115 The strain history of tectonically deformed rocks may be deduced by petrofabric study with the help of shape, orientation and axial ratio determination of deformed minerals and grains in the rock. Under the high stress the minerals are stretched reoriented and new growth occurred parallel to the less stress direction and represent a distinct fabric. Thus the individual grain shapes and their orientation constitute the rock petrofabric. Maximum deformed rocks contain paramagnetic and ferromagnetic minerals with distinct orientation respond under the deformational stress in which magnetic fabric study is useful to deduce the strain pattern. The magnetic fabric study through Anisotropy of Magnetic Susceptibility (AMS) is first time used by Graham (1954) as a petrofabric element and which reflects the magnetic susceptibility anisotropy ellipsoid in a rock as the strain ellipsoid. The AMS, a physical property of the rock, represents more perfect picture of deformation then microscopic strain fabric study. Its relationship with fabric of the rock arises because the most magnetically susceptible minerals can have distributions of shape orientations or lattice orientations influenced by the kinematic history of the fabric, and the magnitude ellipsoid of susceptibility may be a faithful representation of the total fabric (Borradaile, 1988; Aranguren, et al., 1996). Borradaile (1988), Housen et al. (1993) and Aranguren, et al. (1996) have shown the geometrical relationship between the magnetic foliation and field structures and proposed the different models of the composite magnetic fabrics. ANISOTROPY OF MAGNETIC SUSCEPTIBILITY; STRAIN FABRIC CHAPTER-V Estelar
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CHAPTER-V ANISOTROPY OF MAGNETIC Estelarshodhganga.inflibnet.ac.in/.../10603/28444/5/chapter5.pdf115 SUSCEPTIBILITY; STRA The strain history of tectonically deformed rocks may be deduced
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115
The strain history of tectonically deformed rocks may be deduced by petrofabric
study with the help of shape, orientation and axial ratio determination of deformed
minerals and grains in the rock. Under the high stress the minerals are stretched
reoriented and new growth occurred parallel to the less stress direction and
represent a distinct fabric. Thus the individual grain shapes and their orientation
constitute the rock petrofabric. Maximum deformed rocks contain paramagnetic
and ferromagnetic minerals with distinct orientation respond under the
deformational stress in which magnetic fabric study is useful to deduce the strain
pattern. The magnetic fabric study through Anisotropy of Magnetic Susceptibility
(AMS) is first time used by Graham (1954) as a petrofabric element and which
reflects the magnetic susceptibility anisotropy ellipsoid in a rock as the strain
ellipsoid.
The AMS, a physical property of the rock, represents more perfect picture
of deformation then microscopic strain fabric study. Its relationship with fabric of
the rock arises because the most magnetically susceptible minerals can have
distributions of shape orientations or lattice orientations influenced by the
kinematic history of the fabric, and the magnitude ellipsoid of susceptibility may
be a faithful representation of the total fabric (Borradaile, 1988; Aranguren, et al.,
1996). Borradaile (1988), Housen et al. (1993) and Aranguren, et al. (1996) have
shown the geometrical relationship between the magnetic foliation and field
structures and proposed the different models of the composite magnetic fabrics.
ANISOTROPY OF MAGNETIC
SUSCEPTIBILITY; STRAIN FABRIC
CHAPTER-V
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The AMS study is very useful to explain the neotectonic stresses and
active tectonics (Borradaile and Henry, 1997; Borradaile and Hamilton, 2004;
Dubey and Bhakuni, 2008). Jayangondaperumal et al. (2010b) have used AMS
fabric to understand the kinematics and infer recent tectonics in the Garhwal
Inner Lesser Himalaya.
The rocks of the area are metamorphosed under the greenschist and
amphibolite facies and contain mainly diamagnetic and paramagnetic minerals,
also explained by Agarwal et al. (2010).
The strain ratios and the orientation of the strain ellipse estimated by
different methods on the fabrics of deformed rocks by different workers.
Srivastava (2004) has used elongated porphyroblasts in augen gneisses to
determine the shape of finite strain ellipsoid, and explained multiple deformations
in the Dudatoli-Almora crystallines. Two dimensional strain estimation from
weakly deformed rocks, where it is difficult to precisely define the longer and
shorter axis of ellipse/grain, have been performed by Srivastava (1995, 2009).
In present work, the petrofabric strain is measured by using AMS
technique and correlated with strain fabric results obtained by using Rf/φ
technique (Ramsay, 1967; Dunnet 1969; Dunnet and Siddan, 1971) and also by
plotting Flinn diagram (Zingg, 1935; Flinn, 1962) of axial ratio of microscopic
elliptical markers.
Application of AMS technique and correlation with meso-microscopic
fabric is also attempted by Jayangondaperumal et al. (2010a), Devrani et al.
(2009) and Agarwal et al. (2010). Mamtani and Vishnu (2011) have investigated
the use of AMS data to provide the information about the shape of the strain
ellipsoid in the micaceous quartzites.
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5.1 ANISOTROPY OF MAGNETIC SUSCEPTIBILITY (AMS)
TECHNIQUE:
AMS technique is very sensitive to read the schistosity developed at the last
phase of deformation with early schistosity or bedding. The orientation of
principal susceptibilities represents distribution of magnetic minerals fabric in
rock; however, the rock composition and metamorphic grade may affect the
anisotropy of magnetic susceptibility and bulk susceptibility of rock type
(Borradaile and Henry, 1997; Nakamura and Borradaile, 2004). The bulk
susceptibility (Km), anisotropy susceptibility and other forms of magnetic
anisotropy commonly play a great roll to determine the state of strain and
petrofabric, and are also used as strain indicators. The AMS may be represented
by magnitude ellipsoids, geometrically shaped by three magnetic principal axes
(K1≥ K2≥K3), those are closely related to the strain axes (λ1>λ2 >λ3). There are
two elements, magnetic foliation ‘F’ (K1- K2 Plane) and magnetic lineation ‘L’ (K1)
(Tarling and Hrouda, 1993; Aubourg, et al., 2000; Sidman, et al., 2005) and their
anisotropy parameters are described by eccentricity ‘Pj’ and its shape ‘T’.
