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Andean-style subduction zones produce a high variety of magma compositions over time and space. The diversity of magmas in these settings can be driven by the flux from the subducting slab, the melting behaviour of the overlying mantle wedge and crustal differentiation but the dominant process remains debated.

The Rio Blanco-Los Bronces district,~ 30 km northeast of Santiago in Central Chile, provides an ideal field location to examine the temporal evolution of an arc segment over several Myr. The Miocene San Francisco Batholith (~ 30 x 20 km) is intruded by porphyry intrusions of Late Miocene to Early Pliocene age. These porphyries form the Rio Blanco-Los Bronces Copper porphyry deposit cluster, and together with the San Francisco Batholith provide a near continuous igneous rock record over> 13Myr (~ 17–4 Ma). Here, by combining wholerock geochemistry, isotopic tracing, LA-ICP-MS U-Pb zircon geochronology and petrological modelling we develop a temporally resolved geochemical data-set over the entire duration of batholith assembly and porphyry intrusion to examine the processes driving the changes in arc magma composition through time.