Geodynamic models of continental subduction and obduction of overriding plate forearc oceanic lithosphere on top of continental crust

Abstract

Continental subduction takes place in the final stage of subduction when all oceanic lithosphere is consumed and continental passive margin is pulled into the mantle. When the overriding plate is oceanic, dense forearc oceanic lithosphere might be obducted onto light continental crust forming an ophiolite (Tethyan-style ophiolite obduction). Four-dimensional dynamic analog subduction models have been constructed to evaluate the mechanical feasibility of continental subduction and forearc oceanic lithosphere obduction on top of continental crust. The roles of continental crust thickness, passive margin length, subducting lithosphere thickness, and overriding plate thickness were investigated to determine the maximum continental subduction depth, maximum forearc obduction distance, and forearc deformation during continental subduction. Our buoyancy-driven experiments indicate that deep continental subduction occurs in most circumstances (down to~560 km) and that obduction of dense oceanic forearc lithosphere on top of light continental crust is mechanically feasible. Maximum obduction distances are relatively small (~26-37 km) but are sufficient to explain obduction of short ophiolite sheets, such as observed in New Caledonia. When including the thin (5-10 km thick) accretionary wedge of off-scraped deep sea sediments, oceanic crust, and mantle, then maximum obduction distances are much larger,~60-160 km, sufficient to account for the obducted Northland Allochthon in New Zealand. Results indicate that increasing continental crust thickness decreases continental subduction depth, whereas increasing passive margin length and subducting lithosphere thickness increases continental subduction depth. Notably, during continental subduction, backarc extension continues, while forearc deformation (shortening) increases moderately compared to the preceding phase of normal (oceanic) subduction.

The Age, Origin, and Emplacement of the Tsiknias Ophiolite, Tinos, Greece

“…Although, some workers have argued that shear heating would be localized along the particular fault plane or shear zone and the addition of fluids to a serpentinites would produce talc, which would substantially reduce the coefficient of friction and therefore limit the degree of heating (e.g., Dengo & Logan, ; Goswami & Barbot, ). The observation that the highest temperatures are recorded in the highest strained amphibolites closest (0–5 m) to the Tsiknias Thrust and the peak metamorphic assemblages (in the S 2b fabrics) are syntectonic with respect to top‐to‐SW shearing is consistent with the shear heating hypothesis (Wada et al, ; Duarte et al, ; Edwards et al, ; Rice, ; Tarling et al, ). Furthermore, it is demonstrated that dissipative heating is required to explain the measured heat flow discrepancies in many active steady‐state subduction zones (England, ), particularly if the mantle wedge had cooled over a long time period.…”

Neo-Tethys geodynamics and mantle convection: from extension to compression in Africa and a conceptual model for obduction

“…Recent analogues experiments (Agard et al 2014;Edwards et al 2015) suggest that subducting a continental margin below a denser oceanic lithosphere is feasible once subduction has initiated, which remains the main problem. In a set of models comparable to the Tethyan system, Agard et al (2014) show that the jamming of the northern subduction can lead to subduction initiation further south, leading to obduction on the African margin, reemphasizing the model proposed by Agard et al (2007) in which faster plate velocity renders subduction more difficult, putting the system in compression and inducing the formation of a new subduction zone.…”

Ediacaran Obduction of a Fore‐Arc Ophiolite in SW Iberia: A Turning Point in the Evolving Geodynamic Setting of Peri‐Gondwana

“…Ophiolite obduction is a common process in subduction‐related orogens (Dewey, ; Edwards et al, ; Wakabayashi & Dilek, ). Examples of ophiolite obduction in the peripheral domains of the northern margin of Precambrian Gondwana include the case of the Bou Azzer Ophiolite in the Anti‐Atlas of Morocco (El Hadi et al, ), the Frolosh Ophiolite in Kraishte zone, Bulgaria (Kounov et al, ), and the Calzadilla Ophiolite in SW Iberia (Arenas et al, ).…”