African Large Low Shear Velocity Province Research Articles

Imaging deep-mantle plumbing beneath La Réunion and Comores hot spots: Vertical plume conduits and horizontal ponding zones.

Whether the two large low-shear velocity provinces (LLSVPs) at the base of Earth's mantle are wide compact structures extending thousands of kilometers upward or bundles of distinct mantle plumes is the subject of debate. Full waveform shear wave tomography of the deep mantle beneath the Indian Ocean highlights the presence of several separate broad low-velocity conduits anchored at the core-mantle boundary in the eastern part of the African LLSVP, most clearly beneath La Réunion and Comores hot spots. The deep plumbing system beneath these hot spots may also include alternating vertical conduits and horizontal ponding zones, from 1000-km depth to the top of the asthenosphere, reminiscent of dyke and sills in crustal volcanic systems, albeit at a whole-mantle scale.

Surface wave phase velocity variations underneath the Indian Ocean geoid low

The Indian plate has undergone a long tectonic journey since its separation from the Gondwanaland. Its protracted rift-drift motion has rendered several enigmatic features in the Indian Ocean. One such feature is the large geoid deficit (−106 m), observed in the south of Sri Lanka that is known as the Indian Ocean geoid low (IOGL). A broad consensus about plausible explanations behind the IOGL anomaly still remains elusive. For the first time, 17 Ocean Bottom Seismometers (OBSs) were deployed in the IOGL region to characterize the subsurface structural variations. Here, we examine the inter-station Rayleigh wave phase velocity variations within the period range of 15–197 s. We construct 1-D velocity-depth sections down to c.a.380 km or less along with N-S and E-W profiles, using ≥5.2 magnitudes (Mw) earthquake data that occurred at a depth ≤ 100 km at regional/teleseismic distances. Our result demarcates the regional Moho depths varying from c.a.11.6 ± 0.8 km to c.a.19.8 ± 1.2 km along the OBS array from south to north respectively. A thickened oceanic crust (c.a.9–10 km) is attributed to magmatic underplating in the lower crust near the aseismic Comorin ridge. The lithospheric thickness ranges between c.a.47.6 ± 2.9 km and c.a. 75.1 ± 3.6 km along a south-north profile. We observe a c.a. 20–23 km thick lithosphere-asthenosphere boundary (LAB). The depth interval between c.a.87 km and c.a. 280 km is characterized by a distinct low-velocity zone (LVZ). A thick LVZ appears to be associated with a thin lithosphere, which implies a hot thermal regime in the upper mantle. We envisage a possible connection of this hot thermal regime with the African LLSVP (large low shear velocity province) and/or a vertically deep mantle upwelling directly beneath the IOGL region. Our findings have significant implications for deciphering the possible causes behind the source of mantle upwelling, the large geoid anomaly and extensive lithospheric deformation across this region.

The Indian Ocean Geoid Low at a plume-slab overpass

The Indian Ocean Geoid Low (IOGL) appears as a prominent feature if the geoid is, as usual, shown with respect to the Earth's reference shape. However, if it is shown relative to hydrostatic equilibrium, i.e. including excess flattening, it appears as merely a regional low on a north-south trending belt of low geoid. For a mantle viscosity structure with an increase of 2–3 orders of magnitude from asthenosphere to lower mantle, which is suitable to explain the long-wavelength geoid, a geoid low can result from both negative density anomalies in the upper mantle and positive anomalies in the lower mantle. Here we propose that the IOGL can be explained due to a linear, approximately north-south-trending high-density anomaly in the lower mantle, which is crossed by a linear, approximately West-Southwest–East-Northeast trending low-density anomaly in the upper mantle. While the former can be explained due to its location in a region of former subduction and inbetween the two Large Low Shear Velocity Provinces (LLSVPs), we propose here that the latter is due to an eastward outflow from the Kenya plume rising above the eastern edge of the African LLSVP. We show that, with realistic assumptions we can approximately match the size, shape and magnitude of the geoid low.

