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Multi-disciplinary perspectives on mantle-surface and plume-plate interactions through time and space

Geomorphic and geologic observations at the Earth's surface reflect the combined effects of mantle, lithospheric, and surface processes. Hence surface observations provide important constraints on mantle convection patterns and plume-plate interactions both at plate boundaries and in intraplate settings through space and time. These observations complement geophysical data and are important constraints for theoretical models and numerical simulations. For instance, at plate boundaries, surface observations can provide key constraints on the rheology and kinematics of lithospheric and mantle processes. In both plate boundary and intraplate settings, mantle plumes can trigger continental rifting and break-up, subduction initiation, orogeny, microcontinent formation, and/or the development of dynamic topography. However, using surface observations to constrain mantle processes is complicated by (1) our as yet incomplete understanding of how mantle dynamics manifest at the surface, and (2) spatio-temporal variations in tectonic processes, climate, isostatic adjustment, lithology, biota, and human alteration of landscapes. In this session, we aim to bring together researchers interested in mantle-surface and plume-plate interactions. We welcome studies that cover a range of techniques from data-driven approaches to numerical modelling or laboratory experiments.
We hope this session will provide opportunities for presenters from a range of disciplines, demographics, and stages of their scientific career to engage in this exciting and emerging problem in Earth Science.

Co-organized by GM9/SSP2/TS5
Convener: Audrey MargirierECSECS | Co-conveners: Lucia Perez-DiazECSECS, Kimberly HuppertECSECS, Maelis ArnouldECSECS, Megan HoldtECSECS, Maria Seton, Simon StephensonECSECS, Pietro Sternai
Presentations
| Tue, 24 May, 13:20–15:54 (CEST)
 
Room -2.91

Tue, 24 May, 13:20–14:50

Chairpersons: Audrey Margirier, Kimberly Huppert, Simon Stephenson

13:20–13:22
Dynamic topography

13:22–13:32
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EGU22-3756
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ECS
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solicited
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Highlight
Gregory Ruetenik et al.

It has been hypothesized that Australia is experiencing long-wavelength uplift and subsidence in response to intraplate stresses and/or dynamic topography (e.g. Beekman et al., 1997; Czarnota et al., 2013). In central Australia, intraplate stresses are of particular interest due to the presence of several enigmatically long-lived (500+ Myr) Bouguer anomalies of magnitude + 150 mgal. Additionally, a recent study by Jansen et al. (2022) showed that the Finke river, which drains away from a large gravity high, is actively responding to cyclic changes in uplift. Here, transient uplift and subsidence of up to ~150 m may be driven by the the flexural response to variable in-plane stresses in the presence of large loads embedded within the lithosphere.  The in-plane stress changes may be associated with shear at the base of the lithosphere and therefore inherently linked to plate velocity and mantle dynamics.
     Here, we explore mechanisms of uplift in central Australia and investigate their signatures within the geomorphic record through numerical modeling and χ analysis. We observe strong χ variations across drainage divides associated with gravity anomalies, which we link to episodic transitions from exorheic to endorheic drainage during periods of uplift and subsidence.  Landscape evolution models that incorporate flexural uplift in response to time-transient variations in horizontal stresses suggest that depositional patterns, spatial χ variations, and river profiles can be explained by this uplift mechanism.  In a more general sense, these results demonstrate that the cyclic loss and gain of drainage area during periods of endorheism and exorheism can result in drastic, sudden changes in χ which correspond to waxing and waning of basinal areas.

How to cite: Ruetenik, G., Jansen, J., Sandiford, M., and Moucha, R.: Large-scale drainage disequilibrium in central Australia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3756, https://doi.org/10.5194/egusphere-egu22-3756, 2022.

