The late Mesozoic closure of the Mongol‐Okhotsk Ocean (MOO) is critical for understanding the tectonics of East Asia. There is a considerable mismatch (~40 million years) between the timing of MOO ...closure based on paleomagnetic data and geological evidence. We review paleomagnetic data from Mongolia, Siberia, and North China and argue that previously published apparent polar wander paths (APWPs) for North China and Siberia are insufficient to constrain the timing of MOO closure. Our new analysis incorporates newly published paleomagnetic data from North China and a refined geochronology for the key Siberian poles. We combine this with an updated global APWP incorporating large‐scale Jurassic true polar wander and argue that the MOO was closed by the Middle Jurassic. This temporal shift is compatible with geology‐based models. The Middle Jurassic reconstruction of Eurasia suggests that the East Asian blocks had become a quasi‐rigid part of Pangea prior to breakup.
Plain Language Summary
A wide, eastward‐opening ocean, known as the Mongol‐Okhotsk Ocean (MOO), lay between Siberia and Mongolia during Paleozoic and Mesozoic time (~250–130 Ma). Geological data and tectonic models posit that the MOO was nearly closed by the Middle Jurassic (~174 Ma), whereas paleogeographic interpretations based on paleomagnetic data indicate a large gap of 1,000–3,000 km between Siberia and Mongolia in the Late Jurassic (~164–145 Ma). In general, the paleomagnetic data obtained from North China, Mongolia, and Siberia lack proper age control needed to resolve this conundrum. Based on newly published paleomagnetic data from North China and a critical selection of data from Siberia, this work argues that the MOO was closed by the Middle Jurassic and brings harmony to these previously conflicting data sets.
Key Points
Paleomagnetic data from the North China‐Amuria block and Siberia are reviewed and analyzed
Paleomagnetic analysis suggests a closure of the Mongol‐Okhotsk Ocean by the Middle Jurassic that is compatible with geological evidence
East Asian blocks formed a quasi‐rigid part of Pangea by the Middle Jurassic
Although the axial and dominant geocentric character of the Earth's magnetic field means that paleolongitude is indeterminate, paleomagnetism is otherwise the only truly quantitative method available ...to the Earth scientist for constraining paleogeography and reconstructing the kinematic evolution of continental blocks. During the past half-century numerous paleomagnetic results have provided substantial quantitative constraints on the origin and tectonic evolution of the major tectonic divisions now comprising Eastern Asian. In this paper we first assess the available Early Paleozoic to Early Cretaceous paleomagnetic results from the South China, North China, and Tarim blocks using internationally-recognized reliability criteria. We then construct a running mean through a 20 Ma window by weighting the poles according to their Q-factors and fit a spherical spline with smoothing factor of 300 to derive apparent polar wander (APW) paths for these three major blocks during this Early Paleozoic to Late Mesozoic time interval. Together with Late Paleozoic to Early Mesozoic paleomagnetic poles from the Qaidam, Qiangtang, Lhasa, Sibumasu, Indochina, and some other smaller blocks/terranes of East Asia, we produce a series of paleogeographic reconstructions for these major blocks and lesser terranes of East Asia between mid-Ordovician and late Jurassic times (~460–160 Ma) which, although based primarily upon paleomagnetic evidence, aim to embrace the geological constraints. Finally, we discuss the current evidence for closure times of the Paleo-Asian, Mianlue, and East Paleo-Tethyan oceans which incorporate fundamental issues concerning the formation of the East Asian continental collage and collision with the northern main body of the Pangean supercontinent. We use the collective evidence to argue that these major paleo-oceans had closed by the Late Triassic, and that the East Asian sector of the supercontinent had united to become an integral part of Pangea by that time (~220 Ma).
