Petrology and geochemistry of mafic rocks from mélange and flysch units adjacent to the Yarlung Zangbo Suture Zone, southern Tibet

mafic rocks from the flysch are mostly gabbros. They are clinopyroxene-rich. Interstitial quartz is common. Ilmenite and titanite are abundant and relatively well preserved. REE patterns are the most LREE-enriched of any analyzed samples from the sedimentary units, with average (La/Yb)N of 6.9, while multi-element patterns show slight negative Nb-Ta and Ti anomalies. These last patterns are similar to patterns in volcanic rocks from the western Deccan Traps of India, whose geochemical behavior reflects mixing between an enriched mantle end-member of Réunion island-type and Indian continental lithospheric material. Hence, these rocks are interpreted to have been derived from an enriched intraplate mantle source, with additional crustal assimilation resulting from disaggregation of the Indian Plate during the opening of the Neo-Tethys ocean. AFC processes have been modelled and strongly suggest a felsic component analogous to Cambro-Ordovician granites as the major contaminant.