Late Cenozoic calc-alkaline volcanism over the Payenia shallow subduction zone, South-Central Andean back-arc (34°30?-37°S), Argentina

LITVAK, V.D.; SPAGNUOLO, M.G.; FOLGUERA, A.; POMA, S.; JONES, R.; RAMOS, V.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2015 vol. 64 p. 365 - 380

0895-9811

A series of mesosilicic volcanic centers have been studied on the San Rafael Block (SRB), 300 km to theeast of the present-day volcanic arc. K-Ar ages indicate that this magmatic activity was developed in atleast two stages: the older volcanic centers (~15e10 Ma) are located in the central and westernmost partof the SRB (around 36S and 69W) and the younger centers (8e3.5 Ma) are located in an eastern position(around 36S and 69300W) with respect to the older group. These volcanic rocks have andesitic todacitic compositions and correspond to a high-K calc-alkaline sequence as shown by their SiO2, K2O andFeO/MgO contents. Elevated Ba/La, Ba/Ta and La/Ta ratios show an arc-like signature, and primitivemantle normalized trace element diagrams show typical depletions of high field strength elements(HFSE) relative to large ion lithophile elements (LILE). Rare earth element (REE) patterns suggest pyroxeneand amphibole crystallization. Geochemical data obtained for SRB volcanic rocks support theproposal for a shallow subduction zone for the latest Miocene between 343000e37S. Regionally, SRBvolcanism is associated with a mid-Miocene to early Pliocene eastward arc migration caused by theshallowing of the subducting slab in the South-Central Andes at these latitudes, which represents theevolution of the Payenia shallow subduction segment. Overall, middle Miocene to early Pliocenevolcanism located in the Payenia back-arc shows evidence for the influence of slab-related components.The younger (8e3.5 Ma) San Rafael volcanic rocks indicate the maximum slab shallowing and theeasternmost extent of slab influence in the back-arc.