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www.elsevier.com/locate/jappgeo
Journal of Applied Geophysics 55 (2004) 239–248
GPR exploration for groundwater in a crystalline rock terrain
Jandyr de Menezes Travassosa,1, Paulo de Tarso Luiz Menezesb,*
aCNPq-Observatorio Nacional, Rua General Jose Cristino 77, 20921-400, Rio de Janeiro, BrazilbGEFEX/FGEL/UERJ, Rua Sao Francisco Xavier 524-4006A, 20550-013, Rio de Janeiro, Brazil
Received 21 October 2002; accepted 19 January 2004
Abstract
The Ground Penetrating Radar (GPR) method has been extensively used to map shallow subsurface features. Such kind of
information is very important for different types of studies, ranging from archaeological to groundwater search. Almost all GPR
surveys for groundwater exploration are usually conducted in sedimentary terrains. In this paper, we demonstrate the
applicability of the GPR method in the exploration of underground water in a crystalline terrain. An example of fixed offset data
collected at one known spring in the district of Petropolis (Brazil) is given. Common Mid Point (CMP) data were also collected
to estimate the velocity of the radar waves. The saturated region is clearly outlined in the GPR section as a zone of attenuation
and inversion of the wavelet phase polarity.
D 2004 Elsevier B.V. All rights reserved.
Keywords: GPR; Groundwater; Crystalline rocks; Geophysical prospecting
1. Introduction The available data indicates that the majority of the
Fresh water is a valuable resource for human
needs, specially in Brazil, which has a large portion
of its territory affected by a semiarid climate, and
where droughts are frequent events. To supply the
great demand, the Brazilian market for mineral water
has increased in the last few years at a rate of 3% per
year (DNPM, 1997). The main producing regions are
located in the southeastern part of the country (Fig.
1a) in the States of Sao Paulo, Minas Gerais and Rio
de Janeiro (Martins et al., 1997).
0926-9851/$ - see front matter D 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jappgeo.2004.01.001
* Corresponding author. Tel./fax: +55-21-587-7598.
E-mail addresses: [email protected] (J. de Menezes Travassos),
[email protected] (P. de Tarso Luiz Menezes).1 Tel.: +55-21-5807081; fax: +55-21-5853782.
Brazilian groundwater resources are located in faults
and fractures in crystalline rock (DNPM, 1997). It is
important to mention here that about 60% of the
Brazilian territory, or about 4,600,000 km2, consists
of crystalline rocks. This indicates the great potential
for mineral water exploration in this type of terrain.
Traditionally, electrical and electromagnetic meth-
ods are the most popular geophysical tools for
groundwater exploration in crystalline rocks (Meju,
2002, and references therein). The Ground Penetrating
Radar (GPR) method has been used extensively in
hydrogeological exploration (Van Overmeeren, 1994;
Beres and Haeni, 1991) and soil studies (Aranha et al.,
2002). In particular, it has demonstrated its effective-
ness in mapping aquifers in sedimentary rocks (Car-
dimona et al., 1998). As far as we are aware, however,
the literature provides no example of the GPR method
Fig. 1. (a) Map of Brazil with the main producing States (Minas Gerais (MG), Sao Paulo (SP) and Rio de Janeiro (RJ) in the figure). (b)
Location of the studied spring (black square in the center portion of the map) superimposed on a geologic map of the region (DNPM, 1998).
Sr—Serra dos Orgaos Batholith. Prn—Rio Negro Complex.
J. de Menezes Travassos, P. de Tarso Luiz Menezes / Journal of Applied Geophysics 55 (2004) 239–248240
being used for groundwater exploration in crystalline
rocks. The imaging of 3D subsurface structures, as
fractured reservoirs in crystalline environment, pres-
ent a higher complexity than the interpretation of the
traditional horizontal/sub-horizontal reflector of the
water bearing level at sedimentary terrains. A similar
situation occurs with the seismic method, that is
widely used for exploring sedimentary basins, but
still not for mineral and groundwater exploration in
complex terrains. Recent advances in seismic imaging
are overcoming these difficulties (Berrer et al., 2000;
Drumond et al., 2000).
In the present work, we demonstrate that the GPR
method can be highly effective in the groundwater
exploration in crystalline rocks. A case study at a
known spring is presented.
