Vol.2, No.1, 402-408 (2010) Natural Science
http://dx.doi.org/10.4236/ns.2010.24049
Review: the charnockite problem, a twenty first century
perspective
Samarendra Bhattacharya
Geological Studies Unit, Indian Statistical Institute, Calcutta, India;
Received 11 December 2009; revised 12 January 2010; accepted 5 February 2010.
ABSTRACT
Beginning of the twentieth century was marked
by coinage of a new rock name, Charnockite,
first described as a hypersthene-bearing granite
from Southern India. Since then charnockites
have been described from most of the conti-
nents and mostly restricted to high-grade belts.
Later half of the last century saw a lively debate
over an igneous versus metamorphic origin.
However, two factors acted as deterrents for the
resolution of the debate. First, charnockites and
associated rocks occur in a variety of different
structural setting and display diverse field rela-
tions, attesting to possible different mode of
origin. Second and possibly more important is
the lack of consensus on the nomenclature of
charnockites and associated rocks and this is
commonly linked with the metamorphic versus
magmatic perspective. Scanning the literature
of this period makes one believe that both
metamorphic and magmatic hypotheses are
valid, but applicable to different field setting
only. Before critically evaluating individual
cases, it is imperative that a uniform approach
in nomenclature should be agreed upon. It is
proposed that name charnockite be adopted for
any quartzofeldspathic rock with orthopyroxene,
irrespective of its mode of occurrence, struc-
tural setting and mode of origin. The associated
more mafic varieties, be better described as
mafic granulite, rather than basic charnockite.
For the patchy charnockites of east Gondwana
(including parts of Peninsular India, Sri Lanka
and Antarctica), metamorphic transformation
from amphibolite facies gneiss, by two different
mechanisms: CO2 ingress from deep level, and
drop in fluid pressure, has been proposed.
However, all such patchy occurrence is not
amenable to explanation by metamorphic trans-
formation. In some instances, migmatisation of
older charnockitic rocks is evident. Also pro-
gressive charnockitisation relating patchy char-
nockite to banded variety could be argued
against on two counts: grain-size relation and
time-relation. Larger bodies or bands have been
explained as magmatic, but in many instances,
from geochemical consideration alone. The
compositional variation, commonly encoun-
tered in many high-grade belts, if not described
in terms of field relation, may lead to wrong no-
tions of magmatic differentiation of mantle-de-
rived melts. Crustal melting of dry granulite fa-
cies source rocks has been proposed from
geochemical and isotopic data of charnockitic
intrusions. This model proposes high-tempera-
ture melting of previously dehydrated and dry
granulite source rocks. However, tectonic per-
turbation subsequent to granulite facies meta-
morphism that might have been responsible for
such high temperatures, is not well constrained
in this model. Finally, with advent of high-
pressure dehydration-melting experiments in
the nineties, dehydration-melting of mafic to
intermediate composition, syn-kinematic with
granulite facies metamorphism has been pro-
posed.
Keywords: Incipient Growth; Progressive
Charnockitisation; Plutonic Charnockite; Partial
Melting; Plutonic Metamorphism
1. INTRODUCTION
Holland [1] first described charnockite from south India,
as hypersthene-bearing granite; and Howie [2] intro-
duced the concept of plutonic metamorphism: char-
nockite magma emplaced at lower crustal depth, result-
ing in slow recrystallisation under great heat and uni-
form pressure. Recent researches, particularly, dehydra-
tion melting under granulite conditions in the deep crust,
both experimental and empirical results is compatible
with the concept of plutonic metamorphism.
Since then charnockite has been described from most

S. Bhattacharya / Natural Science 2 (2010) 402-408
403
of the continents [3-9]. However, a variety of different
mode of occurrence and structural setting, particularly
the patchy occurrence first reported by Pichamuthu from
Karnataka, south India [10] led to a lively debate over an
igneous versus metamorphic origin. The first attempt for
resolution of the charnockite problem was made by
Ravich [11].
Another contentious issue relates to nomenclature,
and to this day, this issue remains unresolved and no
consensus among practicing earth scientists is a serious
deterrent.
