Dinamics of passive margins / Динамика пассивных окраин

In the study of the geodynamics of passive continental margins greatest emphasis has been placed on the evolution of the crystalline crust and deeper rocks. Contributions from detailed studies of the sedimentary succession have perhaps played a smaller, but nonetheless important role in determining the mechanisms of evolution. As a consequence, this review concentrates on the crystalline rocks, only mentioning the important aspects of the sediments in passing. It also concentrates on the rifted passive margins at the expense of the sheared ones in view of the fact that the state of the art on the latter is less advanced, and they are, in terms of length, less important. A few comments on sheared margins will be made now, however.
A good indication of the way our knowledge of passive margins has advanced in the last decade is given by the relatively new awareness of sheared margins. Prior to the 1970s it was thought that passive margins were, in effect, rifted margins, despite the work of Wilson (1965) relating fracture zones to margin offsets. In the early 1970s the rectilinear pattern of passive margins was explained in terms of orthogonal rifted and sheared segments, making it possible to understand abrupt changes in margin direction, such as at the southern tip of South Africa (Francheteau and Le Pichon, 1972). The formation of marginal plateaus and of microcontinents was also easily explained by invoking the presence of sheared segments of margin and their associated fracture zones (Falvey, 1972).
By the time the Geodynamics Project reached its end a distinction between rifted and sheared margins could be drawn from most types of observational data (Scrutton, this volume).
The understanding of thermal and dynamic mechanisms at rifted margins has advanced at a rapid rate, helped by an ever-increasing input of new geophysical and geological data of all sorts from university, government and industrial research groups. Methods of investigation have improved most importantly in three ways -the wider use of multichannel seismic reflection <...>