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Investigating Along-strike Differences in Crust and Upper Mantle Structure of the Central Andes Through High-resolution Receiver Functions

Description: 

To obtain a comprehensive image of the Andean Cordilleran structure, we embarked on a joint broadband-nodal passive seismic deployment between Summer 2022 – April 2024 constructing two profile lines perpendicular to the orogen strike. Line 1 (~23-24⁰S) was deployed from the Chilean coast, across the volcanic arc, Puna plateau, and into the Chaco Plain where the high Andes (greater than 2000 m elevation) are ~500 km wide. Line 2 (~35.5-36⁰S) was deployed from the Chilean coast across the volcanic arc to the backarc Payun Matru Volcanic Field in the northern Neuquén basin where the high Andes are ~250 km wide. Both lines allow a juxtaposition of the differing deformational styles and volcanic arc magma storage systems that we can use to compare the state of the crust and upper most mantle. We use receiver functions to image the discontinuities that relate to seismic velocity changes with depth and migrate the data using composite velocity models aggregated from the literature.

Our results show shallow low velocity zones (LVZ) associated with arc and backarc magmatism in each region. The northern LVZ is associated with the large Altiplano-Puna Volcanic Complex and is more voluminous and laterally covers a region from the arc across the Puna plateau. The southern profile shows a smaller LVZ below and presumably associated with the Laguna del Maule volcanic complex. Along the northern profile we see clear dipping interfaces consistent with the slab Moho and top of the subducting Nazca oceanic crust that disappears at depths between ~120-140 km suggesting eclogitization of the Nazca crust. In contrast, the southern profile lacks a clear seismic signal of the subducting slab that may be related to its younger age and warmer temperature. In the northern profile we image a west-dipping discontinuity with an increase in velocity with depth that may be related to the to the Main Andean Decollement. These two transects reflect different mountain building and magmatic processes that we will discuss including volumetric models of melt distribution of the Laguna Maule volcano and along strike models of crustal thickness.

Session: Earth’s Structure from the Crust to the Core - I

Type: Oral

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Jim

Student Presenter: Yes

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