GD1.6

Geologic evidence of island uplift and subsidence can provide important observational constraints on the rheology, thermal evolution, and dynamics of the lithosphere and mantle – all of which have implications for understanding Earth’s heat budget, the styles of deformation that develop at plate boundaries, and the surface expression of mantle convection. Hotspot ocean islands, like the Hawaiian Islands, result from mantle plumes, which may originate as deep as the core-mantle boundary. They often host paleoshorelines, which preserve a geologic record of surface deformation, and they can also be situated far from complex plate boundaries that obscure evidence of dynamic topography – long wavelength, low amplitude topography resulting from mantle flow. Ocean islands therefore provide a unique window to deep earth processes operating today and in the geologic past.

We examine the relative contribution of lithosphere and mantle processes to surface deflection at ocean hotspots. The seafloor surrounding ocean hotspots is typically 0.5 - 2 km shallower than expected for its age over areas hundreds to >1000 km wide, but the processes generating these bathymetric swells are uncertain. Swells may result from reheating and thinning of the lithosphere and the isostatic effect of replacing colder, denser lithosphere with hotter, less dense upper mantle. Alternately, they may be supported by upward flow of ascending mantle plumes and/or hot, buoyant plume material ponded beneath the lithosphere. Because these two end-member models predict different patterns of seafloor and island subsidence, swell morphology and the geologic record of island drowning may reveal which of these mechanisms dominates the process of swell uplift. We examine swell bathymetry and island drowning at 14 hotspots and find a correspondence between island lifespan and residence time atop swell bathymetry, implying that islands drown as tectonic plate motion transports them past mantle sources of uplift. This correspondence argues strongly for dynamic uplift of the lithosphere at ocean hotspots. Our results also explain global variations in island lifespan on fast- and slow-moving tectonic plates (e.g. drowned islands in the Galápagos <4 Myr old versus islands >20 Myr old above sea level in the Canary Islands), which strongly influence island topography, biodiversity, and climate.

Over shorter timescales, paleoshorelines on hotspot ocean islands may constrain transient changes in local swell morphology. Accounting for flexural isostatic adjustment of the lithosphere to volcanic loading, we also examine patterns in the residual deflection of paleoshorelines across the Hawaiian Islands that might correspond to non-steady state behavior of the Hawaiian plume. Together, these analyses highlight the unique constraints that island paleoshorelines and topo-bathymetry can place on plume-plate interactions at ocean hotspots.

How to cite: Huppert, K., Perron, J. T., Royden, L., and Toomey, M.: Characterizing plume-plate interactions at ocean hotspots from the vertical motion history of volcanic ocean islands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13169, https://doi.org/10.5194/egusphere-egu21-13169, 2021.

Hotspots are thermal instabilities that originate in the mantle and manifest themselves on the surface by volcanism, continental breaks or "traces" observed in the oceans. Theirs effects under the continents are still debated: in addition to a phase of activity associated with surface volcanism, a residual thermal anomaly could persist durably under the lithosphere along the trajectory of the hotspot.
For a simple model of thermal anomaly (parallelogram aligned in a fixed direction), we compute the perturbations of the geoid, of the gravity vector and of the associated gravity gradients. We show that in a coordinate system aligned with the parallelogram, gravity gradients have a characteristic signal with an order of magnitude of a few hundred mEotvos, well above the current data detection level. Thus for four real cases: in North Africa (with the Hoggar, Tibesti, Darfur and Cameroon hotspots), in Greenland (Iceland and Jan Mayen), in Australia (Cosgrove) and in Europe (Eifel), we calculate the paleo-positions of the hotspots during the last 100 Ma in a reference frame linked to the lithospheric plates, and we build maps of gravity gradients at different altitudes filtered at the spatial scale of a few hundred kilometers (scale of the hotspot) and oriented along the direction of the trajectory.
We clearly find signals aligned in the direction of the movement of the plates on spatial scales of a few hundred kilometers.
This signal is sometimes correlated with the topography and it is difficult to separate the sources resulting from volcanic edifices and their associated isostatic crustal roots from that induced by residual thermal anomaly. These results show that gradiometric data are able to detect and follow the tracks of hotspots in the continental lithosphere, during at least a few tens of millions of years, providing new clues to constrain their trajectory and improve reference frame tied to the mantle.

How to cite: Greff-Lefftz, M., Panet, I., and Besse, J.: Continental Hotspots Tracks from Analysis of GOCE Gravity Gradients Data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4669, https://doi.org/10.5194/egusphere-egu21-4669, 2021.

