Are the long-lasting isotope trends in central Patagonia independent from slab dynamics and upper-plate architecture?

Shifts in isotopic and trace element composition in magmatic zircon are commonly related to internal forcing independent of plate parameters (e.g., crustal thickness, delamination), or external factors that are governed by parameters of the down-going plate, particularly the slab dip. U-Pb geochronology, trace elements and Hf-O isotope analyses on detrital zircon from central Patagonia (45 °S – 48 °S) were used in this study as fingerprint for monitoring slab dip variations and related processes (e.g., arc migration, slab rollback) as well as upper-plate stress regime evolution. According to literature, main geodynamic events include: (i) two shallow slab episodes during late Triassic and late Early Cretaceous – early Paleogene times, the latter characterized by significant contraction; (ii) two phases of slab rollback during Jurassic – Early Cretaceous and late Paleogene, associated to a steep slab configuration, extensional processes and crustal thinning; (iii) a slab window episode during the Paleogene; and (iv) a Miocene contractional phase following an increase of plate convergence rates. Although slab dynamics seems structurally related with upper-plate architecture, it appears to exert little to null control on the magmatic arc reservoirs. Indeed, our results, integrated with published data from a larger area (40 °S – 52 °S), show long-lasting trends ( > 70 Ma) in the isotopic and trace elements record, that are mostly independent of these events. We thus consider that other processes, eventually coeval, controlled the enrichment of magmas and may overtake the influence of slab dip and upper-plate architecture on the isotopic and trace elements signature. These other processes include subduction erosion, ridge subduction, subduction of a younger slab, potential slab tearing, and/or change in convergence rates that affects mantle flow.