Abstract
The Central Andes are the Earth's highest mountain belt formed by ocean–continent collision1,2. Most of this uplift is thought to have occurred in the past 20 Myr, owing mainly to thickening of the continental crust2,3,4,5,6, dominated by tectonic shortening7,8,9,10. Here we use P-to-S (compressional-to-shear) converted teleseismic waves observed on several temporary networks in the Central Andes to image the deep structure associated with these tectonic processes. We find that the Moho (the Mohorovičić discontinuity—generally thought to separate crust from mantle) ranges from a depth of 75 km under the Altiplano plateau to 50 km beneath the 4-km-high Puna plateau. This relatively thin crust below such a high-elevation region indicates that thinning of the lithospheric mantle may have contributed to the uplift of the Puna plateau. We have also imaged the subducted crust of the Nazca oceanic plate down to 120 km depth, where it becomes invisible to converted teleseismic waves, probably owing to completion of the gabbro–eclogite transformation; this is direct evidence for the presence of kinetically delayed metamorphic reactions in subducting plates. Most of the intermediate-depth seismicity in the subducting plate stops at 120 km depth as well, suggesting a relation with this transformation. We see an intracrustal low-velocity zone, 10–20 km thick, below the entire Altiplano and Puna plateaux, which we interpret as a zone of continuing metamorphism and partial melting that decouples upper-crustal imbrication from lower-crustal thickening.
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Acknowledgements
We thank R. Trumbull and F. Lucassen for discussions, J. Mechie and D. Harlov for comments on the manuscript, and G. Chong and M. Wilke for supporting the experiments. The field experiments were supported by the Collaborative Research Center (SFB) 267 of the Deutsche Forschungsgemeinschaft, the GeoForschungsZentrum Potsdam, the Freie Universität Berlin, the US National Science Foundation, the PASSCAL project, the Universidad de Chile (Santiago) and the Universidad Catolica del Norte (Antofagasta).
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Yuan, X., Sobolev, S., Kind, R. et al. Subduction and collision processes in the Central Andes constrained by converted seismic phases. Nature 408, 958–961 (2000). https://doi.org/10.1038/35050073
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DOI: https://doi.org/10.1038/35050073
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