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Decoding melt-rock reactions in the deep crust of a magmatic arc: Insights from La Higuera ultramafic-mafic complex, Famatinian arc, Argentina

Emanuel Giovanini1, Andrea Galli1, Olivier Bachmann1, Tomas Guerreiro2, Eber Cristofolini2

  • Affiliations: 1Department of Earth and Planetary Sciences, ETH Zürich, Zürich, Switzerland; 2Departamento de Geología, Universidad Nacional de Rio Cuarto, Rio Cuarto, Argentina

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 211

  • Programme No: 1.9.18

  • Theme 1 > Session 9

Abstract

Understanding and quantifying thermo-mechanical and thermo-chemical processes in the deep crust, especially during the early stages of magmatic evolution in trans-lithospheric magmatic systems, remains challenging. Ultramafic-mafic complexes in exposed deep crustal sections provide valuable opportunities to address these challenges. The Sierras Valle Fértil--La Huerta in the Famatinian Arc, northwestern Argentina, preserves an exceptional exposure of the deep levels of an Ordovician continental magmatic arc. This region features a continuous crustal section, from gabbronorite- and diorite-dominated lower crust in the west to tonalites and granodiorites in the mid-to-upper crust in the east, interlayered with hundreds of meter thick sequences of metapelites. Within the 10 km-thick mafic unit, at least 10 ultramafic-mafic complexes exhibit textural and chemical heterogeneities, offering insights into the emplacement mechanisms of mantle-derived magmas into the lower crust. We focus on La Higuera ultramafic-mafic complex, characterized by at least 3, up to 700 meters large, nearly concentric bodies with peridotite cores surrounded by olivine gabbronorite, amphibole gabbronorite and tonalites. Lithological transitions preserve extensive reaction zones that reveal evidence of melt-rock interactions, which follow two major geochemical and mineralogical trends: (1) a pervasive reactive melt trend associated with the formation and internal evolution of the ultramafic cores, and (2) a reaction trend between the ultramafic bodies and their more evolved mafic-to-intermediate hosts. These trends provide critical insights into magmatic processes governing the evolution and transfer of mantle-derived magmas into the lower and mid-crust, suggesting that reactive flow may be crucial in the early stages of magmatic evolution.