High-temperature Magnetization Component Research Articles

Paleomagnetic study of terrigenous rocks of the Uryuk Formation in the Southern Urals

In order to obtain new paleomagnetic data on Vendian rocks in the Southern Urals, we studied the high-temperature magnetization component in sandstones of the Uryuk Formation, the carrier of which is hematite. The distinguished hematite vector in the collection of samples differs from the previously obtained intermediate-, intermediate-high-temperature magnetization component of magnetite, which is part of the same rocks. The average directions of the hematite component of magnetization of the Uryuk Formation were compared with the average directions of the overlying Basu Formation. The metachrony of the magnetite component and the synchrony of the hematite component are suggested.

First Results of the Intraformational Conglomerate Test of the Late Riphean Katav Formation (Southern Urals)

Detailed petrographic, electron-microscopic, and paleomagnetic studies were conducted on flatbedded synsedimentary carbonate breccias from three blocks of rocks (one block from Minyar, two blocks from Katav-Ivanovsk) to verify the ideas about the time of formation of the high-temperature component (HTC) of natural remanent magnetization (Jn) of limestones from the Upper Riphean Katav Formation, Southern Urals. Petrographic and electron-microscopic observations revealed that the composition of pebbles corresponds to that of the host matrix rocks, thus enabling the use of an intraformational conglomerate test. In all the studied blocks, the distribution of paleomagnetic directions for pebbles is generally chaotic, with the concentration parameter not exceeding 3. These test results meet the Graham criterion. The pebbles’ average Jn have a larger confidence oval and differ significantly from the matrix’s directions with a much smaller confidence oval. The Hodges-Ajne test was applied to the blocks from Katav-Ivanovsk. The Rayleigh test was used for the block from Minyar. The results obtained at this stage indicate that the HTC of magnetization of the Katav limestones may have a primary origin. If this is confirmed, the Katav Formation would be a good paleomagnetic record of the Earth’s Neoproterozoic history and provide valuable insights into the geomagnetic field behavior in the Late Precambrian.

New paleomagnetic data from the central Tethyan Himalaya refine the size of Greater India during the Campanian

Knowledge of the size of Greater India is critical to deciphering the geodynamic processes of the India-Asia collision, as the size of this landmass primarily determines the amount of continental subduction and crustal shortening. Recently, paleomagnetic data revealed the rapid drift of a Himalayan microcontinent (i.e., the Tibetan Himalaya) during ca. 75–61 Ma, which resulted in a triple-stage India-Asia collision scenario. This scenario implies a relatively small Greater India at 75 Ma (Late Cretaceous), but this hypothesis is only based on one high quality Campanian paleomagnetic pole from the eastern part of the Tethyan Himalaya. Here we report comprehensive petrographic, rock magnetic and paleomagnetic studies on Upper Cretaceous oceanic affinity red beds (CORBs) of the Chuangde Formation from the central part of the Tethyan Himalaya at 83.6°E longitude. These CORBs are characterized by multi-component magnetizations carried dominantly by detrital hematite, which retains a primary remanent magnetization. Accordingly, the high temperature magnetization components (585−690°C) were isolated by high-resolution thermal demagnetization. The new paleomagnetic data provide, after applying an inclination shallowing correction, a Campanian paleopole of 43.3°N/258.3°E, which places the central part of the Tethyan Himalaya at a paleolatitude of 16.7° ± 1.8°S at ca. 75 Ma. Comparison of this paleolatitude with the expected paleolatitude of India, using its apparent polar wander path, shows that the N-S extent of central Greater India was ∼910 km during the middle Campanian. Our paleomagnetic data are in agreement with balanced cross section reconstructions and seismologic interpretations of the India-Asia collision zone and provide additional support for the North India Sea hypothesis. The improved estimate of the size of Greater India has several implications for Indian continental crust behavior and results in an updated reconstruction of the India-Asia collision system in the Campanian.

