Apparent Polar Wander Path Research Articles

The geodynamic evolution of the Famatinian orogen from the paleomagnetic record of El Hongo trondhjemite (Early Paleozoic, Sierras Pampeanas de Córdoba, Argentina)

The Pampia cratonic block is juxtaposed to the Paleoproterozoic Río de la Plata craton through the Córdoba fault, an extension of the Transbrasiliano lineament. As a fragment of hyperextended crust, it was the locus of several magmatic belts during the Paleozoic. The Ordovician Famatinian orogen, for example, developed on its western margin as a consequence of subduction, which would lead to the accretion of Cuyania at ~460 Ma. The El Hongo trondhjemite is a small Famatinian pluton emplaced at ~ 500 Ma, close to the eastern margin of Pampia, controlled by shear belts in the foreland setting. New Ar–Ar ages verified that the cooling lasted at least until 430 Ma. Protracted cooling of this intrusion recorded magnetic remanence comprising several magnetic components, all of them carried mainly by hematite, and subordinately by magnetite. Hematite is present as a product either of exsolution from ilmeno-hematitess, or of low-temperature oxidation of magnetite (martite). The remanence is interpreted to have been acquired thermochemically during repeated pulses of fluid migration and deuteric oxidation. The A and B directions are predominant and have an arcuate distribution identifying clockwise rotation during acquisition. Other two directional groups, C and D are less represented, restricted to narrow patches; they seem to be acquired later, and coincide roughly with the ill-defined Silurian-Devonian Gondwana apparent polar wander path for the Early Paleozoic, implying that rotations had finished by then. An emplacement along dextral strike-slip fault systems is envisaged for El Hongo trondhjemite, where faulting occurred through shear belts in the weakened back-arc and foreland of the Famatinian belt, in response to the oblique subduction that would have accompanied the clockwise rotation of Laurentia around Gondwana during the Early Paleozoic. Strike-slip and rotations would have finished at ~460 Ma, coinciding with the final docking of Cuyania.

On the Early Permian shape of Pangea from paleomagnetism at its core

Although central to an understanding of Earth's paleogeography and the myriad processes that it affects, the geometry of Pangea during the early phase of its lifetime has remained a topic of contention since the plate tectonic revolution. Despite decades of analysis and discussion, the crux of this debate still largely hinges on sparse, legacy paleomagnetic data derived from early Permian rocks of the Moroccan Meseta. In this work, we present the results of a study designed to revisit, update and expand on those key data, with the provision of new geochronologic and paleomagnetic results from six Permo-Carboniferous basins in central Morocco. New U-Pb zircon ages from volcanic rocks substantiate and refine existing geochronological data and reveal that volcanism among the studied basins spanned approximately 30 Ma, from at least 305 to 277 Ma, but was possibly punctuated by a more intense pulse in the mid-early Permian (~285 Ma). These new U-Pb data furthermore suggest that the age estimates previously assigned to the key poles from the Moroccan Meseta are probably too young, by some ~10 Ma. New paleomagnetic results from six basins yielded a common, well-defined remanent magnetization from 20 sites that is demonstrated to be pre-middle Permian in age. However, it remains unclear whether this magnetization (which is directionally similar to the previous paleomagnetic data from the same basins) is a primary magnetization acquired at ~285 Ma, or a syn-folding remagnetization that was acquired shortly thereafter, at ~275 Ma. In adopting both interpretations as alternative hypotheses, we examine the corresponding paleogeographic implications of both. Through exhaustive comparisons with reference apparent polar wander paths and the direct reconstruction of Gondwana using these new paleomagnetic results, we demonstrate that in either case (i.e. whether the remanent magnetization is primary or was acquired soon after during folding) the data is compatible with a Pangea A geometry during the early Permian. We close with a topical discussion of some persisting arguments used to defend Pangea B and why we consider them to be flawed.

