Plume-induced sinking of the intracontinental lithosphereas a fundamentally new mechanism of subduction initiation.

Abstract

<p>Although many different mechanisms for subduction initiation have been proposed, few of them are viable in terms of agreement with observations and reproducibility in numerical experiments. In particular, it has recently been demonstrated that intra-oceanic subduction triggered by an upwelling mantle plume could contribute greatly to the onset and functioning of plate tectonics in the early Earth and, to a lesser extent, in the modern Earth. In contrast, the onset of intracontinental subduction is still underestimated. Here we review 1) observations demonstrating the upwelling of hot mantle material flanked by sinking proto-slabs of the continental mantle lithosphere, and 2) previously published and new numerical models of plume-induced subduction initiation. Numerical modelling shows that under the condition of a sufficiently thick (> 100 km) continental plate, incipient down thrusting at the level of the lowermost lithospheric mantle can be triggered by plume anomalies with moderate temperatures and without significant strain and/or melt-induced weakening of the overlying rocks. This finding is in contrast to the requirements for plume-induced subduction initiation in oceanic or thin continental lithosphere. Consequently, plume-lithosphere interactions in the continental interior of Paleozoic-Proterozoic (Archean) platforms are the least demanding (and therefore potentially very common) mechanism for triggering subduction-like foundering in Phanerozoic Earth. Our findings are supported by a growing body of new geophysical data collected in a variety of intracontinental settings. A better understanding of the role of intracontinental mantle downthrusting and foundering in global plate tectonics and, in particular, in triggering "classic" oceanic-continental subduction will benefit from further detailed follow-up studies.</p>

A Review of the Dynamics of Subduction Zone Initiation in the Aegean Region

“…Determining the Hellenic arc SZI is also important because the timing constraints shed light on the mode of initiation (i.e., induced or spontaneous; from compression or extension; Gurnis et al, 2004;Stern, 2004;Gerya, 2011;Stern & Gerya, 2018) based on our understanding of the geology at that time. Subduction initiation requires breaking a zone of weakness in the lithosphere (e.g., Stern & Gerya, 2018;Baes et al, 2020a;Cloetingh et al, 2021). The process may be accommodated along passive margins (e.g., Cloetingh et al, 1984), although the conversion of a passive margin into an active one has not been observed to have occurred during the Cenozoic (Gurnis et al, 2004;Cloetingh et al, 2021).…”

“…Subduction initiation requires breaking a zone of weakness in the lithosphere (e.g., Stern & Gerya, 2018;Baes et al, 2020a;Cloetingh et al, 2021). The process may be accommodated along passive margins (e.g., Cloetingh et al, 1984), although the conversion of a passive margin into an active one has not been observed to have occurred during the Cenozoic (Gurnis et al, 2004;Cloetingh et al, 2021). Subduction initiation could also occur due to motion along transform or fracture zones associated with mid-ocean ridges due to largescale changes in plate motion (e.g., Hall et al, 2003).…”

“…Subduction initiation could also occur due to motion along transform or fracture zones associated with mid-ocean ridges due to largescale changes in plate motion (e.g., Hall et al, 2003). This process could occur across extinct mid-ocean ridges or within back-arc regions within mature subduction zones, as well as mantle plume interactions with old oceanic lithosphere (Baes et al, 2020a,b;Cloetingh et al, 2021). No evidence or hypothesis exists for a mantle plume as triggering the development of the Hellenic arc.…”