Publikasjoner
-
-
Biggin, Andrew J.; Bono, Richard K.; Meduri, Domenico G.; Sprain, Courtney J.; Davies, Christopher J. & Holme, Richard
[Vis alle 7 forfattere av denne artikkelen]
(2020).
Quantitative estimates of average geomagnetic axial dipole dominance in deep geological time.
Nature Communications.
ISSN 2041-1723.
11.
doi:
10.1038/s41467-020-19794-7.
Fulltekst i vitenarkiv
Vis sammendrag
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.
-
-
-
Doubrovine, Pavel; Veikkolainen, Toni; Pesonen, Lauri; Piispa, Elisa; Ots, Siim & Smirnov, Aleksey
[Vis alle 8 forfattere av denne artikkelen]
(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.
ISSN 1525-2027.
20(3),
s. 1240–1279.
doi:
10.1029/2018GC007863.
Fulltekst i vitenarkiv
Vis sammendrag
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.
-
-
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.
ISSN 2375-2548.
3(11).
doi:
10.1126/sciadv.aao2303.
Fulltekst i vitenarkiv
-
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),
s. 1073–1087.
doi:
10.1139/cjes-2015-0228.
Fulltekst i vitenarkiv
-
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),
s. 4945–4953.
doi:
10.1002/2016GL068827.
-
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.
ISSN 1525-2027.
17(3),
s. 1130–1163.
doi:
10.1002/2015GC006044.
Fulltekst i vitenarkiv
-
Torsvik, Trond Helge; Amundsen, Hans E. Foss; Trønnes, Reidar G; Doubrovine, Pavel; Gaina, Carmen & Kusznir, Nick J.
[Vis alle 12 forfattere av denne artikkelen]
(2015).
Continental crust beneath southeast Iceland.
Proceedings of the National Academy of Sciences of the United States of America.
ISSN 0027-8424.
112(15),
s. E1818–E1827.
doi:
10.1073/pnas.1423099112.
Vis sammendrag
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.
-
Torsvik, Trond Helge; Van Der Voo, R; Doubrovine, Pavel; Burke, K; Steinberger, Bernhard & Ashwal, LD
[Vis alle 9 forfattere av denne artikkelen]
(2014).
Deep mantle structure as a reference frame for movements in and on the Earth.
Proceedings of the National Academy of Sciences of the United States of America.
ISSN 0027-8424.
111(24),
s. 8735–8740.
doi:
10.1073/pnas.1318135111.
-
Torsvik, Trond Helge; Doubrovine, Pavel & Domeier, Mathew
(2014).
Continental Drift (Paleomagnetism).
Springerin.
ISSN 1029-1830.
doi:
10.1007/978-94-007-6326-5_107-1.
-
-
-
-
Van Hinsbergen, Douwe; Lippert, Peter C.; Dupont-Nivet, Guillaume; McQuarrie, Nadine; Spakman, Wim & Torsvik, Trond Helge
[Vis alle 7 forfattere av denne artikkelen]
(2012).
Greater India Basin hypothesis and a two-stage Cenozoic collision between India and Asia.
Proceedings of the National Academy of Sciences of the United States of America.
ISSN 0027-8424.
109(20),
s. 7659–7664.
doi:
10.1073/pnas.1117262109.
-
-
Se alle arbeider i Cristin
-
Smirnov, Aleksey V.; Kulakov, Evgeniy; Sprain, Courtney; Doubrovine, Pavel; Paterson, Greig & Hawkins, Louise
[Vis alle 9 forfattere av denne artikkelen]
(2019).
A view on the long-term history of dipole moment through the Mesozoic from the analysis of an updated paleointensity database (QPI-PINT) for 65-200 Ma.
-
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. .
-
Domeier, Mathew; Torsvik, Trond Helge; Conrad, Clinton Phillips; Steinberger, Bernhard; Doubrovine, Pavel & Trønnes, Reidar G
[Vis alle 9 forfattere av denne artikkelen]
(2019).
On the stability of Earth’s degree 2 mantle structures.
-
Doubrovine, Pavel
(2017).
Estimating true polar wander from plate models.
Vis sammendrag
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.
-
Doubrovine, Pavel; Torsvik, Trond Helge & Domeier, Mathew
(2017).
Paleomagnetism and paleosecular variation from the late Miocene to recent lavas of Mauritius.
Vis sammendrag
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.
-
Torsvik, Trond Helge; Doubrovine, Pavel & Steinberger, Bernhard
(2013).
PALEOMAGNETISM, LONGITUDE AND TRUE POLAR WANDER.
Vis sammendrag
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.
-
Bull, Abigail Louise; Torsvik, Trond Helge; Domeier, Mathew & Doubrovine, Pavel
(2013).
The initiation, temporal evolution and dynamics of deep mantle heterogeneities.
Vis sammendrag
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.
Se alle arbeider i Cristin
Publisert
27. nov. 2014 11:22
- Sist endret
3. juli 2023 12:00