- 1Università degli Studi di Torino, Dipartimento di Scienze della Terra, Torino, Italy (claudio.robustellitest@unito.it)
- 2School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth, UK
- 3School of Earth Sciences, University College Dublin, Science Centre, Belfield Dublin 4, Ireland
- 4Interdisciplinary School of Science, Savitribai Phule Pune University, Pune, India
- 5School of Ocean and Earth Science, University of Southampton, Southampton, UK
- 6Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
- *A full list of authors appears at the end of the abstract
Marine magnetic anomalies provide fundamental information on plate tectonics, seafloor spreading, and geomagnetic field variations over time. It has long been debated whether the long-term variations of the marine magnetic anomalies are related to records of paleointensity variations or the progressive off-axis hydrothermal oxidation of magnetic minerals in mid-ocean-ridge basalts (MORBs). However, these processes are highly dependent on rock type and textures. Moreover, the style and extent of off-axis low-temperature alteration in MORBs varies and can be pervasive through the rock matrix or localized in vein halos, leading to significant heterogeneities in the upper crust. Studying the magnetic properties of both fresh and altered MORBs from transects covering a range of crustal ages is essential to assess and constrain the factors affecting the origin and evolution of magnetic anomalies.
In this study, we combined rock magnetic investigation with petrography and geochemical data to characterize the magnetic behaviour of basalts formed between ~7 and 61 Ma across the western flank of the Mid-Atlantic Ridge, recovered during the South Atlantic Transect (SAT) ocean drilling expeditions. This transect provides the opportunity to test the influence of primary and secondary factors on the magnetic signature of MORBs.
Our results show the strong influence of primary igneous features on the intensity of the remanent magnetization of MORBs. For example, the grain sizes and concentrations of magnetic minerals change according to different emplacement styles, with finer and coarser-grained magnetite in basaltic pillows and massive lava flows, respectively. Moreover, the combination of rock magnetic and major elements analyses reveals variation in primary and alteration mineral assemblages (clay minerals and goethite), composition (e.g., changes in Ti-content) and grain-size across the alteration halos, which in turn affects the intensity of the magnetic signature.
Overall, the variation of magnetic properties across the ridge flank testifies to a complex interplay of factors such as the nature of volcanic units and the style and evolution of hydrothermal alteration on the nature and long-term variation of the marine magnetic anomalies.
Teagle D.A.H., Reece J., Coggon R.M., Sylvan J.B., Christeson G.L., Williams T.J., Estes E.R., Albers E., Amadori C., Belgrano T., Borrelli C., D’Angelo T., Doi N., Evans A., Guerin G.M., Harris M., Hajnacki V.M., Hong G., Jin X., Jonnalagadda M., Kuwano D., Labonte J.M., Lam A.R., Latas M., Lu W., Moal-Darrigade P., Pekar S., Robustelli Test C., Ryan J.G., Santiago Ramos S., Shcheptikina A., Villa A., Wee A.Y., Widlansky S.J., Zhang G.
How to cite: Robustelli Test, C., Amadori, C., Harris, M., Belgrano, T., Jonnalagadda, M., Evans, A., Grant, L., Albers, E., Coggon, R., Teagle, D., and Zanella, E. and the The South Atlantic Transect IODP Expedition 390 & 393 Scientists: Unveiling factors affecting the magnetic signature of MORBs and their long-term variation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10493, https://doi.org/10.5194/egusphere-egu25-10493, 2025.