Table 1.
Summary of New In Situ 40Ar/39Ar Geochronology
| Sample | Analysis | Microstructure | 40Ar/39Ar date (Ma) | ±1σ (Ma) | %40Ar | Mica Composition | |
|---|---|---|---|---|---|---|---|
| EV22‐03: albite‐white mica schist (n: 12/14) | Si (apfu) | XMg | |||||
| Chip 1 | 1 | Foliation | 46.8 | 0.9 | 86.0 | 3.36–3.42 (mean: 3.39) | 0.74–0.81 (mean: 0.79) |
| 2 | Foliation | 36.8 | 1.0 | 74.6 | |||
| 3 | Strain shadow | 42.4 | 0.9 | 79.1 | |||
| 4 | – | 27.3 | 1.4 | 50.0 | |||
| Chip 2 | 1 | Coarse, blocky, vein fill | 22.9 | 0.9 | 65.8 | ||
| 2 | Coarse, after albite | 24.3 | 1.0 | 73.6 | |||
| 3 | Coarse, blocky, vein fill | 23.9 | 0.8 | 77.6 | |||
| 4 | Strain shadow | 35.2 | 1.1 | 74.3 | |||
| Chip 3 | 1 | Strain shadow | 37.8 | 0.9 | 72.4 | ||
| 2 | – | 22.5 | 1.2 | 46.9 | |||
| 3 | Coarse, after albite | 28.2 | 0.8 | 71.9 | |||
| 4 | Foliation | 44.7 | 0.7 | 82.0 | |||
| 5 | Foliation | 38.1 | 0.8 | 79.3 | |||
| 6 | Coarse, high‐angle fan | 25.1 | 0.7 | 82.8 | |||
| EV21‐07: epidote‐white mica schist (n: 8/8) | Si (apfu) | XMg | |||||
| Chip 2 | 1 | Foliation | 27.0 | 0.9 | 84.7 | 3.12–3.52 (mean: 3.36) | 0.58–0.76 (mean: 0.69) |
| 2 | Foliation | 23.7 | 0.9 | 81.5 | |||
| 3 | Fan | 28.5 | 0.9 | 81.7 | |||
| 4 | Foliation | 26.6 | 0.9 | 85.9 | |||
| Chip 3 | 1 | Foliation | 27.1 | 0.7 | 73.9 | ||
| 2 | Foliation | 23.4 | 0.7 | 80.7 | |||
| 3* | Strain shadow | 36.6 | 0.8 | 85.0 | |||
| 4 | Strain shadow | 27.0 | 0.7 | 85.1 | |||
| EV20‐20: albite‐white mica schist (n: 8/8) | Si (apfu) | XMg | |||||
| Chip 1 | 1 | Foliation | 34.9 | 1.3 | 81.7 | 3.35–3.46 (mean: 3.41) | 0.67–0.73 (mean: 0.70) |
| Chip 2 | 2 | Foliation | 29.8 | 2.2 | 63.2 | ||
| 3 | Fan | 34.4 | 1.2 | 82.6 | |||
| 4 | Foliation | 31.3 | 0.8 | 59.2 | |||
| Chip 4 | 1 | Foliation | 35.9 | 1.0 | 93.6 | ||
| 2 | Foliation | 29.3 | 1.6 | 69.9 | |||
| 3 | Fan | 40.6 | 1.4 | 78.9 | |||
| 4 | Foliation/strain shadow | 32.4 | 1.4 | 85.9 | |||
| EV22‐17: albite‐white mica schist (n: 12/12) | Si (apfu) | XMg | |||||
| Chip 1 | 1 | Foliation | 34.0 | 1.4 | 63.8 | 3.33–3.59 (mean: 3.46) | 0.72–0.82 (mean: 0.77) |
| Chip 2 | 1 | Coarse, blocky, vein fill | 30.4 | 0.5 | 77.0 | ||
| 2 | Coarse, blocky, vein fill | 24.5 | 1.2 | 55.2 | |||
| 3 | Coarse, blocky, vein fill | 27.4 | 1.1 | 56.6 | |||
| 4 | Coarse, blocky, vein fill | 30.1 | 0.6 | 74.9 | |||
| Chip 3 | 1 | Shear band | 29.4 | 0.7 | 84.3 | ||
| 2 | Shear band | 40.0 | 0.6 | 89.6 | |||
| 3* | Foliation | 61.2 | 3.9 | 58.2 | |||
| 4 | Shear band | 46.5 | 0.7 | 86.9 | |||
| Chip 4 | 1 | Shear band | 39.8 | 0.5 | 88.1 | ||
| 2* | Shear band | 57.2 | 0.4 | 90.5 | |||
| 3 | Foliation | 35.2 | 0.9 | 50.9 | |||
| EV22‐07: paragonite‐tourmaline schist (n: 11/13) | Si (apfu) | XMg | |||||
| Chip 2 | 1pg | Foliation | 31.8 | 4.4 | 87.8 | phengite: 3.24–3.39 (mean: 3.32) | phengite: 0.60–0.66 (mean: 0.65) |
| 2pg | Foliation | 26.4 | 1.8 | 66.0 | |||
| 3 pg | – | 25.8 | 1.5 | 40.2 | |||
| 4 | Foliation | 21.1 | 0.8 | 72.3 | |||
| 5pg | Fan | 42.0 | 0.7 | 71.6 | |||
| 6* | Foliation | 55.3 | 0.6 | 81.0 | |||
| Chip 4 | 1pg | Foliation | 28.6 | 2.6 | 71.6 | paragonite: 2.96–3.02 | paragonite: N/A |
