A geochemical study of island-arc and back-arc tholeiites from the Scotia Sea

  • Hawkesworth C
  • O'Nions R
  • Pankhurst R
 et al. 
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Abstract

87Sr/86Sr and143Nd/144Nd ratios, REE and selected minor and trace elements are presented and compared for present-day volcanic rocks in the Scotia Sea. Tholeiitic basalts from the South Sandwich Islands show widely ranging contents of some lithophile elements, e.g. K2O (0.09-0.55%) and Rb (1.55-14.2 ppm), but fairly constant Na2O and Sr. Total REE contents range from about 4-20 times chondritic abundances with significant light-REE depletion and both positive and negative Eu anomalies. The variations in minor and trace element abundances are consistent with low-pressure fractional crystallization of plagioclase and clinopyroxene but only minor amounts of olivine. The87Sr/86Sr and143Nd/144Nd ratios of the parental magmas are thought be 0.7038-0.7039 and 0.51301-0.51314 respectively, and indicate derivation of at least some87Sr from subducted ocean crust. The back-arc tholeiites in the Scotia Sea have lower87Sr/86Sr ratios (0.7028-0.7033), similar143Nd/144Nd ratios (0.51305) and are variably light-REE-enriched (CeN/YbN= 1.0-1.6). Total REE contents are comparable to those of the South Sandwich Islands tholeiites. © 1977.

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