Abstract

New abundance data for Ti, Zr, Y, Sr, Cr, Hf, Ta, and Th in metamorphosed late Paleozoic basalts from the northern Sierra Nevada confirm that these rocks originated in an island arc. Furthermore, the data show that the original basalts belonged to the tholeiitic — rather than calc-alkalic — rock association of island arcs. Standard discrimination diagrams identify the island-arc tholeiite magma type; their utility was sternly tested by these thoroughly recrystallized (greenschist facies) rocks, whose island-arc origin had already been suggested by their petrography.

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