| 2 | Fan | 39.5 | 0.6 | 89.2 | |||
| 3pg | Foliation | 29.4 | 2.7 | 82.6 | |||
| 4 | Fan | 35.2 | 0.7 | 77.4 | |||
| 5 pg | – | 29.5 | 3.5 | 33.7 | |||
| 6 | Foliation | 22.5 | 0.8 | 75.4 | |||
| 7 | Foliation | 23.7 | 0.7 | 82.0 | |||
| EV19‐03: pumpellyite‐albite schist (n: 11/11) | Si (apfu) | XMg | |||||
| Chip 1 | 1 | Foliation | 25.0 | 1.4 | 83.3 | 3.38–3.61 (mean: 3.45) | 0.84–0.88 (mean: 0.85) |
| 2 | Foliation | 25.7 | 1.0 | 88.5 | |||
| 3 | Foliation | 24.7 | 1.1 | 83.8 | |||
| 4 | Foliation | 23.3 | 1.0 | 74.4 | |||
| 5 | Foliation | 26.5 | 0.9 | 89.8 | |||
| 6 | Foliation | 26.5 | 0.9 | 90.3 | |||
| Chip 2 | 1 | Fan, high‐angle | 22.9 | 1.1 | 85.9 | ||
| 2 | Fan, high‐angle | 25.3 | 1.2 | 88.2 | |||
| 3 | Fan, high‐angle | 23.3 | 1.5 | 90.5 | |||
| 5 | Fan, high‐angle | 21.7 | 1.2 | 79.7 | |||
| 6 | Fan, low‐angle, large single crystal | 25.1 | 1.2 | 88.9 | |||
| EV20‐14: schistose impure marble (n: 6/9) | Si (apfu) | XMg | |||||
| Chip 1 | 1 | Foliation, micaceous microlithon | 43.9 | 1.0 | 88.0 | 3.50–3.64 (mean: 3.54) | 0.73–0.79 (mean: 0.76) |
| 2 | Foliation, micaceous microlithon | 37.6 | 1.1 | 49.4 | |||
| 3 | Foliation, micaceous microlithon | 38.6 | 1.0 | 57.1 | |||
| 4 | Foliation, micaceous microlithon | 41.6 | 0.9 | 52.2 | |||
| 5 | Foliation, micaceous microlithon | 42.0 | 1.1 | 58.3 | |||
| 6 | Foliation, micaceous microlithon | 40.6 | 1.4 | 38.8 | |||
| Chip 2 | 1 | Foliation, micaceous microlithon | 47.0 | 1.4 | 48.1 | ||
| 2 | Foliation, micaceous microlithon | 49.4 | 1.6 | 44.7 | |||
| 3 | Foliation, micaceous microlithon | 45.8 | 1.0 | 79.8 | |||
| EV22‐06B: epidote‐albite‐tourmaline schist (n: 8/8) | Si (apfu) | XMg | |||||
| Chip 1 | 1 | Fan, high‐angle | 22.8 | 0.6 | 79.5 | 3.30–3.47 (mean: 3.37) | 0.54–0.65 (mean: 0.60) |
| 3 | Strain shadow | 29.1 | 0.5 | 102.0 | |||
| 4 | Shear band | 25.7 | 0.5 | 89.6 | |||
| Chip 2 | 1 | Strain shadow | 23.0 | 0.6 | 98.4 | ||
| 2 | Strain shadow | 30.3 | 0.6 | 93.4 | |||
| 3 | Foliation | 25.4 | 0.7 | 60.1 | |||
| 4 | Foliation | 23.3 | 0.6 | 83.0 | |||
| 5 | Foliation | 25.9 | 0.6 | 71.7 | |||
| EV22‐14.5: carbonate‐silicate schist (n: 12/12) | Si (apfu) | XMg | |||||
| Chip 1 | 1 | Foliation‐parallel cleavage domain | 27.5 | 0.6 | 89.0 | 3.48–3.64 (mean: 3.57) | 0.76–0.81 (mean: 0.79) |
| 2 | Crenulated relic foliation | 31.4 | 0.6 | 83.6 | |||
| Chip 2 | 1 | Foliation‐parallel cleavage domain | 28.1 | 0.6 | 88.7 | ||
| 2 | Crenulated relic foliation | 26.7 | 0.5 | 80.2 | |||
| 3 | Isolated blocky crystal in chlorite | 25.0 | 0.8 | 75.0 | |||
| 4 | Foliation | 29.5 | 0.7 | 93.3 | |||
| 5 | High‐angle coarse blocky crystals | 25.9 | 0.6 | 77.8 | |||
| 6 | Foliation‐parallel cleavage domain | 30.3 | 0.6 | 87.4 | |||
| 7 | Crenulated relic foliation | 31.6 | 1.0 | 83.2 | |||
| Chip 3 | 1 | Foliation‐parallel cleavage domain | 31.5 | 0.7 | 62.3 | ||
| 2 | Crenulated relic foliation | 31.4 | 0.6 | 69.6 | |||
| 3 | Foliation‐parallel cleavage domain | 31.8 | 0.7 | 76.4 | |||
Note. Italics indicate analyses rejected due to low 40Ar*. *Analysis excluded from weighted mean calculation in Figure 10. pg—paragonite.