New insights on regional tectonics and basement composition beneath the eastern Sierras Pampeanas (Argentine back-arc region) from seismological and gravity data

Lithospheric density structure of the southern Central Andes constrained by 3D data-integrative gravity modelling

“…Our results suggest that the middle and lower crustal levels also have mafic compositions. The higher crustal densities in this part of the foreland compared to the orogen interior could be associated with partial eclogitization of the lower crust, as has been previously suggested on the basis of geophysical studies, in particular in view of the increase in V p and the V p /V s ratio beneath the foreland (Gilbert et al 2006;Alvarado et al 2007Alvarado et al , 2009Ammirati et al 2013Ammirati et al , 2015Ammirati et al , 2018Marot et al 2014). The factors causing partial eclogitization in the lower crust remain unclear (e.g., Ammirati et al 2015), although some studies suggest that this process could be facilitated by small amounts of water released from the sub-horizontal section of the subducted oceanic crust (Leech 2001;Yang et al 2008).…”

“…The alternative tomographic model used for the sensitivity analysis of the mantle density distribution was the SEM μm 2 model (French et al 2013). The factor f is calculated by dividing the relative density variation by the absolute value of the ΔThkLC and measures how uncertainties in the parametrization affect the derived intracrustal structure is no geophysical evidence for westward-directed thrusting of the cratonic material beneath the Andes between 29° S and 39° S (e.g., Alvarado et al 2005Alvarado et al , 2009Heit et al 2008;McGlashan et al 2008;Porter et al 2012;Perarnau et al 2012;Ammirati et al 2015Ammirati et al , 2016Ammirati et al , 2018Pérez-Luján et al 2015). The low average crustal density beneath the orogen may be characteristic of ocean-continent subduction scenarios, as has previously been suggested in other gravity modelling studies of the Central Andes (e.g., Tassara et al 2006;Ibarra et al, 2019).…”

“…Westto-east variations in the velocities of P and S waves have also been identified in the sub-horizontal slab region, with a relatively low-velocity zone beneath the orogen (between 69° W and 70° W) and the easternmost part of the foreland (between 65° W and 67° W), and a high-velocity zone in the back-arc and the westernmost part of the foreland (i.e., between ~ 67° W and 69° W; e.g. Ward et al 2013;Marot et al 2014;Ammirati et al 2015Ammirati et al , 2016Ammirati et al , 2018. Most of these researchers have interpreted each of these velocity zones to reflect crustal terranes with different compositions that were accreted to the Gondwana margin during the early Paleozoic (e.g., Ramos et al 2010).…”

“…Their results have placed the Moho at an average depth of ~ 70 km below mean sea level (b.m.s.l) in the orogen and at depths ranging between 35 and 55 km b.m.s.l. in the foreland, with the depth decreasing eastwards (Alvarado et al 2005(Alvarado et al , 2009Heit et al 2008;McGlashan et al 2008;Porter et al 2012;Perarnau et al 2012;Ammirati et al 2015Ammirati et al , 2016Ammirati et al , 2018Pérez-Luján et al 2015). Westto-east variations in the velocities of P and S waves have also been identified in the sub-horizontal slab region, with a relatively low-velocity zone beneath the orogen (between 69° W and 70° W) and the easternmost part of the foreland (between 65° W and 67° W), and a high-velocity zone in the back-arc and the westernmost part of the foreland (i.e., between ~ 67° W and 69° W; e.g.…”

“…Seismic data from a number of different sources have been used to constrain the first-order discontinuities and seismic properties of the South American lithosphere, focusing primarily on the sub-horizontal slab region (e.g., from CHARGE, SIEMBRA, and ESP seismic experiments; Alvarado et al 2005;Ammirati et al 2013Ammirati et al , 2018. These investigations were mainly used to generate data with which to construct 2D cross-sections or establish 3D models of sub-regions of the SCA.…”