2. Geological setting
The studied area is located within the district of
Petropolis in the State of Rio de Janeiro (Fig. 1b). The
topography is uneven being on the scarp of Serra do
Mar chain of mountains, reaching an altitude of 2000
J. de Menezes Travassos, P. de Tarso Luiz Menezes / Journal of Applied Geophysics 55 (2004) 239–248 241
m. The formation of the relief is related to Gondwana
break-up, which began in Middle Cretaceous, with a
strong increment at the Early Tertiary (Tupinamba et
al., 2000).
The main tectonic unit of the region is the Serra dos
Orgaos batholith (see Fig. 1b). That batholith is made
up of granite and gneiss with a granitic and granodio-
ritic composition. The surrounding rocks belong to the
Rio Negro Complex, an assemblage of migmatites,
gneisses, gneiss-schist with interleaved quartzite layers
(paragneiss). The main rock types in the area are the
migmatites and high grade metamorphosed (Amphib-
olite facies) gneiss-schist, both classified as the Santo
Aleixo Unit (DNPM, 1998). Themigmatites frequently
exhibit estromatic, flebitic and schollen structures and
are mainly composed of biotite–hornblende gneiss/
amphibolite with interleaved pegmatite layers. The
gneiss frequently exhibit structures and foliations in
anti-form and syn-form with two independent folding
phases. Due to the high metamorphism and intense
folding it is very difficult to observe S0 (original sedi-
mentary bedding). Low-angle dipping metamorphic
foliation and several NW shear zones are also charac-
teristic in the studied region (Tupinamba et al., 2000).
Fig. 2 shows a migmatite outcrop of Santo Aleixo
Unit in a nearby quarry. The hammer is positioned
over a small leucossome boudin structure within a
mafic layer. At the left corner of the picture a
stromatic migmatitic structure, characterized by inter-
calation of felsic and mafic layers, is dominant. These
Fig. 2. Banded leucossome boudin (indicated by the hammer
position) in a migmatite of Santo Aleixo Unit. A stromatic migmatite
structure dominate in the left corner of the photo. These structures are
typical of Santo Aleixo Unit (courtesy of Miguel Tupinamba).
structures are very common in the studied region and
occurs at all size scales, from centimeters to tens of
meters. The occurrence of mineral water in the area is
usually associated with zones of fractures in the
banded and folded migmatite and paragneiss of the
Santo Aleixo Unit (Fig. 2). The reader can find several
examples of structures and rocks of Rio Negro Com-
plex and Serra dos Orgaos batholith elsewhere in the
literature (Tupinamba et al., 2000).
3. Hydrogeological setting
The hydrogeological knowledge of Rio de Janeiro
State is still not well established. At the whole state the
government has only 527 producing wells registered.
In a first attempt to characterize the hydrogeological
potential, CPRM (Brazilian Geological Survey) recent-
ly published the hydrogeological map of Rio de Janeiro
State in the 1:500,000 scale (Barreto et al., 2000). This
regional study was based on a multi-criteria analysis
integrated in a Geographic Information System (GIS).
The main parameters analyzed, in descending impor-
tance order, were: slope, fracture density (interpreted
from LANDSAT-TM images), soil type, soil manage-
ment, lithology and drainage density. The employed
methodology was partially based on the work devel-
oped by Lanvegin et al. (1991) when studying a
fractured granite in France.
Two mains aquifers systems, sedimentary and
crystalline, were identified by Barreto et al. (2000).
In the crystalline system, our target, groundwater
circulate through fractures and fissures. The storage
capacity of a crystalline aquifer is related to the
number and connectivity of fractures. Therefore, one
of the most important parameter to analyze is the
fracture density. This parameter is defined as the total
length (L) of the existing fractures at an area (L2)
divided by this area (L/L2). Five density ranges were
defined by Barreto et al. (2000), from the lowest to
highest, they are (in km/km2): 0–0.36; 0.36–0.72;
0.72–1.08; 1.08–1.44; >1.44.
The district of Petropolis is located in an area of
high fracture density range (1.08–1.44), therefore
being a high favorably area for groundwater occur-
rence. Indeed, just one mineral water company in-
stalled in that district, is responsible for about 27% of
the production of mineral water of Rio de Janeiro
J. de Menezes Travassos, P. de Tarso Luiz Menezes / Journal of Applied Geophysics 55 (2004) 239–248242
State (Martins et al., 1997). The production zone,
composed by four springs, is located at 1000 m of
altitude, by the scarp of Serra do Mar mountain chain.
