Hanqing Zhao

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.

The North China Craton (NCC) has long been regarded as tectonically quiescent during the Cambrian, yet detrital zircons of the early Cambrian to earliest Ordovician age are widespread in Cambrian strata across the craton, and their provenance remains controversial. This study presents new zircon U–Pb geochronological, trace-element and Lu–Hf isotopic data, together with whole-rock geochemical data, for a basaltic andesite (informally named the Xiaowenzhigou Andesite) near Xiaowenzhigou Village in eastern Liaoning, northeastern NCC. The unit was previously mapped as a volcanic interlayer within the Lower Cretaceous Lishugou Formation. Five euhedral, oscillatory-zoned magmatic zircons yield a weighted mean ²⁰⁶Pb/²³⁸U age of 528.4 ± 5.6 Ma (2σ; MSWD = 0.51, n = 5), corroborated by a concordia age of 529.3 ± 5.4 Ma (2σ), providing, to our knowledge, the first direct evidence of early Cambrian magmatism in the northeastern NCC. Consequently, the unit is distinguished from the Lishugou Formation. The rock is a metaluminous, high-K calc-alkaline pyroxene basaltic andesite, enriched in large-ion lithophile elements and light rare earth elements and depleted in Nb–Ta, with high Sr contents and only weak negative Eu anomalies. Magmatic zircons have negative εHf(t) values of −3.5 to −0.9 and Paleoproterozoic two-stage Hf model ages of 1.54–1.71 Ga, and abundant inherited zircons (1.82–2.69 Ga) correspond to the Archean–Paleoproterozoic basement of the northeastern craton. These characteristics indicate that the parental magma was primarily generated by partial melting of Paleoproterozoic lower crust, accompanied by assimilation of local basement during ascent. The Xiaowenzhigou Andesite is identified as a potential local source for the early Cambrian detrital zircons found in Paleozoic strata of the craton, challenging the prevailing view that the northeastern craton was magmatically inactive during the early Paleozoic. We acknowledge that our conclusions are necessarily preliminary, as our understanding of this unit is constrained by the presence of only one small outcrop and the limited number of zircon grains recovered (n = 5). The primary objective of this initial documentation is to draw attention to the unit and to stimulate further investigation.

Paleomagnetic data from carbonate rocks are fundamental to Precambrian paleogeography. However, many dolostone-dominated successions have suffered pervasive remagnetization. To investigate the magnetization mechanisms of Ediacaran dolostones, we present a detailed paleomagnetic and rock magnetic study of the cap dolostone of the Doushantuo Formation at the Jiulongwan section, South China. Anisotropy of magnetic susceptibility reveals weak tectonic deformation. Thermal demagnetization isolates three remanence components. A low-temperature component (LTC) aligns with the present-day field at the sampling area, indicating a viscous remanent magnetization. The intermediate-temperature (ITC) and high-temperature (HTC) components show antipodal clustering (ITC: Dg=21.0°, Ig=45.2°, α95=1.1°; HTC: Dg=196.0°, Ig=–43°, α95=2.2° in geographic coordinates), and their grouping does not improve after tilt correction, demonstrating a post-folding origin. The corresponding paleomagnetic poles (ITC: 71.2°N, 208.3°E, A95=1.1°; HTC: 74.7°N, 219.5°E, A95=2.1°) overlap the Late Jurassic pole of the South China Block (SCB), indicating that the cap dolostone acquired its remanence during the Late Jurassic. Rock magnetic results show that authigenic magnetite is the dominant magnetic carrier, which was transformed from precursor pyrite through metasomatic replacement by the oxidative orogenic fluids, with minor hematite also present. These results imply that Yanshanian orogenic fluids migrated along the periphery of the Huangling dome. Furthermore, five distinct types of demagnetization paths are recognized within the succession, reflecting varying degrees of remagnetization due to different intensities of fluid alteration.