Chronology of serpentinization: Paleomagnetic evidence for 20 Ma serpentinization of the Oeyama ophiolite, Wakasa, Southwest Japan

Serpentinization of mantle peridotite generates magnetite that is able to acquire a remanent magnetization parallel to the ambient geomagnetic field. The paleomagnetic direction of serpentine provides insights as to the timing of serpentinization. This study examines paleomagnetic properties of serpentine in the Paleozoic Oeyama ophiolite in Wakasa (35.39°N, 134.39°E), Southwest Japan. Reversed polarity magnetizations with clockwise deflections from the south were observed in the serpentine in the high temperature component (HTC) magnetization with an unblocking temperature (Tub) of ∼580°C. The mean reversed polarity direction was D = 226.0°, I=−37.8°, α95=5.9°, and n=30. The remaining samples with an HTC of Tub between 400-450°C show the present-day geomagnetic field direction. Rock magnetism reveals that the reversed direction is carried by single-domain (SD) grains of magnetite, whereas multi-domain (MD) magnetite grains carry the present-day geomagnetic field direction. Magnetite grains originated from olivine during serpentinization grew to SD size and acquired the chemical remanent magnetizations during a reversed polarity interval. As serpentinization progresses, SD magnetite grains increased to MD magnetite grains and/or were subjected to maghemitization. The mean reversed direction yielded a paleomagnetic pole at 47.4°N, 230.3°E (A95 = 5.7°), which overlaps with the 20 Ma segment of the apparent polar wander path for SW Japan. We conclude that serpentinization occurred in the Oeyama ophiolite at approximately 20 Ma during the clockwise rotation of SW Japan.

Reconciling Patagonia with Gondwana in early Paleozoic? Paleomagnetism of the Valcheta granites, NE North Patagonian Massif

A paleomagnetic study was carried out in the Ordovician granitoids located in the northeastern North Patagonian Massif (NPM), close to Valcheta town (Río Negro Province, Argentina), to provide new evidence on the relation between Patagonia and Gondwana during the Early Paleozoic. A paleomagnetic paleopole (VA1) was calculated out of 14 VGPs yielding a mean at 12.7°N, 275.5°E with K = 13.3 and A95 = 11.3°. A second result (VA2-remag), computed on other component found in 12 sites is located at 76.4°S, 84°E, K = 11.8 and A95 = 5°. VA2-remag fits very well with the Lower Jurassic segment of the apparent polar wander path of Gondwana. We interpret that it corresponds to a remagnetization carried mostly by high-coercitive components acquired during the hydrothermal activity associated with the Early Jurassic effusion of the Marifil-Chon Aike volcanic province. VA1 paleopole becomes consistent with the Gondwana apparent polar wander path at ~450 Ma, after applying a 30–40° CCW rotation of the NPM to restore a V-shaped basin (Sierra Grande sea) opened before Permian-Triassic times. This rotation restores the paleogeographical position of the Ordovician granites of northeast NPM to the south of the Sierras Pampeanas aligning them with the eastern domain of the Famatinian orogenic and magmatic belt. VA1 paleopole suggests that the position of the NPM was close to the South American margin of Gondwana and separated by the Sierra Grande Sea from the Rio de la Plata-Kalahari cratons from, at least, late Ordovician times, which favors a para-autochthonous origin for the NPM. A former hypothesis suggesting a connection of the NPM and the TransAntarctic Mountains is unlikely for the late Ordovician according to our new data, which only allows an allochthonous NPM close to the Kalahari craton.

Rapid emplacement of massive Duluth Complex intrusions within the North American Midcontinent Rift

Abstract The Duluth Complex (Minnesota, USA) is one of the largest mafic intrusive complexes on Earth. It was emplaced as the Midcontinent Rift developed in Laurentia’s interior during an interval of magmatism and extension from ca. 1109 to 1084 Ma. This duration of magmatic activity is more protracted than is typical for large igneous provinces interpreted to have formed from decompression melting of upwelling mantle plumes. While the overall duration was protracted, there were intervals of more voluminous magmatism. New 206Pb/238U zircon dates for the anorthositic and layered series of the Duluth Complex constrain these units to have been emplaced ca. 1096 Ma in <1 m.y. (duration of 500 ± 260 k.y.). Comparison of paleomagnetic data from these units with Laurentia’s apparent polar wander path supports this interpretation. This rapid emplacement bears similarities to the geologically short duration of well-dated large igneous provinces. These data support hypotheses that call upon the co-location of lithospheric extension and anomalously hot upwelling mantle. This rapid magmatic pulse occurred >10 m.y. after initial magmatism following >20° of latitudinal plate motion. A likely scenario is one in which upwelling mantle encountered the base of Laurentian lithosphere and flowed via “upside-down drainage” to locally thinned lithosphere of the Midcontinent Rift.

