GSA Data Repository 2018157 Papa et al., 2018, The fate of garnet during (deep-seated) coseismic frictional heating: The role of thermal shock: Geology, https://doi.org/10.1130/G40077.1 ITEM DR1 - Microstructures of Mont Mary pseudotachylytes

Figure caption: (A) clouds of fine grained fragmented quartz (black), within the pseudotachylyte matrix, still locally surrounding larger clasts. B) In-situ fragmented garnet (lower part of the image) at the boundary of a garnet-free pseudotachylyte vein embedding abundant small clasts of quartz and sillimanite (black grains). C) Clast of plagioclase in the foliated matrix of a ductilely sheared pseudotachylyte showing clasts of sillimanite and quartz stretched into the foliation. D) Sillimanite clasts in a foliated pseudotachylyte. E) Foliation-parallel fault vein (fv) and injection veins (iv) of pseudotachylyte overprinting the amphibolite facies foliation of the quartz-biotite-plagioclase-garnet-sillimanite metapelite mylonite. The mylonite is disrupted by a network of micro-fractures (not crosscutting the pseudotachylyte) and is included as lithic clasts in the fault vein. F) In-situ fractured garnet from the wall rock of the pseudotachylyte injection vein. Note the absence of garnet clasts within the vein as in (B). All photographs are SEM backscattered images except (E) (optical image; plane parallel light). All samples were collected in the Mont Mary nappe (Western Alps) – outcrop coordinates: 45.80 N, 7.41E

ITEM DR2 - EDS element maps of garnet

Figure caption: (A) BSE image of a garnet clast within the pseudotachylyte matrix showing a bright overgrowth rim. (B)-(D) EDS element maps of the area in (A) for Mn (B), Mg (C), and Fe (D). The elements maps show that the garnet rim is characterized by an enrichment in Mn and depletion in Mg and Fe. EDS analysis indicates that Mn varies from 1-2 weight % in the core of the garnet clast, to as much as 5 weight % in the rim.

10 μm Mn

A B

Mg Fe

DC

ITEM DR3 - Isochors of rock-forming minerals for the relevant temperature range of 500-1200 °C

Isochors of (A) almandine garnet, (B) An37 plagioclase, (C) sillimanite, and (D) quartz. The black lines are isochors drawn at 0.2 GPa intervals at 0 °C. The green line is an isochor passing through the estimated initial conditions of 0.35 GPa at 500 °C. The two grey circles illustrate how to calculate the thermal pressure due to heating at constant volume (i.e. zero strain of a completely constrained mineral). If the original conditions are 500 °C and 0.35 GPa, then shock heating to 1200 °C with no volume change raises the pressure along the isochor to about 3.15 GPa for garnet. The thermally-induced pressure change is thus 2.8 GPa. For the same starting point the thermal pressure generated by shock heating to 1200 °C at constant volume for An37 plagioclase is only 1.0 GPa, much less than garnet, because the isochors are shallower (primarily because plagioclase is much softer than garnet). The isochors of sillimanite have steeper slopes than those of plagioclase, primarily because sillimanite has a significantly higher bulk modulus. The isochors of quartz are steeper than feldspar, but less steep than garnet, but the isochors are flat in quartz because its thermal expansion is almost zero. As a consequence, the thermal pressure for shock heating is 2.1 GPa for our example.  

A

C

B

D

Data sources are listed in detail in Item DR3.

ITEM DR4 - Complete list of input thermo-elastic parameters and source references

TABLE DR3. MINERAL PROPERTIES USED FOR CALCULATIONS

Property Almandine An37 plagioclase Quartz Sillimanite

Room T, room p

Kc (MPa m1/2) 1.31(1) 0.75(1) 1.50(2) 1.60(2)

(Kg m-3) 4318(3) 2700(3) 2650(3) 3250(3)

500°C, room p

k (W m-1 K-1) 1.58* 1.60(4) 3.05(5) 3.64†(6)

(m2 s-1 x 10-6) 0.68(7) 0.54§ 0.98§ 1.17§

Cp (J mol-1 K-1) 463(8) 1100(7) 1180(7) 1130(7)

