Metamorphic Evolution of the Amphibolites from Bundelkhand Craton, Central India: P-T Constraints and Phase Equilibrium Modelling

Abstract

The amphibolites from the Mauranipur and Babina regions are located in the central part of the Bundelkhand Craton (BuC), northern India. During the geodynamic evolution of the BuC, these amphibolites underwent medium-grade metamorphism. This study combines textural observations of amphibolites from two distinct regions (Mauranipur and Babina) with mineral chemistry and phase equilibrium modelling. Observations suggest that the amphibolites of both areas have gone through three stages of metamorphism. The pre-peak stage in the amphibolites from the Mauranipur and Babina regions is marked by the assemblages Ep-Amp-Cpx-Pl-Ilm-Ru-Qz and Ep-Amp-Cpx-Pl-Ab-Ilm-Qz respectively; the peak metamorphic stage is characterized by the mineral assemblages Amp-Cpx-Pl-Ilm-Ru-Qz and Amp-Cpx-Pl-Ilm-Qz-H 2 O, which is formed during the burial process, and the post-peak stage is represented by the assemblages Amp-Pl-Ilm-Ru-Qz and Amp-Pl-Ilm-Qz-H 2 O respectively, which is formed by exhumation event. By applying the phase equilibria modelling in the NCFMASHTO system, the P-T conditions estimated from pre-peak, peak to post-peak stages are characterized as 6.7 kbar/510 o C, 7.3 kbar/578 ºC and > 3.0 kbar/>585 ºC, respectively, for the Mauranipur amphibolites; and 6.27 kbar/520 ºC, 5.2 kbar/805 ºC and > 3.0 kbar/>640 ºC respectively for Babina amphibolites. The textural association and P-T conditions of both amphibolites suggest that these rocks were affected by burial metamorphism followed by an exhumation process during subduction tectonism in the BuC.

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Journal of Environmental & Earth Sciences | Volume 04 | Issue 01 | April 2022
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*Corresponding Author:
Pratigya Pathak,
Department of Civil Engineering, Indian Institute of Technology (BHU), Varanasi, 221005, India;
Email: pratigyapathak.rs.civ17@itbhu.ac.in
DOI: https://doi.org/10.30564/jees.v4i1.4397
ARTICLE
Metamorphic Evolution of the Amphibolites from Bundelkhand
Craton, Central India: P-T Constraints and Phase Equilibrium
Modelling
Pratigya Pathak* Shyam Bihari Dwivedi Ravi Ranjan Kumar
Department of Civil Engineering, Indian Institute of Technology (BHU), Varanasi, 221005, India
ARTICLE INFO ABSTRACT
Article history
Received: 24 January 2022
Accepted: 17 March 2022
Published Online: 6 April 2022
The amphibolites from the Mauranipur and Babina regions are located in
the central part of the Bundelkhand Craton (BuC), northern India. During
the geodynamic evolution of the BuC, these amphibolites underwent
medium-grade metamorphism. This study combines textural observations
of amphibolites from two distinct regions (Mauranipur and Babina)
with mineral chemistry and phase equilibrium modelling. Observations
suggest that the amphibolites of both areas have gone through three
stages of metamorphism. The pre-peak stage in the amphibolites from the
Mauranipur and Babina regions is marked by the assemblages Ep-Amp-
Cpx-Pl-Ilm-Ru-Qz and Ep-Amp-Cpx-Pl-Ab-Ilm-Qz respectively; the peak
metamorphic stage is characterized by the mineral assemblages Amp-Cpx-
Pl-Ilm-Ru-Qz and Amp-Cpx-Pl-Ilm-Qz-H2O, which is formed during the
burial process, and the post-peak stage is represented by the assemblages
Amp-Pl-Ilm-Ru-Qz and Amp-Pl-Ilm-Qz-H2O respectively, which is formed
by exhumation event. By applying the phase equilibria modelling in the
NCFMASHTO system, the P-T conditions estimated from pre-peak, peak
to post-peak stages are characterized as 6.7 kbar/510 oC, 7.3 kbar/578 ºC
and > 3.0 kbar/>585 ºC, respectively, for the Mauranipur amphibolites;
and 6.27 kbar/520 ºC, 5.2 kbar/805 ºC and > 3.0 kbar/>640 ºC respectively
for Babina amphibolites. The textural association and P-T conditions
of both amphibolites suggest that these rocks were affected by burial
metamorphism followed by an exhumation process during subduction
tectonism in the BuC.
Keywords:
Bundelkhand craton
Amphibolite
P-T pseudosection
Subduction setting
1. Introduction
Continental crust formation began in the Hadean ages
(4.4 Ga-4.0 Ga), as reported by the Acasta gneisses of
northwestern Canada [1-3]. However, the current continen-
tal crust was developed through multiple mechanisms and
stages before 2.5 Ga [4-6]. The Archean cratons have been
well-known for their ability to provide insight into Earth’s
earlier crustal history. These Archean cratons contain a

