Volcanic stratigraphy and evidence of magma mixing in the Quaternary Payun Matru volcano, andean backarc in western Argentina

Abstract

AbStRAct. The Payún Matrú Volcanic Field is located in the Payenia Basaltic Province of the recent back-arc of western Argentina (35°S-38°S). This province is younger than 5 Ma, and most of its volcanic activity took place since 2 Ma. The Payún Matrú Volcanic Field contains two composite volcanoes, Payún Matrú and Payún Liso, and two basaltic fields in an E-W oriented zone, located east and west of the Payún Matrú volcano. Payún Matrú is the largest volcano of this volcanic field, and consists of a shield-shaped edifice with a circular summit caldera of 8 km in diameter. The composition of both composite volcanoes is alkaline and predominantly trachytic, having also minor intermediate lavas.The basaltic fields consist of basalts and trachybasalts, with clinopyroxene and abundant olivine as phenocrysts and also in the groundmass. Textures indicating mixing and mingling processes, such as dusty plagioclases along with clear ones, biotite replaced by anhydrous minerals and two groundmasses with a fluid-fluid relationship, are common in the early pre-caldera stage of Payún Matrú and some post-caldera lavas. The latest post-caldera lavas are trachytic, with clean sanidine phenocrysts without disequilibrium textures. A remarkable characteristic of the Payún Matrú Volcanic Field is the fact that the Payún Matrú caldera is surrounded by basaltic fields at its base, while no basalts were erupted in the caldera region. We propose that the absence of basaltic lavas in the Payún Matrú volcano is due to the presence of a magmatic chamber below it, and that the mafic magmas rising from deeper levels were unable to erupt without interaction with more evolved melts. Intermediate hybrid magmas produced as a consequence of magma mixing and mingling between basaltic and trachytic magmas, are present in the early and mid-history of Payún Matrú volcano. We present here new information about the Quaternary Payún Matrú Volcanic Field derived from field work, petrography, and major element geochemistry and 87 Sr/ 86 Sr isotopic ratios. For the first time a detailed map of the Payún Matrú Volcanic Field and its volcanic stratigraphy, primarily based on field observations, are presented. RESuMEn. Estratigrafía volcánica y evidencia de mezcla de magmas en el volcán Payún Matrú del cuaternario, en el retroarco andino de Argentina occidental. El Campo Volcánico Payún Matrú está localizado en la Provincia Basáltica Payenia, en el retroarco reciente al oeste de Argentina (35°S-38°S). Esta provincia es más joven que 5 Ma, y la mayor parte de su actividad volcánica tuvo lugar desde hace 2 Ma. El Campo Volcánico Payún Matrú contiene dos volcanes compuestos, el Payún Matrú y el Payún Liso, así como dos campos basálticos en una franja E-W, ubicados al este y oeste del Payún Matrú. El Payún Matrú es el volcán más grande de este campo volcánico, y consiste en un edificio en forma de escudo con una caldera circular en su cúspide de 8 km de diámetro. La composición de ambos volcanes compuestos es alcalina y predominantemente traquítica, con menor...

Geochronological, morphometric and geochemical constraints on the Pampas Onduladas long basaltic flow (Payún Matrú Volcanic Field, Mendoza, Argentina)

“…The issue of crustal contamination in the PMVF is not clear as there are no crustal Sr-isotopic values for this area (Espanon et al, 2014). The Sr isotope values for the Pampas Onduladas flow are in agreement with those previously presented for the PMVF (Pasquarè et al, 2008;Bertotto et al, 2009;Hernando et al, 2012;Jacques et al, 2013;Søager et al, 2013;Espanon et al, 2014).…”

“…In addition, a small Eu peak is noticeable in Figure 7e (Figure 7f). Sr isotope values are low, ranging from 0.703747 (Espanon et al, 2014) to 0.704151 (Pasquarè et al, 2008), which are comparable with 87 Sr/ 86 Sr values reported by Hernando et al (2012) for pre-caldera basalts (0.703766 to 0.703906).…”

“…The eastern end of La Carbonilla fracture has been one of the major feeding systems for basaltic flows in this sector and has been active since probably the early Quaternary (Pasquarè et al, 2008). The oldest basalts erupted from La Cabonilla fracture pre-date the formation of the Payún Matrú caldera (Llambías et al, 2010;Hernando et al, 2012) which were then partially covered by the ignimbrite during the caldera formation stage and later partly overlain by younger basaltic flows. Despite the difficulty in determining the eruption point for the extensive Pampas Onduladas flow, it has been assigned to La Carbonilla fracture (Núñez, 1976;Pasquarè et al, 2005;2008).…”

Cosmogenic 3He and 21Ne surface exposure dating of young basalts from Southern Mendoza, Argentina

“…Furthermore, due to the low precipitation rate, it is unlikely that the bombs were transported from their airfall impact sites. In addition, Hernando et al (2012) indicated that the bombs are in-situ as they preserve their aerodynamic or irregular shape and have preserved a small crater under each bomb, generated by their impact. However, considering the 8 cm maximum thickness of the bombs, the production rate for a potentially rotated bomb would be approximately 7% lower than at the original upper surface of the bomb.…”

Análisis comparativo de los controles tectónicos y eustáticos sobre la estratigrafía de post-rift (Jurásico Inferior-Cretácico Inferior) en el sector central de la Cuenca Neuquina, Argentina

“…El Campo Volcánico Payún Matrú contiene dos volcanes compuestos, el Payún Matrú y el Payún Liso, así como dos campos basálticos ubicados al este y oeste del Payún Matrú. Este último es el volcán más grande de este campo volcánico, y consiste en un edificio con forma de escudo con una caldera circular en su cúspide de 8 kilómetros de diámetro (Hernando et al, 2012) y una altura de 3680 msnm.…”