"It is suggested that the Scotia arc was formed after the disruption of a Palaeozoic continental strip between South America and Antarctica by an eastward advance of the Pacific crust in post-Carboniferous to pre-Jurassic times. Along the discontinuity between the Pacific and Atlantic crustal types volcanic island arcs and associated trenches were developed. Sediments derived from the island arcs were subsequently metamorphosed, intruded by granitic rocks, and uplifted in Cretaceous and early Tertiary times. As a result of the igneous activity and orogeny the Pacific crust underlying the Scotia sea has become more sialic. A further eastward advance of the already modified Pacific crust by the development of volcanic island arcs in the South Shetland and south Sandwich islands probably took place in the late Tertiary."