The evolution of the Neotethyan realm played an important role in shaping the Phanerozoic paleogeographic framework of Earth, as well as the formation of the Tibetan Plateau. However, there is ...considerable debate regarding the timing of the opening and initial phases of subduction of the Neotethys Ocean. The Gangdese magmatic belt is located along the southern margin of the Lhasa terrane in southern Tibet and was formed during the subduction of Neotethyan oceanic lithosphere. In this paper, we discuss a Late Triassic cumulate appinite suite along the southern margin of the Gangdese magmatic belt. The appinite suite exhibits a cumulate structure, with hornblende and plagioclase being the primary mineral phases. Isotopic data indicate a hydrous magma source derived from the mantle wedge that was modified by slab dehydration. Geochemical discriminators suggest that the appinite suite was formed in an intra-oceanic arc setting with crystallization ages of ca. 220-213 Ma. Hornblende, hornblende-plagioclase, and ilmenite geothermometers yielded crystallization temperatures of 750-900 °C for the appinite. Hornblende and hornblende-plagioclase geobarometers yielded emplacement depths between 14.5 and 19.5 km, which is consistent with arc-related cumulates. The occurrence of this appinite constitutes a line of evidence for intraoceanic arc magmatism that was coeval with similar magmatism in Turkey; this suggests that there was a vast east-west intra-oceanic subduction system within the Neotethys. A pre-Middle Triassic opening of the Neotethys would be required to explain the vastness of this subduction system. Our research provides a robust constraint for evaluating the Mesozoic framework of the Neotethyan realm and the evolutionary history of the Gangdese magmatic belt in southern Tibet.
Paleocene lavas of the Dianzhong Formation preserved in the Linzhou Basin of South Tibet provide a unique opportunity to constrain the initial geometry of the India‐Asia collision; however, earlier ...studies argued a complex magnetic signature resulting from thermal and/or chemical remagnetizations. To better characterize the remanences obtained from the Dianzhong lavas, we carried out an intraformational conglomerate test on a previously‐studied section in the Linzhou Basin. The positive conglomerate test suggests that the characteristic remanences reported from the Dianzhong Formation are primary. The updated Paleocene pole confirms a paleolatitude of 6.7° ± 4.4°N for the Lhasa terrane and positions the southern margin of Asia in the equatorial humid belt. An initial collision, between India, Asia and an intra‐oceanic arc in the equatorial humid belt, may have intensified silicate weathering and resulted in an extra consummation of carbon dioxide, which contributes to a long‐term cooling of the Earth during the Cenozoic.
Plain Language Summary
The locus of the initial India‐Asia collision can be constrained using paleomagnetic studies on the Paleocene volcanics from the Linzhou Basin, South Tibet. However, the primary nature of the magnetic signature previously reported from the Dianzhong Formation was questioned. This study carries out an intraformational conglomerate test collected from the middle part of the Dianzhong Formation. The stable remanences isolated from a layer of intercalated lava cobbles yield a random distribution in contrast to the well‐grouped directions obtained from the over‐ and underlying lava layers resulting in a positive conglomerate test. We therefore argue for a primary nature for the characteristic remanence recorded by the Dianzhong lavas from the Linzhou Basin. Our study confirms a low latitude of ∼7°N, that is, within the equatorial humid belt, for the southern margin of Asia during ∼64–60 Ma. An initial low‐latitude collision between India and Asia is critical for understanding the tectonic and climatic significance of the India‐Asia collision.