Measurement of AMS is a fast method for investigating the fabric pattern
in plastically deformed rocks, and comment about strain in them (e.g., Borradaile,
1991; Tarling and Hrouda, 1993; Nakamura and Nagahama, 1997; Borradaile
and Jackson, 2004; Mukherji et al., 2004; Mamtani and Greiling, 2005; Sen et al.,
2005; Sen and Mamtani, 2006; Mamtani and Sengupta, 2009, 2010; Majumder
and Mamtani, 2009; Agarwal et al., 2010; Vishnu et al., 2010; Pant et al., 2011). It
is the useful method in delineating the changes induced due to brittle deformation
in fractured rocks in faults/thrust zones (Ozima and Kinoshita, 1964; Hallwood et
al., 1992; Nakamura and Nagahama, 2001; Pant, et al., 2011). AMS has been
used successfully to understand deformation and tectonic setup of the Himalayan
region by earlier workers (Jayangondaperumal and Dubey, 2001; Dubey et al.,
2004; Dubey and Bhakuni, 2008; Tripathy et al., 2009; Agarwal et al., 2010;
Jayangondaperumal et al., 2010). In present work the AMS analyses of rocks
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from the NASZ (Pancheshwar-Seri-Seraghat-Dwarahat- Gairsen region) are
performed with the aim of evaluating the deformation and tectonics of the region
(Fig. 1). Field and AMS data are compared, and data from thermal
demagnetization of some samples are presented to evaluate the magnetic
carriers of the AMS.
Detail study has been done of the structures along the NASZ, by carrying out the
AMS analysis, which is a useful tool to study fabrics in tectonites.
5.1.1 AMS Parameters
All minerals have magnetic properties at temperatures above absolute
zero (0 K) (Tarling and Hrouda, 1993). The results of the AMS data for all
transects of the area are given in table I, II, III and IV. The magnetic susceptibility
(K) is defined as the ratio between the induced magnetization (M) of the
specimen and the applied magnetic field (H).
K = M/H
The AMS is a second rank tensor with three principal axes (K1≥K2≥K3),
where K1 is the magnetic lineation and K3 is normal to the magnetic foliation
(Tarling and Hrouda, 1993). The bulk magnetic susceptibility ‘Km’ is the arithmetic
mean of the principal susceptibilities (Km = K1+K2+K3/3).
The magnitude of anisotropy is expressed by ‘Pj’ parameter based on
logarithmic values of susceptibility (Jelinek, 1981; Tarling and Hrouda, 1993;
The shape of the anisotropy ellipsoid or eccentricity of the ellipsoid is given
by the shape parameter ‘T’ (Jelinik, 1981; Hrouda, 1982; Borradaile, 1988).
T= [2 In (K1/K2)/In (K1/K2)]-1
The value of T varies from -1 to +1. T>0 implies the oblate shape, whereas T<0
suggests the prolate shape of magnetic susceptibility ellipsoids.
5.2 METHODOLOGY
Oriented rock samples were collected from the area across the NAT. 316 cores
(25.4 mm x 22 mm) from 65 oriented rock specimens were obtained for AMS
analysis. AMS data were generated in the Palaeomagnetic Lab of the Wadia
Institute of Himalayan Geology, Dehradun, India. To determine the AMS, each
core was analyzed in 15 different directions with reference to the north using a
KLY-3 Kappabridge (AGICO, Czech Republic), which has a sensitivity of 2 x 10-6
(SI) and accuracy of 0.1%. AMS study of the specimens of the area revealed the
mean susceptibility values <800 x 10-6 SI, and has been grouped according to
their mean magnetic susceptibility ranges in five groups (i) >500 x 10-6 (SI), (ii)
500-300 x 10-6 (SI), (iii) 300-200 x 10-6 (SI), (iv) 200-100 x 10 -6 (SI) and (v) 100-
10 x 10-6 (SI). These low susceptibilities indicate a minor contribution from
ferromagnetic minerals (Rochette, 1987). In AMS study, the knowledge of
magnetic carriers is very important for reliable results. The recognition of these
magnetic carriers was done in our samples through petrography and
thermomagnetic curves. In order to constrain the ferromagnetic and
paramagnetic contribution, 10 samples of various mean susceptibilities (Gh25, D3,
S5, C105, Gh12, D2, C38, S4, C72 and C10 in order of decreasing susceptibility) were
selected and examined through measuring temperature variation of the bulk
magnetic susceptibility on the samples by using TSD-2 Schonstedt thermal
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demagnetizer and temperature variation of susceptibility by using the
Kappabridge (Jelinek and Pokorny, 1997) (Table 5).
In addition to the AMS, the petrofabric strain study with the help of Rf/φ and
Flinn plots was carried out of 13 samples across the NASZ. In this petrofabric
measurement the elliptically deformed feldspar and quartz grains have been used
for strain analysis at the microscopic level. For which sections were prepared by
cutting the specimens in XZ and YZ directions. The mineral elongation lineation
direction is the X-direction of finite strain ellipsoid (Lister and Hobbs, 1980; Joy
and Saha, 2000; Joshi and Tiwari, 2004; Bhattacharya and Weber, 2004),
foliation plane is XY plane and Z is perpendicular the XY plane. The Rf/φ and
Flinn plots are prepared by using the versatile Windows based software, the
“Window32.Bit Platform” developed by Roday (2003).
5.3 AMS STUDY
5.3.1 Petrography and Magnetic Mineralogy
Debacker et al. (2010, 2011), Mamtani and Vishnu, (2011) investigated the
magnetic properties of a variety of lithostratigraphic units of the Brabant Massif.
Magnetic techniques employed are the determination of (a) magnetic
susceptibility (MS, for methodology, see Ellwood et al., 2000 and references
therein), (b) the temperature-dependent variation in MS within the “room
temperature interval” (for methodology, see Herbosch et al., 2008 and Debacker
et al., 2009, 2010), (c) the anisotropy of magnetic susceptibility (AMS) at room
temperature (for methodology, see Jelinek and Pokorny, 1997), (d) the magnetic
mineralogy by means of a stepwise thermal demagnetisation of a three-axis
isothermal remnant magnetism (for methodology, see Lowrie, 1990).
