Formation
Oceanic core complex structures form at slow spreading oceanic plate boundaries which have a limited supply of upwelling magma. These zones have low upper mantle temperatures and long transform faults develop. Rift valleys do not develop along the expansion axes of slow spreading boundaries. Expansion takes place along low-angle detachment faults. The core complex builds on the uplifted side of the fault where most of the gabbroic (or crustal) material is stripped away to expose mantle peridotite. They comprise peridotites ultramafic rocks of mantle and to a lesser extent gabbroic rocks from the Earth's crust.
Each detachment fault has three notable features: a breakaway zone where the fault began, an exposed fault surface that rides over the dome and a termination, which is usually marked by a valley and adjacent ridge.
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