Volume 38: January - December 1997

Issue 8: August 1997

Abstract

Mexican peridotite xenoliths and tectonic terranes: correlations among vent location, texture, temperature, pressure, and oxygen fugacity

  • Mexican peridotite xenoliths and tectonic terranes: correlations among vent location, texture, temperature, pressure, and oxygen fugacity

    • JF. Luhr and JJ. Aranda-Gomez2

    1Department of Mineral Sciences, NHB-119, Smithsonian Institution, Washington, DC 20560, USA and 2Estacion Regional del Centro, Instituto de Geologia, Universidad Nacional Atonoma de Mexico, Guanajuato, MexicoCorresponding author Email: luhr@volcano.si.edu

    ABSTRACT

    Twenty-six spinel peridotite xenoliths were studied from five Quaternary volcanic fields that define a transect extending for 1700 km from southeast to northwest across the southern Basin and Range Province in Mexico. Calculated equilibration temperatures and pressures are highest for xenoliths from Ventura-Espiritu Santo (1073+-41oC, 19.6+-3.0 kbar; n=9) and Durango (1082+-21oC, 17.0+-1.7 kbar; n=7). These fields lie near the center of the transect in the interior of the Tepehuano tectonic terrane and have xenoliths dominated by coarse-equant and coarse-tabular textures. Spinel-pyroxene clusters, interpreted as decompression reaction products of garnet+olivine, are only found at these fields, only in xenoliths with calculated pressures >15 kbar. In contrast, calculated temperatures and pressures are lowest for the Santo Domingo (1026+-19oC, 14.4+-2.0 kbar; n=4) and San Quintin (1034+-66oC, 10.7+-2.5 kbar; n=5) fields, where xenoliths display porphyroclastic or granuloblastic textures. These two fields mark the ends of our transect and lie near tectonic terrane boundaries. Calculated oxygen fugacities, expressed relative to the fayalite-magnetite-quartz buffer ([Delta]RMQ), increase from southeast to northwest along the transect: Santo Domingo, -1.3+-0.7 (n=4); Ventura-Espiritu Santo, -0.6+-0.4 (n=9); Durango, -0.2+-0.3 (n=7); Mesa Cacaxta, 0.3 (n=1); San Quintin, 0.0+-0.2 (n=5). The lithosphere closest to the Mesozoic-Cenozoic paleotrench appears to have been most strongly affected by slab-derived, oxidized fluids or melts.

    Keywords: mantle; Mexico; peridotite; petrology; xenolith

    Pages: 1075 - 1112

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