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also reviewed the application of lineament name in
describing linear features, without any genetic
implication. Sabins (1986) also discussed several
geomorphic and/or tonal features that may give rise to
a lineament.
3.2. Typology of lineaments
A look-over at many papers dealing with lineaments
showed that lineament extraction is just done in a
quantitative sense. This was the point used by Wise
(1982) to criticize the methods of lineament extraction
summarized in his 32 rules. According to Wise (1982),
"it is not the quality of the lines which counts, but rather
their number and their potential for compilation into
artistically pleasing patterns".
Amaro & Strieder (1994) emphasized that any
lineament in images have topographic relief and/or
associated tonal features which are due to the
underground 3D structure in the Earth’s crust. Then,
most of them may be considered topographic high
(positive lineaments), or topographic lows (negative
lineaments), when seen in the lightening direction of the
image. The patterns and the nature of the lineaments
are different according the association of positive,
negative or tonal lineaments. Based in this kind of
differences, Amaro & Strieder (1994) proposed to
distinguish between two types of lineaments: type 1 and
type 2.
3.2.1. Characterization of type 1 lineaments
The type 1 lineaments are associated to regionally
penetrative structures. Such structures develop parallel
positive and negative geomorphologic features,
distributed in linear or curvilinear patterns. Type 1
lineaments can be considered composite lineaments,
because they are also characterized by a tonal banding
related to the lithological component. For the analysis
of this kind of lineament, it is important to evaluate
parameters such as: density, geometric disposition,
azimuthal trend and length. The penetrative ductile
structures present the best geomorphological
expression of this kind of lineament; however, these
lineaments can also characterize sedimentary and/or
volcanic layers slightly folded. They represent the
differential erosion of penetrative structural features
associated to lithology. These lineaments can model
structural forms, like folds and shear zones.
3.2.2. Characterization of type 2 lineaments
The type 2 lineaments are associated to brittle
disjunctive structures. They are mainly topographic
lows (negative lineaments), which cut across
lithological boundaries; this is the case for brittle faults
and fracture zones. However, this type of lineaments
can also develop associated positive and negative
features, sometimes with tonal banding, when regarded
to brittle-ductile fault zones. Type 2 lineaments are
often rectilinear to slightly curvilinear features and
control drainage pattern. Type 2 lineaments may be
analysed through their spatial distribution pattern,
azimuthal trend and length.
175
4. RESULTS AND DISCUSSION
The discrimination of both types of lineaments were
performed in the Porto Nacional (TO) region, through
monoscopic analysis of LANDSAT TM-5 paper images
(color composition 3-4-5). The images are WRS
222/067 and 222/068, obtained at 24/JUL/1991 (EL 41
and 40, AZ 052 and 051, respectively). According to
Moore & Waltz (1983), good lightening elevation to
lineaments analysis is from 35° to 45°. July is the driest
month in the region, what is also good for lineament
extraction.
4.1. Type 1 lineaments analysis
4.1.1 General characteristics: morphology and
geometry
The type 1 lineaments in the Porto Nacional region are
characterized by rectilinear to curvilinear segments, are
fine spaced and have mean length around 1100 m
(figure 1). They are associated to positive and negative
lineaments parallel to a tonal banding.
Type 1 lineaments occur by three different manner in
the SW portion of the area: a) they are part of a
regional pattern of rectilinear and curvilinear segments
disposed in an open regional fold (position 1, fig. 1); 2)
they define a rectilinear to slightly curvilinear zone with
thickness as much as 3700 m (position 2), which
obliterate the lineaments of the position 1; c) they
define a circular to elliptical pattern centered in
position 3, which is rimmed by the lineaments of
position 2. This circular to elliptical structure were also
recognized in position 4, where it is rimmed by
rectilinear zones of positions 8 and S.
The regional folded pattern of position 1 is also
observed in the central-east portion of the mapped area
(position 5). The type 1 lineaments of position 2 extend
NNE to NE toward the central and NE part of the
mapped area, where they define zones of variable
thicknesses (positions 6, 7, 8, 9 e 10).
In the NW part of the area, the type 1 lineaments are
concentrated in another thick zone (4600 m thick) and
are longer than in other similar position (position 11);
this zone extend for than 45 km toward NNE.
In the central part of the area, there are many places
where type 1 lineaments could not be precisely defined,
since this part correspond to the most eroded one.
4.1.2. Discussion and interpretation
The interpretation of the nature of different type 1
lineaments recognized in the Porto Nacional region was
proceeded through field works dealing with structural
geology.
Type 1 lineament pattern in the positions 1 and 5
characterizes regional Fn+2 folds developed upon NMS
rocks. Then, the lineaments themselves are the
geomorphic results of erosion upon S,//Sh+1 foliations.
The regional Fn+2 folds are obliterated by shear zones in
the positions 6, 8, 9 and 10; then, the lineament in
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