13:32–13:34
Questions

13:34–13:40
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EGU22-354
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ECS
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Highlight
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Chia-Yu Tien et al.
Dynamic topography is the surface expression of sub-plate mantle convective processes. In recent years, there has been considerable interest in combining a wide range of geophysical, geological and geomorphic observations with a view to determining the amplitude, wavelength and depth of mantle thermal anomalies. Here, we are interested in exploring how quantitative modelling of major, trace and rare earth elements can be used to constrain the depth and degree of asthenospheric melting for a mantle peridotitic source. Our focus is on a region that encompasses the Iberian Peninsula where previous research suggests that long-wavelength topography is supported by a significant sub-plate thermal anomaly which is manifest by reduced shear-wave velocities. Stratigraphic and fluvial studies imply that this dynamic support is a Neogene phenomenon. We analyzed 48 Neogene basaltic rocks that were acquired from Iberia in September 2019 and combined these analyses with previously published datasets. Both major element thermobarometry and rare earth element inverse modelling are used to determine the asthenospheric potential temperature and lithospheric thickness. These values are compared with those estimated from calibrated shear-wave tomographic models. Our geochemical results indicate that potential temperatures and lithospheric thicknesses are 1300-1375 °C and 50-80 km, respectively. These values broadly agree with calibrated tomographic models which yield values of 1300-1360 °C and 45-70 km. We conclude that a region encompassing Iberia is dynamically supported by a combination of warm asthenosphere and thinned lithosphere.

How to cite: Tien, C.-Y., White, N., Maclennan, J., and Conway-Jones, B.: Constraining Neogene Mantle Dynamics of Western Mediterranean Region Encompassing Iberia by Quantitative Modeling of Basalt Geochemistry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-354, https://doi.org/10.5194/egusphere-egu22-354, 2022.

13:40–13:41
Questions

13:41–13:47
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EGU22-13092
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Aisling Dunn et al.

Constraining the dynamic topography of Antarctica and its surrounding seas is required in order to gauge the pattern of mantle convection beneath this continent. However, such studies are limited by this continent’s geographical remoteness, by the lack of bedrock exposure and by extensive glaciation. Oceanic residual depth measurements provide a well-established proxy for offshore dynamic topography. Here, over 400 seismic reflection profiles have been interpreted to calculate residual depth measurements throughout the oceans that surround Antarctica. These measurements have been carefully corrected for sedimentary loading and, where possible, for crustal thickness variations. When combined with previous global compilations, these new residual depths significantly improve spatial resolution across the region, providing excellent constraints on dynamic topographic basins and swells. In the continental realm, an improved understanding of dynamic topography will help to quantify temporal and spatial variations in ice sheet stability. Volcanism and slow shear wave velocity anomalies beneath the continent indicate dynamic support.  By mapping offshore dynamic topography to a higher resolution, greater context is provided for future onshore studies.

How to cite: Dunn, A., White, N., Holdt, M., and Larter, R.: Dynamic topographic observations of Antarctica and its fringing oceanic basins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13092, https://doi.org/10.5194/egusphere-egu22-13092, 2022.

13:47–13:48
Questions

13:48–13:54
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EGU22-373
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ECS
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Philippa Slay et al.

Mantle convection generates transient vertical motion at the surface, which is referred to as dynamic topography. The bulk of topography and bathymetry is isostatically supported by variations in the thickness and density of both the crust and the lithosphere which means that dynamic topography generated by sub-plate density anomalies needs to be isolated from these dominant isostatic signals. Australia’s isolation from plate boundaries and its rapid northwards translation suggest that long-wavelength dynamic topography is primarily controlled by the interplay between plate motion and sub-plate convection. Along the eastern seaboard of Australia, the coincidence of elevated topography, positive long-wavelength free-air gravity anomalies and Cenozoic basaltic magmatism imply that a combination of asthenospheric temperature anomalies and thinned lithosphere generate and maintain regional topography. Distributions of onshore and offshore intraplate magmatism reflect both plate motion and convective instabilities. Compilations of deep seismic reflection profiles, wide-angle surveys and receiver function analyses are used to determine crustal velocity structure across Australia. Residual (i.e. dynamic) topographic signals are isolated by isostatically correcting local crustal structure with respect to a reference column that sits at sea level. The resultant pattern of dynamic topography is consistent with residual bathymetric anomalies from oceanic lithosphere surrounding Australia. Significant positive dynamic topography occurs along the eastern seaboard and in southwest Australia (e.g. Yilgarn Craton). These signals are corroborated by independent geologic evidence for regional uplift.

