Tags:
Geophysics,
Geodynamics,
Paleomagnetism,
Plate tectonics
Publications
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Kulakov, Evgeniy; Torsvik, Trond Helge; Doubrovine, Pavel V.; Slagstad, Trond; Ganerød, Morgan & Silkoset, Petter
[Show all 7 contributors for this article]
(2021).
Jurassic fast polar shift rejected by a new high-quality paleomagnetic pole from southwest Greenland.
Gondwana Research.
ISSN 1342-937X.
97,
p. 240–262.
doi:
10.1016/j.gr.2021.05.021.
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A selective compilation of paleomagnetic data from North America indicates that a vast amount of rapid polar motion occurred in Late Jurassic time. The over 30° polar shift that accumulated during a relatively short time interval (~160–145 Ma) suggests an episode of fast true polar wander (TPW) and was referred to as the Jurassic “monster polar shift” by some workers. However, this rapid TPW event is not supported by paleomagnetic data on a global scale. Here, we scrutinize the Jurassic apparent polar wander path (APWP) by virtue of a new paleomagnetic and 40Ar/39Ar geochronology study of Mesozoic coast-parallel dykes exposed in southwest Greenland. Combined with existing geochronological data, our results show that the dykes were emplaced during a prolonged period centered at 147.6 ± 3.4 Ma (2σ). A primary nature of the characteristic remanent magnetization is supported by multiple positive baked contact tests and a reversal test. The paleomagnetic pole calculated from 40 site-mean paleomagnetic directions is located at Plat = 69.3°S, Plong = 5.0°E (A95 = 4.6°), or at Plat = 73.9°S and Plong = 0.4°E when reconstructed to North America. Our new high-quality paleomagnetic pole and an updated global APWP do not support the fast Jurassic polar shift but instead indicate steady polar motion with moderate rates of about 0.7°/Myr. The new pole effectively reduces the mismatch between the APWPs for Laurentia and Europe. Our critical reassessment of the monster polar shift indicates that it may be an artifact of paleomagnetic and geochronological data that were previously used to argue for its existence.
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Biggin, Andrew J.; Bono, Richard K.; Meduri, Domenico G.; Sprain, Courtney J.; Davies, Christopher J. & Holme, Richard
[Show all 7 contributors for this article]
(2020).
Quantitative estimates of average geomagnetic axial dipole dominance in deep geological time.
Nature Communications.
11.
doi:
10.1038/s41467-020-19794-7.
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A defining characteristic of the recent geomagnetic field is its dominant axial dipole which provides its navigational utility and dictates the shape of the magnetosphere. Going back through time, much less is known about the degree of axial dipole dominance. Here we use a substantial and diverse set of 3D numerical dynamo simulations and recent observation based field models to derive a power law relationship between the angular dispersion of virtual geomagnetic poles at the equator and the median axial dipole dominance measured at Earth’s surface. Applying this relation to published estimates of equatorial angular dispersion implies that geomagnetic axial dipole dominance averaged over 107–109 years has remained moderately high and stable through large parts of geological time. This provides an observational constraint to future studies of the geodynamo and palaeomagnetosphere. It also provides some reassurance as to the reliability of palaeogeographical reconstructions provided by palaeomagnetism.
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Kulakov, Evgeniy; Sprain, Courtney; Doubrovine, Pavel; Smirnov, Aleksey V.; Paterson, Greig & Hawkins, Louise
[Show all 9 contributors for this article]
(2019).
Analysis of an Updated Paleointensity Database (QPI‐PINT) for 65–200 Ma: Implications for the Long‐Term History of Dipole Moment Through the Mesozoic.
Journal of Geophysical Research (JGR): Solid Earth.
ISSN 2169-9313.
124(10),
p. 9999–10022.
doi:
10.1029/2018JB017287.
