Paleointensity of the Earth's magnetic field using SQUID microscopy

Abstract

Knowledge of the paleointensity of magnetic fields is valuable for our understanding of the origin and evolution of planetary dynamos and the history of planetary interiors. Until recently, quantitative paleomagnetic and paleointensity analyses were limited to magnetometry of bulk samples. The most sensitive of these moment magnetometers use superconducting quantum interference devices (SQUIDs), which measure the net moment of samples typically millimeters to centimeters in size with sensitivities of 10 − 9 Am 2. Recently, SQUIDs have been adapted to map the fine-scale magnetic fields of geological thin sections with unprecedented spatial resolutions of better than 100 μm and moment sensitivities better than 10 − 15 Am 2. Here we present a detailed study of the magnetization within basalts from the Hawaii Scientific Drilling Project using SQUID microscopy and moment magnetometry in combination with borehole magnetometry, petrographic and geologic data. We demonstrate how SQUID microscopy can be used to measure the paleointensity of the Earth's field which magnetized these basalts during the last 500 ky. These experiments are the first time alternating field demagnetization and paleointensity experiments have been conducted on natural remanent magnetization using submillimeter magnetic imaging techniques. Our high resolution field maps enable us to make thousands of paleointensity measurements on a single thin section which can be correlated with the minerals, petrologic textures, and alteration zones within the samples.