How to cite: Slay, P., White, N., and Stephenson, S.: Dynamic Topography of the Australian Continent and its Margins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-373, https://doi.org/10.5194/egusphere-egu22-373, 2022.

13:54–13:55
Questions

13:55–14:01
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EGU22-9038
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ECS
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Camilo Conde-Carvajal et al.

The north Andean block evidences by its shallow to intermediate seismicity a juxtaposition of a southern, relatively steeply dipping slab segment with a correlating volcanic arc and a northern flat slab domain, where a margin-parallel volcanic arc became extinct since the Late Miocene. The clear-cut offset of the seismic pattern suggests the presence of a slab tear, which has its correlative morphological expression by a distinct lineament in the Cauca Valley and separates, within the Eastern Cordillera of Colombia, a southern narrow antiformal cordilleran tract from a northern composite belt with an axial depression that constitutes the High Plain of Bogotá. Faults are consistently blind and associated with tight, basement-cored folds with inverted limbs at the mountain front and distinct domes separated by marginal synclines. These structures belong to a young deformation phase as they were superposed on older cylindrical fold trains. Their ductile deformation style may be associated with a thermal anomaly as evidenced by abnormally high Ro data. In order to assess the age of this folding we extracted zircons from a rhyolitic dike that straddles a marginal syncline of a major dome. U-Pb age data indicate a recycling of these crystals from a Neoproterozoic volcanoclastic sequence that composes the basement of this marginal part of the Cordillera. Euhedral overgrowths yield, however, Quaternary ages that we tentatively associate to the advance of the outer bend of the flat slab to its present position.

How to cite: Conde-Carvajal, C., Kammer, A., Avila-Paez, M., Cubillos, S., Piraquive, A., and von Quadt, A.: Quaternary magmatism above a slab tear, Northern Andes of Colombia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9038, https://doi.org/10.5194/egusphere-egu22-9038, 2022.

14:01–14:02
Questions

14:02–14:08
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EGU22-443
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ECS
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John He and Paul Kapp

Lithosphere removal beneath orogenic plateaus are transient events that must often be inferred from the absence of evidence: for example, unexplained topographic uplift in the geologic record, or the absence of high-velocity mantle lithosphere. Even when foundering events do leave traces of their occurrence on the surface, the low preservation potential of such evidence leaves incomplete and ambiguous records. Distinctive features include isotopically juvenile magmatism and transient surface subsidence that form localized, internally drained hinterland basins and playas. However, basaltic volcanism and related lacustrine sediments are rarely well preserved, and this limits our ability to evaluate the role of lithosphere removal in orogenesis to only select localities. To develop a more comprehensive record of this process, and facilitate comparisons between regions with copious surface and/or geophysical evidence of lithospheric foundering with regions where the evidence is scant, whether poorly preserved or not yet recognized, we present the detrital record from young strata in internally-drained hinterland basins as a proxy for foundering-related magmatism. The detrital samples include unconsolidated to poorly consolidated lacustrine sediment of the Bidahochi paleolake from the Colorado Plateau, which is associated with the isotopically juvenile (positive epsilon Nd) Hopi Buttes Volcanic field; Oligocene siltstone from the Pamir Plateau with juvenile isotopic signature (positive epsilon Hf); and Eocene-Oligocene sandstone from several localities on the Tibetan Plateau. Integration of isotope geochemistry, trace element geochemistry, and thermochronology of detrital zircon and apatite presents a promising approach to reconstruct a continuous record of low-volume magmatism, both eroded and preserved. Ti-in-zircon thermometry, Ce-U-Ti oxybarometry, and REE proxies for depth of magmatic differentiation potentially provide a means of distinguishing zircon crystals associated with hinterland magmatism from that associated with arc magmatism. Using these datasets, we consider whether lithospheric foundering can be associated with recognizable patterns that are similar across orogens, and whether geochemical shifts in hinterland magmatism reveal first-order differences in the temporal scale of lithosphere removal in different orogens. 

