Seismic and magmatic evidence for lithospheric delamination and the shape of the seismic zone in the Puna Austral región.

KAY, S., HEIT, B., CALIXTO, F., MULCAHY, P., LIANG, X., COIRA, B. AND THE SOUTHERN PUNA SEISMIC TEAM

Córdoba

Congreso; XIX Congreso Geológico Argentino; 2014

AGA

The southern Puna was proposed as a site of crustal destruction by delamination or foundering of thickened continental crust with the continental lithosphere in the early 1990s (Kay et al., 1994).  The proposal was based on seismic evidence for low Sn attenuation and a gap in intermediate depth earthquakes in the down-going slab, a low effective elastic thickness, a change in fault kinematics and the distribution and chemical and isotopic signatures of mafic lava flows, glassy andesites, and the Cerro Galan ignimbrite.  Seismic evidence was sparse and the delamination model was controversial. This changed as groups from the Univ. Arizona and Carnegie Institute produced seismic images from the southern Altiplano showing a mantle lithospheric gap that they attributed to the removal of the lithosphere. Subsequent seismic studies 400 km to the south by the German group at Potsdam revealed a low velocity region above the subducting slab and below the lithosphere that they interpreted as a delaminated block.  Since that time, the delamination or foundering hypothesis has become a popular model to explain the uplift, ignimbrites, and basins of the Puna and Altiplano with the size and frequency of the blocks or drips being hotly debated.