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Journal of Environmental & Earth Sciences | Volume 04 | Issue 01 | April 2022
variety of igneous rocks that exhibit structural indicators,
as well as supracrustal rocks such as amphibolites, tonal-
ite-trondhjemite-granodiorite gneisses (TTGs), and band-
ed iron formations (BIFs) displaying various metamorphic
stages [7]. Supracrustal rocks contributed significantly to
the formation of microcontinents, supercontinents, conti-
nental evolution, and the stabilization of continents [8-10].
As a result, the metamorphic study of supracrustal rocks
is tremendously benecial and required for better under-
standing the geodynamic evolution and stabilization of
cratons and continental crust.
The Bundelkhand Craton (BuC) is located in northern
Indian Shield and also the best example of an Archean
craton for studying supracrustal rocks because it contains
a record of geological events from the Archean (3.5 Ga-
2.7 Ga; TTGs and gneisses) to the Paleoproterozoic (2.5
Ga-2.4 Ga; granitoid pulses) periods [11-13]. Despite that,
the BuC experienced various metamorphic events, and
it preserves medium to high-grade metamorphism in
multiple rock types. P-T conditions of 5.4 kbar/730 °C
and 6.2 kbar/720 °C have been reported from the Mau-
ranipur metapelites [14,15]. Similarly, high-grade horn-
blende-biotite-plagioclase bearing gneisses of P-T = 6.5-
8.5 kbar/630-720 °C has been reported in the Sukwan
(Babina) area [16]. High to ultrahigh-pressure metamor-
phism is reported in chlorite-phlogopite-corundum schists
with P-T condition as 11 kbar/630 °C and 18 kbar/630 °C
respectively, from the Babina region [11]. The garnet-bear-
ing BIF from the Mauranipur region reveals a peak tem-
perature of ~500 °C at 0.1 GPa-0.2 GPa, suggesting lower
amphibolite facies [17]. The peak metamorphic condition of
garnet-biotite gneiss has been revealed as 6.35-6.75 kbar/
755-780 ºC [18]. Several authors concluded that the mac
and ultramafic rocks of the BuC underwent greenschist
to amphibolite facies metamorphism based on textural
and mineralogical observations [19,20]. Field investigations
imply that amphibolites are connected with multiple
metamorphic Archean terrains, and hence, understanding
the geological history of that terrain requires a complete
understanding of amphibolites. Amphibolites have been
reported from various cratons in the Indian shield. Am-
phibolites (hornblende-garnet-epidote-glaucophane-au-
gite-chlorite) have been reported from the Nagaland
Ophiolite Complex, with P-T conditions of 13.8 kbar-
12.6 kbar and 625 °C-645 °C [21]. However, low-pressure
amphibolites (amphibole-plagioclase-biotite-quartz-gar-
net-chlorite-epidote-magnetite) have also been delineated
from the Western Dharwar Craton with P-T conditions of
5 kbar/600 °C [22].
One of the most contentious and exciting issues in
metamorphic petrology has always been the origin of
amphibolites. These rocks have a variety of origins and
have been determined to be the most difcult in nature, as
well as playing a signicant role in revealing the history
of Archean terrain crustal evolution [23]. Amphibolites are
thought to be formed from igneous rocks of basic and
tholeiitic magma that represent pieces of earlier oceanic
crust. Amphibolites can also be produced by metasoma-
tism of calcareous sediments [24]; some amphibolites can
be formed from pre-existing rocks that have undergone a
succession of mineral and chemical transformations as a
result of metamorphism [21]. Most researchers believe that
three processes, namely meta-igneous, meta-sedimentary,
and metasomatism, are the most valid mechanisms for the
production of amphibolites [25]. However, multiple mech-
anisms have been reported to give rise to amphibolites
hence predicting the origin of different amphibolites is the
most debated and intriguing subject in metamorphic pe-
trology.
To better understand the metamorphic development of
amphibolites from the BuC, we used petrographical study,
mineral chemistry of numerous minerals, and phase equi-
libria modelling of amphibolites from the Mauranipur and
Babina region. The field evidences of amphibolites and
textural relationship of existing minerals are explained in
this study, as well as pseudosection modelling is used to
create the P-T trajectory paths.
2. Geological Backgrounds
The Indian shield comprises two cratonic blocks,
namely the northern cratonic block consisting of Araval-
li and Bundelkhand cratons, and the southern cratonic
block, which includes Dharwar, Bastar, and Singhbhum
cratons [26] (Figure 1a). The BuC has a semi-circular shape
and is located in the north-central section of the Indian
subcontinent covering a 30,000 km2 area [27]. It is separat-
ed from the southern cratonic block by the Central Indian
Tectonic Zone (CITZ) [9]. The BuC is separated from the
Aravalli Craton by the NE-SW trending Great Boundary
Fault (GBF) and from the Himalaya by the Yamuna Fault.
The BuC is covered by Indo-Gangetic alluvium in the
north, by Vindhyan rocks in the east as well as south, and
by Deccan basalts in the southwest [28] (Figure 1b). The
Paleoproterozoic (2.0 Ga-1.8 Ga) peripheral sedimentary
basins of Gwalior, Sonrai, and Bijawar border the BuC
from the northwest, south, and southeast, respectively [29].
These basins are homotaxial, with clastic sedimentary
rocks at the bottom and carbonates with banded iron for-
mations (BIFs) at the top [30].
The BuC was primarily created throughout the Paleoar-
chean to Neoarchean periods, with the multistage crustal
formation. The BuC is divided into two crustal segments

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by an E-W trending Bundelkhand Tectonic Zone (BTZ)
that runs roughly 200 kilometres from Mahoba to Ba-
bina (Figure 1b). The rst segment is the central domain,
known as the central Bundelkhand greenstone terrane
(CBGT), the second is the southern domain, known as
the southern Bundelkhand greenstone terrane (SBGT) [30].
NW-SE trending mafic dykes of Proterozoic age (~1.98
Ga, 1.8 Ga, and 1.0 Ga) and NE-SW trending quartz veins
of Palaeoproterozoic age (1.9 Ga-1.8 Ga) dissect the
whole BuC.
Figure 1. (a) Inset map showing the location of the Bun-
delkhand Craton in India. (b) The geological map shows
different lithological units and tectonic elements of the
Bundelkhand Craton [30].
The CBGT is mainly dominated by Tonalite-Trondh-
jemite-Granodiorite (TTG) gneisses of Mesoarchean
age, greenstones of Neoarchean age, intrusive granites,
quartz reefs, mafic dykes, BIFs, and metabasites [16,31].
The CBGT, mostly exposed in the Babina and Maurani-
pur regions, contains metamorphosed mac rocks of the
Paleo-Mesoarchean period [28], felsic volcanic rocks of
the Mesoarchean period [32] and metasedimentary rocks
(BIFs). Ultramac-mac volcanic rocks from the Babina
and Mauranipur regions have been emplaced during the
Paleoarchean age (3.44 Ga) [31]. This volcanism is likely to
have occurred after the emplacement of TTGs (3.55 Ga-
3.20 Ga) in a subduction scenario from a depleted mantle
source. Pink granites and granodiorites (2.58 Ga-2.52 Ga)
cross this belt in various directions, indicating an intrusive
link with CBGT rocks [33]. According to available geo-
chronological data [34], the CBGT has been formed during
three stages of volcanic activity. Early felsic volcanic
activity occurred in the Mauranipur region around 2.82
Ga, implying Mesoarchean subduction tectonics [34]. At
2.54 Ga, a new period of volcanic activity was identied
in the Babina region [34], whereas the third stage has been
culminated during ~2.5 Ga by the accretion of massive
continental chunks [31].
Figure 2. (a) Local geological map of the study area around
Mauranipur region [19]. (b) Local geological map around the
Babina region, elucidating various geological occurrences [47].
3. Field and Megascopic Description
The amphibolite samples were collected from a vari-
ety of locations in the Babina and Mauranipur regions.
Amphibolites were exposed in the Mauranipur (Latti-
tude 25º11’54” N to 25º14’48” N, Longitude 79º05’ S to
79º09’35” S; Figure 2a) as well as in the Babina region
(Lattitude 25º09’45” N to 25º15’ N, Longitude 78º25’ S to
78º35’S; Figure 2b). Amphibolites are found as enclaves

