Geochemistry of peridotites from the Yap Trench, Western Pacific: implications for subduction zone mantle evolution

ABSTRACT

This study examines the major and trace elements of peridotites from the Yap Trench in the western Pacific to investigate mantle evolution beneath a subduction zone. Major element results show that the peridotites are low in Al₂O₃ (0.31–0.65 wt.%) and CaO (0.04–0.07 wt.%) contents and high in Mg# (Mg/(Mg+Fe)) (0.91–0.92) and have spinels with Cr# (Cr/(Cr+Al)) higher than 0.6 (0.61–0.73). Trace element results show that the peridotites have extremely low heavy rare earth element (HREE) contents compared with abyssal peridotites but have U-shaped chondrite-normalized rare earth element (REE) patterns. The degree of mantle melting estimated based on the major elements, HREEs, and spinel Cr# range from 19% to 25%, indicating that the Yap Trench peridotites may be residues of melting associated with the presence of water in the mantle source. In addition to light rare earth element (LREE) enrichment, the peridotites are characterized by high contents of highly incompatible elements, positive U and Sr anomalies, negative Ti anomalies, and high Zr/Hf ratios. The correlations between these elements and both the degree of serpentinization and high field strength element (HFSE) contents suggest that fluid alteration alone cannot account for the enrichment of the peridotites and that at least the enrichment of LREEs was likely caused by melt–mantle interaction. Comparison between the peridotites and the depletion trend defined by the primitive mantle (PM) and the depleted mantle (DM) suggests that the Yap Trench mantle was modified by subduction-related melt characterized by high contents of incompatible elements, high Zr/Hf ratios, and low HFSE contents. Hydrous melting may have been enhanced by tectonic erosion of the subducting Caroline Plate with complex tectonic morphostructures at the earliest stages of subduction initiation.

KEYWORDS:

• Peridotite
• mantle melting
• Yap Trench
• geochemistry
• subduction zone

Acknowledgements

We are thankful to the crew and scientists involved in the first cruise of the Jiaolong submersible with experimental applications. We also thank Editor-in-Chief Robert J. Stern, Scott A. Whattam, and an anonymous reviewer for their insightful comments which greatly improved the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

SUPPLEMENTARY MATERIAL

Supplementary material can be accessed here.

Additional information

Funding

This work was supported by the National Basic Research Program (973 Program) of China (Grant No. 2015CB755905); the National Natural Science Foundation of China (Grant No. 41706041; 41506070); the Natural Science Foundation of Zhejiang province, China (Grant No. LQY18D060002); the Scientific Research Fund of the Second Institute of Oceanography, SOA (Grant No. JG1603; JG1803; JT1304) and the China Ocean Mineral R&D Association (COMRA) project (Grant No. DY135-N1-1-01; DY135-G2-1-01-03).