes from altered volcanic ash layers of the Sverdrup Basin, Canada, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15074, https://doi.org/10.5194/egusphere-egu21-15074, 2021.
Alaska is made up of a mosaic of terranes that have enigmatic origins. Several plate restorations for the assembly of Alaska have been proposed, but their validity remains debated, partly due to the removal of vast volumes of oceanic plate material via subduction at the accretionary margins. The position, depth and volume of this subducted lithosphere, recognised as seismically fast anomalies in tomographic images, can be used to track the locations of subduction plate boundaries of the past, thus serving as an important constraint for plate restorations of convergent margins. Existing plate tectonic reconstructions can be assessed and developed further by integrating seismic tomographic models of the mantle with geological and palaeomagnetic bedrock datasets, a procedure which we term “tomotectonic analysis”.
Previous tomotectonic studies (e.g., Sigloch & Mihalynuk, 2017, GSA Bulletin) have highlighted various discrepancies between the most generally accepted tectonic reconstruction models of the western coast of North America and tomographic observations of slabs in the mantle. For example, the kinematic reconstruction of Laurentia, constrained by the opening of the Atlantic Ocean, places the Cordilleran margin thousands of kilometres east of the tomographically imaged Angayucham and Mezcalera slabs in the mantle during the Early to Late Jurassic. This suggests that there was extensive westward subduction beneath the Insular and Intermontane superterranes that involved multiple plates, rather than a single subduction zone. Though a recent plate reconstruction that employed tomotectonic methods (Clennett et al., 2020, G-Cubed) provided a coherent explanation of bedrock, plate kinematic and mantle observations for the Cordilleran margin, application of this model to Alaska and the Arctic was hindered by low tomographic resolution beneath that region and requires further investigation. In particular, restoration of the Arctic Alaska terrane is complicated further by its possible relationship with the proposed Arctic Alaska-Chukotka microcontinent and its involvement in the accretionary development of the Siberian peninsula and the opening of the Canada Basin, for which several working hypotheses continue to be debated.
In this study we consider the application of tomotectonic analysis to Mesozoic reconstructions of the western Arctic and central Alaska. We will compare and contrast these tectonic reconstructions with respect to the distribution of slabs in the deep mantle based on observations from the latest seismic tomographic models, such as DETOX-P1, P2 and P3 (Hosseini et al., 2020, GJI). We will also highlight the limitations of current tomographic models and the need for targeted seismic investigations with greater resolution of the underlying mantle. This discussion provides the motivation and rationale for a new seismic tomographic model of the mantle beneath North America currently being produced by the authors using a more complete USArray dataset.
How to cite: Kemp, M., Parsons, A., Sigloch, K., Mihalynuk, M., and Stephenson, S.: Tomotectonic constraints on the assembly of the western Arctic region and central Alaska: progress, problems and future direction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12554, https://doi.org/10.5194/egusphere-egu21-12554, 2021.
The Eastern Arctic is poor studied by offshore drilling. There are some wells drilled on the Alaska shelf, but Russian sedimentary basins are separated from Alaska basins by tectonic structures, therefore seismic complexes could not be traced confidently from Alaska to the North Chukchi Basin. Nevertheless, seismic lines in the Eastern Arctic acquired in last decade, samples from seafloor scarps on the Mendeleev Rise (Skolotnev et al., in preparation) and geologic data from adjacent onshore geology allows to assume the mechanisms and timing of the Eastern Arctic Basins forming. According to data from De-Longa Islands and from sampling on the scarps of the Mendeleev rise, the wide basalt volcanism was acting during ±125-100 Ma. The volcanism related to forming of rift basins all over the Eastern Arctic. On the seismic lines crossing the Mendeleev Rise some structures that could be interpreted as volcanos and Seaward Dipping Reflectors (SDR) are identified at the base of geological section. The top of these structures are traced on the seismic lines, and continue from the Mendeleev rise to the North Chukchi Basin where they are covered by clastic complexes that prograde from the territory of the Early Cretaceous Verkhoyansk-Chukotka Orogen. On this account the North Chukchi Basin started to form not earlier than in Barremian-Aptian. Continuation of Mendeleev Rise into the North Chukchi Basin is confirmed by the data of magnetic anomalies. To the south of the North Chukchi Basin on the Wrangel-Gerald High the volcanic build-ups and associated intrusions are interpreted. Presence of magmatic features in this area is confirmed on the magnetic anomaly map. The volcanic horizons lay below the sedimentary cover of the North Chukchi Basin. Our main conclusion is that Mendeleev Rise and North Chukchi Basin started to form nearly simultaneously during Aptian (Barremian) - Albian time and they compile connected geodynamic system.
How to cite: Startseva, K., Nikishin, A., and Rodina, E.: Mendeleev Rise basalts compile an acoustic basement of the North Chukchi Basin?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8840, https://doi.org/10.5194/egusphere-egu21-8840, 2021.
The Mendeleev Rise is represented by an asymmetric uplifted crustal block with strongly rugged by half-graben and horst structures. High-amplitude reflectors similar to SDR (Seaward Dipping Reflectors) were found in half-grabens. Similar structures were found in the Toll and Podvodnikov basins.
The top of the SDR complex is usually relatively well defined and corresponds to the rift-post-drift boundary with an age of about 100 Ma. Small, sharp conical build-ups with a chaotic internal structure are often observed at the top of the SDR – probably submarine volcanoes. There may have been two stages of volcanism. The bottom of the SDR complex corresponds to the top of the acoustic basement (about 125 Ma). The thickness of one wedge is about 1, 5 - 3 sec. The length of distinct wedges in the Mendeleev Rise’s area is about 25-50 km, in the Podvodnikov basin’s area – 50-100 km.