Key Points
Characteristic remanences reported from the Dianzhong lavas in the Linzhou Basin are primary in origin
The updated Paleocene pole confirms a low latitude of ∼7°N for the Lhasa terrane
An initial collision between India, Asia and an oceanic arc in the equatorial humid belt may contribute to the Cenozoic cooling of the Earth
We report a paleomagnetic study of Paleocene marine sediments in the Gamba area of the Tethyan Himalayan terrane, southern Tibet, which aims to accurately locate the position of the northern margin ...of Greater India and further constrain timing of initial contact between India and Asia. Following detailed rock magnetic and paleomagnetic experiments on a total of 675 drill-core samples collected from the Zongpu and Upper Jidula formations, characteristic remanent magnetizations (ChRMs) were successfully isolated from most samples following alternating field (AF) or integrated thermal and AF demagnetization. The ChRMs are of dual polarity and pass fold and reversal tests indicating a pre-folding origin. Together with detailed biostratigraphic investigation of the sampling section, a magnetic polarity sequence is constructed from data at 167 sampled horizons and satisfactorily correlates with polarity chrons C24r to C27r dating the Zongpu Formation between ~
56.2 and 61.8
Ma on the geomagnetic polarity time scale. The ChRM directions from the Zongpu Formation are grouped stratigraphically into 33 sites and yield two paleopoles of 71.6°N, 277.8°E (A
95
=
2.5°) and 67.3°N, 266.3°E (A
95
=
3.5°) for the time intervals comprising 56 to 59
Ma and 59 to 62
Ma, respectively. These new paleopoles imply that the Tethyan Himalayan terrane was sited at low latitudes in the Northern Hemisphere during the interval ~
62–56
Ma, suggesting that initial contact between the Tethyan Himalaya and Lhasa terranes was established before 60.5
±
1.5
Ma, and very likely occurred near the Cretaceous–Tertiary boundary, at least in the central part of the suture zone. The results also indicate that at least 1500
±
480
km of post-collisional crustal shortening occurred within the Himalayas. From the analysis of available paleomagnetic data obtained on both sides of the suture zone, we propose a conceptional collision model for the India–Asia collision.
► The Zongpu Formation in the area of Gamba was dated between ~
56.2 and 61.8
Ma. ► The timing of India–Asia collision was constrained to be 60.5
±
1.5
Ma to 68
±
3
Ma. ► The northern extension of Greater India was constrained to be at least 1500
±
480
km. ► The Main Central Thrust (MCT) was inferred to have initiated as early as ~
35
Ma.
A major uncertainty in the paleogeography of Pangea is the position of the East Asian blocks (EABs). Climate models developed for Pangea with the EAB's in an isolated position aided in the ...development of the mega-monsoon hypothesis. We report paleomagnetic and geochronological data from late Triassic dykes and sills in North China aiming to refine the paleogeography of Pangea. The high-quality late Triassic paleomagnetic pole (33.5° N, 136.1° E with A=956.8°) positions the EABs at 75.6° ± 6.8° N at ∼220 Ma using Beijing as a reference site. This is ∼50° further north than previously suggested. Along with robust geological evidence, our study reveals a full amalgamation between the EABs and Pangea by ∼220 Ma. The updated paleogeography of Pangea based on our new reconstruction is compatible with a zonal climate model, which obviates the need for the Pangean mega-monsoon hypothesis.
•A new paleomagnetic pole of ∼220 Ma was reported from the sills and dykes in North China.•The Eastern Asian blocks (EAB) was located at 75.6° ±6.8° N at ∼220 Ma using Beijing as a reference site.•A full amalgamation between the EABs and Pangea was established by ∼220 Ma.•The updated late Triassic paleogeography suggests a zonal climate for Pangea.
In this work, a novel core-shell structure material, NiFe layered double hydroxide (NiFe LDH) loaded on SiO2 microspheres (SiO2@NiFe LDH), was synthesized by a one-step hydrothermal method, and the ...spontaneous electrostatic self-assembly process. The morphology, structure, and microwave absorption properties of SiO2@NiFe LDH nanocomposites with different NiFe element ratios were systematically investigated. The results show that the sample of SiO2@NiFe LDH-3 nanocomposite has excellent microwave absorption properties. It exhibits broadband effective absorption bandwidth (RL < −10 dB) of 8.24 GHz (from 9.76 GHz to 18.0 GHz) and the reflection loss is −53.78 dB at the matched thickness of 6.95 mm. It is expected that this SiO2@NiFe-LDH core-shell structural material can be used as a promising non-precious, metal-based material microwave absorber to eliminate electromagnetic wave contamination.
