Shear heating and clumped isotope reordering in carbonate faults

Shalev Siman-Tov*, Hagit P. Affek, Alan Matthews, Einat Aharonov, Ze'ev Reches

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

Natural faults are expected to heat rapidly during seismic slip and to cool quite quickly after the slip event. Here we examine clumped isotope thermometry for its ability to identify such short duration elevated temperature events along frictionally heated carbonate faults. Our approach is based on measured δ47 values that reflect the distribution of oxygen and carbon isotopes in the calcite lattice, measuring the abundance of 13C18O bonds, which is affected by temperature. We examine three types of calcite rock samples: (1) crushed limestone grains that were rapidly heated and then cooled in static laboratory experiments, simulating the temperature cycle experienced by fault rock during an earthquake slip; (2) limestone samples that were experimentally sheared to simulate earthquake slip events; and (3) samples from Fault Mirrors (FMs) collected from principle slip surfaces of three natural carbonate faults. Extensive FM surfaces are believed to form during earthquake slip. Our experimental results show that δ47 values decrease rapidly (in the course of seconds) with increasing temperature and shear velocity. On the other hand, carbonate shear zones from natural faults do not show such δ47 decrease. We suggest that the δ47 response may be controlled by nano-size grains, the high abundance of defects,and highly stressed/strained grain boundaries within the carbonate fault zone that can reduce the activation energy for diffusion, and thus lead to an increased rate of isotopic disordering during shear experiments. In our laboratory experiments the high stress and strain on grain contacts and the presence of nanograins thus allows for rapid disordering so that a change in δ47 occurs in a very short and relatively low intensity heating events. In natural faults it may also lead to isotopic ordering after the cessation of frictional heating thus erasing the high temperature signature of δ47.

Original languageAmerican English
Pages (from-to)136-145
Number of pages10
JournalEarth and Planetary Science Letters
Volume445
DOIs
StatePublished - 1 Jul 2016

Bibliographical note

Publisher Copyright:
© 2016 Elsevier B.V.

Keywords

  • Calcite
  • Clumped isotope thermometry
  • Diffusion
  • Fault-mirror
  • High-velocity shear
  • Shear heating

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