First cosmic-ray muography of a crust-mantle transition zone

Studying the structure and composition of ophiolitic crustal-mantle boundaries provides insights into the nature of oceanic lithosphere. In this work, we conducted the first muography of an ophiolite segment at Wadi Fizh in the northern Samail Ophiolite, which represents an analogue of crust-mantle boundaries formed at fast-spreading mid-ocean ridges. A multi-wire-proportional-chamber-based muographic observation system was operated at a distance of 400 meters from the crust-mantle transition zone (Moho Transition Zone, MTZ) for 171 days. The resulting high-resolution muographic image resolves the internal density structure of the ophiolite segment with a spatial resolution of approximately 3.5 meters. Mean density was measured as 3.03 g cm-3 for the layered gabbros, consistent with weakly serpentinized gabbroic intrusions. A significantly lower value of 2.72 g cm-3 was obtained for the MTZ, indicating a highly serpentinized MTZ, in contrast with petrological profiles which previously revealed gradational transition from the mantle to the crust at Wadi Fizh. A mean density of 3.38 g cm-3 was revealed in the lower part of ophiolite rige that indicates the presence of fresh peridotites beneath the thin layer of gabbroic cover. These results demonstrate that muography can provide complementary information about the density structure of ophiolites and, by extension, on the architecture of the oceanic lithosphere.