Kevin M. Ward, George Zandt, Susan L. Beck, Ryan C. Porter, Lara S. Wagner, Estela Minaya, Hernando Tavera

V. Sajama, Bolivia

Central Andean Plateau (CAP) •  Average elevation ~4 km

•  Max width ~300 km

•  Total length ~2,000 km

•  Abundant arc magmatism

Central Andean Plateau (CAP) •  Average elevation ~4 km

•  Max width ~300 km

•  Total length ~2,000 km

•  Abundant arc magmatism •  Data from 315 broadband

seismic stations

•  Deployed piecemeal from May 1994 through August 2012

Ambient Noise Tomography Method

Ambient Noise Tomography Method

Ambient Noise Source •  Lower periods ~ ocean waves

against the shore •  Higher periods ~ atmospheric

disturbances •  Not limited by event distribution

Ambient Noise Tomography Method

Ambient Noise Source •  Lower periods ~ ocean waves

against the shore •  Higher periods ~ atmospheric

disturbances •  Not limited by event distribution

Raw Waveform Processing •  Visually inspect waveforms •  5 to 150 sec band-pass filter •  Spectral whitening and running

absolute mean normalization

Ambient Noise Tomography Method

Ambient Noise Source •  Lower periods ~ ocean waves

against the shore •  Higher periods ~ atmospheric

disturbances •  Not limited by event distribution

Raw Waveform Processing •  Visually inspect waveforms •  5 to 150 sec band-pass filter •  Spectral whitening and running

absolute mean normalization

Cross Correlations •  CC each station pair for each day •  3,519,011 CCs •  Stack each CC station pairs to

approximate the EGF

Ambient Noise Tomography Method

Ambient Noise Source •  Lower periods ~ ocean waves

against the shore •  Higher periods ~ atmospheric

disturbances •  Not limited by event distribution

Raw Waveform Processing •  Visually inspect waveforms •  5 to 150 sec band-pass filter •  Spectral whitening and running

absolute mean normalization

Cross Correlations •  CC each station pair for each day •  3,519,011 CCs •  Stack each CC station pairs to

approximate the EGF

Empirical Green’s Function •  Approximates the seismic

response of a Rayleigh wave traveling between stations

•  Frequency-time analysis to extract dispersion curves

Rayleigh Wave Dispersion Curves

Rayleigh Wave Dispersion Curves

Phase Velocity Inversion Results

Phase Velocity Inversion Results

Phase Velocity Inversion Results

Shear Wave Inversion Results

Shear Wave Inversion Results

Shear Wave Inversion Results •  Low velocity zone is

too shallow to represent a zone of crustal !ow

Shear Wave Inversion Results •  Low velocity zone is

too shallow to represent a zone of crustal !ow

Shear Wave Inversion Results •  Low velocity zone is

too shallow to represent a zone of crustal !ow

•  Resistivity studies indicate the low velocity zone is not a body of interconnected aqueous !uids

Shear Wave Inversion Results •  Low velocity zone is

too shallow to represent a zone of crustal !ow

•  Resistivity studies indicate the low velocity zone is not a body of interconnected aqueous !uids

•  Previous work in the Altiplano-Puna Volcanic Complex (APVC) and Cretaceous Sierra Nevada Batholith (CSNB) might provide answer

Model of Batholith Formation

Shear Wave Inversion Results

Shear Wave Inversion Results

Looking for the Batholith •  "e 3.25 km/s velocity contour

outlines the extent of the APVC

Looking for the Batholith •  "e 3.25 km/s velocity contour

outlines the extent of the APVC

•  "e 3.25 km/s velocity contour correlates well with known Neogene ignimbrite eruption centers

Looking for the Batholith •  "e 3.25 km/s velocity contour

outlines the extent of the APVC

•  "e 3.25 km/s velocity contour correlates well with known Neogene ignimbrite eruption centers

•  "e 3.25 km/s velocity contour agrees with low isostatic gravity anomalies

3D view of the Neogene “Batholith”

Concluding Remarks

•  "e 3.25 km/s velocity contour correlates well with known Neogene ignimbrite eruption centers and low isostatic gravity anomalies

•  Our interpretation of a large Neogene batholith associated with active volcanism revisits the idea of magmatic addition as a contributing mechanism to the growth of the western portion of the CAP

•  How much of a contributing mechanism?

Supplementary Material ~ PV Inversion

Supplementary Material ~ Vsv Inversion

Supplementary Material ~ Vsv Mis#t