Study On Mineralogy Of Suspended Particulate Matter In The Eastern Pacific Rise Area-Mineral Composition And Its Connection With Hydrothermal Activities

Based on the77samples of suspended matter at5stations in the EasternPacific Rise hydrothermal active area during DY-22Cruise in2011, using SEM andEDS methods, we studied morphology, composition and distribution of the suspendedparticulate minerals, analyzed the sedimentation and preservation mechanisms oftypical oceanic suspended particulates, and then explored the role of suspendedparticles’ mineral composition in indicating seafloor hydrothermal activities.The concentration of total suspended matter in the water columns in the EPRarea ranges from0.01to0.58mg/L, is quite low and varies greatly between differentstations and different water depths in the same station. Its vertical profile shows thatthe concentration of total suspended matter is reducing from the surface tointermediate layer, and increases as it reached the bottom layer.Total34categories of mineral were discerned, including terrigenous debris,biogenic clast, authigenic minerals and hydrothermal minerals. Among which, Bornite（FeCu₂S₃） and hydrothermal nontronite were first discovered in the suspended matterin the area.The distribution of suspended mineral particles varies in both vertical andhorizontal direction. Most of the biogenic clasts appear in the surface water at allstations, while hydrothermal minerals and terrigenous debris are dominance particlesat the Southern stations. In contrast, the dominate minerals at the Northern Stationsare authigenic minerals, hydrothermal minerals and terrigenous debris. In addition,Pyrite, sphalerite and barite are found at all stations.Sulfide quantity anomalies and assemblages could be used as indicators topresence of seafloor hydrothermal activity and the nature of the hydrothermal fluids.The pyrite-sphalerite-chalcopyrite assemblage at the3southern stations is a typical sulfide combination influenced from the high-temperature hydrothermal vents. Thesulfide quantity at the stations reaches maximum around1000m-2500m, showsconsistency with buoyant hydrothermal plume diffusion height, which confirms itsorigin. The Fe-rich, Al-poor hydrothermal nontronite is the characteristic mineral ofnorthern stations, indicating the appearance of a low-temperature vent system nearby.Hydrothermal activities play an important role in the distribution and assemblageof the mineral in the suspended particle matter. Sulfide assemblages and itsmorphology are directly linked with nearby hydrothermal plumes. Hydrothermalauthigenic minerals are found in whole water column at some station. Generally,sulfide and hydrothermal nontronite quantity anomalies are very useful in identifyingand locating hydrothermal plumes site, reconstructing vent temperature and evolutionprocesses.