Oceanic ridge off-axis deep structure in the Mansah region (Sumail massif,Oman ophiolite)

Large scale structural mapping of the Oman ophiolite indicates that the Man sah area (Sumail massif) was a ridge off-axis region at the time the ophiol ite was detached. This paper presents a detailed structural mapping of the region. We show that, as opposed to other off-axis areas, it contains plung ing lineations, correlated with a thick Moho transition zone and chromite p ods, indicative of a mantle diapir. However this diapir has a discontinuous structure, it is bounded by shear zones and types of diabases that are not found elsewhere in Oman; it also has a broken crust, strongly affected by hydrothermal alteration. This suggests that Mansah fossilized an off-axis d iapir intruding a cooling lithosphere. It may be a good candidate to be the root of an off-axis seamount such as those found in the East Pacific, and may bring new insights into this particular volcanism which we are only beg inning to explore.