Yiming Ma

To better constrain the post‐collisional southward displacement of the Indochina Block (ICB) and the crustal deformation of the southeastern Tibetan Plateau, we present a reliable paleomagnetic study of Upper Cretaceous Nanxin Formation redbeds exposed in the Lanping area, at the northern edge of the Lanping‐Simao Terrane (LST). The tilt‐corrected site‐mean direction derived from 30 sites is D s = 39.3°, I s = 48.4° with α ₉₅ = 4.3°, corresponding to a paleomagnetic pole at 55.3°N, 175.5°E with dp / dm = 3.7°/5.6° and a paleolatitude of 29.4°N ± 3.7°N for the sampling area (26.6°N, 99.4°E). This paleomagnetic data set passes both positive fold and reversal tests at 95% and 99% confidence levels. Comparison with the Late Cretaceous pole of the South China Block and the East Asia apparent polar wander path shows that the entire ICB underwent a coherent southward displacement of ∼900 km between the Late Cretaceous and Late Eocene.

Recent paleomagnetic studies of Apollo and Chang’e returned samples suggest that the lunar dynamo was active from ∼4.2 billion years ago (Ga) and ceased by ∼1.0 Ga. However, uncertainties remain regarding the temporal and spatial distribution of the lunar paleomagnetic field, as almost all of the returned samples are from the nearside, except for those returned by Chang’e-6. Here, we present the first paleomagnetic analysis of a lunar meteorite, Northwest Africa 15528, which is a feldspathic regolith breccia likely from the farside of the Moon. Our results not only indicate that it recorded a near-zero magnetic field (below a few hundred nanoteslas) at ∼0.7 Ga but also show that lunar meteorites can provide critical paleomagnetic information. Combined with two young Apollo samples from the nearside, Apollo 15015 (formed at ∼0.9 Ga) and Apollo 15465 (formed at ∼0.5 Ga), our findings suggest the absence of a global dynamo-generated lunar magnetic field for the past one billion years.

The South Atlantic Anomaly (SAA) is the most prominent feature of Earth's magnetic field. Understanding past geomagnetic field variations in the SAA region is crucial for improving our knowledge of the geodynamo. Site Ocean Drilling Program (ODP) 1233, located within the modern SAA and characterized by a high sedimentation rate (∼190 cm/kyr), provides a valuable archive for reconstructing the anomaly's history. Although paleomagnetic data from shipboard and u‐channel measurements spanning the past 70 ka (Lund et al., 2006, 2024) have been reported, they have not been validated by rock magnetic analyses. Notably, during the 65–40 ka interval, which includes the Norwegian‐Greenland Sea and Laschamps excursions, relative paleointensity (RPI) and inclination from site ODP 1233 differ markedly from nearby and global records. SEM–EDS and rock magnetic results show alternating intervals dominated by silicate‐hosted magnetite inclusions, likely associated with reduced supply and partial dissolution of detrital titanomagnetite during Patagonian Ice Sheet retreat, and intervals dominated by detrital titanomagnetite. We therefore applied a log‐transformed RPI normalization that accounts for the magnetic properties of these carriers and rescales amplitudes to a common reference. The resulting RPI curve aligns well with regional and global paleointensity records. When the axial dipole moment was comparable to the present value at ∼57.5 and ∼47 ka, paleointensity minima appear confined to the South Atlantic region, analogous to the present‐day SAA behavior.

Paleomagnetic studies typically assume that the long‐term, time‐averaged geomagnetic field behaves as a geocentric axial dipole (GAD). While paleodirectional data over the past five million years generally agree with GAD predictions, mid‐to‐low latitude paleointensity records fail to show GAD, with high values from Hawaii. Possible causes include experimental biases, non‐dipole field contributions, and uneven temporal sampling. In this study, we conduct alternating field and thermal demagnetization measurements, as well as paleointensity experiments, on 12 late Pleistocene (∼0.2–0.5 Ma) lava flows from northern Hainan Island (∼20°N, ∼110°E) of the Brunhes normal polarity chron. Eleven sites yield stable paleomagnetic directions ( D = 9.1°, I = 24.3°, α ₉₅ = 4.0°), defining a virtual geomagnetic pole (VGP) at 78.7°N, 237.7°E, with VGP dispersion of 12.9°. Paleointensity results from four qualified sites range from 28.8 to 48.9 μT (mean = 37.8 ± 6.9 μT), which are in agreement with the Brunhes Hawaiian data from the same latitude. The directional and intensity results from Hainan are consistent with previous studies at similar latitudes but deviate from GAD predictions. Our results suggest that the high paleointensity values observed in the Hawaiian region may result from differences in age distributions compared with records from other latitudes. Considering these temporal differences, the observed non‐GAD characteristics at mid‐to‐low latitudes may partly reflect comparisons between time‐averaged field properties over distinct geological intervals.

