International Journal of Geosciences, 2011, 2, 398-405
doi:10.4236/ijg.2011.24043 Published Online November 2011 (http://www.SciRP.org/journal/ijg)
Relative Chronology in High-Grade Crystalline Terrain of
the Eastern Ghats, India: New Insights
Samarendra Bhattacharya1, Rajib Kar2, Amit Kumar Saw3, Prasanta Das4
1Indian Statistical Institute, Kolkata, India
2J.K. College, Purulia, India
3National Mineral Development Corporation Limited, Hyderabad, India
4Uranium Corporation of India Limited, Turamdih, India
Received May 27, 2011; revised July 25, 2011; accepted September 7, 2011
Abstract
The two major lithology or gneiss components in the polycyclic granulite terrain of the Eastern Ghats, India,
are the supracrustal rocks, commonly described as khondalites, and the charnockite-gneiss. Northern Eastern
Ghats belt, north of the Godavari rift has been defined as the Eastern Ghats Province, while that to the south
has been defined as the Ongole domain; and although, these distinct crustal domains also record different
ages of granulite metamorphism, both of these domains are dominated by the two lithologies. Many of the
workers considered the khondalites as the oldest component with unknown basement and the charnockite-
protoliths as intrusive into the khondalites. However, published geochronological data do not corroborate the
aforesaid relations. Onset of khondalite sedimentation in the Proterozoic Eastern Ghats Province, constrained
by detrital zircon data, as around 1.3 Ga and the charnockite-protolith emplacement between 1.9 and 2.9 Ga,
argue against intrusion of felsic magma (tonalite, now enderbite!) in to the khondalites. The field relations of
the hornblende-mafic granulite with the two gneiss components together with Sm-Nd isotopic data of the
hornblende-mafic granulites (both the xenoliths within charnockites and those interbanded with the khon-
dalites) indicate that khondalite sediments were deposited on older mafic crustal rocks. Mafic basement and
supracrustal rocks were subsequently deformed and metamorphosed together during collisional orogeny at
high to ultra-high temperatures—partial melting of mafic rocks producing the charnockitic melt; and partial
melting of pelitic sediments producing the peraluminous granitoids. This is compatible with all the geochro-
nological data as well as the petrogenetic model of partial melting for the charnockitic rocks in the Eastern
Ghats Belt. The Ongole domain, south of the Godavari rift, though, is distinct in terms of the age of first/
earliest UHT metamorphism, but here too the charnockite-protoliths are older mafic rocks evidently not in-
trusive in to the khondalites..
Keywords: Hornblende-Mafic Granulite, Xenolith, Interbanded, Mafic Basement, Partial Melting.
1. Introduction
High-grade crystalline terrains are characterized by
gneissic fabrics resulting from tectonic and metamorphic
processes and hence do not reflect the original stratifica-
tion of the sedimentary or volcanic protoliths [1]. More-
over, many of the high-grade terrains have suffered
polyphase deformation and metamorphism, which fur-
ther complicate the relative chronological relation be-
tween different units or gneiss-components. It is impera-
tive then to distinguish the different generations of the
gneissic fabrics in different components. Finally applica-
tion of geochronological methods is useful to reconstruct
the history of the crystalline terrains. The Eastern Ghats
Granulite Belt, India, with polyphase deformation and
complex metamorphic record may be taken up as a case
study.
2. Geological Background
The Eastern Ghats Belt along the east coast of India
comprises several rock types that can be grouped into the

399 S. BHATTACHARYA ET AL.
following: a) metapelitic granulites including khondalite,
quartzite and calc-granulite (supracrustals); b) char-
nockitic gneisses; c) mafic granulites; d) migmatitic
gneisses including garnetiferous granite gneisses and
leptynites; e) anorthosites; and f) alkaline complexes
(Figure 1). Detailed field studies in several sectors have
revealed three phases of folding with development of
pervasive foliations, often truncating and transposing
earlier fabrics on different scales [2-4]. On regional-scale
gneissic foliations S1 and S2 are parallel and may be de-
scribed as a S1-S2 composite fabric. Isoclinal and rootless
F1 folds with a NE-SW trending steep axial-plane folia-
tion, S1 and common structural repetitions suggest a re-
gional NW-SE directed compression and shortening dur-
ing the development of first generation folds [4]. Beside
the polyphase deformation history, the Eastern Ghats
Belt is also characterized by polycyclic metamorphic
record and dehydration melting in different crustal proto-
liths [5-9]. However, in view of different crustal resi-
dence ages from different parts of the regional granulite
terrain, as also distinct isotopic records of granulite fa-
cies metamorphism across this regional granulite terrain,
the tectonic-metamorphic evolution should be discussed
separately for the different crustal domains & provinces
identified [10,11]. Barring the Archean domains of Ren-
Figure 1. Generalized geological map of the Eastern Ghats
Belt, modified after Ramakrisnan et al., [36], showing the
broad lithological distributions.
