Organic thermal maturity as a proxy for frictional fault heating: Experimental constraints on methylphenanthrene kinetics at earthquake timescales

Abstract

Biomarker thermal maturity is widely used to study burial heating of sediments over millions of years. Heating over short timescales such as during earthquakes should also result in measurable increases in biomarker thermal maturity. However, the sensitivity of biomarker thermal maturity reactions to short, higher-temperature heating has not been established. We report on hydrous pyrolysis experiments that determine the kinetic parameters of methylphenanthrene maturation at timescales and temperatures relevant to earthquake heating. Samples of Woodford Shale were heated at temperatures up to 343°C over 15-150 min. The thermal maturity of the samples as measured by the methylphenanthrene index-1 (MPI-1) increased with heating time and temperature. We find that MPI-1 increases with time and temperature consistent with a first-order kinetic model and Arrhenius temperature relationship. Over the timescales tested here, MPI-1 is strongly affected by maximum temperature and less sensitive to heating duration. Production of new phenanthrene isomers and expulsion of a liquid pyrolyzate also occurred. Differential expulsion of methylphenanthrene isomers affected the apparent maturity of the rock at lower temperatures and may need to be considered for organic-rich fault rocks. Our results demonstrate that the overall MPI-1 reaction extent in both the rock and pyrolyzate are a useful measure of thermal maturity and reflect temperature history during rapid heating.

Earthquake slip surfaces identified by biomarker thermal maturity within the 2011 Tohoku-Oki earthquake fault zone

“…We use these concentrations to calculate the n-alkane parameters used in the analysis (Supplementary Data 2). The CPI is calculated by dividing the summed concentrations of odd chain-length n-alkanes by the summed concentrations of even chain-length n-alkanes between chain lengths of 26-35 (ΣC odd,27-35 /ΣC even, [26][27][28][29][30][31][32][33][34] ). The ADI, defined by Rabinowitz et al 33 , is calculated as (C 27 + C 31 )/(C 28 + C 29 + C 30 ).…”

Paleoseismic Slip Records and Uplift of the Longmen Shan, Eastern Tibetan Plateau

“…Recent studies of fault rocks have revealed that a range of reaction products can be considered as seismic slip signatures, such as frictional devolatilization of carbonates (Collettini et al, ; Han et al, ; Rowe, Fagereng, et al, ) and hydrous silicates (Collettini et al, ; Lockner et al, ; Sheppard et al, ), trace element mobility (Ishikawa et al, ), maturation of organic material (Savage et al, ; Sheppard et al, ), fault mirrors (Kirkpatrick et al, ; McDermott et al, ; Siman‐Tov et al, , ; Viti et al, ), fluidized granular flow (Kirkpatrick & Shipton, ; Meneghini et al, ), clast‐cortex aggregates (Boullier et al, ; Boutareaud et al, , ), and amorphous material (Kirkpatrick et al, ). In addition, features formed under extreme transient stress conditions associated with the propagating tip of an earthquake rupture, such as injection veins (Rowe, Kirkpatrick, et al, ), pulverization (Mitchell et al, ), and fault breccias (Melosh et al, ), can also be preserved in rocks as seismic records (Rowe & Griffith, ).…”

Seismic heating signatures in the Japan Trench subduction plate-boundary fault zone: evidence from a preliminary rock magnetic ‘geothermometer’

“…• C (Polissar et al 2011;Sheppard et al 2015). For a meaningful application, the fault and the surrounding rock should have the same original hydrocarbon population before the slip event(s) (Savage et al 2014).…”