Study On The Formation Of Seamounts Distributed By Cobalt-rich Crust In The Central-west Pacific

This paper calculates the effective elastic thickness of the lithosphere (Te) with the elastic plate flexure and the position of the hotspot with the hot-spot-produced seamounts tracking methods based on the plate tectonic theory and hotspot-mantle plume theory in the central-west Pacific. And then we analyze the formation of seamounts distributed by cobalt-rich crust in central-west Pacific, especially the Magellan seamount trail (MST) and the Mid-Pacific mountains (MPM), according to these results and some information from geochemistry, oryctology and petrography. This region is much particular, which has the most complicated magnetic anomaly lineations, the densest seamounts, the most peculiar geological feature and the strongest tectonic activity. At the same time, there are many seamounts distributed by cobalt-rich crust in the region. As a whole, Te slowly drops from the west part to the east part in the region. Te of the MST is higher in the middle of the trail than that in the north and the south part. Te of the MPM is higher in the west part of the mountains than that in the east part. Furthermore, Te of these two typical areas is close to that of the present French Polynesia region. And the positions of the hotspots forming hot-spot-produced seamounts are situated on the present French Polynesian region. The formation of the MST is relative to several hotspots in the western part of the region while the MPM relate to some hotspots in the eastern part of the region. Thus, the MST and the MPM are intraplate seamounts which were produced by several hotspots. The large volcanism formed these seamounts during the Cretaceous time in the present French Polynesia. After then they slowly moved to the present position with the drifting of the Pacific plate. There were also vertical displacement for these seamounts and they changed to guyots. But the hotspots are actually different between the MST and the MPM. In addition, their tectonic activities which they suffered during the formation are not similar. These factors affected the distribution of the cobalt-rich crust in their seamount. The hot-spot-produced seamounts tracking methods present the position of the hotspots producing the seamounts and the seamount age is obtained by Te. According to these two results, we can know the seamounts originated from the same hotspots and the distribution of cobalt-rich crust in these seamounts. This can effectively help us to find the seamounts distributed by cobalt-rich crust in future.