Publication: Geological, geophysical and geochemical structure
of a fault zone developed in granitic rocks: Implications
for fault zone modeling in 3-D
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Publication Date
2004
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Springer Science Business Media
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Abstract
The structure of a fault zone developed in
granitic rocks can be established on the basis of the spatial
variability of geological, geophysical and geochemical
parameters. In the North Fault of the Mina Ratones area
(SW Iberian Massif, Spain), fault rocks along two studied
traverses (SR-2 and SR-3 boreholes) exhibit systematic
changes in mineralogy, geochemistry, fabrics and microstructures
that are related to brittle deformation and
alteration of granite to form cataclasite and subsequent
gouge. The spatial distribution and intensity of these
changes suggest a North Fault morphology that is
consistent with the fault-core/damage-zone model proposed
by Chester et al. (1993) to describe a fault zone
architecture. North Fault damage zone thickness can be
defined by the development of mechanically related
mesoscopic faults and joints, that produce a Fracture
Index (FI)>10. High FI values are spatially correlated
with relative low seismic velocity zones (VP<5 km/s and
VS<2.5 km/s in the well-logs), more probably related to a
high concentration of fractures and geochemical alteration
produced by meteoric water-granite interaction along
fault surfaces. This correlation is the base of a geostatistical
model proposed in the final part of this study to
image the fault zone architecture of a granitic massif.