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\begin{document}

\title{Frictional Properties of Feldspar-chlorite Altered Gouges and
Implications for Fault Reactivation in Hydrothermal Systems}



\author[1]{Zijuan Hu}%
\author[2]{Chongyuan Zhang}%
\author[3]{Lei Zhang}%
\author[4]{Derek Elsworth}%
\author[5]{Quan Gan}%
\author[3]{Huiru Lei}%
\author[6]{Man-chao He}%
\author[7]{Leihua Yao}%
\affil[1]{School of Engineering and Technology, China University of Geosciences (Beijing)}%
\affil[2]{Institute of Geomechanics, Chinese Academy of Geological Sciences}%
\affil[3]{Institute of Geology, China Earthquake Administration}%
\affil[4]{Pennsylvania State University}%
\affil[5]{State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University}%
\affil[6]{China University of Mining and Technology (Beijing)}%
\affil[7]{China University of Geosciences, Beijing}%


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  \date{May 17, 2024}


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\begin{abstract}
As a particularly common minerals in granites, the presence of feldspar
and altered feldspar-chlorite gouges at hydrothermal conditions have
important implications in fault strength and reactivation. We present
laboratory observations of frictional strength and stability of feldspar
(K-feldspar and albite) and altered feldspar-chlorite gouges under
conditions representative of deep geothermal reservoirs to evaluate the
impact on fault stability. Velocity- stepping experiments are performed
at a confining stress of 95 MPa, pore pressures of 35-90 MPa and
temperatures of 120-400\selectlanguage{ngerman}°C representative of in situ conditions for such
reservoirs. Our experiment results show that the feldspar gouge is
frictionally strong (\selectlanguage{greek}μ\selectlanguage{english}\textasciitilde{}0.71) at all experimental
temperatures (\textasciitilde{}120-400) but transits from
velocity-strengthening to velocity-weakening at T\textgreater{}120\selectlanguage{ngerman}°C.
Increasing the pore pressure increases the friction coefficient
(\textasciitilde{}0.70-0.87) and the gouge remains velocity weakening,
but this weakening decreases as pore pressures increase. The presence of
alteration-sourced chlorite leads to a transition from velocity
weakening to velocity strengthening in the mixed gouge at experimental
temperatures and pore pressures. As a ubiquitous mineral in reservoir
rocks, feldspar is shown to potentially contribute to unstable sliding
over ranges in temperature and pressure typical in deep hydrothermal
reservoirs. These findings emphasize that feldspar minerals may increase
the potential for injection-induced seismicity on pre-existing faults if
devoid of chlorite alteration.%
\end{abstract}\selectlanguage{ngerman}%



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