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Journal of Environmental & Earth Sciences | Volume 04 | Issue 01 | April 2022
within TTG gneisses and felsic granitoid (Figure 3a),
but they have also been seen as intrusive dykes in TTG
gneisses in the Mauranipur and Babina regions (Figure
3b). Amphibolites have been found associated with a
variety of rock types, including BIF, calc-silicate rocks,
white schists, quartzites, and metapelites. Mauranipur am-
phibolites are found with garnetiferrous gneisses, whereas
Babina amphibolites are associated with meta-ultramac
rocks. Amphibolites from both sites have a nematograno-
blastic texture that overwrites all previous textures and
structures [32]. The amphibolites are primarily dark in col-
our and reveal a fractured nature in several areas of the re-
search eld (Figure 3b). Amphibolites from the Mauranipur
region show a massive emplacement of felsic magmatism
(Figure 3c) with folded and distorted structures (Figure 3d).
Babina amphibolites (near the Sukwa-Dukwa dam) resemble
Mauranipur amphibolites in appearance and are likewise in-
truded by felsic magma (Figure 3e,f).
Figure 3. Field photographs of the amphibolites from the study area (a) Amphibolites exposed along with TTG gneisses
in Mauranipur, (b) Small scale eld photograph of amphibolites along with deformational features in Mauranipur, (c)
Felsic magma intrusion in amphibolites of Mauranipur (d) Folding in the layers of amphibolites of Mauranipur (e,f)
Amphibolites of Babina (near Sukwa-dukwa dam) intruded by felsic magma.

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4. Petrography
The principal minerals in amphibolites from both re-
gions are amphibole, clinopyroxene, and plagioclase, with
K-feldspar, epidote, quartz, and opaque minerals (rutile,
ilmenite, and magnetite) occurring as accessory phases.
Table 1 shows the mineral assemblages and modal abun-
dances of various amphibolite samples from the Maura-
nipur and Babina regions. The mineral assemblages’ par-
agenesis is as follows:
a. Amphibole-clinopyroxene-plagioclase-rutile-epi-
dote-ilmenite-quartz
b. Amphibole-clinopyroxene-plagioclase-albite-epi-
dote-ilmenite-quartz
c. Amphibole-clinopyroxene-plagioclase-rutile-ilmen-
ite-quartz
d. Amphibole-clinopyroxene-plagioclase-ilmen-
ite-quartz
e. Amphibole-plagioclase-rutile-ilmenite-quartz
f. Amphibole-plagioclase-ilmenite-quartz
The petrographical investigation of amphibolites from
both sample MM-1 and BB-1 has revealed three differ-
ent modes of occurrence of amphiboles. These all three
amphiboles have characteristics feature and textural as-
sociation, which are depicted in the following way; the
inclusion-type amphibole (Amp1) enclosed in clinopy-
roxene, the porphyroblastic amphibole (Amp2) associated
with clinopyroxene crystals, and the retrograde amphibole
(Amp3) replacing clinopyroxene crystal. The rst-gener-
ation amphibole (Amp1) is light brown to green color and
occurs as inclusions within porphyroblast clinopyroxene,
intergrown with plagioclase, a textural feature indicat-
ing that Amp1 is a result of the prograde metamorphism
(Figure 4a,b). Porphyroblastic and subhedral grains of
amphiboles are considered as the second generation of
amphiboles (Amp2), closely associated with clinopyrox-
ene porphyroblast; and textural features suggest that it
would be a product of peak metamorphism (Figure 4c,d).
The Amp2 has a green color and contain inclusions of
discrete plagioclase, quartz, and ilmenite, representing
sieve texture. Amphibole crystals are mainly medium to
coarse-grained in nature as well as subhedral to anhedral
in shape depicting two sets of cleavage, present with
porphyroblasts of clinopyroxene (Figure 4c). Green to
grey clinopyroxene up to 1 cm in length, intergrown with
plagioclase, displays ophitic texture (Figure 4d). The tex-
tural relationship of amphibole replacing clinopyroxene
suggests retrograde metamorphism (Figure 4e,f). This
petrographical evidence indicates that the third generation
of amphibole (Amp3) is preserved in the studied amphib-
olites. Plagioclase is an essential mineral in amphibolites,
and it records essential metamorphic information. The
plagioclase is ne to medium-grained 0.1 mm-0.2 mm in
size and anhedral shape and is characterized by colorless
prismatic crystals and first-order grey color. In spite of
the presence of the plagioclase as inclusions within clino-
pyroxene and amphibole, it also occurs as the dominant
phase of the matrix (Figure 4g). Epidotes occur as <50
µm rounded subhedral crystals associated with amphibole
and plagioclase but mostly appeared as inclusion within
amphibole and clinopyroxene crystals (Figure 4a,b). Pla-
gioclase can also be found as an inclusion inside the am-
phibole and clinopyroxene matrix (Figure 4h). At the con-
uence of amphibole and plagioclase, Figure 4i displays a
lengthy lath of ilmenite.
Table 1. Summary of approximate modal composition (in percentage) of the Amphibolites of Mauranipur (MM-1, MM-
2, MM-3, MM-4, MM-5) and Babina (BB-1, BB-2, BB-3, BB-4, BB-5) samples observed under a petrological micro-
scope through Lieca Qwin software.
Sample
Model %
Amp Cpx Pl Kfs Ep Qz Opq
MM-1 52 30 6 1 4 1 6
MM-2 49 32 8 - 3 2 6
MM-3 53 27 5 2 4 1 8
MM-4 50 33 7 1 4 1 4
MM-5 55 21 10 1 5 1 7
BB-1 48 33 8 2 3 1 5
BB-2 52 24 11 - 3 2 8
BB-3 51 29 9 1 5 1 4
BB-4 53 35 5 1 2 1 3
BB-5 54 31 9 1 2 1 2

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5. Mineral Chemistry
5.1 Analytical Method
Based on petrological interpretations, two amphibolite
samples, namely MM-1 (from Mauranipur) and BB-1
(from Babina), were selected for the electron microprobe
analysis (EPMA). The mineral chemical analysis was
carried out using the EPMA (CAMECA SX ve EPMA)
at the Department of Geology, Banaras Hindu University,
Varanasi, India, under operating conditions of 15 kV and
current 10 nA.
5.2 Amphibole
All the analysed amphiboles (sample MM-1 and BB-
1) have (Na + K)<0.50, Ti<0.5, CaB > 1.5 pfu. Further-
more, according to Leak’s, classification [35], these are
Ca-amphibole groups in composition. When the analyzed
amphiboles are plotted on the leaks classication diagram,
they all occupy the tschermakite and Mgnesio-hornblende
domain (Figure 5a). All the analyzed amphiboles (sam-
ple MM-1 and BB-1) based on 23 oxygens are present-
ed in Table 2. Amp1 has a value of 0.75 for XMg [Mg/
(Fe2++Mg)], Amp2 has a value of 0.78-0.79, and Amp3
has a value of 0.71-0.72 for the sample MM-1. The XCa
values range from 0.31-0.33 for the amphiboles of MM-1.
The sample BB-1 also includes three types of amphibole,
compositionally distinct, and their XMg values are 0.71-0.74
for Amp1, 0.79-0.82 for Amp2 and 0.68-0.69 for Amp3.
Figure 4. Photomicrographs (plane-polarized light, PPL) and back-scattered electron (BSE) images of the amphibolites
(MM-1 and BB-1): (a & b) First generation Amp1 and Ep present as inclusions in Cpx with Pl, (c) Prismatic crystals
Amp2 depicting two sets of cleavage with porphyroblastic Cpx, (d) Laths of Pl embedded within Cpx crystals depicting
ophitic texture, (e) Third generation Amp3 contains inclusions of Cpx, (f) Cpx crystals partially replaced by third-gen-
eration Amp3, (g) Ep crystals occurring as inclusions within Amp and Pl, (h) Pl present as inclusion within the matrix
of Amp and Cpx, (i) Long lath shaped grain of Ilm at a junction of Amp and Pl. Mineral abbreviations are taken from
Whitney and Evans [49].