Palaeomagnetism of the Vendian traps of Volyn, southwestern margin of the East European Platform, P. 2: magnetostratigraphy

We present new results of palaeomagnetic studies of the Vendian (Ediacaran) rocks of the Volyn Basalt Province revealed by six boreholes on the NW Ukraine. This is a continuation of previous studies of upper part of the Volyn series described by Bakhmutov et al. [2021]. In the recent works [Shcherbakova et al., 2020; Thallner et al., 2022], the results of palaeointensity determinations of the Volyn series basalts showed the ultra-low dipole moment of Earth’s magnetic field which coincident with other palaeomagnetic data for Ediacaran indicating an extremely weak geomagnetic field. Clear stratification and correlation of the basalt and tuff layers by magnetic parameters allow us to determine the magnetic field reversals throughout the stratigraphic succession of the Volyn series of about 400 m thick. In basalts, tuffs and baked contact rocks, a high-temperature characteristic component of remanent magnetization (ChRM) with all signs of primary magnetization have been isolated. For the directions of inclination of ChRM-components at least six magnetic polarity reversals were revealed. The geochronological ages of rocks is in the range of 580—545 Ma, but the errors in the age estimation are too large for separation of individual formations within the pulses of activity or differentiation of individual eruptions. Therefore the formation time of the entire stratum remains uncertain, and the key issue for interpretation of the magnetic polarity reversal frequency is the duration of accumulation of traps. Two possible interpretations of palaeomagnetic results are considered. In the first, which takes into account different stages of magmatic activity, the time interval of accumulation can be about 10 million years. Then the average frequency of geomagnetic inversions is close to mean for the Phanerozoic. We prefer the other interpretation when the formations of the Large Igneous Provinces have been occurred over a short time interval (e.g. 0.5 Myr). Taking into account the results of palaeointensity estimations for the same samples, which shown the extremely weak geomagnetic field, the hypothesis of the «hyperactivity» of the field with a frequency of at least 12 reversals per one million years on the end of the Ediacaran gain the additional confirmation.

An improved apparent polar wander path for southwest Japan: post-Cretaceous multiphase rotations with respect to the Asian continent

To construct the Mesozoic apparent polar wander path (APWP) for the inner arc of the southwestern Japanese islands (referred to as southwest Japan) and compare it to that of East Asia, a 110 Ma paleomagnetic pole for southwest Japan was determined. Mudstone and sandstone samples were collected from 16 sites for paleomagnetic analysis in the Lower Cretaceous Inakura Formation of the Inakura area in the central part of southwest Japan. A high-temperature magnetization component, with unblocking temperatures of 670–695 °C, was isolated from 12 sites of red mudstone. Of these, 11 sites revealed a primary remanent magnetization during the Early Cretaceous. The primary directions combined with the previously reported ones provide a new mean direction (D = 79.7°, I = 47.4°, α95 = 6.5°, N = 17), and a corresponding paleomagnetic pole that is representative of southwest Japan (24.6° N, 203.1° E, A95 = 6.8°). The Early Cretaceous paleomagnetic pole, together with the Late Cretaceous and Cenozoic poles, constitute a new APWP for southwest Japan. The new APWP illustrates a standstill polar position during 110–70 Ma, suggesting tectonic quiescence of this region. This standstill was followed by two large tracks during the Cenozoic. We interpret these tracks as clockwise tectonic rotations of southwest Japan that occurred twice during the Cenozoic. The earlier tectonic rotation occurred for a tectonic unit positioned below northeast China, the Liaodong and Korean Peninsulas, and southwest Japan (East Tan-Lu Block) during the Paleogene. The later rotation took place only under southwest Japan during the Neogene. Cenozoic multiphase rifting activity in the eastern margin of the Asian continent was responsible for the tectonic rotations that are observed from the paleomagnetic studies. Intermittent rifting may constitute a series of phenomena due to asthenospheric convection, induced by the growth of the Eurasian mega-continent in the Mesozoic.

Rock magnetism of ejected basaltic boulders from Lonar crater, India: Implications for the existence of a short‐lived impact‐generated weak magnetic field