Paleomagnetism of Late Neoproterozoic African Dike Swarms from the South Eastern Desert and the Paleo-Neoproterozoic Dataset from Egypt

Paleomagnetic analysis has been carried out on Late Neoproterozoic dike swarms from two areas along the Red Sea coast: 13 dikes (87 samples) close to the Um Rus gold mine and eight dikes (59 samples) at Sadi Salem. Rock magnetic experiments indicate that the main carrier of magnetization of these dikes is titanomagnetite and/or magnetite. Most samples display a component of magnetization (CA) that is in agreement with previously published Paleo-Late Neoproterozoic poles from other dikes and from one ore complex. But they cluster around the Cenozoic (0–60 Ma) portion of Torsvik's Gondwana apparent polar wander path (APWP) when plotted in southern African coordinates. We suggest two causes of this behavior (remagnetization related to the opening of the Red Sea or later emplacement of the dikes along pre-existing Paleo-Late Neoproterozoic fractures) will have to be tested with new reliable paleomagnetic data on carefully dated rocks. A second component (CB) seen in many of our samples but which is difficult to estimate is in agreement with Late Neoproterozoic granite poles and a dike supposed to be Triassic in age. However, all these poles plot on the Jurassic-Cretaceous portion (80–200 Ma) of Torsvik's path. These results, as well as the Cambro-Carboniferous sediments from Sinai and the Late Neoproterozoic Dokhan volcanic formation that cluster around the Late Paleozoic portion (280–300 Ma) of Torsvik's APWP, are tentatively interpreted as global viscous remagnetizations acquired, respectively, during the Cretaceous Normal and the Kiaman Reverse superchrons.

Paleomagnetism of Paleocene‐Maastrichtian (60–70 Ma) Lava Flows From Tian Shan (Central Asia): Directional Analysis and Paleointensities

AbstractThe Tuoyun volcanics from the Tian Shan range (Central Asia) give an opportunity to investigate the variability of the Earth's magnetic field during the Cretaceous and Early Paleogene. In the paper we focus on Maastrichtian‐Paleocene basalts and report new paleomagnetic results from 70 lava flows (respectively 45 directional groups) sampled near Tuoyun village (75.33°E; 40.18°N) from three distinct sections. Combined with previous results, our new data set yields a virtual geomagnetic pole at φS = 180.2°E, ϑS = 49.5°N with an angular standard deviation (for N = 93 directional groups). The mean inclination Is = 36.2° is indicative of an emplacement of the Tuoyun volcanics at a paleolatitude around 20°N, consistent with the high dispersion k = 14.6 of the directions. Such an inclination value is 10–15° lower than the predictions from the apparent polar wander paths for stable Europe and East Asia. This observation can be partly explained by crustal shortening within the East Asian plate during the India‐Asia convergence, but also needs to invoke a local field anomaly in Central Asia as previously proposed. Our absolute paleointensity experiments conducted on two lava flows and two baked sedimentary layers yield a mean virtual dipole moment of 58.9 ± 6.9 ZA·m2, consistent with the values at 60–70 Ma in the global paleointensity database. Compared to relative paleointensity results during the Cretaceous Normal Superchron and during the Plio‐Pleistocene, the relative variability in intensity—supposed to be a proxy for the geodynamo's activity—estimated here at 31 ± 5% (N = 15) from pseudo‐Thellier experiments possibly corroborates a correlation between geomagnetic reversal frequency and paleosecular variation rate during the past 120 Myr.

Paleomagnetism and microtextures reveal Neohimalayan deformation pattern in the northwestern Tethys Himalaya

Abstract The India-Asia collision produced the Himalayan orogenic belt. The kinematics of crustal blocks within the orogenic belt can shed insights into the tectonic processes related with the continental collision. We report a combined study of paleomagnetism and microtextures from the Zhongba microterrane, northwestern Tethys Himalaya. The Zhongba microterrane is located in the southwestern part of Tibet. A total of 71 samples collected from Permian formations yield a distinct remanent component carried by pyrrhotite, which failed fold tests. Compared with the apparent polar wander path of India, it is suggested that this overprint component is acquired recently (10–0 Ma), and a ~16° clockwise rotation is also indicated. Microtextures from several localities show E-W directed shear. Together with reported GPS observations and clockwise rotations, a bookshelf-style deformation pattern associated with strike-slip faulting is proposed for the Neohimalayan tectonics in the Tethys Himalaya. Bookshelf-style rotation of small blocks coordinated by strike-slip faults is not only a practical model to absorb the crustal shortening caused by the convergence of the Indian-Eurasian plate, but also an important way for the escape of the Tibetan Plateau to the southeast.

