Abstract
AbstractMountain height at convergent plate margins is limited by the megathrust shear force, but it remains unclear how this constraint affects the topographic evolution and mountain building at the transition from subduction to collision. Generally, mountain height increases during the subduction‐collision transition in response to crustal thickening or processes like mantle delamination and slab breakoff, but the main parameters controlling how much mountain height increases remain poorly understood. Here we show, based on analytical and finite‐element force‐balance models, that the increase in mountain height depends on the magnitude of the megathrust shear force and the reduction of submarine margin relief. During the subduction stage, the shear force is balanced by the gravitational effect of the margin relief and the deviatoric stresses in the upper plate are low. When the submarine margin relief is reduced during the closure of the ocean basin, the effect of the gravitational force decreases and the upper plate experiences enhanced deviatoric compression, which allows the mountain height to increase until a near‐neutral stress state beneath the high mountains is restored. If the increase in mountain height cannot keep pace with the submarine relief reduction, the compression of the upper plate increases by a few tens of MPa, which promotes tectonic shortening and mountain building. Our analysis implies that mountain height can increase by hundreds of meters to a few kilometers during collision, depending primarily on the trench depth during the subduction stage and possible syncollisional changes of the megathrust shear force.
Highlights
With the transition from oceanic subduction to continental collision, mountain ranges at convergent plate margins typically experience a phase of surface uplift and an increase in mountain height (Figure 1)
When the submarine margin relief is reduced during the closure of the ocean basin, the effect of the gravitational force decreases and the upper plate experiences enhanced deviatoric compression, which allows the mountain height to increase until a near-neutral stress state beneath the high mountains is restored
Based on analytical and finite-element force-balance models, we showed that the balance between gravitational forces and the megathrust shear force requires an increase in mountain height when the submarine relief is reduced at the subduction-collision transition
Summary
With the transition from oceanic subduction to continental collision, mountain ranges at convergent plate margins typically experience a phase of surface uplift and an increase in mountain height (Figure 1). Stable isotope and paleo-drainage basin analyses indicate that the central European Alps grew in elevation from about 0.3 ± 0.2 km to 1.9 ± 1.0 km between 31 Ma and 22 Ma, and to 2.9 ± 1.0 km after 15 Ma, suggesting an elevation increase of ≥2 km following the late Eocene subduction-collision transition (Campani et al, 2012; Schlunegger & Kissling, 2015). Stable isotope paleoaltimetry data indicate that the Himalaya reached its present elevation by Early Miocene (Gébelin et al, 2013). A present-day margin where a lateral transition from subduction to collision can be observed is the Arabian-Eurasian convergent plate boundary, which exhibits an increase in upper-plate mountain height from the Makran subduction zone in the east to the continental collision zone with the Zagros fold-and thrust-belt to the west (Mouthereau et al, 2012; Penney et al, 2017)
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