To better understand the tectonic evolution of West Junggar in the western Altaids, we have conducted a combined paleomagnetic and geochronological study on Late Devonian (D3), Late Carboniferous ...(C2) and Early Permian (P1) successions from the Tacheng Basin, northwest of China. Both primary and secondary characteristic remanent magnetization components have been successfully isolated and yield three reliable paleomagnetic poles of C2 and Late Permian (P2) ages. The C2 and P2 poles reveal a significant clockwise rotation of 35.6°±10.4° which is comparable to the rotation deduced in the western part of the Chingiz Range during the time interval C2 to P2. Similar rotation patterns for the two units suggest that the Chingiz–West Junggar has remained as a quasi-rigid block by the P2 time and constituted the northeast limb of the Kazakhstan Orocline. The differential rotation of ca. 25° to 30° deduced between the northeast and middle limbs of the Kazakhstan Orocline further suggests that at least a part of the curvature of the Balkhash Arc was acquired during the C2 to P2 interval and was a continuation of the middle Paleozoic oroclinal bending. Moreover, the C2 poles for West Junggar and the Junggar Block are significantly different while the P2 ones almost overlap supporting the view that final closure of the Balkhash–Junggar Ocean occurred during the C2 to P2 interval. On the other hand, a large-scale counterclockwise rotation of ca. 80° to 90° is observed in West Junggar and Junggar relative to the western part of the Chingiz Range since the P2 time, and this rotation probably represents an important intra-continental deformation within the western part of the Altaids. A reconstruction of the Paleo-Asian Ocean has been proposed in which the Kazakhstan Orocline was emphasized by using the paleomagnetic results and geological evidence.
Display omitted
•Three reliable late Paleozoic paleopoles are reported from West Junggar (WJ).•Evolution of WJ is characterized by oroclinal bending followed by wrench tectonics.•Closure of the Junggar Ocean occurred between Late Carboniferous and Late Permian.
The timing, kinematics, and geodynamic evolution of the India-Asia continental collision are crucial to understanding the geological and geomorphological evolution of the Himalayan-Tibetan orogen. ...However, the debate over how and when the collision occurred persists due to disputes concerning the reliability of paleomagnetic data obtained on both sides of the suture zone. This paper presents a comprehensive analysis and evaluation of paleomagnetic studies to address this controversial issue. The study focuses on well-preserved Cretaceous-Paleocene rocks from the Lhasa and Tethyan Himalaya (TH) terranes over the past two decades. We conclude that: (1) the paleomagnetic data of the Linzizong Group of the Lhasa Terrane and the Zongpu Formation of the TH are in their primary origin and can be used for tectonic reconstruction; (2) the Tethys Himalaya Basin (THB) was generated due to the rifting of the TH from Greater India before the Late Cretaceous; (3) the southern margin of Asia was aligned in the NW-SE direction before the India-Asia collision. The study suggests a quasi-synchronous multi-stage collision where the TH collided with the Trans-Tethyan subduction system in Late Cretaceous-Early Paleocene times (∼65 Ma), followed by collision with Asia at 56–59 Ma. Finally, the India Craton collided with the TH, resulting in the synchronous closure of the THB at approximately 40 Ma.
A neoteric round sieve diatomite (De) decorated with sea-urchin-like alpha-type iron trioxide (α-Fe2O3) synthetics was prepared by the hydrothermal method and further calcination. The results of the ...electromagnetic (EM) parameters of α-Fe2O3-decorated De (α-Fe2O3@D) showed that the minimum reflection loss (RLmin) of α-Fe2O3@D could reach −54.2 dB at 11.52 GHz and the matched absorber thickness was 3 mm. The frequency bandwidth corresponding to the microwave RL value below −20 dB was up to 8.24 GHz (9.76–18 GHz). This indicates that α-Fe2O3@D composite can be a lightweight and stable material; because of the low density of De (1.9–2.3 g/cm3), the density of α-Fe2O3@D composite material is lower than that of α-Fe2O3 (5.18 g/cm3). We found that the combination of the magnetic loss of sea-urchin-like α-Fe2O3 and the dielectric loss of De has the most dominant role in electromagnetic wave absorption and loss. We focused on comparing the absorbing properties before and after the formation of sea-urchin-like α-Fe2O3 and explain in detail the effects of the structure and crystal shape of this novel composite on the absorbing properties.
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