- 1Department of Geophysics, Stanford University, Stanford, U.S.A.
- 2School of Geography, Earth and Environmental Sciences, University of Plymouth, Plymouth, UK.
- 3Institute of Geosciences and Geography, Martin-Luther-University Halle-Wittenberg, Halle, Germany.
- 4Department of Geology and Geophysics, University of Wyoming, Laramie, WY, USA.
- 5School of Biological, Environmental, and Earth Sciences, University of Southern Mississippi, Hattiesburg, MS, USA.
Large-offset oceanic detachment faults play a key role in accommodating asymmetric plate spreading at slow and ultraslow mid-ocean ridges. IODP Expedition 399 drilled a 1268-m-deep borehole (Hole U1601C; 30°N, Mid-Atlantic Ridge) into the footwall of an oceanic detachment near the southern wall of Atlantis Massif, recovering variably serpentinized peridotites (~70%) with lesser gabbro (~30%). In contrast, Hole U1309D (IODP Expeditions 304/305), drilled ~5 km to the north toward the segment center, predominantly recovering gabbros (99%).
Previous paleomagnetic analyses of reoriented, declination-constrained samples from Hole U1309D (Morris et al., 2009) document ≥46±6° of anticlockwise footwall rotation around a horizontal, ridge–parallel axis; the majority of this rotation occurred after the C1r.1r chron (i.e. within the past 781k years). The magnitude of this rotation is consistent with predictions from conventional single-axis flexural rotation models that use the average site inclination (–38° for U1309D) as input. In contrast, our new paleomagnetic analyses of Hole U1601C show characteristic remanent magnetizations with inclinations that match the site-specific expected geomagnetic field at the time of magnetization acquisition (~ –49°, independent of rock type). Applying single-axis rotation models to these U1601C inclinations implies minimal horizontal-axis rotation (~<20°), despite the site lying in the same footwall beneath the same detachment surface, some 5 km from U1309D. The consistent inclinations recorded by serpentinized peridotites and gabbros at U1601C constrain the timing of deformation, indicating that <20° rotation occurred below ~350 °C, after formation of magnetite during serpentinization, and little to no rotation between gabbroic remanence acquisition (~580°C), and later magnetite-forming serpentinization.
These contrasting inclination results (U1309D vs U1601C) indicate that both sites are not easily explained by a simple, single rotation axis, and instead imply that vertical transport dominated footwall exhumation at U1601C. A vertically dominated component may reflect the mechanical influence of the adjacent transform fault, which could act to shallow rotation axes. Together, these paleomagnetic findings point to spatially heterogeneous structural evolution within a single oceanic core complex. Possible structural frameworks and evolutionary pathways for the Atlantis Massif will be discussed.
How to cite: Lopes, E., Tikoo, S., Parsons, A., Kuehn, R., John, B., and Deans, J.: Complex Kinematics During Exhumation of the Atlantis Massif: New Paleomagnetic Evidence from Hole U1601C, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14895, https://doi.org/10.5194/egusphere-egu26-14895, 2026.