Origin of ULVZs near the African LLSVP: Implications from their distribution and characteristics

Ultra-low velocity zones (ULVZs) provide important information on the composition and dynamics of the core-mantle boundary (CMB). However, their global distribution and characteristics are not well constrained, especially near African large low-shear velocity provinces (LLSVPs). Here, we used ScS precursor (SdS) and postcursor (ScscS) phases recorded by various seismic networks in Africa and South America to investigate the ULVZ characteristics underlying the South Atlantic Ocean. We found no evidence of ULVZs near the SE boundary of South America, but an ULVZ was found within the SW boundary of the African LLSVP, with thicknesses ranging from 11–18 km and reductions in S-wave velocities of 18%–34%. Our results, combined with the global distribution of ULVZs, suggest that thermal activity may be essential to ULVZ formation. Moreover, subducted slab and mantle flow may also play a key role, depending on the location of the ULVZs.

Multi‐Mode Waveform Tomography of the Indian Ocean Upper and Mid‐Mantle Around the Réunion Hotspot

AbstractRéunion Island in the western Indian Ocean is well known as one of the most active volcanic hotspots on Earth. Its birth, Ma ago, created the Deccan volcanic traps in India (almost 2 million ), associated with the Cretaceous‐Tertiary boundary and with the extinction of about 90% of life on the Earth, including dinosaurs. However, the deep structure of the underlying mantle, the potential presence of a rising plume and its exact geometry in the lower and in the upper mantle are still subjects of debates. The use of seismic data acquired by the French‐German RHUM‐RUM experiment in the Indian Ocean around the Réunion volcanic hotspot (2012–2013) and the collection of broadband seismic data from temporary experiments and from the FDSN (Federation of Digital Seismograph Networks) data center make it possible to investigate the deep structure of the Réunion mantle plume along its complete track, from its birth to its present stage, with a lateral resolution of km. So far, global seismic tomography models cannot provide such high resolution images of the transition zone or lower mantle in this region. In this study, we used the spectral element method (SEM) to perform waveform forward modeling for several thousand paths beneath the Indian Ocean, and normal mode perturbation theory to compute the gradient and the Hessian for the inverse part of the tomography. Using this hybrid method, we derived a regional tomographic model (including teleseismic and regional events) beneath the Indian Ocean, down to km depth, from simultaneous inversion of fundamental and higher mode three components waveforms down to 40 s period. Our model retrieves a low‐velocity channel extending from West to East in the western side of the Central Indian Ridge, in the depth range of 150–250 km. It also reveals a plume conduit with a broad head in the upper mantle and narrow tail anchored in the lower mantle at 1,200 km depth or deeper. The connection between the Réunion hotspot and the South‐Africa Large Low‐Shear Velocity Province (LLSVP) is also brought to light. Our findings suggest a long‐lived Réunion hotspot, since the lower part of the conduit appears to be anchored in the lower mantle, likely fed by the African LLSVP. Our results will guide further geochemical and geodynamic studies on the interaction between the lower transition zone (660–1,000 km) and the deep lower mantle beneath the Réunion hotspot.

Paired EMI-HIMU hotspots in the South Atlantic-Starting plume heads trigger compositionally distinct secondary plumes?

Age-progressive volcanism is generally accepted as the surface expression of deep-rooted mantle plumes, which are enigmatically linked with the African and Pacific large low-shear velocity provinces (LLSVPs). We present geochemical and geochronological data collected from the oldest portions of the age-progressive enriched mantle one (EMI)-type Tristan-Gough track. They are part of a 30- to 40-million year younger age-progressive hotspot track with St. Helena HIMU (high time-integrated 238U/204Pb) composition, which is also observed at the EMI-type Shona hotspot track in the southernmost Atlantic. Whereas the primary EMI-type hotspots overlie the margin of the African LLSVP, the HIMU-type hotspots are located above a central portion of the African LLSVP, reflecting a large-scale geochemical zonation. We propose that extraction of large volumes of EMI-type mantle from the margin of the LLSVP by primary plume heads triggered upwelling of HIMU material from a more internal domain of the LLSVP, forming secondary plumes.

How Thermochemical Piles Can (Periodically) Generate Plumes at Their Edges

AbstractDeep‐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.

