Convergent plate boundaries have long been recognized as zones where deep-sea sediments become accreted to plate margins, causing the margin to grow with time1. However, our understanding of the evolution of these margins is limited because accreted rocks are often too poorly exposed to unravel the complex history theyrecord. Recent results from field, deep-sea drilling and high-resolution seismic-reflection studies indicate that various processes can occur in time along a specific margin2. For example, both the middle America and Japan trenches are believed to record a history of strike-slip faulting and/or tectonic erosion before the periods of subduction accretion which presently characterize these margins3,4. Here, we propose that growth of the Kodiak continental margin in south-west Alaska, one of the largest accretionary prisms in the world, has been dominated by two relatively short episodes of accretion; the first in the late Cretaceous and the second in the early Eocene. These two periods of growth appear to account for >70% of the margin growth during the past 75-100 Myr.
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