In present work the magnetic mineral study was done by means of
petrography and stepwise thermal demagnetization method (for methodology,
see Lowrie, 1990).
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Each rock unit in the NASZ shows intense deformation and attendant
recrystallization. Petrographic study shows that the mylonitic to proto-mylonite
rocks consist of fine to medium grained quartz, K-feldspar and some amount of
muscovite and biotite. Ultra-mylonitized granite-gneiss contains very fine and lineated
grains of quartz, feldspar, muscovite and biotite with very small ferromagnetic
(pyrrhotite) minerals (Fig. 5.1 a). Schists are mainly composed of biotite,
muscovite, chlorite and garnet (Fig. 5.1 b). Garnet in schists is associated with
quartz, muscovite, biotite, chlorite and plagioclase minerals. Almora quartzite
often displays schistosity that is defined by micaceous minerals. Quartzarenite of
the Rautgara Formation dominantly consists of quartz (diamagnetic minerals)
with <10% paramagnetic minerals. However, at the NAT contact the
metasedimentary rocks are characterized by the presence of biotite and
muscovite (>10%). Thin sections of fractured rocks along the fault zone exhibit
nucleation of very fine grained (~6μm) iron oxides in the micro veinlets intruded
along the microfractures (Fig. 5.1 c, d).
A simple thermal heating of rock sample may cause of not only magnetic
phase transformation but it can change the magnetic mineral grain size. Since
under the different successively applied heating treatment the rock is not
modified, and measurement gives accurate data to determine the magnetic
carriers.
The thermal magnetic heating curves of ten samples represent to discrete
susceptibility and temperature determinations (up to 750°C), which have direct
relation with magnetic carriers and used to identify the magnetic minerals in the
rock specimen (Fig. 5.2). It is noted that samples C105, D2, C38, S4, C72, C10 and
Gh8 contain paramagnetic minerals. Samples D3, S6 and Gh12 show sudden
decrease in susceptibility around 300 to 380°C; this may be due to presence of
some monoclinic pyrrhotite (Dekkers, 1988, 1989; Aubourg et al., 2000). Sample
C105 shows an increase in susceptibility at ~500°C, suggesting that magnetite has
possibly formed during experiment at this temperature (Hrouda, 1994; Hrouda et
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al., 1999). The rock units contain predominantly phyllosilicates, which are the
paramagnetic minerals and main source of AMS in schist and gneissic rocks.
Phyllosilicates are important and strongly anisotropic component of tectonites,
and their contribution to AMS has been well documented by Henry (1990, 1992),
Borradaile and Werner (1994), Borradaile (2001), Borradaile and Jackson (2009).
The growth of phyllosilicates (i.e. biotite >10%) controls the magnetic
susceptibility of the rock unit in highly sheared quartzarenite along the thrust/fault
contact (samples C64, C61, C100 and D2). Similarly, the nucleation of iron oxides
(very fine grain magnetite) along the microfractures is found (samples C73, C75,
C98 and C100).
Figure 5.1: Microphotographs showing (a) magnetic mineral vein within quartz and mica grains aggregate, (b) garnet, quartz, mica and feldspar minerals in the garnet mica schist, (c) and (d) veins of iron oxide minerals along the micro-fractures in quartzo-feldspathic rock. Scale bar 1mm.
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Figure 5.2: Thermal demagnetization plots of magnetic susceptibility (Km) of 10 core samples at different temperatures up to 750º C.
5.3.2 Analytical Results of AMS study
Petrography and thermal demagnetization studies reveal that the most samples
are not significantly influenced by ferromagnetic minerals. However, there are
some samples of ultra-mylonitized granite (Gh12, S6, C98 and D3) from the sharp
contact of the fault plane show relatively high susceptibility with high degree of
anisotropy which is due to presence of ferromagnetic minerals (pyrrhotite,
magnetite). Mylonitized, proto-mylonitized and ultra-mylonitized granite rocks
exposed along the NAT have high magnetic susceptibility (200 – 796 x 10-6 SI),
whereas schistose rocks have relatively low susceptibility (70 – 337 x 10-6 SI).
However the specimens G25 and C105 those have relatively high susceptibility
(Tables I, II, III and IV) due to the presence of porphyroblasts of garnet. Garnet is
characterized by volume susceptibility of the same magnitude as biotite. Although
it does not contribute to anisotropy, it may influence bulk susceptibility (Hrouda
and Ullemeyer, 2001). In general quartzarenite gives negative susceptibility
(contains diamagnetic minerals i.e. quartz) (Gh10). In the study area due to
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presence of mica content and growth of very fine grain iron oxides, it is giving
positive susceptibility (3 - 192.8 x 10-6 SI) and in some samples it is cause of
high susceptibility with high anisotropy. Few specimens of quartzarenite are
giving high anisotropy (~1.3) with low susceptibility (1 - 8 x 10-6 SI) (Tables I, II, III
and IV), which is due to presence of very thin discrete layers (<20µm) of very fine
grain iron oxide along the microfractures in the specimens (D8A, D36, S8, D25, D5
and C81).
AMS data represents well defined magnetic foliations in the rocks of the
Saryu Formation and shows association to field foliations and deformation in the
area. In thin sections, Shape Preferred Orientation (SPO) is commonly inclined to
the compositional layering, and AMS data are inferred to give resultant schistosity
due to superimposition of crystal orientation on compositional layering.
As early described the whole area is divided into four sectors and AMS
study is taken up accordingly and each sector described in detail domain-vise.
I. Pancheshwar-Seri Sector
Eastern part of the NASZ is studied by taking various traverses across the NAT in
Pancheshwar-Seri sector (Fig 5.3):
The Pancheshwar area comprises N-S and ENE-WSW trending fault
across the NAT inferred by geomorphic and structural data, and strongly
supported by the AMS fabric data of the area. Magnetic foliation planes do vary
with the NAT trend and field foliation, whereas they are showing good
relationship with the N-S and ENE-WSW oriented faults. Due to limited approach
along the ENE and WSW oriented fault plane only two samples were collected,
which are giving N-S (P1 specimen) and ENE-WSW (P2 specimen) magnetic
foliation plane orientation respectively away and near the fault plane trace (ENE-
WSW). Here N-S orientation of the magnetic foliation plane in P1 specimen
represents the impact of the N-S oriented fault (Fig 5.4a).