Paleosecular variation provides a statistical test of long‐term geomagnetic field morphology, but its behavior across Precambrian polarity regimes remains poorly constrained. We compile a virtual geomagnetic pole dispersion data set spanning 1130–1070 Ma and apply nonlinear Model G fitting to evaluate field structure across the interval associated with the Keweenawan Normal Superchron. The combined data set yields Model G parameters a = 12.54° and b = 0.225, consistent with a broadly geocentric axial dipole‐compatible field at ca. 1100 Ma. When the data set is divided into reversal‐rich pre‐superchron and predominantly single‐polarity superchron intervals, the superchron subset lacks high‐paleolatitude estimates, limiting constraints on the Model G latitude‐dependence parameter b . The split data sets allow a cautious comparison of latitude‐invariant scatter, but they do not resolve polarity‐related changes in field morphology. Our results support substantial axial‐dipole contribution at ca. 1100 Ma and show the present superchron data set cannot robustly test reversal‐dependent latitude structure.

The spatial relationships of the widely distributed latest Jurassic–Early Cretaceous igneous rocks in the Tethyan Himalaya, northeastern India, and southeastern Australia are crucial for understanding the breakup of eastern Gondwana. However, available paleomagnetic datasets from the central Tethyan Himalaya are limited. To better constrain the distribution of these igneous rocks, new paleomagnetic data were obtained from the Weimei Formation volcanic rocks in the central Tethyan Himalaya. The tilt-corrected site-mean directions for 11 sites is Ds = 315.4°, Is = −58.4°, ks = 17.2, α₉₅ = 11.3°, corresponding to a paleopole at 9.6° N, 297.3° E with dp/dm = 16.7°/12.4° and a paleolatitude of ~39.1 ± 12.4° S for the study area (29.7° N, 83.7° E). A positive regional fold test and the occurrence of dual polarity suggest that the characteristic remanent magnetization is of pre-fold origin. These new results, together with those from the eastern Tethyan Himalaya, northern India, and southwestern Australia, show that the ~147–130 Ma circum-eastern Gondwana large igneous province spans a latitudinal range of ~40.7–58.1° S, centered at ~49.4° S, which is consistent with the present Kerguelen hotspot (~49.0° S). Integrating other evidence, we consider that the Kerguelen mantle plume played a key role in the breakup of eastern Gondwana.

The drift history of the Tethyan Himalaya provides key constraints on the India‐Asia collision, Himalayan‐Tibetan orogenesis, and associated global climate change. Here we present rock magnetic, petrographic, geochronologic, and paleomagnetic results of the Bolinxiala Formation limestones in the western Tethyan Himalaya. In situ calcite U‐Pb dating and biostratigraphy indicate that the Bolinxiala Formation limestones were formed during the Early Cretaceous (∼125–100 Ma), not Middle Jurassic as previously thought. The site‐mean direction for the 23 sites is D _g = 23.3°, I _g = +10.0°, k _g = 40.1 and α ₉₅ = 4.8° in situ and D _s = 20.8°, I _s = +19.0°, k _s = 67.2 and α ₉₅ = 3.7° after tilt‐correction, yielding a paleomagnetic pole position at 61.6°N, 212.9°E with A ₉₅ = 2.7°, corresponding to a paleolatitude of 10.3° ± 2.7°N. A positive fold test indicates a prefolding origin. When compared with reliable Cretaceous–Eocene paleopoles from the western Tethyan Himalaya, we suggest that the Bolinxiala Formation limestones likely underwent remagnetization during ∼54–49 Ma. Petrologic evidence, including the presence of framboidal oxides derived from sulfides (primarily pyrite) and calcite veins, supports chemical remanent magnetization as the primary mechanism responsible for the remagnetization. Our new results, combined with reliable Cretaceous paleomagnetic data from the western Lhasa terrane, indicate that the western part of the India‐Asia collision occurred no later than ∼54–49 Ma.

