IGEBA   23946
INSTITUTO DE GEOCIENCIAS BASICAS, APLICADAS Y AMBIENTALES DE BUENOS AIRES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
CORONA CHICO VOLCANITES IN LAS LOMADAS AREA, SOMUN CURA MAGMATIC PROVINCE. NORTHERN EXTRANDEAN PATAGONIA. ARGENTINA
Autor/es:
MARÍA ELENA, CERREDO; PABLO D. CORDENONS; MARCELA B. REMESAL ; JUAN MANUEL ALBITE
Lugar:
Córdoba
Reunión:
Congreso; XIII Congreso de Mineralogía, Petrología Ígnea y Metamórfica, y Metalogenia; 2019
Institución organizadora:
Asociación Mineralógica Argentina y COMPETRO (Asociación Geológica Argentina)
Resumen:
Vulcanitas Corona Chico en el área Las Lomadas, Provincia Magmática deSomún Curá. Norte de la Patagonia Extrandina. Argentina. Esta contribuciónaporta al conocimiento de un sector de las Vulcanitas Corona Chico, dentro de laProvincia Magmática de Somún Curá en el norte de la Patagonia Extrandina. El sector estudiado se extiende al Norte del Complejo Volcánico Alta Sierra de Somún Curá, y comprende una variedad morfológica de edificios volcánicos en términos basálticos: conos de salpicadura, anillos de tobas y flujos lávicos relacionados a pequeños volcanes en escudo (tipo scutulum), enumerados en secuencia temporal relativa. La petrografía (caracterizadas por rocas porfíricas con fenocristales esencialmente de clinopiroxeno y olivina), así como la composición química de roca total indican un progresivo aumento de la alcalinidad desde los componentes más tempranos de carácter transicional hasta los estadios finales con términos basaníticos. La simulación de la fuente mantélica modelada de las rocas de Las Lomadas indica manto astenosférico en facies de granate ? espinelo con bajos porcentajes de fusión parcial (< 7-8%). Dentro del conjunto estudiado, la secuencia de los conos de salpicadura muestra una afinidad geoquímica con los términos basálticos del Complejo de Alta Sierra de Somún Curá.The youngest post-plateau volcanic assemblages within the the Somún CuráMagmatic Province is represented by the basalt to trachyte Alta Sierra de Somún Curá Magmatic Complex (ASSCVC) which is enveloped by the mostly basaltic CoronaChico Vulcanites (CChV). Several whole rock K/Ar radiometric and one zircon SHRIMP determinations yielded ages bracketed between 8 and 12 Ma for the trachytes of the ASSCVC (Linares 1979; Franchi et al., 2001; Remesal et al., 2018), whereas an 87Rb/86Sr errorchrone including samples of ASSCVC and CChV indicates an approximated Langhian/Serravalian age for both units (14 ± 8 Ma, MSWD=1; Remesal et al., 2017). Therefore, a roughly synchronous activity is inferred for these post-plateauassociations.Las Lomadas (LLs) area, a restricted sector of CChV located to the north ofASSCVC is the subject of this contribution. Several volcanic landforms aredistinguished within LLs area; all of them share a common morphology of low aspect ratio and shallow relief. The oldest and most outstanding volcanic construction corresponds to a central shallow elliptical crater surrounded by a tuff ring: Las Lomadas (LLtr) of dominant N-S strike, composed of pyroclastic deposits (basal coarse ash to upper agglomerate). Numerous spatter cones flank LLtr both to the west as to the east (i.e. El Mojón, Chajaijó at the West and El Durazno spatter cones, among others).Rocks are transitional trachybasalts, porphyric with clinopyroxene, plagioclase andorthopyroxene crystals displaying variable degrees of disequilibrium. The youngest volcanic buildings of scutulum type surround from the south the previous landforms: Las Cortaderas emission center is associated with long lava lobes which flowed northwards enveloping the above mentioned volcanic morphologies. Las Cortaderas flows are composed of porphyric, trachybasalts rich in clinopyroxene and olivine phenocrysts. This facies, is in turn surrounded by another northward directed flows: the Laguna Valerio with several emission centers located further south. Laguna Valerio lava flows are of basanite composition, porphyric with phenocrysts of clinopyroxene andolivine. Petrographic characteristics as well as whole rock chemical composition suggest a time progressive increase in alkalis content and a shift from early transitional terms to basanitic rocks in the latest stages. A simulation of the source yielded for Las Lomadas rocks an astenospheric source in the garnet-spinel facies, with associated low partial melting percentages (< 7-8%). Within the studied rock set, the spatter cones sequence displays geochemical affinities with the basaltic component of ASSCVC