Flat subduction dynamics and deformation of the South American plate: Insights from analog modeling

Abstract

We present lithospheric-scale analog models,\ud investigating how the absolute plates’ motion and\ud subduction of buoyant oceanic plateaus can affect both\ud the kinematics and the geometry of subduction,\ud possibly resulting in the appearance of flat slab\ud segments, and how it changes the overriding plate\ud tectonic regime. Experiments suggest that flat\ud subductions only occur if a large amount of a\ud buoyant slab segment is forced into subduction by\ud kinematic boundary conditions, part of the buoyant\ud plateau being incorporated in the steep part of the slab\ud to balance the negative buoyancy of the dense oceanic\ud slab. Slab flattening is a long-term process (10 Ma),\ud which requires the subduction of hundreds of\ud kilometers of buoyant plateau. The overriding plate\ud shortening rate increases if the oceanic plateau is large\ud enough to decrease the slab pull effect. Slab flattening\ud increases the interplate friction force and results in\ud migration of the shortening zone within the interior of\ud the overriding plate. The increase of the overriding\ud plate topography close to the trench results from (1) the\ud buoyancy of the plate subducting at trench and (2) the\ud overriding plate shortening. Experiments are\ud compared to the South American active margin,\ud where two major horizontal slab segments had\ud formed since the Pliocene. Along the South\ud American subduction zone, flat slab segments below\ud Peru and central Chile/NW Argentina appeared at\ud 7 Ma following the beginning of buoyant slab\ud segments’ subduction. In northern Ecuador and\ud northern Chile, the process of slab flattening\ud resulting from the Carnegie and Iquique ridges’\ud subductions, respectively, seems to be active but not\ud completed. The formation of flat slab segments below\ud South America from the Pliocene may explain the\ud deceleration of the Nazca plate trenchward velocity

The dynamics of laterally variable subductions: laboratory models applied to the Hellenides

“…For descriptive convenience, we geographically orient our models, such that West is on the foreland side of the plate (the unsubducted part of the plate). When present, the overriding plate is decoupled from the subducting plate by a thin layer of glucose syrup (see Heuret et al, 2007;Espurt et al, 2008;Guillaume et al, 2009), which reduces the shear stresses to negligible values (because stresses scale with viscosity) and prevents plates sticking to one another. It is somehow equivalent to introducing a weak zone in numerical models that is used to mimic the effect of a fault subduction zone (e.g.…”

“…2). Such an approach has already been used to study how the subduction of positively buoyant ridges and oceanic plateaux impact the subduction dynamics (Martinod et al, 2005;Espurt et al, 2008;Martinod et al, 2013). To compare the experimental results to the kinematics of the Hellenic subduction, we restrict the length of the subduction zone within the range 1200-2400 km and we fix the subducting plate at its trailing edge, in analogy with the Hellenic subduction zone that is embedded into the massive, slowly moving African plate.…”

“…Cloos, 1993). Not surprisingly, analogue (Bellahsen et al, 2005;Martinod et al, 2005;Espurt et al, 2008), semi-analytical (Royden and Husson, 2009), and numerical (van Hunen et al, 2002;De Franco et al, 2008;Magni et al, 2012) models show that temporal variations of slab buoyancy exert a primary control on slab dip and migration of the subduction hinge relative to the upper plate. The downdip descent of positively buoyant material into the subduction zone initiates a transient mode during which the slab steepens and the subduction rate decreases.…”

Destruction of the North China Craton Induced by Ridge Subductions

“…Ridge subduction is generally inferred to result in flat slabs that can extend several hundreds of kilometers or more inboard from the subduction zone beneath the overriding continent (Espurt et al 2008). Subduction of ridges with axes perpendicular to the subduction zone can form linearly distributed adakites commonly associated with Cu-Au porphyry deposits (Cooke et al 2005;Sun et al 2010Sun et al , 2011.…”

“…Ridge subduction was a common phenomenon along the margins of the Pacific Plate and other convergent margins (Uyeda and Miyashiro 1974;Kinoshita 1995Kinoshita , 2002Maruyama et al 1997;Kim et al 2005;Cole et al 2006;Espurt et al 2008;Cole and Stewart 2009;Ling et al 2009;Tang et al 2010). It is presumably a general process in the Earth's history, because when oceans close, all the ocean ridges must be consumed along convergent margins.…”