Distinguishing the garnet signatures in a global database of adakites
Yajie Gao, Hugh O’Neill, John Mavrogenes · Goldschmidt2022 abstracts · 2022
Some intermediate and more evolved magmas from convergent margin settings, termed adakites, have been proposed as slab melts from their trace-element geochemistry, primarily Sr-Y systematics. Adakites are characterized by high Sr and low Y. The low Y (and Yb) is commonly attributed to garnet control, hence the inference of melting at depth. Sr and Y are relatively well determined by XRF, which may explain why they were chosen at the time of the initial hypotheses for examining geochemical data for this signature [1] . Since then, advances in trace-element analysis have revolutionized geochemical databases, and garnet signatures may now be more certainly identified using complete Rare Earth Element (REE) patterns, which have become routinely measured to high precision. Interpretation of Sr-Y systematics is often ambiguous, and has not been helped by a tradition of plotting Sr/Y against Y, which introduces spurious correlation, obfuscating rather than illuminating relations. Simply plotting Sr against Y on a logarithmic scale shows the same information more clearly.