Schlieren–block inclusion interactions as indicators of magma-chamber dynamics: The Chuquis pluton (NW Argentina)

Abstract

Previous studies of schlieren–inclusion interactions typically emphasize a single dominant mechanism—such as incomplete mixing during mafic replenishment, disaggregation and assimilation of host-rock fragments, or crystal sorting driven by magma flow and high-energy processes, likely slurry currents or crystal avalanching. Our integrated structural mapping, petrography, and mineral chemistry of the Early Carboniferous Chuquispluton (NW Argentina) reveal three distinct schlieren types: internal, contact-parallel, and block-marginal. Internal schlieren display folding and truncation, recording dynamic convection and instabilities within the crystalrich mush, whereas contact-parallel schlieren are undeformed and reflect marginal fluidization. In contrast, block-marginal schlieren are spatially associated with metapelitic xenoliths and contain peritectic garnet and cordierite; geothermometry indicates that these aluminous phases formed through incongruent melting of the host rocks at high temperatures (~730 ◦C).The formation of block-marginal schlieren documents a hybrid system in which xenolith assimilation acts as a catalyst for localized flow instabilities, modifies melt composition, and likely promotes block subsidence through reactive melt migration. These observations demonstrate that schlieren–inclusion pairs are not passive features but sensitive recorders of complex chamber dynamics. This combined perspective allows us to propose a simple conceptual framework integrating mixing, magma flow, and assimilation processes to illustrate how thesimultaneous operation of these mechanisms can generate diverse schlieren geometries and inclusion assemblages, providing a more comprehensive understanding of magmatic dynamics.