Major and trace element, Sr^Nd^Pb isotope and mineral chemical data are presented for newly discovered ultrapotassic lavas in the Tangra Yumco^Xuruco graben in southernTibet. The ultrapotassic lavas are characterized by high MgO, K2O and TiO2, low Al2O3 and Na2O contents, and also have high molar K2O/Al2O3, molar (K2OþNa2O)/Al2O3 and K2O/Na2O ratios. Their high abun-dances of incompatible trace elements such as large ion lithophile ele-ments (LILE) and light rare earth elements (LREE) reach the extreme levels typical of lamproites. The lamproites show highly radiogenic 87Sr/86Sr (07166^07363) and unradiogenic 143Nd/144Nd (0511796^0511962), low 206Pb/204Pb (18459^ 18931), and elevated radiogenic 207Pb/204Pb (156732^15841) and 208Pb/204Pb (39557^40058) ratios. On the basis of their geochem-ical and isotopic systematics, the lamproites in south Tibet have a distinct magma source that can be differentiated from the sources of
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Gao et al. (2007) studied this question.
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