The role of subduction in the formation and evolution of continental fragments and microcontinents

Abstract

Microcontinents are small continental pieces that have been separated from their parent continent. We often find such microcontinents in oceans that form after the breakup of a large continent (e.g. the North Atlantic, forming c. 56 million years ago). Understanding microcontinent formation leads to a better understanding of plate tectonics. This is important because plate tectonics influences numerous other processes such as climate change and natural hazards. However, in recent years various microcontinents have been identified that have formed in subduction settings. Subduction is a convergent process wherein one tectonic plate moves underneath another. However, microcontinents require divergent motion to separate from their parent continent. This thesis resolves this (apparent) paradox of (divergent) microcontinent formation in a (convergent) subduction setting. Geological and geophysical data show that microcontinents in subduction settings form quickly (less than 50 million years) in complex tectonic settings. They are then reincorporated into continents after, at most, 60 million years. Digital and scale models show that pre-existing scars in the parent continent and rotational extensional movements are necessary to create the local divergence that drives microcontinent formation. The results of this doctoral study show that formation of microcontinents in subduction settings may be indicative of rapid changes in plate tectonic processes.