Article

Quasi-equilibrium melting of quartzite upon extreme friction

  • Nature Geoscience volume 10, pages 436441 (2017)
  • doi:10.1038/ngeo2951
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Abstract

The friction on fault planes that controls how rocks slide during earthquakes decreases significantly as a result of complex fault-lubrication processes involving frictional melting. Fault friction has been characterized in terms of the preferential melting of minerals with low melting points—so-called disequilibrium melting. Quartz, which has a high melting temperature of about 1,726 °C and is a major component of crustal rocks, is not expected to melt often during seismic slip. Here we use high-velocity friction experiments on quartzite to show that quartz can melt at temperatures of 1,350 to 1,500 °C. This implies that quartz within a fault plane undergoing rapid friction sliding could melt at substantially lower temperatures than expected. We suggest that depression of the melting temperature is caused by the preferential melting of ultra-fine particles and metastable melting of β-quartz at about 1,400 °C during extreme frictional slip. The results for quartzite are applicable to complex rocks because of the observed prevalence of dynamic grain fragmentation, the preferential melting of smaller grains and the kinetic preference of β-quartz formation during frictional sliding. We postulate that frictional melting of quartz on a fault plane at temperatures substantially below the melting temperature could facilitate slip-weakening and lead to large earthquakes.

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Acknowledgements

This work was supported by the National Research Foundation (NRF), Korea to S.K.L. (2014-053-046), by the Korea Meteorological Administration Research and Development Program to R.H. (KMIPA 2015-7050), by the NRF, Korea to G.Y.J. (2011-0028597) and by JSPS KAKENHI to T.H. (16H04064). We are grateful for helpful comments by Y. Wang. We thank K. Oohashi for his help in one of the experiments and J. O. Jeong for his technical assistance in EPMA and SEM analyses. We are grateful for careful and constructive suggestions by M. Bestmann and M. Violay, which greatly improved the manuscript’s quality and clarity.

Author information

Author notes

    • Sung Keun Lee
    •  & Raehee Han

    These authors contributed equally to this work.

Affiliations

  1. School of Earth and Environmental Sciences, Seoul National University, Seoul 151-742, Korea

    • Sung Keun Lee
    • , Eun Jeong Kim
    •  & Hoon Khim
  2. Department of Geology and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, Korea

    • Raehee Han
  3. Department of Earth and Environmental Sciences, Andong National University, Andong 36729, Korea

    • Gi Young Jeong
  4. Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Kochi 783-8502, Japan

    • Takehiro Hirose

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Contributions

S.K.L. and R.H. developed the project. S.K.L. wrote the manuscript and developed the frictional melting model. R.H. wrote the section describing mechanical data and temperature measurements. R.H. and T.H. performed the rotary-shear experiment and temperature analyses. R.H. performed the SEM-EDS/EPMA analyses. G.Y.J. performed the TEM analyses. S.K.L., E.J.K. and H.K. performed the NMR, Raman and XRD experiments; S.K.L. and E.J.K. analysed the data. All authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Sung Keun Lee.

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