Long-lived, widespread intraplate volcanism without age progression is one of the most controversial features of plate tectonics. The eastern margin of Australia and Zealandia has experienced extensive mafic volcanism over the last 100 million years. A plume origin has been proposed for three distinct chains of volcanoes, however, the majority of eruptions exhibit no clear age progression. Previously proposed edge-driven convection, asthenospheric shear, and lithospheric detachment fail to explain the non age-progressive eruptions across the ~5000 km wide intraplate volcanic province from Eastern Australia to Zealandia. We model the subducted slab volume over 100 million years and find that slab flux drives volcanic eruption frequency, indicating stimulation of an enriched mantle transition zone reservoir. Volcanic isotope geochemistry allows us to distinguish a HIMU reservoir (>1 Ga old) in the slab-poor south, from a northern EM1/EM2 reservoir, reflecting a more recent voluminous influx of oceanic lithosphere into the mantle transition zone. We provide a unified theory linking plate boundary and slab volume reconstructions to upper mantle reservoirs and intraplate volcano geochemistry.

How to cite: Mather, B., Muller, D., Seton, M., Ruttor, S., Nebel, O., and Mortimer, N.: Intraplate volcanism triggered by bursts in slab flux, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6857, https://doi.org/10.5194/egusphere-egu21-6857, 2021.

Large parts of Central Europe have experienced exhumation in Late Cretaceous to Paleogene time. Previous studies mainly focused on thrusted basement uplifts to unravel magnitude, processes and timing of exhumation. In this study we present a comprehensive thermochronological dataset from mostly Permo-Triassic strata exposed adjacent to and between the major basement uplifts in central Germany, comprising an area of at least some 250-300 km across. Results of apatite fission track and (U-Th)/He analyses from >100 new samples reveal that (i) km-scale exhumation affected the entire region, suggesting long-wavelength domal uplift, (ii) thrusting of basement blocks like the Harz Mountains and the Thuringian Forest focused in the Late Cretaceous (about 90-70 Ma) while superimposed domal uplift of central Germany appears slightly younger (about 75-55 Ma), and (iii) large parts of the domal uplift experienced removal of 3 to 4 km of Mesozoic strata. Using spatial extent, magnitude and timing as constraints we find that thrusting and crustal thickening alone can account for no more than half of the domal uplift. Most likely, dynamic topography caused by upwelling asthenosphere has contributed significantly to the observed pattern of exhumation in central Germany.

How to cite: von Eynatten, H., Kley, J., and Dunkl, I.: Late Cretaceous to Paleogene exhumation in Central Europe – localized inversion vs. large-scale domal uplift, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7279, https://doi.org/10.5194/egusphere-egu21-7279, 2021.

Mineral fillers can significantly affect the application properties of plastic materials. The structural and chemical properties of phyllosilicates provide the conditions to change the properties of polymeric material, e.g. flexural and tensile strength or thermal properties, according to the required application. Mineral fillers frequently used are clay minerals with a two-layer structure (serpentine-kaolin group) or three-layer structure (talc-pyrophyllite group, mica group, smectite group). The mineral fillers can be directly used or after surface modification, depending on the polar nature of the polymer. Polymers containing polar groups (hydrophilic polymers) are water-soluble, like polyvinyl alcohols and polysaccharides or can form hydrogen bonds, like polyamides, polyesters and polyvinyl fluorides. Hydrophobic (non-polar) polymers show an absence of polar groups (e.g. polyethylene, polypropylene) or mutual cancelling electrical dipole moments (e.g. polytetrafluorethylene). Minerals with a hydrophilic surface are directly applicable with polar polymers. For the application with non-polar polymers their surface require hydrophobization, whereas non-polar two-layer silicates are directly applicable with these polymers.

Serpentinized rock material is investigated with regard to its suitability as a polymer filler and its influence on the performance characteristics of various polymers. The samples origin from the Kraubath Ultramafic Massif, which represents part of an Early Paleozoic ophiolite, at the basement of the Austro-Alpine. The Kraubath complex is dominated by metamorphosed dunites and harzburgites, which origin from fractionation processes of the primary peridotite magma. Hydrothermal alteration led to a partly or entirely serpentinization of the ultramafic rocks. The serpentinization process of dunite, ortho-pyroxenite and harzburgite transformed Mg-containing silicates, like olivine and pyroxene to serpentine group minerals. Rock material with a high grade of serpentinization offers favourable conditions for the application as mineral filler.