500°C, 0.35 GPa

KT (GPa) 163.9(9) 67.0(10,11,12) 30.1(13) 160.4(14)

V (K-1 x 10-5) 2.44(9) 2.13(10,11,12) 6.81(13) 1.48(14)

pth to 1200°C (GPa) 2.83# 1.02# 2.12# 1.70#

* Calculated from diffusivity (. † Data of k at 500°C are not available for sillimanite. k decreases with increasing T in silicates (except for feldspars). We consider a decrease of 60% from room temperature to 500°C, similar to those of garnet and quartz. § Calculated from conductivity (k). # Calculations performed with EosFit7c15. (1-15) Source references: see list below    1. Tromans, D., and Meech, J. A., 2002, Fracture toughness and surface energies of minerals:

theoretical estimates for oxides, sulphides, silicates and halides: Minerals Engineering, v. 15, p. 1027-1041.

2. Whitney, D. L., Broz, M., and Cook, R. F., 2007, Hardness, toughness, and modulus of some common metamorphic minerals: American Mineralogist, v. 92, p. 281-288.

3. Deer, W.A., Howie, R.A., Zussman, J., 1992, An introduction to the rock forming minerals. Second Edition: Longman Group UK Limited, London.

4. Birch, A. F., and Clark, H., 1940, The thermal conductivity of rocks and its dependence upon temperature and composition: American Journal of Science, v. 238, p. 529-558.

5. Kanamori, H., Fujii, N., and Mizutani, H., 1968, Thermal diffusivity measurement of rock‐forming minerals from 300 to 1100 K: Journal of geophysical research, v. 73, p. 595-605.

6. Horai, K. I. (1971). Thermal conductivity of rock‐forming minerals: Journal of Geophysical Research, v. 76, p. 1278-1308.

7. Robie, R. A., and Waldbaum, D. R., 1968, Thermodynamic Properties of Minerals and Related Substances at 298.15° K (25.0° C) and One Atmosphere (1013 Bars) Pressure and at Higher Temperatures: U.S. Geological Survey Bulletin, v. 1259, p. 256.

8. Bosenick, A., Geiger, C. A., and Cemič, L., 1996, Heat capacity measurements of synthetic pyrope-grossular garnets between 320 and 1000 K by differential scanning calorimetry: Geochimica et Cosmochimica Acta, v. 60, p. 3215-3227.

9. Milani, S., Nestola, F., Alvaro, M., Pasqual, D., Mazzucchelli M. L., Domeneghetti, M. C., and Geiger, C., 2015, Diamond–garnet geobarometry: The role of garnet compressibility and expansivity: Lithos, v. 227, p. 140-147.

10. Johnson, E., 2007, The Elastic Behavior of Plagioclase Feldspar at High Pressure [MSc thesis]: Blacksburg VA, Virginia Polytechnic Institute and State University, 115 p.

11. Tribaudino, M., Angel, R. J., Camara, F., Nestola, F., Pasqual, D., and Margiolaki, I., 2010, Thermal expansion of plagioclase feldspars: Contributions to Mineralogy and Petrology, v. 160, p. 899-908.

12. Tribaudino, M., Bruno, M., Nestola, F., Pasqual, D., and Angel, R. J., 2011, Thermoelastic and thermodynamic properties of plagioclase feldspars from thermal expansion measurements: American Mineralogist, v. 96, p. 992-1002.

13. Angel, R. J., Alvaro, M., Miletich, R., and Nestola, F., 2017, A simple and generalised P–T–V EoS for continuous phase transitions, implemented in EosFit and applied to quartz: Contributions to Mineralogy and Petrology, v. 172, p. 29.

14. Holland, T. J. B., and Powell, R., 2011, An improved and extended internally consistent thermodynamic dataset for phases of petrological interest, involving a new equation of state for solids: Journal of Metamorphic Geology, v. 29, p. 333-383.

15. Angel, R. J., Gonzalez-Platas, J., and Alvaro, M., 2014, EosFit-7c and a Fortran module (library) for equation of state calculations: Zeitschrift für Kristallographie, v. 229, p. 405-419.