How fluid infiltrates dry crustal rocks during progressive eclogitization and shear zone formation: insights from H2O contents in nominally anhydrous minerals

Abstract Granulites from Holsnøy (Bergen Arcs, Norway) maintained a metastable state until fluid infiltration triggered the kinetically delayed eclogitization. Interconnected hydrous eclogite-facies shear zones are surrounded by unreacted granulites. Macroscopically, granulite–eclogite interface is sharp and there no significant compositional changes in bulk chemistry, indicating composition was quickly rock buffered. To better understand link between deformation, influx, fluid–rock interaction one cm-wide zone at incipient eclogitization studied here. Granulite eclogite consist of garnet, pyroxene, plagioclase. These nominally anhydrous minerals (NAMs) can incorporate H 2 O form OH groups. contents increase granulite to eclogite, as documented garnet ~ 10 50 µg/g O, pyroxene 310 granulitic plagioclase 140 O. Bowl-shape profiles characteristic for with lower grain cores higher rims, which suggest prograde water influx into NAMs. Omphacite displays content range 150 425 depending on amount phases surrounding grain. The first separates hydrous, more albite-rich isolated clinozoisite before being replaced new fine-grained like clinozoisite, kyanite quartz during ongoing infiltration. Results indicate twofold different mechanisms act simultaneously scales rates. Fast pervasive proton diffusion recorded NAMs that retain major element granulite-facies equilibration where hydrogen decorates pre-existing defects crystal lattice leads increase. Contemporaneously, slower boundary-assisted aqueous enables transfer results progressive formation minerals, e.g., phases. Both lead 450 2500 towards convert system rigid weak. incorporation groups reduces activation energy creep, promotes smaller sizes (phase separation plagioclase), synkinematic metamorphic mineral reactions. processes part transient weakening, enhance sensitivity deform.