AbstractThe continuous ejecta deposit around the rim of Lonar impact crater, central India, contains angular basaltic boulders of size ≤5 m. These boulders experienced varying level of shock between 2–30 GPa due to impact, as indicated by the extreme fracturing of these basaltic boulders, fragmentation of plagioclase and titanomagnetite constituents of these ejected boulders, and the presence of maskelynite in them. We measure some rock magnetic properties, e.g., NRM/χ (natural remanent magnetization [NRM]/bulk magnetic susceptibility [χ]), REM (=NRM/saturation isothermal remanent magnetization [SIRM] ratio expressed in %), and anisotropy of magnetic susceptibility (AMS) on 53 subsamples from 18 oriented drill cores of the shocked ejected basaltic boulders from the eastern half of ejecta deposit in the present study. The measured data are similar in many respects to our previous observations on Lonar crater rim shocked basalts (Arif et al. 2012b). For example, a small population of the ejected basaltic boulder samples show very high NRM/χ (between 378 and 989 Am−1; n = 7) and REM (between 1.5 and 7%; n = 4) and the AMS axes of these ejected basaltic boulders show triaxial distributions in stereographic projections. Moreover, some of the ejected basaltic boulders show higher values of squareness ratio (Mrs/Ms) and median destructive field (MDF) suggesting permanent changes in the intrinsic magnetic properties due to impact shock pressure. In stereographic plot, the high coercivity and high temperature (HC_HT) magnetization component of these ejected basaltic boulders are distributed in discrete clusters on the periphery of a small enveloping circle whose center (D = 108.0°, I = +69.2°) lies close to the HC_HT cluster of the crater rim shocked basalts. The center of this enveloping circle and the average HC_HT component of Lonar crater rim shocked basalts have the same statistical orientation, although the former has steeper dip. This distribution suggests the possibility that the ejected basaltic boulders, which were deposited during the modification stage of Lonar crater evolution, were magnetized in an impact‐induced magnetic field that was rapidly decaying just after the impact. Our present study suggests that the ejected basaltic boulders and Lonar crater rim shocked basalts experienced high shock pressure (≥2 GPa) magnetization during impact.

Paleomagnetism and provenance of the lower Cambrian sedimentary rocks of the Udzha Uplift (north of the Siberian platform)

Lately, data have been increasingly indicating an unusual, abnormal state of the magnetic field at the boundary of the Precambrian and Phanerozoic. This fact significantly limits the possibility of employing the paleomagnetic approach for creating various paleoreconstructions in this time interval, and it allows a better understanding of the evolution of the Earth’s magnetic field. Until recently, there was no exact binding of Lower Cambrian sections bearing an anomalous paleomagnetic record to the chronostratigraphical chart, which made it impossible to obtain adequate estimates of the duration of the anomalous state of the magnetic field. In this study we present the results of a paleomagnetic study of the Lower Cambrian terrigenous-carbonate rocks of the Udzha and Anabar Uplifts (Emyaksa and Medvezh Formations). New evidence has been obtained of the anomalous paleomagnetic record in these rocks, which manifests itself in the objective existence of two significantly different directions of the high-temperature magnetization components, the formation of which cannot be explained by a later remagnetization. U-Pb dating of detrital zircons constrains the maximum depositional age of the Manykay and Emyaksa Formations to ~520 Ma, which, in combination with the faunistic characteristic of the upper part of the Emyaksa Formation, points to the Atdaban age of studied successions. The age constraints obtained indicate a specific paleomagnetic record, and due to the peculiarities of the generation of the geomagnetic field of the terminal Precambrian–Early Cambrian Period, trace the paleomagnetic record back to the Atdaban age, inclusive.

A Paleomagnetic Study of Sariolian Conglomerates of the Onega Structure of the Karelian Protocraton: The Problem of Global Paleoproterozoic Remagnetization

A paleomagnetic study of Sariolian (2.4–2.3 Ga) conglomerates of the Onega structure distinguished two characteristic magnetization components. The average direction of the mid-temperature magnetization component has a concentrated distribution and coincides with the direction of the Svecofennian remagnetization within the Karelian protocraton. The directions of high-temperature magnetization components distinguished in conglomerates show a wide scatter of values that is evidence of the primary origin of this magnetization component. Two clusters of high-temperature components associated not only with the protolith composition, but also with the different conditions of rock transformation, in particular their fluid saturation, are distinguished.

Paleomagnetic studies sariolyiski conglomerates of the Onega structure of the Karelian craton: Paleoproterozoic global remagnetization

As a result of paleomagnetic studies Sariolian 2,4–2,3 Ga conglomerates of the Onega basin of the Karelian protoctaton, two characteristic components of magnetization have been separated. Mean direction of the medium-temperature component has a heap distribution and coincides with mean direction of the Svecofennian remagnetization within the Karelian protocraton. The directions of high-temperature magnetization components isolated in conglomerates have a significant spread, which indicates the primary nature of this magnetization component. Two clusters of high-temperature components associated not only with the composition of protolites, but also with different conditions of rock transformations, including their fluid saturation, are distinguished.