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The global paleointensity database for 65–200 Ma was analyzed using a modified suite of paleointensity quality criteria (QPI) such that the likely reliability of measurements is assessed objectively and as consistently as possible across the diverse data set. This interval was chosen because of dramatic extremes of geomagnetic polarity reversal frequency ranging from greater than 10 reversals per million years in the Jurassic hyperactivity period (155–171 Ma) to effectively zero during the Cretaceous Normal Superchron (CNS; 84–126 Ma). Various attempts to establish a relationship between the strength of Earth's magnetic field and the reversal frequency have been made by previous studies, but no consensus has yet been reached primarily because of large uncertainties in paleointensity estimates and sensitivity of these estimates to data selection approaches. It is critical to overcome this problem because the evolution of the dipole moment is a first order constraint on the behavior of the geodynamo. Here we show that conventional statistical tests and Bayesian changepoint modeling consistently indicate the strongest median/average virtual dipole moment during the CNS. In addition, the CNS and Jurassic hyperactivity period are characterized by the highest and lowest percentage of virtual dipole moments exceeding the overall median for the 65‐ to 200‐Ma interval, respectively. These observations suggest that the superchron dynamo was able to generate stronger fields than the dynamo operating in the frequently reversing regime. While the precise mechanism remains unclear, our results are compatible with the hypothesis that field strength and reversal rate variation are controlled by changes in core‐mantle boundary thermochemical conditions.
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Torsvik, Trond Helge; Steinberger, Bernhard; Shephard, Grace; Doubrovine, Pavel; Gaina, Carmen & Domeier, Mathew
[Show all 8 contributors for this article]
(2019).
Pacific‐Panthalassic reconstructions: Overview, errata and the way forward.
Geochemistry Geophysics Geosystems.
20(7),
p. 3659–3689.
doi:
10.1029/2019GC008402.
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We have devised a new absolute Late Jurassic‐Cretaceous Pacific plate model using a fixed hot spot approach coupled with paleomagnetic data from Pacific large igneous provinces (LIPs) while simultaneously minimizing plate velocity and net lithosphere rotation (NR). This study was motivated because published Pacific plate models for the 83.5‐ to 150‐Ma time interval are variably flawed, and their use affects modeling of the entire Pacific‐Panthalassic Ocean and interpretation of its margin evolution. These flaws could be corrected, but the revised models would imply unrealistically high plate velocities and NR. We have developed three new Pacific realm models with varying degrees of complexity, but we focus on the one that we consider most realistic. This model reproduces many of the Pacific volcanic paths, modeled paleomagnetic latitudes fit well with direct observations, plate velocities and NR resulting from the model are low, and all reconstructed Pacific LIPs align along the surface‐projected margin of the Pacific large low shear wave velocity province. The emplacement of the Shatsky Rise LIP at ~144 Ma probably caused a major plate boundary reorganization as indicated by a major jump of the Pacific‐Izanagi‐Farallon triple junction and a noteworthy change of the Pacific‐Izanagi seafloor spreading direction at around chron M20 time.
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Doubrovine, Pavel; Veikkolainen, Toni; Pesonen, Lauri; Piispa, Elisa; Ots, Siim & Smirnov, Aleksey
[Show all 8 contributors for this article]
(2019).
Latitude dependence of geomagnetic paleosecular variation and its 2 relation to the frequency of magnetic reversals: Observations from the Cretaceous and Jurassic.
Geochemistry Geophysics Geosystems.
20(3),
p. 1240–1279.
doi:
10.1029/2018GC007863.
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Nearly three decades ago paleomagnetists suggested that there existed a clear link between latitude dependence of geomagnetic paleosecular variation (PSV) and reversal frequency. Here we compare the latitude behavior of PSV for the Cretaceous Normal Superchron (CNS, 84-126 Ma, stable normal polarity) and the preceding Early Cretaceous-Jurassic interval (pre-CNS, 126-198 Ma, average reversal rate of ~4.6 Myr-1). We find that the CNS was characterized by a strong increase in the angular dispersion of virtual geomagnetic poles (VGPs) with latitude, which is consistent with the results of earlier studies, whereas the VGP dispersion for the pre-CNS period was nearly invariant with latitude. However, the PSV behavior for the last 5 or 10 million years (average reversal frequency of ~4.4-4.8 Myr 1) shows that the latitude invariance of VGP scatter cannot be considered as a characteristic feature of a frequently-reversing field, and that a strong increase in VGP dispersion with latitude was not restricted to the long periods of stable polarity. We discuss models describing the latitude dependence of PSV and show that their parameters are not reliable proxies for reversal frequency and should not be used to make inferences about the geomagnetic field stability. During the pre-CNS interval, the geodynamo may have operated in a regime characterized by a high degree of equatorial symmetry. In contrast, more asymmetric geodynamos suggested for 0-10 Ma and the CNS were evidently capable of producing a very wide range of reversal frequencies.
