Determination of Intensity of Earth's Magnetic Field During the Cretaceous and Tertiary Using Dated Chinese Basalts

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9706439 Zhao Measurements of the intensity of the Earth's magnetic field in the past are critical for understanding the processes in the core that give rise to the Earth's magnetic field, and how and why the Earth's magnetic field reverses polarity. In addition, variation of the intensity of the Earth's magnetic field over geologic time may signal modulation of dynamo action in the core by the convective state of the lower mantle, and thus could also carry information about the rates of sea-floor spreading, hot-spot volcanism and Earth's tectonic cycle. The PIs propose studies of two important geophysical problems which are currently debated: (1) to obtain mid-Cretaceous paleointensities (91 Ma) to examine the question of intensity of the geomagnetic field during the Cretaceous Superchron, in particular whether the field was persistently low or unusually high during times of low reversal rate; (2) to determine the paleointensity from 7 Ma and 32 Ma old basalts to test whether the field strength is responsible for the relatively higher amplitude of marine magnetic anomalies that is observed in most of the world's oceans between 30 and 80 Ma. ***