The role of magma mixing and mafic recharge in the evolution of a back-arc quaternary caldera: The case of Payún Matrú, western Argentina

HERNANDO, I. R.; PETRINOVIC, I. A.; LLAMBÍAS, E. J.; D'ELIA, L.; GONZÁLEZ, P. D.; ARAGÓN, E.

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 p. 150 - 169

0377-0273

p { margin-bottom: 0.25cm; line-height: 120%; }The Quaternary Payún Matrú volcano is along-lived edifice that developed a summit caldera 8 km wide, withabundant pre- and post-caldera volcanic activity. It is the mainvolcano of the Payún Matrú Volcanic Field, which is located in theback-arc Payenia Basaltic Province, at mid-western Argentina. Thecomposition of Payún Matrú is mainly trachytic, with lesser amountsof trachyandesitic and basaltic trachyandesitic lavas. The PayúnMatrú Volcanic Field includes also the Payún Liso stratovolcano andmore than 200 monogenetic basaltic cones and associated lava flowsthat are located east and west of the caldera. The aim of this workis to show the Payún Matrú evolution based on the mineralogical andtextural characterization and to make inferences on the triggermechanism for the explosive eruption which lead to the calderaformation. Some intermediate lavas and trachytes include phenocrystswith contrasting textures and composition, such as inverse zoning inplagioclase and clinopyroxenes, sieved plagioclases with a morecalcic rim and calcic plagioclases with a more sodic rim, indicatingthat they could not have formed together and suggesting magma mixingprocesses. In addition, a few lavas show mafic enclaves or texturallydifferent groundmasses with fluidal contacts, indicating minglingbetween two magmas. These lavas are found in the pre-caldera stageand the early post-caldera stage of Payún Matrú.The trachytic pyroclastic deposits related to the caldera collapsedo not exhibit evidenceof hybridization, althoughtheypresent a minorproportion of dissolvedfeldspars and biotite replaced by anhydrous minerals, suggestingthat a restricted zone of the chamber wasreheated. This may beexplained by a mafic recharge event wherepart of the host trachytic magma was heated, butwithout acomplete homogenizationbetween the hostand recharging magmas. These features, in addition to theabundant basaltic volcanism east and west of the caldera, suggestthat the trigger mechanism for the explosive eruption was theinjection of basaltic magma into the trachytic chamber of PayúnMatrú.