Economic and Environmental Geology

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Table. 1.

Table. 1.

Summary of microstructures and deformation conditions from the biotite gneiss and Gamaksan metasyenite samples in the Munsan area of the Imjingang Belt

Rock Sample# Classification Microstructures Deformation conditions
Quartz Feldspar Quartz Feldspar
Biotite gneiss IM952 mylonite undulose extinction, subgrain, quartz ribbon (Fig. 5a) deformation twinning, subgrain, marginal recryst. (Fig. 5a) 300 - 400°C Lower greenschist facies 450 - 600°C Amphibolite facies
IM961 mylonite undulose extinction, grain boundary migration, recryst. (Fig. 5b) subgrain, marginal recryst., transgranular fracture (Fig. 5b) 300 - 500°C Greenschist facies 450 - 600°C Amphibolite facies
IM777 mylonite undulose extinction, grain boundary migration, recryst., ECC (Fig. 5c) subgrain, marginal recryst., intracrystalline fracture (Fig. 5c) 300 - 500°C Greenschist facies 450 - 600°C Amphibolite facies
IM871 (annealed) mylonite recryst. (Fig. 5d) deformation twinning (Fig. 5d) 300 - 400°C Lower greenschist facies 300 - 400°C Lower greenschist facies
Gamaksan metasyenite IM843 protomylonite undulose extinction, recryst. (Fig. 5e) intracrystalline fracture (Fig. 5e) 300 - 400°C Lower greenschist facies 300 - 400°C Lower greenschist facies
IM775 protomylonite undulose extinction, grain boundary migration, recryst, basal <a> slip (Fig. 5f) sericitization (Fig. 5f) 300 - 500oC Greenschist facies
IM831 mylonite recryst., subgrain (Fig. 5g) subgrain, patchy extinction, marginal recryst., intracrystalline fracture, intergranular fracture (Fig. 5g) 300 - 400°C Lower greenschist facies 300 - 600°C Greenschist to amphibolite facies
IM948 mylonite undulose extinction, grain boundary migration, recryst. (Fig. 5h) subgrain, patchy extinction, deformation twinning, kink twinning (Fig. 5h) 300 - 500°C Greenschist facies 300 - 600°C Greenschist to amphibolite facies

References: deformaion conditions are from Debat et al. (1978), Mitra (1978), Hanmer (1982), Simpson (1985), Behrmann and Mainprice (1987), Tullis and Yund (1987), Bell and Johnson (1989), Hirth and Tullis (1992), and Stipp et al. (2002a, b). Abbreviation: recryst.-recrystallization, ECC-ExtensionalCrenulationCleavage

Econ. Environ. Geol. 2021;54:271-83 https://doi.org/10.9719/EEG.2021.54.2.271
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