Major Elements And Viscosity Statistical Characteristics Of Basalt On The Mid-atlantic Ridge And Their Implications For Hydrothermal Vents

Major-element concentrations were extracted from the geochemical data of 9,818 basalt/basalt glass samples collected from the Mid-Atlantic Ridge(MAR,78°N–53°S),and the viscosity of each sample was estimated.On the basis of the spatial distance from and topography coherence with 11 known hydrothermal vents,the basalt/basalt glass samples were classified into three categories: basalt near known vent(BNV)(focal objects of the research,29 samples),basalt around known vent(observed objects,155 samples),and basalt of the MAR(background basalt).The geochemical and viscosity characteristics of the three basalt categories were statistically analyzed.The following were noted:(1)The viscosities of BNV are more consistent(fall into a narrower range)than the background viscosities and are significantly different in value.(2)Only 31.1% of the background viscosities fall within the range of the BNV viscosity(46.8–68.5 Pa·s).It appears that basalts with medium viscosity(e.g.,46.8–68.5 Pa·s)favor the formation and development of hydrothermal vents.A potential mechanism is that medium viscosity magmas easily form stable channels that link the seabed to the deep earth.However,very fluid magmas will block the existing channels,whereas very viscous magmas will easily form a stable oceanic crust;both the mechanisms will inhibit the formation of vents.In this paper,the phenomenon that the medium viscosity basalt is suitable for the development of hydrothermal vent,is named as the medium viscosity rate of hydrothermal vents(MVRHV).