U-Pb and 40Ar/39Ar constraints on the cooling history of the northern Oaxacan Complex, southern Mexico

Tectonic implications

J. Duncan Keppie*, Luigi A. Solari, Fernando Ortega-Gutiérrez, Amabel Ortega-Rivera, James K W Lee, Robert Lopez, Willis E. Hames

*Corresponding author for this work

    Research output: Contribution to journalArticle

    17 Citations (Scopus)


    To better define the cooling history of the northern Oaxacan Complex, titanite and phlogopite from metasedimentary calc-silicate and biotite from a pegmatite were collected. All these rocks were involved in the granulite-facies Zapotecan orogeny between ca. 1004 and 978 ± 3 Ma, inferred to result from underthrusting the Oaxacan Complex beneath an arc or continent. Fragments of 2 × 5 cm2 titanite crystals yielded a concordant U-Pb age of 968 ± 9 Ma, whereas 40Ar/39Ar analyses of phlogopite and biotite gave ages of 945 ± 10 Ma and 856 ± 10 Ma, respectively. These ages are inferred to date cooling through 660-700 °C, 450 °C, and 300-350 °C, respectively. When combined with published ages (Sm-Nd garnet, 40Ar/39Ar hornblende, Rb-Sr biotite and whole rock, and K-Ar biotite and K-feldspar) the data define a two-stage cooling curve: (1) 8 °C/m.y. between 978 and 945 Ma, cooling through 450 °C by which time the rocks had risen through a depth of 15 km; and (2) 2 °C/m.y., which, by extrapolation, brought the rocks to the surface between 710 and 760 Ma. The first stage of exhumation is interpreted in terms of tectonic switching between steep and flat slab subduction, a result of interactions of a ridge, a plume, or an oceanic plateau with the trench. The second stage may be related to thermal relaxation of the lithosphere, ending with the breakup of Rodinia, which brought the rocks to the surface.

    Original languageEnglish
    Pages (from-to)771-781
    Number of pages11
    JournalMemoir of the Geological Society of America
    Publication statusPublished - 2004


    • Geochronology
    • Mexico
    • Oaxaca
    • Rodinia
    • Tectonics

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