Paleomagnetism, polar wandering, and the rejuvenation of crustal mobility
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Abstract:
The decade from 1951 to 1961 witnessed the birth of a new geophysical subdicipline, paleomagnetism. Early studies in Europe, North America, and Australia led to the following conclusions: (1) rocks could preserve directions of magnetiziation for hundreds of millions of years in red beds, (2) late Cenozoic lavas had directions of magnetiziation that led to the conclusion that the mean geomagnetic field was a geocentric dipole aligned along the axis of rotation, (3) rocks of Triassic age and older yield directions which depart widely from the present axis of rotation, (4) if these directions are used to calculate pole positions, then poles for older and older rocks fall farther and farther from the present pole of rotation, (5) these data may be used to construct polar wander curves, (6) polar wander curves from different continents do not coincide with one another, (7) they may be reconciled if the continents move with respect to each other, and (8) the distribution of climatic indicators show that the pole of rotation of Earth and the paleomagnetic pole for the same periods coincide for Phanerozoic time. These observations changed the perspectives of many Earth scientists and paved the way for seafloor spreading and plate tectonics.Keywords:
Apparent polar wander
Polar wander
Geomagnetic pole
Seafloor Spreading
Polar motion
Geomagnetic secular variation
Geomagnetic pole
Geomagnetic reversal
Core–mantle boundary
Mantle plume
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Late Mesozoic and Cenozoic palaeomagnetism of Australia?I. A redetermined apparent polar wander path
Palaeomagnetic measurements have been carried out on one Cretaceous and five Cenozoic sedimentary sequences of Australia; of those, one is in the Carnarvon Basin of north-western Australia, and the others are in the Otway Basin of south-eastern Australia. The new results are used together with those published previously to define a revised late Mesozoic—Cenozoic apparent polar wander path for Australia. This path differs from earlier, basalt-derived paths by the absence of a large westward excursion and zig-zag irregularities. It is characterized instead by a substantially straight Cenozoic trajectory, a sharp bend in the Late Cretaceous, and a non-uniform rate of apparent polar wander.
Apparent polar wander
Polar wander
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In this paper we show that: (1) The positions of the Cretaceous palaeomagnetic poles (PP) for South America and Africa exhibit elongated distributions that are due to rapid movement of these continents from the south pole. (2) The positions of the Middle—late Jurassic virtual geomagnetic poles for South America exhibit an elongated distribution along the meridians 20–200° E; it is suggested that this is due to a rapid shift of South America in Middle—late Jurassic time. (3) The late early—early late Cretaceous sections of the apparent polar wandering paths for South America and Africa are consistent with South Atlantic seafloor spreading data. On the basis of the comparison of the reliable late Palaeozoic—late Cretaceous PPs for South America and Africa, taking into account the restrictions established by geological, palaeontological and seafloor spreading data, it is suggested that minor movements could have occurred within Western Gondwana in middle—late Jurassic time along a narrow zone which later became the South Atlantic divergent boundary. Four 'hairpins' are defined in the late Palaeozoic—late Cretaceous section of the apparent polar wandering path for South America; the two youngest of these can be correlated with the origin of the South Atlantic Ocean basin and the onset of the Andean Orogeny, respectively. The magnetostratigraphy for the Serra Geral lava flow sequence suggests that some of these flows were poured out rapidly without significant interruption.
Magnetostratigraphy
Apparent polar wander
Polar wander
Geomagnetic pole
Seafloor Spreading
Red beds
Oceanic basin
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Apparent polar wander
Pacific Plate
Polar wander
Hotspot (geology)
Geomagnetic pole
Pillow lava
Magnetostratigraphy
Seamount
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Geomagnetic pole
Apparent polar wander
Geomagnetic secular variation
Polar wander
Secular Variation
Magnetic dip
Hotspot (geology)
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Some studies of global paleomagnetic data have found an offset of the magnetic pole during the Plio‐Pleistocene which has been interpreted as indicating a period of rapid True Polar Wander, with a rate of movement comparable to the present‐day rate of polar motion deduced from astronomical observations. We show that much of the polar offset determined from the paleomagnetic data may be due to deviations in pole position caused by persistent non‐dipole zonal components of the geomagnetic field. A correction of paleomagnetic poles for the long‐term non‐dipole field reduces the polar offset and thus suggests a slower or shorter episode of True Polar Wander over the past 5 million years.
Polar wander
Plio-Pleistocene
Apparent polar wander
Polar cap
Polar motion
Geomagnetic pole
Secular Variation
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Polar motion
Speed wobble
Secular Variation
Geomagnetic pole
Apparent polar wander
Polar wander
Geomagnetic secular variation
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We present palaeomagnetic results from the Durgapipal and Rudraprayag formations, which are basic volcanic formations in the Lesser Himalayas of Uttar Pradesh State. NRM measurements and AF demagnetization stability tests were made on specimens cored from oriented block samples collected at representative sites. Mean stable remanent magnetic directions were used for calculating the Virtual Geomagnetic Pole (VGP) positions; where necessary tectonic corrections were applied. The virtual geomagnetic north poles were found to be located at: (a) Durgapipal (Permian): λp = 10° S, Lp = 42° W; (b) Rudraprayag (Silurian-Devonian): λp = 30° S, Lp = 12° W. A new, continuous Phanerozoic apparent polar wandering curve for the Indian subcontinent has been plotted from the available palaeomagnetic data and the VGP positions reported in this paper. As a result, the gap in the Indian palaeomagnetic data from the Lower Carboniferous to the Cambrian has been partially filled. The locations of the pole positions for the two formations on the Phanerozoic polar wandering curve for the Indian subcontinent, have been found to coincide with the stratigraphic ages assigned to them on the basis of rather limited geological and palaeontological evidence. The Cambrian and Permian poles for the Salt Range in the NW Himalayas and the Permian pole for the Kumaon Himalayas are grouped along with the pole positions of contemporaneous formations of the Peninsular Shield. The palaeomagnetic data thus suggests that the two formations are autochthonous in nature.
Geomagnetic pole
Polar wander
Apparent polar wander
Devonian
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Apparent polar wander
Geomagnetic pole
Baltica
Laurentia
Polar wander
Geomagnetic secular variation
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