Geodynamics of oceanic plateau and plume head accretion and their role in Phanerozoic orogenic systems of China

Abstract

a b s t r a c tWe present three 3D numerical models of deep subduction where buoyant material from an oceanic plateau and a plume interact with the overriding plate to assess the influence on subduction dynamics, trench geometry, and mechanisms for plateau accretion and continental growth. Transient instabilities of the convergent margin are produced, resulting in: contorted trench geometry; trench migration parallel with the plate margin; folding of the subducting slab and orocline development at the convergent margin; and transfer of the plateau to the overriding plate. The presence of plume material beneath the oceanic plateau causes flat subduction above the plume, resulting in a "bowed" shaped subducting slab. In plateau-only models, plateau accretion at the edge of the overriding plate results in trench migration around the edge of the plateau before subduction is re-established directly behind the trailing edge of the plateau. The plateau shortens and some plateau material subducts. The presence of buoyant plume material beneath the oceanic plateau has a profound influence on the behaviour of the convergent margin. In the plateau þ plume model, plateau accretion causes rapid trench advance. Plate convergence is accommodated by shearing at the base of the plateau and shortening in the overriding plate. The trench migrates around the edge of the plateau and subduction is re-established well behind the trailing edge of the plateau, effectively embedding the plateau into the overriding plate. A slab window forms beneath the accreted plateau and plume material is transferred from the subducting plate to the overriding plate through the window. In all of the models, the subduction zone maintains a relatively stable configuration away from the buoyancy anomalies within the downgoing plate. The models provide a dynamic context for plateau and plume accretion in Phanerozoic accretionary orogenic systems such as the East China Orogen and the Central Asian Orogen (Altiads), which are characterised by accreted ophiolite complexes with diverse geochemical affinities, and a protracted evolution of accretion of exotic terranes including oceanic plateau and terranes with plume origins.

A Paleoproterozoic Andean-type iron oxide copper-gold environment, the Great Bear magmatic zone, Northwest Canada

“…9) and are similar to 4D synthetic modeling of plateau-collision, and subduction re-initiation ( Fig. 10; Betts et al, 2015). The Great Bear shoshonitic magmatism and associated mineralization followed this…”

“…First, the polarities are both east-dipping; there is no evidence of west-dipping subduction. Moresi and Willis (2015) built 4D numerical model simulations (based on Moresi et al, 2014;Betts et al, 2015) to demonstrate the effects of ridge or plateau collision within an evolving subduction zone. In their study, when a 250 to 500 km-diameter ocean plateau is introduced into the subduction zone, the model evolves to a configuration that is geometrically similar to what is observed in the 3D model as shown in Figure 9.…”

“…It is not currently possible to test this more thoroughly and other factors require considerations, such as the precise timing of subduction, other potential driving mechanisms such as plume subduction (Betts et al, 2015), and the exact relationships between relatively flatslab subduction, magmatism, and IOCG mineralization.…”

“…In the models of Moresi and Willis (2015) and Betts et al (2015), following plateau collision, a new oceanic slab began subducting behind the accreted plateau (or similar). The time-frame from collision to subduction re-initiation was ca.…”

Mantle plume–subduction zone interactions over the past 60 Ma

“…By examining past plate A C C E P T E D M A N U S C R I P T Betts et al (2015) consider the case where a plateau and its feeder plume both interact with a subduction zone.…”