Paleomagnetism and rock magnetism of early Cretaceous Rajmahal basalts, NE India: Implications for paleogeography of the Indian subcontinent and migration of the Kerguelen hotspot

Abstract We present here new paleomagnetic and rock magnetic results from Rajmahal Traps (RT), India. The results are comprising of 350 standard specimens collected from 18 sites (90 samples). The detailed rock magnetic studies indicate that a Single Domain (SD) magnetite [Fe3O4] is the dominant magnetic carrier with ilmenite, pyrrhotite, and maghemite in the accessory form. The calculated Characteristic Remanent Magnetization (ChRM) directions yield a mean declination of 317.51°; mean inclination of −61.92° (α95 = 3.6°; k = 93.39). The obtained Virtual Geomagnetic Pole (VGP) position of the RT at ~117 Ma is 11.37°N, 297.58°E (62.42°W) with A95 = 3.5°, k = 99.99, dp = 4.33, dm = 5.58, and the calculated paleolatitude is at 43.1°S indistinguishable from that of earlier works. This paleomagnetic pole of RT basalts has minimal effect of secular variation and comply with the Geocentric Axial Dipole (GAD) model. The VGP is plotted on synthetic Apparent Polar Wander Path (APWP) for India, constrained better, and agrees well with the previously reported poles. The postulation of migration of mantle plume and the global mantle circulations are tested, and the present study results are in accord with this, suggesting the southward migration of the Kerguelen hotspot (mantle plume) by at least 6°.

A Closure of the Mongol‐Okhotsk Ocean by the Middle Jurassic: Reconciliation of Paleomagnetic and Geological Evidence

AbstractThe 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.

The amalgamation of Pangea: Paleomagnetic and geological observations revisited

AbstractThe supercontinent Pangea formed by the subduction of the Iapetus and Rheic oceans between Gondwana, Laurentia, and Baltica during mid-to-late Paleozoic times. However, there remains much debate regarding how this amalgamation was achieved. Most paleogeographic models based on paleomagnetic data argue that the juxtaposition of Gondwana and Laurussia (Laurentia-Baltica) was achieved via long-lasting highly oblique convergence in the late Paleozoic. In contrast, many geology-based reconstructions suggest that the collision between the two continents was likely initiated via a Gondwanan promontory comprising the Iberian, Armorican, and Bohemian massifs, and parts of the basement units in the Alpine orogen during the Early Devonian. To help resolve this discrepancy, we present an updated compilation of high-quality paleopoles of mid-to-late Paleozoic ages (spanning Middle Ordovician and Carboniferous times) from Gondwana, Laurentia, and Baltica. These paleopoles were evaluated with the Van der Voo selection criteria, corrected for inclination error where necessary, and were used to revise their apparent polar wander (APW) paths. The revised APW paths were constructed using an innovative approach in which age errors, A95 ovals, and Q-factors of individual paleopoles are taken into account. By combining the resulting APW paths with existing geological data and field relationships in the European Variscides, we provide mid-to-late Paleozoic paleogeographic reconstructions which indicate that the formation of Pangea was likely initiated at 400 Ma via the collision between Laurussia and a ribbon-like Gondwanan promontory that was itself formed by a scissor-like opening of the Paleotethys Ocean, and that the amalgamation culminated in the mostly orthogonal convergence between Gondwana and Laurussia.

