Supporting Information & Supplementary Tables for "Eocene Lamproitic Magmatism in Gangdese: Melting Sub-arc Lithospheric Mantle and Implications for the Early Cenozoic Magmatic “Flare Up” in Southern Tibet"

The role of sub-arc mantle lithosphere in the build-up of a batholith is an outstanding issue that is still not well resolved. Lamproite is a mantle-derived magmatic rock that provides a window to learn the composition and the enrichment processes of subcontinental lithospheric mantle (SCLM). Zircon and titanite U-Pb age data on a dike of lamproite from the Gangdese batholith indicate that this dike was generated at ~44 Ma. These lamproitic samples are of ultrapotassic with high K2O contents, high Sr and Ba concentrations. They show strong enrichment in light rare earth elements (LREE), depletion in heavy rare earth elements (HREE) and substantial negative anomalies in Ti, Nb, and Ta. These lamproitic rocks are characterized by radiogenic unradiogenic ɛNd(t) ( -11.6 to -12.5), low 206Pb/204Pb(t) (18.71-18.73), elevated 207Pb/204Pb(t) (15.75-15.76) and 208Pb/204Pb(t) (39.62-39.73) isotope compositions, suggesting that the lamproite was derived from a fluid-metasomatized sub-arc lithospheric mantle. Monte Carlo modeling indicates that this metasomatic event happened at 174 Ma during the subduction of the Tethyan oceanic lithosphere. The ~44 Ma Tunba lamproitic magmatism represents a magmatic response to the early Cenozoic slab breakoff of the Neo-Tethyan oceanic lithosphere. During the early Cenozoic magmatic “flare up”. Melting of a metasomatized sub-arc lithospheric mantle could increase the magma production in addition to the magmas from asthenospheric mantle. This process could be another important factor that enhance the magmatic “flare up” in the Gangdese batholith in particular and other batholith worldwide.