This occurrence has been explored since 1953, with
average annual production of 28,000,000 l (Martins et
al., 1997). Physical and chemical characteristics of the
mineral water can be found in the literature (Martins et
al., op. cit.). The water is classified as radioactive at
the spring, probably due to the radionuclide present in
the percolated rocks. The water has a pH of 6.1 at 25
jC, a conductivity of 3.5 mS/m and 34.8 mg/l of
dissolved salts in its composition.
4. Data acquisition
Virtually all the data were collected keeping the
transmitter and the receiver in a fixed offset configura-
tion. AGPR section ismade up ofmany traces collected
along a profile thus allowing the observer to locate
targets. Each new trace is obtained while dragging the
two antennas together along the profile. The wavelets
reflected from two targets appear on the corresponding
traces plotted as a function of known as two-way time
(TWT). This is the time it takes the pulse to be emitted,
to bounce back, and to be recorded at the receiver. The
TWT can be converted to depth when velocity of radar
waves in the subsurface is known. An estimate of
velocity can be achieved through velocity analysis of
Common Mid Point (CMP) sections. In the CMP field
configuration, the transmitter and receiver are moved
away each other up to a maximum distance. This
distance is a compromise between achieving greater
investigation depths and consequent increased absorp-
tion of the electromagnetic waves in the medium with
increased transmitter–receiver distance.
The data were collected with a Pulse Ekko IV GPR
(Davies and Annan, 1989) with a 1000-V pulser. The
transmitter antenna radiates a broadband wavelet that
has an amplitude spectrum as wide as its center
frequency: 100 MHz. The transmitting antenna has a
broad radiation pattern reaching apertures between
90j and 180j. The bi-static antenna configuration
allows a great flexibility of data collection strategies.
Antennas were dragged along the profiles with a
constant step of 0.20 and 0.25 m, keeping their mutual
distance constant (fixed offset) or increasing that
distance continuously (CMP).
The total time window used in the fixed-offset
profiles was 250 ns, enough to reach depths of 10–12
m. That time window, however, was increased to 350
ns for the CMP profiles.
The whole survey amounted to more than 500 m of
fixed-offset reflection profiles mostly deployed on
uneven terrain. The spatial density of traces was
0.25 m/trace throughout. The antennae were kept 1
m apart. A section of a 120-m-long profile on a
relatively flat terrain and crossing the main one of
the four known springs in the area is used here to
illustrate the effectiveness of the GPR to locate water
in fractures. A producing well was drilled at the spring
till 145 m depth. The hydrostatic level is confined
between 4.9 (static) and 62 (dynamic) m depth (Bar-
reto et al., 2000).
Two 25-m CMP profiles were done at two locations
in the survey area in order to estimate an average
velocity to be used in the fixed-offset sections. Anten-
nae separation was increased stepwise in increments of
0.1 m from an initial separation of 1 m. The two CMP
profiles yielded similar results. We show here the CMP
profile done at the well location (Fig. 3a).
5. Velocity analysis
The propagation velocity of radar waves, Vr, is a
function of the dielectric constant of the subsurface.
The dielectric constant, in turn, is affected by its water
content. The propagation velocity can be determined
by CMP measurements. From a CMP section, it is
possible to infer the velocity of the direct waves (in air
as well as the ground wave), the velocity of the
reflected waves, and of the refracted waves in some
special circumstances. Here, we concentrate on the
velocity of reflected waves.
The reflections from the interfaces between layers
with different dielectric constants appear as hyperbolas
in CMP sections (Fig. 3a). This characteristic shape is
based on the assumption that the arrival time for signals
from reflectors varies hyperbolically with the separa-
tion between the transmitter and the receiver. This
assumption is valid as long as the reflectors have small
dip. The curvature of a given hyperbola depends on the
velocity of the radar waves. Therefore, the velocity
analysis of a given hyperbola will give an average
velocity to the depth of the reflector.
Fig. 3. (a) CMP profile at the studied spring. The airwave is represented by the first straight line in time. The groundwave is represented by the
second straight line, note that beyond 10 m, this wave is highly attenuated. Subsurface reflectors are represented by hyperbolas. (b) Velocity
analysis for the CMP profile. Velocity is incremented in 0.001 m/ns steps from 0.01 to 0.15 m/ns.