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Domeier, Mathew; Shephard, Grace; Jakob, Johannes; Gaina, Carmen; Doubrovine, Pavel & Torsvik, Trond Helge
(2017).
Intraoceanic subduction spanned the Pacific in the Late Cretaceous–Paleocene.
Science Advances.
3(11).
doi:
10.1126/sciadv.aao2303.
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The notorious ~60° bend separating the Hawaiian and Emperor chains marked a prominent change in the motion of the Pacific plate at ~47 Ma (million years ago), but the origin of that change remains an outstanding controversy that bears on the nature of major plate reorganizations. Lesser known but equally significant is a conundrum posed by the pre-bend (~80 to 47 Ma) motion of the Pacific plate, which, according to conventional plate models, was directed toward a fast-spreading ridge, in contradiction to tectonic forcing expectations. Using constraints provided by seismic tomography, paleomagnetism, and continental margin geology, we demonstrate that two intraoceanic subduction zones spanned the width of the North Pacific Ocean in Late Cretaceous through Paleocene time, and we present a simple plate tectonic model that explains how those intraoceanic subduction zones shaped the ~80 to 47 Ma kinematic history of the Pacific realm and drove a major plate reorganization.
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Torsvik, Trond Helge; Doubrovine, Pavel; Steinberger, Bernhard; Gaina, Carmen; Spakman, Wim & Domeier, Mathew
(2017).
Pacific plate motion change caused the Hawaiian-Emperor Bend.
Nature Communications.
8.
doi:
10.1038/ncomms15660.
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A conspicuous 60° bend of the Hawaiian-Emperor Chain in the north-western Pacific Ocean has variously been interpreted as the result of an abrupt Pacific plate motion change in the Eocene (∼47 Ma), a rapid southward drift of the Hawaiian hotspot before the formation of the bend, or a combination of these two causes. Palaeomagnetic data from the Emperor Seamounts prove ambiguous for constraining the Hawaiian hotspot drift, but mantle flow modelling suggests that the hotspot drifted 4–9° south between 80 and 47 Ma. Here we demonstrate that southward hotspot drift cannot be a sole or dominant mechanism for formation of the Hawaiian-Emperor Bend (HEB). While southward hotspot drift has resulted in more northerly positions of the Emperor Seamounts as they are observed today, formation of the HEB cannot be explained without invoking a prominent change in the direction of Pacific plate motion around 47 Ma.
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Doubrovine, Pavel; Steinberger, Bernhard & Torsvik, Trond Helge
(2016).
A failure to reject: Testing the correlation between large igneous provinces and deep mantle structures with EDF statistics.
Geochemistry Geophysics Geosystems.
17(3),
p. 1130–1163.
doi:
10.1002/2015GC006044.
