Palaeomagnetic Pole Research Articles

Intraplate deformation during Gondwana breakup: a study of the Jurassic units of the Cañadón Asfalto Basin (extra-Andean Patagonia, Argentina)

SUMMARY In this study, we present the results of palaeomagnetic research conducted on Jurassic units of the Cañadón Asfalto Basin (CAB) in Patagonia, formed during Gondwana breakup. This basin is a key locality for understanding intraplate deformation within Patagonia during the Jurassic. The nature of this basin has been a subject of debate, based on the dynamics of the blocks that constitute its depocentres. In this context, the palaeomagnetic study of the Jurassic units of this basin provides a unique methodology to characterize the tectonic motions of its crustal blocks during its formation and development. To achieve this, we collected 350 samples from 53 sites in the sedimentary units of Las Leoneras (ca. 189 Ma) and Cañadón Calcáreo Formations (ca. 160–157 Ma), as well as the volcanic Lonco Trapial Group (ca. 185–172 Ma). The palaeomagnetic results from the sedimentary units show a regional remagnetization due to hydrothermal activity that obliterated the original remanence and overprinted a new one, simultaneously imprinting a secondary remanence in the volcanic units of the Lonco Trapial Group. When comparing the direction of the palaeomagnetic pole obtained from the remagnetized units with respect to average poles of equivalent ages, it is observed that the remagnetization must have occurred during the Late Jurassic (ca. 145 Ma). The age range in which this process occurred (Oxfordian to Aptian) and the direction of the calculated pole dispute a monster polar shift postulated for Late Jurassic to Early Cretaceous times. In addition, the primary magnetization recorded in the units of the Lonco Trapial Group indicates a counterclockwise rotation of the studied crustal blocks between 21° and 11°, which, in line with previous studies, refutes large-scale dextral motion along the Gastre Fault System since the Jurassic. Similar counterclockwise rotations of equivalent magnitudes are found along the units overlying the Palaeozoic Central Patagonian Igneous–Metamorphic Belt, which represents the opposite shear sense compared to the Jurassic units beyond this belt. This is interpreted as a reactivation of the Palaeozoic belt structures in the opposite sense, from transpressive during the Palaeozoic to transtensive during the Mesozoic.

Time constraint on global-scale plate reorganizations using records of continental deformation

ABSTRACT Seafloor fabric indicators are the main features used for dating global-scale plate reorganizations. However, the lack of oceanic crusts older than 200 Ma limits their application only to the Mesozoic and Cenozoic eras. Furthermore, in cases such as the mid-Cretaceous time when reversals in Earth’s magnetic field did not occur, the plate reorganization ages obtained from seafloor fabric indicators are imprecise. I propose the record of continental deformation as an alternative approach for dating these events. A compilation of cooling/deformation, migmatization, and unconformity ages recorded around the globe collectively indicates that continental deformation associated with the mid-Cretaceous plate reorganization culminated at 107 Ma. This age strongly correlates with ages obtained from other data such as palaeomagnetic poles. Considering that the deformational features similar to which are compiled in this study appear to be temporally correlated with other reorganization events, the record of globally distributed continental deformation might be used for other reorganization events whose timing is poorly constrained.

Completing the loop of the Late Jurassic–Early Cretaceous true polar wander event

The reorientation of Earth through rotation of its solid shell relative to its spin axis is known as True polar wander (TPW). It is well-documented at present, but the occurrence of TPW in the geologic past remains controversial. This is especially so for Late Jurassic TPW, where the veracity and dynamics of a particularly large shift remain debated. Here, we report three palaeomagnetic poles at 153, 147, and 141 million years (Myr) ago from the North China craton that document an ~ 12° southward shift in palaeolatitude from 155–147 Myr ago (~1.5° Myr−1), immediately followed by an ~ 10° northward displacement between 147–141 Myr ago (~1.6° Myr−1). Our data support a large round-trip TPW oscillation in the past 200 Myr and we suggest that the shifting back-and-forth of the continents may contribute to the biota evolution in East Asia and the global Jurassic–Cretaceous extinction and endemism.