J. de Menezes Travassos, P. de Tarso Luiz Menezes / Journal of Applied Geophysics 55 (2004) 239–248 243
The velocity analysis used here uses the concept of
velocity stack in a constant velocity earth (Yilmaz,
1987). CMP traces are compensated for normal move-
out assuming a constant velocity hyperbolic equa-
tion. Traces are then stacked. A range of velocity
from 0.05 to 0.15 m/ns was covered with increments of
0.001 m/ns. When a given velocity in that range
matches the normal moveout velocity, a reflector will
stack coherently. This will result in larger amplitude in
the stack. On the other hand, when a given velocity
does not match that of the reflector, traces add together
incoherently. This will result in smaller amplitudes.
J. de Menezes Travassos, P. de Tarso Luiz Menezes / Journal of Applied Geophysics 55 (2004) 239–248244
The velocity analysis using the CMP profile yields
a three-layered velocity model of 0.065, 0.076 and
0.072 m/ns (Fig. 3b). We adopt an average velocity of
Vr = 0.07 m/ns for the whole section, which is close to
the estimate given by the first important reflector at 60
ns, arrowed in Fig. 3b. That reflector is probably the
interface between the saprolite and the granite-gneiss
below. As a matter of fact, the shallower part of the
saprolite has a higher velocity (0.07 m/ns) than the
remainder of the section, as estimated directly from
the groundwave signature, a straight line in Fig. 3a.
The adopted velocity is 54% less than it is usually
tabulated for granite-gneiss (0.13 m/ns). This can be
attributed to a higher water content in soil and rock.
There is one continuous reflector at 150 ns, i.e., below 5
m deep, yielding the almost the same velocity as it can
be seen in Fig. 3b. Note that the static hydrostatic level
measured at the well is 4.9 m, corroborating our
interpretation.
6. Groundwater signature
The water in the area appears in fractures indicating
that our target is not a long and continuous reflector as
would be the case of a water table. Due to the fractures,
Fig. 4. (a) Raw GPR time section on crystalline rock, note the several diff
and 50 in the profile. (b) Same GPR section f–k migrated and converted to
Compare with (a), migration untied the bowties on the section and turn th
level at 4.9 m depth is located at trace 32 m.
we expect that reflection sections will be cluttered with
diffractions. Diffractions are hyperbolic events caused
by the discontinuities in the rock that may interfere with
each other obscuring the sections. Diffractions and
interference patterns can be dealt with by using migra-
tion, an imaging technique that focuses the energy
along hyperbolas to the true spatial position fromwhich
the energy originated. Migration moves dipping reflec-
tions to their true subsurface position and collapses
diffractions, thus increasing spatial resolution. The goal
of migration is to make the fixed-offset section appear
similar to the geologic cross-section in depth along a
GPR profile. The section presented in this paper (Fig.
4) is migrated assuming that the rocks below the
saprolitic layer are more or less homogeneous.
In this work, we use the f–k migration approach of
Stolt (Yilmaz, 1987). It is assumed that the GPR data
can be considered as zero offset and that the average
velocity estimated through the velocity analysis above
can be taken as a constant background velocity along
the profile: Vr = 0.07 m/ns. We have also chosen a
relatively flat profile to apply the migration. The data
is dewowed, clipped, resampled and tapered before
migration.
A limitation in this procedure lies in the fact that
our data is 2D and out-of-plane diffractions will be not
raction patterns (bowties) below 100 ns, specially between traces 40
depth, an uniform velocity of Vr = 0.07 m/ns is assumed throughout.
em into dipping reflectors. A producing well, with static hydrostatic
J. de Menezes Travassos, P. de Tarso Luiz Menezes / Journal of Applied Geophysics 55 (2004) 239–248 245
correctly dealt with the migration process. That will
harm our section smearing out the data at the fracture
zone. Such effect can only be dealt with in a true 3D
survey, where the inline and cross-line spatial sam-
pling are compatible. In that case, one could possibly
perform a two-step migration that is satisfactory for a
simple subsurface. For a more involved structure, one
would require a full 3D migration (Jakubowicz and
Levin, 1983).
