Secular compositional changes in granitoids and felsic volcanics: the tectonic setting control

Condie, Kent C.; Puetz, Stephen J.; Spencer, Christopher J.; Roberts, Nick M.W.

Secular compositional changes in granitoids and felsic volcanics: the tectonic setting control

Condie, Kent C.; Puetz, Stephen J.; Spencer, Christopher J.; Roberts, Nick M.W.. 2025 Secular compositional changes in granitoids and felsic volcanics: the tectonic setting control. Chemical Geology, 692, 122950. 10.1016/j.chemgeo.2025.122950

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Official URL: https://doi.org/10.1016/j.chemgeo.2025.122950

Abstract/Summary

This study presents results for secular compositional change of 12 geochemical variables in granitoids and felsic volcanics in the last 3 Gyr grouped into two tectonic settings, orogenic and within-plate. Time series are constructed from median values of geochemical data compiled in 250-Myr bins. Within-plate granitoid and felsic volcanic time series (high SiO2, (Na2O + K2O)/CaO, Fe Index, Y + Nb, Ga/Al; low Sr/Y, Eu/Eu*, La/Nb) are displaced from the orogenic series, consistent with shallow depths of magma generation and an overall lower degree of partial melting or/and more fractional crystallization for within-plate magmas through time. Orogenic granitoid and felsic volcanic geochemical time series for La/Yb, Th/Yb, La/Nb, Y + Nb, and Yb are similar and show a transition at the end of the from dominantly restitic garnet-amphibole-rutile to plagioclase control, the latter reflecting shallower depths of magma generation. Relatively high Eu/Eu* in Archean granitoids and felsic volcanics (and high Sr/Y in Archean granitoids) may imply that plagioclase accumulation is more effective before 2.5 Ga than afterwards, consistent with large volumes of TTG (tonalite-trondhjemite-granodiorite) in the Archean. Low Sr/Y and Eu/Eu* of granitoids and felsic volcanics in the last 1750 Myr likely require significant plagioclase removal by fractional crystallization or/and plagioclase presence in the melting restite. Fractionation of Th from La beginning at 1500 Ma may reflect a change to an apatite-dominated restite, perhaps in response to greater amounts of subducted P-rich sediments entering the sources of felsic magma. Increases in Yb, Y + Nb, and Fe Index and decreases in La/Nb, Eu/Eu*, Sr/Y, La/Yb and Th/Yb in orogenic settings during assembly of Columbia (1800–1500 Ma) reflect shallowing of magma sources, perhaps in hot back-arc basins. Our findings show the importance of tectonic setting on the compositional evolution of felsic magmas, highlighting the need to consider the differences between orogenic and within-plate processes when reconstructing the compositional history of the continental crust into deep time.

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1016/j.chemgeo.2025.122950

ISSN:

00092541

Date made live:

24 Sep 2025 13:04 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/540277