Mariana Trough basalts (MTB): trace element and SrNd isotopic evidence for mixing between MORB-like and Arc-like melts

Mariana Trough basalt (MTB) glasses from zones of of active seafloor volcanism have incompatible trace element compositions which are intermediate between normal MORB and basaltic rocks from the active northern Mariana Island Arc (MIAB). The chemical variation is observed in trace elemental abundances and ratios such as LIL/LIL and LIL/HFS. MTB glasses with high LIL/HFS and Ba/Sm ratios, and low K/Rb, K/Ba, and Sm/Nd ratios have more enriched Sr and Nd isotopic compositions.Comparison of the SrNd isotopic compositions of MTB and MIAB suggests that the source region within the mantle wedge is heterogeneous. The diverse trace element and isotopic compositions of MTB glasses both within and between dredge sites near 18°N imply small-scale source heterogeneity. Correlation between Sm/Nd and¹⁴³Nd/¹⁴⁴Nd of the MTB glasses is interpreted as due to recent binary mixing, rather than closed system evolution of a common homogeneous source. Mixing of melts at or near the source region between a mantle component with long-term LREE and LIL element depletion (MORB-like) and a relatively enriched component with lower integrated¹⁴³Nd/¹⁴⁴Nd (Arc-like) is suggested by trends of the MTB data on ratio-ratio, ratio-element and element-element plots.