Publikasjoner
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Xue, Yi; Domeier, Mathew Michael; Silkoset, Petter; Gallo, Leandro Cesar; Tonti-Filippini, Justin Antony Dean & Walderhaug, Harald James
(2026).
Cryptic Paleomagnetic Complexity in the Ediacaran Egersund Dikes.
Geochemistry Geophysics Geosystems.
27(5).
doi:
10.1029/2025GC012730.
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The Ediacaran Period (∼635–539 Ma) represents a critical interval in Earth's evolution, yet its paleomagnetic record remains complex and contentious. One of the few Ediacaran paleomagnetic results from Baltica considered robust is a pole from the ca. 616 Ma Egersund dikes in southwest Norway, which is interpreted to represent a primary thermoremanent magnetization. However, we report on a new paleomagnetic and rock magnetic investigation of these dikes that suggests that their paleomagnetic record is more complex than previously recognized. Our results reveal a multicomponent remanence structure, and we identify a new high-temperature component that positive baked contact tests suggest to be the primary thermoremanent magnetization. Together with microscopic and geochemical analyses, we demonstrate that another distinct component represents a remagnetization acquired during Caledonian orogenesis. Although we also identified a stable direction similar to that interpreted as the primary component in earlier studies, our analysis suggests this component may be an artifact resulting from vector overlap of the other components. The origins of two additional directions, which deviate markedly from the other components and known Phanerozoic reference directions, remain uncertain. They may reflect transitional geomagnetic states, hinting at the possibility of a more dynamic and unstable Ediacaran geomagnetic field. Our revised pole position (20.8°N, 89.0°E) differs from earlier results by more than 40°, with important implications for Baltica's paleogeographic evolution. This study underscores the value of integrated approaches and highlights the importance of reinvestigating key paleomagnetic results, particularly from data-poor intervals of time and space.
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Gallo, Leandro Cesar; Domeier, Mathew Michael; Antonio, Paul Yves Jean; sapienza, facundo; Rapalini, Augusto & Font, Eric
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(2025).
Unraveling remagnetization sources using statistical learning.
Earth and Planetary Science Letters.
ISSN 0012-821X.
662.
doi:
10.1016/j.epsl.2025.119390.
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The paleomagnetic archive provides invaluable insights into Earth's history, but its records are often obscured by various geological processes. A prime example is remagnetization, which can replace the original natural remanent magnetization. Although magnetic overprints can be detected by traditional paleomagnetic tests, the mechanisms responsible for them often remain elusive because linking bulk magnetic properties to their microscopic sources is inherently challenging. Here, we bridge this gap by pairing an extensive rock magnetic and geochemical dataset with statistical learning techniques for the first time. Using a Random Forest regressor trained on geochemical data, we accurately predict the growth of fine-grained magnetite in an undeformed late Ediacaran section of remagnetized carbonate rocks from Paraguay. Our modeling results identify the K/Al ratio—alongside K and Sr contents—as key predictors of this remagnetization mechanism. Notably, clay mineralogy analyses further link the K/Al ratio to enhanced clay authigenesis (illitization) driven by K-feldspar dissolution and albitization—processes that also release iron. Together, these findings indicate that remagnetization occurred via authigenic magnetite formation under isochemical diagenesis—without the involvement of external fluids. This novel application of statistical learning to uncover the geochemical drivers of chemical remagnetizations provides a robust framework to investigate and understand these events. It could also open new avenues for their direct dating, thereby significantly enriching the global paleomagnetic record.
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Kulakov, Evgeniy; Torsvik, Trond Helge; Doubrovine, Pavel V.; Slagstad, Trond; Ganerød, Morgan & Silkoset, Petter
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(2021).
Jurassic fast polar shift rejected by a new high-quality paleomagnetic pole from southwest Greenland.
Gondwana Research.
ISSN 1342-937X.
97,
s. 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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Svensen, Henrik; Hammer, Øyvind; Chevallier, Luc; Jerram, Dougal Alexander; Silkoset, Petter & Polteau, Stephane
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(2020).
