Support for an “A-type” Pangea reconstruction from high-fidelity Late Permian and Early to Middle Triassic paleomagnetic data from Argentina
Mathew DomeierRob Van der VooRenata N. TomezzoliE. TohverB.W.H. HendriksTrond H. TorsvikHaroldo VizánAda R. Dominguez
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[1] A major disparity is observed between the late Paleozoic-early Mesozoic apparent polar wander paths (APWPs) of Laurussia and Gondwana when the landmasses are re-assembled in a conventional "A-type" Pangea. This discrepancy has endured from the earliest paleomagnetic reconstructions of the supercontinent, and has prompted discussions of non-dipole paleomagnetic fields and alternative paleogeographic models. Here we report on a joint paleomagnetic-geochronologic study of Late Permian and Early to Middle Triassic volcanic and volcaniclastic rocks from Argentina, which demonstrates support for an A-type model, without requiring modification to the geocentric axial dipole hypothesis. New SHRIMP U-Pb and 40Ar-39Ar isotopic dating has reinforced the inferred age of the sequences, which we estimate at ∼264 Ma (Upper Choiyoi Group) and ∼245 Ma (Puesto Viejo Group). Field-stability tests demonstrate that the volcanic rocks are carrying early/primary magnetizations, which yield paleopoles: 73.7°S, 315.6°E, A95: 4.1°, N: 40 (Upper Choiyoi) and 76.7°S, 312.4°E, A95: 7.3°, N: 14 (Puesto Viejo). A comprehensive magnetic fabric analysis is used to evaluate structural restorations and to correct for magnetization anisotropy. The paleomagnetic results derived from volcaniclastic rocks are interpreted to be affected by inclination shallowing, and corrections are discussed. A comparison of these new results with the existing Permian-Triassic paleomagnetic data from Gondwana suggests the presence of widespread bias in the latter. We contend that such bias can explain the observed APWP disparity, at least for Late Permian-Middle Triassic time, and that alternative paleogeographic reconstructions or non-dipole paleomagnetic fields do not need to be invoked to resolve the discrepancy.Keywords:
Apparent polar wander
Early Triassic
The Late Paleozoic-Early Mesozoic apparent polar wander path of Gondwana is largely constructed from relatively old paleomagnetic results, many of which are considered unreliable by modern standards.Paleomagnetic results derived from sedimentary sequences, which are generally poorly dated and prone to inclination shallowing, are especially common.Here we report the results of a joint paleomagneticgeochronologic study of a volcanic complex in central Argentina.U-Pb dating of zircons has yielded a robust age estimate of 263.0 +1.6/-2.0Ma for the complex.Paleomagnetic analysis has revealed a pretilting (primary Permian) magnetization with dual polarities.Rock magnetic experiments have identified pseudosingle domain (titano)magnetite and hematite as the mineralogic carriers of the magnetization.Lightninginduced isothermal remagnetizations are widespread in the low-coercivity magnetic carriers.The resulting paleomagnetic pole is 80.1°S, 349.0°E,A 95 = 3.3°, N = 35, and it improves a Late Permian mean pole calculated from a filtered South American paleomagnetic data set.More broadly, this new, high-quality, igneous-based
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Apparent polar wander
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Red beds
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Abstract To test the hypothesis that a Cretaceous hairpin turn is absent in the apparent polar wander path (APWP) of the inner arc of southwestern Japanese island (southwest Japan), we refined a mid-Cretaceous (100 Ma) paleomagnetic pole from southwest Japan. Red mudstone samples from the 100 Ma Hayama Formation were collected for paleomagnetic analysis from eight sites in the Hayama area in the central part of southwest Japan. A high-temperature remanent magnetization component carried by hematite was isolated from these sites and was found to be of primary mid-Cretaceous origin. The primary nature of the magnetization is supported by the detrital character of the magnetic carrier. The primary directions provided a paleomagnetic pole (35.0°N, 209.6°E, A 95 = 6.1°, N = 8), which represented southwest Japan at 100 Ma. This pole falls into a cluster of Cretaceous poles in southwest Japan. An APWP for southwest Japan between 110 and 70 Ma was updated to ascertain the stationarity of the pole positions for this region. Therefore, it is unlikely that the APWP for southwest Japan experienced a hairpin turn during the Cretaceous.