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Absolute reconstructions of large igneous provinces (LIPs) for the past 300 Ma reveal a remarkable spatial pattern suggesting that almost all LIPs have erupted over the margins of the two large‐scale structures in the Earth's lower mantle commonly referred to as the Large Low Shear‐wave Velocity Provinces (LLSVPs). This correlation suggests that mantle plumes that have triggered LIP eruptions rose from the margins of LLSVPs, implying long‐term stability of these structures and suggesting that they may be chemically distinct from the bulk of the mantle. Yet, some researchers consider the LLSVPs to be purely thermal upwellings, arguing that the observed distribution of LIPs can be explained by plumes randomly forming over the entire areas of LLSVPs. Here we examine the correlation between the LIPs and LLSVPs using nonparametric statistical tests, updated plate reconstructions, and a large number of alternative definitions of LLSVPs based on seismic tomography. We show that probability models assuming plume sources originating at the margins of LLSVPs adequately explain the observed distribution of reconstructed LIPs. In contrast, we find strong evidence against the models seeking to link LIPs with plumes randomly forming over the entire LLSVP areas. However, the hypothesis proposing that the correlation can be explained by plumes randomly forming over a larger area of slower‐than‐average shear wave velocities in the lowermost mantle cannot be ruled out formally. Our analysis suggests that there is no statistically sound reason for questioning the hypothesis that the LIPs correlate with the margins of LLSVP globally. This research was originally published in Geochemistry, Geophysics, Geosystems. © 2016 American Geophysical Union
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Domeier, Mathew; Doubrovine, Pavel; Torsvik, Trond Helge; Spakman, Wim & Bull, Abigail
(2016).
Global correlation of lower mantle structure and past subduction.
Geophysical Research Letters.
ISSN 0094-8276.
43(10),
p. 4945–4953.
doi:
10.1002/2016GL068827.
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Torsvik, Trond Helge; Steinberger, Bernhard; Ashwal, Lewis D.; Doubrovine, Pavel & Trønnes, Reidar G
(2016).
Earth evolution and dynamics—a tribute to Kevin Burke.
Canadian journal of earth sciences (Print).
ISSN 0008-4077.
53(11),
p. 1073–1087.
doi:
10.1139/cjes-2015-0228.
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Kevin Burke’s original and thought-provoking contributions have been published steadily for the past 60 years, and more than a decade ago he set out to resolve how plate tectonics and mantle plumes interact by proposing a simple conceptual model, which we will refer to as the Burkian Earth. On the Burkian Earth, mantle plumes take us from the deepest mantle to sub-lithospheric depths, where partial melting occurs, and to the surface, where hotspot lavas erupt today, and where large igneous provinces and kimberlites have erupted episodically in the past. The arrival of a plume head contributes to continental break-up and punctuates plate tectonics by creating and modifying plate boundaries. Conversely, plate tectonics makes an essential contribution to the mantle through subduction. Slabs restore mass to the lowermost mantle and are the triggering mechanism for plumes that rise from the margins of the two large-scale low shear-wave velocity structures in the lowermost mantle, which Burke christened TUZO and JASON. Situated just above the core–mantle boundary, beneath Africa and the Pacific, these are stable and antipodal thermochemical piles, which Burke reasons represent the immediate after-effect of the moon-forming event and the final magma ocean crystallization. This research has been accepted and published in the Canadian Journal of Earth Sciences. © 2016 NRC Research Press
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Torsvik, Trond Helge; Amundsen, Hans E. Foss; Trønnes, Reidar G; Doubrovine, Pavel; Gaina, Carmen & Kusznir, Nick J.
[Show all 12 contributors for this article]
(2015).
Continental crust beneath southeast Iceland.
Proceedings of the National Academy of Sciences of the United States of America (PNAS).
ISSN 0027-8424.
112(15),
p. E1818–E1827.
doi:
10.1073/pnas.1423099112.
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The magmatic activity (0–16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland—and especially the Öræfajökull volcano—is characterized by a unique enriched-mantle component (EM2-like) with elevated 87Sr/86Sr and 207Pb/204Pb. Here, we demonstrate through modeling of Sr–Nd–Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2–6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume.
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Torsvik, Trond Helge; Amundsen, Hans; Hartz, Ebbe Hvidegård; Corfu, Fernando; Kusznir, Nick & Gaina, Carmen
[Show all 10 contributors for this article]
(2013).
A Precambrian microcontinent in the Indian Ocean.
Nature Geoscience.
ISSN 1752-0894.
6(3),
p. 223–227.
doi:
10.1038/ngeo1736.