Understanding thermogenic degassing in large igneous provinces: Inferences from the geological and statistical characteristics of breccia pipes in the western parts of the Karoo Basin.
I Adatte, Thierry; Bond, David P.G. & Keller, Gerta (Red.),
Mass extinctions, volcanism, and impacts.
The Geological Society of America.
ISSN 9780813725444.
s. 67–84.
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Andersen, Torgeir Bjørge; Austrheim, Håkon Olav; Deseta, Natalie; Silkoset, Petter & Ashwal, Lewis D.
(2014).
Large subduction earthquakes along the fossil Moho in Alpine Corsica.
Geology.
ISSN 0091-7613.
42(5),
s. 395–398.
doi:
10.1130/G35345.1.
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ABSTRACT
Subduction earthquakes release vast amounts of energy to crust and mantle lithosphere. The products of such drastic events are rarely observed in the field because they are mostly lost by subduction. We present new observations of deformation products formed by a few very large and numerous small intermediate-depth Alpine subduction earthquakes that are pre- served along the exhumed gabbro–mantle peridotite contact of the Piemont-Liguria oceanic basin in Corsica. The abrupt release of energy resulted in shear heating events that completely melted both gabbro and peridotite. The large volumes of melt that were generated can be stud- ied in the fault and injection vein breccia complex along the fault zone. The energy required for wholesale melting of a large volume of peridotite along the fault combined with previous esti- mates of stress drops show that very large earthquakes took place along the Moho of the sub- ducting plate. Because these fault rocks formed by intraplate seismicity, we suggest, by analogy with present-day subduction, that they represent a proxy for the lower seismogenic zone.
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Kulakov, Evgeniy; Doubrovine, Pavel V.; Torsvik, T.H; Werner, Stephanie C. & Silkoset, Petter
(2018).
Paleomagnetism of Late Jurassic – Early Cretaceous coast-parallel dykes in SW Greenland.
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It is a well-known and still unresolved problem of the Jurassic to Early Cretaceous apparent polar wander paths (APWP) discrepancy between those for North America (Laurentia) and Eurasia. Paleomagnetic poles derived from coeval rocks from the two continents differ significantly with North American poles characterized by shallower pole latitudes. The APWP mismatch cannot be resolved by correction for inclination shallowing or using different plate circuits. One of the possible explanations for the observed phenomenon is that paleomagnetic data from North America show the effects of younger remagnetizations and/or tectonic rotation. In an attempt to resolve this problem, paleomagnetic study of samples from ~35 Late Jurassic to Early Cretaceous coast-parallel mafic dykes exposed in SW Greenland (part of Laurentia) was carried out. Paleomagnetic samples have been subjected to a step-wise thermal and alternating field demagnetization techniques which yielded well-defined characteristic remanent components. A primary nature of the characteristic remanence is supported by positive baked-contact tests and the presence of paleomagnetic directions of both polarities that pass a reversal test. Our results indicate that the paleomagnetic pole for Greenland has higher latitude than the coeval North American poles and plots closer to the APW path for Eurasia. We will discuss the results and their implications for global Mesozoic apparent polar wander and paleogeography during Jurassic and early Cretaceous times.
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Andersen, Torgeir Bjørge; Deseta, Natalie; Silkoset, Petter; Austrheim, Håkon Olav & Ashwal, Lewis D.
(2014).
Large Subduction Earthquakes along the fossil MOHO in Alpine Corsica: what was the role of fluids?
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Silkoset, Petter; Svensen, Henrik & Planke, Sverre
(2014).
Breccia pipes in the Karoo Basin, South Africa, as conduits for metamorphic gases to the Early Jurassic atmosphere.
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Silkoset, Petter; Andersen, Torgeir Bjørge; Austrheim, Håkon Olav; Magraso, Anna & Wheeler, John
(2013).
Microstructure of ultramafic pseudotachylyte from Alpine Corsica – insights into earthquakes in mantle lithosphere.
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Publisert
14. sep. 2015 11:39
- Sist endret
30. jan. 2024 13:15