Mesozoic evolution of large-scale drainage systems in the Indochina Block: evidence from palaeomagnetic and U–Pb geochronological constraints

The collage of the Indochina Block to the Eurasian continent during the Mesozoic resulted in major changes in source-to-sink systems of East Asia, whilst the sedimentation in the Khorat–Simao Basin of the Indochina Block transited from marine to continental environments. Previous studies uncovered the existence of transcontinental river systems in the East Asia mainland during the Cretaceous to Early Cenozoic, although there have been few studies on pre-Cretaceous drainage systems. To determine the impact on the evolution of palaeo-drainage systems triggered by tectonic movement of the Indochina Block, we performed palaeomagnetic and U–Pb geochronologic analyses on the Late Triassic to Early Cretaceous sedimentary rocks in the Simao Basin. Palaeomagnetic data indicate stable Jurassic tectonic environments between the Indochina and Songpan–Ganzi–South China blocks, following their Late Triassic collision. Based on detrital zircon U–Pb dating, the Late Triassic age spectra consist mainly of Phanerozoic components, while the Jurassic to Cretaceous age spectra display more Precambrian age peaks. The contribution of potential provenance to the Simao Basin changed during the Early Cretaceous, suggesting several sedimentary provenance transitions. Also, we believe that large continental-scale drainage systems flowing through the North Qiangtang, Sichuan, Simao and Khorat Basins were sourced from the Songpan–Ganzi Block since the end of the Late Jurassic. Supplementary material: The findings of a quantitative statistical study (Fig. S1; Table S5), the location of the Late Triassic to Early Cretaceous samples from the Simao Basin (Table S1), palaeomagnetic poles for Eurasia, South China, Indochina, North Qiangtang and Tarim (Table S2), the result of quantitative analysis for the Late Triassic and Middle Jurassic sedimentary rocks from the Simao and Sichuan basins (Table S3), and results of zircon U–Pb dating (Table S4) are available at https://doi.org/10.6084/m9.figshare.c.6862918 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

New palaeomagnetic data for Palaeoproterozoic AMCG complexes of the Ukrainian Shield

A palaeomagnetic study of rocks for two Palaeoproterozoic anorthosite-mangerite-charnockite-granite (AMCG) complexes in the Ukrainian Shield was done to put additional constraints on the interpretation of palaeogeography of Fennoscandia and Volgo-Sarmatia in the Palaeoproterozoic. With this study, 5 sites of Korsun-Novomyrhorod and 3 sites of Korosten AMCG complexes in central and north-western parts of the shield, respectively, were chosen for palaeomagnetic sampling given the geological, modern geochronological and previous palaeomagnetic data. Primary remanent magnetization was isolated on samples of anorthosites, Gabbro, and monzonites within a narrow time interval of U-Pb geochronology dataset of 1.76—1.75 Ga. The palaeomagnetic poles calculated for Korosten and Korsun-Novomyrhorod complexes are almost identical, which indicates that the Volyn and Ingul Domains developed within a single structure of the Ukrainian Shield since at least 1.75 Ga. The new palaeomagnetic pole calculated for all 8 sites (Plat=22.7 °N, Plon=167.4 °E, A95=3.3°) agrees well with previous studies by Elming et al. [2001, 2010]. The selection of the most reliable palaeomagnetic poles for Fennoscandia and Volgo-Sarmatia of this time indicates that the present position of the Ukrainian Shield relative to Fennoscandia is not the same as for about 1.75 Ga, when Fennoscandia occupied a subequatorial position within palaeolatitudes of 5—20 °N, and Volgo-Sarmatia was located close to the equator and rotated relative to Fennoscandia counterclockwise by about 40° compared to its present position.

