High-field-strength-element enriched arc rocks witness subducted mélange recycling in upwelling asthenosphere

Abstract

Arc rocks, as the most common product of plate subduction factory, are generally characterized by high field strength element (HFSE) depletions. However, HFSE-enriched arc rocks are also identified, and their origin is still controversial. We conduct combined radiogenic and stable isotope analyses on two ocean island basalt (OIB)-associated HFSE-enriched mafic intrusions in the Yunnan-Burma region. Median incompatible trace element compositions argue for a binary mixing between OIB-like asthenosphere dominated mantle source and a complex arc-like component. The high radiogenic Pb [(206Pb/204Pb)i = 17.99–18.85, (207Pb/204Pb)i = 15.53–15.71 and (208Pb/204Pb)i = 38.16–39.20] and heavy Mg (δ26Mg = −0.115‰ to 0.357‰) isotopes could only be inherited from subducted marine sediments. Altered oceanic crust (often abbreviated to AOC) is also involved in the source as evidenced by light Li isotopes (δ7Li = −2.54‰ to −1.31‰). Therefore, we argue that this arc-like component is inherited from subducted mélange (i.e., bulk marine sediment and AOC) recycling, rather than the more common melt and/or fluid metasomatism. In summary, the OIB associated HFSEs-enriched arc rocks are products of and witnessed the subducted mélange recycling and its interaction with the upwelling asthenosphere.