Sedimentation at Plate Boundaries in Transition

Abstract

From inception to termination convergent margins are dynamic regions. Subduction initiation is poorly understood with arguments for both induced and spontaneous processes. Geodynamic models help to predict the sedimentary-volcanic records of such events, but there are few areas where these models have been tested, particularly pre-Cenozoic examples. Where subduction is induced, the sedimentary signatures should include evidence for rapid uplift (unconformity), then rapid subsidence (finingand deepening-upward succession), followed by building of the arc edifice. Where subduction is spontaneous, the proto-forearc experiences subsidence and early magmatism prior to development of the magmatic arc. Once initiated, there are other opportunities for tectonic overprinting of the forearc owing to the formation and migration of plate triple junctions. There are several well-studied modern to Cenozoic examples that suggest differing signatures depending on the plate configuration. In the case of a triple junction involving purely subduction (trench-trench-trench) the overriding signature is associated with arc terrane accretion, whereas the interaction of a spreading ridge at a trench-ridge-trench triple junction can result in anomalous neartrench magmatism, thermal overprinting of the forearc, and subduction erosion. In triple-junction cases where subduction is superceded by transform plate motion (e.g., trench-fault-fault) the transition is marked by progressive uplift and deformation of the forearc concomitant with cessation of arc magmatism. The demise of a convergent margin can be through simple abandonment and subsidence, or transition to a transform plate margin, or where a spreading ridge is involved, result in deformation, uplift, and thermal/volcanic overprinting of the forearc prior to abandonment.

Stratigraphic record of subduction initiation in the Permian metasedimentary succession of the El Paso Mountains, California

“…Cenozoic sedimentary records of subduction initiation along Puysegur Ridge, New Zealand, referenced in the modeling, also show an ongoing sedimentary pattern of rapid uplift, rapid subsidence, and then shallowing (Gurnis et al, 2004;Sutherland et al, 2006). In contrast, "spontaneous" subduction initiation should result in a sedimentary pattern of initial subsidence and magmatism in the protoforearc (Stern, 2004;Marsaglia, 2012).…”

“…Recent geodynamical modeling of subduction initiation suggests that this plate-tectonic process should produce distinct sedimentary records on the overriding plate margin depending on the manner of subduction initiation (cf. Marsaglia, 2012; for distinctions between "forced" or "induced" subduction initiation and "spontaneous" subduction initiation, see Gurnis et al, 2004;Stern, 2004;Nikolaeva et al, 2011). However, subsequent magmatism and deformation may obscure or remove this record (Sutherland et al, 2006;Gurnis et al, 2004;Stern, 2004;Hall et al, 2003).…”

Changing kinematics of the Ouse Fault during the Cretaceous–Neogene tectonic evolution of eastern Marlborough

“…Opposing accounts infer that Phoenix Plate subduction persisted through part (e.g., Gardiner and Hall, 2021;Mazengarb and Harris, 1994), or even the majority, of the Late Cretaceous, with some models proposing complex subduction of this plate continuing locally to as late as 70 Ma (e.g., Cooper and Ireland, 2015;Cooper and Palin, 2018). Alternative scenarios are not necessarily mutually exclusive, given the possibility of diachronous subduction termination along different segments of the margin (e.g., Jabaloy et al, 2003;Marsaglia, 2012).…”