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The Laccadive–Chagos Ridge and Southern Mascarene Plateau in the north-central and western Indian Ocean, respectively, are thought to be volcanic chains formed above the Réunion mantle plume1 over the past 65.5 million years2,3. Here we use U–Pb dating to analyse the ages of zircon xenocrysts found within young lavas on the island of Mauritius, part of the Southern Mascarene Plateau. We find that the zircons are either Palaeoproterozoic (more than 1,971 million years old) or Neoproterozoic (between 660 and 840 million years old). We propose that the zircons were assimilated from ancient fragments of continental lithosphere beneath Mauritius, and were brought to the surface by plume-related lavas. We use gravity data inversion to map crustal thickness and find that Mauritius forms part of a contiguous block of anomalously thick crust that extends in an arc northwards to the Seychelles. Using plate tectonic reconstructions, we show that Mauritius and the adjacent Mascarene Plateau may overlie a Precambrian microcontinent that we call Mauritia. On the basis of reinterpretation of marine geophysical data4, we propose that Mauritia was separated from Madagascar and fragmented into a ribbon-like configuration by a series of mid-ocean ridge jumps during the opening of the Mascarene ocean basin between 83.5 and 61 million years ago. We suggest that the plume-related magmatic deposits have since covered Mauritia and potentially other continental fragments.
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Steinberger, Bernard; Torsvik, Trond Helge & Dubrovin, Pavel
(2012).
Absolute plate motions in a reference frame defined by moving hot spots in the Pacific, Atlantic, and Indian oceans.
Journal of Geophysical Research (JGR): Solid Earth.
ISSN 2169-9313.
117.
doi:
10.1029/2011JB009072.
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We defined a new global moving hot spot reference frame (GMHRF), using a comprehensive set of radiometric dates from arguably the best‐studied hot spot tracks, refined plate circuit reconstructions, a new plate polygon model, and an iterative approach for estimating hot spot motions from numerical models of whole mantle convection and advection of plume conduits in the mantle flow that ensures their consistency with surface plate motions. Our results show that with the appropriate choice of a chain of relative motion linking the Pacific plate to the plates of the Indo‐Atlantic hemisphere, the observed geometries and ages of the Pacific and Indo‐Atlantic hot spot tracks were accurately reproduced by a combination of absolute plate motion and hot spot drift back to the Late Cretaceous (∼80 Ma). Similarly good fits were observed for Indo‐Atlantic tracks for earlier time (to ∼130 Ma). In contrast, attempts to define a fixed hot spot frame resulted in unacceptable misfits for the Late Cretaceous to Paleogene (80–50 Ma), highlighting the significance of relative motion between the Pacific and Indo‐Atlantic hot spots during this period. A comparison of absolute reconstructions using the GMHRF and the most recent global paleomagnetic frame reveals substantial amounts of true polar wander at rates varying between ∼0.1°/Ma and 1°/Ma. Two intriguing, nearly equal and antipodal rotations of the Earth relative to its spin axis are suggested for the 90–60 Ma and 60–40 Ma intervals (∼9° at a 0.3–0.5°/Ma rate); these predictions have yet to be tested by geodynamic models. © 2012 American Geophysical Union
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Torsvik, Trond Helge; Voo, Rob Van der; Preeden, Ulla; Niocaill, Conall Mac; Steinberger, Bernard & Hinsbergen, Douwe Van
[Show all 13 contributors for this article]
(2012).
Phanerozoic polar wander, palaeogeography and dynamics.
Earth-Science Reviews.
ISSN 0012-8252.
114(3-4),
p. 325–368.
doi:
10.1016/j.earscirev.2012.06.007.
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A significant number of new palaeomagnetic poles have become available since the last time a compilation was made (assembled in 2005, published in 2008) to indicate to us that a new and significantly expanded set of tables with palaeomagnetic results would be valuable, with results coming from the Gondwana cratonic elements, Laurentia, Baltica/Europe, and Siberia. Following the Silurian Caledonian Orogeny, Laurentia's and Baltica's Apparent Polar Wander Paths (APWPs) can be merged into a Laurussia path, followed in turn by a merger of the Laurussia and Siberia data from latest Permian time onward into a Laurasian combined path. Meanwhile, after about 320 Ma, Gondwana's and Laurussia/Laurasia's path can be combined into what comes steadily closer to the ideal of a Global Apparent Polar Wander Path (GAPWaP) for late Palaeozoic and younger times. Tests for True Polar Wander (TPW) episodes are now feasible since Pangaea fusion and we identify four important episodes of Mesozoic TPW between 250 and 100 Ma. TPW rates are in the order of 0.45–0.8°/M.y. but cumulative TPW is nearly zero since the Late Carboniferous. With the exception of a few intervals where data are truly scarce (e.g., 390–340 Ma), the palaeomagnetic database is robust and allows us to make a series of new palaeogeographic reconstructions from the Late Cambrian to the Palaeogene.
