29-32 Downhole Alteration and Magnetic Property Variabilities of Basaltic Rocks with Different Cooling Rates from the Reykjanes Ridge (IODP Expedition 395C)

Session: Undergraduate Research, Part II (Posters)

Poster Booth No.: 83

Presenting Author:

Emma Robinson

Authors:

Robinson, Emma Joy¹, Friedman, Sarah², Satolli, Sara³, Di Chiara, Anita⁴, Dwyer, Deepa⁵

(1) School of Earth, Environment and Sustainability,, Georgia Southern University, Statesboro, GA, USA, (2) School of Earth, Environment and Sustainability, Georgia Southern University, Statesboro, GA, , (3) Department of Engineering and Geology, University of Chieti-Pescara, Pescara, Italy, (4) National Institute of Geophysics and Volcanology, Rome, Italy, (5) College of Earth Ocean and Atmospheric Sciences, Oregon State University, Corvallis, Orgeon, USA,

Abstract:

Paleomagnetic studies of basaltic rocks provide critical insights into oceanic crust evolution. Indeed titanomagnetite, a key ferromagnetic mineral in basalts, exhibits grain-size- dependent behaviors that influence magnetic retention. Prior paleomagnetic research on titanomagnetite has focused on synthetic samples or limited regions, leaving natural systems with complex cooling histories underexplored. Basaltic samples rich in titanomagnetite collected during International Ocean Discovery Program (IODP) Expedition 395C from the Reykjanes Ridge were evaluated on how downhole alteration processes and cooling rates affect different basalt types: pillow lava, sheet/massive flows, and lava. Seventy-two cubic (8 cm 3 ) basalt samples from Hole U1555I, underwent alternating field demagnetization, magnetic hysteresis test, isothermal remanent magnetization (IRM) test, temperature dependence of magnetic

susceptibility, and thin section analysis. These methods quantify coercivity and magnetic remanence, identify domain-state transitions and minerals present, and compare alteration percentiles. Magnetic hysteresis properties reveal grain-size dependence, with a clear single- domain grouping identifying the quickly cooled pillows. Flows and lavas show overlap in hysteresis behavior, with the flows favoring multi-domain characteristics. Due to limited samples, thin section analysis was constrained to rapidly cooling pillow basalts and slowest cooling lavas. Heavy hydrothermal alteration can be seen in vesicles, veins, large crystals, and the matrix of all thin sections. Textures, including variolitic, vesicular, skeletal, dendritic, and sieve, are observed in thin sections, indicating that the samples cooled quickly.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1, 2026

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