How to cite: He, J. and Kapp, P.: Evaluating scant surface evidence of deep lithosphere removal: Towards a more comprehensive record, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-443, https://doi.org/10.5194/egusphere-egu22-443, 2022.

14:08–14:09
Questions

14:09–14:15
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EGU22-226
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ECS
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Veleda Astarte Paiva Muller et al.

Late Miocene calc-alkaline intrusions in the back-arc of Southern Patagonia mark an eastward migration of the arc due to accelerated subduction velocity of the Nazca plate or slab flattening preceding active ridge subduction. Amongst these intrusions are the emblematic Torres del Paine (51°S) and Fitz Roy (49°S) plutonic complexes, crystalised at ca. 12.5 and ca. 16.5 Ma, respectively (Leuthold et al., 2012; Ramírez de Arellano et al., 2012). Both intrusions are located at the eastern boundary of the Southern Patagonian Icefield and form prominent peaks with steep slopes that are ~3 km higher in elevation than the surrounding low-relief foreland. Their exhumation has been proposed as a response to glacial erosion and associated glacial rebound since ca. 7 Ma (Fosdick et al., 2013), and/or by regional dynamic uplift between 14 and 6 Ma due to the northward migration of subducting spreading ridges (Guillaume et al., 2009). Here we present a new data set of apatite and zircon (U-Th)/He from both plutonic complexes, numerically modelled to unravel their late-Neogene to Quaternary thermal histories. Our results show three rapid cooling periods for the Fitz Roy intrusion: at ca. 9.5 Ma, at ca. 7.5 Ma, and since ca. 1 Ma. For Torres del Paine, inverse thermal modelling reveals short and rapid cooling at ca. 6.5 Ma followed by late-Quaternary final cooling. The 10 Ma cooling signal only evidenced in the northern plutonic complex (Fitz Roy) may represent an exhumation response to the northward migrating subduction of spreading ridge segments, causing localized dynamic uplift. Thus, the absence of exhumation signal before 6.5 Ma in the southern part (Torres del Paine) suggest that the spreading ridge subduction must have occurred before its 12.5 Ma emplacement. On the other hand, rapid cooling by similar magnitude in both plutonic complexes between ca. 7.5–6.5 Ma, likely reflects the onset of late-Cenozoic glaciations in Southern Patagonia. Finally, the late-stage Quaternary cooling signals differ between Torres del Paine and Fitz Roy, likely highlighting different exhumation responses (i.e. relief development vs. uniform exhumation) to mid-Pleistocene climate cooling. We thus identify and distinguish the causes of rapid exhumation periods in the Southern Patagonian Andes, and propose a first Late Miocene exhumation pulse due to subduction of spreading ridge dynamics, and two Late Cenozoic exhumation episodes due to regional climate changes that have shaped alpine landscapes in this region.

References:

Leuthold J., et al. 2012. Time resolved construction of a bimodal laccolith (Torres del Paine, Patagonia). EPSL.

Ramírez de Arellano C., et al. 2012. High precision U/Pb zircon dating of the Chaltén Plutonic Complex (Cerro Fitz Roy, Patagonia) and its relationship to arc migration in the southernmost Andes. Tectonics.

Fosdick J. C., et al. 2013. Retroarc deformation and exhumation near the end of the Andes, southern Patagonia. EPSL.

Guillaume B. 2009. Neogene uplift of central eastern Patagonia: Dynamic response to active spreading ridge subduction? Tectonics.

How to cite: Paiva Muller, V. A., Sue, C., Valla, P., Sternai, P., Simon-Labric, T., Martinod, J., Ghiglione, M., Baumgartner, L., Herman, F., Reiners, P., Gautheron, C., Grujic, D., Shuster, D., and Braun, J.: Exhumation signals and forcing mechanisms in the Southern Patagonian Andes (Torres del Paine and Fitz Roy plutonic complexes), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-226, https://doi.org/10.5194/egusphere-egu22-226, 2022.

14:15–14:16
Questions

14:16–14:22
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EGU22-5992
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ECS
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Highlight
Riccardo Lanari et al.

