Lithosphere Delamination and Relamination Reconcile Craton Longevity and Temporal Variations

The classic isopycnicity model helps to explain the stability and longevity of cratons. However, this model cannot readily explain some important features of cratonic lithosphere, such as its internal layering and topographic changes. Here, we show that cratonic mantle lithosphere with net negative buoyancy close to that of a pure-thermal boundary layer (McKenzie et al., 2005) could resolve these problems. In this model, we assume that the lower cratonic lithosphere hosts most of the high-density materials (e.g., iron-enriched composition) (OReilly and Griffin, 2013). Under enough tectonic perturbations, this dense lower lithosphere could delaminate, causing prominent surface uplift and erosion. This scenario is consistent with the widespread upper-mantle fast seismic anomalies below South Atlantic, proposed to represent delaminated continental lithosphere during the Cretaceous (Hu et al., 2018). Our simulation reveals that after these delaminated lithosphere segments sink into the hot mantle, the increasing thermal buoyancy and/or removal of the dense components may reverse their trajectory and most of the foundered fragments can relaminate to the base of the above lithosphere. This relamination process causes another rapid episode of surface uplift, followed by gradual subsidence as the relaminated materials cool and consolidate. The lithosphere that experiences initial delamination and subsequent relamination has an eventual thickness of ~200 km, typical for cratonic keels, implying long-term mass conservation of cratonic lithosphere. Since these processes are all sub-solidus, the ancient igneous ages of these recycling lithosphere portions remain unchanged. Therefore, our model can reconcile the apparent longevity and temporal variations of cratons.