MI2023 - 03 Po-Yen Tung: Machine learning and microscopy: the search for primary magnetic carriers
Channel: MagNetZ
Date: 2023-01-16

Magnetic Interactions 2023 conference at the University of Cambridge
Session 1: Solar System and Asteroid Magnetism

Title: Machine learning and microscopy: the search for primary remanence carriers in calcium-aluminium-inclusions (CAIs)
Author: Po-Yen Tung from the University of Cambridge, UK (presented by Richard Harrison)

Identification of unknown micro- and nano-sized mineral phases is commonly achieved by analysing chemical maps generated from hyperspectral imaging datasets, particularly scanning electron microscope - energy dispersive X-ray spectroscopy (SEM-EDS) and scanning transmission electron microscope - energy dispersive X-ray spectroscopy (STEM-EDS). However, the accuracy and reliability of mineral identification are often limited by subjective human interpretation, non-ideal sample preparation, and the presence of mixed chemical signals generated within the electron-beam interaction volume. In the context of rock and mineral magnetism, a core task is to peer through the fog of these complex chemical signals to unmix, identify and map out the distribution of remanence carrying phases.

Machine learning has emerged as a powerful tool to overcome this class of problem. Here, we introduce a user-friendly Python code (SIGMA - Spectral Interpretation using Gaussian Mixtures and Autoencoder) with a graphical user interface to identify unknown phases and unmix their overlapped chemical signals. This approach leverages the guidance of Gaussian mixture modeling clustering fitted on an informative latent space of pixel-wise elemental datapoints modeled using a neural network autoencoder, and unmixes the overlapped chemical signals of phases using non-negative matrix factorization.

In this talk we demonstrate the value of this new approach as part of a correlative SEM/(S)TEM workflow to search for primary remanence carriers in calcium-aluminium inclusions (CAIs) in the CO3.00 carbonaceous chondrite Dominion Range (DOM) 08006. This is one of the most pristine, least-altered carbonaceous chondrites and therefore may retain a record of the magnetic field present at the time and location of CAI formation and/or thermal processing. Despite the low overall levels of aqueous alteration in DOM08006 we identify two styles of alteration in the CAIs that can lead to the occurrence of secondary magnetite. The first is associated with alteration of primary forsterite that occurs as part of the primary nebula condensation sequence. The second is associated with altered matrix material flushed into forcibly opened cracks in the CAI. Altered regions correlate closely with strong SIRM signals mapped using QDM. Regions with strong SIRM not apparently linked to secondary magnetite formation (at least at the sample surface analysed) have also been identified, and linked to the presence of pre-accretionary metal grains in the SDPSD size range. These observations suggest that if the remanence from the preaccretionary metal in unaltered regions can be isolated, these CAIs do have the potential to retain a nebular remanence.

https://github.com/poyentung/sigma

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00:00 - Intro
00:20 - Presentation
16:50 - Questions