Imaging Micrometer Scale Rock Magnetism Using a Quantum Diamond Microscope

Abstract:

Optically-detected magnetometry using quantum defects in diamond, known as nitrogen-vacancy (NV) color centers, is an emerging technology that allows high sensitivity and high resolution mapping of magnetic fields. Recent measurements of live magnetotactic bacteria demonstrate that such a “quantum diamond microscope” can image individual magnetic sources with <500 nm resolution, >1 mm field-of-view, and magnetic moment sensitivity <10^-16 A m² under ambient temperatures and pressures.

The unprecedented combination of spatial resolution and magnetic sensitivity of the quantum diamond microscope permits magnetic analyses of previously inaccessible geologic samples in which the regions of interest are mixed with undesirable magnetic field sources at the <<100 µm scale. Here we apply this technique to chondritic meteorites, primordial aggregates formed during the accretional phase of the solar system. These meteorites consist of fine-grained matrix mixed with chondrules and other inclusions with characteristic sizes of 0.1 - 1 mm. Each chondrule records a unique magnetic history and potentially constrains nebular magnetic fields, which likely played a key role in accretion disk dynamics. The quantum diamond microscope is unique in its ability to resolve the magnetic signal of single inclusions from surrounding material.

We applied the quantum diamond microscope to a variety of natural and artificial samples. Magnetic field maps of a single chondrule from the Allende CV carbonaceous chondrite (Fig. 1) show that the strongest magnetic sources are located in its 20 µm thick rim. Magnetic field sources in the chondrule interior occur in the mesostasis as isolated 10-100 µm patches that generate magnetic fields ~10 times weaker than the rim. These maps highlight the importance of spatial resolution for paleomagnetic measurements of chondrites; lower resolution measurements would permit the nearby rim material to dominate the magnetic signal, precluding accurate recovery of paleomagnetic data from chondrule interiors. In addition to these results we will report NV-diamond maps of other meteorites, including Antarctic finds, that contain secondary weathering veins. These maps will enable the exclusion of terrestrial magnetic signals in paleomagnetic analyses of these samples.