gali and Jaypore, the northern Eastern Ghats Belt, north
of the Godavari rift is now described as the Eastern
Ghats Province (EGP) and south of the Godavari rift is
the Ongole domain (Figure 2).
Both clockwise and anti-clockwise P-T-t paths have
been reported from different parts in the EGP and two
contrasting tectonic interpretations have been proposed
[8,12,13]. Sengupta et al. related the anti-clockwise P-T-t
path with “compressive orogeny that was associated with
high heat flux through mafic magmatism”. According to
these authors granulite metamorphism was caused by
magmatic underplating, as in the model of Bohlen [14].
But Bhattacharya et al. [15] argued against the magmatic
underplating causing granulite metamorphism, on the
grounds that mafic magmatism (given by Nd-model dates
of mafic granulites) and granulite metamorphism (given
by U-Pb zircon dates) are different events, widely sepa-
rated in time. On the other hand, the reported clockwise
P-T-t paths were interpreted by Bhattacharya and Kar [8]
as the result of homogeneous shortening in a compres-
sional setting. In this context it may be noted that Tho-
mpson [16] concluded that “a simple orogenic clockwise
P-T path of burial, heating, exhumation, then cooling
will result in dehydration melting reactions during the
heating and decompression phases”.
Despite such divergent interpretations, high to ultra-
high temperatures (≥950˚C) and dehydration melting in
different crustal protoliths are commonly associated with
the first or earliest granulite facies metamorphism in the
Eastern Ghats Province [17,18]. The high to ultra-high
temperature records and the P-T-t paths reported from
the Eastern Ghats Belt are summarized in Figure 2. Al-
though, there is still some debate for the timing of this
high temperature event, Mukhopadhyay and Basak [18]
argued that the early UHT metamorphic event affected
the entire EGP; these authors also noted that the absence
of UHT assemblage in some locales may be due to the
absence of suitable bulk composition. Simmat and Raith
[17] also noted that the earliest and ultra-high tempera-
ture granulite metamorphism is recorded from both pe-
litic and charnockitic assemblages.
3. Charnockite-Khondalite Relation
One significant outstanding issue concerning the tectono-
metamorphic evolution in the Eastern Ghats Belt is the
relation between the khondalites and charnockites, the
two major gneiss components. In this communiqué we
focus on this problem, both in terms of field relations and
petrological and isotopic relations. In conjunction with
our earlier publications, additional field features and
some new isotopic data presented here, led us to propose
new tectonic interpretation of the early/first, and high a

S. BHATTACHARYA ET AL.
400
Figure 2. Different crustal domains of the Eastern Ghats Belt; or provinces shown. Im portant locations also shown. 1. Ongole,
2. Naraseraopet, 3. Kondapalle, 4. Rajamundri, 5. Paderu, 6. Anantagiri, 7. Anakapalle, 8. Garbham, 9. Sunki, 10. Jaypore,
11. Rayagada, 12. Deobhog, 13. Chilka, 14. Angul, 15. Jenapore, 16. Rengali, 17. Paikmal. P-T paths reported from different
locations are shown in boxes.References to the above: 3: [31]. 4: [32]. 5: [8]. 6: [12] 7: [5] 8: [33]. 9: [34]. 12: [35] 13: [6] 15:
[9].
to ultra-high temperature granulite metamorphism, that is
separately applicable for the EGP and the Ongole do-
main.
