Variable dynamic styles of primordial heterogeneity preservation in the Earth's lower mantle

Gülcher, Anna; Gebhardt, David; Ballmer, Maxim D.; Tackley, P. J.

doi:10.1016/j.epsl.2020.116160

Cited by 26 publications

(39 citation statements)

References 55 publications

(65 reference statements)

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“…Our results further contribute to the ongoing debate about whether thermochemical piles are intrinsically stable features in the deep mantle, which spatially determine mantle convective patterns (Dziewonski et al, 2010;Torsvik et al, 2014) or are instead pushed around by subduction zones (McNamara and Zhong, 2005;Zhang et al, 2010). In our models, piles and blobs both mostly reside well away from lower-mantle downwellings, as they are pushed away from them (videos in the Supplement, Gülcher, 2021). Indeed, as noted in previous studies (e.g., McNamara and Zhong, 2005;Zhang et al, 2010;Schierjott et al, 2020), we observe that downgoing slabs are mainly controlling the spatial distribution of piles (as well as viscous blobs) and not the other way around.…”

Section: Linking Recycled Piles Primordial Blobs and Mantle Dynamicssupporting

confidence: 63%

“…Video supplement. Video Supplements are available at Zenodo under the identifier https://zenodo.org/record/4767426 (Gülcher, 2021).…”

Section: Discussionmentioning

confidence: 99%

“…Model predictions for this sub-regime are also consistent with the stagnation of some slabs in a depth range that is similar to primordial-domain roofs, while other slabs readily sink into the deep mantle (Fukao and Obayashi, 2013), as seen in Figs. 2, 7, and videos in the Supplement (Gülcher, 2021). Furthermore, the presence of viscous domains in the midmantle may explain the observation of sharp seismic velocity contrasts in the uppermost lower mantle (850-1100 km depth), usually occurring away from major upwellings and downwellings (Jenkins et al, 2017;Waszek et al, 2018).…”

Section: Styles Of Mantle Mixingmentioning

confidence: 95%

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Coupled dynamics and evolution of primordial and recycled heterogeneity in Earth's lower mantle

2021

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Abstract. The nature of compositional heterogeneity in Earth's lower mantle remains a long-standing puzzle that can inform about the long-term thermochemical evolution and dynamics of our planet. Here, we use global-scale 2D models of thermochemical mantle convection to investigate the coupled evolution and mixing of (intrinsically dense) recycled and (intrinsically strong) primordial heterogeneity in the mantle. We explore the effects of ancient compositional layering of the mantle, as motivated by magma ocean solidification studies, and of the physical parameters of primordial material. Depending on these physical parameters, our models predict various regimes of mantle evolution and heterogeneity preservation over 4.5 Gyr. Over a wide parameter range, primordial and recycled heterogeneity are predicted to co-exist with each other in the lower mantle of Earth-like planets. Primordial material usually survives as medium- to large-scale blobs (or streaks) in the mid-mantle, around 1000–2000 km depth, and this preservation is largely independent of the initial primordial-material volume. In turn, recycled oceanic crust (ROC) persists as large piles at the base of the mantle and as small streaks everywhere else. In models with an additional dense FeO-rich layer initially present at the base of the mantle, the ancient dense material partially survives at the top of ROC piles, causing the piles to be compositionally stratified. Moreover, the addition of such an ancient FeO-rich basal layer significantly aids the preservation of the viscous domains in the mid-mantle. Finally, we find that primordial blobs are commonly directly underlain by thick ROC piles and aid their longevity and stability. Based on our results, we propose an integrated style of mantle heterogeneity for the Earth involving the preservation of primordial domains along with recycled piles. This style has important implications for early Earth evolution and has the potential to reconcile geophysical and geochemical discrepancies on present-day lower-mantle heterogeneity.

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Section: Linking Recycled Piles Primordial Blobs and Mantle Dynamicssupporting

confidence: 63%

“…Video supplement. Video Supplements are available at Zenodo under the identifier https://zenodo.org/record/4767426 (Gülcher, 2021).…”

Section: Discussionmentioning

confidence: 99%

Section: Styles Of Mantle Mixingmentioning

confidence: 95%

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Coupled dynamics and evolution of primordial and recycled heterogeneity in Earth's lower mantle

2021

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“…Mechanisms for the long-term preservation of the Hadean geochemical anomalies are imperfectly understood 229 , but storage in dense, viscous domains of the deep mantle can isolate Hadean-formed reservoirs from convective motions of the mantle 146,150,230 . The two LLSVP regions at the core-mantle boundary are attractive locations in this regard 83,118 and plume-fed hotspots may provide important clues.…”