Rock magnetic study on the Yetti–Eglab Intrusions, Sahara: contribution to the West African Craton geology

Abstract New palaeopoles have been calculated for the West African Craton (WAC) using palaeomagnetic data obtained on 178 cores of the Yetti–Eglab intrusions and stromatolite-bearing formation. One, two or three components of magnetization on 172 (14 sites) and 37 (6 sites) oriented specimens or cores were isolated mainly on doleritic dykes. High and low unblocking temperature components were evidenced in the dykes but also at four sites of the well-dated Hank stromatolite-bearing formation (875–890 Ma). Rock magnetic analyses show stable remanent magnetizations mainly carried by magnetite (or titanomagnetite) but may also reveal the presence of hematite, pyrrhotite and goethite. Regarding the recently constructed apparent polar wander path of the WAC until 500 Ma, these newly computed remanent components seem to be mainly older, some of which could be remagnetizations at different periods. However, according to geological dating and literature, the Yetti and Eglab terranes belonging to the WAC were amalgamated around 1.9 Ga and involved in the formation of the Columbia Supercontinent. The palaeopole computed for the stromatolite-bearing formation corresponds with the location of Rodinia Supercontinent at its early stages of amalgamation. The geodynamic evolution of the WAC with respect to both supercontinents suggests that the Eglab and Yetti could be separated by oceanic crust before 1.9 Ga. A volcanic arc developed during the subduction of this ocean followed by crustal thickening that generated an intrusive suite (Aftout granites) when it was at low northern latitudes. Baltica and Rio de la Plata cratons were close to the WAC after 1.7 Ga, following a nearly similar path between 1.7 and 0.9 Ga. In Africa, the collapse of the Birimian orogen was probably contemporaneous with the fragmentation of Columbia. At 0.9 Ga, Baltica was probably not attached to the WAC since the latter was not affected by the later Grenvillian orogen.

Response of remanent magnetization to deformation in geological processes using 3D-printed structures

Palaeogeographic reconstructions and construction of apparent polar wander paths are dependent on having reliable palaeomagnetic directions. The importance of inclination flattening in biasing the palaeomagnetic record has been debated for over 60 yrs. Correction for this effect often assumes that the palaeomagnetic vector deforms as a passive line. In a novel approach using 3D printed analogue rocks, we revisit the question of how a palaeomagnetic vector responds to deformation, specifically compaction. Maghaemite nanoparticles were mixed in the printing resin with a concentration of 0.15 wt. %, and five series of cylinders with 1 cm height and diameter were printed with porosities between 0% and 20%. Samples were given an anhysteretic remanent magnetization, and were subjected subsequently to incremental compaction. The magnetic fabric shows an initially weak compaction in the printing plane that becomes larger with increased compaction. The palaeomagnetic inclination changes according to the strain that the sample undergoes, and the amount of deflection is less than predicted by a passive line model of deformation. Our results demonstrate that using a single correction factor for inclination flattening is questionable, and show the need for a method that considers how the rock deforms. Further we demonstrate the usefulness of 3D printed analogue rock, which can inspire more realistic methods to correct for inclination flattening.

Верхнедевонские отложения (франский ярус) северо-запада Русской платформы: палеомагнитные данные

Paleomagnetic determinations for the Devonian strata of the Main Devonian Field, available in the international paleomagnetic data base, do not make it possible to construct both detailed magnetostratigraphic scales and reliable trajectories of the apparent polar wander path of the paleomagnetic pole. This is primarily due to the insufficient amount of data that determine modern reliability criteria. Obtaining more complete series of reliable paleomagnetic determinations is one of the important tasks of paleomagnetic studies. The paper presents new paleomagnetic determinations from a collection of rocks of the Frasnian stage of the Upper Devonian (Ilmen and Bureg Beds of the Semiluky Formation), sampled on the southern shore of Lake Ilmen, east of the village. Korostyn in 2009. Magnetomineralogical studies were carried out to determine the magnetic minerals of carriers of natural remanent magnetization. Three characteristic components of natural remanent magnetization have been identified. Two components correspond to the Late Paleozoic magnetization reversal (in the Carboniferous and Permian times). The third, bipolar component of the Frasnian age passes the reverse polarity test of the geomagnetic field.. The obtained position of the paleomagnetic pole by the bipolar component of the natural remanent magnetization is consistent with the available data on the section of the Late Upper Devonian of the Main Devonian Field.