Disentangling short‐duration (≤10 Ma) true polar wander (TPW) events in the Precambrian presents a significant challenge, necessitating the acquisition of high‐resolution and ‐quality paleomagnetic data and well‐determined age relations. This study reports new paleomagnetic results from carbonate sequences of the Jingeryu Formation in the North China craton (NCC), which correlate with the lower part of the ca. 1,100 Ma Nanfen Formation. Detailed rock magnetic examination, the presence of magnetic reversals and the distinguishable characteristic remanent magnetization isolated from different parts of the section support the interpretation that the remanence is primary. Integrated with cyclostratigraphic age models, these quasi‐continuous data document a rapid paleolatitudinal drift of the NCC from mid‐to high‐latitudes at ∼28 cm/yr. The average pole shift rate of ∼5.4°/Ma during deposition of the Jingeryu Formation represents a TPW event preceding the ca. 1,109–1,083 Ma volcanism within the North American Midcontinent Rift. This newly identified short‐duration TPW episode (∼9.3 Ma duration) likely operated independently from the long‐term (ca. 1,165–1,015 Ma) inertial interchange TPW. We interpret this rapid TPW as Earth's rotational response to transient solid Earth mass redistribution during the Nuna–Rodinia supercontinent transition. Mass anomalies arising from widely distributed mafic dike swarms, subduction‐related magmatism, and accretionary orogenies may have contributed to this rapid TPW event. Critically, validating this global event requires more high‐resolution paleomagnetic records from temporally precisely coeval sections in other continental blocks.

A new paleomagnetic study is carried out on the ca. 1150 Ma mafic dykes from the North China Craton (NCC). After stepwise thermal demagnetization, most samples yielded two components. The low-temperature component directs north and down with intermediate inclination, which is interpreted as a viscous remanent magnetization of the present magnetic field. The high-temperature component (HC) directs east and down with steep inclination. Positive baked-contact tests and a reversal test suggest the HC is primary. Combined with the relevant paleomagnetic data previously published (Hou et al., 2009; Wang et al., 2020), a new pole is calculated from more than thirty high-quality virtual geomagnetic poles. The pole has averaged out the paleo-secular variation and is different from any younger paleomagnetic poles of the NCC. The pole places the NCC in a mid-latitude region. Combined with the reported 1230-780 Ma paleomagnetic poles from NCC and Laurentia, the new results suggest the two continents assembled during ca. 1150–1110 Ma at high-latitude region. They then together moved to low-latitude region and merged with Amazonia, Baltica, Kalahari to become a part of Rodinia.

We present new rock magnetic and paleomagnetic results from late Mesoproterozoic carbonate successions of the Jingeryu Formation (Fm) in the northern North China craton (NCC). Rock magnetic experiments, including thermomagnetic susceptibility curves, isothermal remanent magnetization (IRM) and thermal demagnetization of three-axis IRM, carried out for representative samples from the Jingeryu Fm indicate that both hematite and magnetite are abundant in the purplish-red limestone in the lower part of strata and the magnetic carriers of the pale blue limestone in the upper part are magnetite grains. For most samples subjected to stepwise thermal demagnetization, a high-temperature component (HTC) was isolated after removing a low-temperature component of viscous magnetic remanence acquired in recent geomagnetic fields. The HTC is characterized by steep inclinations, whose primary nature is supported by the presence of geomagnetic reversals. The similarities in paleomagnetic results and the correlatable lithologic sequence support that the Jingeryu Fm, the Nanfen Fm in the eastern Liaoning region in northeastern NCC and the Xinxing Fm in the Xuzhou region in southeastern NCC are correlative strata deposited in the polar region. Recently published radiogenic isotopic results constrain the depositional age of the Nanfen and Xinxing formations around ca. 1.1 Ga. Those high-latitude carbonate rocks widely distributed in the NCC predict an extraordinary climate condition around ca. 1.1 Ga.