Assessing the Validity of Negative High Field Strength-Element Anomalies as a Proxy for Archaean Subduction: Evidence from the Ben Strome Complex, NW Scotland

摘要: The relative depletion of high field strength elements (HFSE), such as Nb, Ta and Ti, on normalised trace-element plots is a geochemical proxy routinely used to fingerprint magmatic processes linked Phanerozoic subduction. This has increasingly been applied ultramafic-mafic units in Archaean cratons, but these assemblages have commonly affected by high-grade metamorphism hydrothermal alteration/metasomatism, the likelihood element mobility examples. To assess validity HFSE anomalies reliable for subduction, we here investigate their origin ultramafic rocks from Ben Strome Complex, which 7 km2 complex Lewisian Gneiss Complex NW Scotland. Recently interpreted deformed layered intrusion, subject multiple phases metamorphism, including separate granulite- amphibolite-facies deformation events. Additional bulk-rock geochemistry, present detailed petrography, major- mineral chemistry 35 samples, 15 display negative anomalies. Our data indicate that magnitude are correlated with light rare earth-element (LREE) enrichment likely generated during interaction H2O CO2-rich fluids associated amphibolitisation, rather than primary (subduction-related) processes. Consequently, consider alone be an unreliable subduction terranes experienced comprehensive assessment petrography minimum requirement prior assigning geodynamic interpretations data.