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inversion


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A reversal of a particular trend. 1. A rock sequence in which the younger sediments are at the bottom. Inversion can be caused by overfolding or thrusting. It is a major feature of an accretionary wedge in which progressively younger oceanic and trench sediment is underthrust, so that while each thrust slice is not inverted, each new thrust affects younger sediment, so producing the inversion. In a positive inversion, normal faults on passive margins become thrusts on collision. In a negative inversion thrusts become normal faults at the end of an orogeny. The inversion of sediments takes place during strike-slip faulting. 2. During an orogeny, the uplift that follows subsidence as a reversal of vertical direction. 3. Seismic velocity usually increases with depth, but occasionally a zone of anomalously low velocity occurs between layers of higher velocities giving rise to a velocity inversion. 4. See polarity reversal, geomagnetic. 5. See temperature inversion.

1. A rock sequence in which the younger sediments are at the bottom. Inversion can be caused by overfolding or thrusting. It is a major feature of an accretionary wedge in which progressively younger oceanic and trench sediment is underthrust, so that while each thrust slice is not inverted, each new thrust affects younger sediment, so producing the inversion. In a positive inversion, normal faults on passive margins become thrusts on collision. In a negative inversion thrusts become normal faults at the end of an orogeny. The inversion of sediments takes place during strike-slip faulting. 2. During an orogeny, the uplift that follows subsidence as a reversal of vertical direction. 3. Seismic velocity usually increases with depth, but occasionally a zone of anomalously low velocity occurs between layers of higher velocities giving rise to a velocity inversion. 4. See polarity reversal, geomagnetic. 5. See temperature inversion.

Subjects: Earth Sciences and Geography.


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