Os Isotope Chronology Of The Co-rich Polymetallic Crust From Western And Central Pacific And Its Paleoceanographic Significance

The seamounts in west and central Pacific are the most enriched regions ofCo-rich crust. In the paper,8samples that come from7seamounts in the region wereanalyzed. We made the following understanding:1.The crust of the seamounts mainly are hydrothermal deposits. Individual crustsare mixed deposits. Mn and Fe in the Co-rich crusts is the most important ore-formingelements,so they are anti-correlated. But Mn and Fe in earlier layers of MP3D22ispositively correlated, and the latter （after45Ma） was transformed intoanti-correlation. According to the time of formation, the Mn and Fe of the layersformed before the Cenozoic may have the same source-endogenous. After Eocene, Fepossible mainly was from terrestrial input, Mn is still the endogenous input.2.Accurate Os isotope chronology indicated,187Os/188Os distributioncharacteristics of the study area ferromanganese crust samples basically obey styleevolution of the ocean. According to that, samples can be constructed thegrowth-interrrupted chronology frame. The west side one of two that got fromMagellan seamount, MS-1, began growing from~56Ma, continuous growth~3Ma,and then stop growing. When the crust began to continue to grow is the lateEocene(~36Ma). The interruption does not appear until Quaternary. While MP3D22likely to grow in the late Cretaceous(~72Ma) and stopped growing in the LateCretaceous-Ealy Eocene(~63Ma), continue to growing~7Ma. And then thedeposition continued intermittently~25Ma. The sedimentary record began to appear,continued to growing~10Ma, and then stopped growing until now. Both growth-discontinuous mode with various patterns are known there are some differences,reflecting the distinctive regional characteristics, the reason will be in-depth analysis.3.Os isotope of the Cobalt-rich crust sample,MS-1,change obviously iscontrolled by terrigenous of input to the Pacific Ocean. Fluctuations187Os/188Oswith the growth layer has not only chronological significance, but also reflects the profound changes in the marine environment. The187Os/188Os continue to rise sincethe E/O reflect the impact of the Asian continent to the Pacific deposition enhancingsubstances, which may be closely related to completely shut down East Road Tethyschange accelerated uplift of the North Pacific circulation patterns and the presence ofthe Tibetan Plateau.4.Co-rich crust, MS-1, paleo-oceanography research shows that, at~56Ma,terrestrial input less and undersea volcanic activity frequent lead to slower growth rateand higher grade. At~25Ma，Weakened Antarctic bottom water is weakenedtransmission speed carried oxygen and minerals. At the time, the crust was slowestgrowth rate. at~15Ma,with the strengthening of ocean circulation and Antarcticbottom water, increase of terrigenous input, the crust growth rate became faster,and the grade became lower.