Geochemistry of hydrothermal Mn-oxide deposits from the S.W. Pacific island arc

Geochemistry of marine sediments from the Lau Basin, Havre Trough, and Tonga—Kermadec Ridge

“…These include a volcaniclastic component which decreases rapidly westwards from the TongaKermadec Ridge: carbonate ooze which is dominant west of 177°W; a reddish-brown semiopaque Fe-Mn oxide component which exceeds 10% only in the central Lau Basin; and terrigenous sediment which is dominant immediately north of New Zealand. In addition, hydrothermal manganese crusts were recovered at three sites along the western fianks ofthe Tonga-Kermadec Ridge; these have been reported on elsewhere (Cronan et al 1982;Moorby et al 1984).…”

“…Fe-oxides Significant amounts of semiopaque Fe-Mn oxides were identified only in the central Lau Basin sediments (Cronan et al 1984) in what is otherwise a predominantly biogenie carbonate sediment regime with an increasing volcaniclastic component towards the Tonga Ridge. Semiopaque Fe-Mn oxides occur as amorphous coatings on particles, rather than as discrete crystalline oxides, and rarely exceed 15% of the total sediment.…”

“…Sediments were recovered from more than 180 of the 191 sampling stations occupied. A schematic map showing the locations of these stations has been given by Cronan et al (1984).…”

“…A preliminary report on the results of these two cruises has been presented by Cronan et al (1984) and a more detailed study of the sediment distribution, mineralogy, and grain size of the sediments, as weil as a regional description, has been prepared by Moorby et al (1986). In this paper we present geochemical data which illustrate the major regional compositional trends for the sediments.…”

Hydrothermal Manganese Minerals in Leg 126 Cores

“…The growth of these two types of deposits requires very slow or no sedimentation in the deep-sea basin or on old seamounts over a long geological time interval (on the order of millions of years). In contrast, recent hydrothermal manganese deposits have been observed only around the volcanically active areas, such as mid-oceanic ridges, backarc spreading centers, and submarine volcanos (Corliss et al, 1978;Lonsdale et al, 1980;Moorby et al, 1984;Usui et al, 1989).…”