Publication Date:
2017-04-04
Description:
Using a case study from the island of Elba, Italy, we seek to test the hypothesis that
7 the presence of minerals with low frictional strengths can explain prolonged slip on
8 low-angle normal faults. The central core of the Zuccale low-angle normal fault
9 contains a distinctive fault rock zonation that developed during progressive exhumation.
10 Most fault rock components preserve microstructural evidence for having accommodated
11 deformation entirely, or partly, by frictional mechanisms. One millimeter thick sample
12 powders of all the major fault rock components were deformed in a triaxial deformation
13 apparatus under water-saturated conditions, at room temperature, and at constant effective
14 normal stresses of 25, 50, and 75 MPa. Pore fluid pressure was maintained at 50 MPa
15 throughout. Overall, the coefficient of friction (m) of the fault rocks varies between
16 0.25 and 0.8, emphasizing the marked strength heterogeneity that may exist within
17 natural fault zones. Also, m is strongly dependent on fault rock mineralogy and is
18 〈0.45 for fault rocks containing talc, chlorite, and kaolinite and 〉0.6 for fault rocks
19 dominated by quartz, dolomite, calcite, and amphibole. Localization of frictional slip
20 within talc-rich portions of the fault core can potentially explain movements along the
21 Zuccale fault over a wide range of depths within the upper crust, although the
22 mechanical importance of the talc-bearing fault rocks likely decreased following their
23 dismemberment into a series of poorly connected fault rock lenses. Additionally, slip
24 within clay-bearing fault gouges with m between 0.4 and 0.5 may have facilitated
25 movements in the uppermost (〈2 km) crust. For several other fault rock components,
26 m varies between 0.5 and 0.8, and mineralogical weakening alone is insufficient to
27 account for low-angle slip. In the latter fault rock components, other weakening
28 mechanisms such as the development of high fluid pressures, or dissolution-precipitation
29 creep, may have been particularly important in reducing fault strength.
Description:
In press
Description:
3.3. Geodinamica e struttura dell'interno della Terra
Description:
JCR Journal
Description:
reserved
Keywords:
Friction
;
Low-Angle Normal Faults
;
Experiments
;
Weakening
;
04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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