Fig.1 Simplified tectonic map of (a) Tibetan Plateau and (b) Himalayan terrane (Fig.a and Fig.b adapted from [13]) and (c) geological map of the Yalaxiangbo dome (Fig.c adapted from [20])

Fig.2 Petrological characteristics of metamorphic basic rocks and amphibolites from Yalaxiangbo. (a) Outcrop of metamorphic basic rocks. (b) Weakly deformed metamorphic basic rocks. (c) Strongly deformed metamorphic basic rocks. (d) Hand specimens of amphibolite. (e-f) Microscopic characteristics of weakly deformed metamorphic basic rocks containing garnet, hornblende and a small amount of epidote. (g) Microscopic characteristics of strongly deformed metamorphic basic rocks composed of epidote and hornblende. (h) Microscopic characteristics of amphibolite composed of hornblende and plagioclase.

Fig.3 Zircon CL characteristics (a) and U-Pb ages (b, c) of Yalaxiangbo metamorphic basic rocks

Fig.4 Nb/Y-Zr/TiO2 (a, adapted from [23]), Co-Th (b, adapted from [24]), Th/Yb-Zr/Y (c, adapted from [25]) and Zr-Ti (d, adapted from [26]) diagrams for metamorphic basic rocks and plagioclase amphibolites from Yalaxiangbo

Fig.5 Chondrite-normalized REEs (a) and primitive mantle-normalized trace elements (b) variation diagrams for metamorphic basic rock and plagioclase amphibolite from Yalaxiangbo. Chondrite, primitive mantle, OIB, N-MORB and E-MORB data from [27].

Fig.6 Si-Mg/(Mg+Fe2+) classification diagram for hornblende in metamorphic basic rocks and amphibolites from Yalaxiangbo. Adapted from [30].

Fig.7 (Th/Nb)PM vs. (La/Nb)PM diagram for metamorphic basic rocks and amphibolites from Yalaxiangbo (adapted from [34]). MC (middle crust) and LC (lower crust) data from [31].

Fig.8 La-La/Sm (a) and La-La/Zr (b) diagrams for metamorphic basic rock and plagioclase amphibolite from Yalaxiangbo

Fig.9 La/Yb-Dy/Yb (a) and La/Sm-Sm/Yb (b) diagrams for metamorphic basic rocks and plagioclase amphibolites from Yalaxiangbo, showing the partial melting curves obtained using the nonmodal batch melting equations. Tick marks on each curve correspond to degrees of partial melting (%) for a given mantle source. Depleted MORB mantle (DMM) and enriched DMM (E-DMM) compositions from [42]; primitive mantle compositions from [27].

Fig.10 Discrimination diagram of tectonic setting for metamorphic basic rocks and plagioclase amphibolites from Yalaxiangbo. (a) Th/Yb-Nb/Yb diagram (adapted from [26]). (b) 2Nb-Zr/4-Y diagram (adapted from [44]). A1—Intraplate alkaline basalt; A2—Intraplate alkaline basalt + Intraplate tholeiite. B—E-MORB; C—Intraplate tholeiite + Volcanic arc basalt; D—Volcanic arc basalt + N-MORB. (c) Hf/3-Th-Ta diagram (adapted from [45]). (d) Hf/3-Th-Nb/16 diagrams (adapted from [45]). A—N-MORB; B—E-MORB/Intraplate tholeiite; C—Intraplate alkaline basalt; D—Island arc tholeiite.