The Cenozoic magmatism of East Africa: Part V – Magma sources and processes in the East African Rift

The generation of magmas in the East African Rift System (EARS) is largely the result of either: (A) melting of easily fusible compositions located within the lithospheric mantle due to thermobaric perturbations of the lithosphere, or (B) melting of the convecting upper mantle due to decompression caused by thinning of the plate during extension. Melt generated from amphibole- or phlogopite-bearing metasomes within the lithospheric mantle yields alkaline, silica-undersaturated lavas, while more silica-saturated lavas are primarily a function of melting material within the convecting upper mantle. Sourcing of silica-undersaturated melts within the lithospheric mantle is consistent with the observed tendency for initial melts within any given region to exhibit trace element characteristics consistent with melting of lithospheric metasomes, likely reflecting the initial destabilization and thinning of the lithospheric mantle. With continued lithospheric thinning, the trend towards more silica-saturated compositions coincides with a shift towards compositions interpreted as melting of the convecting upper mantle. Contributions from these two sources may oscillate where extension is pulsed – melts of the convecting upper mantle are favored during periods of plate thinning; melting of either existing or recently formed metasomes may be favored during periods of relative extensional quiescence. The isotopic systematics of East African magmatism reveals significant complexity as to the specific reservoirs that may participate in the melting processes noted above. The lithospheric mantle beneath East Africa has undergone enrichment through the percolation of sub-lithospheric derived melts and fluids over an extended interval, which close to the Tanzania craton has resulted in a layered lithospheric mantle exhibiting extreme isotopic ratios. Elsewhere, the lithospheric mantle has also undergone enrichment but given the more juvenile age of this lithosphere, less extreme isotopic values have developed. Material rising from the African Large Low Shear Velocity Province (LLSVP) has also metasomatized the lithospheric mantle, and thus lavas exhibiting a trace element signature linked to melting within the lithospheric mantle may exist as any number of reservoirs or mixtures of the same. Material derived from the convecting upper mantle incorporates the Afar Plume endmember, a depleted mantle endmember, and some form of lithospheric endmember. The isotopic characteristics of magma suites from throughout the region form arrays that broadly converge on the composition of the Afar Plume, despite some complexity where the plume material has formed a hybrid plume-lithosphere component. The convergence of these arrays strongly supports a model whereby the prevalent composition of material rising from the African LLSVP beneath the EARS is broadly equivalent to the composition of the Afar Plume.

Coupled supercontinent–mantle plume events evidenced by oceanic plume record

AbstractThe most dominant features in the present-day lower mantle are the two antipodal African and Pacific large low-shear-velocity provinces (LLSVPs). How and when these two structures formed, and whether they are fixed and long lived through Earth history or dynamic and linked to the supercontinent cycles, remain first-order geodynamic questions. Hotspots and large igneous provinces (LIPs) are mostly generated above LLSVPs, and it is widely accepted that the African LLSVP existed by at least ca. 200 Ma beneath the supercontinent Pangea. Whereas the continental LIP record has been used to decipher the spatial and temporal variations of plume activity under the continents, plume records of the oceanic realm before ca. 170 Ma are mostly missing due to oceanic subduction. Here, we present the first compilation of an Oceanic Large Igneous Provinces database (O-LIPdb), which represents the preserved oceanic LIP and oceanic island basalt occurrences preserved in ophiolites. Using this database, we are able to reconstruct and compare the record of mantle plume activity in both the continental and oceanic realms for the past 2 b.y., spanning three supercontinent cycles. Time-series analysis reveals hints of similar cyclicity of the plume activity in the continent and oceanic realms, both exhibiting a periodicity of ∼500 m.y. that is comparable to the supercontinent cycle, albeit with a slight phase delay. Our results argue for dynamic LLSVPs where the supercontinent cycle and global subduction geometry control the formation and locations of the plumes.

Lowermost Mantle Anisotropy Beneath Africa From Differential SKS‐SKKS Shear‐Wave Splitting

AbstractWe investigate seismic anisotropy in the lowermost mantle in the vicinity of the African large low shear velocity province (LLSVP) using observations of differential SKS‐SKKS shear‐wave splitting. We use data from 375 permanent and temporary stations in Africa which enable us to map the spatial distribution of the anisotropic regions of the lowermost mantle in unprecedented detail. Our results corroborate previous findings that anisotropy is most clearly observed at the margins of the LLSVP, indicating strong deformation at its border, and they are generally consistent with a mostly isotropic LLSVP interior. We find that most discrepant SKS‐SKKS measurements sample the lowermost mantle close to what is inferred to be the root of the Afar plume. We also identify strongly discrepant splitting in the vicinity of a previously mapped ultralow velocity zone (ULVZ) at the base of the LLSVP, beneath Central Africa. This represents an unusual observation of lowermost mantle anisotropy that is spatially coincident with a ULVZ and may reflect a unique anisotropic mechanism such as alignment of partial melt or the presence of strongly anisotropic magnesiowüstite. We interpret discrepant measurements outside of the LLSVP as likely reflecting a change in flow direction from the horizontal plane to a more vertical direction, which may be caused by deflection at the steep LLSVP border. We propose that our observations of D″ anisotropy associated with the African LLSVP can be explained by a mantle flow regime that maintains passive thermochemical piles with slab‐driven flow and allows for the formation of upwellings at their edges.