Paleomagnetism of Ordovician-Silurian volcanics of the western slope of the Southern Urals

The paper presents new paleomagnetic data on dated Ordovician-Silurian volcanics from four sections in the western frame of the Taratash massif in the Southern Urals. Geological data indicate that the region under study has been part of the paleocontinent Baltica since the beginning of Mesoproterozoic. Paleomagnetic data from studies of the rocks of the most western part of the Ural fold belt did not reveal local and regional rotations with respect to the Baltica. Consequently, the pole obtained can be extrapolated to the entire platform. The presented result has a fairly high degree of reliability and can clarify the part of apparent polar wander path (APWP) for the paleocontinent Baltica on the Late Ordovician - Early Silurian segment, where reliable paleomagnetic data are not available, and can be used for paleoreconstructions.

Quantifying the Similarity of Paleomagnetic Poles

AbstractAn ability to compare paleomagnetic poles quantitatively is fundamental to paleogeographic reconstruction. The Fisher distribution provides a statistical framework for both constructing and relating paleomagnetic poles to enable comparison of estimated pole positions in paleomagnetic reconstructions. However, Fisher distribution‐based confidence regions for paleomagnetic poles are often compared using empirical rules of thumb rather than by quantitative analysis of their full structure. Here we demonstrate potential shortcomings of such comparisons and propose continuous metrics for quantitative comparison of paleomagnetic poles. These metrics are simple to apply for Fisher distributions and can be modified readily for a broad range of alternative distributions that may be more appropriate for representing some paleomagnetic data sets. We demonstrate how our proposed metrics provide both quantitative and probabilistic approaches to common tasks in paleomagnetic reconstruction, such as comparing estimated mean pole positions with apparent polar wander paths.

Paleomagnetism of Ordovician–Silurian Volcanics on the Western Slope of the Southern Urals

This work presents new paleomagnetic data on previously dated Ordovician–Silurian volcanics from four sections in the western framework of the Taratash massif (Southern Urals). The geological data indicate that the region under study was a part of the Baltica paleocontinent since the early Mesoproterozoic. The paleomagnetic data obtained for rocks of the westernmost part of the Ural Fold Belt show no evidence of local and regional rotations relative to Baltica. Consequently, the pole obtained can be extrapolated to the entire platform. The result obtained is characterized by a rather high degree of reliability and can clarify the trajectory of the apparent polar wander path (APWP) for the Baltica paleocontinent during the Late Ordovician–Early Silurian, where reliable paleomagnetic data are not available, and can be used for further paleoreconstructions.

Triassic (Anisian and Rhaetian) palaeomagnetic poles from the Germanic Basin (Winterswijk, the Netherlands)

In this paper, we provide two new Triassic palaeomagnetic poles from Winterswijk, the Netherlands, in the stable interior of the Eurasian plate. They were respectively collected from the Anisian (~ 247–242 Ma) red marly limestones of the sedimentary transition of the Buntsandstein Formation to the dark grey limestones of the basal Muschelkalk Formation, and from the Rhaetian (~ 208–201 Ma) shallow marine claystones that unconformably overlie the Muschelkalk Formation. The magnetization is carried by hematite or magnetite in the Anisian limestones, and iron sulfides and magnetite in the Rhaetian sedimentary rocks, revealing for both a large normal polarity overprint with a recent (geocentric axial dipole field) direction at the present latitude of the locality. Alternating field and thermal demagnetization occasionally reveal a stable magnetization decaying towards the origin, interpreted as the Characteristic Remanent Magnetization. Where we find a pervasive (normal polarity) overprint, we can often still determine well-defined great-circle solutions. Our interpreted palaeomagnetic poles include the great-circle solutions. The Anisian magnetic pole has declination D ± ∆Dx = 210.8 ± 3.0°, inclination I ± ∆Ix = − 26.7 ± 4.9°, with a latitude, longitude of 45.0°, 142.0° respectively, K = 43.9, A95 = 2.9°, N = 56. The Rhaetian magnetic pole has declination D ± ∆Dx = 32.0 ± 8.7°, inclination I ± ∆Ix = 50.9 ± 8.1°, with a latitude, longitude of 60.6°, 123.9° respectively, K = 19.3, A95 = 7.4°, N = 21. The poles plot close to the predicted location of global apparent polar wander paths (GAPWaPs) in Eurasian coordinates and are feasible for future apparent polar wander path construction. They confirm that the intracontinental, shallow-marine Germanic Basin, in which the Muschelkalk Formation was deposited, existed at a palaeolatitude of 14.1° [11.3, 17.1] N, in a palaeo-environment reminding of the Persian Gulf today. In Rhaetian times, palaeolatitudes of 31.6° [24.8, 39.8] N were reached, on its way to the modern latitude of 52°N.