Most orogenic belts are close to convergent plate margins. However, some orogens are formed far away from plate boundaries, as a result of compressional stress propagating within plates, basal loading, or a combination of thereof. We focus on the Atlas of Morocco, which is such an intraplate orogeny and shows evidence of mantle driven uplift, and plume-related volcanism. How these processes interact each other is still poorly constrained and it provides clues about intraplate stress propagation, strain localization, and lithospheric weakening due to mantle dynamics. 

We present three sets of observations constructed by integrating previous data with new analyses. Crustal and thermal evolution constraints are combined with new analyses of topographic evolution and petrological and geochemical data from the Anti-Atlas volcanic fields. Our findings reveal that: i) crustal deformation and exhumation started during middle/late Miocene, contemporaneous with the onset of volcanism; ii) volcanism has an anorogenic signature with a deep source; iii) a dynamic deep mantle source supports the high topography. Lastly, we conducted simple numerical tests to investigate the connections between mantle dynamics and crustal deformation. This leads us to propose a model where mantle upwelling and related volcanism weaken the lithosphere and favor the localization of crustal shortening along pre-existing structures due to plate convergence.

How to cite: Lanari, R., Faccenna, C., Natali, C., Sengul, E., Fellin, G., Becker, T., Gogus, O., Youbi, N., and Conticelli, S.: Mantle dynamics and intraplate orogeny: The Atlas of Morocco, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5992, https://doi.org/10.5194/egusphere-egu22-5992, 2022.

14:22–14:23
Questions

14:23–14:29
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EGU22-11947
Laetitia Le Pourhiet et al.

14:29–14:30
Questions

14:30–14:36
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EGU22-5561
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ECS
Arushi Saxena et al.

Geodynamic models based on seismic tomography have been utilized to understand a wide range of physical processes in the Earth's mantle ranging from lithospheric stress states to plate-mantle interactions. However, the influence of various model components and the associated physical properties of the mantle on the observed surface deformation is still an open question and requires further research. In this study, we develop global mantle flow models based on high-resolution seismic tomography to quantify the relative importance of the plate driving and resisting forces on the surface motions. Our models include temperature and density variations based on seismic tomography, lithospheric structure, and the observed locations of subducted slabs, using the geodynamics software ASPECT. We use a diffusion/dislocation creep rheology with different parameters for the major mantle phases. To facilitate plate-like deformation, we prescribe weak plate boundaries at the locations given by global fault databases. We resolve the resulting strong viscosity variations using adaptive mesh refinement such that our global models have a minimum resolution of <10 km in the lithosphere. We analyze the influence of slab viscosity, plate boundary friction, asthenospheric viscosity, and plate boundary geometry on reproducing the observed GPS surface velocities. Our parameter study identifies model configurations that have up to 85% directional correlation and a global velocity mean within 10% difference with the observed surface motions. Our results also suggest that the modeled velocities are very sensitive to the plate boundary friction, particularly to variations in viscosity, dip angles, and the plate boundary geometry, i.e., open vs closed boundaries, or localized vs. diffused deformation zones. These models show the relative influence of plate-driving forces on the surface motions in general, and in particular the importance of using accurate models of plate boundary friction for reproducing observed plate motions. In addition, they can be used as a starting point to separate the influences of lithospheric structure and mantle convection on surface observables like strain rate, stress field, and topography.

How to cite: Saxena, A., Dannberg, J., and Gassmoeller, R.: Investigating the effects of plate-driving forces on observed surface deformation using global mantle flow models , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5561, https://doi.org/10.5194/egusphere-egu22-5561, 2022.

14:36–14:37
Questions

14:37–14:43
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EGU22-2113
Barbara Romanowicz et al.

