Evaluating the paleomagnetic potential of single zircon crystals using the Bishop Tuff

TL;DR

This study demonstrates that zircon crystals from the Bishop Tuff can reliably record paleomagnetic signals, with high-precision experiments confirming their potential to constrain the early Earth's magnetic field, provided their magnetic carriers are carefully characterized.

Contribution

The paper provides the first high-precision paleointensity measurements on ancient zircons, validating their use in paleomagnetic studies and highlighting the importance of characterizing ferromagnetic minerals within zircons.

Findings

Zircons record paleointensity consistent with whole rock data.

Magnetization is mainly carried by Fe oxides in inclusions.

Quantum diamond magnetometry aids in mineralogical characterization.

Abstract

Zircon crystals offer a unique combination of suitability for high-precision radiometric dating and high resistance to alteration. Paleomagnetic experiments on ancient zircons may potentially constrain the earliest geodynamo, which holds broad implications for the early Earth interior and atmosphere. However, the ability of zircons to record accurately the geomagnetic field has not been fully demonstrated. Here we conduct thermal and room temperature alternating field (AF) paleointensity experiments on 767.1 thousand year old (ka) zircons from the Bishop Tuff, California. The rapid emplacement of these zircons in a well-characterized magnetic field provides a high-fidelity test of the zircons intrinsic paleomagnetic recording accuracy. Successful dual heating experiments on nine zircons measured using a superconducting quantum interference device (SQUID) microscope yield a mean paleointensity of 46.2 +/- 18.8 microtesla (1sigma), which agrees closely with high-precision results from Bishop Tuff whole rock (43.0 +/- 3.2 microtesla). High-resolution quantum diamond magnetic mapping, electron microscopy, and X-ray tomography indicate that the bulk of the remanent magnetization in Bishop Tuff zircons is carried by Fe oxides associated with apatite inclusions, which would be susceptible to destruction via metamorphism and aqueous alteration in older zircons. As such, while zircons can reliably record the geomagnetic field, robust zircon-derived paleomagnetic results require careful characterization of the ferromagnetic carrier and demonstration of their occurrence in primary inclusions. We further conclude that a combination of quantum diamond magnetometry and high-resolution imaging can provide detailed, direct characterization of the ferromagnetic mineralogy of geological samples.