Chlorine enrichment in central Rio Grande Rift basaltic melt inclusions; evidence for subduction modification of the lithospheric mantle
Chlorine enrichment in central Rio Grande Rift basaltic melt inclusions; evidence for subduction modification of the lithospheric mantle
Geology (Boulder) (May 2009) 37 (5): 439-442
- assimilation
- basalts
- Cenozoic
- chemical ratios
- chlorine
- electron probe data
- enrichment
- Espanola Basin
- experimental studies
- Farallon Plate
- fluid inclusions
- fractional crystallization
- geochemistry
- halogens
- igneous rocks
- inclusions
- ion probe data
- Laramide Orogeny
- lava
- lithophile elements
- lithosphere
- magma contamination
- magmas
- mantle
- mass spectra
- melt inclusions
- metasomatism
- New Mexico
- North America
- orogeny
- rift zones
- Rio Grande Rift
- spectra
- subduction
- trace elements
- United States
- upper mantle
- volatiles
- volcanic rocks
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 D (sub Cl) nearly equal D (sub Nb) <D (sub K) . The observed trace element enrichment does not correlate with host Mg# or melt SiO (sub 2) 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.