Although seismic tomography has provided important constraints on the long-wavelength structure of the mantle and its planform of convection, much is yet not well understood about the dynamic interaction of tectonic plates and deep mantle circulation at intermediate wavelengths (i.e., below plate-scale). In particular, a better understanding of the seismic structure of the oceanic upper mantle could potentially help unraveling the relationships between different scales of mantle convection, hotspot volcanism, and surface observables (e.g., MORB geochemistry, gravity gradients and bathymetry). We here present a new tomographic model of the shear-wave velocity and radial anisotropy structure beneath the central and southern Atlantic ocean constructed from the inversion of surface and body waves waveforms down to 30s period. Preliminary results confirm the existence of quasi-periodically distributed low-velocity regions in the upper mantle (200–350 km depth) organized in horizontally elongated bands some of which are parallel to the direction of absolute plate motion, as previously found in a lower resolution global tomographic models SEMum2 (French et al., 2013) and SEMUCB_WM1 (French and Romanowicz, 2014). Many of these elongated structures overlie vertically elongated plumelike conduits that appear to be rooted in the lower mantle, located, when projected vertically to the surface, in the vicinity of major hotspots.  However, there is no direct vertical correspondence between the imaged plumelike conduits and hotspots locations suggesting a complex interaction between the upwelling flow and the lithosphere/asthenosphere system. We discuss possible relations of this structure with trace element geochemistry of the corresponding hotspots.

How to cite: Romanowicz, B., Munch, F., Rudolph, M., and Mukhopadhyay, S.: Imaging the meso-scale structure of the upper mantle beneath the southern and central Atlantic ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2113, https://doi.org/10.5194/egusphere-egu22-2113, 2022.

14:43–14:44
Questions

Tue, 24 May, 15:10–16:40

Chairpersons: Lucia Perez-Diaz, Megan Holdt

15:10–15:12
Plume plate interaction

15:12–15:22
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EGU22-6571
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ECS
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solicited
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Highlight
Ben Mather et al.

Deep mantle plumes are buoyant upwellings rising from the Earth’s core-mantle boundary to its surface, and describing most hotspot chains. Mechanisms to explain dual chains of hotspot volcanoes for the Hawaiian-Emperor and Yellowstone chains fail to explain the geochemical similarity and large distances between contemporaneous volcanoes of the Tasmantid and Lord Howe chains in the SW Pacific. Using numerical models of mantle convection, we demonstrate how slab-plume interaction can lead to sustained plume branching over a period of >40 million years to produce parallel volcanic chains that track plate motion. We propose a three-part model: first, slabs stagnate in the upper mantle, explaining fast upper mantle P-wave velocity anomalies; second, deflection of a plume conduit by a stagnating slab splits it into two branches 650-900 km apart, aligning to the orientation of the trench axis; third, plume branches heat the stagnating slab causing partial melting and release of volatiles which percolate to the surface forming two contemporaneous volcanic chains with slab-influenced EM1 signatures. Our results highlight the critical role of long-lived subduction on the evolution and behaviour of intraplate volcanism.

How to cite: Mather, B., Seton, M., Williams, S., Whittaker, J., Carey, R., Arnould, M., Coltice, N., Rogers, A., Ruttor, S., and Nebel, O.: Parallel volcanic chains generated by plume-slab interaction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6571, https://doi.org/10.5194/egusphere-egu22-6571, 2022.

15:22–15:24
Questions

15:24–15:30
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EGU22-12422
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ECS
Ingo Stotz et al.

Earth's surface moves in response to a combination of tectonic forces from the thermally convective mantle and plate boundary forces. Plate motion changes are increasingly well documented in the geologic record and they hold important constraints. However, the underlying forces that initiate such plate motion changes remain poorly understood. I have developed a novel 3-D spherical numerical scheme of mantle and lithosphere dynamics, aiming to exploit information of past plate motion changes in quantitative terms. In order to validate the models and single out those most representative of the recent tectonic evolution of Earth, model results are compared to global plate kinematic reconstructions. Additionally, over the past years a pressure driven, so-called Poiseuille flow, model for upper mantle flux in the asthenosphere has gained increasing geodynamic attention–for a number of fluid dynamic arguments. This elegantly simple model makes a powerful testable prediction: Plate motion changes should coincide with regional scale mantle convection induced elevation changes (i.e., dynamic topography). For this the histories of large scale vertical lithosphere motion recorded in the sedimentary record holds important information.

