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Table 1 Results from automated SEM Mineral Liberation Analysis (MLA) of petrographic thin sections of monazite-bearing garnet micaschist samples from the Alpeiner Valley, Stubai region. Modal mineralogy of major phases, from XMOD point counting routine with ~ 106 EDX analyses per thin section. Ca and Al bulk rock compositions in wt%, as calculated assay from modal mineralogy. Area, number of grains and grain size as MD50 (grain size at 50 wt% of cumulative grain size distribution) in µm for zircon (Zrn), monazite (Mnz) and xenotime (Xtm) from automated SEM Spare Phase Lineup (SPL) routine. The monazite grains are in contact with diverse other phases, as biotite (Bt), plagioclase (Pl), quartz (Qtz), apatite (Ap) and ilmenite (Ilm). These microstructural relationships are reported as ternary locking in %. Note high degree of ternary locking of monazite with allanite (Aln) and epidote (Epi) in sample RZ29 with corona structures

From: Electron microprobe petrochronology of monazite-bearing garnet micaschists in the Oetztal-Stubai Complex (Alpeiner Valley, Stubai)

Mineral RZ29 RZ31 RZ33 RZ42
Quartz wt% XMOD 22.51 25.66 25.39 26.63
Albite + K-feldspar 7.47 3.90 9.72 2.21
Plagioclase 2.05 18.27 23.24 5.53
Biotite 1.60 15.55 7.65 4.47
Chlorite 15.10 4.65 6.46 2.89
Muscovite 31.40 23.70 6.11 27.88
Garnet 14.21 4.11 12.71 19.42
Staurolite 0.00 1.96 1.30 6.59
Epidote 2.33 0.49 3.82 0.32
Apatite 0.52 0.27 0.66 0.18
Area (106µm2) 293 173 269 318
Ca bulk wt% calc 1.10 0.89 2.04 0.92
Al bulk wt% calc 10.81 9.94 8.34 11.41
Zircon SPL (µm2) 192,229 116,786 209,182 436,128
Xenotime SPL (µm2) 221 4053 4754 1146
Monazite SPL (µm2) 8306 72,675 34,580 110,212
Zrn grains (SPL) 904 638 1103 1347
Zrn size MD50 (µm) 25 23 22 50
Xtm grains (SPL) 2 38 32 6
Xtm size MD50 (µm) 12 14 22 24
Mnz grains (SPL) 23 292 142 36
Mnz size MD50 (µm) 42 30 22 95
Mnz ternary locking     
Locked in Bt (%) 49.25 37.59 25.14 61.41
Locked in Pl 0.52 27.79 23.65 0.22
Locked in Qtz 6.4 19.04 2.8 2.82
Locked in Aln + Epi 32.63 5.45 18.37 3.91
Locked in Ap 3.07 0.83 2.16 0
Locked in Ilm 0.12 0.38 14.71 3.46
Mnz microstructure Corona Cluster Corona Large
Age ± wght.av. (Ma) 335 ± 4 319 ± 4 320 ± 4 319 ± 3