Fig. 4a shows a 70-m raw data section clipped
from the 120-m-long profile crossing the studied
spring (trace 32 m). A spreading and exponential
compensation gain assuming an attenuation of 0.1
dB/m was applied to the section. Data were low-pass
filtered with a cutoff at 250 MHz to reduce high-
frequency noise and clipped in time to chop off values
earlier than the first break. The section was migrated
assuming a constant velocity throughout (0.07 m/ns),
the final result is shown in Fig. 4b. Water-filled
fractured rock appears in the section as a region of
lower amplitude reflections beyond trace 25 m and
below 5 m depth. That region gets deeper towards the
end of the section, extending to trace 60 m. Fracture
induced diffraction were virtually eliminated by the
energy focusing provided by the migration.
The wavelet phase polarity can also be used to
determine the presence of water. The phase of the
wavelet is defined in this paper as the sequence of
phase polarities as seen along a given trace. Fig. 5
shows the end portion of the trace obtained at 35 m
Fig. 5. End section of trace 35 m. The arrow shows the first of a
series of phase inversions, occurring at the top section of the water-
filled fractured rock. Amplitudes are clipped at a maximum of 3.2.
The vertical scale is arbitrary.
along the section shown in Fig. 4. The trace was AGC
gained and appears clipped at an arbitrary maximum.
The AGC attempts to equalize the signals by applying a
gain which is inversely proportional to signal strength,
and therefore does not preserve relative amplitude
information. The first of a series of phase polarity
inversions occurs at 178 ns as seen in Fig. 5. This gives
the top of the water-filled fractured rock at 6.23 m, less
than 1 m deeper than it appears to be in Fig. 4b. This
discrepancy may be due to the uncertainty in recogniz-
ing the phase polarity sequence properly, because the
leading edge of the wavelet cannot be ascertained due
to closed spaced reflections, as may be the case on the
top of the fractured rock.
7. Interpretation
A great deal of effort in interpreting radar profiles
goes into not only understanding reflections and
diffractions but also into deciphering of interference
patterns. The focusing of energy provided by migra-
tion make that task easier. The expected product is to
recognize changes in reflector characteristics such as
configuration, continuity, frequency and amplitude so
to characterize radar facies. Radar facies are 3D
regions representing particular combinations of phys-
ical properties like lithology, stratification, fracturing
and fluid contents. Recovering the full geometry of
such regions is not an issue here as we are dealing
with a 2D profile, but with the data we can have an
idea of the layering of the gneiss and recover the
contact between less and more fractured rock.
The section in Fig. 4 gives a good image of the
subsurface, revealing features such as the top portion
of the water-filled fractured rock and the structure of
the gneiss. The interpreted section is shown in Fig. 6.
The most prominent feature is the top of the fractured
rock delimiting an extensive saturated zone (35 m
wide), which is responsible for the high drainage rate
of the spring. This interpretation is corroborated by
the existence of the producing well at trace 32 m.
In the radar section of Fig. 4b, it is possible to
identify a series of semi-parallel folded reflectors all
long the profile and small structures such as a lens
shape between 0 and 30 m in the profile that is very
similar to a boudin structure (B in Fig. 6). As said
before these structures (Fig. 2) are very common in
Fig. 6. Interpretation of the radar section shown in Fig. 4. The F’s are interpreted as fractures and B is interpreted as a boudin structure, very
common in the region, refer to Fig. 2.
J. de Menezes Travassos, P. de Tarso Luiz Menezes / Journal of Applied Geophysics 55 (2004) 239–248246
the region. The overall pattern of the reflectors along
the profile resembles a migmatitic texture, with alter-
nated veined/folded mafic (biotite–hornblende) and
felsic layers (quartz). Another important feature iden-
tified are the sub-vertical fractures (F in Fig. 6) that
occur all long the section. These fractures are associ-
ated to the main conduits to water ascension in the
area.
Independent geophysical data is in accordance
with the GPR data. 1D Interpretation of one VES
positioned at trace 42 m along the profile indicate
a four-layer earth (S. Berrino, personal communi-
cation, 1997). Schlumberger soundings, due to its
low costs and simplicity of use, are still tradition-
ally employed in many regions to enhance the
odds of finding groundwater in crystalline terrains
(Carrasquilla et al., 1997). The main idea behind
these surveys is, after identifying a favorable
fracture in aerial photo-interpretation, to try to
find lower resistivity zones within high resistive
rocks. That lowering in the resistivity pattern
should be associated to groundwater. The success
rate of that type of approach reaches 85–90% of
the drilled boreholes.
