Age constraints on faulting and fault reactivation: a multi-chronological approach

Abstract

Movement within the Earth's upper crust is commonly accommodated by faults or shear zones, ranging in scale from micro-displacements to regional tectonic lineaments. Since faults are active on different time scales and can be repeatedly reactivated, their displacement chronology is difficult to reconstruct. This study represents a multi-geochronological approach to unravel the evolution of an intracontinental fault zone locality along the Danube Fault, central Europe. At the investigated fault locality, ancient motion has produced a cataclastic deformation zone in which the cataclastic material was subjected to hydrothermal alteration and K-feldspar was almost completely replaced by illite and other phyllosilicates. Five different geochronological techniques (zircon Pb-evaporation, K-Ar and Rb-Sr illite, apatite fission track and fluorite (U-Th)/He) have been applied to explore the temporal fault activity. The upper time limit for initiation of faulting is constrained by the crystallization age of the primary rock type (known as ''Kristallgranit'') at 325 ± 7 Ma, whereas the K-Ar and Rb-Sr ages of two illite fractions \2 lm (266-255 Ma) are interpreted to date fluid infiltration events during the final stage of the cataclastic deformation period. During this time, the ''Kristallgranit'' was already at or near the Earth's surface as indicated by the sedimentary record and thermal modelling results of apatite fission track data. (U-Th)/He thermochronology of two single fluorite grains from a fluorite-quartz vein within the fault zone yield Cretaceous ages that clearly postdate their Late-Variscan mineralization age. We propose that later reactivation of the fault caused loss of helium in the fluorites. This assertion is supported by geological evidence, i.e. offsets of Jurassic and Cretaceous sediments along the fault and apatite fission track thermal modelling results are consistent with the prevalence of elevated temperatures (50-80°C) in the fault zone during the Cretaceous.

Polyphase movement on the Lavanttal Fault Zone (Eastern Alps): reconciling the evidence from different geochronological indicators

“…Bigot-Cormier et al 2006;Malusá et al 2005Malusá et al , 2006Wölfler et al 2008); (c) correlation among fault-rock types, deformation mechanisms, hydrothermal regimes and low-temperature geochronometers (Malusá et al 2009); (d) thermochronological analyses of low-temperature systems at short distance across fault zones (Murakami et al 2002;Tagami and Murakami 2007); (e) combination of some of these approaches (Siebel et al 2010). In this work, we will follow the approach that near-surface brittle faulting may lead to thermal anomalies by infiltration of hydrothermal fluids or frictional heating (e.g., Maddock 1983;d'Alessio et al 2003;Otsuki et al 2003;Wölfler et al 2010).…”

Repeated hydrothermal quartz crystallization and cataclasis in the Bavarian Pfahl shear zone (Germany)

“…Later deformation along the Pfahl shear zone took place in the late Cretaceous to Paleocene during reactivation of the south-western Bohemian border zone (Schr€ oder et al, 1997), evidenced by Upper Cretaceous SW-directed thrusting along the northern extension of the Pfahl zone in Mesozoic rocks of the South German Basin near Amberg (Gudden, 1956) (Fig. 1), along Danube (Siebel et al, 2010) and the Rodl shear zones (Brandmayr et al, 1995).…”

Post-Caledonian brittle deformation in the Bergen area, West Norway: results from K–Ar illite fault gouge dating

“…Illite is one of these newly grown minerals, and since illite fixes potassium in its crystal structure and can retain the radiogenic daughter product argon over many millions of years, it is amenable to radiometric dating by the K-Ar or Ar-Ar method (e.g., review by Clauer, 2013). Depending on the mineralogy of the host rock and availability and chemistry of fluids, illite can grow by illitisation of smectite or dissolution and reprecipitation of pre-existing clays (in clay-bearing host rocks; e.g., Vrolijk & van der Pluijm, 1999;Solum et al, 2005;Haines & van der Pluijm, 2008), by retrograde hydration reactions of feldspar and mica (mainly in crystalline host rocks; e.g., Zwingmann & Mancktelow, 2004;Siebel et al, 2010;Zwingmann et al, 2010b) or even by direct neocrystallisation from a fluid phase. The growth of illite during fault activity is promoted by a number of factors, including temperature (frictional heating and advective heating by hydrothermal fluids), grain comminution (increased surface area), strain (increase of crystal defects) and changes in fluid composition (mainly availability of potassium) and fluid/rock ratio (Vrolijk & van der Pluijm, 1999;Yan et al, 2001).…”