Marine magnetic anomalies   The origin of the stripes
Channel: Paul Wessel
Date: 2020-02-05

Dr. Jeff Gee (Scripps Institution of Oceanography, UCSD) gave a guest lecture via Skype in Spring 2012 for a graduate class on Advanced Plate Tectonics in SOEST, University of Hawaii at Manoa.  The students recorded the lecture and produced video podcasts of the event.  This is one of 8 such lectures from the course which was taught by Prof. Paul Wessel.

ABSTRACT:

"Marine magnetic anomalies provide the framework for the geomagnetic polarity time scale for the late Jurassic to Recent (since 160 Ma) and are a principal data source for plate reconstructions. Although polarity reversals constitute the dominant signal, there are a number of other factors that can affect the amplitude and shape of magnetic anomalies. I will briefly review our current understanding on the source of the anomalies, highlighting several aspects that might influence tectonic interpretations. For example, crustal accretionary processes exert a fundamental control on the spatial distribution of magnetization sources, limiting the temporal resolution of the geomagnetic signal resolvable from marine magnetic anomalies and, in some cases, modulating their shape (skewness). In addition, the remanent magnetization vector may be rotated during accretion (e.g., tilt due to lava loading) or by subsequent tectonic deformation. Any tectonic rotation of the magnetic source layer about a ridge-parallel rotation axis will result in an equivalent phase shift of the magnetic anomaly. Anomalous skewness, the phase shift not accounted for by a standard thin layer block model, therefore provides a strong constraint on any tectonic tilt of the magnetization source as well as nonvertical polarity boundaries. There is increasing evidence that marine magnetic anomalies are capable of recording a broad spectrum of geomagnetic field behavior, including intensity fluctuations that may ultimately provide additional time markers within constant polarity intervals that can be used for tectonic studies and to address outstanding problems in crustal accretion processes."