Mean 206 Pb/ 238 U age = 26.2 ± 0.6 (2 ) (n = 13, MSWD = 2.8) Pb/ 235 U

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2 .8.6 T16 Mean age = 26.2 ±.6 (2 ) (n = 13, MSWD = 2.8) ET Mean age = 17. ±.5 (2 ) (n =, MSWD = 3.66) ET25C Mean age = 15. ±.4 (2 ) (n = 12, MSWD = 1.82) Appendix I. Plots of U-Pb zircon data

3 Appendix Table DR2. Summary of Ar/ Ar dating results of adakites from southern Tibet Sample Phase Plateau N dated date (Myr ± ) (steps) Ar proportion (%) Intercept ( Ar/ 36 Ar) i MSWD date (Myr ± ) (± ) T41D Whole rock 15.± ±.8 297± T81 Whole rock 18.4± ± ± ET25B Sanidine 15.2± ±.3 6± ET25E Whole rock 13.2± ±.3 3± ET26C Whole rock 16.6± ±.9 29± 1.81 ET26D Sanidine 16.4± ±.1 7± Note: Step-heating Ar/ Ar age determinations were performed at National Taiwan University using a Varian-MAT GD 1 mass spectrometer coupled with a double-vacuum resistance furnace. Whole rock chips or mineral grains, handpicked and sieved to the range of 1-25 µm, were ultrasonically cleaned in distilled water and dried, and then irradiated in the THOR Reactor at National Tsing-Hua University in Taiwan. To monitor the neutron flux, aliquots of the LP-6 biotite standard (1.4±.2 Ma), weighted 6- mg, were stacked with the samples. More analytical details can be found in Chung et al. (1998). The results, summarized in a table and plotted in age spectra and correlation diagrams, are given in Appendix II.

4 T41D(wr) Fraction of Ar Released _.3 Ma T81(wr) ET25B(sa) _.4 Ma _.2 Ma Intercept date=15.1 +_.8 Ma 36 ( )i=297+_ 22 MSWD= Intercept date=18.6+_ 1.3 Ma 36 ( )i=291+_ 7 MSWD= Intercept date=14.8 +_.3 Ma 36 ( )i=6 +_ 3 MSWD= ET25E(wr) _.2 Ma ET26C(wr) _.2 Ma ET26D(sa) _.9 Ma Intercept date=16.7+_.9 Ma 36 ( )i=29+_ MSWD= Intercept date=12.9+_.3 Ma 36 ( )i=3+_ 21 MSWD= Intercept date=15.7+_.1 Ma 36 ( )i=7+_ 27 MSWD= Appendix. Plots of dating results.

5 Appendix Table DR3. Major and trace element data of representative adakite samples from southern Tibet sample T65C T41D T81 T16 ET23 ET25B ET25E ET26C ET26D AGV-1 locality Majiang Xigaze Xigaze Linzhi Jiama Jiama Jiama Nanmu Nanmu lithology dike dike dike plug plug plug dike plug dike USGS-std. longitude E E E E 91.6 E E E 9.87 E 9.87 E latitude N N N N N N N N N altitude(m age (Ma) ~-16** 15. ± ± ± ± ± ± ± ± 1.8 method* Ar-Ar (sa) Ar-Ar (wr) Ar-Ar (wr) U-Pb (zr) U-Pb (zr) U-Pb (zr) Ar-Ar (wr) Ar-Ar (sa) Ar-Ar (wr) 15.2 ±.4 Ar-Ar (sa) (wt.%) SiO TiO Al 2 O Fe 2 O MnO MgO CaO Na 2 O O P 2 O Mg# (ppm) (n=13; ±2 ) Rb ± 1.3 Ba ± 25 Th ±.9 U ±.4 Nb ±.2 Ta ±.2 La ±.4 Ce ±.7 Pb ±.3 Pr ±.7 Sr ± 13 Nd ±.5 Zr ± 4 Hf ±.8 Sm ±.12 Eu ±.3 Gd ±.12 Tb ±.16 Dy ±.6 Y ±.3 Ho ±.1 Er ±.3 Tm ±.7 Yb ±.4 Lu ±.6 * wr: whole rock; zr: zircon; sa: sanidine. ** Data from Coulon et al. (1986). total Fe. Mg# =(Mg/Mg+.9Fe). Major and trace elements were determined at National Taiwan University by X-ray fluorescence method using a Rigaku RIX- spectrometer and by inductively coupled plasma-mass spectrometry using an Agilent 75s quadrupole ICP-MS, respectively. The routine analytical precision and accuracy for most elements measured are estimated to be <5%. To make sure the completion of digestion of the plug-type, coarser-grained samples, fused whole rock glasses made for XRF analyses were used for ICP-MS trace element analyses and these were then checked by duplicate runs of powders digested using high-pressure teflon bombs. Results obtained by both procedures show good consistency, generally with RSD < %.