48-2 Plio-Holocene magmatic evolution during a steepening subduction regime in the Southern Central Andes

Session: Tectónica de las Américas: Sesión en español

Presenting Author:

Sofía Iannelli

Authors:

Iannelli, Sofía Belén¹, Greco, Carina², Fernández Paz, Lucía³, Rizzo, Martina⁴, Litvak, Vanesa Dafne⁵, Pallares, Carlos⁶, Folguera, Andrés⁷

(1) National Scientific and Technical Research Council (CONICET), Instituto de Estudios Andinos ‘Don Pablo Groeber’ (UBA-CONICET), Ciudad Autónoma de Buenos Aires, Argentina; University of Buenos Aires (UBA), Department of Geological Sciences, Ciudad Autónoma de Buenos Aires, Argentina, (2) Dirección de Geología Regional, Instituto de Geología y Recursos Minerales, Servicio Geológico Minero Argentino (SEGEMAR), Ciudad Autónoma de Buenos Aires, Argentina, (3) National Scientific and Technical Research Council, University of Buenos Aires, Instituto de Estudios Andinos ‘Don Pablo Groeber’, Ciudad Autónoma de Buenos Aires, Argentina; University of Buenos Aires, Department of Geological Sciences, Ciudad Autónoma de Buenos Aires, Argentina, (4) National Scientific and Technical Research Council, University of Buenos Aires, Instituto de Estudios Andinos ‘Don Pablo Groeber’, CONICET, Ciudad Autónoma de Buenos Aires, Argentina; University of Buenos Aires, Department of Geological Sciences, Ciudad Autónoma de Buenos Aires, Argentina, (5) National Scientific and Technical Research Council, University of Buenos Aires, Instituto de Estudios Andinos ‘Don Pablo Groeber’, Ciudad Autónoma de Buenos Aires, Argentina; University of Buenos Aires, Department of Geological Sciences, Ciudad Autónoma de Buenos Aires, Argentina, (6) CNRS, Université Paris-Saclay, Orsay, France, (7) National Scientific and Technical Research Council, University of Buenos Aires, Instituto de Estudios Andinos ‘Don Pablo Groeber’, Ciudad Autónoma de Buenos Aires, Argentina; University of Buenos Aires, Department of Geological Sciences, Ciudad Autónoma de Buenos Aires, Argentina,

Abstract:

From the late Pliocene to Holocene times, magmatism in the Southern Central Andes (34-38.5°S) underwent significant geochemical changes, displaying systematic variations through time and location. These geochemical trends have been primarily attributed to the steepening of the Nazca plate after its shallow subduction configuration in the latest Miocene. As a result, Plio-Holocene magmatism developed along three N-S magmatic belts, located within the present-day arc front, the rear-arc, and the back-arc areas. This study focuses on understanding the development of the rear-arc belt, particularly in its northern and southern segments. Rear-arc magmatic sequences are compared with coeval back-arc magmatism through geochemical (major and trace elements, and Sr-Nd-Pb isotopes) and geochronological (Ar-Ar, K-Ar, U-Pb) data to evaluate the evolution of magmatism since the beginning of the Nazca plate steepening in the latest Pliocene. This work aims to elucidate the influence of major tectonic changes on the spatial variations in the composition of Andean arc-related magmatism. The back-arc volcanic sequences show a decrease in arc-like geochemical features and an increase in the concentration of incompatible elements from the northern to the southern back-arc units. This change has been attributed to variations in the mantle source, as southern magmatism is associated with an EM-1 OIB type source, while northern volcanism is linked to an N-MORB mantle source. However, other processes, such as changes in the thermal structure of the mantle wedge, along-strike variations in crustal thickness, and forearc subduction erosion, are essential for explaining other geochemical features. On the other hand, the geochemistry of the Plio-Holocene rear-arc magmatism slightly reflects the geochemical patterns of the back-arc magmatism. The northern rear-arc units display arc-like features, while the southern rear-arc exhibits an incipient intraplate-like signature. Thus, regarding the varying distances to the trench between back-arc and rear-arc units, first-order controls, such as heterogeneities in the ambient mantle composition and the thermal structure of the mantle wedge, have influenced the magmatism of the Southern Central Andes.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4706

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