18O-Enrichment of silicic magmas caused by crystal fractionation at the Galapagos Spreading Center |
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| Authors: | Karlis Muehlenbachs Gary Byerly |
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| Institution: | (1) Department of Geology, University of Alberta, T6G 2E3 Edmonton, Alberta, Canada;(2) Department of Geology, Louisiana State University, 70803 Baton Rouge, LA, USA;(3) Bundesanstalt für Geowissen-schaften und Rohstoffe, Postfach 510153, D-3000 Hannover 51, Federal Republic of Germany |
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| Abstract: | An extremely differentiated suite of unaltered volcanic rocks dredged from the Galapagos Spreading Center ranges in 
18O from 5.7 to 7.1 At 95°W, low K-tholeiites, FeTi-basalts, andesites and rhyodacites were recovered. Their lithologic and major element geochemical variation can be accounted for by crystal fractionation of plagioclase, pyroxenes, olivine and titanomagnetite in the same proportions and amounts needed to model the
18O variation by simple Rayleigh fractionation. More complicated behaviour was observed in a FeTi-basalt suite from 85°W. This study shows that 90% fractionation only enriches the residual melt by about 1.2 in 18O. It also implies that the magma chambers along parts of the Galapagos Spreading Center were static and isolated such that extreme differentiation could occur. |
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