%0 Journal Article
%T Middle Miocene calc-alkaline volcanism in Central Patagonia (47¡ãS): petrogenesis and implications for slab dynamics Volcanismo calcoalcalino durante el Mioceno Medio en Patagonia Central (47¡ãS): petrog¨¦nesis e implicaciones en la din¨¢mica de placas
%A Felipe Espinoza
%A Diego Morata
%A Mireille Polv¨¦
%A Yves Lagabrielle
%J Andean Geology
%D 2010
%I Servicio Nacional de Geolog¨ªa y Miner¨ªa (SERNAGEOMIN)
%X We present a chronological (K-Ar), petrologic and geochemical study (major and trace elements, Sr-Nd isotopes) of Middle Miocene (ca. 16-14 Ma) calc-alkaline rocks (basalts to andesites) extruded in the present-day back-arc region of Central Patagonia (Zeballos Volcanic Sequence (ZVS), 47¡ãS). This magmatism started shortly after mafic plutonism ceased in the are region (ca. 16 Ma, 200 km west), and ended ca. 2 My before the onset of volumi-nous slab tear-related back-arc alkaline basaltic magmatism (ca. 12 to Pliocene). The studied calc-alkaline rocks have a typical subduction-related signature (high LILE/HFSE ratios, depletion in Nb, Ta and Ti; Ba/La >20; Ta/Hf <1.5; (87Sr/86Sr)o=0.70366-0.70402, ¦ÅNd=+0,1¡À3,8). Major and trace elements contents are consistent with their evolution by closed system fractional crystallization of a presumed parental liquid similar in composition to the most basic rock of the suite. Moreover, a strong subducted sediment imprint is recognized (increasing Th/HFSE and decreasing Ce/Pb during differentiation). However, these rocks show striking similarities with volcanic complexes emplaced above areas where a gently dipping slab oceurs (high K contents; similar LREE/HREE, Nb/Zr, Ba/Nb; Th/Hf; Th/Ta, Ta/Hf<0.3), particularly the present-day Andean flat-slab region and the Neuqu¨¦n Basin during the Late Miocene. A comprehensive tectono-magmatic model is here presented to explain the generation and extrusion of these calc-alkaline magmas during the Middle Miocene. The development of a transient low-angle subduction and the resulting eastward migration of the volcanic front are then proposed. Mixing between stored remnants of calc-alkaline magmatism and later primitive alkaline melts is envisioned as the most likely process accounting for the transitional signature (Le., intermediate between calc-alkaline and alkaline, La/Nb >1; TiO2 <2 wt%) of some basalts extruded synchronously with genuine alkaline lavas in the Neogene Patagonian Plateau Lavas province. En este trabajo se presenta un estudio cronol¨®gico (K-Ar), petrol¨®gico y geoqu¨ªmico (elementos mayores y trazas, is¨®topos de Sr-Nd) de rocas calcoalcalinas (basaltos a andesitas) del Mioceno Medio (16-14 Ma) que ocurren en una posici¨®n de trasarco en Patagonia Central (47¡ãS; Secuencia Volc¨¢nica Zeballos, SVZ). Este magmatismo comenz¨® poco despu¨¦s de que el plutonismo m¨¢fico cesara en la region bajo el arco (ca. 16 Ma, 200 km al oeste), y termin¨® ca. 2 My antes del comienzo de un voluminoso evento magm¨¢tico bas¨¢ltico alcalino desarrollado en el trasarco, relacionado con ventanas ast
%K Trasarco de Patagonia Central
%K Magmatismo calcoalcalino
%K Subducci¨®n de bajo ¨¢ngulo
%K Mioceno
%K Central Patagonia back-arc
%K Calc-alkaline magmatism
%K Low-angle subduction
%K Miocene
%U http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0718-71062010000200003