Geochemistry and metallogenic evolution of co-rich crust on Weijia Guyot in the Western Pacific Ocean

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Through research on the structure, geochemistry and metallogenic evolution of the gravel-like crust with complete growth layers on Weijia Guyot in the western Pacific Ocean, the crust chronology framework has been established, the planar distribution and vertical change characteristics of the elements in cross-section of crust are further understood, and the completely temporal-spatial metallogenic evolution process of crust was revealed. • The gravel-like crust have formed at 74.5 Ma and undergone two growth hiatuses. During the period from its initial formation to 41 Ma, the crust have subjected to phosphatization. • Geochemistry and metallogenic evolution of the crust are influenced by changes in its transport trajectory as well as paleo-oceanographical environment. Previous researchers have conducted in-depth studies on the distribution, geochemical characteristics, formation age, and resource potential of cobalt-rich crusts on Pacific seamounts. However, in the past, the majority of research samples were platy crust samples with fewer growth layers, and there were relatively few reports on the gravel-like crust which appearing together with platy crust. At present, people know very little about the internal structure, formation age, and mineralization evolution process of gravel-like crusts on seamounts, and researching on the differences between platy crusts and gravel-like crusts is not deep enough, which seriously hinders our overall understanding of the mineralization laws of cobalt-rich crusts on seamounts. Through research on the structure, geochemistry and metallogenic evolution of the gravel-like crust with complete growth layers on Weijia Guyot in the western Pacific Ocean, the crust chronology framework has been established and the vertical change characteristics of the elements in the cross-section of the crust have been further understood, and the complete temporal-spatial metallogenic evolution process of the crust has been revealed. Research indicates that gravel-like crust is mainly hydrogenic. The gravel-like crust can be divided into three main growth layers. Comparison to platy crusts, gravel-like crusts demonstrate heightened sensitivity to fluctuations in marine environmental conditions during their formation, resulting in the development of multi-layered structures. Due to the different shapes of the two type crusts, there are also differences in their formation processes. Compared to platy crusts, gravel-like crusts have relatively fewer growth hiatuses caused by phosphatization. The crust first formed at 74.5 Ma, followed by two periods of growth hiatus between 73.6 – 69.6 Ma and 66 – 64.7 Ma respectively. The development of two interfaces of angular unconformity within the crust was the result of the combined effects of phosphatization and regional volcanic activity. During the Late Cretaceous to the mid to late Eocene, the crust experienced continuous phosphatization. The intensity of phosphatization varies from high to low. Following its initial formation in the South Pacific Ocean, the crust drifted northwestward with the Pacific Plate, crossed the equator into the Northern Hemisphere, and ultimately arrived at its current position. The formation age, layered structure, growth hiatuses, and variations in geochemical characteristics of the crust are all influenced by changes in its transport trajectory as well as paleo-oceanographical environment.

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