Björn Holger Heyn

• Thomas, Christine; Heyn, Björn Holger; Tölle, Lena & Tent, Rûna Van (2025). Investigating the D" Reflector Beneath the Indian Ocean with Source Arrays. SEISMICA. 4(2). doi: 10.26443/seismica.v4i2.1418. Full text in Research Archive Show summary

  We used seismic P-wave reflections to search for the discontinuity at the top of the D" region beneath the Indian Ocean. Due to a lack of seismic receiver arrays to target this region, we build source arrays using earthquakes in Indonesia and taking advantage of the long-running history of GEOSCOPE stations located in the western Indian Ocean and Antarctica, as well as three additional stations (Seychelles and Antarctica). Despite restricting the earthquake depth range, source-array stacks were difficult to interpret due to complications arising from differing earthquake depths, violating the plane wave assumption. Therefore, we use a source-array scatter imaging method, that does not rely on travel-times calculated for a plane wave. Using this technique in conjunction with source normalization, we found evidence for a D" P-wave reflector for several stations with reflector depths varying between 230-160 km above the CMB South of Australia and 190 to 270 km above the CMB beneath the Indian Ocean, where the depth of the reflector in the north of our study area is consistent with previously imaged D" depths using S-waves and agrees with receiver array data. We suggest that earlier imaged subducted lithosphere in this region is responsible for our D" reflections.

• Heyn, Björn Holger; Shephard, Grace & Conrad, Clinton Phillips (2024). Prolonged Multi-Phase Magmatism Due To Plume-Lithosphere Interaction as Applied to the High Arctic Large Igneous Province. Geochemistry Geophysics Geosystems. 25(6). doi: 10.1029/2023GC011380. Full text in Research Archive Show summary

  The widespread High Arctic Large Igneous Province (HALIP) exhibits prolonged melting over more than 50 Myr, an observation that is difficult to reconcile with the classic view that large igneous provinces (LIPs) originate from melting in plume heads. Hence, the suggested plume-related origin and classification of HALIP as a LIP have been questioned. Here, we use numerical models that include melting and melt migration to investigate a rising plume interacting with lithosphere of variable thickness, that is, a basin-to-craton setting applicable to the Arctic. Models reveal that melt migration introduces significant spatial and temporal variations in melt volumes and pulses of melt production, including protracted melting for at least about 30–40 Myr, because of the dynamic feedback between migrating melt and local lithosphere thinning. For HALIP, plume material deflected from underneath the Greenland craton can re-activate melting zones below the previously plume-influenced Sverdrup Basin after a melt-free period of about 10–15 Myr, even though the plume is already ∼500 km away. Hence, actively melting zones do not necessarily represent the location of the deeper plume stem at a given time, especially for secondary pulses. Additional processes such as (minor) plume flux variations or local lithospheric extension may alter the timing and volume of HALIP pulses, but are to first order not required to reproduce the long-lived and multi-pulse magmatism of HALIP. Since melting zones are always plume-fed, we would expect HALIP magmatism to exhibit plume-related trace element signatures throughout time, potentially shifting from mostly tholeiitic toward more alkalic compositions.

• Heyn, Björn Holger & Conrad, Clinton Phillips (2022). On the Relation Between Basal Erosion of the Lithosphere and Surface Heat Flux for Continental Plume Tracks. Geophysical Research Letters. ISSN 0094-8276. 49(7). doi: 10.1029/2022GL098003. Full text in Research Archive Show summary

  While hotspot tracks beneath thin oceanic lithosphere are visible as volcanic island chains, the plume-lithosphere interaction for thick continental or cratonic lithosphere often remains hidden due to the lack of volcanism. To identify plume tracks with missing volcanism, we characterize the amplitude and timing of surface heat flux anomalies following a plume-lithosphere interaction using mantle convection models. Our numerical results confirm an analytical relationship in which surface heat flux increases with the extent of lithosphere thinning, which is primarily controlled by the viscosity structure of the lower lithosphere and the asthenosphere. We find that lithosphere thinning is greatest when the plate is above the plume conduit, while the maximum heat flux anomaly occurs about 40-140 Myr later. Therefore, younger continental and cratonic plume tracks can be identified by observed lithosphere thinning, and older tracks by an increased surface heat flux, even if they lack extrusive magmatism.

• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2020). Core-mantle boundary topography and its relation to the viscosity structure of the lowermost mantle. Earth and Planetary Science Letters. ISSN 0012-821X. 543. doi: 10.1016/j.epsl.2020.116358. Full text in Research Archive Show summary

  Two large areas of anomalously low seismic velocities are visible in all tomographic models of the lowermost mantle. Depending on the density structure of these Large Low Shear Velocity Provinces (LLSVPs), the core-mantle boundary (CMB) will deform upwards or downwards due to isostatic and dynamic topography, the latter being sensitive to the viscosity structure of the lowermost mantle. Heterogeneities in the viscosity structure, although difficult to constrain, might be especially important if the LLSVPs are thermochemical piles with elevated intrinsic viscosity as suggested by mineral physics. Based on numerical models, we identify a short-wavelength (about 80-120 km wide, up to a few km deep) topographic depression that forms around the pile edges if the pile is more viscous than the surrounding mantle. The depression forms when a wedge of thermal boundary layer material becomes compressed against the viscous pile, and is enhanced by relative uplift of the CMB beneath the pile by plumes rising above it. The depth and asymmetry of the depression constrain the magnitude of the viscosity contrast between pile and the surrounding mantle. Furthermore, (periodic) plume initiation and pile collapse at the pile margin systematically modify the characteristic depression, with a maximum in asymmetry and depth at the time of plume initiation. Core-reflected waves or scattered energy may be used to detect this topographic signature of stiff thermochemical piles at the base of the mantle.

• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2020). How Thermochemical Piles Can (Periodically) Generate Plumes at Their Edges. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 125(6). doi: 10.1029/2019JB018726. Full text in Research Archive Show summary

  Deep-rooted mantle plumes are thought to originate from the margins of the Large Low Shear Velocity Provinces (LLSVPs) at the base of the mantle. Visible in seismic tomography, the LLSVPs are usually interpreted to be intrinsically dense thermochemical piles in numerical models. Although piles deflect lateral mantle flow upward at their edges, the mechanism for localized plume formation is still not well understood. In this study, we develop numerical models that show plumes rising from the margin of a dense thermochemical pile, temporarily increasing its local thickness until material at the pile top cools and the pile starts to collapse back toward the core-mantle boundary (CMB). This causes dense pile material to spread laterally along the CMB, locally thickening the lower thermal boundary layer on the CMB next to the pile, and initiating a new plume. The resulting plume cycle is reflected in both the thickness and lateral motion of the local pile margin within a few hundred km of the pile edge, while the overall thickness of the pile is not affected. The period of plume generation is mainly controlled by the rate at which slab material is transported to the CMB, and thus depends on the plate velocity and the sinking rate of slabs in the lower mantle. A pile collapse, with plumes forming along the edges of the pile's radially extending corner, may, for example, explain the observed clustering of Large Igneous Provinces (LIPs) in the southeastern corner of the African LLSVP around 95–155 Ma.

• Trønnes, Reidar G; Baron, Marzena Anna; Eigenmann, Katarina R.; Guren, Marthe Grønlie; Heyn, Björn Holger & Løken, Andreas [Show all 7 contributors for this article] (2019). Core formation, mantle differentiation and core-mantle interaction within Earth and the terrestrial planets. Tectonophysics. ISSN 0040-1951. doi: 10.1016/j.tecto.2018.10.021. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2018). Stabilizing effect of compositional viscosity contrasts on thermochemical piles. Geophysical Research Letters. ISSN 0094-8276. 45(15), p. 7523–7532. doi: 10.1029/2018GL078799. Full text in Research Archive Show summary

