Mid-Cenozoic Activity on Lithospheric Plates

Abstract

Widespread mid-Cenozoic (25 to 40 m.y. ago) changes in deformation, deposition, and volcanism on continents and island arcs reflect discontinuities in the behavior of lithospheric plates. Varied mid-Cenozoic activity near leading plate edges includes major orogeny and molasse accumulation along most of the western Tethyan belt and the southern Andes (with prevalent volcanism), and a distinct phase of deformation and igneous activity on the Alaska Peninsula, in Central America, and on cratonic Middle Europe. Tectonic stability following early Cenozoic orogeny was established in most of the West Indies and in the eastern ranges of the Rocky Mountains. At the end of mid-Cenozoic time, major orogeny, a new style of deformation or of sedimentation, or a major episode of volcanism occurred in the Red Sea-African rift zone, along most of the Pacific border of the United States and Mexico, in northern South America, in New Zealand and New Guinea, on the large island arcs of the Indian and western Pacific basins, and along the eastern Tethyan belt (with only minor volcanism). On trailing margins of continents most of the marine embayments underwent extensive regression during mid-Cenozoic time while interior continental Eurasia was flooded by a broad sea. Dott (1969) has aptly called attention to profound mid-Cenozoic changes in land-sea relations, sedimentation, and structural disturbances (Fig. 1) that imply roughly synchronous changes in sea floor development. Current tectonic speculation postulates that volcanism, deformation, and deposition along edges of lithospheric plates (Fig. 2) are controlled largely by their interaction on a global scale, and especially by the direction, rate, and duration of their movements (Mitchell and GENERAL STATEMENT