Geology, petrology and geochronology of sierra Valle Fértil - La Huerta batholith: Implications for the construction of a middle-crust magmatic-arc section

TIBALDI, ALINA; ROMERO, RURIK; BARZOLA, MATÍAS; OTAMENDI, JUAN; LEISEN, MATHIEU; ARMAS, PAULA; CAMILLETTI, GIULIANO; CRISTOFOLINI, EBER; BARRA, FERNANDO

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2020 vol. 97

0895-9811

The Valle Fértil-La Huerta batholith is a differentially tilted, compositionally stacked, calc-alkaline plutonicsequence in the central Famatinian arc of Argentina. It consists of two major lithologic units: these are (1) anintermediate unit largely dominated by amphibole- and biotite-bearing tonalites but encompassing from gabbroto leucogranite; and (2) an overlying silicic unit that shows the same petrological diversity as the intermediateunit, but granodiorite and monzogranite are its prevailing lithologies. The silicic unit is separated into foursubunits using lithological changes at regional mapping scale. All the boundaries are gradational among lithologicunits and subunits. The internal fabric along the entire batholith is either magmatic or submagmatic andit was developed during the arc formation. The original magmatic foliation is north?south striking and steeplydipping.The magmatic foliation crosses over and transposes the gradational contacts among lithologic units.Petrological architecture, structural geology, geobarometric estimates and geochronology show that the entirebatholith is a comagmatic system exposing more than 13 km of a middle arc crust. Crystallization-fractionationmodels computed using whole rock and mineral chemistry account for the mineralogy of plutonic rocks andcoincide with the results of experimental petrology. Mass-balanced modeling predicts that the unexposed cumulateroots of the Famatinian arc should have been about 1.3 times larger than the intermediate and silicicplutonic batholith. However, the mass of calculated cumulate would diminish significantly if a portion of thehost metasedimentary material were consumed in constructing the batholith. The batholith grew progressingupward from the lowest levels and acquired a stratified compositional organization. The driving mechanism wascontinuous influxes of mantle-derived mafic magmas that made up the lower crust, caused crustal-level meltingand magma mixing, and formed intermediate ? silicic rocks at increasingly shallower depths.