Detailed description of samples from the Buteel MCC for which ^40Ar-^39Ar is
otopic analyses were carried out, chemical compositions of hornblende from these samples and thermobarometry

Sample 1116 was collected from an exposure situated in the centre of the Burgutoy ridge (the footwall of the Buteel complex). It is an amphibolite from an outcrop of biotite-amphibole gneiss and amphibolite, intruded by foliated granites. The main mineral phases of the sample are magnesiohastingsite, biotite (TiO_2 = 2.3-3.0 wt. %), plagioclase, and quartz, and it has 50.57 wt. % SiO_2. P-T conditions of metamorphism, calculated for sample 1116 by using hornblende geothermobarometry (Gerya et al. 1997) yielded 3.4 kbar at 616-618 °C (amphibolite facies) (Table).

Sample 1610 is a mylonitized gabbro-dolerite intruding Permo-Triassic mylonitized volcano-sedimentary rocks of the footwall of the Buteel complex (Burgutoy) not far from the detachment fault on the southern flank of the complex. The sample exhibits a primary magmatic texture and a secondary mylonitic fabric. Sample 1610 (50.86 wt. % SiO_2) contains magmatic minerals that are almost completely replaced by syntectonic magnesiohornblende, magmatic plagioclase (labradorite with An_56), syntectonic plagioclase – oligoclase (An_24-25), syntectonic biotite (TiO_2 = 0.66-2.00 %) and quartz. The P-T conditions of metamorphism calculated for this sample by using hornblende geothermobarometry (Gerya et al. 1997) are 1.7-2.3 kbar at 510-541 °C (greenschist facies) (Table).

Hornblende microprobe analyses have been carried out at the Geological Institute, Siberian Branch, Russian Academy of Sciences in Ulan-Ude on a MAR-3 electron microprobe with 20 kV accelerating voltage, 40 nA beam current, and 2–3 µm beam diameter. The analyses were calibrated using natural mineral standards.

Reference
Gerya, T.V., Perchuk, L.L., Triboulet, C., Audren, C. & Sez’ko, A.I. 1997. Petrology of the Tumanshet zonal metamorphic complex, Eastern Sayan. Petrology, 5, 503-533.

Table. Electron microprobe analyses (wt. %) and cation
proportions of hornblendes from rocks of the Buteel MCC

Sample | 1116 | 1116 | 1610 | 1610
Grain | 1 | 2 | 1 | 2
SiO_2 | 42.95 | 43.64 | 47.92 | 49.81
TiO_2 | 0.85 | 0.84 | 0.37 | 0.48
Al_2O_3 | 10.23 | 10.33 | 6.79 | 5.17
FeO | 18.18 | 18.18 | 15.25 | 13.54
MnO | 0.42 | 0.43 | 0.35 | 0.32
MgO | 10.69 | 11.05 | 13.44 | 14.64
CaO | 11.80 | 11.82 | 11.93 | 12.20
Na_2O | 1.49 | 1.49 | 0.79 | 0.65
K_2O | 1.35 | 1.35 | 0.48 | 0.33
Total | 97.96 | 99.11 | 97.31 | 97.15
Si | 6.512 | 6.526 | 7.095 | 7.305
Ti | 0.096 | 0.094 | 0.041 | 0.053
Al | 1.828 | 1.820 | 1.185 | 0.894
Fe | 2.305 | 2.273 | 1.889 | 1.660
Mn | 0.054 | 0.054 | 0.044 | 0.040
Mg | 2.417 | 2.464 | 2.966 | 3.202
Ca | 1.916 | 1.893 | 1.893 | 1.917
Na | 0.439 | 0.433 | 0.226 | 0.186
K | 0.260 | 0.258 | 0.091 | 0.062
Total | 15.827 | 15.815 | 15.430 | 15.319
P, kbar* | 3.4 | 3.4 | 2.3 | 1.7
T, ºC* | 618 | 616 | 541 | 510

* P, kbar; T, ºC  - pressures and temperatures of metamorphism estimated
with using hornblende geothermobarometry (Gerya et al., 1997)