Several types of SDR have been identified. The first type is identified within the Toll basin and the Mendeleev Rise. This is the most classic type. Wedges of this type are characterized by greater thickness, but less length. Wedges are strongly curved. Several distinct wedges stand out. Distinct wedges overlap each other towards the stretch center and start from one point. SDR have longer wedges and slightly less thickness in the Podvodnikov basin’s area. The SDR complex is highly spaced apart. Wedges are less curved. Distinct wedges are located in separate half-grabens and have no common starting point. The reflectors cool down and become brighter in the central part of the Podvodnikov basin, near the axial horst. Both complexes are characterized by probable existence volcanic edifices in the top.
We traced the distribution and direction of SDRs, the bottom of the grabens, the position of probable volcanic edifices and made a map. There is symmetry and logic in the distribution of SDR. In the Toll basin, reflectors fall into each other – from the Mendeleev Rise and from the Chukotka plateau – and meet at a structure reminded of an interrupted rift. The rift is parallel to the Mendeleev Rise and the Chukotka Plateau. We can see at on Magnetic Anomalies Map. This probably corresponds to the central axis of extension of the Toll basin. Oppositely directed SDRs from the Mendeleev Rise and the Lomonosov Ridge meet near a raised block in the Podvodnikov basin. Nature of raised block is not fully understood. We call it axial horst. This uplift is subparallel to the Mendeleev Rise. This is probably associated with the central extension axis for the Podvodnikov basin.
Mendeleev Rise, Podvodnikov and Toll basins were formed approximately at the same time according to the seismic correlation.
This study was supported by RFBR grant (18-05-70011).
How to cite: Rodina, E., Nikishin, A., and Startseva, K.: SDR (Seaward Dipping Reflectors) types in the water area of the Mendeleev Rise, Arctic Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11058, https://doi.org/10.5194/egusphere-egu21-11058, 2021.
New seismic, magnetic and gravity data of the continental margin of the Laptev Sea shelf indicate: (1) Absence of the Lomonosov-Khatanga transform fault between the Eurasia Basin and Laptev Sea shelf. On a number of new seismic lines we do not observe evidence for transtension or transpressional deformation along this lineament whereas some typical deformation for the continental slopes is recognized. Recent seisimicity is absent along the lineament. (2) The pull-apart Laptev-Gakkel continental basin along the Laptev Sea continental slope is in an orthogonal position to the Gakkel Ridge axial rift. This pull-apart basin was tectonically active during Eocene-Oligocene times. (3) Evidence exists for number possible intrusions just below the rift/postrift (break-up) unconformity (56 Ma) on some seismic lines in the area between the Taimyr Shelf and the continental slope of the Eurasia Basin. Evidence is also found for the existence of possible volcanics just below the break-up unconformity in this area. (4) Intrusions might also be present just below the 56 Ma break-up unconformity recognized on some seismic lines in the area between the Lomonosov Ridge and the continental slope of the Eurasia Basin. Buried volcanoes are likely present as well. These two magmatic provinces are symmetric to each other on both sides of the Eurasia Basin and well expressed on the new magnetic anomaly map.(5) The Eurasia Basin has a conical shape in its Southern near-Laptev domain. Opening of the basin appears to be controlled by propagation of oceanic crust spreading to the south. (6) We assume that the continental margin between the Laptev Sea Shelf and the Eurasian Basin could be a passive volcanic margin. This margin is characterized by a structure that is very similar to the North Atlantic margin of almost the same age. This study was supported by RFBR grant (18-05-70011).
How to cite: Nikishin, A., Savin, V., Cloetingh, S., Gaina, C., Malyshev, N., Petrov, E., Poselov, V., Rodina, E., Startseva, K., and Verzhbitsky, V.: A volcanic passive continental margin between the Laptev Sea Shelf and the Eurasia Basin?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9428, https://doi.org/10.5194/egusphere-egu21-9428, 2021.
Nordensheld Archipelago is a relatively large cluster of islands in the eastern part of the Kara Sea located north of the Taymyr Peninsula. Belonging to the Northern Taimyr tectonic domain of the Taimyr-Severnaya Zemlya fold-and-thrust belt, this area in Late Paleozoic represented southern part of the Kara Terrane.
Samples were collected from outcrops across the Nordensheld Archipelago and shallow offshore wells in the close proximity to the archipelago and from offshore well located in Toll bay (eastern part of the Kara sea). Studied plutons are represented by coarse- to medium-grained biotite, two mica and hornblende-biotite granites. U-Pb dating of the granites yelled ages of ca. 334 and 326 Ma. The granitoids are high- to medium acidic, mainly calc-alkalic to alkali-calcic, ferroan and magnesian, metalumious and peraluminous.
The U-Pb zircon age from the Toll Bay well is the first granite age obtained offshore within eastern part of the Kara Sea. Petrographic and geochemical features of the Nordensheld Archipelago and eastern Kara Sea Visean-Serpukhovian granites indicate their suprasubduction origin. This correlates well with data from Northern Taimyr and provides new evidence for the Uralian Ocean subduction magmatism within Taimyr-Severnaya Zemlya fold-and-thrust belt.
This research was supported by RFBR grant № 19-35-90006, Russian Science Foundation grant № 20-17-00169.
How to cite: Kurapov, M., Ershova, V., Khudoley, A., and Schneider, G.: Carboniferous granitic plutons of Nordensheld Archipelago (eastern part of the Kara Sea, Russian High Arctic), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3344, https://doi.org/10.5194/egusphere-egu21-3344, 2021.
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