Fish tooth U-Pb dating reveals the late Miocene REY enrichment of the Clarion-Clipperton Fracture Zone

Abstract Deep-sea sediments enriched in rare earth elements and yttrium (REY) are promising mineral resources and are extensively developed in the Pacific Ocean. However, REY enrichment mechanisms of deep-sea sediments remain poorly constrained due to a lack of chronological constraints on associated geological events. We integrated bioapatite U-Pb geochronometry with geochemical data to elucidate the temporal evolution and genetic processes of REY-rich sediments located in the Clarion-Clipperton Fracture Zone (CCFZ) in the central North Pacific Ocean. Fish tooth specimens, separated from deep-sea sediments collected from core MG026, were subjected to in situ trace-element analysis and U-Pb dating on their enamel-protected dentin layers using laser ablation–inductively coupled plasma–mass spectrometry. The bioapatite samples exhibited higher enrichments in total REY (ΣREY) and uranium than bulk sediments, and a moderate positive correlation between ΣREY and uranium concentrations. These bioapatite samples yielded Tera-Wasserburg lower intercept ages ranging from 15.8 ± 1.2 Ma to 9.5 ± 1.4 Ma, robustly constraining the depositional age of the host sediments and revealing a pronounced REY enrichment episode from 12.0 Ma to 9.0 Ma. Our results demonstrate a mean sedimentation rate of ~0.48 m/m.y. for the REY-rich sediments in the CCFZ. Multivariate analysis of bulk geochemical data indicates that REY-enrichment in CCFZ sediments is controlled not only by slow deposition rate but also by REY-bearing mineral phases and depositional environment conditions (including redox conditions and biological productivity). The REY enrichment event (ca. 12.0–9.0 Ma) is characterized by a significant transition toward more oxygenated and higher productivity conditions, as documented by trace metal enrichment factors (EF) of MoEF, UEF, CuEF, and NiEF. This event coincided with the progressive closure of the Central American Seaway, which enhanced the advection of oxygen-enriched, nutrient-bearing bottom waters into the CCFZ, promoting extensive formation of Fe-Mn (oxyhydr)oxides and facilitating REY enrichment. Our study establishes a reliable geochronological framework for late Miocene REY enrichment and provides exploration strategies linking tectonic events to deep-sea REY mineralization in the CCFZ.