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5. Neogene |
Bullard Laboratories, Madingley Rise, Madingley Road, Cambridge, CB3 OEZ
The purpose of this paper is to emphasize the importance of vertical and horizontal rotations in the evolution of geological structures. In the Aegean region pervasive normal faulting, probably listric in nature, is responsible for substantial vertical rotation of footwall and hanging wall blocks as well as fault planes. The experience of the Basin and Range Province suggests that strain fields deduced from micro- or macro-structural analyses of fault planes in such an environment are unlikely to be correct unless the detailed 3-dimensional geometry of the motion on the largest faults is known. A particular hazard is the interpretation of rotated low angle gravity glides and high angle antithetic normal faults as thrusts and reverse faults respectively.
In northeast Iran, a combination of thrust and strike slip faulting has led to substantial horizontal rotations whose sense can only be deduced by a knowledge of the history of movement on major structures or by palaeomagnetism. In zones of major continental deformation present day strike azimuths, as well as horizontal and vertical directions, are of no particular significance, and the interpretation of even quite young structural data without a knowledge of the rotations involved may lead to incorrect geological reconstructions.
