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"paleomagnetism"
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Decadal‐Scale In Situ Scanning of a Stalagmite From Southwest China Reveals Blake Geomagnetic Excursion Structure
We present a decadal‐scale paleomagnetic analysis of a stalagmite collected from Shuixi Cave, southwest China, spanning 89−123 ka. Our findings include: (a) Magnetite is the dominant magnetic mineral, and paleomagnetic directions can be obtained via demagnetization; (b) Magnetic scanning at 0.1‐mm resolution captures key magnetic features, identifying eight reversed intervals; (c) The consistency between two measurements confirms the reliability of in situ magnetic scanning and shows that reversed intervals can be discerned from shifts in inclination and declination. Comparison with global geomagnetic records suggests that this interval consists of three major phases, namely the Blake, post‐Blake, and Skalamaelifell, characterized by four, two, and two reversed intervals occurring at 108,810−119,090 years BP, 99,780−103,140 years BP, and 90,950−94,470 years BP, respectively. These decadal‐resolution results illuminate the fine structure of the previously‐proposed Blake interval and highlight the potential of high‐resolution in situ magnetic scanning of precisely dated speleothems for resolving geomagnetic behavior.
Journal Article
Burma Terrane part of the Trans-Tethyan arc during collision with India according to palaeomagnetic data
Convergence between the Indian and Asian plates has reshaped large parts of Asia, changing regional climate and biodiversity, yet geodynamic models fundamentally diverge on how convergence was accommodated since the India–Asia collision. Here we report palaeomagnetic data from the Burma Terrane, which is at the eastern edge of the collision zone and is famous for its Cretaceous amber biota, to better determine the evolution of the India–Asia collision. The Burma Terrane was part of a Trans-Tethyan island arc and stood at a near-equatorial southern latitude at ~95 Ma, suggesting island endemism for the Burmese amber biota. The Burma Terrane underwent significant clockwise rotation between ~80 and 50 Ma, causing its subduction margin to become hyper-oblique. Subsequently, it was translated northward on the Indian Plate by an exceptional distance of at least 2,000 km along a dextral strike-slip fault system in the east. Our reconstructions are only compatible with geodynamic models involving an initial collision of India with a near-equatorial Trans-Tethyan subduction system at ~60 Ma, followed by a later collision with the Asian margin.
Journal Article
Magnetic Reversals During the Deccan Volcanism: Paleomagnetic Insights From the Pachmarhi Dykes
The three main dyke swarms that are linked to the Deccan Continental Flood Basalts are the Nasik‐Pune, Western Coastal, and Narmada‐Satpura‐Tapi (N‐S‐T) swarms. Encompassing approximately 244 mapped basaltic dykes, mainly trending E‐W and positioned along an ancient tectonic zone, the Pachmarhi dyke swarm is situated in the eastern N‐S‐T segment. The length of these dykes varies from 140 m to 22 km, with a mean abundance between 5 and 15 km. According to petrographic and rock magnetic analyses, the main magnetic remanence carriers are high‐ and low‐titanium magnetite particles, primarily in the pseudo‐single domain state. Paleomagnetic analyses of 14 dykes show that two of them exhibit both polarities within the same dyke, seven have reverse polarity, and five have normal polarity. This implies periodic intrusion of magma during geomagnetic reversals. The mean ChRM directions for normal and reverse polarity dykes are Dm = 329.3°, Im = −40.3° (k = 80.1, α95 = 8.6°, n = 31) and Dm = 154.4°, Im = 39.5° (k = 122, α95 = 5.5°, n = 69), respectively. The combined mean ChRM direction (Dm ≈ 332°, Im ≈ −39.8°) yields a paleopole at 37°N, 68.6°W, closely aligning with the Nandurbar‐Dhule (N‐D) dykes and the Deccan Superpole. The results indicate that the Pachmarhi dykes were formed during a mostly synchronous magmatic episode along the Narmada–Son Lineament. Due to the lack of direct geochronological constraints for these dykes, their precise correlation with the eruptive history of the Deccan Traps remains unresolved.
Journal Article
PMTools: New Application for Paleomagnetic Data Analysis
This paper introduces PMTools (
https://pmtools.ru
), a novel cross-platform open-source web application designed for the analysis of paleomagnetic data. Our software offers a user-friendly interface and supports the most commonly used data formats in paleomagnetism, including .
pmd
, .
dir
, .
pmm
, .
rs3
, .
squid
, .
vgp
, and .
gpml
. It encompasses all the necessary functionalities for principal component analysis of natural remanent magnetization and computing mean paleomagnetic directions along with corresponding virtual geomagnetic (paleomagnetic) poles. PMTools facilitates the application of various paleomagnetic tests to user data, such as the fold test, conglomerate test, and reversals test. Notably, the application allows for seamless import and export of paleomagnetic data (tables) in formats compatible with .
csv
and MS Excel. Additionally, all generated figures can be exported as high-quality vector graphics in .
svg
format, specifically designed for direct integration into publications and presentations. Furthermore, PMTools enables the export of sets of paleomagnetic poles in GMap and GPlates software formats, enabling researchers to promptly use their paleomagnetic data for paleotectonic reconstructions. PMTools has an intuitive interface, customizable hotkeys, and an extensive array of graph elements, all of which contribute to making PMTools an appealing, cutting-edge tool for processing and analyzing the results of paleomagnetic studies.
Journal Article
Young inner core inferred from Ediacaran ultra-low geomagnetic field intensity
An enduring mystery about Earth has been the age of its solid inner core. Plausible yet contrasting core thermal conductivity values lead to inner core growth initiation ages that span 2 billion years, from ~0.5 to >2.5 billion years ago. Palaeomagnetic data provide a direct probe of past core conditions, but heretofore field strength data were lacking for the youngest predicted inner core onset ages. Here we present palaeointensity data from the Ediacaran (~565 million years old) Sept-Îles intrusive suite measured on single plagioclase and clinopyroxene crystals that hosted single-domain magnetic inclusions. These data indicate a time-averaged dipole moment of ~0.7 × 1022 A m2, the lowest value yet reported for the geodynamo from extant rocks and more than ten times smaller than the strength of the present-day field. Palaeomagnetic directional studies of these crystals define two polarities with an unusually high angular dispersion (S = ~26°) at a low latitude. Together with 14 other directional data sets that suggest a hyper-reversal frequency, these extraordinary low field strengths suggest an anomalous field behaviour, consistent with predictions of geodynamo simulations, high thermal conductivities and an Ediacaran onset age of inner core growth.A late onset of inner-core growth is inferred from ultra-low palaeomagnetic field strengths about 565 million years ago, as measured in magnetic inclusions in Ediacaran crystals.
Journal Article