Central Andean mantle and crustal seismicity beneath the Southern Puna plateau and the northern margin of the Chilean-Pampean flat slab.

MULCAHY, P.; CHEN, CH.; KAY, S.M.; BROWN, L.D.; ISACKS, B.L.; SANDVOL, E.; HEIT, B.; YUAN, X.; COIRA, B.; KIND, R.

TECTONICS

AMER GEOPHYSICAL UNION

Lugar: NY; Año: 2014 vol. 33 p. 1636 - 1658

0278-7407

Well-constrained crustal and mantle earthquake hypocenters recorded in the Andean Southern 27 Puna seismic array (25-28°S; 70-65°W) provide new constraints on the shape of the subducting Nazca plate beneath the Puna plateau and transition to the Chilean-Pampean flatslab, and on the thermal state of the mantle and crust. The 271 new mantle hypocenters confirm that the slab shoals more abruptly further to the north than in previous geometries in line with post 5 Ma volcanic activity ending at the southern Central Volcanic Zone Incapillo center. Evidence for this sharper bend comes from 3 hypocenters clusters in the Pipanaco nest (27.5-29°S, 68-66°W), whose origins are attributed to increased slab bending stresses. Four low magnitude earthquakes with strong S wave attenuation confirm the continuity of the slab through the long recognized Antofalla intermediate depth gap (25.5- 27.5°S). The 230 new crustal earthquakes, which were largely at depths under 5 km, are concentrated along faults like the Acazoque Fault, in a persistent backarc cluster north of Cerro Blanco, and in short swarms under the resurgent dome of the 2 Ma Cerro Galán caldera and under a near arc dome at 26.65°S. New focal mechanisms for 17 of these crustal earthquakes, like the 2 that existed, mainly show strike slip, oblique reverse, and oblique normal solutions with orientations indicating regional E-W compression and N-S extension. The paucity of seismicity in the Antofalla gap and the shallow crustal events support a hot mantle and crust beneath the southern Puna in line with recent lithospheric delamination.