Publications

Variations in the subduction angle of the Nazca plate beneath the South American plate has lead to the uplift of the Central Andean Plateau. The southern Puna plateau is the southernmost part of this plateau, and one of the transition zones from steep subduction to flat subduction of the Nazca plate. It is characterized by many unique geological and geochemical features with respect to the rest of the Andean plateau, such as a distinct magmatic style, a potentially thinner mantle lid, and a lack of intermediate depth slab seismicity. A major Pliocene delamination event has previously been inferred from geochemical and geological and preliminary geophysical data. The mountain building process of the southern Puna plateau is probably a key to understanding the Andean-type orogenic process. The PUNA passive seismic experiment was operated from the 2007-2009 at southern Puna plateau between 25-28°S. Using the new collected seismic waveform data from PUNA project, we apply the attenuation tomography to resolve both compressional and shear quality factor (Qp and Qs) in the crust and uppermost mantle. The images show a clearly high Q Nazca slab subducting eastward beneath the Puna plateau and another high Q block with a westward dip beneath the Eastern Cordillera, which may indicate the presence of a piece of delaminated South American lithosphere. A significant low Q zone extends between the Nazca slab and South American lithosphere from the northern margin of the array at 25°S and vanishes around 27.5°S. This low Q zone extends further west in the crust and uppermost mantle at the southern end of the array. The low Q zone reaches ~100 km depth beneath the north part of the array, but only ~50 km in the south. The depth of the Nazca slab shows a decreasing trend from north to south beneath the plateau, which is consistent with the steep-flat transition of the angle of the subducting slab.

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Liang, X.; Sandvol, E. A.; Brown, L. D.; Heit, B.; Yuan, X.; Mulcahy, P.; Chen, C.; Mahlburg, S. (2011): The Q images of southern Puna plateau from bodywave attenuation tomography. AGU 2011 Fall Meeting (San Francisco 2011).