An array of 74 seismological stations was deployed in the Argentine Puna and adjacent regions for a period of two years. The aim is to investigate the seismic structure in the crust and upper mantle in order to address fundamental questions regarding the processes that form, modify and destroy continental lithosphere and control lithospheric dynamics in this part of the Central Andes. This portion of the Central Andes is an ideal locale to address these questions given that there is geologic evidence that there has been recent lower crustal and mantle lithospheric delamination. 2We performed a teleseismic P wave tomography study using seismic events at both teleseismic

[1] We make use of S receiver function to investigate the structure and thickness of the crust and mantle lithosphere in the South American continent and adjacent areas. The Moho discontinuity has been detected at all stations and goes from 18 km beneath the coast of the continent to 80 km in the Andean region. The depth of the lithosphereasthenosphere boundary can be clearly detected below those stations that are located on stable areas from 50 km to 160 km. The identification of this phase becomes more difficult when the stations are located near subduction zones. We also observed the base of the subducted oceanic lithosphere down to depths of 220 km.

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SUMMARY The Alborz Mountains build the northern part of the Alpine–Himalayan orogen in western Asia. They are located south of the Caspian Sea and form an east–west range across the north of Iran. This region is one of the most active tectonic areas, as it undergoes extensive crustal deformation and shortening. In the present work, we used data from 11 permanent stations of the Tehran Telemetry Seismic Network to estimate the thickness of the crust and mantle lithosphere beneath the Central Alborz region by P‐ and S‐receiver function methods. Results of both P and S receiver functions revealed a relatively large crustal thickness beneath this region (∼51–54 km), which can be associated with the shortening process related to the orogenic belt. No remarkable crustal thickening has been detected below the high topography of Central Alborz. A thick crust (∼67.5 km) is observed locally in the region beneath the Damavand volcano, which is possibly related to the magmatic addition at the base of the crust beneath the volcanic region. The S receiver functions exhibit the existence of a seismic discontinuity in the upper mantle at a depth of ∼90 km, which we interpreted as the base of the lithosphere. The missing crustal root and the relatively thin lithosphere beneath the Alborz may imply that sublithospheric mantle could be responsible for and support the elevation of the Alborz.

Earthquake hypocenters recorded in the Andean Southern Puna seismic array (25-28°S, 70-65°W) provide new constraints on the shape of the subducting Nazca plate beneath the Puna plateau, the transition into the Chilean-Pampean flat slab and the thermal state of the mantle and crust. Some 270 new mantle hypocenters suggest that the subducting slab under the Puna shoals into the flat-slab segment more abruptly and farther to the north than previously indicated. The revised geometry is consistent with the Central Volcanic Zone Incapillo caldera being the southernmost center with Pleistocene activity until reaching the southern side of the flat-slab region. Evidence for the revised slab geometry includes three well-defined hypocenter clusters in the Pipanaco nest (27.5-29°S, 68-66°W), which are interpreted to reflect slab-bending stresses. A few low-magnitude earthquakes with strongly attenuated S waves in the long-recognized Antofalla teleseismic gap (25.5-27.5°S) support a continuous slab under the Southern Puna. The paucity of gap earthquakes and the presence of mafic magmas are consistent with a hot mantle wedge reflecting recent lithospheric delamination. Evidence for a hot overlaying Puna crust comes from new crustal earthquake hypocenters concentrated at depths shallower than 5 km. Two notable short-duration swarms were recorded under the resurgent dome of the~2 Ma back-arc Cerro Galán caldera and the near-arc Cerro Torta dome. New crustal earthquake focal mechanisms from 17 events in the array along with two existing mechanisms have strike slip, oblique reverse, and oblique normal solutions fitting with regional E-W compression and N-S extension.