GEOCHEMICAL AND TECTONIC TRANSITIONS IN THE EVOLUTION OF THE MOGOLLON-DATIL VOLCANIC FIELD, NEW-MEXICO, USA

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    Abstract

    The mafic to intermediate rocks of the Mogollon-Datil Volcanic Field have been subdivided petrologically and geochemically into three groups: Pre-30 Ma, 30-20 Ma and Post-20 Ma. The Pre-30- and 30-20-Ma rocks are broadly calc-alkaline, with high LILE/HFSE ratios and enriched radiogenic isotope compositions. Their Pb isotope ratios define a linear array on a Pb-Pb diagram with a slope corresponding to an age of similar to 1.7 Ga and they appear to have been derived largely from within the mantle lithosphere. The Post-20-Ma lavas are small-volume alkali olivine basalts, that typically have OIB-like isotope and trace-element ratios and are therefore inferred to have been derived from the underlying asthenosphere. Most of the igneous rocks of the Mogollon-Datil Volcanic Field were generated in a period of extensional tectonics. The peak of extension occurred at similar to 28.5 Ma and, although there was a small contribution from asthenosphere-derived magmas in the 29-20-Ma rocks, such magmas only became dominant (greater than or equal to 75%) at similar to 14 Ma, i.e. 15 Ma after the peak of extension. Published models are used to evaluate the temperature of the upper mantle at the time of magmatism and in particular whether the presence of GIB-like magmas should be regarded as evidence for a mantle plume. Partial melting in the mantle lithosphere is thought to have taken place in the presence of small amounts of H2O and CO2, whereas the underlying asthenosphere is assumed to have been anhydrous. For mechanical boundary layer thicknesses in the range 80-100 km and beta<2, partial melting in the asthenosphere is initiated at the relatively low potential temperatures of similar to 1320 degrees C. This is consistent with the low eruption rates in the Mogollon-Datil Volcanic Field and it is concluded that magmatism took place in response to lithospheric extension over mantle that was only slightly hotter than that beneath mid-oceanic ridges.

    Original languageEnglish
    Pages (from-to)31-53
    Number of pages23
    JournalChemical Geology
    Volume119
    Issue number1-4
    Publication statusPublished - 5 Jan 1995

    Keywords

    • SOUTHWESTERN UNITED-STATES
    • RIO-GRANDE RIFT
    • NEUTRON-ACTIVATION ANALYSIS
    • LITHOSPHERIC MANTLE
    • CONTINENTAL-CRUST
    • NORTH-AMERICA
    • ROCKS
    • USA
    • ASTHENOSPHERE
    • CONSTRAINTS

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