Along-strike dredging reveals a crust-dominated section at the Marie Celeste Fracture Zone, Central Indian Ridge

Abstract Scarps along oceanic fracture zones provide key tectonic windows into the architecture of oceanic lithosphere. Recent investigations along the Mid-Atlantic Ridge (MAR) demonstrate that such scarps can expose both crust- and mantle-dominated sections. However, integrated datasets combining bathymetry, seafloor imagery, and systematic rock sampling remain spatially uneven, limiting direct comparisons among fracture-zone systems. Here, we address this issue at the Marie Celeste Fracture Zone (MCFZ) along the Central Indian Ridge. The MCFZ includes a ~215-km-long active transform fault with an ~11 Myr lithospheric age offset. The southern wall of the active transform valley comprises three morphological domains from west to east: abyssal hills, oceanic core complexes (OCCs), and a prominent transverse ridge. During the KH-24-4 cruise of the R/V Hakuho-maru in 2024, we conducted dredging at 10 sites distributed along depth transects ranging from the deepest part of the transform-fault valley to the top of the transform wall. These sites were spaced up to ~40 km apart along the transform fault. At each site, one to six dredge hauls were conducted, for a total of 27 dredge hauls. Descriptions of the dredged samples, bathymetric profiles, and seafloor photographs were combined to construct interpreted lithologic sections. Abyssal hill scarps expose pillow lava-dominated basalts, including plagioclase ultraphyric basalts typical of slow- to intermediate-spreading ridges. The OCC-adjacent scarps yield a mixed assemblage of basaltic, gabbroic, and ultramafic rocks, including strongly altered gabbros and epidosite. In contrast, the eastern transverse ridge appears to expose a crust-dominated section. Basalt is abundant across the shallower intervals, whereas dolerite and evolved olivine–oxide gabbro become more abundant at greater depths, and ultramafic rocks remain a minor component restricted to the deepest sampled interval. Comparisons with transverse ridges at the Vema and Vernadsky FZs of the MAR indicate that, despite similar spreading rates, the proportions and depth distributions of basaltic, gabbroic, and ultramafic rocks vary markedly among the systems. The MCFZ represents a crust-dominated end-member of oceanic fracture-zone architecture and highlights the structural diversity of transform lithosphere in slow-spreading settings.