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A Detailed Pb Isotopic Study Of Crustal Contamination Assimilation : The Edgecumbe Volcanic Field, Se Alaska, James Myers, A. K. Sinha

James Myers

To better understand the process of crustal contamination/assimilation, 23 Pb isotopic compositions and 12 concentrations have been measured on lavas and basement rocks from the Edgecumbe volcanic field, SE Alaska. Measured isotopic ratios have the following ranges: 206Pb204Pb = 18.477–19.161; 207Pb204Pb = 15.562–15.679; 208Pb204Pb = 38.17–38.85. While the data form well-constrained linear arrays on Pb-Pb diagrams, no simple correlation exists with major element composition. Basaltic lavas (≤ 51 wt% SiO2) are characterized by two isotopic groups. The olivine basalt (≤ 48% SiO2) is more radiogenic than the plagioclase basalt (48–51%) which also shows more heterogeneity. In the silica range 52–55%, …