Solid Earth (Nov 2024)

The protocataclasite dilemma: in situ <sup>36</sup>Cl and REE-Y lessons from an impure limestone fault scarp at Sparta, Greece

  • B. W. Goodfellow,
  • B. W. Goodfellow,
  • B. W. Goodfellow,
  • B. W. Goodfellow,
  • M. W. Caffee,
  • M. W. Caffee,
  • G. Chmiel,
  • R. Fritzon,
  • R. Fritzon,
  • R. Fritzon,
  • A. Skelton,
  • A. Skelton,
  • A. P. Stroeven,
  • A. P. Stroeven

DOI
https://doi.org/10.5194/se-15-1343-2024
Journal volume & issue
Vol. 15
pp. 1343 – 1363

Abstract

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Reconstructions of palaeoseismicity are useful for understanding and mitigating seismic hazard risks. We apply cosmogenic 36Cl exposure-age dating and measurements of rare-earth elements and yttrium (REE-Y) concentrations to the palaeoseismic history of the Sparta Fault, Greece. Bayesian-inference Markov chain Monte Carlo (MCMC) modelling of 36Cl concentrations along a 7.2 m long vertical profile on the Sparta Fault scarp at Anogia indicate an increase in the average slip rate of the scarp from 0.8–0.9 mm yr−1 6.5–7.7 kyr ago to 1.1–1.2 mm yr−1 up to the devastating 464 BCE earthquake. The average exhumation of the entire scarp up to the present day is 0.7–0.8 mm yr−1. Modelling does not indicate additional exhumation of the Sparta Fault after 464 BCE. The Sparta Fault scarp is composed of fault breccia, containing quartz and clay-lined pores, in addition to host-rock-derived clasts of calcite and microcrystalline calcite cement. The impurities control the distribution of REE-Y in the fault scarp surface and contribute spatial variation to 36Cl concentrations, which precludes the identification of individual earthquakes that have exhumed the Sparta Fault scarp from either of these data sets. REE-Y may illustrate processes that localize slip to a discrete fault plane in the Earth's near-surface, but their potential use in palaeoseismicity would benefit from further evaluation.