Section: Primordial and Recycled Reservoirs Inferred From Plume-fed Hotspotsmentioning

confidence: 99%

Mantle plumes and their role in Earth processes

Koppers

Becker

Jackson

et al. 2021

Nat Rev Earth Environ

114

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The existence of mantle plumes was first proposed in the 1970s to explain intra-plate, hotspot volcanism, yet owing to difficulties in resolving mantle upwellings with geophysical images and discrepancies in interpretations of geochemical and geochronological data, the origin, dynamics and composition of plumes and their links to plate tectonics are still contested. In this Review, we discuss progress in seismic imaging, mantle flow modelling, plate tectonic reconstructions and geochemical analyses that have led to a more detailed understanding of mantle plumes. Observations suggest plumes could be both thermal and chemical in nature, can attain complex and broad shapes, and that more than 18 plumes might be rooted in regions of the lowermost mantle. The case for a deep mantle origin is strengthened by the geochemistry of hotspot volcanoes that provide evidence for entrainment of deeply recycled subducted components, primordial m an tle domains and, potentially, materials from Earth's core. Deep mantle plumes often appear deflected by large-scale mantle flow, resulting in hotspot motions required to resolve past tectonic plate motions. Future research requires improvements in resolution of seismic tomography to better visualize deep mantle plume structures at smaller than 100-km scales. Concerted multi-proxy geochemical and dating efforts are also needed to better resolve spatiotemporal and chemical evolutions of long-lived mantle plumes.

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“…This possible geographic (hemispheric) separation of the most geochemically enriched DUPAL domain in the southern hemisphere from the highest‐ 3 He/ 4 He (anti‐DUPAL) domain in the northern hemisphere suggests that reservoir dynamics are not solely controlled by the density and/or viscosity of the primordial reservoir (Coltice et al., 2005; Dechamps et al., 2011; Gülcher et al., 2020; Samuel & Farnetani, 2003), but that geographic separation from addition of recycled continental crust is also important. The extraordinarily high U and Th concentrations (reflecting enrichment in incompatible trace elements) in continental crust, which are over an order of magnitude higher than in oceanic crust (Gale et al., 2013; Rudnick & Gao, 2003), will ultimately have a greater impact on the 3 He/ 4 He of primordial domains, and may help explain why the highest 3 He/ 4 He hotspot is furthest from the continental crust‐rich DUPAL domain.…”

Section: Discussionmentioning

confidence: 99%

Spatial Characteristics of Recycled and Primordial Reservoirs in the Deep Mantle

Jackson

Becker

Steinberger

2021

Geochem Geophys Geosyst

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The spatial distribution of the geochemical domains hosting recycled crust and primordial (high-3 He/ 4 He) reservoirs, and how they are linked to mantle convection, are poorly understood. Two continent-sized seismic anomalies located near the core-mantle boundary-called the Large Low Shear Wave Velocity Provinces (LLSVPs)-are potential geochemical reservoir hosts. It has been suggested that high-3 He/ 4 He hotspots are spatially confined to the LLSVPs, hotspots sampling recycled continental crust are associated with only one of the LLSVPs, and recycled continental crust shows no relationship with latitude. We reevaluate the links between LLSVPs and isotopic signatures of hotspot lavas using improved mantle flow models including plume conduit advection. While most hotspots with the highest-3 He/ 4 He can indeed be traced to the LLSVP interiors, at least one high-3 He/ 4 He hotspot, Yellowstone, is located outside of the LLSVPs. This suggests high-3 He/ 4 He is not geographically confined to the LLSVPs. Instead, a positive correlation between hotspot buoyancy flux and maximum hotspot 3 He/ 4 He suggests that it is plume dynamics (i.e., buoyancy), not geography, which determines whether a dense, deep, and possibly widespread high-3 He/ 4 He reservoir is entrained. We also show that plume-fed EM hotspots (enriched mantle, with low-143 Nd/ 144 Nd), signaling recycled continental crust, are spatially linked to both LLSVPs, and located primarily in the southern hemisphere. Lastly, we confirm that hotspots sampling HIMU ("high-μ," or high 238 U/ 204 Pb) domains are not spatially limited to the LLSVPs. These findings clarify and advance our understanding of deep mantle reservoir distributions, and we discuss how continental and oceanic crust subduction is consistent with the spatial decoupling of EM and HIMU. JACKSON ET AL.

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Variable dynamic styles of primordial heterogeneity preservation in the Earth's lower mantle

Cited by 26 publications

References 55 publications

Coupled dynamics and evolution of primordial and recycled heterogeneity in Earth's lower mantle

Coupled dynamics and evolution of primordial and recycled heterogeneity in Earth's lower mantle

Mantle plumes and their role in Earth processes

Spatial Characteristics of Recycled and Primordial Reservoirs in the Deep Mantle

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