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Fig
ure
5.3
: G
eo
log
ical m
ap
of
the P
an
ch
esh
wa
r-S
eri
secto
r sh
ow
ing
dis
trib
uti
on
of
vari
ou
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ith
ou
nit
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nd
po
sit
ion
of
sam
ple
s c
oll
ecte
d f
or
AM
S s
tud
y.
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Figure 5.4: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in Pancheshwar domain, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the NASZ, Pancheshwar-Seri sector. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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P3a, P3b and P4 samples were taken along the N-S oriented fault plane
and across the NAT, represent parallel to sub-parallel magnetic foliation
orientations with the fault plane. Magnetic lineations are horizontal to sub-
horizontal, gently plunging towards N (samples P3a, P3b, P4) and W (sample P2).
However somewhere they lie on the intersection of field foliation and magnetic
foliation plane (P2, P4). In figure 5.3 b, Pj vs. Km plot of the granitic gneiss shows
inverse relationship between the values of Pj and Km. The AMS data for mica
schist, micaceous quartzite, granitic gneiss and mylonites lie in neutral to oblate
field (T=1 and T>0) (Fig. 5.4 c, d), which is due to development of flaky
micaceous minerals and may be also due to flattening strain (Mukherji et al.,
2004; Mamtani and Sengupta, 2010; Vishnu et al., 2010).
In Netra domain, the strike of magnetic foliation plane do vary from WNW-
ESE to NW-SE, which are parallel- sub parallel to the NAT trend and making low
angle with field foliation. Magnetic lineations are horizontal to sub-horizontal,
whereas magnetic foliations do vary from gentle to steeply dipping (Fig. 5.5 a). P j
vs. Km plot of the granitic gneiss shows inverse relationship, whereas schist and
ultramylonites representing positive relation between the values of Pj and Km (Fig.
5.5 b). In T vs. Km and Pj vs. T plots data lie completely in oblate field (T>0) (Fig.
5.5 c, d).
In the Ghat domain the geomorphic and structural data inferred NW-SE
trending fault parallel to the NAT (in SW of the NAT) (Fig. 5.6 a). Magnetic
lineations are gentle to steeply plunging towards WSW to SSE directions.
Magnetic foliation planes are vertical to sub-vertical and variably oriented from N-
S to ENE-WSW whereas near the NAT and its subsidiary fault plane, they show
parallel to sub-parallel orientation with the NAT and NW-SE oriented fault (Fig.
5.6 a).
Pj vs. Km plot shows inverse relationship in the granitic gneiss and
protomylonite units (Fig. 5.6 b). Highly sheared quartzarenite represents prolate
to oblate field in the T vs. Km and Pj vs. T plots. The data of granitic gneiss, mica
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bearing quartzite and mylonite lie in the neutral to oblate and oblate field,
respectively. Here micaceous quartzite (Saryu Fm.) is showing high anisotropy
with high susceptibility (Fig. 5.6 c, d).
Figure 5.5: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in Netra domain, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the domain in the NASZ, Pancheshwar-Seri sector. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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Figure 5.6: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in Ghat domain, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the domain in NASZ, Pancheshwar-Seri sector. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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Figure 5.7: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in Rameshwar domain, (b) Pj vs. Km (c), T vs. Km and Jelinek plot (T vs. Pj) for all samples of the domain in the NASZ, Pancheshwar-Seri sector. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
The Rameshwar area is characterized by two faults trending NNE-SSW and
NE-SW. The magnetic foliation planes varyingly oriented ESE-WNW to NNW-
SSE. Near NAT, the magnetic foliations are trending parallel to the NAT plane,
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whereas in the proximity of the faults their orientation swings from ESE-WNW
through NW-SE to NNW-SSE. At and around the intersection area of the fault
planes, the strike of magnetic foliation planes are NW-SE and NNW-SSE, where
minimum magnetic axes (K3) on an average oriented towards NE and
representing σ1 of the conjugate set of the faults (Fig. 5.7 a). Pj and Km plot is
giving independent values of mylonite, schist and granitic gneiss (Fig.5.7 b). T vs.
Km and Pj vs. T plots are showing prolate to oblate shape of magnetic ellipsoids
(Fig. 5.7 c, d).
II. Seri-Seraghat Sector
This sector of the NASZ is characterized by superposed transverse Rantoli fault
(Valdiya, 1976) or Saryu River Fault (Pant et al., 2007) which coincide with the
trend of the NAT (Fig. 5.8).
At the NW terminal part of the Rantoli Fault the NAT swings from SW to
SSE orientation and coincides with NNW-SSE trend of the fault. Here the
magnetic foliations show parallelism with the NAT and become parallel/sub-
parallel to the Rantoli Fault as moving toward the Fault plane. Stereo projections
show that the magnetic foliations are vertical to sub-vertical, and lineations (K1)
are horizontal near the Fault plane (Fig. 5.9 a), however near the NAT contact
they are gently dipping (with variable orientation) (Fig. 5.9 a). Pj and Km plot
shows positive relationship in the schist and micaceous quartzite (Fig. 5.9 b). T
vs. Km and Pj vs. T plots show prolate to oblate shape of magnetic ellipsoids (Fig.
5.9 c, d).
In the Naichun-Rantoli area the AMS data shows that the magnetic
foliations dominantly represent to NNW-SSE oriented Rantoli Fault. Near the fault
plane the magnetic foliation are parallel to sub-parallel to the Fault plane and
trending NNW-SSE to N-S, whereas one specimen (S7) away from the fault plan
giving WNW-SES trend. Magnetic foliation planes are steeply inclined with
horizontal magnetic lineation except one specimen S6 (gently plunging) (Fig. 5.10
a).
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Figure 5.8: Geological map of the Seri-Seraghat sector showing distribution of various lithounits and position of AMS samples.