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Table 2. EPMA (wt%) and structural formula of amphibole, from the Amphibolites of Mauranipur and Babina (Sample
MM-1 and BB-1).
Sample MM-1 BB-1
Domain 5/1 6/1 7/1 8/1 22/1 25/1 43/1 45/1 46/1 47/1 50/1 52/1
Position Amp1 Amp2 Amp3 Amp1 Amp2 Amp3
SiO243.40 43.56 43.62 43.66 44.68 44.27 43.96 43.72 44.81 43.66 44.32 45.30
TiO20.41 0.39 0.42 0.50 0.43 0.42 0.48 0.35 0.40 0.43 0.44 0.41
Al2O314.22 14.32 14.87 13.41 12.94 13.61 13.10 14.83 12.20 16.08 14.62 13.50
FeO 12.11 12.14 11.95 14.21 12.41 13.03 13.77 12.13 13.50 11.58 13.65 13.28
MnO 0.26 0.10 0.06 0.18 0.23 0.33 0.16 0.18 0.10 0.11 0.16 0.24
MgO 11.89 12.13 12.57 12.30 11.99 11.55 11.81 11.83 12.93 12.33 11.12 11.41
CaO 11.65 11.68 11.92 11.64 11.69 11.26 11.98 11.84 11.74 11.44 11.80 11.34
Na2O 1.38 1.59 1.33 1.62 1.49 1.69 1.35 1.29 1.39 1.50 1.37 1.66
K2O 0.18 0.17 0.20 0.18 0.21 0.18 0.25 0.21 0.17 0.19 0.23 0.20
Total 95.49 96.07 96.93 97.69 96.06 96.34 97.56 97.12 97.24 97.32 97.70 97.35
23 oxygens
Si 6.37 6.36 6.28 6.29 6.55 6.46 6.42 6.36 6.46 6.23 6.40 6.56
AlIV 1.63 1.64 1.72 1.71 1.45 1.54 1.58 1.64 1.54 1.77 1.60 1.44
AlVI 0.83 0.82 0.81 0.57 0.78 0.81 0.67 0.90 0.54 0.94 0.89 0.86
Ti 0.05 0.04 0.05 0.05 0.05 0.05 0.05 0.04 0.04 0.05 0.05 0.05
Fe3+ 0.61 0.59 0.73 0.95 0.44 0.60 0.62 0.58 0.87 0.79 0.53 0.48
Fe2+ 0.87 0.89 0.71 0.76 1.08 0.99 1.06 0.90 0.76 0.59 1.11 1.13
Mn 0.03 0.01 0.01 0.02 0.03 0.04 0.02 0.02 0.01 0.01 0.02 0.03
Mg 2.60 2.64 2.70 2.64 2.62 2.52 2.57 2.57 2.78 2.62 2.39 2.46
Ca 1.83 1.83 1.84 1.80 1.84 1.76 1.88 1.84 1.81 1.75 1.83 1.76
Na 0.39 0.45 0.37 0.45 0.42 0.48 0.38 0.36 0.39 0.41 0.38 0.47
K 0.03 0.03 0.04 0.03 0.04 0.03 0.05 0.04 0.03 0.03 0.04 0.04
XMg 0.75 0.75 0.79 0.78 0.71 0.72 0.71 0.74 0.79 0.82 0.68 0.69
XMg = Mg/(Fe2++ Mg)
Figure 5. (a) Plots of the analyzed amphiboles obtained from the amphibolites of Mauranipur and Babina on classica-
tion diagram [35], (b) Pyroxene classication diagram showing the augite nature of the clinopyroxenes, from both am-
phibolites [36], (c) Plots of the orthoclase-albite-anorthite ternary diagram, showing andesine and labradoritic nature (d)
Plots of the ternary epidote diagram [37].