A new Siberian record of the ∼1.0 Gyr-old Maya superchron

We report new magnetostratigraphic data from the Late Mesoproterozoic Linok Formation consisting of clayed carbonates, together with paleomagnetic data from the Neoproterozoic carbonate Sukhaya Tunguska, Burovaya and Turukhansk formations, located in the Turukhansk region (northwestern Siberian platform). We also re-analyzed demagnetization data previously obtained from the Derevnya Formation. Paleomagnetic analyses revealed up to four magnetization components. First, a steep-inclination component, likely of recent origin, is isolated in all sections in the low temperature range. Second, a magnetization is recovered in most samples between ∼250 °C and ∼350–400 °C. It shows a single magnetic polarity and is interpreted as a remagnetization acquired during the Kiaman Permo-Carboniferous reverse superchron. Third, a magnetization component is isolated between ∼400 °C and ∼500 °C in samples from the Burovaya and Turukhansk formations. This component is interpreted as a remagnetization that occurred before the end of the Neoproterozoic. A fourth high-temperature (HT) magnetization component is observed up to ∼575 °C in samples from the Linok and Burovaya formations and up to ∼680 °C for those of the Derevnya and Turukhansk formations. A series of magnetic polarity reversals is observed in the lower and middle parts of the Linok Formation, whereas a single polarity interval is found in its upper part. The syn-depositional origin of this magnetization is attested by positive reversal, conglomerate and fold tests. The HT magnetization component isolated in the Derevnya and Burovaya formations shows a single magnetic polarity. Its primary origin is supported by the fact that the Derevnya and Burovaya HT mean directions are positioned in the continuity of the directional evolution observed through the Linok Formation. It is further constrained by very consistent Late Mesoproterozoic to Early Neoproterozoic apparent polar wander paths obtained from different regions of the Siberian platform. A single magnetic polarity reversal is observed in a ∼40 m-thick section of the Turukhansk Formation. The HT directions found in the upper part of the Linok Formations, over a stratigraphic thickness of ∼200 m, and in the Derevnya and Burovaya formations strengthen the existence of the normal polarity Maya superchron around 1.0 Ga, at the transition between the Mesoproterozoic and the Neoproterozoic.

Systematics of Early Cambrian Paleomagnetic Directions from the Northern and Eastern Regions of the Siberian Platform and the Problem of an Anomalous Geomagnetic Field in the Time Vicinity of the Proterozoic–Phanerozoic Boundary

Representative paleomagnetic collections of Lower Cambrian rocks from the northern and eastern regions of the Siberian platform are studied. New evidence demonstrating the anomalous character of the paleomagnetic record in these rocks is obtained. These data confidently support the hypothesis (Pavlov et al., 2004) that in the substantial part of the Lower Cambrian section of the Siberian platform there are two stable high-temperature magnetization components having significantly different directions, each of which is eligible for being a primary component that was formed, at the latest, in the Early Cambrian. The analysis of the world’s paleomagnetic data for this interval of the geological history shows that the peculiarities observed in Siberia in the paleomagnetic record for the Precambrian–Phanerozoic boundary are global, inconsistent with the traditional notion of a paleomagnetic record as reflecting the predominant axial dipole component of the geomagnetic field, and necessitates the assumption that the geomagnetic field at the Proterozoic–Phanerozoic boundary (Ediacaran–Lower Cambrian) substantially differed from the field of most of the other geological epochs. In order to explain the observed paleomagnetic record, we propose a hypothesis suggesting that the geomagnetic field at the Precambrian–Cambrian boundary had an anomalous character. This field was characterized by the presence of two alternating quasi-stable generation regimes. According to our hypothesis, the magnetic field at the Precambrian–Cambrian boundary can be described by the alternation of long periods dominated by an axial, mainly monopolar dipole field and relatively short epochs, lasting a few hundred kA, with the prevalence of the near-equatorial or midlatitude dipole. The proposed hypothesis agrees with the data obtained from studies of the transitional fields of Paleozoic reversals (Khramov and Iosifidi, 2012) and with the results of geodynamo numerical simulations (Aubert and Wicht, 2004; Glatzmayer and Olson, 2005; Gissinger et al., 2012).