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Figure 5.9: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in the Sartola- Nali domain, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the domain in the NASZ, Seri-Seraghat sector. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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Figure 5.10: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in the Naichun- Rantoli domain, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the domain in the NASZ, Seri-Seraghat sector. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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Mica bearing quartzarenite shows high anisotropy with positive susceptibly
(Fig. 5.10 b). Pj and Km data of proto-mylonite, mylonite to ultramylonites explain
the decrease in the susceptibility with increase in anisotropy (proto-mylonite to
mylonite) and then increase in susceptibility with increase in anisotropy (mylonite
to ultramylonites) (Fig. 5.10 b). Here plots are showing positive relationship in the
data of schist and micaceous quartzite. Km vs. T and Pj vs. T plots are
representing neutral to oblate shape of magnetic ellipsoids (T=0 and T>0) (Fig.
5.10 c and d).
III. Seraghat-Dwarahat Sector
Seraghat-Dwarahat sector comprises a large area, has been further subdivided
for detail study into two regions i.e. Seraghat-Someshwar and Someshwar-
Dwarahat.
(i) Seraghat-Someshwar Domain
This region is characterized by NNW-SSE oriented Takula Fault and NE-
SW oriented Rasiyari Fault, however the fabrics of the rock units are dominatingly
controlled by the NAT. the detail AMS study is done across the NAT (Fig. 5.11).
Sampling in the Kaphligair area was carried out across the NAT and along
the Rasiyari fault. Here the magnetic foliation planes have parallel to sub-parallel
orientation with the NE-SW oriented fault plane. Magnetic lineations are
horizontal to gently plunging with vertical magnetic foliation planes (Fig. 5.12 a).
Similar to other area, here AMS data of mylonite in plot Pj vs. Km shows inverse
relation ship (Fig. 5.12 b). In Km vs. T and Pj vs. T plots data lie in oblate (T>0) to
prolate field (T<0) (Fig. 5.12 c, d).
The Kanarichhina area is mainly deducing the NAT dominating AMS
results. Magnetic foliations are steeply inclined, parallel to sub-parallel to the NAT
and lineation gentle to steeply plunging with variable orientations (Fig. 5.13 a).
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Fig
ure
5.1
1:
Geo
log
ical
ma
p o
f th
e S
era
gh
at-
So
me
sh
war
do
ma
in s
ho
win
g d
istr
ibu
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f vari
ou
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ith
ou
nit
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sit
ion
of
sam
ple
s t
aken
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r A
MS
stu
dy.
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Figure 5.12: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in the Kaphligair region, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the region in the NASZ, Seraghat-Someshwar domain. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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Figure 5.13: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in the Kanarichhina region, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the region in the NASZ, Seraghat-Someshwar domain. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
Magnetic foliation orientations in the Saryu rock units support N-S or
NNW-SSE compression in the area. Similar to other area, AMS data of proto-
mylonite and mylonite in the Pj vs. Km plot infers inverse relation ship, whereas
schist and mica bearing quartzarenite show positive relation ship between Pj and
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Km (Fig. 5.13 b). In Km vs. T and Pj vs. T plots data lie in oblate (T>0) to prolate
field (T<0) (Fig. 5.13 c, d).
(ii) Someshwar-Dwarahat Domain
The Someshwar-Dwarahat is characterized by NNE-SSW trending faults
in Binta-Bagwalipokhar and Someshwar-Ranman areas. AMS study is carried out
precisely in detail, along these faults and across the NAT (Fig. 5.14).
A NNE-SSW oriented fault is passing along the Gagas river across the
NAT and termed Gagas River Fault (Kothyari and Pant, 2008). AMS data
represent vertical to sub-vertical magnetic foliations and gentle to steeply
plunging magnetic lineations with varying orientations. Magnetic foliation planes
near the fault trace are parallel/sub-parallel to the fault, whereas at the vicinity of
the NAT they are parallel/ sub-parallel to the thrust plane (Fig. 5. 15 a). Figure
5.15 b shows inverse relation ship in the Pj and Km data of protomylonite and
mylonite units, whereas mica-bearing quartzite and micaceous-quartzarenites
giving positive relation. In Km vs. T and Pj vs. T plots data lie in oblate (T>0) to
prolate field (T<0) (Fig. 5.15 b, d).
Someshwar-Manan segment is characterized by a NNE-SSW/ Manan
Fault across the NAT. Here magnetic foliations are parallel/ sub-parallel to the
fault trace (NNE-SSW), whereas at the terminal part, magnetic foliations is sub-
parallel (WNW-ESE) to the NAT (ENE-WSW). Magnetic foliation planes show
high angle with the field foliation along the fault trace and at the terminal part they
are at low angle (D25) (which seems to be slightly rotated ENE-WSW to WNW-
ESE due to the movement along the fault) (Fig. 5.16 a). Here also granitic gneiss,
proto-mylonite and mylonite show inverse relationship between Pj and Km (Fig.
5.15 b). In Km vs. T and Pj vs. T plots data lie in oblate (T>0) to prolate field (T<0)
(Fig. 5.16 c, d).
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Fig
ure
5.1
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Figure 5.15: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in the Binta-Lodh region, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the region in the NASZ, Someshwar-Dwarahat domain, T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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Figure 5.16: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in the Someshwar-Manan region, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the region in the NASZ, Someshwar- Dwarahat domain. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic
anisotropy.
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IV. DWARAHAT-GAIRSEN SECTOR
Besides the Seraghat-Seri Sector the northwestern margin of the Almora
Nappe is also superposed by a transverse Chaukhutiya Fault that coincides with
the northeastern margin of the NAT (Valdiya, 1976; Kothyari and Pant, 2008,
Pant et al., 2011). Based upon the homogeneity of structures and tectonites, the
Chaukhutiya Fault is sub-divided into the three domains (Fig. 5.17).
In and around Dwarahat region, the NASZ is relatively narrow. Magnetic
lineations and foliations near the thrust plane are vertical to sub-vertical (Fig. 5.18
a). Magnetic foliations are characterized by variation in their orientations from E-
W to NNE-SSW and magnetic lineation from W to SW, as the trace of the NAT
swings from E-W to NNW-SSE (Fig. 5.18 a). Magnetic lineations in the ultra-
mylonite (sample D3), lie at the intersection of the field and magnetic foliations.
