Petrological And Geochemical Features Of Basalt Glass From The East Pacific Rise And Their Significance

In order to understand composition and significance of basalt glass and whole basalt rocks,basalts collected by the"Dayang 1"Voyage 21 and Voyage 22 from the East Pacific Rise region were analyzed.The studied area was divided into three areas:Area A,B and C.Pyroxene phenocrysts in the studied samples were not observed.Most of porphyroblast is plagioclase,and the rest is peridot.Sample EPR2 from Area A contained much abundant phenocrysts than other samples.Matrix is dominated by aphanitic,with abundant labradorite microcrystalline needles.Devitrification occured at matrix edge in most of samples while palagonite was seen at matrix edge in Sample EPR12.Based on features of major elements,all studied samples falled into class of sub-alkaline tholeiitic hypokalemia.Mg#in basalt glass samples is slightly lower than it in whole basalt rock,while value of Al₂O₃ is vice versa.All samples of basalt glass and whole rock in Areas B and C showed a positive correlation between Al₂O₃ and MgO.No significant difference in trace element feature was observed between basalt glass and whole rock samples studied.and all of them belong to E-MORB.Studied basalt samples belong to T-MORB or E-MORB,however,glass samples were more closed to N-MORB more than whole rock.Studied samples were featured with high values of?REE?glass:59.30ppm,whole rock:60.50ppm;in average?,LREE/HREE?>1.50?,and LREE enrichment.These records might be resulted by presence or influence from enriched components of mantle source underlying the studied area.Two methods were tested for estimating original magma components:methods of“MgO=8wt%”and“Mg#=72”.Results showed that values of major element derived from the first methods were higher than those from the second method,for example,Na₈>Na₇₂ and Fe₈>Fe₇₂.Futhermore,it was found that“Mg#=72”method might reasonable for applying in studied samples,and much suitable for analyzing whole rock data than glass data.High content of Pb was seen from all samples,meantime it is higher in whole rock than in glass samples Relative high values of Loss on ignition and content Pb in studied samples that indicated that influence effect of hydrothermal alteration on inner part/layer of basalt rock is much clearer than on glass layer.A comparison analysis of geochemical data suggested that Galapagos mantle plume enriched-component has little impact to basalts from study area.