Buried Cobalt-rich Ferromanganese Crusts from Weijia Guyot and their Implications for Pacific Plate Motion

Abstract

Weijia Guyot, located in the western Pacific Ocean, has become a research focus due to its abundant cobalt-rich ferromanganese (Fe-Mn) crusts. While most studies on Fe-Mn crusts on seamounts have focused on the exposed variety, less attention has been paid to potential buried crusts. This study presents a preliminary geochemical and chronological study of buried Fe-Mn crusts at Weijia Guyot. The findings suggest that these buried crusts began to form around 57.5 Ma and ceased growing at approximately 46.3 Ma. Following the formation of Weijia Guyot through volcanic eruption, it did not experience continuous and steady subsidence to its current depth. Instead, an exhumation process took place from deep to shallow depths between 46.3 and 11.6 Ma. This process brought the Fe-Mn crusts into shallow water environments, halting their growth. During this time, Weijia Guyot was located near the equatorial Pacific Ocean and was exposed to an extended period of phosphatization. This exposure led to a depletion of key metallogenic elements, such as Co, Ni and Cu, within the Fe-Mn crusts, while P₂O₅ and CaO levels increased significantly. Since the Middle Miocene, the crusts have been progressively buried by pelagic sediments.