The qualitative and quantitative XRD-analyses reveal a predominant occurrence of the antigorite. Further serpentine group minerals, like lizardite, occur in small amounts. Talc represents the second largest mineral phase. The rock material contains a few percentage of amphibole, chlorite, olivine (forsterite) and less than two percent of chromite and bronzite. In the two-layer structure of the main component antigorite, the charge of the tetrahedral layer is compensated by the charge of the octahedral layer. The three-layer structure of talc is electrostatically neutral, with no interlayer material. Therefore, serpentine minerals and talc are suitable for the application as mineral fillers in non-polar polymers, like polypropylene. Both influence the mechanical and tribological properties of polymers. Serpentine improves elasticity, tensile strength, stress at break, elongation at break, the mass wear rate and the coefficient of friction of the polymer but reduces the impact strength. Talc positively influences rigidity, shrinkage, creep properties, heat distortion under load and the coefficient of linear thermal expansion, however reduces toughness, long thermal ageing, impact strength and tensile strength. The further mineral phases are not considered to affect the application properties negatively. Regarding tensile strength and elasticity the ratio of serpentine to talc can influence the increase and decrease of these properties in non-polar polymers. The applicability of the practical implementation is investigated with nanoparticles of the serpentinized rock material in combination with polypropylene in varying proportions.

How to cite: Wegerer, E., Aust, N., and Mayer, A.: Suitability of serpentinized rock material as mineral filler in polymer matrices, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12123, https://doi.org/10.5194/egusphere-egu21-12123, 2021.

Western Europe experienced a major rift system initiated during Bartonian times (41 Ma). This evolution is coeval with long wavelength deformations (several hundreds of kilometers) that control the topography and the sediment production beyond the rift. The climate during this time interval was first increasingly arid and then wetter.

This study is based on both landform and sediment analysis of southern England, France, Belgium and western Germany. The landforms are mainly large pediments, dated by the intersection with sediments deposited in low to high subsiding areas and volcanism. A set of paleogeographic maps with paleotopographic reconstructions, is used to constrain the uplifting and subsiding areas, their wavelength and the critical periods of intraplate deformations.

The main periods of deformations and sedimentary systems changes area as follow.

41Myrs (base Bartonian) was the beginning of a major tilting of Western Europe with subsidence of France and uplift of the Brabant/Ardennes/Rhenish Massif. Even a dense network of basement faults was reactivated, biochemical sedimentation prevailed.

35-31Myrs (Late Priabonian-Early Rupelian) initiated a period of general subsidence even along the Ardennes/Rhenish Massif and the French Massif Central. Two major marine floodings are recorded, with a differential preservation according to the balance between deformation and eustasy.

27-25Myrs (Chattian) was a period of uplift of Western Europe except the Aquitaine Basin, followed by a relaxation favoring eustatic floodings in (very) low subsiding domains. Chattian siliciclastic deposits are preserved as lowstand wedges in the surrounded basins (North Sea, Atlantic Margin).

14-11Myrs (Serravallian-Early Tortonian) initiated the overall uplift of Western Europe, still operating today. This is the beginning of a period of major denudation in southern England, Western Germany (SW Germany flat - “Stufenland”) and along the southern limb of the Franch Massif Central.

The causes and the consequences in term of sediment production are discussed.

How to cite: Guillocheau, F. and Robin, C.: Intraplate deformations, topographic evolution and sediment production of Western Europe from 40 to 5 Myrs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13087, https://doi.org/10.5194/egusphere-egu21-13087, 2021.

The evaporitic Haselgebirge Formation hosts in many places small occurrences of basaltic rocks. The geochemistry of these basalts can potentially provide information about the tectonic setting of the Haselgebirge Formation and the evolution of the Meliata ocean, respectively. We present here 70 new XRF analyses of these basaltic rocks from various localities (Pfennigwiese, Annaberg, Wienern, Hallstatt, Moosegg, Lammertal) and compare the results with previous data from local studies (GRUBER et al., 1991; KIRCHNER 1979; KIRCHNER 1980a; KIRCHNER 1980b; KRALIK et al, 1984; LEITNER et al., 2017; SCHORN et al., 2013; ZIEGLER, 2014; ZIRKL, 1957). Based on the concentrations of immobile trace elements (Zr, Nb, Y, Ti), a predominance of MORB-like compositions is observed for the Lower Austrian occurrences and for the locality Wienern (Grundlsee). On contrast, basalts from the localities Lammertal, Moosegg and Hallstatt have predominantly within-plate-type compositions.