The Sm-Nd whole-rock isotopic analyses were carried
out at the Center of Research in Geochronology of Sao
Paulo University, Brazil, using the two-column tech-
nique, as described by Richard et al. [19] with the addi-
tion of some improvements. An ion exchange resin was
used for primary separation of the REE, followed by a
second HDEHP-coated Teflon powder column for sepa-
ration of Sm & Nd. The Sm & Nd abundances were de-
termined by isotope dilution. The isotope ratios were
measured on a VG 354 multi-collector mass spectrome-
ter. The measured ratio of 143Nd/144Nd obtained for La
Jolla standard was 0.511857 ± 0.000046 (2σ). The labo-
ratory blanks for the chemical procedure during the pe-
riod of analysis yielded maximum values of 0.4 ng for
Nd and 0.7 ng for Sm. Nd-model dates (TDM) are calcu-
lated using depleted mantle model of DePaulo [20].
It is intriguing that in the Eastern Ghats Belt, horn-
blende-mafic granulites with abundant prograde horn-
blende, are not recognized or ignored by most of the
workers. Here we demonstrate the significance of the
hornblende-mafic granulites, both in terms of their field
relations with the charnockitic gneiss and the metasedi-
mentary granulites, and in terms of the petrological and
isotopic relations.
In the Eastern Ghats Belt, hornblende-mafic granulites
occur as xenoliths within massif-type charnockites in
both the Eastern Ghats Province and the Ongole domain
(Figure 3). Our petrogenetic studies indicate charnockitic
melt as product of partial melting in mafic rocks under
granulite facies conditions [9,15,21]. Hence the proto-
liths of the charnockite-gneiss are mafic rocks, now rep-
resented by the hornblende-mafic granulites. This mafic
magmatism may be represented by TDM (crustal resi-
dence ages) of the protoliths of charnockitic gneiss as
between 1.9 and 2.9 Ga [10]. Our Sm-Nd isotopic data
on hornblende-mafic granulite xenoliths of both the East-
ern Ghats Province (Sunki and Paderu) and Ongole do-
main (Naraseraopet) indicate the mafic magmatism
around 2.5 Ga [22]. Hornblende-mafic granulites also
occur interbanded with the khondalites at several loca-
tions (Figure 4). It is interesting to note that these minor
bands of hornblende-mafic granulites interbanded with
the khondalites have similar mineralogy, namely with

401 S. BHATTACHARYA ET AL.
(a)
(b)
Figure 3. (a) Mafic granulite xenoliths in massif-type char-
nockite at Naraseraopet of the Ongole domain. S1 gneissic
foliation in host charnockitic gneiss marked. CH = char-
nockite; MG = mafic granulite; (b) Mafic granulite xeno-
liths in massif-type charnockite at Sunki of the Eastern
Ghats Province. S1 gneissic foliation in host charnockitic
gneiss marked.
abundant prograde hornblende (Figure 5). Sm-Nd whole
rock isotopic data of these mafic granulites interbanded
with the khondalites indicate the emplacement of their
protoliths, the mafic magmatism, between 1.9 and 2.9 Ga
(Table 1). That similar dates were reported by Rickers et
al. [10] for the precursors of charnockite-enderbite, may
not be fortuitous and highlights the fact that horn-
blende-mafic granulites in both the associations (xeno-
liths within charnockitic rocks and interbanded with the
khondalites) represent the same entity.
4. Discussion
4.1. Field Relation and Fabric Development
Although several reports have been published, correla-
tion of deformational events and attendant gneissic folia-
tion, in different areas or in different lithologies in the
same area still remains problematic. In terms of field
relation between two major gneiss components, several
workers have argued that khondalites or the sedimentary
granulites are the oldest components (supposed xeno-
liths), and multiply intruded by magmatic rocks, includ-
ing enderbites and charnockites [10,17]. However, the
question of the basement to these sediments remains illu-
sive. On the other hand, correlation between gneissic
(a)
(b)
Figure 4. (a) Minor mafic granulite bands interbanded with
khondalites and folded together, at Sunki of the Eastern
Ghats Province. S1-S2 composite foliation shows broad warp;
axial trace, S3 is marked by the pen. KH = khondalite; MG
= mafic granulite. (b) Mafic granulite interbanded with the
khondalite at Naraseraopet of the Ongole domain. S1-S2
composite fabric marked.
fabrics in the two components remains debatable. From
the Chilka Lake area, Bhattacharya et al., [2] proposed a
generalized deformation history from similar styles of
deformation and fabric development in the two major
gneiss-components, namely the metasedimentary granu-
lites and charnockitic rocks. Also from the same area
Dobmeier and Raith [23] observed “the enderbitic and
metasedimentary rocks have identical structural history”.
