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| Titel |
Frictional properties of mylonite from Longmenshan fault zone under hydrothermal conditions |
| VerfasserIn |
Lei Zhang, Changrong He |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095738
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| Publikation (Nr.) |
 EGU/EGU2014-11206.pdf |
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| Zusammenfassung |
| To investigate the frictional sliding behavior of typical fault rocks as related to dynamics of
faulting under different temperature and pressure conditions, we collected phyllosilicate-rich
mylonite (~60wt.% phyllosilicates which are mainly chlorite and muscovite) from a ductile
thrust zone along Gengda-Wenmao fault of Longmenshan fault zone and conducted
frictional sliding experiments under hydrothermal conditions. The experiments were
conducted under elevated temperatures in the range of 100oC-600oC and effective
normal stress of 200MPa and 300MPa to represent the deep portion conditions
(elevated temperature and pressure) of the fault zone. In order to obtain velocity
dependence of friction, shearing rates were stepped up and down in the range of
0.0488μm/s-6.1μm/s.
In our experiments, the frictional coefficient of mylonite exhibits systematic increase with
increasing temperature (100oC-600oC). The frictional behavior of mylonite shows a
transition from initial velocity-strengthening behavior to velocity-weakening behavior
at about 300oC, and then transitions back to velocity-strengthening behavior as
temperature is elevated. The velocity dependence of mylonite also shows strong
pressure sensitivity. When the effective normal stress is increased to 300MPa, the
stable frictional behavior is significantly enhanced with larger (a - b) compared to
that under the lower pressure condition. The transition from velocity weakening
to velocity strengthening frictional behavior may be controlled by competition
between pressure-solution healing and dilation weakening processes in the mylonite
gouge.
In the framework of rate and state friction constitutive law, the effects of frictional
properties of mylonite on faulting dynamics are discussed. From our experimental results of
mylonite, unstable slip events may nucleate in mylonite gouge under 250oC -550oC
temperature conditions at 200MPa effective normal stress, and transitional behavior is found
at 600oC which is rate dependent. At 300MPa effective normal stress, the temperature
condition for the nucleation of unstable slip events is constrained to 260oC -320oC
(corresponding to 15-19km depth of Longmenshan fault zone), and rate dependent,
transitional behavior is found at 400oC. For velocity-strengthening cases, a large loading
disturbance from neighbouring area may cause triggered slip events at the corresponding
depth. |
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