Hotspot motion caused the Hawaiian-Emperor Bend and LLSVPs are not fixed

Controversy surrounds the fixity of both hotspots and large low shear velocity provinces (LLSVPs). Paleomagnetism, plate-circuit analyses, sediment facies, geodynamic modeling, and geochemistry suggest motion of the Hawaiian plume in Earth’s mantle during formation of the Emperor seamounts. Herein, we report new paleomagnetic data from the Hawaiian chain (Midway Atoll) that indicate the Hawaiian plume arrived at its current latitude by 28 Ma. A dramatic decrease in distance between Hawaiian-Emperor and Louisville chain seamounts between 63 and 52 Ma confirms a high rate of southward Hawaiian hotspot drift (~47 mm yr−1), and excludes true polar wander as a relevant factor. These findings further indicate that the Hawaiian-Emperor chain bend morphology was caused by hotspot motion, not plate motion. Rapid plume motion was likely produced by ridge-plume interaction and deeper influence of the Pacific LLSVP. When compared to plate circuit predictions, the Midway data suggest ~13 mm yr−1 of African LLSVP motion since the Oligocene. LLSVP upwellings are not fixed, but also wander as they attract plumes and are shaped by deep mantle convection.

The Cenozoic magmatism of East-Africa: Part I — Flood basalts and pulsed magmatism

Cenozoic magmatism in East Africa results from the interplay between lithospheric extension and material upwelling from the African Large Low Shear Velocity Province (LLSVP). The modern focusing of East African magmatism into oceanic spreading centers and continental rifts highlights the modern control of lithospheric thinning in magma generation processes, however the widespread, and volumetrically significant flood basalt events of the Eocene to Early Miocene suggest a significant role for material upwelling from the African LLSVP. The slow relative motion of the African plate during the Cenozoic has resulted in significant spatial overlap in lavas derived from different magmatic events. This complexity is being resolved with enhanced geochronological precision and a focus on the geochemical characteristics of the volcanic products. It is now apparent that there are three distinct pulses of basaltic volcanism, followed by either bimodal lavas or silicic volcanic products during this period: (A) Eocene Initial Phase from 45 to 34Ma. This is a period of dominantly basaltic volcanism focused in Southern Ethiopia and Northern Kenya (Turkana). (B) Oligocene Traps phase from ~33.9 to 27Ma. This period coincides with a significant increase in the aerial extent of volcanism with broadly age equivalent 1 to 2km thick sequences of dominantly basalt centered on the NW Ethiopian Plateau and Yemen, (C) Early Miocene resurgence phase from ~26.9 to 22Ma. This resurgence in basaltic volcanism is seen throughout the region at ca. 24–23Ma, but is less volumetrically significant than the prior two basaltic pulses. With our developing understanding of the persistence of LLSVP anomalies within the mantle, I propose that the three basaltic pulses are ostensibly manifestations of the same plume–lithosphere interaction, requiring revision to the duration, magmatic extent, and magma volume of the African–Arabian Large Igneous Province.

The deep Earth origin of the Iceland plume and its effects on regional surface uplift and subsidence

Abstract. The present-day seismic structure of the mantle under the North Atlantic Ocean indicates that the Iceland hotspot represents the surface expression of a deep mantle plume, which is thought to have erupted in the North Atlantic domain during the Palaeocene. The spatial and temporal evolution of the plume since its eruption is still highly debated, and little is known about its deep mantle history. Here, we use palaeogeographically constrained global mantle flow models to investigate the evolution of deep Earth flow beneath the North Atlantic since the Jurassic. The models show that over the last ∼ 100 Myr a remarkably stable pattern of convergent flow has prevailed in the lowermost mantle near the tip of the African Large Low-Shear Velocity Province (LLSVP), making it an ideal plume nucleation site. We extract model dynamic topography representative of a plume beneath the North Atlantic region since eruption at ∼ 60 Ma to present day and compare its evolution to available offshore geological and geophysical observations across the region. This comparison confirms that a widespread episode of Palaeocene transient uplift followed by early Eocene anomalous subsidence can be explained by the mantle-driven effects of a plume head ∼ 2500 km in diameter, arriving beneath central eastern Greenland during the Palaeocene. The location of the model plume eruption beneath eastern Greenland is compatible with several previous models. The predicted dynamic topography is within a few hundred metres of Palaeocene anomalous subsidence derived from well data. This is to be expected given the current limitations involved in modelling the evolution of Earth's mantle flow in 3-D, particularly its interactions with the base of a heterogeneous lithosphere as well as short-wavelength advective upper mantle flow, not captured in the presented global models.