The ultra-mylonites located at the sharp contact of NAT yield high Km and Pj
values, as shown by sample D3 (Fig. 5.18 b). Granite-gneiss and schistose rocks
show linear inverse relationship between Pj and Km values, whereas the
ultramylonite represents totally independent Pj and Km (Fig. 5.18 b). Here the
data, except the ultramylonite sample (D3), falls within the field of lower
amphibolite facies (Borradaile and Henry, 1997; Nakamura and Borradaile,
2004). The shape of the AMS ellipsoid varies from oblate (T>0) to prolate (T<0)
as shown by plots (T vs. Km and T vs. Pj) (Fig. 5.18 c, d). The schist of the Saryu
Formation and mica-bearing quartzarenite of the Rautgara Formation have oblate
shape of stain ellipsoids, whereas mylonite and ultramylonites of the Saryu
Formation show prolate to oblate shapes of AMS ellipsoids.
In Chaukhutiya-Masi area, samples were taken across the NAT, where
magnetic foliations are vertical to sub-vertical (Fig. 5.19a). The strike of magnetic
foliations vary from ESE-WNW to NW-SE and magnetic lineation from SE to
WNW (except C98 sample). The NW-SE orientation of magnetic foliations is sub-
parallel to the trend of the Chaukhutiya Fault.
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Structural data and geomorphic features represent the E-W oriented
subsidiary brittle faults Ramganga (near Chaukhutiya) and Mahalchauri faults,
their presence are also supported by AMS data (Kothyari, 2008; Pant et al.,
2011).
The magnetic foliation planes are parallel to the Ramganga Fault plane
(Fig. 5.19a). Magnetic lineations are gently plunging in the rock units of the Saryu
Formation and horizontal in the mica-bearing quartzarenite of the Rautgara
Formation. Magnetic lineations at the junction of the Chaukhutiya and Ramganga
faults (sample C98) lie at the intersection of the field foliation and magnetic
foliations (Fig. 5.19 a). In figure 5.19 b, Pj vs. Km plot of the schist rocks shows
inverse relationship between the values of Pj and Km. The ultramylonitized granite
(specimen C98) yields high Km with high Pj value may be due to presence of minor
ferromagnetic minerals (pyrrhotite and magnetite) along with paramagnetic
minerals. On the other hand the data of micaceous quartzite reveals positive
relationship between Km and Pj values. The AMS data for mica schist, micaceous
quartzite and mylonites lie completely in oblate field (T>0). The quartzarenite
(Rautgara Formation) shows a less anisotropy (Pj), and symmetry shows more
neutral (T = 0) to prolate (T<0) shapes of magnetic ellipsoid (Fig. 5.19c and d).
In the Panduakhal region the magnetic foliations are sub-vertical to vertical
having a general E-W orientation with E to ESE plunging magnetic lineation. Near
the Mahalchauri Fault, the lineations are horizontal (samples C76 and C81). The E-
W orientation of magnetic foliations is parallel to the axial plane orientation and to
the Mahalchauri Fault plane, and also varies with orientation of field foliation (Fig.
5.20 a). This variation is inferred to be due to the growth of some magnetic
minerals in the E-W direction due to later influence of deformation that developed
the magnetic foliation trending E-W. Plot Pj vs. Km illustrates inverse relation in
schist rocks and positive in micaceous quartzite, which is similar to the
Chaukhutiya area. It suggests that the anisotropy is high in proximity of NAT
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plane and is low away from it (Fig. 5.20 b). Data of Pj, Km and T fall in oblate field
(Fig. 5.20 c, d), which is due to development of flaky micaceous minerals.
In Gairsen-Dewalikhal section samples were collected from a narrow shear
zone across the NAT (Fig. 5.21). This domain shows identical orientations of field
and magnetic foliations. The magnetic foliations are nearly parallel to the field
foliations (except specimen C57). Similar magnetic foliations in the Gairsen area
show E-W to NW-SE swing in their orientations and become parallel to thrust
plane towards the NAT. The magnetic lineations vary from E to W and NNW to
SSE in the rock units of the Saryu Formation whereas in the quartzarenite, it is
vertically dipping. The magnetic lineations in the samples C55, C56 and C60 lie at
the intersection of the field foliation and the magnetic foliations. In the Dewalikhal
area it shows WNW-ESE orientation, which is sub-parallel to the NW-SE oriented
NAT plane. Besides this the magnetic lineations show ESE orientation in the
rocks of the Saryu Formation and WNW orientation in the quartzarenite (Fig.
5.21).
In the Gairsen area, mica schists show inverse relationship, however
quartzarenite of the Rautgara Formation show positive relationship between Km
and Pj (Fig. 5.22 a). In the Pj vs. Km plot, there is a positive relationship in
micaceous quartzite (Saryu Formation) that is similar to other domain while mica-
bearing quartzarenite (Rautgara Formation) do not show any such relationship
(Fig. 5.23 a).
In the both regions of NW terminal of the NAT, T vs. Pj plots represent
that the mylonitized granite gneiss and mica schist have oblate AMS ellipsoids
(Gairsen region) and micaceous quartzite and quartzarenite have AMS ellipsoid
that vary from oblate to prolate (Dewalikhal region) (Figs. 5.22 c, d and 5.23 c, d).
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Figure 5.17: Geological map of the Dwarahat-Gairsen sector showing distribution of various lithounits and position of samples collected for AMS study.
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Figure 5.18: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in the Dwarahat domain, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the domain in the NASZ, Dwarahat-Gairsen sector. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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Figure 5.19: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in the Chaukhutiya domain, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the domain in the NASZ, Dwarahat-Gairsen sector. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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Figure 5.20: (a) Lower hemisphere equal area projections of magnetic and field foliation at different sites in the Panduakhal domain, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the domain in the NASZ, Dwarahat-Gairsen sector. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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Figure 5.21: Lower hemisphere equal area projections of magnetic and field foliation at different sites in the Gairsen and Dewalikhal domains, Dwarahat-Gairsen sector.