New palaeoproterozoic palaeomagnetic data from Central and Northern Finland indicate a long-lived stable position for Fennoscandia

SUMMARYThe Svecofennian gabbro intrusions coincide temporally with the global 2100–1800 Ma orogens related to the amalgamation of the Mesoproterozoic supercontinent Nuna. We provide a new reliable 1891–1875 Ma palaeomagnetic pole for Fennoscandia based on rock magnetic and palaeomagnetic studies on the Svecofennian intrusions in central Finland to fill gaps in the Palaeoproterozoic palaeomagnetic record. By using the new pole together with other global high-quality data, we propose a new palaeogeographic reconstruction at 1885 Ma. This, together with previous data, supports a long-lived relatively stable position of Fennoscandia at low to moderate latitudes at 1890–1790 Ma. Similar stable pole positions have also been obtained for Kalahari at 1880–1830 Ma, Siberia at 1880–1850 Ma, and possibly India at 1980–1775 Ma. A new reconstruction at the beginning of this period indicates the convergence of several cratons at 1885 Ma in the initial stages of the amalgamation of the Nuna supercontinent at low to moderate latitudes. The close proximity of cratons at low to moderate latitudes is further supported by global and regional palaeoclimatic indicators. Stable position of several cratons could indicate a global period of minimal apparent drift at ca. 1880–1830 Ma. Before this period, the global palaeomagnetic record indicates large back-and-forth swings, most prominently seen in the high-resolution 2020–1870 Ma Coronation loops of the Slave craton. These large back-and-forth movements have been explained as resulting from an unstable geomagnetic field or basin- or local-scale vertical-axis rotations. However, the most likely explanation is inertial interchange true polar wander (IITPW) events, which is in line with the suggestion of large amplitude true polar wander events during the formation of the supercontinent.

The Puduhush gabbro in Griqualand West, South Africa: extendingca.1.89 to 1.83 Ga intraplate magmatism across the proto-Kalahari Craton

AbstractThe Puduhush gabbro is located on the western margin of the proto-Kalahari Craton in Southern Africa. This gabbro intrudes the Volop Formation, which conformably overlies the Hartley Formation lava of the late Palaeoproterozoic Olifantshoek Group. Here we report a new U-Pb ID-TIMS baddeleyite age as well as petrographic, whole-rock geochemical and palaeomagnetic results for the Puduhush gabbro. The gabbro shows a well-preserved sub-ophitic texture between clinopyroxene and plagioclase, with minor amounts of amphibole, olivine, biotite and Fe-Ti oxides. The new U-Pb ID-TIMS baddeleyite age of 1 881 ± 1 Ma reported here for the Puduhush gabbro, together with existing ages for the Hartley Formation, define a ca.1 916 to 1 881 Ma age bracket for the Volop Formation. Our 1 881 ± 1 Ma age is also within error of ages reported for the oldest episode (so-called Episode 1) of the ca.1.89 to 1.83 Ga magmatism in the eastern and northern parts of the proto-Kalahari Craton. Our geochemical results also suggest compositional similarities between the Puduhush gabbro and Episode 1 magmatism, particularly the post-Waterberg sills. The virtual geomagnetic pole calculated here for the Puduhush gabbro (VGP: 1.6°N; 352.0°E; A95 = 14.2°) is consistent with the Episode 1 pole. All data are therefore combined to produce a new palaeomagnetic pole (11.7°N; 8.8°E, A95 = 9.3°) for Episode 1 magmatism. The present study provides the first evidence that the ca.1.89 to 1.83 Ga magmatism had a wider footprint that previously thought, extending to the western margin of the proto-Kalahari Craton. This wide-scale magmatism, previously proposed to be related to a back-arc extension setting, is here reinterpreted in the context of a mantle plume. Our results are consistent with the lithostratigraphic-based notion that at least parts of the red-bed successions (i.e., Olifantshoek and Waterberg Groups) that are hosts to the ca.1.89 to 1.83 Ga magmatism could be correlative units, representing an extensive sedimentary sequence that once covered large expanses of the proto-Kalahari Craton.