But from Angul area Mukhopadhyay and Basak [18]
noted that “gneissosity in khondalites formed earlier than
that in the charnockitic gneisses, though the two are gen-
erally parallel”.
4.2. Geochronology
During the last decade or so significant isotopic data on
different granulite lithologies have been published; but
still these could not resolve the problem of the chrono-
logical relation between metasedimentary granulites and
charnockitic gneiss. The metasedimentary granulites are
thought as the oldest component and intruded by mag-
matic rocks, enderbites and charnockites [10,17]. It is
important to note that coarse-grained pegmatitic char-
nockites are commonly recognized as distinct from the
large-scale charnockitic bodies and an intrusive relation
f this pegmatitic variety into khondalites was reported o

S. BHATTACHARYA ET AL.
402
Homblende-m afic granuli te interbanded with khondalite at Naraseraopet
Homblende-mafic granulite interbanded with khondalite at Paikmal
(a) (b)
Horrblend e-mafic gra nu lite int e rb anded wit h khonda lite at Surki Horrblende-mafic granulite interbanded with khondalite at Paderu
(c) (d)
Figure 5. Photomicrographs of hornblende-mafic granulites interbanded with khondalites from differe nt loc ations.
Table 1. TDM ages for mafic granulites interbanded with the khondalites.
Location Lat & Long Sample Sm (ppm) Nd (ppm) 147Sm/144Nd 143Nd/144Nd TDM (Ga)
Paikmal 20˚50′48″N;
82˚44′36″E 4P/05 3.77 14.274 0.1597 ± 9 0.512375 ± 9 1.9
Paderu 18˚7′46.8″N;
82˚39′28.8”E Pa34C 3.775 14.604 0.1563 ± 6 0.511940 ± 12 2.9
Sunki 18˚26′46.8″N;
83˚0′52.8″E D2/2 6.17 24.35 0.1532 ± 7 0.511999 ± 8 2.7
Naraseraopet 16˚4′22.3″N;
80˚1′28″E A5/1 6.02 22.36 0.1629 ± 5 0.512216 ± 11 2.8
by Subba Rao and Divakara Rao [24]. But an intrusive
relation of the large-scale charnockitic bodies into the
metasedimentary granulites (supracrustals) is not cor-
roborated by the published isotopic data, as discussed in
the following lines.
Based primarily on Nd-mapping, several crustal do-
mains or provinces with unrelated pre-metamorphic his-
tories have been identified in the Eastern Ghats Belt [10,

403 S. BHATTACHARYA ET AL.
11]. Moreover, considering the metamorphic records in
terms of their age two provinces are also recognized. The
north and central parts of the Eastern Ghats Belt, north of
the Godavari rift, is now described as the Proterozoic
Eastern Ghats Province and the earliest granulite event in
this province is recorded as 1.2 Ga [17]. South of the
Godavari rift is the Ongole domain of the Krishna Prov-
ince, and the earliest granulite event in this domain is
recorded as around 1.6 Ga [25]. This 1.6 Ga metamor-
phism and partial melting has been recorded from both
metapelites and charnockitic gneiss [15,17]. It is impera-
tive that the relative chronology between the two gneiss
components should be discussed separately for the afore-
said two provinces or domains.
In the Eastern Ghats Province, Simmat and Raith [17]
suggested that “U-Pb detrital zircons preserved in meta-
pelitic granulites and high-Mg-Al granulites provide an
upper age limit of ~1.37 Ga for the deposition of sedi-
ments”. Also these authors indicated the earliest granu-
lite facies metamorphism of 1.2 Ga in the EGP. These
authors further suggested that in the Chilka Lake area
(EGP) the metasedimentary granulites “form the oldest
component” and “it was intruded by concordant bodies
of tonalite (now enderbite) of unknown age…” These
authors also suggested that in the eastern khondalite do-
main (Anakapalle area in EGP) “high-grade supracrustal
package was intruded by basic magmas (two-pyroxene
granulites)”. It is evident from these data and interpreta-
tions that intrusion of charnockite-gneiss protolith must
be younger than 1.37 Ga. But according to the hypothesis
of charnockitic magmatism and emplacement (tonalite)
followed by granulite metamorphism [17,26], the intru-
sion of charnockite-gneiss protolith must be older than
1.2 Ga. On the other hand, Rickers et al. [10] indicated
that intrusion of the charnockite-gneiss protolith is given
by TDM as between 1.9 and 2.9 Ga. It is evident from the
aforesaid discussions that neither the khondalites as the
oldest component, nor the intrusion of charnockite-gneiss
protolith into the metasedimentary granulites (supracrus-
tals) are valid propositions.