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Figure 5.22: In the Gairsen domain (a) Pj vs. Km plot showing negative relation (arrow) in granitic gneiss and schist, (b) Pj vs. Km (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the domain in the NASZ, Dwarahat-Gairsen sector. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
Figure 5.23: In the Dewalikhal domain (a) Pj vs. Km plot showing positive relation (arrow) in micaceous quartzite, (b) Pj vs. Km, (c) T vs. Km and (d) Jelinek plot (T vs. Pj) for all samples of the domain, Dwarahat-Gairsen sector in the NASZ. T= shape parameter and Km= mean susceptibility; Pj =corrected degree of magnetic anisotropy.
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5.4 RF/Φ AND FLINN PLOTS TECHNIQUE
Rf/φ plots are prepared, by using the data obtained through measuring the
axial ratios (Rf) and angle (φ) between the long axis and principal extension
direction, of two dimensional sections (i.e. XZ, YZ) (Figs. 5.24, 5.25, 5.26 and
5.27). In three dimensional strain studies, only two sections are required to
determine the three principal strain ratios (Dunnet, 1969; Ramsay and Huber,
1983). For three dimension value X/Y ratio is obtained from other two ratios i.e.
X/Z and Y/Z. Flinn (1962, 1978) plots are prepared by taking the axial ratio X/Y
and Y/Z in order to find shape anisotropy in strain ellipsoid across the NAT (Fig.
5.28). Rock units of the area are polymineralic and individual mineral grain
behaves differently under the stress, and strain accumulation is variable at grain
level. So it is tough to find out that which grains are giving accurate finite strain
data, however after some limitation it is useful to determine the average finite
strain in a particular rock unit.
5.4.1 RESULTS
In order to compare the AMS strain fabric only three but significant samples
of protomylonite to ultramylonite (especially of mylonitised granitic gneiss) from
each sector, are analyzed by this method (Rf/φ), and representative plots are
shown (Figs. 5.24, 5.25, 5.26 and 5.27). The major objective was to compute the
strain variation across the NAT plane with this method and compare with the
AMS stain data.
The Harmonic mean (H) (Lisle, 1977) of ‘RS’ values thus obtain by this
method, gives more accurate strain values then geometric mean and arithmetic
mean, checked by Srivastava (2004).
The Strain ellipsoid ratios (X > Y > Z) measured from the NASZ are shown
below:
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Sectors Strain ellipsoid ratios
Pancheshwar-
Seri
Protomylonite 1.45 : 1.2 : 1
Mylonite 2: 1.3 : 1
Ultramylonite 2: 1.12 :1
Seri- Seraghat Protomylonite 1.45 : 1.11 : 1
Mylonite 1.98 : 1.7 : 1
Ultramylonite 3.2 : 2.9 :1
Seraghat-
Dwarahat
Protomylonite 1.5 : 1.5 :1
Mylonite 1.92 : 1.2 :1
Ultramylonite 2.03 : 1.2 : 1
Dwarahat-
Gairsen sector
Protomylonite 1.74 : 1.57 : 1
Mylonite 2.11 : 1.57 :1
Ultramylonite 3.11 : 3 : 1
The above strain estimation represent that the mylonites to ultramylonites
across the NAT show high strain ratio of major and minimum axes of strain
ellipses. Here high strain ratio explained by intensely stretched and elongated
grains of quartz and feldspars in the mylonites and ultramylonites.
.
The strain ellipsoids shown on Flinn plots, determined from elliptical grains of
quartz and feldspars. Data of specimens of Pancheshwar-Seri and Seraghat-
Dwarahat sectors are falling flattening (k<1) to constriction (k>1) field. Whereas
strain ellipsoid of the Seri-Seraghat and Dwarahat- Gairsen sectors lying
dominatingly in flattening field (Fig. 5.28 b and d).
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Figure 5.24: Rf/φ plots in XZ and YZ section of the Pancheshwar-Seri sector of the samples
taken across the NAT.
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Figure 5.25: Rf/φ plots in XZ and YZ section of the Seri-Seraghat sector of the samples taken across the NAT.
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Figure 5.26: Rf/φ plots in XZ and YZ section of the Seraghat-Dwarahat sector of the samples taken across the NAT.
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Figure 5.27: Rf/φ plots in XZ and YZ section of the Dwarahat-Gairsen sector of the samples taken across the NAT
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Figure 5.28: Flinn plots of the samples taken across the NAT of (a) Pancheshwar-Seri, (b) Seri-Seraghat, (c) Seraghat-Dwarahat and (d) Dwarahat-Gairsen sectors.
5.5 DISCUSSION
Magnetic fabrics can reflect the shearing, folding and later faulting impacts in the
rocks (Hallwood et al., 1992; Tarling and Hrouda, 1993; Nakamura and
Nagahama, 2001; Mamtani and Sengupta, 2010). Petrography and magnetic
mineralogy (high temperature demagnetization curves) reveals that the
anisotropy is controlled mostly by paramagnetic minerals and also yielded
negligible contribution of ferromagnetic minerals. The study area is traversed by
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two regional transverse faults (NNW-SSE oriented Rantoli and Chaukhutiya
faults) and numbers of subsidiary faults (relatively small scale and variably
oriented). Through magnetic fabric study their tectonic impacts on the
surrounding rocks can be easily observed. Sub-vertical to vertical magnetic
foliation planes with their variable orientations represent the superimposition of
later developed fabrics due to continuous horizontal compressional forces.
Parallel to sub-parallel magnetic foliation planes to the transverse faults with
steep dip and horizontal to gently plunging magnetic lineations, represent the
effect of the strike slip movement of NNW-SSE oriented Rantoli and Chaukhutiya
faults along the NAT. Magnetic foliations remain parallel to the field foliations
along with steep magnetic lineation at the terminal part of the transverse fault,
also proves rotational movement along the faults. In the Central part of
transverse faults the variation in attitudes of magnetic foliation and field foliation
manifests high impact of the transverse faults and their subsidiary faults, contrary
to this in the terminal parts of the transverse faults the parallelism of magnetic
foliation with field foliation is noted. This indicates that the impact of faulting is
negligible in the terminal parts. Parallelism of magnetic foliation planes with
subsidiary faults also reflecting their tectonic impact on the magnetic fabric of the
nearby rock units. Whereas their parallelism with the NAT trend show thrusting
effect on the magnetic fabric of the rock units near the NAT.
