Terrane accretion explains thin and hot ocean-continent back-arcs.

Abstract

The origin of hot ocean-continent back-arc regions with very thin mantle lithosphere and very high surface heat flow in both extensional and contractional ocean-continent subduction systems is highly enigmatic and unresolved. These first-order characteristics have often been explained with either convective mantle lithosphere removal or by back-arc extension. However, it is unclear what may cause the proposed convective thinning and/or delamination of eclogitic lower crust over very wide regions, whereas back-arc extension is either not observed or insufficient to explain the observed very thin mantle lithosphere. Notably, many of these ocean-continent systems have a long history of terrane accretion. Here, we show, using thermomechanical model experiments, that terrane accretion provides a consistent explanation for the observed key characteristics and naturally leads to rheologically weak back-arcs with continental crust directly on top of the hot sublithospheric mantle.