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Hinsbergen, Douwe Van; Steinberger, Bernard; Gassmöller, René & Dubrovin, Pavel
(2011).
Acceleration and deceleration of India-Asia convergence since the Cretaceous: Roles of mantle plumes and continental collision.
Journal of Geophysical Research (JGR): Solid Earth.
ISSN 2169-9313.
116.
doi:
10.1029/2010JB008051.
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A strong 50–35 Ma decrease in India‐Asia convergence is generally ascribed to continent‐continent collision. However, a convergence rate increase of similar magnitude occurred between ∼65–50 Ma. An earlier increase occurred at ∼90 Ma. Both episodes of accelerated convergence followed upon arrival of a mantle plume below and emplacement of a large igneous province (LIP) on the Indian plate. We here first confirm these convergence rate trends, reassessing the Indo‐Atlantic plate circuits. Then, using two different numerical models, we assess whether plume head arrival and its lateral asthenospheric flow may explain the plate velocity increases and whether decreased plume flux and increasing continent‐plume distance may explain deceleration, even without continental collision. The results show that plume head arrival can indeed lead to absolute Indian plate motion accelerations on the order of several cm/yr, followed by decelerations on timescales similar to the reconstructed fluctuations. The 90 Ma increase could potentially be explained as response to the Morondova mantle plume alone. The 65–50 Ma convergence rate increase, however, is larger than can be explained by plume head spreading alone. We concur with previous hypotheses that plume‐induced weakening of the Indian continental lithosphere‐asthenosphere coupling and an increased slab pull and ridge push efficiency are the most likely explanations for the large convergence rate increase. The post‐50 Ma decrease is best explained by orogeny‐related increased trench resistivity, decreased slab pull due to continental subduction, and possibly restrengthening of lithosphere‐asthenosphere coupling upon plume demise. © 2011 American Geophysical Union
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Kulakov, Evgeniy; Slagstad, Trond; Doubrovine, Pavel; Ganerod, MOrgan & Torsvik, T.H
(2019).
Paleomagnetism, geology and 40Ar/39Ar geochronology of Proterozoic rocks from the Sveconorwegian Orogen, SW Norway: Revisiting Baltica in the Rodinia context.
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Doubrovine, Pavel; Torsvik, Trond Helge & Domeier, Mathew
(2017).
Paleomagnetism and paleosecular variation from the late Miocene to recent lavas of Mauritius.
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We present new paleomagnetic data from the late Miocene to recent lavas of the island of Mauritius in the southwestern Indian Ocean (20.3°S, 57.6°E). The island is a shield volcano that has formed over the Reunion hotspot and is composed of three temporally-distinct series of basaltic lavas: the Older Series (4.7-8.9 Ma), the Intermediate Series (1.7-3.5 Ma) and the Younger Series (0-1 Ma). Oriented core specimens were collected from 36 sampling sites covering all three lava series. Rock magnetic analyses indicate that the remanence carriers in these basalts are pseudo-single-domain titanomagnetites with variable degrees of high-temperature oxidation. Nearly half of the sites showed pervasive magnetic overprints imparted by lightning strikes. Nonetheless, in almost all cases (35 sites), we were able to isolate the characteristic (primary) remanence directions through detailed thermal and alternating field demagnetization experiments, using the principal component analysis of demagnetization data and the analysis of remagnetization circles. Both normal and reverse polarity directions were observed, with the mean direction of the reversely-magnetized lavas (15 sites, D = 189.2°, I = 44°, a95 = 5.3°) being steeper than and ca. 9° of antiparallel from the mean direction of the normal-polarity flows (20 sites, D = 1.1°, I = -37.3°, a95 = 6.9°). The mean normal and reverse directions yield a negative reversal test that is just significant at the 5% probability level (P = 4.5%). However, when our new data set is combined with previously published paleomagnetic results from Mauritius, the difference between the normal mean direction and the antipode of the reverse mean is not significant at the 5% level, yielding a positive reversal test. The paleomagnetic pole corresponding to the combined polarity data set excluding transitional directions (86.7°N, 186.2°E, A95 = 3.5°, n = 32) is slightly far-sided, but the difference between its position and the geographic pole is not statistically significant. The estimates of paleosecular variation (PSV) and inclination anomaly (Sb = 11°, DI = -2°) are in good agreement with the results of PSV studies of recent lavas erupted at low latitudes. The implications of our new results for the structure of time-averaged geomagnetic field and the latitude dependence of PSV will be discussed.
