Abstract: Ancient and Modern Continental Margins, Perspective for Future Research

A. W. Bally

Reconstruction of ancient mobile belts reveals the presence of old continental margins. Information from folded belts is derived mostly from surface and subsurface observations, whereas continental margins generally are described from geophysical data. This contrast in the nature of information helps to focus on a number of problem areas.

1. Passive margins appear to be emplaced on a previously attenuated crust characterized by extensive rifting. Several intriguing geophysical models have been proposed to explain the attenuation process, but they remain to be documented. Sedimentation and erosion during the rifting process are present in many ancient foldbelts (Alps, Caledonides). The nature of volcanism associated with and immediately following the attenuation process should be studied in ancient analogs.

2. Reflection-seismic work on passive margins reveals stratigraphic geometries which should inspire a new look at the stratigraphy of miogeosynclinal sequences.

3. Much has been written about marginal highs on passive margins, but equivalents in folded belts are difficult to document.

4. The angularity of the outline of passive margins commonly is due to transform faults. The pattern of mobile belts reflects former angular outlines, but the anatomy of the relation remains to be studied.

5. Ancient marginal seas have been postulated in many areas (southern Andes, western Cordillera, eastern Australia). Marginal seas appear to be destined for destruction by folding, yet there is little evidence for this in modern marginal seas.

6. Active margins continue on land, where "accretionary wedges" can be studied in detail both on the surface and in subsurface.

7. The lithospheric and thermal regime in subduction zones has been modeled by geophysicists, but remains to be documented on the landward side of subduction zones.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC