Geochemical constraints on the origin of late Cenozoic basalts in the Mt. Changbai volcanic field, NE China: evidence for crustal recycling

We conducted a systematic geochemical study of the Mt. Changbai basalts (MCBs) in NE China to better constrain their mantle sources and petrogenesis. The MCBs display ocean island basalt-like trace element patterns (e.g., positive Nb-Ta anomalies) and variable MgO contents (3.2-10.0 wt.%), trace element ratios (e.g., Ba/Nb and Rb/Nb), and Sr-Nd-Pb-Hf isotopic ratios (Sr-87/Sr-86((i)) = 0.704497-0.705629; epsilon Nd-(i) = - 2.8 to +3.3; Pb-206/Pb-204((i)) = 16.9-18.1; epsilon Hf = -1.2 to +6.2), which indicate derivation from a heterogeneous mantle source. The least evolved samples (MgO > 7 wt.%), with moderate Fe/Mn and FC3MS (defined as FeOT/CaO - 3MgO/SiO2) values, require a hybrid pyroxenite-peridotite mantle source. The isotopic compositions indicate the mantle source is a mixture between depleted mid-ocean ridge basalt mantle and two enriched mantle components. Our geochemical and published geophysical data indicate that these two enriched components are recycled ancient sediments and Pacific oceanic crust, which were derived from the mantle transition zone. An upwelling wet plume from the mantle transition zone transported these two enriched components into the asthenospheric mantle. These enriched components were then transformed into pyroxenite and/or eclogite through melt-rock reaction or mechanical mixing with asthenospheric mantle peridotite. We further propose that partial melting of this heterogeneous asthenospheric mantle containing fusible pyroxenite and/or eclogite (i.e., the enriched components) and refractory peridotite produced the MCBs.