Seismic anisotropy in the lowermost mantle near the Perm Anomaly

AbstractThe lower mantle is dominated by two large structures with anomalously low shear wave velocities, known as Large Low‐Shear Velocity Provinces (LLSVPs). Several studies have documented evidence for strong seismic anisotropy at the base of the mantle near the edges of the African LLSVP. Recent work has identified a smaller structure with similar low‐shear wave velocities beneath Eurasia, dubbed the Perm Anomaly. Here we probe lowermost mantle anisotropy near the Perm Anomaly using the differential splitting of SKS and SKKS phases measured at stations in Europe. We find evidence for lowermost mantle anisotropy in the vicinity of the Perm Anomaly, with geographic trends hinting at lateral variations in anisotropy across the boundaries of the Perm Anomaly as well as across a previously unsampled portion of the African LLSVP border. Our observations suggest that deformation is concentrated at the boundaries of both the Perm Anomaly and the African LLSVP.

Antiquity of the South Atlantic Anomaly and evidence for top-down control on the geodynamo

The dramatic decay of dipole geomagnetic field intensity during the last 160 years coincides with changes in Southern Hemisphere (SH) field morphology and has motivated speculation of an impending reversal. Understanding these changes, however, has been limited by the lack of longer-term SH observations. Here we report the first archaeomagnetic curve from southern Africa (ca. 1000–1600 AD). Directions change relatively rapidly at ca. 1300 AD, whereas intensities drop sharply, at a rate greater than modern field changes in southern Africa, and to lower values. We propose that the recurrence of low field strengths reflects core flux expulsion promoted by the unusual core–mantle boundary (CMB) composition and structure beneath southern Africa defined by the African large low shear velocity province (LLSVP). Because the African LLSVP and CMB structure are ancient, this region may have been a steady site for flux expulsion, and triggering of geomagnetic reversals, for millions of years.

The long‐wavelength geoid from three‐dimensional spherical models of thermal and thermochemical mantle convection

AbstractThe Earth's long‐wavelength geoid anomalies have long been used to constrain the dynamics and viscosity structure of the mantle in an isochemical, whole mantle convection model. However, there is strong evidence that the seismically observed large low shear velocity provinces (LLSVPs) in the lower mantle underneath the Pacific and Africa are chemically distinct and likely denser than the ambient mantle. In this study, we have formulated dynamically self‐consistent 3‐D spherical mantle convection models to investigate how chemically distinct and dense piles above the core‐mantle boundary may influence the geoid. Our dynamic models with realistic mantle viscosity structure produce dominantly spherical harmonic degree‐2 convection, similar to that of the present‐day Earth. The models produce two broad geoid and topography highs over two major thermochemical piles in the lower mantle, consistent with the positive geoid anomalies over the Pacific and African LLSVPs. Our geoid analysis showed that the bottom layer with dense chemical piles contributes negatively to the total geoid, while the layer immediately above the chemical piles contributes positively to the geoid, canceling out the effect of the piles. Thus, the bottom part of the mantle, as a compensation layer, has zero net contribution to the total geoid, and the thickness of the compensation layer is ~1000 km or 2 to 3 times as thick as the chemical piles. Our results help constrain and interpret the large‐scale thermochemical structure of the mantle using surface observations of the geoid and topography, as well as seismic models of the mantle.