We discuss this striking regional (east-west) difference of basalt types in terms of existing palinspastic models for the Haselgebirge formation (LEITNER et al., 2017; STAMPFLI & BOREL, 2002; McCANN et al., 2006).

GRUBER, P., FAUPL, P., KOLLER, F. (1991) Mitt. Österr. Miner. Ges., 84, 77-100.

KIRCHNER, E. (1979) Tschermaks Min. Petr. Mitt. 26, 149-162.

KIRCHNER, E. (1980a) Mitt. Österr. Miner. Ges.71/72, 385-396.

KIRCHNER, E. (1980b) Verh. Geol. Bundesanstalt 1980, 249-279.

KRALIK, M., KOLLER, F., POBER, E. (1984) Mitt. Österr. Miner. Ges., 77, 37-55.

LEITNER, C., WIESMAIER, S., KÖSTER, M.H., GILG, H.A, FINGER, F, NEUBAUER, F. (2017) GSA Bulletin 129, 1537-1553.

McCANN, T., PASCAL, C., TIMMERMAN, M.J., KRZYWIEC, P., LÓPEZ-GÓMEZ, J., WETZEL, L., KRAWCZYK, C.M., RIEKE, H., LAMARCH, J. (2006) Mem. Geol. Soc. London, 32, 355-388.

SCHORN A, NEUBAUER F, GENSER J, BERNROIDER M (2013) Tectonophysics 583, 28-48.

STAMPFLI G.M., BOREL G.D. (2002) Earth Planet. Sci. Lett. 196, 17-33.

ZIEGLER, T. (2014) Unpubl. MSc thesis University of Salzburg, p. 174.

ZIRKL, E.J. (1957) Jb. Geol. Bundesanstalt 100, 10-137-177.

How to cite: Leitner, C.: Two different basalt provinces (MORB vs. WPB) in the evaporitic Permian Haselgebirge Formation (Eastern Alps, Austria) and possible tectonic implications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13129, https://doi.org/10.5194/egusphere-egu21-13129, 2021.

In 2016, approximately 850 km of high-resolution multichannel seismic reflection data of the BALTEC survey have been acquired offshore Poland within the transition zone between the East European Craton and the Paleozoic Platform. Data processing, focused on removal of multiples, strongly overprinting geological information at shallower intervals, included SRME, TAU-P domain deconvolution, high resolution parabolic Radon demultiple and SWDM (Shallow Water De-Multiple). Entire dataset was Kirchhoff pre-stack time migrated. Additionally, legacy shallow high-resolution multichannel seismic reflection data acquired in this zone in 1997 was also used. All this data provided new information on various aspects of the Phanerozoic evolution of this area, including Late Cretaceous to Cenozoic tectonics and sedimentation. This phase of geological evolution could be until now hardly resolved by analysis of industry seismic data as, due to limited shallow seismic imaging and very strong overprint of multiples, essentially no information could have been retrieved from this data for first 200-300 m. Western part of the BALTEC dataset is located above the offshore segment of the Mid-Polish Swell (MPS) – large anticlinorium formed due to inversion of the axial part of the Polish Basin. BALTEC seismic data proved that Late Cretaceous inversion of the Koszalin – Chojnice fault zone located along the NE border of the MPS was thick-skinned in nature and was associated with substantial syn-inversion sedimentation. Subtle thickness variations and progressive unconformities imaged by BALTEC seismic data within the Upper Cretaceous succession in vicinity of the Kamień-Adler and the Trzebiatów fault zones located within the MPS documented complex interplay of Late Cretaceous basin inversion, erosion and re-deposition. Precambrian basement of the Eastern, cratonic part of the study area is overlain by Cambro-Silurian sedimentary cover. It is dissected by a system of steep, mostly reverse faults rooted in most cases in the deep basement. This fault system has been regarded so far as having been formed mostly in Paleozoic times, due to the Caledonian orogeny. As a consequence, Upper Cretaceous succession, locally present in this area, has been vaguely defined as a post-tectonic cover, locally onlapping uplifted Paleozoic blocks. New seismic data, because of its reliable imaging of the shallowest substratum, confirmed that at least some of these deeply-rooted faults were active as a reverse faults in latest Cretaceous – earliest Paleogene. Consequently, it can be unequivocally proved that large offshore blocks of Silurian and older rocks presently located directly beneath the Cenozoic veneer must have been at least partly covered by the Upper Cretaceous succession; then, they were uplifted during the widespread inversion that affected most of Europe. Ensuing regional erosion might have at least partly provided sediments that formed Upper Cretaceous progradational wedges recently imaged within the onshore Baltic Basin by high-end PolandSPAN regional seismic data. New seismic data imaged also Paleogene and younger post-inversion cover. All these results prove that Late Cretaceous tectonics substantially affected large areas located much farther towards the East than previously assumed.