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5.3 Clinopyroxene
All the analyzed clinopyroxenes (sample MM-1 and BB-
1) based on 6 oxygens are presented in Table 3. The calcu-
lated XMg value of clinopyroxene from amphibolites of the
study area ranges from 0.40-0.63 (samples MM-1) and 0.43-
0.52 (sample BB-1). The triangular plot [36] for the pyroxene
end member shows clinopyroxenes from both samples plots
in the augite composition eld (Figure 5b). The Ca content of
clinopyroxene ranged from 0.74 pfu to 0.79 pfu for sample
MM-1 and from 0.75-0.77 pfu for sample BB-1, providing
evidence of the high Ca content of clinopyroxene.
5.4 Plagioclase
Plagioclase in samples MM-1 and BB-1 has a wide
range in anorthite content (Table 4). Plagioclases from
both samples are dominated by anorthite and albite, with
minor orthoclase. However, the plagioclase of sample
MM-1 (An = 42.92 mol%-44.49 mol%, Ab = 55.06 mol%-
56.67 mol%) has less content in anorthite and higher con-
tent in albite in comparison to sample BB-1, which has
(An = 41.50 mol%-56.09 mol%, Ab = 43.55 mol%-58.32
mol%). Feldspar in both samples contains a small amount
of total iron in the form of FeO (up to 0.47 in sample
MM-1 and 0.16 in sample BB-1). The triangular plot for
plagioclase end-members shows that plagioclase is plotted
in the andesine and labradorite composition fields from
both samples (Figure 5c).
5.5 Other Minerals
Representative chemical compositions of the analyzed
epidotes based on 25 oxygens for both the samples (MM-
1 and BB-1) are listed in Table 5. As an inclusion within
amphibole and clinopyroxene, epidote is present in both
amphibolites (MM-1 and BB-1). Subtle variations are
observed in the chemical composition of epidotes from
both samples. The values of XAl [XAl= Al/(Al+Fe3+)] for
Table 3. EPMA (wt%) and structural formula of clinopyroxenes, from the Amphibolites of Mauranipur and Babina
(Sample MM-1 and BB-1).
Sample MM-1 BB-1
Domain 11/1 12/1 13/1 14/1 23/1 44/1 45/1 88/1
SiO249.22 49.55 48.89 47.45 48.25 48.74 47.24 48.56
TiO20.14 0.12 0.16 0.1 0.10 0.15 0.18 0.16
Al2O30.49 0.55 0.77 0.5 0.60 0.99 0.55 0.47
Cr2O30.09 0.08 0.08 0.1 0.10 0.07 0.02 0.01
FeO 23.79 21.2 23.26 21.34 22.30 23.15 24.16 22.78
MnO 0.22 0.33 0.23 0.24 0.30 0.23 0.45 0.34
MgO 8.12 10.11 8.29 11.43 9.92 8.45 8.79 9.22
CaO 17.22 17.65 17.66 18.52 17.56 17.56 18.22 18.05
Na2O 0.12 0.13 0.11 0.02 0.10 0.1 0.01 0.12
K2O 0 0.02 0.01 0 0.00 0.01 0.02 0.01
Total 99.41 99.74 99.46 99.7 99.23 99.45 99.64 99.72
6 oxygens
Si 1.96 1.95 1.95 1.89 1.92 1.94 1.90 1.93
Al 0.02 0.03 0.04 0.02 0.03 0.05 0.03 0.02
Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ti 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00
Fe3+ 0.07 0.11 0.09 0.29 0.18 0.10 0.23 0.17
Fe2+ 0.72 0.58 0.68 0.40 0.55 0.67 0.56 0.58
Mn 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.01
Mg 0.48 0.59 0.49 0.68 0.59 0.50 0.53 0.55
Ca 0.74 0.74 0.75 0.79 0.75 0.75 0.79 0.77
Na 0.01 0.01 0.01 0.00 0.01 0.01 0.00 0.01
K 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
XMg 0.40 0.51 0.42 0.63 0.52 0.43 0.48 0.48
XMg = Mg/(Fe2++ Mg)

23
Journal of Environmental & Earth Sciences | Volume 04 | Issue 01 | April 2022
both representatives range from 0.84 to 0.85. All epidotes
belong to the clinozoisite-epidote-piemontite series, and
the triangular plot [37] (Figure 5d) shows that epidotes
from both the samples are dominated by clinozoisite com-
position (83.53 mol%-84.59 mol%) for sample MM-1,
whereas it is 83.39 mol%-84.97 mol% for sample BB-1.
Ilmenite reveals that TiO2 content ranges between 49.87
wt%-50.15 wt% in sample MM-1 and 45.00 wt%-45.46
wt% in sample BB-1 (Table 6). Ilmenite minerals did not
show zoning as analyses on different points on the same
grain showed almost identical values supported by BSE
images (Figure 4i).
Table 4. EPMA (wt%) and structural formula of plagioclase from Amphibolites (MM-1 and BB-1).
Sample MM-1 BB-1
Domain 37/1 38/1 39/1 40/1 144/1 142/1 149/1 150/1
SiO256.53 56.13 56.24 55.38 55.08 54.38 55.39 56.82
Al2O325.17 27.24 27.31 27.38 27.58 27.78 26.70 25.69
FeO 0.47 0.00 0.00 0.00 0.00 0.00 0.13 0.16
CaO 9.92 9.58 9.24 9.87 11.41 12.10 9.44 9.82
Na2O 6.92 6.65 6.74 6.75 5.53 5.19 7.33 6.47
K2O 0.06 0.04 0.07 0.08 0.02 0.06 0.03 0.02
Total 99.07 99.63 99.60 99.47 99.61 99.52 99.03 98.98
8 Oxygens
Si 2.58 2.53 2.54 2.51 2.50 2.47 2.53 2.58
Al 1.35 1.45 1.45 1.46 1.47 1.49 1.44 1.38
Fe2+ 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.01
Ca 0.48 0.46 0.45 0.48 0.55 0.59 0.46 0.48
Na 0.61 0.58 0.59 0.59 0.49 0.46 0.65 0.57
K 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Total 5.05 5.03 5.03 5.05 5.01 5.01 5.08 5.01
An 44.06 44.24 42.92 44.49 53.21 56.09 41.50 45.54
Ab 55.63 55.56 56.67 55.06 46.67 43.55 58.32 54.36
Or 0.32 0.20 0.41 0.45 0.12 0.35 0.18 0.09
Table 5. EPMA (wt%) and structural formula of epidote, from the Amphibolites of Mauranipur and Babina (Sample
MM-1 and BB-1).
Sample no. MM-1 BB-1
Domain 45/1 46/1 47/1 48/1 49/1 54/1
SiO235.04 36.44 35.37 36.30 36.54 36.52
TiO20.09 0.10 0.11 0.12 0.10 0.03
Al2O323.52 23.73 24.47 23.69 23.36 24.13
Fe2O313.89 13.90 13.74 12.85 14.11 13.20
MnO 0.28 0.15 0.10 0.12 0.21 0.11
CaO 23.31 22.47 22.55 23.05 22.77 23.11
Total 96.42 96.80 96.35 96.13 97.10 97.12
25 oxygens
Si 6.14 6.31 6.16 6.29 6.33 6.27
Al 4.86 4.84 5.021 4.84 4.77 4.88
Ti 0.01 0.01 0.01 0.02 0.01 0.00
Fe3+ 0.92 0.91 0.90 0.84 0.92 0.85
Mn 0.04 0.02 0.01 0.02 0.03 0.02
Ca 4.38 4.17 4.21 4.28 4.22 4.25
Total 16.42 16.26 16.32 16.28 16.28 16.28
Cz 83.53 83.93 84.59 84.97 83.39 84.89
Ep 15.75 15.69 15.17 14.71 16.08 14.83
Pie 0.72 0.37 0.24 0.31 0.53 0.28
XAl 0.84 0.84 0.85 0.85 0.84 0.85
XAl = Al/(Fe3++ Al)