The clusters of magnetic axes (K1, K2 and K3) are well defined in the rocks
of the Saryu Formation as well as in the highly sheared micaceous quartzarenites
of the Rautgara Formation (Gh16, S4, S8, D37, J20, G30, D8, D25, C61, C64, and C100),
as shown by stereoplots, whereas less deformed quartzarenite rock samples
away from the NAT have almost randomly oriented axes (samples Gh10, Gh5, D5,
C81 and C65), e.g. mixed maximum, intermediate and minimum axes and shows
no significant results in fabric study.
Schists are showing positive as well as negative relation between Pj and
Km. Positive relation is due to the growth of very fine grain iron oxides and
negative relation is due to alteration of paramagnetic minerals as strain
increases, which is verified by the petrography study. Granitic gneiss and proto-
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mylonite to mylonite in the study area, are consistently showing negative relation
between Pj and Km due to the decreasing the size of the paramagnetic minerals
on increasing the strain near the thrust plane. High Km value of ultramylonitized
granite is a consequence of the presence of ferromagnetic minerals (pyrrhotite,
size < 0.1mm). High Pj value at the NAT plane is due to the localization of high
strain in the rocks of the contact. Pj values across the NAT represent the
increasing amount of degree of anisotropy as well as increasing strain towards
the NAT plane.
Rf /φ plots are giving high Rs values, obtained in the ultramylonites rock
due to the presence of highly stretched and elongated grains of quartz (quartz
ribbons) and feldspars at the vicinity of the NAT, and low values are from a
distant area from the NAT in the shear zone. it represent high strain in the central
part of the NASZ.
Highly fractured and sheared rocks in the fault zones show distinct
magnetic foliations, which are parallel or sub-parallel to the fault plane. Their
parallel orientations are due to the development of fractures parallel to the fault
zone and growth of very fine grain iron oxides along the microscopic fractures,
which have changed the magnetic properties drastically. These results of
fractured rocks are significant in finding out the effects of the main transverse
faults as well as of the small scale subsidiary faults (Nakamura and Nagahama,
2001).
The plots of magnetic parameters (T vs. Pj) show dominating oblate
magnetic ellipsoids in the central part of the transverse faults, and prolate to
oblate magnetic ellipsoids in terminals of the transverse faults and along the
NAT. In comparison to AMS fabric the Flinn plot of axial ratio studied at
microscopic level also show the similar results. Therefore it is inferred that
deformation was mostly of flattening in the central part and constrictional in
terminal parts of the transverse faults. Whole study along the NASZ represents
the dominating oblate shape magnetic ellipsoid in the transverse faults area is the
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cause of flattening strain, whereas prolate to oblate shape in other parts of the
NASZ is due to constrictional to flattening strain. In addition to this Rf /φ plot
represents high strain value at the contact of NAT, which decreases away from
the NAT plane, whereas φ angle decreases towards the NAT contact or at the
center of the NASZ.
5.6 CONCLUSION
Magnetic fabric studies along the NASZ and associated transverse faults
reveal the finite-strain in ductile to brittle fields of deformation. The steep
magnetic foliations are interpreted to be on account of regional compression.
Strike of the magnetic foliations and plunge direction of magnetic lineations are
parallel/ sub-parallel to the NAT trace but where the transverse faults are
encountered they become parallel to sub-parallel to these faults. AMS results
revealed a strong strike-slip movement with rotational component especially
along the Rantoli and Chaukhutiya faults. Detail study along the transverse faults
also explains that they are more active in the Central part, whereas there is a little
effect in terminal parts. However near the NAT trace in the Pancheshwar-Seri
and Seraghat-Dwarahat sectors, AMS study and classical strain study (Rf / φ)
revealed the dominating effect of thrusting.
Km value decreases and anisotropy increases in the magnetic fabric of the
granitic gneiss and proto-mylonite to mylonite as moving towards the NAT
contact and proved the high strain near the thrust plane. High susceptibility in
ultramylonites indicates the presence of the pyrrhotite ferromagnetic minerals
within the lattice of paramagnetic minerals. Similarly RS values obtained in Rf/ φ
strain analysis are showing increasing strain value toward the NAT plane within
NASZ.
Dominating oblate magnetic ellipsoids indicate that strain was dominantly
flattening type along the transverse faults, and prolate to oblate magnetic and
micro-fabric strain ellipsoids along the NAT imply constrictional as well as
flattening strain and thrusting effects.
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TABLE 1: AMS data from rocks of the Pancheshwar-Seri sector of study area under low
temperature: Km (10-6 SI), mean magnetic susceptibility; K1, K2 and K3, are maximum,
intermediate and minimum susceptibility axes respectively; L and F are the intensity of
magnetic lineation and foliation respectively ; Pj, corrected anisotropy degree; T- shape
TABLE 2: AMS data from rocks of the Seraghat-Seri sector of study area under low temperature: Km (10-6 SI), mean magnetic susceptibility; K1, K2 and K3, are maximum, intermediate and minimum susceptibility axes respectively; L and F are the intensity of magnetic lineation and foliation respectively ; Pj , corrected anisotropy degree; T- shape factor.
TABLE 3: AMS data from rocks of the Seraghat-Dwarahat sector of study area under low temperature: Km (10-6 SI), mean magnetic susceptibility; K1, K2 and K3, are maximum, intermediate and minimum susceptibility axes respectively; L and F are the intensity of magnetic lineation and foliation respectively ; Pj, corrected anisotropy degree; T- shape factor.
TABLE 4: AMS data from rocks of the Dwarahat-Gairsen sector of study area under low temperature: Km (10-6 SI), mean magnetic susceptibility; K1, K2 and K3, are maximum, intermediate and minimum susceptibility axes respectively; L and F are the intensity of magnetic lineation and foliation respectively ; Pj, corrected anisotropy degree; T- shape factor.