Continental Margins, Geosynclines, and Ocean Floor Spreading

On Atlantic-type continental margins there is no differential movement between ocean floor and continent. On Andean-type margins spreading ocean floor descends beneath a submarine trench and continental mountain arc, and on island arc-type margins ocean floor descends beneath a trench and island arc bordering a small ocean basin of Japan Sea type. The corresponding modern geosynclines of Atlantic. Andean, island arc, and Japan Sea type each have distinct associations of sediments and volcanics. Geosynclines of Mediterranean type occur in small ocean basins between continents. Orogeny of Andean and island arc type occurs during development of the respective geosynclines. Himalayan-type orogeny results from collision of migrating continents. Development of the types of continental margin and associated geosynclines, and changes in type of geosyncline, are related to the oscillation of continents between ocean rises. The sequence pre-flysch→ flysch → molasse in many ancient geosynclines can be interpreted in terms of modern geosynclinal deposits and continental margins.