24 Undergraduate Research Posters

This poster session highlights geoscience research conducted and presented by undergraduate students. Abstracts must be written by students (but may include non-student co-authors). Research topics may include any area of the earth sciences.

Thursday, 23 April 2026
8:00 AM - 5:30 PM
LMH, 5th Floor Chapel

What is magnetic in the garnet-facies mantle

Paper number: 24-7
Program: Technical Sessions
Time: 8:15 AM – 8:15 AM

Authors

Abstract

The mantle was previously considered to contain no magnetically-remanent phases and be too hot to carry magnetization. Subsequent investigations, have shown that primary magnetite occurs widely within olivine grains of unaltered spinel-facies mantle xenoliths. In cold geotherm settings from 30-70 km depth, such as cratons and subduction zones, the mantle is cold enough to contribute to long-wavelength magnetic anomalies. This view is also supported by geophysical observations indicating that deep magnetic sources lie within the upper mantle. At depths greater than 80 km, spinel and clinopyroxene react to form garnet, a mineral phase that remains stable down to depths >300 km. As a recent study has shown, hematite and Fe2O3 polymorphs remain magnetic down to the transition zone ~1,200 K and 670 km depth. Hence, garnet-bearing mantle xenoliths and other eclogites could theoretically host magnetically-remanent phases such as Fe3O4, and Fe2O3 polymorphs. We plan on testing this hypothesis by measuring the magnetic properties of a collection of worldwide unaltered mantle xenoliths and eclogites from which we have obtained garnet and olivine separates. 

Preliminary Magnetic measurements are being conducted using the  Agico JR6 spinner magnetometer, a LakeShore Cryotronics 8606 VSM vibrating sample magnetometer (sensitivity 15 x 10⁻⁹ Am²), and Kappabridge KLY-5 susceptometer systems. The experimental sequence begins with. We measured the Natural Remanent Magnetization (NRM), Alternating Field demagnetization (AF) demagnetized the NRM, and measured the low-field magnetic susceptibility, magnetic hysteresis properties, performed first-order reversal curve analysis, and acquired isothermal remanent magnetization. Further experiments will address the Curie temperature and thermal demagnetization of NRM.

 Roughly one-third of samples will then undergo Curie temperature testing and extended thermal demagnetization to assess high-temperature stability. A key component of this project is reinterpreting existing data in light of new measurements. The two goals of these investigations are to quantify the nature and concentration of magnetically remanent phases in these olivine and garnet samples, and to evaluate the petrologic implications for the stability / metastability of iron oxides in the upper mantle. The anticipated results may also have bearing on possible magnetic sources for LWMA at depths from 80 to 300 km in cold geotherm settings on Earth and Mars..

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410876

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