Geology, petrology and geochronology of sierra Valle Fértil - La Huerta batholith: Implications for the construction of a middle-crust magmatic-arc section. (January 2020)

• Record Type: Journal Article
• Authors: Camilletti, Giuliano; Otamendi, Juan; Tibaldi, Alina; Cristofolini, Eber; Leisen, Mathieu; Romero, Rurik; Barra, Fernando; Armas, Paula; Barzola, Matías
• Is Part Of: Journal of South American earth sciences. Volume 97(2020)
• Publication Date: 2020-01
• Subjects: Ordovician -- Gondwana -- Famatinian arc -- Igneous petrology -- Magmatic system; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2019.102423
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: The Valle Fértil-La Huerta batholith is a differentially tilted, compositionally stacked, calc-alkaline plutonic sequence in the central Famatinian arc of Argentina. It consists of two major lithologic units: these are (1) an intermediate unit largely dominated by amphibole- and biotite-bearing tonalites but encompassing from gabbro to leucogranite; and (2) an overlying silicic unit that shows the same petrological diversity as the intermediate unit, but granodiorite and monzogranite are its prevailing lithologies. The silicic unit is separated into four subunits using lithological changes at regional mapping scale. All the boundaries are gradational among lithologic units and subunits. The internal fabric along the entire batholith is either magmatic or submagmatic and it was developed during the arc formation. The original magmatic foliation is north–south striking and steeply-dipping. The magmatic foliation crosses over and transposes the gradational contacts among lithologic units. Petrological architecture, structural geology, geobarometric estimates and geochronology show that the entire batholith is a comagmatic system exposing more than 13 km of a middle arc crust. Crystallization-fractionation models computed using whole rock and mineral chemistry account for the mineralogy of plutonic rocks and coincide with the results of experimental petrology. Mass-balanced modeling predicts that the unexposed cumulate roots of the Famatinian arc should have been about 1.3 times larger than the intermediate and silicic plutonic batholith. However, the mass of calculated cumulate would diminish significantly if a portion of the host metasedimentary material were consumed in constructing the batholith. The batholith grew progressing upward from the lowest levels and acquired a stratified compositional organization. The driving mechanism was continuous influxes of mantle-derived mafic magmas that made up the lower crust, caused crustal-level melting and magma mixing, and formed intermediate – silicic rocks at increasingly shallower depths. Highlights: The plutonic middle crust of the Famatinian arc was at least 13 km thick. The plutonic crust grew progressing upward and acquiring a stratified organization. Pre-arc metasedimentary sequences play a role in fertilizing the magmatic system. Modeling yields a 1.3:1 ratio of cumulates over derivatives to make the magmatic column. A few tens of kilometers of cogenetic cumulates are lost in the Famatinian arc.