Palinspastic restoration of Variscan oroclines – implications for dextral transpression and terrane affinities

Abstract The Paleozoic Variscan orogen in Europe has a markedly circuitous trace for which several different origins have been postulated, including deformation around promontories on the colliding continental margins, extrusion within the collision zone, folding of a ribbon continent and collision with a substantial dextral component. Adopting the latter assumption, unfolding of the large, steeply plunging folds (‘oroclines’) of Iberia and the Moroccan Meseta requires more than 4000 km of dextral lateral translation of Laurussia with respect to Gondwana. Constraints on the age of the folding require that this lateral translation occurred in mid-late Carboniferous time. Significant dextral translation of Laurussia with respect to Gondwana late in the Variscan collision is supported by palaeomagnetic data for the two supercontinents, although the exact timing of this relative motion is not well constrained due to large uncertainties in the palaeomagnetic pole positions. Our palinspastic reconstruction of the major Variscan folds of Iberia places the rocks of the South Portuguese Zone of western Iberia adjacent to the Rhenish Massif; for instance, as part of Avalonia. By the same token, the Sehoul Block in the Moroccan Meseta probably originated at the western end of Cadomia, although nothing in our analysis precludes it also being derived from Avalonia.

Demagnetization studies in the North Singhbhum Mobile Belt, Eastern India: new palaeomagnetic poles, tectonics, and GRM

Demagnetization studies in the North Singhbhum Mobile Belt, Eastern India: new palaeomagnetic poles, tectonics, and GRM

Phases of Magmatic Activities in South Wadi Hodein-Shalatein, Egypt: Resolving controversy about their age using Paleomagnetism and AMS

ABSTRACT Several exposures of basaltic intrusions are distributed near Red Sea coast at Wadi Hodein Southern Egypt. There is some disagreement about the palaeomagnetic pole results of these basalts; some claim it is Tertiary in age, while others claim it is of Cretaceous age. To our knowledge, no Anisotropy of Magnetic Susceptibility (AMS) results have ever been published from these rocks. Therefore, palaeomagnetic and AMS studies were performed on these basalts in order to identify phases of magmatism, paleomagnetic pole position and types of magmatic intrusions. In the present study, eight sites (219 oriented core specimens) were sampled from eight location. Rock magnetic studies reflect the presence of magnetite as the chief mineral in these rocks. Alternating field technique in association with Thermal Demagnetisation process revealed presence of one magmatic phase took place in Cretaceous age with VGP (65°N, 250°E; A 95 = 5.3). AMS results showed that the basaltic intrusions in the study area are still holding their primary fabrics.

High-resolution palaeomagnetic results of Ethiopian trap series from Lima Limo section: implications for the Oligocene geomagnetic field behaviour and timing of volcanism

SUMMARY We present high-resolution palaeomagnetic and rock magnetic results from 92 successive volcanic units on a 2 km tall Lima Limo (LL) section of the Oligocene Ethiopian flood basalts (OEFB). A total of 85 well-defined flow-mean characteristic remanent magnetization directions representing seven stable magnetic polarity zones with six transitional/excursional directions were determined. These results indicate the identification of four more polarity reversals than previous palaeomagnetic studies; the resulting magnetostratigraphy has, therefore, more polarity zonation. Comparison of this result with the most recently revised geomagnetic polarity time scale (GPTS, hereafter GPTS2016), by using available radiometric age data, could not find a unique correlation. Instead, it strongly suggests the recording of at least one very brief polarity chron or putative geomagnetic excursion. Our magnetostratigraphic interpretation infers that the relative timing between the OEFB eruptions and the Oi-2 global cooling estimated two possible scenarios: one where the lowermost reverse-polarity (R1) interval for the LL section is correlated to Chron C11r of GPTS2016, same as the interpretations of earlier studies, would make a causal linkage between the OEFB eruptions and the Oi-2 cooling less possible; and, the eruption timing estimated in another scenario correlating the R1 to Chron C12r might preserve the probability of its causal influence in the Oi-2 cooling. The resulting overall mean pole for the LL section of this study, 78.2° N in latitude and 213.0° E in longitude (A95 = 3.4°, N = 79), is closer to other co-eval palaeomagnetic poles from different regions and the reference pole of Africa. Our analysis of geomagnetic palaeosecular variation (PSV) shows that, compared to the Plio-Pleistocene, the Early Oligocene has higher degrees of PSV but its slightly weaker latitude dependence.

