T201 From the Micro to Macro in Metamorphic Geology: Constraining Tectono-Metamorphic Processes with High-Resolution Approaches

Thursday, 29 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

A NEW GARNET FRACTIONATION MODELLING TECHNIQUE AND ITS APPLICATION TO THE YUKON-TANANA TERRANE OF NORTH-WESTERN BRITISH COLUMBIA

Paper number: T201-7
Program: Technical Sessions
Time: 2:50 PM – 3:05 PM

Authors

Abstract

We present a study on the metamorphic history of garnet-bearing rocks from the Boundary Ranges and Florence Range suites in the Yukon-Tanana terrane of north-western British Columbia. We developed an inverse modelling technique to estimate the pressure-temperature (P-T) paths experienced by the samples during metamorphism. This model utilizes the 3D distribution of garnet volume in each rock as obtained from X-ray micro-computed tomography and links this with the compositional zoning developed in the largest garnets observed in the samples to estimate the chemical fractionation associated with garnet crystallization. The results from this model are combined with THERIAK-DOMINO modelling (de Capitani & Petrakakis, 2010) and Lu-Hf garnet geochronology to constrain prograde and retrograde P-T points for Early Jurassic metamorphism of these two suites. Our results indicate that the Boundary Ranges suite experienced two garnet growth events at 201.7 ± 2.8 Ma and 192.4 ± 0.4 Ma, respectively, and the later event reached peak conditions of ∼550 °C and 700–800 MPa. The Florence Range suite experienced garnet growth between 190.9 ± 3.3 Ma and 185.3 ± 1.1 Ma along a P-T path that reached a peak P of ∼1000 MPa at ∼620 °C and a peak T of 690–730 °C at 600–750 MPa before cooling to ∼610 °C at ∼670 MPa. The results of these models were verified with the garnet growth software THERIA_G (Gaidies et al., 2008) indicating that our new fractionation technique may serve as an alternative means to estimate the evolution of the thermodynamically effective bulk rock composition during the crystallization of garnet with a complex metamorphic history.

References:

de Capitani C, Petrakakis K (2010) The computation of equilibrium assemblage diagrams with Theriak/Domino software. American Mineralogist 95:1006-1016

Gaidies F, de Capitani C, Abart R (2008) THERIA_G: a software program to numerically model prograde garnet growth. Contributions to Mineralogy and Petrology 155:657-671

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357529

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