24
Journal of Environmental & Earth Sciences | Volume 04 | Issue 01 | April 2022
6. Phase Equilibria Modelling
6.1 Analytical Method
The bulk rock chemical compositional analysis for the
major oxides of the representative amphibolite samples of
Mauranipur (MM-1) and Babina (BB-1) was performed at
the Birbal Sahni Institute of Palaeosciences (BSIP), Luc-
know, India. Major oxides were analyzed by X-ray uo-
rescence (XRF) using a wavelength dispersive (WD-XRF
AXIOS MAX) machine with a power of 4 KW, 60 kV-160
mA analytical, on a pressed powder pellet machine using
‘kameyo’ at a pressure of 15-20 tones with a 4 mm pallet
thickness.
6.2 P-T Pseudosection
Phase equilibria modelling was done by constructing
P-T pseudosections for the representative amphibolites
from the Mauranipur and Babina of the specic mineral
assemblages. For this purpose, Perple_X ver.6.9.0 soft-
ware [38,39] was used with an end-member thermodynamic
dataset [40,41]. The various solution models were used for
the pseudosection construction, such as clinopyroxene [42],
amphibole [43], plagioclase [44], epidote [41] and ilmenite [45].
Pseudosections are generally constructed to decipher
the equilibrium relationship among the various mineral
phases in rocks at different metamorphic P-T conditions.
Here, the P-T pseudosections for both amphibolites (MM-1
and BB-1) were calculated in the NCFMASHTO (Na2O-
CaO-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O2) system, where
P2O5 and MnO were removed due to their negligible
amounts, and quartz was taken as a ubiquitous phase (Fig-
ures 6 and 7). Furthermore, because the sample contains
no biotite, muscovite, or K-feldspar, the inuence of K2O
on the T-X(H2O) and P-T pseudosection diagrams was
ignored. The measured whole-rock composition of MM-1
and BB-1 was normalized in mol%, represented in Tables
7 and 8, respectively. The H2O content for both samples
was derived with the help of T-X(H2O) pseudosection;
however, the O2 was evaluated by the composition of min-
eral phases and their modal abundance present in the rock.
6.3 Sample MM-1
T-X(H2O) diagram of sample MM-1 was built in order
to specify the probable water content in stable constraints
to distinct metamorphic stages and associated P-T require-
ments at 7.5 and 4.0 kbar, respectively. The H2O content
is determined by the variation of H2O from 0.0 mol% to
6.0 mol% in the bulk rock composition (Figure 6a,b). In
the NCFMASHTO system, the appropriate mole ratios
of oxides are normalized to 100%, as shown in Table 7.
As illustrated in Figure 6a and 6b, the epidote is unstable
at lower H2O values before breaching the Ep entry line
Table 6. EPMA (wt%) and structural formula of rutile and ilmenite, from the Amphibolites of Mauranipur and Babina
(Sample MM-1 and BB-1).
Sample no. MM-1 BB-1
Position Rt Ilm Rt Ilm
Domain 51/1 14/1 20/1 56/1 21/1 27/1
SiO20.09 0.23 0.01 0.09 0.03 0.00
TiO299.46 49.87 50.15 99.46 51.15 51.10
FeO 0.49 45.31 44.82 0.49 45.46 45.00
MnO 0.05 0.89 1.08 0.05 1.20 0.50
CaO 0.44 0.05 0.09 0.44 0.09 0.15
V2O30.00 2.31 2.32 0.00 2.33 2.53
Total 100.54 98.87 98.55 100.54 100.38 100.04
3 oxygens
Si 0.00 0.01 0.00 0.00 0.00 0.00
Ti 0.99 0.96 0.97 0.99 0.97 0.97
Fe3+ 0.00 0.03 0.02 0.00 0.02 0.00
Fe2+ 0.01 0.94 0.94 0.01 0.94 0.95
Mn 0.00 0.02 0.02 0.00 0.03 0.01
Ca 0.01 0.00 0.00 0.01 0.00 0.00
V 0.00 0.05 0.05 0.00 0.05 0.05
Total 1.01 2.00 2.00 1.01 2.00 2.01

25
Journal of Environmental & Earth Sciences | Volume 04 | Issue 01 | April 2022
(yellow line). The solid red line indicates the appearance
of H2O as the temperature increases. The pre-peak stage
mineral assemblage Ep-Amp-Cpx-Pl-Ilm-Ru-Qz is stable
in X(H2O) values of 0.72-0.85 (long dashed black line).
The observed mineral assemblage of peak stage, Amp-
Cpx-Pl-Ilm-Ru-Qz, is stable for X(H2O) values 0.61-
0.65, while the mineral assemblage of the post-peak stage
Amp-Pl-Ilm-Ru-Qz does not appear at a higher pressure
of 7.5 kbar, this is most likely due to the pressure value
chosen being too high (Figure 6a). When the T-X(H2O)
diagram is calculated at lower pressure values of 4.0 kbar,
the post-peak stage mineral assemblage appears (Figure
6b). Hence, we chose an X(H2O) value of 4.00, which was
calculated on the basis of effective composition (Table 7)
and then normalized to 100% by considering stable elds
of mineral assemblages for pre- peak, peak and post-peak,
which is marked by a black dash line and is also used to
construct the P-T pseudosection diagram (Figure 6c,d).
The mineral assemblages identied in the petrographic
observations include clinopyroxene, amphibole, plagi-
oclase, epidote, quartz, ilmenite, and rutile. A P-T pseu-
dosection for the sample MM-1 is constructed in the P-T
range of 3-8 kbar and 400 ºC-800 ºC in the NCFMASH-
TO system (Figure 6c). Clinopyroxene in the pseudosec-
tion is pressure-dependent and continuously increases
with pressure, and it becomes stable under higher tem-
perature conditions. Amphibole is ubiquitous and stable
in approximately all P-T fields. Plagioclase also mostly
appears in the pseudosection. The signicant occurrence
of amphibole and plagioclase is supported by the presence
of amphibole and plagioclase in petrographic thin sections.
The epidote is present at higher pressures (4.5 kbar-8.0 kbar)
and lower temperatures (400 ºC-600 ºC). To acquire the ap-
propriate P-T conditions for metamorphism of the signicant
mineral assemblage, the isopleths of amphibole, clinopyrox-
ene, and epidote are delineated on the pseudosection (Fig-
ure 6d). During pre-peak metamorphism, clinopyroxene
grains contain epidote, amphibole, plagioclase, ilmenite,
and rutile, as represented by the mineral assemblage Ep-
Amp-Cpx-Pl-Ilm-Ru-Qz, which is stable at a P-T range of
Table 7. Major element concentration (wt%) and calculated effective composition (mol%) of Amphibolites of Maurani-
pur (Sample MM-1).
Composition (wt%) X(H2O)=C0X(H2O)=C1(mol%)
SiO250.27 SiO252.52 49.83 50.42
Al2O315.50 Al2O39.54 8.98 9.16
CaO 8.36 CaO 9.35 8.80 8.98
MgO 7.90 MgO 12.30 11.81 11.81
FeO 11.27 FeO 9.84 9.26 9.45
Na2O 3.78 Na2O 3.83 3.61 3.68
TiO21.33 TiO21.04 0.98 1.0
LOI 1.60 H2O 0 6 4.0
O21.56 1.47 1.50
Total 100.00 Total 100 100.0 100
Data used for gure Figure 6a,b Figure 6c,d
Table 8. Major element concentration (wt%) and calculated effective composition (mol%) of Amphibolites of Babina
(Sample BB-1).
Composition (wt%) X(H2O)=C0X(H2O)=C1(mol%)
SiO250.40 SiO252.90 49.78 50.78
Al2O316.14 Al2O39.98 9.39 9.58
CaO 8.86 CaO 9.96 9.37 9.56
MgO 7.17 MgO 11.22 10.56 10.77
FeO 11.26 FeO 9.89 9.30 9.49
Na2O 3.86 Na2O 3.93 3.70 3.77
TiO20.73 TiO20.57 0.54 0.55
LOI 1.59 H2O 0.00 6.00 4.00
O21.56 1.47 1.50
Total 100.00 Total 100 100.0 100
Data used for gure Figure 7a,b Figure 7c,d