Passive crustal clockwise rotational deformation of the Sichuan Basin since the Miocene and its relationship with the tectonic evolution of the fault systems on the eastern edge of the Tibetan Plateau

Research Article| August 15, 2018 Passive crustal clockwise rotational deformation of the Sichuan Basin since the Miocene and its relationship with the tectonic evolution of the fault systems on the eastern edge of the Tibetan Plateau Yabo Tong; Yabo Tong † 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China2Key Laboratory of Paleomagnetism and Tectonic Reconstruction, the Ministry of Land and Resources, Beijing 100081, China †tyb816@163.com Search for other works by this author on: GSW Google Scholar Yujun Sun; Yujun Sun 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Zhonghai Wu; Zhonghai Wu 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Changping Mao; Changping Mao 3School of Earth Sciences and Engineering, Hohai University, Nanjing 210098, China Search for other works by this author on: GSW Google Scholar Junling Pei; Junling Pei 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China2Key Laboratory of Paleomagnetism and Tectonic Reconstruction, the Ministry of Land and Resources, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Zhenyu Yang; Zhenyu Yang 4College of Resources, Environment and Tourism, Capital Normal University, Beijing 100048, China Search for other works by this author on: GSW Google Scholar Zongwen Pu; Zongwen Pu 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Yue Zhao; Yue Zhao 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China2Key Laboratory of Paleomagnetism and Tectonic Reconstruction, the Ministry of Land and Resources, Beijing 100081, China Search for other works by this author on: GSW Google Scholar Hao Xu Hao Xu 1Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Search for other works by this author on: GSW Google Scholar GSA Bulletin (2019) 131 (1-2): 175–190. https://doi.org/10.1130/B31965.1 Article history received: 07 Nov 2017 rev-recd: 13 Jun 2018 accepted: 15 Jul 2018 first online: 15 Aug 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Yabo Tong, Yujun Sun, Zhonghai Wu, Changping Mao, Junling Pei, Zhenyu Yang, Zongwen Pu, Yue Zhao, Hao Xu; Passive crustal clockwise rotational deformation of the Sichuan Basin since the Miocene and its relationship with the tectonic evolution of the fault systems on the eastern edge of the Tibetan Plateau. GSA Bulletin 2018;; 131 (1-2): 175–190. doi: https://doi.org/10.1130/B31965.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We conducted a paleomagnetic study of the Upper and Lower Cretaceous red-beds in the Yibin area, in the southern part of the Sichuan Basin. High-temperature magnetic components were isolated between 580 °C and 695 °C. An ambiguous fold test resulted in alternative interpretations of the Cretaceous primary magnetization or Oligocene-Miocene remagnetization. Nevertheless, the two different interpretations of the paleomagnetic data consistently show that the Yibin area on the southern edge of the Sichuan Basin experienced clockwise rotation, relative to the eastern edge of the South China Block and Europe. A comparison with the Cretaceous and Paleogene paleomagnetic data from the northern and western part of the Sichuan Basin indicates that, except for the southeastern corner of the Sichuan Basin, the crust of the Sichuan Basin generally experienced significant clockwise rotational deformation since the early Miocene. The northeastward escape of the Songpan-Ganzi Terrane and the counterclockwise rotation of the Yangtze Fold Belt applied a right-lateral shear stress to the region surrounding the Sichuan Basin since the Miocene, which induced the passive crustal clockwise rotational deformation of the Sichuan Basin. Subsequently, the non-synchronous crustal rotational deformation of the Sichuan Basin and its surrounding blocks controlled the tectonic evolution of their boundary tectonic belts: for example, the right-lateral strike-slip movement of the Longmenshan fault belt and the southeastward extension of the Xianshuihe strike-slip fault since the Miocene. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Relationship Between Orogenic Gold Mineralization and Crustal Shearing Along Ailaoshan‐Red River Belt, Southeastern Tibetan Plateau: New Constraint From Paleomagnetism

AbstractA new perspective on the relationship between orogenic gold mineralization and crustal shearing is presented in this case study on the gold deposits along Ailaoshan‐Red River shear zone (ARSZ), southeastern Tibetan Plateau. The sinistral ductile shearing along the zone occurred from ca. 31 to 17 Ma resulting in a displacement of ~1,000 km. A series of orogenic gold deposits, represented by the Zhenyuan and Chang'an deposits, occur on western margin of the ARSZ. The timing of mineralization and its relationship to shearing continues to be debated despite extensive geological and geochemical studies. Here we try to clarify this issue by using paleomagnetism to constrain the paleolatitude of mineralized rocks. High temperature magnetization components were isolated from the mineralized rocks, and they record modification by ore‐forming fluid. Their magnetization yields a paleolatitude of 19.9° ± 3.6°N for the Zhenyuan deposit and 16.2° ± 2.9°N for the Chang'an deposit. The paleolatitudes from these deposits are similar to those of ca. 20 Ma strata (19.0° ± 3.6°N), deposited after the large‐scale shearing. By contrast, they differ significantly from the paleolatitude obtained from ca. 130 to 40 Ma strata (28.4° ± 1.1°N), which formed long before the onset of large‐scale shearing. These observations imply that the orogenic gold mineralization occurred after the main offset and associated ductile deformation of the ARSZ. Gold mineralization is thought to be related to ore‐forming fluids and metals derived from the subcrust, rather than from fluids released from shearing‐induced metamorphism of regional strata.

