Secular variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?

Abstract This study of Sr-Nd initial isotopic ratios plutons from the North Patagonian batholith (Argentina and Chile) revealed that a secular evolution spanning 180 m.y., Jurassic to Neogene, can be established in terms magma sources, which turn are correlated with changes tectonic regime. The provenance composition end-member components source magmas represented by (87Sr/86Sr 143Nd/144Nd) plutonic rocks. Our results support interpretation was determined incorporation varied crustal materials trench sediments via subduction erosion sediment into channel mélange. Subsequent melting subducted mélanges at mantle depths eventual reaction ultramafic proposed as main causes generation, favored during periods fast convergence high obliquity between involved plates. We propose parental diorite (= andesite) precursor arrived lower arc crust, where it underwent fractionation yield silicic melts (granodiorites granites) formed batholiths. could have been fractionated more mafic melt basaltic andesite composition, within complete bulk peridotite. proposal follows model predictions on formation mélange diapirs carry fertile hot regions suprasubduction wedge, batholiths originate. not only accounts for geochemical variations Andean batholiths, but also avoids fundamental paradox classical basalt model: absence cumulates crust continental general.