## 4 Results
### Zircon U-Pb Dating and Hf Isotopic Composition  
The sampling locations for U-Pb and Hf isotope analyses are shown in Figure 2. The U-Pb isotopic data samples include rhylolite (PM9-19-TW1 and ZJ-TW1) and rhylolite porphyry (D4189-TW1 and PM 17-16-TW1). Additionally, Lu-Hf isotopic compositions of zircons from three samples (ZJ-TW1, D4189-TW1, and PM17-16-TW1). The results are shown in the Figures 4 and 5a and listed in the Supplementary Tables S1 and S2.  
The zircon grains from the sample PM9-19-TW1 are generally hypidomorphic prismatic crystals that are 80-130 \(\upmu\)m long with aspect ratios of 1:1-2:1. They are typically transparent, colorless to gray, and show magmatic oscillatory zoning in CL images (Figure 4a) with Th/U ratios of 0.40-0.71. Analysis of nineteen grains yielded concordant \({}^{206}\)Pb/\({}^{238}\)U ages of 408 Ma to 437 Ma, with a weighted mean \({}^{206}\)Pb/\({}^{238}\)U age of 418.7 \(\pm\) 4.6 Ma (MSWD = 1.7, Figure 4e).  
Zircon grains from the sample ZJ-TW1 are 60-150 \(\upmu\)m long and 40-80 \(\upmu\)m wide, with length/width ratios of 1:1 to 3:1. In CL images (Figure 4b), these zircon grains show obvious oscillatory zoning with high Th/U rations (0.29 to 0.79) indicating a magmatic origin. Seventeen grains yielded concordant \({}^{206}\)Pb/\({}^{238}\)U ages of 436 Ma to 389 Ma, with a weighted mean \({}^{206}\)Pb/\({}^{238}\)U age of 414.1 \(\pm\) 6.9 Ma (MSWD = 2.3, Figure 4f). One inherited zircon grain yielded a \({}^{207}\)Pb/\({}^{206}\)Pb age of 1465 Ma. They have \({}^{176}\)Hf/\({}^{177}\)Hf ranging from 0.282758 to 0.282950, and high \(\varepsilon_{\rm Hf}\) (t) (from +8.69 to +14.53) value, as well as the calculated two-stage Hf model ages (T\({}_{\rm DM}^{2}\)) ranging from 469 to 865 Ma.  
Zircon grains from the sample D4189-TW1 have sizes of 80-130 \(\upmu\)m and aspect ratios between 2:1 and 1:1. The grains are primarily euhedral in shape and display oscillatory zoning in Cl images (Figure 4c). Nineteen spots were analyzed on zircon grains. These data points yield a weighted mean \({}^{206}\)Pb/\({}^{238}\)U age of 406.5 \(\pm\) 6.1 Ma (MSWD = 1.7, Figure 4g), with high Th/U ratios of 0.39-0.75, representing a magmatic origin. They yield high \({}^{176}\)Hf/\({}^{177}\)Hf ratios (ranging from 0.282710 to 0.282942), and high \(\varepsilon_{\rm Hf}\) (t) value (from +6.61 to +14.81), with the two-stage Hf model ages ranging from 467 to 982 Ma.  
Zircon grains from the sample PM17-16-TW1 are colorless, transparent, or translucent grains. Their lengths are mostly in the range 70-120 \(\upmu\)m with aspect ratios of 1:1-2:1. The grains are euhedral prismatic crystals with a zoning structure indicative of magmatic origin (Figure 4d). Sixteen spots have concordant \({}^{206}\)Pb/\({}^{238}\)U ages of 421-388 Ma with high Th/U ratios (0.42-0.76) and clear oscillatory zoning, confirming their magmatic origin. The weighted mean age of 408.3 \(\pm\) 5.8 Ma (MSWD = 3.3, Figure 4h) are interpreted as the crystallization age of the rhylolite porphyry. They yield high \({}^{176}\)Hf/\({}^{177}\)Hf ratios (ranging from 0.282692 to 0.282911), and high \(\varepsilon_{\rm Hf}\) (t) value (from +6.13 to +12.99) with Hf model ages ranging from 554 to 1015 Ma.  
Figure 4: Photomicrographs (**a–d**) of representative zircon grains analyzed for U-Pb ages and Hf isotopes, and Zircon U-Pb concordant diagrams (**e–h**) for the volcanic rocks in the Haerdaban area. The white or blue circles indicate the analytical spots for U-Pb isotopes and yellow circles denote the analytical spots for Hf isotopes. (**a,e**): the sample PM9-19-TW1; (**b,f**): the sample ZJ-TW1; (**c,g**): the sample D4189-TW1(**d,f**): the sample PM17-16-TW1  
Figure 5: (**a**) In situ zircon \(\epsilon_{\rm Hf}\)(t) values versus U-Pb ages and (**b**) whole-rock \(\epsilon_{\rm Nd}\)(t) values versus initial \({}^{87}\)Sr/\({}^{86}\)Sr diagrams for the volcanic rocks in the Haerdaban area (previous data are collected from [11] and its references).