Plate reconstruction

[5] The movement of a rigid body, such as a plate, on the surface of a sphere can be described as rotation about a fixed axis (relative to the chosen reference frame).

The reconstruction before Atlantic rifting by Bullard based on a least-squares fitting at the 500 fathom contour still provides the best match to paleomagnetic pole data for the two sides from the middle of Paleozoic to Late Triassic.

[7] Plate reconstructions in the recent geological past mainly use the pattern of magnetic stripes in oceanic crust to remove the effects of seafloor spreading.

The inclination flattening error can nevertheless be estimated and corrected for through re-deposition experiments, measurements of magnetic anisotropy, and the use of theoretical models for the dispersion of paleomagnetic directions.

[9] A paleomagnetic pole is defined by taking the average direction of the primary remanent magnetization for the sampled rocks (expressed as the mean declination and inclination) and calculating the position of a geomagnetic pole for the field of a geocentric magnetic dipole that would produce the observed mean direction at the sampled locality in its present geographic coordinates.

Under the assumption that the mean paleomagnetic direction corresponds to that of the GAD field, the paleolatitude of the sampling location (λ) can be derived from the inclination (I) of the mean direction using a simple equation:[16] The mean declination (D) gives the sense and amount of rotation about a vertical axis passing through the sampling area, which needs to be applied to restore its original orientation with respect to the lines of longitude.

[17] Thus, a paleomagnetic pole defines the paleo-latitudinal position and orientation of the entire tectonic block at a specific time in the past.

However, because the GAD field is azimuthally symmetric about the Earth's rotation axis, the pole does not set any constraint on the absolute longitude.

However, relative longitudes of different crustal blocks can be defined using other types of geological and geophysical data constraining relative motions of tectonic plates, including the histories of seafloor spreading recorded my marine magnetic anomalies, matching of continental borders and geologic terranes, and paleontological data.

[7] Poles from different ages in a single continent, lithospheric plate, or any other tectonic block can be used to construct an apparent polar wander path (APWP).

The second component is commonly referred to as true polar wander (TPW) and on geologic time scales results from gradual redistribution of mass heterogeneities due to convective motions in the Earth's mantle.

[21][13] For the earlier times in the Mesozoic and Paleozoic, TPW estimates can be obtained through the analysis of coherent rotations of the continental lithosphere,[19] which allows linking the reconstructed paleogeography to the large-scale structures in the lower mantle, commonly referred to as Large Low Shear-wave Velocity Provinces (LLSVPs).

It has been argued that the LLSVPs have been stable over at least the past 300 Ma, and possibly longer, and that the LLSVP margins have served as generation zones for the mantle plumes responsible for eruptions of Large Igneous Provinces (LIPs) and kimberlites.

[22][23] Correlating the reconstructed locations of LIPs and kimberlites with the margins of LLSVPs using the estimated TPW rotations makes it possible to develop a self-consistent model for plate motions relative to the mantle, true polar wander, and the corresponding changes of paleogeography constrained in longitude for the entire Phanerozoic,[24] although the origin and long-term stability of LLSVPs are the subject of the ongoing scientific debate.

This method could extend absolute plate motion reconstructions deeply into the geologic history as long as there are reliable APWPs.

This method gives an absolute reconstruction of both latitude and longitude, although before about 90 Ma there is evidence of relative motion between hotspot groups.

[29] Some plate reconstructions are supported by other geological evidence, such as the distribution of sedimentary rock types, the position of orogenic belts and faunal provinces shown by particular fossils.

As oceans narrow before a collision occurs, the faunas start to become mixed again, providing supporting evidence for the closure and its timing.

Earthquake epicenters 1963–98
Ages of oceanic lithosphere
Paleogeographic reconstruction of the Pangea supercontinent at the Permo-Triassic Boundary (250 Ma). Top panel: Synthetic APWP for Africa (the south paleomagnetic poles are shown with their 95% uncertainty ovals). The red dot highlights the 250 Ma paleomagnetic pole. APWP data are from Torsvik et al. (2012). [ 13 ] Middle panel: All continents are assembled in the Pangea configuration at 250 Ma using the estimates of their relative motions, with Africa kept fixed in its present position. The red triangle shows the position of the Euler pole and the red arrow indicates the rotation that would reconstruct the paleomagnetic pole to the south geographic pole. Bottom panel: The Euler rotation has been applied to Pangea, which is now reconstructed paleogeographically. The longitude is arbitrary set to minimize the longitudinal motion of Africa since 250 Ma.
The Hawaiian-Emperor seamount chain
Reconstruction of eastern Gondwana showing position of orogenic belts