Clockwise rotation of the entire Oman ophiolite occurred in a suprasubduction zone setting
Anderson, Mark W.
MacLeod, Christopher John
- Publisher: Geological Society of America
The Oman ophiolite provides a natural laboratory for understanding oceanic lithospheric processes. Previous paleomagnetic and structural investigations have been used to support a model involving rotation of the ophiolite during formation at a mid-oceanic microplate. However, recent geochemical evidence indicates the ophiolite instead formed in a nascent forearc environment, opening the potential for alternative rotation mechanisms. Central to the conundrum is the contrast between ESE to SE magnetizations and NNW magnetizations from the northern and southern ophiolitic massifs respectively, attributed previously to either differential tectonic rotations during spreading or complete emplacement-related remagnetization of the southern massifs. Here we report new paleomagnetic data from lower crustal rocks of the southern massifs that resolve this problem. Sampling of a continuous section in Wadi Abyad reveals ENE magnetizations in the dike rooting zone at the top of the lower crust that change systematically downwards to NNW directions in underlying foliated and layered gabbros. This is only consistent with remagnetization from the base upwards, replacing early remanences in layered and foliated gabbros completely but preserving original ENE magnetizations at higher levels. Comparison with new data from Wadi Khafifah provides a positive fold test that shows this event occurred before late Campanian structural disruption of the regional orientation of the petrologic Moho. These data show that the entire ophiolite experienced large intraoceanic clockwise rotation prior to partial remagnetization, leading to a new tectonic model in which formation, rotation and emplacement of the ophiolite are all linked to Late Cretaceous motion of Arabia and roll-back of the Oman subduction zone.
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