Lithospheric structure beneath the northern Central Andean Plateau from the joint inversion of ambient noise and earthquake‐generated surface waves

Abstract

The Central Andean Plateau (CAP), as defined by elevations in excess of 3 km, extends over 1800 km along the active South American Cordilleran margin making it the second largest active orogenic plateau on Earth. The uplift history of this high Plateau, with an average elevation around 4 km above sea level, remains uncertain as paleoelevation studies along the CAP suggest a complex, nonuniform uplift history. As part of the Central Andean Uplift and the Geodynamics of High Topography (CAUGHT) project, we image the S wave velocity structure of the crust and upper mantle using surface waves measured from ambient noise and teleseismic earthquakes to investigate the upper mantle component of plateau uplift. We observe three main features in our S wave velocity model including (1) a positive velocity perturbation associated with the subducting Nazca slab; (2) a negative velocity perturbation below the sub‐Andean crust that we interpret as anisotropic Brazilian cratonic lithosphere; and (3) a high‐velocity feature in the mantle above the slab that extends along the length of the Altiplano from the base of the Moho to a depth of ~120 km. A strong spatial correlation exists between the lateral extent of this high‐velocity feature and the relatively lower elevations of the Altiplano basin suggesting a potential relationship. Determining if this high‐velocity feature represents a small lithospheric root or foundering of orogenic lithosphere requires more integration of observations, but either interpretation implies a strong geodynamic connection with the uppermost mantle and the current topography of the northern CAP.

Extension and Dynamics of the Andes Inferred From the 2016 Parina (Huarichancara) Earthquake

“…Delamination has been proposed to account for the composition, timing, and volume of ignimbrite and mafic volcanism (e.g., Kay & Mahlburg Kay, ), the Helium isotope ratios of hydrothermal fluids (Hoke & Lamb, ), and the possible rapid Miocene‐recent uplift of the central Andes (e.g., Garzione et al, , , ). However, the relationship between crustal thickening and uplift rates in the Bolivian Altiplano (Lamb, , ), and inconsistent seismic models that independently infer thick, thin, and variable thickness lithospheric mantle beneath the Andes (e.g., Beck & Zandt, ; Phillips et al, ; Priestley & McKenzie, ; Ward et al, ; Whitman et al, ), calls into question whether delamination beneath the central Andes coeval with extension actually occurred.…”

“…A reduction in f would be balanced (F GPE = F u + F p ) by an increase in the viscous resistance to shortening in the ductile lower crust (F p ), extensional viscous strain within the center of the mountain belt, and an increase in the rate of propagation of the mountains over the rigid foreland. Zandt, 2002;Phillips et al, 2012;Priestley & McKenzie, 2013;Ward et al, 2016;Whitman et al, 1992), calls into question whether delamination beneath the central Andes coeval with extension actually occurred.…”

Surface Wave Tomography of the Alps Using Ambient‐Noise and Earthquake Phase Velocity Measurements

“…The AN and EQ observation methods are effective over overlapping, but different frequency bands (Kästle et al, ), so that our new, joint database includes an extremely broad band of surface wave frequencies; as different surface wave frequencies are sensitive to different depth ranges, this in turn helps to constrain structures over a greater range of depths. This approach has been applied in different parts of the Earth (e.g., Kohler et al, ; Shen et al, ; Ward et al, ; Yang, Li, et al, ; Yang, Ritzwoller, et al, ; Zhou et al, ), but ours is the first joint EQ‐AN inversion for the Alpine structure. We accordingly consider this study to represent a significant progress with respect to earlier, similarly minded efforts (Fry et al, ; Molinari et al, ; Stehly et al, ; Verbeke et al, ).…”

Seismic Imaging of the Alaska Subduction Zone: Implications for Slab Geometry and Volcanism

“…Numerous recent studies have used joint inversion of phase velocities from ambient noise and teleseismic surface waves in regional tomography (the central Andean plateau, Ward et al, 2016;Madagascar, Pratt et al, 2017; and the Malawi rift, Accardo et al, 2017). Receiver functions have also been incorporated into 10.1029/2018GC007962 Geochemistry, Geophysics, Geosystems such inversions (e.g., Porritt et al, 2015).…”