Mantle wedge deformation by subducting and rotating slab and its possible implication

Abstract

We have constructed a simple model of the deformation of the mantle wedge caused by the subducting and rotating slab based on corner flow model. By applying this model to the geological settings of the Somuncura plateau volcanic region, northern Patagonia, which is located far from the volcanic front, we constrain the mechanical aspect of the hypothesis that the volcanisms of the Somuncura region are triggered by the dehydrationinduced melting of the up-warped transition zone which may contain more water than other regions do. Assuming that the water concentrates in the transition zone under the Somuncura plateau, we find that the above scenario may be possible, if the speed of the subducting slab is less than ∼2 cm/yr or the dip angle changes significantly (∼50 degrees within ∼8 Myr).

Geochemical variations in Cenozoic back-arc basalts at the border of La Pampa and Mendoza provinces, Argentina

“…The origin of these basalts has been related to mechanical perturbations of the subcontinental mantle, as a consequence of subduction of the oceanic lithosphere below the South American continental plate (Skewes and Stern, 1979). On the other hand, back-arc magmatism of northern Patagonia (Somuncurá Plateau) has been related to the presence of transitory hot spots (Kay et al, 1993), to slab-induced shallow asthenospheric upwelling caused by slab rotation (De Ignacio et al, 2001), and to multiple upwelling of a hydrous melt derived from up-warped mantle transition zone Honda et al, 2006). Farther north, back-arc basalts in Mendoza and La Pampa provinces have been considered as indicators of extensional events produced after the main compressive phase during the Tertiary and probably generated by mechanical and thermal modifications of the upper mantle produced by subduction (Bermúdez et al, 1993).…”

Subduction controls on Miocene back-arc lavas from Sierra de Huantraico and La Matancilla and new 40Ar/39Ar dating from the Mendoza Region, Argentina

“…By contrast, several explanations for OIB-type back-arc magmatism of the Somuncurá Plateau (northern Patagonia) have been suggested. Kay et al (1993) refer the OIB-type signature to the presence of hot spots or 'hot fingers' whereas De Ignacio et al ( 2001) calls for shallow asthenospheric upwelling caused by slab-rotation and upwelling of a hydrous melt derived from an up-warped mantle transition zone was suggested by Orihashi et al(2006) and Honda et al (2006). Stern et al (1990) divided the Pliocene to Quaternary basalts of the SVZ into two groups; transitional and cratonic, based on trace element content and isotope ratios.…”