  The large low shear velocity provinces (LLSVPs) observed in the lowermost mantle are widely accepted as chemically distinct thermochemical 'piles', but their origin and long-term evolution remain poorly understood. The survival time and shape of the LLSVPs are thought to be mainly controlled by their compositional density, while their viscosity has beeen considered less important. Based on recent constraints on chemical reactions between mantle and core, a more complex viscosity structure of the lowermost mantle, possibly including high viscosity thermochemical pile material, seems reasonable. In this study, we use numerical models to identify a trade-off between compositional viscosity and density contrasts required for long-term stability of thermochemical piles, which permits lower-density and higher-viscosity piles. Moreover, our results indicate more restrictive stability conditions during periods of strong deformation-induced entrainment, e.g. during initial pile formation, which suggests long-term pile survival.

• Reiss, Anne-Sophie; Thomas, Christine; Driel, Jac van & Heyn, Björn Holger (2017). A hot midmantle anomaly in the area of the Indian Ocean Geoid Low. Geophysical Research Letters. ISSN 0094-8276. 44(13), p. 6702–6711. doi: 10.1002/2017GL073440. Full text in Research Archive

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• Heyn, Björn Holger; Shephard, Grace & Conrad, Clinton Phillips (2024). Prolonged multi-phase volcanism in the Arctic induced by plume-lithosphere interaction. Full text in Research Archive
• Thomas, Christine & Heyn, Björn Holger (2024). Imaging deep subducted lithosphere beneath the Indian Ocean with seismic source array recordings. Full text in Research Archive
• Shephard, Grace & Heyn, Björn Holger (2024). New insights into the protracted and widespread nature of the High Arctic LIP and mantle plume. Full text in Research Archive
• Shephard, Grace; Heyn, Björn Holger & Conrad, Clinton Phillips (2023). Prolonged multi-phase magmatism due to plume-lithosphere interaction as applied to the High Arctic Large Igneous Province. Full text in Research Archive
• Heyn, Björn Holger; Shephard, Grace & Conrad, Clinton Phillips (2023). Locally amplified plume-lithosphere interaction and multiple melting events for 2-phase flow models. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Shephard, Grace (2023). Plume-lithosphere interaction and continental plume tracks. Full text in Research Archive
• Heyn, Björn Holger & Conrad, Clinton Phillips (2023). Development and implications of a free base for numerical models. Full text in Research Archive
• Heyn, Björn Holger; Shephard, Grace & Conrad, Clinton Phillips (2023). Amplification of sub-lithospheric dynamics by melt migration during plume-lithosphere interaction. Full text in Research Archive
• Shephard, Grace; Heyn, Björn Holger & Conrad, Clinton Phillips (2023). Large-scale volcanism at the top of the world; plume and melt modelling of the High Arctic Large Igneous Province (HALIP). Full text in Research Archive
• Shephard, Grace; Gaina, Carmen; Heyn, Björn Holger; Conrad, Clinton Phillips; Anfinson, Owen & Schaeffer, Andrew [Show all 7 contributors for this article] (2022). Exploring potential lower mantle structures and interactions for the origins of HALIP. Full text in Research Archive
• Heyn, Björn Holger & Conrad, Clinton Phillips (2022). Basal erosion and surface heat flux anomalies associated with plume-lithosphere interaction beneath continents. Full text in Research Archive
• Heyn, Björn Holger (2022). Forskere har undersøkt to enorme, mystiske strukturer i jordens indre. [Journal]. https://www.forskning.no/geologi/forskere-har-undersokt-to-e. Full text in Research Archive
• Rolf, Tobias; Crameri, Fabio; Heyn, Björn Holger & Thielmann, Marcel (2022). Testing a (quasi-)free base for modelling core-mantle boundary topography. Full text in Research Archive
• Heyn, Björn Holger & Conrad, Clinton Phillips (2021). Plume-induced heat flux anomalies and the associated thinning of the continental lithosphere. Full text in Research Archive
• Conrad, Clinton Phillips; Domeier, Mathew; Selway, Kate & Heyn, Björn Holger (2020). A link between seamount volcanism and thermochemical piles in the deepest mantle. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2020). How thermochemical piles initiate plumes at their edges. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2020). How thermochemical piles initiate plumes at their edges. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2020). How thermochemical piles initiate plumes at their edges. European Geosci. Union, Gen. Assembly, Geophys. Res. Abstr.. Full text in Research Archive