Here, I will present analytical results that help to better understand driving and resisting forces of plate tectonics – in particular the plume push force. Moreover, numerical results indicate that mantle convection plays an active role in driving plate motions through pressure driven upper mantle flow. Altogether, theoretical and observational constrains provide powerful insights for geodynamic forward and inverse models of past mantle convection.

How to cite: Stotz, I., Vilacís, B., Hayek, J. N., Bunge, H.-P., and Friedrich, A. M.: Plume push force: a relevant driver of plate tectonics that can be constrained by horizontal and vertical plate motions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12422, https://doi.org/10.5194/egusphere-egu22-12422, 2022.

15:30–15:32
Questions

15:32–15:38
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EGU22-3461
Maxim Ballmer and Valerie Finlayson

Age-progressive volcanic “hotspot” chains result from the passage of a tectonic plate over a thermochemical mantle plume, thereby sampling the otherwise-inaccessible lowermost mantle. A common feature in oceanic hotspot tracks is the occurrence of two parallel volcanic chains with an average separation of ~50 km (e.g., Loa and Kea chains in Hawaii). Some other tracks (including Tristan-Gough, Shona, the Line Islands, Wake seamounts, Tuvalu and Cook-Austral) feature a 200-400 km spacing, but the origin of such widely-spaced melting zones in the mantle remains unknown. Here, we explore 3D Cartesian geodynamic models of thermochemical plume ascent through the upper mantle. We explore various distributions of intrinsically-dense eclogitic material across the plume stem. For a wide range of eclogite distributions, the plume pools in the depth range of 300~410 km, where the excess density of eclogite is greater than above and below, as also predicted by Ballmer et al., EPSL 2013. This “Deep Eclogitic Pool” then splits up into two lobes that feed two separate shallow plumelets, particularly at high eclogite contents in the center of the underlying plume stem. The two plumelets feed two separate melting zones at the base of the lithosphere, which are elongated in the direction of plate motion due to interaction with small-scale convection. This “forked plume” morphology can account for hotspot chains with two widely-spaced (250~400 km) tracks and with long-lived (>5 My) coeval activity along each track. Forked plumes may also provide an ideal opportunity to study geochemical zonation of the lower-mantle plume stem, as each plumelet ultimately samples the opposite side of a deep plume conduit that potentially preserves spatial heterogeneity from the lowermost mantle. We compare this model to geochemical asymmetry evident along the Wake, Tuvalu and Cook-Austral double-chain segments, which make up the extensive (>100 Ma) Rurutu-Arago hotspot track. The preservation of a long-lived NE-SW geochemical asymmetry along the Rurutu-Arago double chain indicates a deep origin, likely from the southern boundary of the Pacific large low shear-velocity province. Our findings highlight the potential of the hotspot geochemical record to map lower-mantle structure over space and time, complementing the seismic-tomography snapshot.

How to cite: Ballmer, M. and Finlayson, V.: Widely-spaced Double Hotspot Chains due to Forked Plumes sample Lower Mantle Geochemical Structure , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3461, https://doi.org/10.5194/egusphere-egu22-3461, 2022.

15:38–15:40
Questions

15:40–15:46
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EGU22-9199
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ECS
Lea Beloša et al.

Typically, the change in lithospheric thickness associated with fracture zones relates directly to the vigor of secondary convection or mantle flow patterns. Therefore, one might expect that mantle flow considerably boosted by the presence of a mantle plume would easily overcome the lithospheric steps created at fracture zone locations. However, to date, there are no studies to verify this assumption. Numerical models based on an example from the SW Indian Ridge suggest that the axial flow driven by a plume (the Marion plume) is indeed likely to be curtailed by the long-offset fracture zones1.

We have investigated the interactions between the Jan Mayen fracture zone and Iceland mantle plume in the NE Atlantic by considering (a) the lithospheric and asthenospheric regional configuration and (b) the geochemistry of rocks produced by submarine volcanism.

Several global lithospheric models indicate a thinning of the lithosphere on both sides of the Jan Mayen Fracture transform, despite the difference in age of the two adjacent oceanic basins. However, the tomographic models indicate a gap in the asthenospheric flow at the lithosphere-asthenosphere depth under Jan Mayen transform fault, and only a narrow northward channel of this flow is visible under the westernmost part of the fracture zone.