Reliability of palaeomagnetic poles from sedimentary rocks

SUMMARY Palaeomagnetic poles form the building blocks of apparent polar wander paths and are used as primary input for quantitative palaeogeographic reconstructions. The calculation of such poles requires that the short-term, palaeosecular variation (PSV) of the geomagnetic field is adequately sampled and averaged by a palaeomagnetic data set. Assessing to what extent PSV is recorded is relatively straightforward for rocks that are known to provide spot readings of the geomagnetic field, such as lavas. But it is unknown whether and when palaeomagnetic directions derived from sedimentary rocks represent spot readings of the geomagnetic field and sediments are moreover suffering from inclination shallowing, making it challenging to assess the reliability of poles derived from these rocks. Here, we explore whether a widely used technique to correct for inclination shallowing, known as the elongation–inclination (E/I) method, allows us to formulate a set of quality criteria for (inclination shallowing-corrected) palaeomagnetic poles from sedimentary rocks. The E/I method explicitly assumes that a sediment-derived data set provides, besides flattening, an accurate representation of PSV. We evaluate the effect of perceived pitfalls for this assumption using a recently published data set of 1275 individual palaeomagnetic directions of a >3-km-thick succession of ∼69–41.5 Ma red beds from the Gonjo Basin (eastern Tibet), as well as synthetic data generated with the TK03.GAD field model. The inclinations derived from the uncorrected data set are significantly lower than previous estimates for the basin, obtained using coeval lavas, by correcting inclination shallowing using anisotropy-based techniques, and by predictions from tectonic reconstructions. We find that the E/I correction successfully restores the inclination to values predicted by these independent data sets if the following conditions are met: the number of directions N is at least 100, the A95 cone of confidence falls within a previously defined A95min-max reliability envelope, no negative reversal test is obtained and vertical-axis rotation differences within the data set do not exceed 15°. We propose a classification of three levels (A, B and C) that should be applied after commonly applied quality criteria for palaeomagnetic poles are met. For poles with classification ‘A’, we find no reasons to assume insufficient quality for tectonic interpretation. Poles with classification ‘B’ could be useful, but have to be carefully assessed, and poles with classification ‘C’ provide unreliable palaeolatitudes. We show that application of these criteria for data sets of other sedimentary rock types classifies data sets whose reliability is independently confirmed as ‘A’ or ‘B’, and that demonstrably unreliable data sets are classified as ‘C’, confirming that our criteria are useful, and conservative. The implication of our analysis is that sediment-based data sets of quality ‘A’ may be considered statistically equivalent to data sets of site-mean directions from rapidly cooled igneous rocks like lavas and provide high-quality palaeomagnetic poles.

Palaeomagnetism of the Dundas–Fossey Trough, Tasmania: Oroclinal rotation and Late Cretaceous overprinting

The Dundas–Fossey Trough, a curved belt of Early Palaeozoic rocks in western and northern Tasmania, is hypothesised to have developed as an orocline driven by asthenospheric flow behind a rapidly retreating subduction zone on the East Gondwana margin. Rocks of the Wurawina Supergroup from the trough were sampled for a palaeomagnetic test of this hypothesis. Rock magnetic analysis identifies both magnetite and hematite remanence carriers. Hematite carries a normal-polarity overprint which was acquired at relatively low temperature. Thermal demagnetisation over the magnetite unblocking range reveals a linear trend that defines component A, which displays both normal and reversed polarity. Component A passes a modified version of the fold test, indicating that it is pre-deformational. The declination of component A correlates linearly with regional strike, thus passing the orocline test. A palaeomagnetic pole for the Cambrian Owen Group, after correction for oroclinal rotation, is displaced from the Gondwana polar wander path, suggesting that the western limb of the trough may have been rotated anticlockwise by about 40° prior to the development of the orocline, presumably during known Early to Middle Ordovician deformation. Adjustment of the palaeomagnetic declination data to account for this earlier phase of rotation improves the fit parameters of the orocline test. The palaeomagnetic results are consistent with the orocline model for the Dundas–Fossey Trough, and support the inference that the trough extends beneath later cover in southeastern Tasmania. Overprint component B yields a mean pole in broad agreement with other overprints previously observed both in Tasmania and the eastern seaboard of the Australian mainland, and like them appears to have been acquired during the Late Cretaceous normal polarity superchron. We speculate that magnetic overprinting in Tasmania is related to enhanced oxidation by meteoric water driven by regional uplift.

