Chlorine enrichment in central Rio Grande Rift basaltic melt inclusions: Evidence for subduction modification of the lithospheric mantle
- 1Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78712, USA
- 2Department of Geoscience, University of Iowa, Iowa City, Iowa 52242, USA
- *E-mail: Michael-rowe{at}uiowa.edu.
Abstract
Shallow subduction of the Farallon plate during the Laramide orogeny (ca. 80–40 Ma) may have resulted in metasomatism of the western North American lithospheric mantle. Olivine- and orthopyroxene-hosted melt inclusions from the central Rio Grande Rift are variably enriched in chlorine relative to fluid-immobile elements. Subparallel trends in Cl/K versus Cl/Nb for alkali basalts and tholeiites can be explained by Cl/K fractionation during low degree partial melting, with DCl ≈ DNb < DK. The observed trace element enrichment does not correlate with host Mg# or melt SiO2 wt% as expected for crustal contamination via an assimilation–fractional crystallization (AFC) process. In addition, examples from other volcanic systems suggest that Cl/K decreases with increasing contamination, contrary to observed positive correlations between Cl/K and Ba/Nb and Sr/Nd. The positive correlation of Cl/K and Cl/Nb with typical indices of subduction enrichment (e.g., Ba/Nb and Sr/Nd) supports a model of mantle metasomatism during subduction.
Footnotes
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↵GSA Data Repository item 2009108, Figure DR1 (sample location map), Table DR1 (whole rock compositions), Table DR2 (melt inclusion compositions and analytical methods), and Table DR3 (inter-laboratory electron microprobe comparison), is available online at www.geosociety.org/pubs/ft2009.htm, or on request from editing{at}geosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.
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- Received 23 September 2008.
- Revision received 13 December 2008.
- Accepted 19 December 2008.
- © 2009 Geological Society of America