26
Journal of Environmental & Earth Sciences | Volume 04 | Issue 01 | April 2022
5.5 kbar-8.0 kbar and 450 oC-600 oC. Amphibole, clinopy-
roxene, and epidote isopleths further narrow down the P-T
conditions of the pre-peak metamorphic stage at 6.7 kbar
and 510 oC. The mineral assemblage of Amp-Cpx-Pl-Ilm-
Ru-Qz characterizes the peak metamorphic stage. The epi-
dote becomes unstable with increasing temperatures. This
assemblage is stable in a P-T range of 7.2 kbar-8.0 kbar
and 560 ºC-580 ºC. Isopleths of amphibole and clinopy-
roxene dened the P-T conditions for the peak metamor-
phic stage at P = 7.3 kbar and T = 578 ºC.
Later, the post-peak metamorphic stage is character-
ized by the mineral assemblage of Amp-Pl-Ilm-Ru-Qz,
which acquires a Cpx free field. Due to a lowering in
pressure, clinopyroxene is no longer stable at the post-
peak metamorphic stage. This assemblage is stable under
a P-T range of 3.0-5.0 kbar and 580 ºC-700 ºC. Isopleths
of amphibole reveal the P-T conditions of the post-peak
metamorphic stage at P = > 3.0 kbar and T = > 585 ºC.
Figure 6. (a) T-X(H2O) pseudosection at 7.5 Kbar, and (b) at 4.0 kbar, showing the effects of varying the molar propor-
tions of bulk-rock H2O (in MM-1). The black dashed line is the modelled composition of H2O (4.00%). (c) P-T pseudo-
section showing pre-peak, peak and post-peak assemblages. (d) Isopleths XCa of Amp, XMg Cpx and XFe of Ep.

27
Journal of Environmental & Earth Sciences | Volume 04 | Issue 01 | April 2022
6.4 Sample BB-1
The same process of computing H2O values was re-
peated for sample BB-1. Table 8 shows how the necessary
mole ratios of oxide are normalized to 100% in the NCF-
MASHTO system. At 6.5 and 4.0 kbar, a T-X(H2O) pseu-
dosection was also displayed (Figure 7a,b). The epidote is
unstable at lower H2O concentrations before breaching the
Ep entry line, as seen in Figure 7a and 7b. As the temper-
ature rises, the solid red line represents the emergence of
H2O. In X(H2O) values of 0.60-0.65, the pre-peak mineral
assemblage Ep-Amp-Cpx-Pl-Ab-Ilm-Qz remains stable
(long dashed black line). While the mineral assemblage
of the peak stage Amp-Cpx-Pl-Ilm-Qz-H2O is stable for
X(H2O) values of 0.61-1.00, the mineral assemblage of the
post-peak stage Amp-Pl-Ilm-Qz-H2O does not appear in
Figure 7a at a higher pressure of 6.5 kbar, and this is most
likely owing to the pressure value chosen being high. The
post-peak and peak stage mineral assemblages became
visible when the T-X(H2O) diagram is calculated at lower
Figure 7. (a) T-X(H2O) pseudosection at 6.6 Kbar and (b) at 4.0 Kbar, showing the effects of varying the molar propor-
tions of bulk-rock H2O in amphibolite (sample BB-1). The black dashed line is the modelled composition of H2O (4.00%).
(c) P-T pseudosection (sample BB-1) of amphibolites showing pre-peak, peak and post-peak metamorphic assemblages
in the NCFMASTHO system. (d) Isopleths XMg of amphibole, XMg of clinopyroxene and XFe of epidote contouring P-T
pseudosection.