Late Miocene to late Pleistocene geomagnetic secular variation at high northern latitudes

SUMMARYWe report a palaeomagnetic study of Icelandic lavas of late Miocene to late Pliocene age to test the geocentric axial dipole hypothesis at high northern latitudes. Cores were sampled from 125 sites in the Fljótsdalur valley in eastern Iceland, and hand samples were taken for 17 new incremental heating 40Ar/39Ar age determinations. 96 per cent of the cores were oriented using both a Brunton compass and a sun compass. Comparison of the magnetic and sun azimuths reveals deviations of ±5°, ±10° and ±20°, respectively, for 42, 16 and 3 per cent of the data points, indicating that core sampling intended for palaeosecular variation (PSV) studies at high northern latitudes should be oriented by sun. A total of 1279 independent specimens were subjected to AF- and thermal-demagnetization for palaeodirectional analysis, and well-grouped site mean directions were obtained for 123 sites of which 113 were found to be independent sites. Applying a selection criteria of k > 50 and N ≥ 5 (Nmean = 9.5), we obtain a combined grand mean direction for 46 normal and 53 reverse (for VGPlat > ±45°) polarity sites of declination = 5.6° and inclination = 77.5° that is not significantly different from that expected from a GAD field. The corresponding palaeomagnetic pole position (VGPlat = 86.3°N, VGPlon = 21.2°E, dp/dm = 4.0°/4.3°) is coincident with the North Pole within the 95 per cent confidence limits. An updated age model is constructed based on the 40Ar/39Ar ages, showing that the majority of the Fljótsdalur lavas fall within 2–7 Ma. We combine the Fljótsdalur data with existing data from the nearby Jökuldalur valley. The 154 palaeodirections are well-dispersed between 1 and 7 Ma and constitute a high-quality data set for PSV analysis. Our results partly support previous conclusions of a generally higher dispersion during reverse polarity intervals. However, when comparing our Matutayma data with Brunhes age data from Jan Mayen, we find no evidence of a higher VGP scatter during the Matuyama as previously suggested. When comparing our VGP scatter to the two commonly used models for VGP dispersion: Model G and TK03, we find a good fit for all 1–7 Ma VGP scatter data SB(1–7) to Model G, whereas SB(1–7) is not fitted by TK03, even when considering the uncertainty of SB(1–7). We also find that all VGP scatter estimates, except that for the Gilbert subset, are consistent with Model G, while the discrepancy with TK03 is generally larger.

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.

A palaeomagnetic study of the Middle Permian and Middle Triassic limestones from Shan State, Myanmar: Implications for collision of the Sibumasu Terrane and Indochina Terrane

We report herein a new palaeomagnetic study on the Middle Permian and Middle Triassic limestones from Shan State of eastern Myanmar, aiming to resolve the spatial location of the Sibumasu Terrane during the collision of tectonic blocks in Southeast Asia and to constrain the timing of convergence between the Sibumasu Terrane and Indochina Terrane. Based on the rock magnetic and palaeomagnetic experiments, three stable characteristic remnant magnetizations are recognized from limestone specimens of Middle Permian and Middle Triassic age. The characteristic Component C of the Middle Permian limestone passed the fold test at 95% confidence level, indicative of a pre‐folding origin. The mean direction of this component is D = 10.7°, I = 17.9° (κ = 130.3, α95 = 10.8°) before and D = 13.7°, I = −25.3° (κ = 1894.9, α95 = 2.8°) after tilt correction, corresponding to a palaeomagnetic pole at 254.1°E, 53.2°N (A95 = 1.7°). This suggests that the Sibumasu Terrane was placed at a palaeolatitude of ~13.0°S during the Middle Permian. The Component C separated from the Middle Triassic samples also passed the fold test with a mean direction of D = 207.3°, I = −8.3° (κ = 12.9, α95 = 6.2°) before tilt correction and D = 205.6°, I = −33.5° (κ = 27.1, α95 = 4.2°) after tilt correction, corresponding to a palaeomagnetic pole at 187.3°E, 65.8°N (dp/dm = 2.7°/4.8°). This implies that the Sibumasu Terrane was located at a palaeolatitude of ~18.3°N during the Middle Triassic. Based upon the detailed palaeomagnetic analysis, this study supports the view that the collision of the Sibumasu Terrane and Indochina Terrance occurred during or before the Middle–Late Triassic times.

