The Miocene K.rich adakitic rocks (KARs) containing dark microgranular enclaves (DMEs) in southern Tibet have been thought to be products of magma mixing/mingling between melts derived from partial melting of pre.existing continental crust in the stability field of garnet and the coeval mantle.derived ultrapotassic volcanic rocks. To test this hypothesis, we conduct an integrated study of petrology, zircon U-Pb dating, mineral geochemistry, and whole.rock elemental and Sr.Nd isotopic geochemistry on the Miocene Mayum KARs and their DMEs from the Zhongba micro.terrane in the western segment of the Yarlung Zangbo suture zone. The results show that the KARs and their DMEs have similar emplacement ages (~17.5 Ma), mineral assemblages (quartz+feldspar+amphibole+biotite) and mineral compositions, but the DMEs contain more amphibole and biotite, and have lower K2O and SiO2, and higher MgO, TiO2 and P2O5 contents than the KARs. In addition, the KARs and their DMEs have similar whole.rock Sr-Nd isotopic compositions: the KARs have （87Sr/86Sr） i of 0.70933~0.70950 and ε Nd( t ) of 8.17~ 6.72; the DMES have （87Sr/86Sr） i of 0.70933~0.70941 and ε Nd( t ) of 7.55~ 6.57. These features indicate that the DMEs are most likely fine.grained cumulates or autholiths related to the host KARs, rather than mixtures formed by magma mixing/mingling of the host KARs and the coeval ultrapotassic volcanic rocks with higher K2O contents. Combined with regional geological data, we conclude that the Mayum KARs resulted from partial melting of earlier crustal components that are rich in K2O in the stability field of garnet, and did not mix or mingle with the coeval ultrapotassic volcanic rocks.