Thermal state of the lithosphere beneath Central Mongolia: evidence from deep-seated xenoliths from the Shavaryn-Saram volcanic centre in the Tariat depression, Hangai, Mongolia

M. G. Kopylova*, S. Y. O'Reilly, Yu S. Genshaft

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    47 Citations (Scopus)

    Abstract

    A suite of garnet-two pyroxene granulites, garnet pyroxenites and garnet peridotites from the pyroclastic facies of the Shavaryn-Saram volcanic centre in the Tariat depression in the northern part of the Hangai dome, Central Mongolia, yields pressure and temperature information for the lower crust and upper mantle in that region. Although a real geotherm cannot be constructed because of the common zoning of the minerals in some of the xenoliths, it can be inferred that the P-T locus from about 900 °C at 45 km to 1050 °C at 60 km defines a likely approximate geothermal gradient for the region around the time of entrainment of the xenoliths (about 1 Ma ago). This geothermal gradient is high relative to cratonic geotherms but is 50-100 °C lower than that for typical alkali basaltic provinces worldwide. The crust-mantle boundary inferred from the incoming of ultramafic rock types in this region is located at about 45 km and granulite rock types extend well into the mantle. This interpretation is consistent with the most recent seismic sections for the area. Analytical data for major and trace elements (by electron- and proton-microprobe respectively) in clinopyroxenes indicate that the Cr-diopside series xenoliths are enriched in basaltic components (including Al2O3, Na2O, TiO2, Sr, Y and Zr). The combination of elevated temperature and fertile composition of the uppermost mantle as revealed by the xenoliths could explain the observed anomalous seismic signatures seen beneath this region.

    Original languageEnglish
    Pages (from-to)243-255
    Number of pages13
    JournalLithos
    Volume36
    Issue number3-4
    DOIs
    Publication statusPublished - 1995

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