Upper crustal differentiation processes and their role in 238U-230Th disequilibria at the San Pedro-Linzor volcanic chain (Central Andes)
Date
Authors
RODRIGUEZ ARANEDA, INES MARIA
Godoy, Benigno E.
McGee, Lucy Emma
González-Maurel, Osvaldo
Rodríguez, Inés
Le Roux, Petrus J.
Morata, Diego
Menzies, Andrew H.
Godoy, Benigno E.
McGee, Lucy Emma
González-Maurel, Osvaldo
Rodríguez, Inés
Le Roux, Petrus J.
Morata, Diego
Menzies, Andrew H.
Authors
Date
Datos de publicación:
10.1016/j.jsames.2020.102672
Keywords
238u Excess - Amphibole Fractionation - San Pedro Linzor Volcanic Chain - Subduction Zone Magmatism - U-series Disequilibria - Differentiation - Disequilibrium - Lava - Magmatism - Stratovolcano - Thorium Isotope - Trace Element - Upper Crust - Andes - Antofagasta - Chile - Linzor - San Pedro Volcano
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Abstract
U-series data are combined with major and trace element constraints to construct a detailed view of the magmatic system feeding the San Pedro-Linzor volcanic chain, aiding the understanding of how stratovolcanoes in extremely thick arc crust evolve. Lavas from the Quaternary San Pedro-Linzor volcanic chain (Central Andes) have (238U/230Th) ranging from 1.015 to 1.072, with 238U excess even in the less evolved (~57 wt% SiO<inf>2</inf>) analyzed lavas. Contrary to well-established trends between fluid mobile elements and 238U excess, (238U/230Th)<inf>0</inf> shows no systematic correlation with ratios indicative of fluid-driven melting (e.g. Ba/Hf and K/La). Moreover, the inverse correlation between (238U/232Th) with the amount of slab-derived fluid and the oxidation state of the mantle below Central Andes, which decreases eastwards, suggests that the main control of the 238U excess is not associated with hydration of the mantle wedge. Changes in (238U/232Th) and (230Th/232Th)<inf>0</inf> are observed with variations in SiO<inf>2</inf> and CaO + Al<inf>2</inf>O<inf>3</inf> contents, and 87Sr/86Sr and Dy/Dy* ratios of the lavas. These changes correspond to increasing (238U/232Th) with decreasing Dy/Dy* and CaO + Al<inf>2</inf>O<inf>3</inf> ratios, which is attributed to changes in crystallization of mineralogical phases within magmatic chambers during differentiation. Also, 230Th in-growth is produced during stagnation within magmatic chambers located below the San Pedro-Linzor volcanic chain. Finally, a positive correlation between (230Th/232Th)<inf>0</inf> and 87Sr/86Sr indicates an important role of crustal contamination, and of new mafic inputs during evolution of the volcanic chain with time. Our observations suggest that better constraints of all magmatic processes are needed to fully understand the U-series disequilibria recognized for the different volcanic structures developed within subduction-related tectonic environments. © 2020 Elsevier B.V., All rights reserved.
Description
Keywords
238u Excess , Amphibole Fractionation , San Pedro Linzor Volcanic Chain , Subduction Zone Magmatism , U-series Disequilibria , Differentiation , Disequilibrium , Lava , Magmatism , Stratovolcano , Thorium Isotope , Trace Element , Upper Crust , Andes , Antofagasta , Chile , Linzor , San Pedro Volcano
Citation
10.1016/j.jsames.2020.102672