Volatile control of contrasting trace element distributions in peralkaline granitic and volcanic rocks |
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| Authors: | R P Taylor D F Strong B J Fryer |
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| Institution: | (1) Department of Geology, Memorial University of Newfoundland, A1B 3X5 St. John's, Newfoundland, Canada |
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| Abstract: | Anomalous enrichments of Zr (>500 ppm), Zn (> 100 ppm), Nb (>25 ppm), Y (>60 ppm), Th (>20 pm), U (> 5 ppm), LREE (>230 ppm)
and HREE (>35ppm), and high Rb/Sr (>5) characterize peralkaline granites, in contrast to their peraluminous and calc-alkaline
equivalents. Within the peralkaline suite, comenditic and pantelleritic volcanics exhibit two- to five-fold increases in the
concentrations of these trace elements over comagmatic granites. These cannot be explained by crystal- liquid fractionation
processes, and require the evolution of a sodium-enriched fluid. Corresponding trace element increases in the granites in
areas of alkali metasomatism support this argument, and reflect the partial confinement of this volatile phase within the
high-level magma chambers. REE studies in particular might eventually allow an evaluation of the role of Cl− versus F− and CO3-complexing in the evolution of the volatile fluid. |
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