28
Journal of Environmental & Earth Sciences | Volume 04 | Issue 01 | April 2022
pressures of 4.0 kbar (Figure 7b). As a result, we chose an
X(H2O) value of 4.00, which was calculated using effec-
tive composition (Table 8) and then normalized to 100%
in the NCFMASHTO system by considering stable elds
of mineral assemblages for pre-peak, peak and post-peak,
which is marked by a black dash line and is also used to
construct the P-T pseudosection diagram (Figure 7c,d).
In the NCFMASHTO model system, a specific P-T
pseudosection for the representative amphibolite sample
(BB-1) has been generated in the P-T range of 3 kbar-8
kbar and 400 oC-900 oC (Figure 7c). In the pseudosection,
clinopyroxene shows a pressure-dependent character and
is stable at higher temperatures with other mineral phas-
es such as amphibole, plagioclase, ilmenite, quartz, and
H2O. Amphibole is ubiquitous in all phases and is stable
over a wide P-T range. Plagioclase is also found mostly in
the pseudosection. Epidote can be found at high and low
pressures (3.0 kbar-8.0 kbar), but only at much lower tem-
peratures (> 680 oC). The most common Ti-bearing phases
are ilmenite and magnetite. This rock is devoid of rutile.
The P-T pseudosection of the BB-1 sample revealed
three stages of metamorphism. The first is the pre-peak
metamorphic stage, which is characterized by epidote,
amphibole, plagioclase, and ilmenite inclusions inside
clinopyroxene grains. This stage produces the mineral as-
semblage Ep-Amp-Cpx-Pl-Ab-Ilm-Qz, stable in the pseu-
dosection at P-T ranges of 4.8 kbar-7.0 kbar and 450 oC-
580 oC. P-T conditions of the pre-peak metamorphic stage
at P = 6.27 kbar and T = 520 oC are further constrained by
isopleths of amphibole, clinopyroxene, and epidote (Figure
7d). The peak metamorphic stage is dened by the min-
eral assemblage Amp-Cpx-Pl-Ilm-Qz-H2O. With the ris-
ing temperature, the epidote becomes unstable, and H2O
forms at a higher temperature. This assemblage obtains a
eld with a P-T of 3.0 kbar-8.0 kbar and a temperature of
680-900 oC. The P-T conditions of the peak metamorphic
stage at P = 5.2 kbar and T = 805 oC are further narrowed
by isopleths of amphibole and clinopyroxene. Finally,
the mineral assemblage Amp-Pl-Ilm-Qz-H2O denotes the
post-peak metamorphic stage. At the post-peak metamor-
phic stage, clinopyroxene is no longer stable. This assem-
blage acquires a eld with a P-T of 3.0 kbar-4.2 kbar and
a temperature of 620 oC-780 oC and is further dened as >
3.0 kbar and > 640 oC by the isopleths of amphibole.
7. Discussion
The Mauranipur and Babina amphibolites were chosen
for this investigation because they demonstrate medium
to high-grade metamorphism in the BuC. The BuC am-
phibolites are primarily found in the Mauranipur-Babina
region as enclaves within the TTGs. The mineralogical as-
semblage of amphibolites is Hbl + Cpx + Pl ± Qz ± Ep [46].
The geochemistry of amphibolites from the CBGT was
also previously studied. According to their findings,
tholeiitic magma is the primary source of amphibolites [34].
The Nd isotopic values of amphibolites provide two
model ages: one for the protolith of amphibolites, 4.9-4.2
Ga, and the other for amphibolites metamorphism, 3.4-
3.3 Ga [31]. Based on the Nd levels, the amphibolites were
generated in a subduction-related environment. Many
researchers have postulated a subduction zone context for
the evolution of the BuC based on the analysis of TTGs,
granitoids, amphibolites, basaltic, and komatiitic rocks [34].
A geodynamic model for the evolution of the CBGT based
on observations of exposed mac-ultramac rocks in the
Babina and Mauranipur regions were also explained ear-
lier [31]. The presence of mac-ultramac rocks, metabasic
rocks, amphibolites, BIFs, and meta-sediments in CBGT
shows that they are remains of earlier oceanic crust. At
2.7 Ga, the oceanic plate subducted, causing the melting
of mac rocks containing garnet and water, which reacted
with the mantle, forming the TTGs [47].
Three metamorphic stages have been identied based
on mineral assemblages, textural correlations, and P-T
pseudosections. The creation of isopleths on the P-T
pseudosection defines the P-T conditions of these three
metamorphic stages. For amphibolites from the Maurani-
pur and Babina regions, they have set up a clockwise P-T
path. Figures 6d & 7d demonstrate the P-T pathways of
Mauranipur and Babina amphibolites, respectively. The
P-T routes of both amphibolites follow a similar pattern,
although the P-T conditions of the different metamorphic
stages differ signicantly. Mauranipur amphibolites reach
a pre-peak metamorphic stage at a lower pressure and
temperature (6.7 kbar, 510 oC) than Babina amphibolites
(6.27 kbar, 520 oC). Peak metamorphism occurs in Babina
amphibolites at 5.2 kbar/805 oC, substantially higher in
temperature and pressure than the peak metamorphic P-T
conditions in Mauranipur amphibolites (7.3 kbar/578 oC).
Due to the availability of rutile, these differences may be
conceivable. Similarly, Mauranipur amphibolites’ post-
peak metamorphic stage is dened by a P-T condition of >
3.0 kbar/ > 585 oC, which is similar in pressure but lower
in temperature than Babina amphibolites (> 3.0 kbar/ >
640 oC). Ep-Amp-Cpx-Pl-Ilm-Ru-Qz and Ep-Amp-Cpx-
Pl-Ilm-Ab-Qz mineral assemblages characterize the pre-peak
stage of Mauranipur and Babina amphibolites, respective-
ly. In the Mauranipur region, rutile is found in both a pre-
peak and a peak metamorphic state, but it is rare in amphi-
bolites from the Babina region. Rutile is a stable mineral
in medium- to high-grade metamorphic belts and serves
as a clue material for subduction tectonic environments [48].

29
Journal of Environmental & Earth Sciences | Volume 04 | Issue 01 | April 2022
Following that, both locations were further buried, re-
sulting in a constant rise in pressure and temperature, and
amphibolites underwent peak metamorphism, generating
mineral assemblages of Amp-Cpx-Pl-Ilm-Ru-Qz and
Amp-Cpx-Pl-Ilm-Qz-H2O in the Mauranipur and Babina
regions, respectively. Under a decompression procedure, a
post-peak stage followed this peak stage, with a reduction
in pressure conditions. The presence of the mineral as-
semblages Amp-Pl-Ilm-Ru-Qz (MM-1) and Amp-Pl-Ilm-
Qz-H2O (BB-1) in the post-peak stage indicates that it was
formed by the decompression and subsequent exhumation
of amphibolites on the surface.
8. Conclusions
1) P-T pseudosections for amphibolites from both re-
gions are plotted in the NCFMASHTO system and
characterized by three metamorphic stages.
2) The pre-peak, peak, and post-peak stages of amphib-
olites of the Mauranipur are designated by the pres-
ence of mineral assemblages Ep-Amp-Cpx-Pl-Ilm-
Ru-Qz, Amp-Cpx-Pl-Ilm-Ru-Qz, and Amp-Pl-Ilm-
Ru-Qz, respectively. However, the pre-peak, peak,
and post-peak stages of amphibolites of the Babina
are demarcated by the mineral assemblage Ep-Amp-
Cpx-Pl-Ab-Ilm-Qz, Amp-Cpx-Pl-Ilm-Qz-H2O, and
Amp-Pl-Ilm-Qz-H2O, respectively.
3) The P-T condition of the pre-peak stage is 6.7
kbar/510 ºC, the peak stage is 7.3 kbar/578 ºC, and
the post-peak stage is > 3.0 kbar/> 585 ºC in the
Mauranipur amphibolites. Similarly, the P-T con-
dition of the pre-peak stage is 6.27 kbar/520 ºC,
the peak stage is 5.2 kbar/805 ºC, and the post-
-peak stage is > 3.0 kbar/> 640 ºC in the Babina
amphibolites.
4) Amphibolites of both regions show a clockwise P-T
path, suggesting burial followed by exhumation.
Authors’ Contributions
Pratigya Pathak: Field sampling, Conceptualization,
Analysis, Investigation, Writing-original draft. Shyam Bi-
hari Dwivedi: Supervision, Reviewing and Editing. Ravi
Ranjan Kumar: Conceptualization, Writing-original
draft.
Conicts of Interest
On behalf of all authors, the corresponding author
would like to declare that this manuscript does not have
any conict of interest whatsoever following the Policy of
the Journal of Environment and Earth Sciences.
Acknowledgements
The authors thank the Director, Indian Institute of
Technology (BHU), for providing the infrastructure to
carry out our work. We are grateful to the Ministry of Hu-
man Resource Development (MHRD) Fellowship Scheme
for providing nancial support. The author expresses her
gratitude to Prof. R.K. Srivastava and Dr G.C. Gautam
from the Department of Geology, Banaras Hindu Univer-
sity (India), for facilitating the Microscopy Laboratory.
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