Similar problem is encountered for the Ongole domain.
Simmat and Raith [17] indicated that “high to ultra-high
grade metamorphism occurred between 1650 and 1540
Ma, after the emplacement of basic and felsic plutonic
complexes into the supracrustal granulites at ca. 1.7 Ga”.
Bhui et al. [26] also described “intrusion of a suite of vo-
luminous felsic magma (protolith of enderbitic gneiss)”
and Kovach et al. [27] suggested that “U-Pb zircon data
from the felsic magma provided the emplacement age of
the felsic magma at 1.7 - 1.72 Ga”. Accordingly, the
sediment deposition in this domain must be older than
1.7 Ga. Although, no unequivocal evidence for the depo-
sitional age of the khondalites in the Ongole domain
have so far been published, Upadhyay et al. [28] indi-
cated that onset of sedimentation in the Eastern Ghats
Belt, could be constrained by the rift-valley Alkaline ma-
gmatism of the Prakasam Province at the western margin
of the Eastern Ghats Belt, as ca. 1.42 Ga. Thus felsic
magma emplaced around 1.7 Ga can not be considered as
intrusive into the supracrustals of younger depositional
age.
In the Eastern Ghats Province considering onset of
sedimentation around 1.3 Ga, constrained by detrital zir-
con data reported by Simmat and Raith [17], the base-
ment is most likely the older crustal rocks (1.9 to 2.9 Ga
mafic rocks reported here; and charnockite-enderbite
precursors of Rickers et al. [10]. And the earliest granu-
lite metamorphism at 1.2 Ga involved both the mafic
rocks and the supracrustal rocks. High to ultra-high tem-
perature granulite metamorphism of the mafic rocks
produced the charnockitic melt by partial melting [9,21,
29]. And the same high to ultra-high temperature granu-
lite metamorphism of the supracrustal rocks (including
khondalites and high-Mg-Al granulites) produced the
peraluminous granitoids [7,8,30].
For the Ongole domain, although no unequivocal evi-
dence for the age of sedimentation is available, it must be
older than 1.6 Ga, earliest granulite metamorphism re-
corded from high Mg-Al metapelites and this way On-
gole sediment deposition is distinct from that in the EGP,
which is said to be related to rifting and alkaline magma-
tism of the Prakasam Province. However, in terms of
field relations the khondalites as the oldest gneiss com-
ponent is not corroborated by the published isotopic data.
But our alternative petrogenetic model, namely, sedi-
mentation on older crustal rocks (1.9 - 2.9 Ga mafic
rocks) followed by granulite metamorphism during colli-
sional orogeny in both the sediments and mafic basement
around 1.6 Ga, is consistent with all the geochronologi-
cal data published so far as also the field relations of the
hornblende-mafic granulites with the two gneiss compo-
nents. However, 1.7 - 1.72 Ga U-Pb data reported from
zircons in the Ongole domain, may not be a separate
event from the UHT metamorphism that invariably leads
to anatexis and hence magmatic zircon morphology. We
would like to interpret this age as representing the peak
of UHT metamorphism and 1.6 Ga representing the
waning phase of the same.
5. Conclusions
Older mafic rocks, now represented by the hornblende-
mafic granulites, were the basement for the khondalite-
protolith sediments, in both the Eastern Ghats Province
and the Ongole domain of the Eastern Ghats Belt, India.
Earliest granulite metamorphism, 1.2 Ga in the EGP

S. BHATTACHARYA ET AL.
404
and 1.6 Ga in the Ongole domain involved both the ma-
fic basement and the khondalite sediments.
High to Ultra-high temperature granulite metamor-
phism of mafic rocks produced the charnockitic melt,
and that of pelitic sediments produced the peraluminous
granitoids, in the Eastern Ghats Belt.
6. Acknowledgements
Indian Statistical Institute has been providing infrastruc-
tural facilities, particularly for extensive fieldwork in the
Eastern Ghats Belt during the last fifteen years. Govern-
ment of India provided funds under several Research
schemes during this period. GeoScience Institute of Sao
Paulo University, Brazil is thankfully acknowledged for
providing Isotopic/geochronological data on Eastern
Ghats rocks.
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