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Magnetic anomalies off west coast of North America. Dashed lines are spreading centers on mid-ocean ridges. The Vine–Matthews-Morley hypothesis correlates the symmetric magnetic patterns seen on the seafloor with geomagnetic field reversals. At mid-ocean ridges, new crust is created by the injection, extrusion, and solidification of magma.
Seafloor spreading. Age of oceanic lithosphere; youngest (light colour) is along spreading centers. Seafloor spreading, or seafloor spread, is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.
A geomagnetic reversal is a change in a planet's dipole magnetic field such that the positions of magnetic north and magnetic south are interchanged (not to be confused with geographic north and geographic south). The Earth's magnetic field has alternated between periods of normal polarity, in which the predominant direction of the field was ...
Magnetostratigraphy uses the polarity reversal history of Earth's magnetic field recorded in rocks to determine the age of those rocks. Reversals have occurred at irregular intervals throughout Earth's history. The age and pattern of these reversals is known from the study of sea floor spreading zones and the dating of volcanic rocks.
Thermoremanent magnetization is the main source of the magnetic anomalies around mid-ocean ridges. As the seafloor spreads, magma wells up from the mantle, cools to form new basaltic crust on both sides of the ridge, and is carried away from it by seafloor spreading. As it cools, it records the direction of the Earth's field.
Plate tectonics (from Latin tectonicus, from Ancient Greek τεκτονικός (tektonikós) 'pertaining to building') [ 1 ] is the scientific theory that Earth 's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. [ 2 ][ 3 ][ 4 ] The model builds on the concept of continental ...
The whole process of seafloor spreading could be divided into two parts, spreading in the Northeast and spreading in the Southwest. [6] [7] During the seafloor spreading process, three episodes of spreading were classified based on the magnetic anomalies. The seafloor spreading center jumps three times, at 25.5 Ma, at 24.7 Ma and at 20.5 Ma. [7]
It is at mid-ocean ridges that one of the key pieces of evidence forcing acceptance of the seafloor spreading hypothesis was found. Airborne geomagnetic surveys showed a strange pattern of symmetrical magnetic reversals on opposite sides of ridge centers. The pattern was far too regular to be coincidental as the widths of the opposing bands ...