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Detailed paleomagnetic studies of Lower Cambrian reference sections of the Siberian platform were performed; the sections are located within the Chekurovka and Bulkur anticlines in the northeasternmost part of the Siberian platform. The bulk of rocks composing the sections studied (including volcanic flows of basic composition) is shown to have been completely remagnetized by the Mesozoic geomagnetic field. The overprinting time coincides (with certainty in the Chekurovka section and with a high probability in the Bulkur section) with the period of fold-thrust deformations that took place in the study area at the end of the Cretaceous and were associated with the formation of the Kharaulakh segment of the Verkhoyansk fold area. Two possible interpretations of the inferred paleomagnetic directions are discussed. It is shown that, regardless of the inter- pretation variant, the resulting paleomagnetic poles are well consistent with the apparent polar wander path (APWP) proposed by Besse and Courtillot (1) for stable Europe. The Late Jurassic pole from the Konder Massif (new data) and the average Permo-Triassic pole from the Siberian platform (37) also lie in the close vicinity of the segments of this curve of the respective ages. This result implies that, at least from the end of the Paleozoic, the North Eurasian plate has behaved like a rigid body (within an accuracy of the paleomagnetic method) and the European APWP can be used as a reference path for the Siberian platform. Based on the results of the paleomagnetic studies, ancient components having the Khramov and directions were identified in rocks of the Upper Vendian-Lower Cambrian part of the Chekurovka section, stratigraphically located below volcanic flow. The existence of the Kirschvink direction being questioned by some researchers, this result is independent evidence for its reality and is thereby of great importance, because the Kirschvink direction and the related pole form a cornerstone of the inertial interchange true polar wander hypothesis (13), implying a substantial (by about 90 ° ) and rapid (over 20-25 Myr) displacement of the Earth's rotation axis rel- ative to the Earth's surface at the beginning of the Phanerozoic.
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Anticline
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Red beds
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Apparent polar wander
Baltica
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Abstract In an attempt to elucidate their ages, the often incomplete and poorly known early Permian marine faunas and sequences of India, Tibet, Pakistan, Afghanistan, Iran and Oman are compared with those of the Perth, Carnarvon and Canning Basins of Western Australia, where faunas are documented and in sequence, and stratigraphic relationships between units are clear. This comparison indicates that the faunas discussed are Latest Asselian or younger in age, and that most of the underlying glacial beds are probably Early Permian (Asselian) in age. By implication, the Permo‐Carboniferous boundary for Gondwana is considered to lie at or near the base of Unit II/Stage 2 and equivalent palynomorph zones throughout Gondwana.
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Red beds
Early Triassic
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Apparent polar wander
Early Triassic
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Jurassic fast polar shift rejected by a new high-quality paleomagnetic pole from southwest Greenland
A selective compilation of paleomagnetic data from North America indicates that a vast amount of rapid polar motion occurred in Late Jurassic time. The over 30° polar shift that accumulated during a relatively short time interval (~160–145 Ma) suggests an episode of fast true polar wander (TPW) and was referred to as the Jurassic "monster polar shift" by some workers. However, this rapid TPW event is not supported by paleomagnetic data on a global scale. Here, we scrutinize the Jurassic apparent polar wander path (APWP) by virtue of a new paleomagnetic and 40Ar/39Ar geochronology study of Mesozoic coast-parallel dykes exposed in southwest Greenland. Combined with existing geochronological data, our results show that the dykes were emplaced during a prolonged period centered at 147.6 ± 3.4 Ma (2σ). A primary nature of the characteristic remanent magnetization is supported by multiple positive baked contact tests and a reversal test. The paleomagnetic pole calculated from 40 site-mean paleomagnetic directions is located at Plat = 69.3°S, Plong = 5.0°E (A95 = 4.6°), or at Plat = 73.9°S and Plong = 0.4°E when reconstructed to North America. Our new high-quality paleomagnetic pole and an updated global APWP do not support the fast Jurassic polar shift but instead indicate steady polar motion with moderate rates of about 0.7°/Myr. The new pole effectively reduces the mismatch between the APWPs for Laurentia and Europe. Our critical reassessment of the monster polar shift indicates that it may be an artifact of paleomagnetic and geochronological data that were previously used to argue for its existence.
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Polar wander
Laurentia
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