To further reduce the ambiguity of the geophys-
ical interpretation of the shallow subsurface we
incorporated the geological knowledge of the weath-
ering profile in the region (Barreto et al., 2000).
Descriptions of the typical weathering profiles of
tropical and subtropical basement complexes are
found elsewhere in the literature (refer to Fig. 4, p.
141 of Meju, 2002).
The 1D model at the spring starts from top to
bottom with a 2-m saprolite layer of 1500 V m,
followed by a 5-m fractured layer of 3000 V m and
then to a fractured saturated zone of 300 V m that may
extend down to 50 m, well beyond the penetration
depth of the GPR data. This 10 times lowering in the
resistivity values indicates a high degree of fracturing
and connectivity. A half-space of highly resistive fresh
rock terminates the model. The resistivity of the
saturated zone is within the range of common frac-
tured aquifers at igneous and metamorphic rocks
(refer to Fig. 5, p. 142 of Meju, 2002). It is interesting
to note that this simple 1D interpretation presented a
reasonable estimate of the top of the saturated zone (7
m) when compared to the borehole log and the radar
section (5.7 m). The main discrepancy, about 20%
error, is associated to the bottom of the saturated zone,
that was estimated in 50 m by the 1D inversion and is
62 m at the borehole. This is comprehensive as we are
interpreting with a 1D method a complex 3D earth.
But as stated before, for exploration purposes, the
main interest is just identify a zone of low resistivity
within crystalline rocks that could associated to
groundwater, so enhancing the chances of a successful
drilling.
8. Conclusions
This work presents the results from a GPR survey
done for water exploration on crystalline terrain
(migmatized gneiss). Reflection data were collected
with the fixed-offset configuration along a profile 70
m long. The velocity was estimated doing velocity
analysis on CMP data. The estimated velocity value
was 0.07 m/ns. This value is 54% less than the
tabulated velocity for granite-gneiss and is attributed
to high water content in rock.
J. de Menezes Travassos, P. de Tarso Luiz Menezes / Journal of Applied Geophysics 55 (2004) 239–248 247
The raw GPR section was cluttered with diffrac-
tions. A migration scheme was applied assuming the
constant value of 0.07 m/ns throughout. The energy
focusing provided by migration can be used to re-
move/attenuate interference patterns and make the
GPR section appear similar to the geologic cross-
section in depth. As expected, the fracture induced
diffractions were virtually eliminated in the migrated
section, enhancing the visualization of the geologic
structures.
In the migrated radar profile the water filled
fractured zone is clearly outlined by a wide (35 m)
region of lower amplitude values. Those are result of
the scattering of the incident energy as well as due to
the smearing out resultant from the process of migrat-
ing out-of-plane diffractions. The depth to the top of
this saturated zone is variable along the profile (4–10
m). The presence of water in the fractured zone can
also be mapped from inversion on the polarity of the
wavelet phase at the radar traces.
To further reduce the inherent ambiguity of the
geophysical interpretation a priori geological knowl-
edge of a borehole located at trace 32 m was
incorporated. In this borehole the water producing
zone is confined within 4.9 and 62 m depth. There is
a very good agreement between the GPR data and
the available borehole information. A priori knowl-
edge of the weathering profile and migmatite struc-
tures of Santo Aleixo Unit were also incorporated to
help in the geological interpretation of the radar
profile.
The main limitation of the method is the relative
shallow depth of investigation. The GPR data provid-
ed a detailed characterization of shape and extension
of the shallow saturated zone. Depth of investigation
was limited to 10 m, insufficient to image the whole
saturated zone (till 62 m depth). The imaging of
greater depths can be achieved by integrating the
GPR data with another geophysical method. In our
case, independent geophysical data from a VES
Schlumberger sounding are in accordance with the
GPR results and the available geological knowledge.
Acknowledgements
We would like to thank the editor-in-chief A.
Hoerdt, S. Hautot and an anonymous reviewer for
their constructive comments that helped to improve
the text. We also thank Miguel Tupinamba for the
photo of Santo Aleixo migmatite. PTLM was
supported by an UERJ-Prociencia scholarship.
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