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Doubrovine, Pavel
(2017).
Estimating true polar wander from plate models.
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Slow convective motions within the dynamic Earth lead to a gradual redistribution of mass heterogeneities within the planet, changing its moment of inertia over geologic time. As a response to these changes, and owing to the conservation of the angular momentum, the entire solid Earth (mantle and lithosphere) undergoes a solid-body rotation with respect to the planetary spin axis, which is referred to as “true polar wander” (TPW) to distinguish it from the apparent polar wander that mainly reflects changes in the paleogeography due to the surface motion of lithospheric plates. Quantifying TPW from plate reconstructions requires a kinematic model in which plate motions are defined both with respect to the mantle (geodynamic reference frame), and with respect to the Earth’s spin axis (paleogeographic frame). Differentiating the motions observed in these two reference frames can then be used to estimate TPW. While the plate motions in the paleogeographic frame are constrained by paleomagnetic data, mantle reference fames have traditionally relied on reconstructions relative to oceanic hotspots sourced by deep mantle plumes. However, the hotspot models cannot be extended further back in time than the Early Cretaceous (~130 Ma), and defining TPW for the earlier Mesozoic and Paleozoic times has always been challenging. Here I will review the recent developments in the research on TPW and discuss our latest hybrid model for absolute plate motions and TPW for the entire Phanerozoic eon (0-540 Ma), which combines estimates based on the hotspot reconstructions back to Early Cretaceous time (0-120 Ma) with those built upon the analysis of coherent rotations of continental lithosphere in the paleogeographic frame for Early Cretaceous to Cambrian time (120-540 Ma), and includes longitudinal constraints on the paleogeography obtained by matching the eruption sites of large igneous provinces and kimberlites with the plume generation zones bordering the two large low shear-wave velocity provinces (LLSVPs) in the lowermost mantle. This model suggests that four episodes of slow, oscillatory TPW have occurred from Early Cretaceous to recent time (0-120 Ma); nine additional episodes were inferred in the earliest Cretaceous to Cambrian time (140-540 Ma), at rates not exceeding 1o/Myr. The possible dynamic causes of these TPW events will be discussed.
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Bull, Abigail Louise; Torsvik, Trond Helge; Domeier, Mathew & Doubrovine, Pavel
(2013).
The initiation, temporal evolution and dynamics of deep mantle heterogeneities.
