Coupling between lithosphere removal and mantle flow

Abstract:

In recent years, lithosphere removal has become recognized as a fundamental process in continental dynamics, distinct from traditional tectonic processes, with a significant influence on mountain building, landscape evolution, and the structure and composition of continental plates. One area where removal has been proposed is the central Andes of South America, the second largest topographic plateau on Earth. Various observations have been interpreted to indicate that lithosphere removal has played a key role in Andean evolution. Specifically, local (~100 km wide) transient basins have developed throughout the high hinterland. Many of these transient basins are systematically found seaward of large ignimbrite complexes, with basin formation predating the eruptions. These transient basins and ignimbrite flare-ups have been interpreted to be caused by lithosphere removal. But neither conventional delamination nor Rayleigh-Taylor-type instabilities (“drips”) can reconcile the diverse observations. In this study, we use numerical models to show that the basins can originate from a local gravitational instability (“drip”) within the orogen. As the instability grows, it becomes entrained by mantle flow, amplifying the instability into regional scale removal and triggering surface magmatism. Our model provides a coherent, self-consistent explanation for geophysical and geological observations in the central Andes, with significant implications for the evolution of the orogen as a whole. More generally, interactions between local lithosphere instabilities and regional mantle flow may play a fundamental role in other continental regions.