New paleomagnetic results from the ca. 1.68–1.63 Ga mafic dyke swarms in Western Shandong Province, Eastern China: Implications for the reconstruction of the Columbia supercontinent

The existence of Paleo-Mesoproterozoic supercontinent Columbia (aka Nuna) was established decades ago, but the position of North China Craton within Columbia is still highly debated due to the paucity of available high-quality paleomagnetic and reliable geological constraints. Precise geochronological dating of extensive Mesoproterozoic mafic dyke swarms in Western Shandong Province (also named the Luxi area), China reveals two phases of dyke emplacement at ~1.68 Ga and ~1.63 Ga. In this paper, we report new paleomagnetic and rock magnetic results obtained from approximate 160 samples (16 sites) collected from these two phases of mafic dyke swarms in the Luxi area with the aim of pinpointing the location of North China Craton within Columbia supercontinent in this time interval. Rock magnetic experiments confirm that either magnetite or titanomagnetite is the main magnetic carrier in these dykes. Stepwise thermal demagnetization revealed two paleomagnetic poles. For the ~1.63 Ga dykes, normal and reversed high-temperature remanent magnetization directions yield a mean direction (D/I) of 86.1°/53.5° (κ = 43.3, α95 = 7.9°, N = 9). These directions pass a reversal test and are interpreted as primary remanences. The corresponding paleomagnetic pole is calculated at 20.8°N, 182.5°E (κ = 28.3, A95 = 8.3°, N = 9). This pole passes the examination of secular variation of geomagnetic field (Deenen et al., 2011, 2014). It fulfills a Van der Voo (1990) value Q = 6 and is therefore suggested to be a ‘key’ pole demarcating the Precambrian North China Craton. For the ~1.68 Ga dykes, only the normal directions are isolated with a mean direction (D/I) of 89.1°/47.1° (κ = 35.0, α95 = 13.1°, N = 5) with a corresponding paleomagnetic pole of 17.8°N, 184.9°E (κ = 29.6, A95 = 14.3°, N = 5). This pole passes the examination of secular variation of geomagnetic field. Finally we select the ~1.63 Ga high-quantity paleomagnetic pole in order to depict a more detailed apparent pole wander path (APWP) to compare with the other major Precambrian cratons. Combined with other geological evidence, our reconstruction scenario supports the spatio-temporal connection between the Baltica, North Australian Craton and North China Craton.

A pan-latitudinal Rodinia in the Tonian true polar wander frame

A new paleomagnetic and geochronological study was conducted on the Tonian Chéngjiāng Formation from Yúnnán Province, South China, to examine the recent reported true polar wander event (TPW) during 825–750 Ma and clarify the position of South China in the Rodinia supercontinent. Detailed thermal demagnetization revealed two remanent magnetic components. A low-temperature component separated below 300°C is interpreted as a recent viscous remanence. Additionally, a high-temperature component (H1) with unblocking temperature up to 690°C is revealed. Passing both the fold test and reversal test, and recording at least two and half magnetochrons, H1 is suggested to be a primary remanence. The paleomagnetic pole (CJH1, 33.4°N, 56.1°E, dp/dm=7.3°/8.9°) calculated from component H1 has no similarities to the Phanerozoic apparent polar wander path of South China. SHRIMP II U-Pb zircon data from a tuff bed near the paleomagnetic sampling sites suggest that the H1 pole has an age of ca. 800 Ma. Combining the reported Tonian paleomagnetic results from South China and Svalbard, we suggest a ∼63° TPW event during 825–790 Ma. Under this TPW paleomagnetic frame and using the reliable Tonian paleomagnetic results from other continents, we reconstruct the main part of Rodinia. This new configuration of Rodinia reconstructs South China and India at its northern periphery, and within the polar or high latitude zone during ca. 900–750 Ma. The polar location of those cratons, together with the mid-high latitudinal distribution of Australia, Congo and Baltica, suggests that Rodinia was a pan-latitudinal rather than an equatorially distributed supercontinent. The reconstruction also suggests that the breakup of the Rodinia should have been after 750 Ma but before 720 Ma. Despite similarities of their assembly and configuration, Rodinia and Pangea affected the Earth system differently.