Lowermost mantle anisotropy and deformation along the boundary of the African LLSVP

AbstractShear wave splitting of SK(K)S phases is often used to examine upper mantle anisotropy. In specific cases, however, splitting of these phases may reflect anisotropy in the lowermost mantle. Here we present SKS and SKKS splitting measurements for 233 event‐station pairs at 34 seismic stations that sample D″ beneath Africa. Of these, 36 pairs show significantly different splitting between the two phases, which likely reflects a contribution from lowermost mantle anisotropy. The vast majority of discrepant pairs sample the boundary of the African large low shear velocity province (LLSVP), which dominates the lower mantle structure beneath this region. In general, we observe little or no splitting of phases that have passed through the LLSVP itself and significant splitting for phases that have sampled the boundary of the LLSVP. We infer that the D″ region just outside the LLSVP boundary is strongly deformed, while its interior remains undeformed (or weakly deformed).

Observations of changing anisotropy across the southern margin of the African LLSVP

We present evidence for the presence of complex anisotropy in the lowermost mantle from 3-D waveform modelling of observed core-diffracted shear waves that sample the southern edge of the African Large Low Shear Velocity Province (LLSVP). The anomalously strong amplitude of the SV component for the shear core-diffracted phase at large distances indicates the presence of anisotropy. We measure shear wave splitting parameters to determine which part of the elastic tensor is constrained by this particular data set. The modelling is performed using the spectral element method. The anisotropy is strong outside the LLSVP, weakens or rotates close to its boundary, and appears to be absent inside the LLSVP. The presence of the LLSVP margin may cause flow in the mantle to change direction. The occurrence of strong anisotropy in the region of fast seismic velocities is compatible with lattice-preferred orientation in post-perovskite due to accommodation of flow through dislocation creep.

Study of the western edge of the African Large Low Shear Velocity Province

It is well established that there is a large low shear velocity province (LLSVP) in the lowermost mantle beneath Africa, extending from beneath the southeastern Atlantic Ocean to the southwestern Indian Ocean. The detailed 3‐D geometry of the LLSVP is crucial to the understanding of how this prominent lower mantle feature developed and evolved. Most studies have concentrated on mapping the southern and eastern edges of African LLSVP using the Kaapvaal array at South Africa. Here we use data from recently deployed arrays in the western Mediterranean to study its northwestern edge and evaluate the sharpness of its boundaries. Travel time and waveform modeling of S and SKS phases suggest the existence of sharp low velocity anomalies in the lowermost mantle beneath the eastern Atlantic Ocean, which agrees with global tomography models. However, the S‐SKS differential times vary up to 6 s across the array. To match the large travel time variations and waveforms, the existence of a slow velocity structure with a sharp top is required. The structure has a 3.5% reduction in shear wave velocity and a height of ∼600 km above the core‐mantle boundary, which is lower in topography than the southern and eastern part of the African LLSVP. Further 3‐D synthetic waveforms and modeling calculations demonstrate the existence of these sharp boundaries for the northwestern portion of the African LLSVP. The strong lateral variation in both travel times and waveforms suggests that this part of the African LLSVP may be as complex as the mid‐Pacific LLSVP. To explain the observed sharp top and large dome‐like structure, a thermochemical origin of the African LLSVP is supported.

Phanerozoic within-plate magmatism of North Asia: Absolute paleogeographic reconstructions of the African large low-shear-velocity province

The phanerozoic within-plate magmatism of Siberia is reviewed. The large igneous provinces (LIPs) consecutively arising in the Siberian Craton are outlined: the Altai-Sayan LIP, which operated most actively 400–375 Ma ago, the Vilyui LIP, which was formed from the Middle Devonian to the Early Carboniferous, included; the Barguzin-Vitim LIP (305–275 Ma); the Late Paleozoic Rift System of Central Asia (318–250 Ma); the Siberian flood basalt (trap) province and the West Siberian rift system (250–247 Ma); and the East Mongolian-West Transbaikal LIP (230–195 Ma), as well as a number of Late-Mesozoic and Cenozoic rift zones and autonomous volcanic fields formed over the last 160 Ma. The trace-element and isotopic characteristics of the igneous rocks of the above provinces are reviewed; their mantle origin is substantiated and the prevalence of PREMA, EM2, and EM1 mantle magma sources are shown. The paleogeographic reconstructions based on paleomagnetic data assume that the Iceland hot spot was situated beneath the Siberian flood basalts 250 Ma ago and that the mantle plumes retained a relatively stable position irrespective of the movements of the lithospheric plates. At present, the Iceland hot spot occurs near the northern boundary of the African large low shear velocity province (LLSVP). It is suggested that the within-plate Phanerozoic magmatism of Siberia was related to the drift of the continent above the hot spots of the African LLSVP.