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Geochemistry and geochronology of intermediate volcanic rocks from the Compostela area, Nayarit, Mexico: Implications for petrogenesis and tectonic setting

journal contribution
posted on 12.07.2021, 10:30 by Vivian Ruiz‐Mendoza, Sanjeet K Verma, Darío Torres‐Sánchez, Tiffany L Barry, Juan A Moreno, José Ramón Torres‐Hernández
The Compostela area is located in the western Trans-Mexican Volcanic Belt, which consists of volcanic rocks that produced during the Pliocene to Recent volcanism. In this paper, we present petrography, whole-rock major- and trace-element concentrations, Ar–Ar ages, and Sr–Nd isotopic data of volcanic rocks from the Compostela area in the south of the city of Tepic, Nayarit, Mexico. These volcanic rocks are of intermediate composition and belong to the transitional series: basaltic trachyandesites [52.72–53.94 wt% SiO2; 0.69–2.53 wt% MgO] and subalkaline series: low-Si [55.11–60.94 wt% SiO2; 0.79–2.74 wt% MgO] and high-Si [61.60–62.71 wt% SiO2; 0.36–0.80 wt% MgO] andesites. The 40Ar/39Ar dating of two basaltic trachyandesites yields plateau ages of 1.05 ± 0.15 Ma and 1.07 ± 0.17 Ma and the andesites yielded a plateau age of 2.42 ± 0.36 Ma. These results indicate that the studied rocks were formed during the Pleistocene in two discrete episodes. The basaltic trachyandesites show enriched light rare earth elements patterns relative to high rare earth elements [(La/Yb)N = 5.81–8.07] with negligible Eu anomalies. The andesites display enriched large-ion lithophile elements (Ba, K) with anomalies of Nb (Th/Ce) and Ti in the three groups identified in the subalkaline series. The basaltic trachyandesites appear in a tight cluster of initial 87Sr/86Sr ratios (0.703519–0.703882) as compared to the basaltic andesite 87Sr/86Sr (0.704073) and positive ɛNd(t) values of +5.6 to +3.4, respectively, indicating that the basaltic trachyandesites were derived from intermediate magmas from a shallow mantle source. Geochemical modelling reveals that both basaltic trachyandesite and andesite rocks were derived by a process of crystal fractionation accompanied by assimilation of crustal rocks at the lower or middle level. Geochemical ratios and multidimensional discrimination diagrams, combined with the cross-section of the subduction zone indicates that basaltic trachyandesites were generated from a rift and/or Ocean Island Basalt-type source, whereas andesites were generated from a slab-derived source in a subduction environment.

Funding

Consejo Nacional de Ciencia y Tecnología. Grant Number: 270565

Newton Advanced Fellowship award - The Royal Society. Grant Number: NA160116

History

Author affiliation

School of Geography, Geology and Environment, University of Leicester

Version

AM (Accepted Manuscript)

Published in

Geological Journal

Publisher

Wiley

issn

0072-1050

eissn

1099-1034

Acceptance date

30/05/2021

Copyright date

2021

Available date

14/06/2022

Language

en