Thermobarometry of metapelites in the Coast shear zone at Mussel Inlet Dave Pearson

Previous P-T-t work Mostly GASP barometry, garnet-biotite thermometry 2-7.5 kbar, 325°C 8.2 kbar, 620-710°C 8.2+1 kbar, 515-650°C 8.5-11.3 kbar, 570-700°C 6.4 kbar, 600-705°C 6+1 kbar, 600+50°C Mostly GASP barometry, garnet-biotite thermometry Ages generally inferred from U-Pb pluton ages 6.3+1 kbar, 685+50°C Previous P-T-t work Generally 3 metamorphic episodes recognized : >101 Ma, 90-80 Ma, and 75-60 Ma 6+1 kbar 4-4.5 kbar 6.3 kbar 10.2 kbar 5.6+0.4 kbar, 710+30°C 8.1 + 1 kbar, ~600°C 6.4 kbar, 525 ºC ~90-60 Ma 5.6+0.5 kbar, 560+20°C 7.4+1.5 kbar, 750+50 ºC ~70-60 Ma 5.4+1.5 kbar, 726+30 ºC ~90 Ma 6.3+0.8 kbar, 680+30 ºC >101 Ma

Previous P-T-t work (cont.) 2-7.5 kbar, 325°C 8.2 kbar, 620-710°C 8.2+1 kbar, 515-650°C 8.5-11.3 kbar, 570-700°C 6.4 kbar, 600-705°C 6+1 kbar, 600+50°C Rusmore et al. (2005) show continuous metamorphism from 90-60 Ma in Central Gneiss near Douglas Channel 6.3+1 kbar, 685+50°C Previous P-T-t work (cont.) West of CSZ, pressures generally increase toward the east 6+1 kbar 4-4.5 kbar 6.3 kbar 10.2 kbar 5.6+0.4 kbar, 710+30°C 8.1 + 1 kbar, ~600°C 6.4 kbar, 525 ºC ~90-60 Ma 5.6+0.5 kbar, 560+20°C 7.4+1.5 kbar, 750+50 ºC ~70-60 Ma 5.4+1.5 kbar, 726+30 ºC ~90 Ma 6.3+0.8 kbar, 680+30 ºC >101 Ma

My preliminary results from Mussell Inlet So far, 2 samples from Mussell Inlet: GJP-48 and GJP-49 These samples consist of: Qtz+bt+plag+sill+kspar+ms More P-Ts to come I will also do Sm-Nd garnet-whole rock dating of these and more samples

My preliminary results 5.6+0.4 kbar, 710+30°C 6.4 kbar, 525 ºC 8.1 + 1 kbar, ~600°C In Mussell Inlet, probably within CSZ Sillimanite-bearing metapelites (Yukon-Tanana protolith), with relict kyanite in some samples For barometry (GASP), used Holland and Powell (1995) data set calibrations For thermometry (grt-bt), took average of 7 different calibrations 5.4+1.5 kbar, 726+30 ºC 5.6+0.5 kbar, 560+20°C 7.4+1.5 kbar, 750+50 ºC 6.3+0.8 kbar, 680+30 ºC GJP-49: 5.03+0.29 kbar, 660+30oC GJP-48: 4.73+0.24 kbar, 640+10oC

~90-60 Ma ~70-60 Ma ~90 Ma >101 Ma 2-7.5 kbar, 325°C GJP-49: 5.03+0.29 kbar, 660+30oC >101 Ma GJP-48: 4.73+0.24 kbar, 640+10oC

P-T-t references Crawford et al., 1979, Crawford et al., 1987, Stowell, 1989, Himmelberg et al., 1991, 1994, Himmelberg et al., 1995, Taylor et al., 1996, 1997; Stowell and Goldberg, 1997, Klepeis et al., 1998, Lindline, 1999, Stowell and Crawford, 2000, Stowell et al., 2001, Rusmore et al., 2005