Vesteris seamount is an alkaline seamount placed in the central part of the Greenland Basin, located ca. 480 km west from slow-spreading Mohn's ridge and ca. 250 km north from the Jan Mayen Fracture Zone. Vesteris is a solitary volcanic center far away from an active ridge regime with an eruptive age ranging from 650 – 10 ka 2. Here we report new results from geochemical analysis of several samples dredged during the East Greenland Sampling campaign EGS-2012 from the flanks of Vesteris. Whole-rock major and trace elements, together with isotopes and olivine phenocryst mineral data, are used to decipher the source of volcanism at Vesteris Seamount.

The Sr-Nd-Pb isotopic signatures indicate that Vesteris volcanism is unrelated to the Iceland mantle plume. Low NiO concentrations in highly forsteritic olivines from Vesteris alkali basalt suggest that the source was dominantly peridotitic. Rare Earth Elements profiles indicate very low degrees of partial melting of a deep mantle source in the presence of residual garnet.

Vesteris seamount was formed in a location of a relatively steep gradient of the lithospheric-asthenospheric boundary and close to the northward mantle flow that is carving the Greenland thick lithosphere. The results suggest that the Iceland mantle flow may not have crossed the Jan Mayen Transform Fault; instead, the seamount tapped into a mantle reservoir in the Greenland Basin that preserved the complex history of the Greenland craton and adjacent terranes.   REFS. (1) Georgen and Lin, 2003, Plume-transform interactions at ultra-slow spreading ridges: Implications for the SW Indian Ridge, G-cubed, doi:10.1029/2003GC000542; (2) Mertz & Renne, 1995, Quaternary multi-stage alkaline volcanism at Vesteris Seamount (Norwegian—Greenland Sea): evidence from laser step heating 40Ar/39Ar experiments, Journal of Geodynamics, doi:10.1016/0264-3707(94)E0001-B.

How to cite: Beloša, L., Gaina, C., Callegaro, S., Mazzini, A., Meyzen, C., Polteau, S., and Bizimis, M.: Plume-Fracture Zone interactions in the NE Atlantic , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9199, https://doi.org/10.5194/egusphere-egu22-9199, 2022.

15:46–15:52
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EGU22-5259
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ECS
Mathurin Dongmo Wamba et al.

Mid-plate volcanoes are well known as hotspots. They represent the surface signature of mantle plumes, nevertheless their origin and their role in geodynamics are still a challenge in the Earth sciences. Even though plate tectonics and mantle plumes were discovered at the same time, the latter cannot be explained by the former. Plumes’ birth, life and death play a fundamental role on the evolution of life on Earth and on plate-tectonic reorganization. La Réunion hotspot is known as one of the largest on the Earth, that created the Deccan volcanic traps in India (almost 2 million km2) and the death of more than 90% of life on the Earth including dinosaurs ~65Ma ago. So far the origin of the mantle plumes and their role in geodynamics are still unclear in Earth sciences. In that respect, we use the dataset from the French-German RHUM-RUM experiment around La Réunion hotspot (2012-2013), from IRIS data center and FDSN to extensively investigate the deep structure of the plume along its complete track from its birth to its present stage, as well as from the upper mantle to the lowermost mantle. Several shear-wave anomalies are resolved underneath Indian Ocean and the upper mantle beneath this region is fed by mantle plume rising from the core-mantle boundary. The lower mantle thermochemical dome associated to the South-African Large Low-Shear Velocity Province (LLSVP) is found to be composed of several conduits. Plume branches are highlighted at ~900 km depth. Thermal instability and thermochemical heterogeneities in the D" layer are likely the principal reasons of the plumes birth at the core-mantle boundary, and therefore an indicator of long-life of the Réunion hotspot.

How to cite: Dongmo Wamba, M., Romanowicz, B., Montagner, J.-P., and Simons, F.: Plume conduits rooted at the core-mantle boundary beneath the Réunion hotspot, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5259, https://doi.org/10.5194/egusphere-egu22-5259, 2022.

15:52–15:54
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