Assimilation of the plutonic roots of the Andean arc controls variations in U-series disequilibria at Volcan Llaima, Chile

Article Article scientifique Article Assimilation of the plutonic roots of the Andean arc controls variations in U-series disequilibria at Volcan Llaima, Chile eng 2011 author Reubi Olivier 673232 author Bourdon B. author Dungan Michael 29150 author Koornneef J.M. author Selles Daniel 536900 author Langmuir C.H. author Aciego S. 37-47 10.1016/j.epsl.2010.12.018 0012-821X http://linkinghub.elsevier.com/retrieve/pii/S0012821X10007703 U-series disequilibria provide important constraints on the processes and time scales of melt production, differentiation, and transport in subduction settings. Such constraints, which are essential for understanding the chemical evolution of the continental crust, are conventionally based on the assumption that the U-series disequilibria measured in mafic lavas are produced during mantle metasomatism and melting, and that intracrustal differentiation and assimilation have limited impacts. Here we show that mantle-derived U-series disequilibria in mafic lavas erupted at Volcán Llaima, Chile are significantly diminished by assimilation of plutonic rocks forming Llaima's subvolcanic basement. This contamination process is extremely subtle in terms of “classical” indicators of crustal assimilation like Sr, Nd or Pb isotopes because it is a manifestation of assimilative recycling of the plutonic roots of the arc. This process results in variations in U-series disequilibria and incompatible trace element ratios that are significant compared to regional and global variability in arc magmas. Furthermore, it yields linear correlations between U-series excesses and incompatible trace element ratios that are generally interpreted as slab-fluid indicators and chronometers, or tracers of sediment recycling in subduction zone. Cannibalization of ancestral magmas by ascending melts warrants careful evaluation when considering the components and chemical fluxes in subduction zones. Linear arrays defined by activity ratios of U-series nuclides with different half-lives may be the most reliable indicators of assimilative recycling of ancestral intrusive magmas. U-series Assimilation Arc magmatism Basaltic andesite Dewey 550 42 Département des sciences de la Terre 154 false 667 Physical Volcanology and Geological Risk Earth and planetary science letters 303 1-2 00dbaa79-1865-450e-8ab2-143432df0d62 Article (Published version) Restricted Reubi et al., 2011 EPSL.pdf 949210 application/pdf restrictedAccess Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département des sciences de la Terre

Title	Published in	Access level	OA Policy	Year	Views	Downloads

Assimilation of the plutonic roots of the Andean arc controls variations in U-series disequilibria at Volcan Llaima, Chile	Earth and planetary science letters			2011	635	1

Archive ouverte UNIGE

Reubi, Olivier