Collaborative Research: Resolving the Origin of the Jurassic Quiet Zone

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

The Earth’s geomagnetic field periodically reverses with the north and south poles switching places. These reversals are preserved in ocean crust as linear magnetic anomalies. Because this process is like a magnetic tape recorder, studying the sequence of magnetic reversals has enabled scientists to develop a time scale used to determine ocean crustal age, plate tectonic movements, and the history of magnetic field evolution. This project will study magnetic reversals during a time known as the Jurassic Quiet Zone where the magnetic anomalies are small in amplitude. A magnetic sensor will be towed near the seafloor to measure these small anomalies. The results will help determine the processes that cause changes in the Earth’s magnetic field. The proposed research examines a poorly understood period of geomagnetic field history, the Jurassic Quiet Zone, during which field strength appears to be much less than normal and the reversal rate much higher than normal. Changes in geomagnetic field behavior are thought to have geodynamic significance, such as indicating heat flux to the mantle from the core, affecting mantle convection. Moreover, the geomagnetic polarity timescale is used as a basis for magnetic field, plate tectonic, and many geodynamic and geologic studies. The proposed research will help define the timescale during a period in which it is poorly constrained. The main objective of this study is to compile a magnetic anomaly sequence over the Phoenix magnetic lineations in Nauru Basin of the Western Pacific for comparison with similar records previously collected over the Japanese lineations of Pigafetta Basin and the Hawaiian lineations near the Magellan Seamounts. This compilation will consist of records from the sea surface, near the seafloor, and in mid-water. This multi-scale approach is done because the extreme detail of anomaly records collected near the seafloor makes correlation with sea surface anomalies (the basis of the geomagnetic polarity timescale) difficult, so the mid-water data complete the picture. Data will be collected near the seafloor using the autonomous vehicle Sentry, at the sea surface using standard magnetometers, and at mid-level using a towed platform. Data will be compiled at each level, correlated, and modeled to determine a polarity sequence. This record will be compared with Japanese and Hawaiian anomaly data to make a composite reversal timescale and to determine the behavior of the low amplitude zone. Multichannel seismic data will be collected with the purpose of defining the top of the magnetic source layer within ocean crust in an area where Mid-Cretacous volcanic sills are known to be emplaced. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.