Restraining bends in high temperature shear zones: The ‘Central Cameroon Shear Zone’, Central Africa

摘要

A detailed structural study of the Central Cameroon Shear Zone (CCSZ) segment, in the Bamoun plateau (BP) and the Tikar plain (TP) (West Cameroon), reveals a complex strain geometry of this shear zone. It shows thick mylonite bands wrapping around lenses of various country rock types, at small, medium and large scales. The mylonite foliation trends N40°E in the Tikar plain, and progressively curves into a N60°E to N70°E direction, to the NE and SW, defining a large scale S-type bend at the transition zone between two en-echelon segments, known as the Foumban and Central Cameroon Shear Zones (CCSZ). The structural, kinematic and metamorphic features of the Tikar mylonites characterize a restraining bend formed at a deep crustal level during a major dextral shear deformation. Its geometry suggests that the western extension of the CCSZ including its Brasiliano southernmost pre-drift counterpart form a left lateral stepping (en-echelon) shear zone system.