Young mafic back-arc volcanic rock as indicator of continental lithospheric delamination beneath the Argentine Puna plateau, Central Andes.

KAY, S.; COIRA, B. AND J., VIRAMONTE

JOURNAL OF GEOPHYSICAL RESEARCH

AMER GEOPHYSICAL UNION

Lugar: Nueva York; Año: 1994 vol. 99 p. 24323 - 24339

0148-0227

Abstract The spatial distribution of some major and trace element and isotopic characteristics of backarc Plio-Quaternary basaltic to high-Mg andesitic (51% to 58% SiO2) lavas an the southern Puna (24º S to 27ºS) of the Central Andean Volcanic Zone (CVZ) reflect varying continental lithospheric thckness and the thermal state of the underlying mantle wedge and subducting plate. These lavas erupted from small cones and fissures associated with faults related to change in the regional stress system in the southern Puna at ~ 2 to 3 Ma. Three geochemical groups are recognized: (1) a relatively high volume intraplate group (high k; La/Ta ratio 25) that occurs over intermediate thckness lithosphere on the margins of the seismic gap and behind the main CVZ and represents an intermediate percentage of mantle partial melt, and (3) a small-volume shoshonitic group (very high K) that occurs over relatively thick continental lithosphere in the northeast Puna and Altiplano and represents a very small percentage of mantle partial melt. Mantle-generated characteristics of these lavas are partially overprinted by mixing with melts of the overlying thickened crust as shown by the partially overprinted by mixing with melts of the overlying thickened crust as shown by the presence of quartz and feldspar xenocrysts, negative Eu anomalies (Eu/Eu*0.7055) and Pb and nonradiogenic Nd (εNd