The PUNA Passive Seismic Array in the Southern Puna: Tests of Lithospheric Delamination in the Region of the Cerro Galán Ignimbrite.

MAHLBURG KAY, S., HEIT, B.S., COIRA, B.L., SANDVOL E., YUAN, X., MCGLASHAN, N., COMTE, D., BROWN, L.D., KIND, R.

Nice, Francia

Simposio; 7th International Symposium on Andean Geodynamics (ISAG 2008); 2008

Géosciences Azur, Francia

A passive seismic array is deployed at present in the southern Puna of the Central Andean plateau between 25°S to 28°S latitude in Argentina and Chile to address fundamental questions on the processes that form, modify and destroy continental lithosphere and control lithospheric dynamics along Andean-type continental margins (Fig. 1). The southern Puna is important in this regard as this is the region where the delamination hypothesis for removal of thickened eclogitic continental crust and mantle lithosphere was initially suggested (Kay and Kay, 1993). The case for young delamination of the lithosphere in the southern Puna was built on magmatic patterns, geochemical signatures and evolutionary models for mafic lavas and silicic ignimbrites (particularly Cerro Galán), changing and mixed deformational styles, high topography accompanied by insufficient crustal shortening, an underlying slab with a gap in intermediate depth seismicity and evidence for Sn attenuation (e.g., Kay et al. 1994; 1999; Whitman et al. 1994).  Since then, the crustal delamination process has gained popularity as it can explain features like formation of giant ignimbrites and the near absence of a mafic crustal root in many orogenic regions (e.g., Beck and Zandt, 2002; Yuan et al., 2002).  On another level, the delamination model provides a way to explain the bulk andesitic composition of the continental crust (e.g., Kay and Kay, 1993). The southern Puna, which overlies a down-going slab with a transitional dip between a steeper dipping segment to the north and a flat-slab to the south, is a benchmark for comparative studies with orogenic systems like those in the western US and Tibet where changing subduction angles, lithospheric delamination and crustal shortening have been used to explain lithospheric evolution and plateau formation.