Evidence for Miocene back‐arc spreading in the central Scotia Sea

Abstract

Extensive marine geophysical surveys within the central Scotia Sea have revealed two areas of lineated magnetic anomalies. The limited length of anomaly sequences makes unique correlation with the reversal time‐scale difficult, but a model is derived for the longer sequence requiring slow spreading during the period 21–6 Myr about a ridge trending 085°. The north—south lineated anomalies in the other sequence are well formed, but their identification is unavoidably ambiguous. The longer spreading sequence is interpreted as back‐arc spreading behind the ‘Discovery Arc’, which was active during at least the period 20–12 Myr ago. The spreading was asymmetric, as is spreading at the present South Sandwich back‐arc ridge. More than two‐thirds of the oceanic crust of the Scotia Sea has now been shown to be less than 30 Myr old, and it is probable that it formed almost entirely within this period, as a complication of the South American—Antarctic plate boundary. Copyright © 1980, Wiley Blackwell. All rights reserved