This study was funded by the Polish National Science Centre (NCN) grant no UMO-2017/27/B/ST10/02316.

How to cite: Krzywiec, P., Słonka, Ł., Nguyen, Q., Malinowski, M., Kufrasa, M., Stachowska, A., Huebscher, C., and Kramarska, R.: Late Cretaceous – Cenozoic history of the transition zone between the East European Craton and the Paleozoic Platform, Polish sector of the Baltic Sea, revealed by new offshore regional seismic reflection data (BALTEC project), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13383, https://doi.org/10.5194/egusphere-egu21-13383, 2021.

The Emeishan flood basalts are part of an important large igneous province along the western margin of the Yangtze Block, Southwest China. The western Guangxi region in southwestern China is geologically a part of the Yangtze Block. Mafic rocks, comprising mainly lavas and dykes in western Guangxi belong to the outer part of the ~260 Ma Emeishan Large Igneous Province (ELIP). Here we present a systematic study of platinum-group elements (PGEs) combined with the LA-ICP-MS zircon U–Pb age, whole-rock geochemical and isotopic data of the lavas and dykes in the Longlin area of outer zone of ELIP to constraints on their origin. On the basis of petrography and major elements characteristics, mafic lavas and dykes display an enrichment of LREE, LILE, HFSE, high (⁸⁷Sr/⁸⁶Sr)_i ratios (0.704227~0.705754), low ε_Nd(t) values(0.42~0.99), high ε_Hf(t) values(5.19~6.04), they are similar to those of Permian Emeishan high-Ti basalts and Ocean island basalts (OIB) features. The Longlin mafic rocks was formed in the Late Permian with the zircon U-Pb dated age of 256.3± 1.7 Ma. The age of the Longlin mafic rocks is close to the formation age of the ELIP large-scale magmatism, suggesting that these lavas and dykes probably belongs to part of the ELIP large-scale magmatism. The Longlin mafic rocks have low total PGE contents ranging from 1.56×10^-9 to 2.28×10^-9, with Os, Ir, Ru, Rh, Pt and Pd contents of 0.040~0.076, 0.046~0.076, 0.027~0.079, 0.037~0.056, 0.6374~1.053 and 0.715~1.021ppb, respectively. They show left-leaning primitive mantle-normalized PGE patterns with depletion in Iridium group(IPGE) and enrichment in Palladium group, which also have lower contents than mafic rocks from the inner zone of the ELIP, suggesting that a low degree of partial melting of the mantle source plays an important role. The Longlin mafic rocks exhibit a marked increase in Cu/Pd ratios (>10⁵,84655 to 174785) albeit with a narrow range of lower Pd/Ir ratios (<50,13.4 to 18.7), different from the PGE-enriched basalts of the Siberian Traps, Emeishan Large Igneous Province (ELIP), East Greenland CFBs and Deccan Traps, indicating that their parent magmas was significantly depleted in chalcophile elements. Calculations based on the available trace element geochemistry reveal that the basalts were originated by low degree of partial melting(<5%)，with sulfides remain in the mantle during partial melting. Sulfide segregation could not happen during the evolution of the Longlin mafic rocks, due to the fact that neither significant fractional crystallization nor crustal contamination has been involved in their formation. Overall, mafic rocks from the outer zone of the ELIP show lower PGE contents than those in the inner zones, we find that the PGE contents in igneous rocks are related with the degrees of partial melting in the mantle source and the removal of sulfides before their emplacement.

This study was financially supported by the Guangxi Natural Science Foundation for Distinguished Young Scholars (2018GXNSFFA281009) and the Fifth Bagui Scholar Innovation Project of Guangxi Province (to XU Ji-feng).

How to cite: Zhao, B., Liu, X., Li, Z., Huang, W., and Zhao, C.: Geochronology, isotopic and Platinum-group elemental geochemistry of lavas and dykes from the western Guangxi in outer zone of Emeishan mantle plume, SW China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13784, https://doi.org/10.5194/egusphere-egu21-13784, 2021.