From Chips to Modules: Tackling the High Temperature Design Challenge

Abstract The paper discusses the challenges of high temperature electronic design and the solutions offered to designers to build reliable systems for harsh environments. First it explains why robust silicon and packaging technologies are equally important to design and manufacture reliable high temperature integrated circuits (ICs). Applying the necessary qualification procedures is also critical. Finally, understanding high temperature specific systems requirements is also important for high temperature ICs vendors in order to offer the right features and the necessary support. As an example, offering simple functions like transistors, logic gates or amplifiers could look basic but is mandatory to build systems and often neglected by large semiconductor companies. Also, supporting modules manufacturers with a bare die offer is critical because, in some cases, hybrid assemblies are the only way to reach size, temperature and reliability requirements. Finally, for more complex functions, e.g. DC-DC Converters or High Voltage Gate Drivers, offering reference designs taking into account the specificities of high temperature passive and magnetic components is mandatory to support reliable modules or systems design.

Paleomagnetism and dating of a thick lava pile in the Permian Bakaly formation of eastern Kazakhstan: Regularities and singularities of the paleomagnetic record in thick lava series

Paleomagnetic results on thick lava series are among the most important sources of information on the characteristics of ancient geomagnetic fields. Most paleo-secular variation data from lavas (PSVL) are of late Cenozoic age. There are far fewer results from lavas older than 5Ma. The Central Asia Orogenic Belt that occupies several million square kilometers in Asia is probably the world’s largest area of Paleozoic volcanism and is thus an attractive target for PSVL studies. We studied a ca. 1700m thick lava pile in eastern Kazakhstan of Early Permian age. Magmatic zircons, successfully separated from an acid flow in this predominantly basaltic sequence, yielded an Early Permian age of 286.3±3.5Ma. Oriented samples were collected from 125 flows, resulting in 88 acceptable quality flow-means (n⩾4 samples, radius of confidence circle α95⩽15°) of the high-temperature magnetization component. The uniformly reversed component is pre-tilting and arguably of a primary origin. The overall mean direction has a declination=242.0° and an inclination=−56.2° (k=71.5, α95=1.8°; N=88 sites; pole at 44.1°N, 160.6°E, A95=2.2°). Our pole agrees well with the Early Permian reference data for Baltica, in accord with the radiometric age of the lava pile and geological views on evolution of the western part of the Central Asia Orogenic Belt. The new Early Permian result indicates a comparatively low level of secular variation especially when compared to PSVL data from intervals with frequent reversals. Still, the overall scatter of dispersion estimates that are used as proxies for SV magnitudes, elongation values and elongation orientations for PSVL data is high and cannot be fitted into any particular field model with fixed parameters. Both observed values and numerical simulations indicate that the main cause for the scatter of form parameters (elongation values and elongation orientations) is the too small size of collections. Dispersion estimates (concentration parameter and standard angular deviation) are more robust, and their scatter stems from other sources, which may include non-stochastic features of datasets like clusters, loops etc., or non-stationary behavior of secular variation magnitude over time intervals of many million years.

Paleomagnetism of Upper Cretaceous red-beds from the eastern Qiangtang Block: Clockwise rotations and latitudinal translation during the India–Asia collision

High-temperature magnetization component was isolated between 600°C and 680°C from Upper Cretaceous red-beds in the Mangkang area, in the eastern end of the Qiangtang Block, Tibetan Plateau. The tilt-corrected site-mean direction is Ds/Is=51.3°/56.1°, with k=31.0 and α95=6.5°, corresponding to a paleolatitude of 36.7±6.7°N. Positive fold and reversal tests indicate a primary magnetization. Inclination shallowing tests show that inclination bias is not present in the Upper Cretaceous red-beds of the Qiangtang Block that might induce through depositional and/or compaction process. However, previous paleomagnetic data obtained from Cretaceous and Paleocene–Eocene volcanic rocks show that the paleolatitudes of the Lhasa Block were 17.1±3.3°N and 22.3±4.4°N, respectively, and 28.7±3.7°N for the central Qiangtang Block yielded from Eocene volcanic rocks. These results show that there was a ∼10° latitudinal discrepancy between the Lhasa Block and Qiangtang relative to Eurasia. However, the Mangkang area of the southeastern Qiangtang Block experienced ∼3.2±7.8° to 7.3±5.2° southward extrusion and ∼40° clockwise rotational movement relative to Eurasia since the Cretaceous, which coincided with the Early Cenozoic rotational extrusion of the Indochina and Shan-Thai Blocks. The crustal deformation in the eastern Qiangtang Block should have been caused by the Indian Plate penetrating into Eurasia in the eastern end of Tibetan Plateau and the formation of the Eastern Himalaya Syntaxis since the Oligocene/Miocene.

