Fingerprinting orogenic delamination

Abstract

A signifi cant portion of the Earth’s lithosphere is recycled into the deeper mantle, as required by mass balance considerations in orogenic environments. The two principal mechanisms for recycling are subduction at plate margins and delamination. Subduction is a well-understood process that is essential to the plate tectonic engine of planet Earth. Delamination, on the other hand, requires recycling via convective removal of the lower parts of the lithosphere, and is more diffi cult to detect. One chief argument for delamination comes from extreme shortening at continental convergent margins, which requires far thicker mantle lithospheres than observed (DeCelles et al., 2009). The second argument comes from the intermediate average composition of the continental crust (Rudnick, 1995), which requires a large ultramafi c complementary residue at the bottom of the continental crust; such a reservoir has not been identifi ed over large portions of continental areas. Delamination (Bird, 1979), convective removal, foundering, and lithospheric dripping are terms used for the process of detachment and sinking of the lower parts of the continental lithosphere other than those that may have been buried into the mantle via continental subduction. Most researchers using the term “delamination” refer to a density-driven process of foundering, and do not imply its original “peeling-off” signifi cance as defi ned by Bird (1979), which is closer to tectonic underplating in shallow subduction environments. Delamination is a form of vertical and spatially localized tectonics often generating amoeba-like or circular surface effects that are regional results of tectonomagmatic processes at convergent plate margins. Mantle delamination is the process of foundering of dense, unstable