T257 Fifty Years of Innovation in Petrology and Orogenic Systems (Posters): A Tribute to Lincoln Hollister

Tuesday, 27 September 2016
9:00 AM - 6:30 PM
Exhibit Hall E/F

PRELIMINARY P-T-TIME MODELS FOR REGIONAL METAMORPHISM IN THE MOUNT WADDINGTON AREA OF THE SOUTHERN COAST MOUNTAINS BATHOLITH, BRITISH COLUMBIA CANADA

Paper number: T257-1
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The Coast Mountains batholith (CMB) is an ideal place to study high-flux events (HFE) because multiple HFE have been identified and metamorphic rocks record deformation and metamorphism above a well-documented Late Cretaceous subduction zone. Driving mechanisms behind HFE are debated; however, one theory suggests that metamorphism in the deeper parts of fold and thrust belts contributes to, if not causes, HFE through metamorphic dehydration and/or partial melting. In this study of the CMB, we present P-T-t paths for metamorphism in order to evaluate the role of metamorphism in HFE.

Preliminary P-T paths for 8 samples from Bute Inlet, the Jewakwa Mountain area, the Mount Waddington area, and the Waddington fold-thrust belt were constructed using THERIAK-DOMINO and garnet compositional isopleths. Observed assemblages include garnet, sillimanite, biotite, quartz, plagioclase, ilmenite, ±staurolite, and ±muscovite, ±clinoamphibole, ±chlorite, ±clinozoisite. Garnet Mn and Fe# zoning for all samples indicate preservation of prograde growth with minimal diffusional resetting. P-T path results indicate that garnet growth began at 4-5 kbar at 550-650°C and continued to peak metamorphic conditions of 5-7 kbar at 600-750°C, with 5 samples reaching peak conditions at ~7 kbar and 3 samples at 5-6 kbar. The predicted peak P-T conditions are similar to previously published thermobarometric estimates in the Waddington fold-thrust belt (5-7 kbar at 675°C) and in the Mount Raleigh area (5.5-6.5 kbar at 675°C). Sillimanite is the only aluminum silicate found in our samples, compatible with similar medium pressure metamorphism throughout the region. The near isothermal pressure increases predicted for the P-T paths are compatible with thrusting and crustal thickening during garnet growth.

Our new peak P-T estimates are similar for all samples, indicating mid-crustal exposures along an ~80 km transect from Bute and Knight inlets eastward to the Waddington fold-thrust belt. Although metamorphic conditions are similar throughout this part of the CMB, two, likely separate, metamorphic events have thus far been identified with garnet Sm-Nd geochronology: 73-71 Ma and 99-90 Ma. Future work will construct new P-T paths, refine existing paths, and evaluate the relationship between metamorphism and the timing and nature of HFE.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-288005

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