Growth history and formation environments of ferromanganese deposits on the Philippine Sea Plate, northwest Pacific Ocean
Article first published online: 23 AUG 2007
Volume 16, Issue 3, pages 420–430, September 2007
How to Cite
Usui, A., Graham, I. J., Ditchburn, R. G., Zondervan, A., Shibasaki, H. and Hishida, H. (2007), Growth history and formation environments of ferromanganese deposits on the Philippine Sea Plate, northwest Pacific Ocean. Island Arc, 16: 420–430. doi: 10.1111/j.1440-1738.2007.00592.x
- Issue published online: 23 AUG 2007
- Article first published online: 23 AUG 2007
- Received 14 January 2007; accepted for publication 21 June 2007.
- 10Be/9Be dating;
- ferromanganese crusts;
- growth rates;
- mineral resources;
- Philippine Sea Plate
Abstract Hydrogenetic ferromanganese crusts are widespread on the floor of the northwestern Pacific Ocean, south and east of the Japanese Islands, despite vigorous tectonic activity, such as subduction and back-arc spreading, since at least the Mid-Paleogene over the Philippine Sea Plate region and nearby. The crusts occur mainly at water depths shallower than 3000 m, but also at greater depths of up to 6000 m. Fine-scale 10Be/9Be dating was undertaken on several 5–10 cm thick hydrogenetic ferromanganese crusts sampled from different geological environments, including inactive submarine volcanoes, tectonic escarpments and abandoned rifts. The results indicate that the crusts have grown at relatively constant rates of 4–7 mm/my without any significant time breaks. These uniform and constant growth rates suggest that the basins have been exposed constantly to oxygenated bottom waters since their formation in the Middle Miocene (ca 15 Ma) or earlier. Local geological or oceanographic environmental changes might have slowed or increased some of the growth rates resulting in correlation of some internal structures. The Philippine Sea Plate region could have economic potential in areas of thick hydrogenetic ferromanganese crusts over a wide range of water depths.