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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
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
Beyond a single-pulse eruption: paleomagnetic evidence for a multi-episode Youngest
The Youngest (74 ka) Toba Tuff (YTT) super-eruption is traditionally interpreted as a single, short-lived event. However, new paleomagnetic data from both southern and northern non-welded exposures of YTT's Units 2, 3, and 4 (in ascending order) challenge this model. Unit 2 samples were obtained from a thin ash layer sandwiched between two ignimbrites at two localities on the northern and southern sides of the caldera, whereas samples from Units 3 and 4 were collected from ignimbrites at one locality each on the southern side of the caldera. Mineral chemistry of matrix-glass and biotite from thin ash layers in both northern and southern deposits shows compositions consistent with YTT. Mean characteristic remanent magnetization (ChRM) directions from Units 3 and 4 are indistinguishable and consistent with those of the welded YTT. Mean ChRM directions of Unit 2 from two different localities are indistinguishable and exhibit a statistically distinct paleomagnetic direction from those of Units 3 and 4. Using a secular variation rate of 0.02 degrees/year, the estimated minimum time gap between Units 2 and 3-4 is 807 ± 193 years. Temporal gaps recorded in non-welded proximal deposits are consistent with recent interpretations from distal marine tephra, suggesting that the YTT eruption was episodic and may have spanned several hundred to thousands of years.
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