75. Umino, S., 2012. Emplacement mechanism of off-axis large submarine lava field from the Oman Ophiolite. J. Geophys. Res., 117, B11210, doi:10.1029/2012JB009198.

Large submarine lava flows with thicknesses >100 m and volumes exceeding a few km3 are not uncommon volcanic constructs of mid-ocean ridges and around Hawaii Islands, yet details of the physical processes of eruption of these large lava flows are poorly understood. The V3 unit of the Oman Ophiolite extruded onto pelagic sediment far off the paleospreading axis as thick lava flows with an areal extent of >11 km by 1.5 km and the maximum thickness >270 m, yielding an estimated volume >1.2 km3. The feeder dike for the V3 flow field has an unusual thickness up to 60 m, striking at a high angle to the paleospreading axis. The skewed variation in thickness suggests an intrusion at the apparent level of neutral buoyancy in off-axis crust. The thick sheet flows consist of massive core and columnar jointed crust. Finer-grained, finely jointed layers and lenses embedded in coarser-grained, roughly jointed lava show a complex cooling and growth history of the lava crust. In the periphery of the flow field, sheet flows lack developed core textures and change laterally into compound flows of pillow and subaqueous pahoehoe lobes, which are occasionally intermingled with pelagic shale. On the other hand, core lacks fine columnar joints and shows a typical doleritic texture. We conclude that the V3 flow field formed by extrusion of lava at low to moderate rates onto a subhorizontal seafloor covered with thick pelagic sediment, burying topographic relief >100 m of abyssal hills and fault grabens.

Keyword: Oman Ophiolite, V3, large submarine lava flow, off-axis volcanism
キーワード: オマーンオフィオライト，V3，海底巨大溶岩流，オフリッジ火山活動