Marine magnetic anomalies are pivotal to our understanding of plate tectonics, geomagnetic fields, and deep Earth dynamics. However, the question of how Ti‐rich titanomagnetites, the primary remanence carriers in oceanic crust rocks, can faithfully preserve geomagnetic field information for tens of millions of years is not well understood. Here, we combine microscopic, micromagnetic, and rock magnetic analyses, including 14‐T high‐field measurements, to show that the magnetic micro‐anisotropy of a fresh pillow lava dredged from the Juan de Fuca Ridge is dominated by internal stress throughout its chilled margin to its interior. Internal stress, which is generated primarily by the contraction of hot lava erupting into cold seawater, increased the natural remanent magnetization in this lava by a factor of ∼3. We suggest that stress‐induced magnetic domain state transformation from multidomain to single vortex (or single domain) in extrusive pillow lavas significantly enhances oceanic crustal magnetic remanence strength and stability.

To refine the postcollisional extrusion and convergence history of the southeastern Tibetan Plateau, we report a quality paleomagnetic data set from Upper Cretaceous redbeds of the eastern Qiangtang Terrane (QT), where is situated at the front edge of eastern Himalayan Syntaxis. The 32 site‐mean directions provide a mean pole at 75.4°N, 176.8°E (A₉₅ = 2.4°) and a paleolatitude of 31.8 ± 2.4°N for the Mangkang area. Comparison with reliable Late Cretaceous paleomagnetic data from the eastern QT and East Asia indicates that the eastern QT experienced a southward extrusion of 940 ± 310 km after the Late Cretaceous. Comparing Late Cretaceous paleolatitudes estimated from the eastern QT and Lhasa terrane (LT) reveals a paleolatitude difference of 2,390 ± 620 km. Such a great latitudinal convergence can be attributed to the fact that some continental terranes originally located between the eastern LT and QT were laterally extruded after the Late Cretaceous.

Meteorite paleomagnetism is fundamental to understanding planetary dynamo processes and the evolution of the early Solar System. However, due to the extraterrestrial and ancient origins of meteorites, their paleomagnetic recording fidelity remains uncertain, which can be tested from a planetary sample formed in a known field. On Earth, historic lavas are used to examine paleomagnetic recording fidelity through the Thellier‐series experiment and other paleointensity methods, which can produce paleointensity estimates to test against the known field strength. But natural terrestrial rocks have different magnetic mineralogy from planetary samples, so they cannot faithfully infer the recording fidelity of meteorites. Here, we used an iron‐particle‐bearing sample from the Syracuse University Lava Project (SULP), which is analogous to the lunar basalts and howardite‐eucrite‐diogenite meteorites and forms in the present‐day Earth's field, to investigate the recording fidelity of these meteorites. No remanence has been identified in the high coercivity range with alternating field (AF) demagnetization due to the sample's low coercivity and AF noise, which produces underestimated paleointensities. Two accurate thermal paleointensities indicate that we may acquire accurate paleointensities from non‐ideal multidomain (MD) iron grains with the Thellier‐Coe and RESET methods, but the success rate is low due to the MD effect and thermal alteration in the experiments. Our results imply that MD iron‐bearing meteorites have the potential to provide accurate paleointensities that can be used to constrain planetary processes.

On-chip spectrometers using silicon photonics offer a practical and economical solution for wearable electronics and portable instruments. However, noise affects the resolution of spectral reconstruction. Here, we propose and demonstrate an on-chip computational spectrometer combining MEMS time-domain modulation of a reconfigurable waveguide coupler and a denoising autoencoder. According to the noise-free assumption, the spectral reconstruction resolution is 0.3 nm. A convolutional autoencoder is designed to reduce noise and minimize its impact on the reconstruction resolution. At a noise level of 30 dB, the reconstruction resolution within a 100 nm bandwidth is improved from 1.1 nm to 0.4 nm, which is close to the 0.3 nm resolution of the condition without noise.

The drift history of the Lhasa terrane is crucial for understanding the tectonic evolution of Tethyan Oceans and Jurassic true polar wander. However, high‐quality Middle Jurassic paleomagnetic data from the Lhasa terrane are limited in number. Here we report a combined paleomagnetic and geochronologic study on the Yeba Formation volcanic rocks, dated at ∼170 Ma, from the Lhasa terrane. Robust field and reversal tests indicate that the characteristic remanent magnetizations are primary. Our results provide a reliable Middle Jurassic (∼170 Ma) paleopole at 29.8°N, 180.7°E with A ₉₅ = 5.7° and a paleolatitude of 14.4 ± 5.7°N for the Lhasa area. Compared with previous paleomagnetic and geologic evidence, we propose that the Meso‐Tethys Ocean probably began to close in the eastern part at ∼168 Ma and that the Lhasa terrane underwent a ∼2,900 km southward “monster shift” during the Late Jurassic.