The Cenozoic rotational extrusion of the Chuan Dian Fragment: New paleomagnetic results from Paleogene red-beds on the southeastern edge of the Tibetan Plateau

Paleomagnetic studies were conducted on the Eocene and Oligocene strata at the western part of the Chuan Dian Fragment in order to describe the crustal deformation induced by continuous penetration of the Indian plate into Eurasia during the late Cenozoic. High-temperature magnetic components with unblocking temperatures of ~680°C were isolated, and positive fold and/or reversal tests reveal the primary nature of the magnetization. The tilt-corrected site-mean directions obtained from the Oligocene and middle-early Eocene strata are, respectively, Ds=200.9°, Is=−31.3°, k=52.8, α95=7.7° and Ds=29.7°, Is=32.0°, k=44.9, α95=5.6°. Comparison of these results with previous paleomagnetic data from the Chuan Dian Fragment shows that the western and central parts of the Chuan Dian Fragment experienced ~20° integral clockwise rotation relative to East Asia since the middle Miocene. However, the eastern part of the Chuan Dian Fragment has experienced different rotational deformation relative to East Asia since the Pliocene, because of the intense regional crustal deformation and activity on fault systems. The eastern boundary of the Chuan Dian Fragment was bounded by the Yuanmou-Luezhijiang left lateral strike-slip fault prior to the Pliocene, and then substituted by the Xiaojiang left lateral strike-slip fault since the Pliocene, due to the eastwards spreading of the clockwise rotational movement of the Chuan Dian Fragment. The evolutionary characteristics of the Ailaoshan-Red River and Xianshuihe-Xiaojiang strike-slip faults were controlled by the difference between the clockwise rotational extrusion velocities of the Chuan Dian Fragment and the Indochina Block.

No nebular magnetization in the Allende CV carbonaceous chondrite

Magnetic fields in the solar nebula may have played a central role in mass and angular momentum transport in the protosolar disk and facilitated the accretion of the first planetesimals. Thought to be key evidence for this hypothesis is the high unblocking-temperature, randomly oriented magnetization in chondrules in the Allende CV carbonaceous chondrite. However, it has recently been realized that most of the ferromagnetic minerals in Allende are products of secondary processes on the parent planetesimal. Here we reevaluate the pre-accretional magnetism hypothesis for Allende using new paleomagnetic analyses of chondrules including the first measurements of mutually oriented subsamples from within individual chondrules. We confirm that Allende chondrules carry a high-temperature component of magnetization that is randomly oriented among chondrules. However, we find that subsamples of individual chondrules are also non-unidirectionally magnetized. Therefore, the high-temperature magnetization in Allende chondrules is not a record of nebular magnetic fields and is instead best explained by remagnetization during metasomatism in a <8 μT magnetic field. This low field intensity suggests that any core dynamo on the CV parent body decayed before the end of metasomatism, likely <40 My after the formation of calcium aluminum-rich inclusions (CAIs). Despite widespread practice, the magnetization in Allende should not be used to constrain magnetic fields in the protosolar nebula.

Correcting for inclination shallowing of early Carboniferous sedimentary rocks from Kyrgyzstan—indication of stable subtropical position of the North Tianshan Zone in the mid-late Palaeozoic