• Selway, Kate; Conrad, Clinton Phillips; Ramirez, Florence; Karlsson, Nanna B; Weerdesteijn, Maaike Francine Maria & Heyn, Björn Holger (2020). How magnetotellurics can aid cryosphere studies: mantle rheology, GIA, surface heat flow, and basal melting. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Selway, Kate (2020). Numerical constraints on heat flux variations and lithospheric thinning associated with passage of the Iceland plume beneath Greenland. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2019). Linking surface volcanism and deep Earth: Piles, plumes, and dynamic topography. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2019). Core-mantle boundary topography and its relation to lowermost mantle viscosity structure. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2019). Periodic plume generation at the edges of thermochemical piles. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2019). What core-mantle boundary topography can tell us about plume locations and the viscosity and density structure of thermochemical piles. Full text in Research Archive
• Conrad, Clinton Phillips; Domeier, Mathew; Selway, Kate & Heyn, Björn Holger (2019). A link between seamount volcanism and thermochemical piles in the deepest mantle. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2019). What core-mantle boundary topography can tell us about plume locations and the viscosity and density structure of thermochemical piles. European Geosci. Union, Gen. Assembly, Geophys. Res. Abstr.. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2019). Core-mantle boundary topography and its relation to lowermost mantle viscosity structure. Ada Lovelace Workshop on Modelling Mantle and Lithosphere Dynamics. Abstr.. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2019). Periodic plume generation at the edges of thermochemical piles. European Geosci. Union, Gen. Assembly, Geophys. Res. Abstr.. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2018). Stabilization of thermochemical piles by compositional viscosity contrasts. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2018). Stabilization of thermochemical piles by compositional viscosity contrasts. EGU Gen. Assembly, EGU2018-12950. Full text in Research Archive
• Heyn, Björn Holger; Conrad, Clinton Phillips & Trønnes, Reidar G (2017). Stabilizing effect of a chemical viscosity contrast on LLSVP structures Abstr., Gordon Res. Conf. on Chemical and dynamical evolution of Earth's deep interior, from formation to today. Mount Holyoke College, South Hadley, MA. Full text in Research Archive
• Heyn, Björn Holger (2020). Geodynamics of Earth's Large Low Shear Velocity Provinces. Interaction with mantle flow, plume formation, and core-mantle boundary deformation. Universitetet i Oslo. Full text in Research Archive
• Heyn, Björn Holger & Conrad, Clinton Phillips (2020). Geodynamics of Earth’s Large Low Shear Velocity Provinces Interaction with mantle flow, plume initiation, and core-mantle boundary deformation. Universitetet i Oslo. Full text in Research Archive Show summary

  Our planet’s interior is actively convecting like boiling water in a pot, although on significantly larger length and time scales. In some locations, such as Hawaii and Iceland, one consequence of this convection is strong, long-lived volcanism that eventually creates island chains. But where does the erupted material come from, why is the volcano located at this specific spot, and what are the mechanisms to trigger this volcanism? To understand the origins of this Hawaiian-type volcanism, we have to dive deep into the interior of Earth, where the driving forces of convection are located. This doctoral study uses numerical simulations to unravel how continent-sized piles of dense and potentially stiff material, residing about 2900 km beneath our feet, affect the formation of strong upwelling “plumes” that are thought to be associated with Hawaiian-type volcanism. Due to internal deformation, such piles periodically perturb a layer of hot material surrounding them, causing some material to rise and eventually erupt into volcanism. Moreover, this triggering mechanism causes a characteristic depression on the core-mantle boundary that may be used to constrain the properties of the deep Earth, and also locate newly emerging plumes before they erupt to the surface to produce Hawaiian-type volcanoes.

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