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Understanding the first-order dynamical structure and temporal evolution of Earth's mantle is a fundamental goal in solid-earth geophysics. Recent tomographic observations reveal a lower mantle characterised by higher-than-average shear-wave speeds beneath Asia and encircling the Pacific, consistent with cold slabs of descending lithosphere beneath regions of ancient subduction, and lower-than-average shear-wave speeds in broad regional areas beneath Africa and the Central Pacific (LLSVPs). The LLSVPs, although not as easily understood from a dynamical perspective, are inferred to be broad upwelling centres between Mesozoic and Cenozoic subduction zones. Heterogeneous mantle models place these anomalies into the context of thermochemical piles, characterised by an anomalously dense component, with their location and geometry being controlled by the movement of subducting slabs. The origin and temporal evolution of the LLSVPs remain enigmatic. Recent numerical studies propose that the LLSVP beneath Africa formed as a result of return flow in the mantle due to circum-Pacific subduction beneath the Pangean supercontinent. This suggests that prior to the formation of Pangea, the lower mantle was dominated by a degree-1 convection pattern, with a major upwelling centred close to the present-day Pacific LLSVP and subduction concentrated in the antipodal hemisphere. The African LLSVP would thus have developed within the time frame of the Pangean supercontinent (i.e., 300Ma-180Ma), in contrast to a much older Pacific LLSVP. It is further proposed that a cyclic alternation between a degree-1 pattern and a degree-2 pattern of mantle convection may accompany the supercontinent cycle and characterise the temporal convective evolution of Earth's mantle. In contrast, a more long-term persistence for both the African and Pacific LLSVPs, and thus for the planform of mantle convection within the Earth as a whole, is suggested by recent palaeomagnetic studies, which show that over 80% of all kimberlites erupted in the past 542 Myr lay, at the time of their eruption, above the edges of the African and Pacific LLSVPs. Such a finding requires both LLSVPs to be stationary in their present-day positions for at least the past 500 Ma, and thus be insensitive, to first-order, to the formation and subsequent break-up of the Pangean supercontinent. In this work, we investigate the temporal evolution and possible long-term persistence of LLSVPs by integrating plate tectonics into numerical models of mantle dynamics. We improve upon previous studies by employing a new palaeomagnetically-derived global plate motion data set to impose surface velocity boundary conditions for a time period which encompasses the creation and subsequent break-up of the Pangean supercontinent. We aim to understand the role that Earth's plate motion history plays on the development of LLSVPs within Earth's mantle. Specifically, we investigate the effect of plate history on the degree-2 structure of the mantle and explore the possibility that both LLSVPs existed prior to the Pangean supercontinent.
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Torsvik, Trond Helge; Doubrovine, Pavel & Steinberger, Bernhard
(2013).
PALEOMAGNETISM, LONGITUDE AND TRUE POLAR WANDER.
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The calibration of longitude in the mid-eighteenth century by the invention of a sea-going chronometer gave mariners confidence that they could reliably calculate their absolute position on the Earth's surface. Until recently, Earth scientists have been in the comparable position of having no way of calculating the longitudes of continents before the Cretaceous, leaving paleomagnetism, which cannot determine longitude, as the only quantitative means of positioning continents on the globe before that time. However, by choosing a reference continent that has moved the least longitudinally (i.e. Africa), longitudinal uncertainty can be minimized. The analytical trick is to rotate all paleomagnetic poles to Africa and calculate a global apparent polar wander path in African co-ordinates, which serves as the basis for subsequent global reconstructions. This method is dubbed the ‘zero-longitudinal motion’ approximation for Africa, and has allowed us to confidently estimate true polar wander (TPW) since Pangea formation (320 Ma), and to demonstrate that ancient large igneous provinces and kimberlites have been sourced by plumes from the edges of the two Large Low Shear-wave Velocity Provinces (LLSVPs) on the core-mantle boundary beneath Africa and the Pacific. Using this surface-to-CMB correlation and a new iterative approach for defining a palaeomagnetic reference frame corrected for TPW, we have developed a model for absolute plate motion back to earliest Paleozoic time that maintains the remarkable link between surface volcanism and the LLSVPs. For the Paleozoic we have for the first time identified several phases of slow, oscillatory TPW (less than 1 degree/Myr) during which the Earth’s axis of minimum moment of inertia was similar to that of Mesozoic times. We model ten phases of clockwise and counter-clockwise rotations since 540 Ma, which can be interpreted as oscillatory swings approximately around the same axis (11 degrees East at equator). Net TPW angles peaked at 22 degrees in the Mesozoic and 62 degrees in the Paleozoic, and paleomagnetic and TPW-corrected (mantle) reconstructions therefore differ significantly in the early Paleozoic.
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Published
Nov. 27, 2014 1:07 PM
- Last modified
Sep. 1, 2026 10:14 AM