Problems of Precambrian paleomagnetism on the territory of Ukraine

Some problems of paleomagnetic research of the Precambrian rocks of Ukraine are considered. The results of paleomagnetic researches of the Proterozoic rocks of the Ukrainian Shield, Ediacaran traps of Volyn and sedimentary rocks of Podolia were analyzed. With the emergence of many new isotopic age data for the Ukrainian Shield rocks we have new opportunities to get reliable palaeomagnetic poles. But our studies of the pilot collections of samples from some key outcrops in the Middle Dnieper, Azov, Dniester-Bug, Ingul and North-Western crustal blocks of the Ukrainian Shield with modern geochronological isotopic ages showed their absence of informativity for palaeo-magnetic determinations. On the Ukrainian Shield the gabbro-anorthosite and granite rapakivi of Korosten and Korsun-Novomyrhorod anorthosite-mangerite-charnockite-granite complexes in the northwestern and central part of the shield are good candidates for palaeomagnetic investigations. New paleomagnetic pole (Φ = 22.7°N, Λ = 164.3°E, dp/dm = 4.9°/9.6°) for ages of 1750 Ma were calculated for six sites within Ingul mega-block. Based on the analysis of paleomagnetic poles for Fennoscandia and the Ukrainian Shield the model of relative position and orientation of these blocks at 1770 and 1750 Ma were calculated. About 1770 Ma Fennoscandia and the Ukrainian Shield occupied low latitudinal positions (15° N and 2° S respectively). At the same time the Ukrainian Shield was rotated anticlockwise about 40° relatively to Fennoscandia. In the next 20 Ma Fennoscandia and the Ukrainian shield drifted southward at about 5° and occupied 10°N and 7°S paleolatitudes respectively, but relative rotation of blocks almost did not occur. The average speed of latitudinal drift of both blocks was near to 2.8 cm/yr. The new results of paleomagnetic studies of Volhyn basalts of Ratnenska suite are presented. We assume that the geometry of the geomagnetic field was not dipole as one of the interpretation of these results. In this context we should study of whole Volyn traps sequence from boreholes and Ediacaran—Cambrian sequences of Podolia in order to gather some data about frequency of geomagnetic reversals.

Assessing the intersection/remagnetization puzzle with synthetic apparent polar wander paths

Palaeomagnetic data are of variable quality. To assist in a systematic assessment of data, a set of seven quality criteria (VQ1–VQ7) were introduced by Van der Voo. The last of those criteria ‘VQ7’ concerns the possibility of remagnetization when a particular palaeomagnetic pole resembles a younger palaeopole from the same stable region. While remagnetizations are often the culprit, the mere resemblance of an older pole to a younger pole does not a priori require that the rocks under investigation are remagnetized. Given that the Earth has a finite surface area, that apparent polar wander paths (APWPs) are represented as wide swathes rather than points, and that continental motion has taken place over several billion years, we ask the question ‘How likely is it for an APWP to loop back on itself?’ To answer this question, we constructed synthetic APWPs in an effort to evaluate the likelihood of self-intersection. We find that given 500 Myr of apparent polar wander, ∼60 per cent of the synthetic APWPs show self-intersection. Given 1000 Myr of apparent polar wander, ∼95 per cent of the synthetic APWPs show self-intersection. These results show that resemblance to younger palaeopoles, over the long term, may be governed by simple probability rather than only remagnetization. We recognize that remagnetization does occur, sometimes pervasively, and must be reckoned with in the assessment of palaeomagnetic data. Perhaps VQ7 should be amended to the first sentence in the original discussion, and focus on satisfying ‘No suspicion of remagnetization’ via other means rather than solely a resemblance to younger poles.

