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Multiple styles and scales of lithospheric foundering beneath the Puna Plateau, Central Andes

Susan L. Beck, George Zandt, Kevin M. Ward and Alissa Scire
Multiple styles and scales of lithospheric foundering beneath the Puna Plateau, Central Andes
Memoir - Geological Society of America (2015) 212: 43-60


Lithospheric foundering or delamination has been long recognized as an important process in the formation of the Andes, but the scale, timing, and surface uplift consequences remain controversial. We use recently completed ambient noise tomography and finite-frequency P-wave tomography results and other geologic and geophysical information to identify two approximately 200-km-diameter regions of piecemeal delamination in the Puna region between 21 degrees S and 27 degrees S. One location in the northern Puna Plateau is centered under the 11-1 Ma large-volume silicic Altiplano-Puna volcanic center, and the other in the southern Puna Plateau is centered approximately between the Arizaro Basin and 6-2 Ma Cerro Galan volcanic field. The foundering in the northern location has progressed to the point where the main thermal anomaly resides in the middle and upper crust, and the surface volcanic flare-up and mantle thermal anomalies are both in a waning stage. In the southern location, the main thermal anomaly is still in its waxing stage in the lower crust and upper mantle, and the foundering mantle material is imaged in the mantle wedge. The differing patterns of back-arc volcanism in the two foundering centers suggest different styles and timing of delamination, with the foundering process coming to completion earlier in the north than in the south. Based on plate-motion reconstructions, the NE-SW-aligned Juan Fernandez Ridge swept southward through this area starting about ca. 14 Ma in the north and ca. 10 Ma in the south. Although we do not think the passage of the Juan Fernandez Ridge initiated foundering, it played an important role in facilitating delamination by increasing interplate coupling, and weakening and perhaps hydrating the upper plate, and its passage allowed the delaminated material to sink into the expanding space of the mantle wedge. Another important factor in this evolution is the upper-plate lithospheric strength variations inherited from the different geologic basements underlying the northern and southern Puna regions. As the larger-scale delamination progressed, leaving behind thin lithosphere and a mantle wedge with a mixture of continental lithospheric fragments and hot asthenosphere, smaller secondary Rayleigh-Taylor instabilities occurred beneath the southern Puna Plateau, influencing basin development, and subsequent melting of this "drip" material was the source of the ensuing low-volume mafic volcanism.

ISSN: 0072-1069
Serial Title: Memoir - Geological Society of America
Serial Volume: 212
Title: Multiple styles and scales of lithospheric foundering beneath the Puna Plateau, Central Andes
Affiliation: University of Arizona, Department of Geosciences, Tucson, AZ, United States
Pages: 43-60
Published: 2015
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 97
Accession Number: 2015-036110
Categories: Solid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch map
S28°00'00" - S18°00'00", W74°00'00" - W62°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201517
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