SUMMARY High-quality palaeomagnetic data for the early Carboniferous of Central Asia are scarce and the palaeogeographic evolution of this area prior to final amalgamation of the region east of the Ural mountains is still rather obscure. Here, we present palaeomagnetic data for early Carboniferous deposits from two areas in the Kyrgyz North Tianshan (NTS). Detailed rockmagnetic analysis indicates the presence of magnetite and haematite as magnetic carriers in these red sediments. In the Kazakh basin section (KEL), we identify a high-temperature component (HTC) of magnetization during stepwise thermal demagnetization at temperatures of up to ∼680 ◦ C yielding a site mean direction of D = 176.2 ◦ , I =− 36.4 ◦ , k = 57.4 and α95 = 8.9 ◦ after tilt correction. Two HTCs of magnetization were identified in samples from the Sonkul Basin (DUN) with maximum blocking temperatures of ∼600 ◦ C (magnetite) and ∼680 ◦ C (haematite). The magnetite component was also identified with alternating field demagnetization. The resulting site mean directions for these two components identified in 16 and 14 sites, respectively, are D = 149.3 ◦ , I =− 50.3 ◦ , k = 73.6 and α95 = 4.3 ◦ for the magnetite and D = 139.6 ◦ , I =− 35.1 ◦ , k = 71.6 and α95 = 4.7 ◦ for the haematite component. All three mean directions show a significant increase of the precision parameter k after tilt correction indicating acquisition of the high-temperature magnetization prior to the main folding event in the Jurassic. We explain the difference of the two components of DUN by a process of inclination bias due to compaction to which the platy haematite particles are more susceptible. Applying the elongation-inclination (E/I) method to directional data from over 100 individual samples from location DUN results in a negligible correction for the magnetite component (<5 ◦ ), whereas the inclination of the haematite component corrects from −35.0 ◦ to −50.3 ◦ (f = 0.6, error interval −41.4 ◦ to −57.9 ◦ ), which is then equal to the uncorrected magnetite inclination. The small number of samples from section KEL does not allow application of the E/I technique and inclination correction based on high field anisotropy of isothermal remanent magnetization was applied, yielding a corrected inclination of −75.2 ◦ ± 4 ◦ . Assuming comparable degrees of compaction for both study areas and applying the flattening factor obtained in DUN on samples from KEL, however, would result in comparable inclinations. The identification of inclination shallowing at both sections indicates that the age of magnetization is close to the deposition age. Assuming a reversed polarity of the directions from both areas results in palaeolatitudes of ∼30 ◦ N for section DUN and ∼60 ◦ N for the anisotropy-based correction of section KEL. The large difference, however, is geologically very unlikely. The inclination of the magnetite component of DUN (unaffected by inclination shallowing) favours a palaeoposition of ∼30 ◦ N. This is supported by the inclination shallowing corrected haematite component of DUN yielding a comparable inclination. Therefore, our results indicate that the NTS domain was situated at ∼30 ◦ Ni n the early Carboniferous. Furthermore, the NTS zone was probably not connected to Baltica or Siberia prior to the late Palaeozoic.

Cenozoic magnetostratigraphy and magnetic properties of the southern Issyk-Kul basin, Kyrgyzstan

We present paleomagnetic data from the northern flank of the Tianshan range, southeast of Lake Issyk-Kul (Kyrgyzstan). 613 cores were collected in two parallel sections with a total thickness of 960m (Chon Kyzylsuu, CK) and 990m (Jeti Oguz, JO), as well as 48 cores at six sites in a nearby anticline. Rock magnetic analyses identify both magnetite and hematite in the fluvial–lacustrine sediments. The concentration of both minerals, the magnetite:hematite ratio, and the average magnetite grain size increase upward in both sections. Anisotropy of anhysteretic remanent magnetization defines a tectonic fabric with sub-horizontal maximum axes that parallel the strike direction together with intermediate and minimum axes that streak out about a great circle orthogonal to the maximum axes suggestive of a tectonic fabric emplaced during folding. Stepwise thermal demagnetization isolates interpretable magnetization components in 284 samples that define 26 polarity chrons in CK and 19 in JO. A positive fold test, dual polarities and systematic changes in rock-magnetic parameters with depth suggest that the high temperature magnetization component was acquired coevally with deposition. An age model based on a visual magnetostratigraphic correlation of both sections with the geomagnetic polarity time scale defines absolute ages from 26.0 to 13.3Ma, with a fairly constant sedimentation rate of 9–10cm/ka. A correlation based on a numerical algorithm arrives at a slightly different conclusion, with deposition ages from 25.2 to 11.0Ma and sedimentation rates from 5 to 8cm/ka. In comparison with sedimentation rates found at other magnetostratigraphic sections in the Tianshan realm, we infer that the sedimentary record in this part of the Issyk-Kul Basin precedes the more rapid phase of uplift of the Kyrgyz Tianshan. The onset of deposition and concomitant erosion of the adjacent Terskey Range is in good agreement with independent assessments of the exhumation history of this mountain range, with erosion increasing at 25–20Ma and accelerating after 11–13Ma.