Dominant Lid Tectonics behaviour of continental lithosphere in Precambrian times: Palaeomagnetism confirms prolonged quasi-integrity and absence of supercontinent cycles

Although Plate Tectonics cannot be effectively tested by palaeomagnetism in the Precambrian aeon due to the paucity of high precision poles spanning such a long time period, the possibility of Lid Tectonics is eminently testable because it seeks accordance of the wider dataset over prolonged intervals of time; deficiencies and complexities in the data merely contribute to dispersion. Accordance of palaeomagnetic poles across a quasi-integral continental crust for time periods of up to thousands of millions of years, together with recognition of very long intervals characterised by minimal polar motions (∼2.6–2.0, ∼1.5–1.25 and ∼0.75–0.6 Ga) has been used to demonstrate that Lid Tectonics dominated this aeon. The new PALEOMAGIA database is used to refine a model for the Precambrian lid incorporating a large quasi-integral crescentric core running from South-Central Africa through Laurentia to Siberia with peripheral cratons subject to reorganisation at ∼2.1, ∼1.6 and ∼1.1 Ga. The model explains low levels of tidal friction, reduced heat balance, unique petrologic and isotopic signatures, and the prolonged crustal stability of Earth's “Middle Age”, whilst density concentrations of the palaeomagnetic poles show that the centre of the continental lid was persistently focussed near Earth's rotation axis from ∼2.8 to 0.6 Ga. The exception was the ∼2.7–2.2 Ga interval defined by ∼90° polar movements which translated the periphery of the lid to the rotation pole for this quasi-static period, a time characterised by glaciation and low levels of magmatic activity; the ∼2.7 Ga shift correlates with key interval of mid-Archaean crustal growth to some 60–70% of the present volume and REE signatures whilst the ∼2.2 Ga shift correlates with the Lomagundi δ13 C and Great Oxygenation events. The palaeomagnetic signature of breakup of the lid at ∼0.6 Ga is recorded by the world-wide Ediacaran development of passive margins and associated environmental signatures of new ocean basins. This event defined the end of a dominant Lid Tectonic phase in the history of Earth's continental lithosphere recorded by the quasi-integral Precambrian supercontinent Palaeopangaea and the beginning of the comprehensive Plate Tectonics which has characterised the Phanerozoic aeon. Peripheral modifications to the lid achieved a symmetrical and hemispheric shape in Neoproterozoic times comparable to the familiar short-lived supercontinent (Neo)Pangaea (∼350–150 Ma) and this appears to be the sole supercontinent cycle recorded by the palaeomagnetic record. Prolonged integrity of a large continental nucleus accompanied by periodic readjustments of peripheral shields can reconcile divergent tectonic analyses of Precambrian times which on the one hand propose multiple Wilson Cycles to explain some signatures of Plate Tectonics, and alternative interpretations which consider that Plate Tectonics did not commence until the end of the Neoproterozoic.

Palaeomagnetism of the Cretaceous Lamproites from Gondwana basin of the Damodar Valley in India and migration of the Kerguelen plume in the Southeast Indian Ocean

The paper presents new palaeomagnetic results and reassesses complete set of published palaeomagnetic results on the lamproite intrusions in the Gondwana formations of the Eastern India. Altogether eleven sites register reliable characteristic magnetisations corresponding to the c. 110 Ma emplacement age of the lamproites. A mean ChRM is estimated with D=331.3°; I=−62.4° (α95=6.2°, k=55; N=11). The palaeomagnetic pole of λ=14.9°: Φ=287.6° (A95=8.4°) is established for the lamproites and it averaged the secular variation and confirms to the Geocentric Axial Dipole (GAD). The pole compares remarkably well with the grand mean pole reported for the Rajmahal traps that are attributed to represent location of the Kerguelen mantle plume head. The palaeolatitudes transferred to Rajmahal coordinates (25.05°: 87.84°) are situated ∼6° north of the present location of the Kerguelen hotspot location. The interpretations are consistent with earlier suggestions of southward migration of the plume based on palaeomagnetic results of Site 1138 of the ODP Leg 183 and with the predictions of numerical models of global mantle circulation.