Lithospheric delamination beneath the southern Puna plateau revealed by local earthquake tomography
Abstract
The Andean Plateau, consisted of Altiplano and Puna, has been formed by the subduction of the oceanic Nazca plate beneath the continental South American plate. The southern Puna plateau is anomalous with respect to the rest of the Andean plateau in having a distinct magmatic and structural history, a large deficit in crustal shortening compared to its elevation, an underlying slab with a transitional dip between a steeper segment to the north and a flat slab to the south, and a thinner continental lithosphere. Based mainly on geochemical and geological observations, a model of lithospheric delamination was proposed to explain these distinct features. Here we present seismological evidences for the lithospheric delamination from local earthquake tomography using travel time data recorded by a network of 75 stations in the southern Puna. Widespread low velocity anomalies are found in the upper crust with a concentration on the main volcanic centers. These low velocity anomalies are confined within the southern Puna plateau, bounded by high velocities beneath the Sierras Pampeanas to the southeast, indicating the presence of magma and melting in the crust. In the uppermost mantle beneath west of the recent (2 Ma) Cerro Galan backarc volcano, a pronounced high velocity anomaly is clearly detected at depths of 75-100 km above the subducted slab. The anomaly coincides with a gap in the slab seismicity and is linked to Cerro Galan by an elongated crustal low velocity zone. We interpret this high velocity body as an expression of a delaminated lithospheric block, which has caused upwelling of fluids and melts above it and triggered the volcanic eruption. The tomography also revealed low velocity anomalies that link the prominent arc magmatism and the slab seismicity clusters at different depths of about 100 and 150 km, indicating fluid flux in the mantle wedge due to dehydration reaction within the subducted slab.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T41J0275Y
- Keywords:
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- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8158 Plate motions: present and recent;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS;
- 8488 Volcanic hazards and risks;
- VOLCANOLOGY