Pyroxenite xenoliths from the Rio Puerco volcanic field, New Mexico: Melt metasomatism at the margin of the Rio Grande rift

2006/01/01 by Courtney Porreca, Jane Selverstone, K. E. Samuels · 34 citations
Earth and Planetary Sciences · #Geological and Geochemical Analysis #earthquake and tectonic studies #High-pressure geophysics and materials #Geology #Carbonatite #Geochemistry #Xenolith #Metasomatism #Mantle (geology) #Basalt #Rift #Volcano #Paleontology #Tectonics

paper · pdf · doi:10.1130/ges00058.1

published in Geosphere 2(7), 333 (Geological Society of America)

openalex publication_date 2006/01/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/26

Abstract

Mantle xenoliths from the Pliocene Rio Puerco volcanic field, New Mexico, record chemical modification of the subcontinental lithosphere in the transition zone between the Colorado Plateau and the Rio Grande rift. The Rio Puerco necks brought a wide variety of mantle xenoliths to the surface, including abundant spinel ± garnet pyroxenites. Garnet pyroxenites equilibrated at pressures within the spinel lherzolite stability field (16–18 kbar) but at higher temperatures (1020–1100 °C) than lherzolite xenoliths (900–1000 °C). Calcite-bearing pyroxenites record temperatures as high as 1145 °C. Textural observations combined with the high equilibration temperatures are consistent with pyroxenite formation in response to melt interaction with a lherzolite precursor in the approximate ratio of 35% lherzolite to 65% melt. Bulk chemical data and the presence of both carbonatitic and basaltic glass inclusions indicate that the infiltrating melt(s) included both carbonatite and silicate components. Different mantle xenolith populations in volcanic centers of different ages in the Rio Grande rift constrain the likely age of melt infiltration and pyroxenite formation beneath the Puerco necks to Miocene–early Pliocene. Orthopyroxene + spinel + clinopyroxene + silicate glass symplectites around relict garnets record continued rift-related decompression ± heating following pyroxenite formation. Carbonatite + silicate melt generation was likely concentrated in areas affected by earlier metasomatism related to devolatilization of the subducted Farallon slab. Deep-seated fractures associated with the Jemez Lineament may have focused melts beneath the Puerco necks and resulted in wholesale conversion of lherzolite into pyroxenite.

Citations

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• Geothermobarometry in Four-phase Lherzolites II. New Thermobarometers, and Practical Assessment of Existing Thermobarometers
• 3He surface exposure dating and its implications for magma evolution in the Potrillo volcanic field, Rio Grande Rift, New Mexico, USA
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• Crust and upper mantle shear wave structure of the southwest United States: Implications for rifting and support for high elevation
• Diversity of Mafic Rocks in the Ronda Peridotite: Evidence for Pervasive Melt-Rock Reaction during Heating of Subcontinental Lithosphere by Upwelling Asthenosphere

Cited by

• Potrillo volcanic field [wikipedia]