2. NOMENCLATURE
As more and more occurrences are reported, controver-
sies on nomenclature cropped up and the IUGS classifi-
cation, based on feldspar ratio, could not be uniformly
implemented, even for the purported plutonic char-
nockites. On the one hand, many practicing earth scien-
tists would use IUGS nomenclature, even for purported
metamorphic charnockites [12-13]. It is noteworthy that
not all the patchy occurrences are charnockite sensu
stricto [14,16,17]. On the other hand, many of the re-
ported plutons are enderbite or charno-enderbite, but
described as charnockite by some workers [17-18].
Again, it has been noted from many granulite terrenes
that large-scale bodies commonly include charnockite
and enderbite, along with intermediate varieties, but are
not distinguishable in the field [15,19,20]. Lack of con-
sensus on charnockite nomenclature continues and some
recent publications use various terms like charnockitic
gneiss of tonalite-trondjhemite affinity, enderbite, ender-
bitic charnockite [21] and charnockites, charnockitic
rocks, chemically quartz-monzodiorite, quartz monzo-
nite, granodiorite and granite [22]. It is important to note
that orthopyroxene also occurs in high-temperature pe-
litic granulites, which should not be confused with
charnockitic rocks [23].
SUMMARY:
The only plausible solution could be a general name for
any quartzofeldspathic rock with orthopyroxene as
charnockite (except of course high aluminous pelites),
irrespective of the mode of occurrence, structural setting
and mineralogical-chemical variations within each oc-
currence; the associated more mafic varieties may be
described as mafic granulite, rather than basic char-
nockite, as first proposed by us [17]. The chemical clas-
sification then may follow Streickeisen’s scheme for
common plutonic rocks and special names like enderbite
etc may be omitted.
3. MODE OF ORIGIN
Naha et al. [24] noted that charnockitic rocks in south
India occur in a variety of different structural settings,
attesting to different styles and time-relations. Since
1960, when Pichamuthu first described patchy char-
nockites from Kabbaldurga in south India, the focus
shifted to metamorphic transformation. Moreover, New-
ton and Hansen [25] questioned the possibility of slow
cooling (and hence magmatic charnockite) and recrystal-
lization of relatively dry granitic to intermediate magma
under deep seated conditions, as proposed by Holland
and Lambert [26]. Lack of experimental evidence on the
primary crystallization of orthopyroxene from such H2O
under saturated SiO2 rich liquid was their main argument
and this created a strong bias in favor of metamorphic
transformation. However, Kramers and Ridley [27] con-
sidered the evolution of the fluid phase during crystalli-
zation in the presence of orthopyroxene, and showed that
fluid saturation curve is reached at the field of high
CO2/H2O ratios and hence fluid inclusions are predicted.
They further argued that “the patchy distribution of am-
phibolite & granulite facies TTG rocks in some high-
grade terrains could be accounted for in this way”.
Melting experiments since the nineties, moreover, have
highlighted the possibility of primary crystallization of
orthopyroxene by dehydration melting reactions in the
deep crust.
3.1. Metamorphic Transformation
From many localities in south India and Sri Lanka,
“patchy” charnockites have been described as “arrested
growth”, “in situ” charnockites or charnockitisation of
amphibolite facies gneisses [28-39].
Two suggested mechanisms of this transformation:
CO2-influx and drop in fluid pressure are reviewed in the
following paragraphs.
Influx of CO2 rich fluid from deep mantle source
along structural weak zones has been proposed by sev-
eral workers [25,28,29,32,33,40]. and Newton [15] men-
tioned three criteria for recognition of charnockitisation
by CO2 influx, namely, 1) diffuseness of patchy altera-
tion, unlike discrete veins; 2) occurrences closely asso-
ciated with warping of foliation or dilation cracks; 3)
open system alteration- often loss of mafic constituents
and gain of Na and Si; Y and sometimes Rb are charac-
teristically depleted. Some of these criteria are not ubiq-
uitous, as argued by Bhattacharya and co-workers [14,16,
17]. From Kerala and from Chilka area of the Eastern
Ghats belt, these workers have argued that, 1) diffuse
boundaries of the charnockite patches could have been
produced by migmatisation of older charnockitic bodies
by a granitic melt; 2) at Elavattum and Kottavattum
quarries in Kerala, the apparent disposition along conju-
gate fractures [41], are actually disrupted segments of
fold limbs (Figure 7 in Reference [14]). In Chilka Lake
area the charnockite patches occur as elongate bodies
parallel to sub horizontal F3 fold axis and along shear

S. Bhattacharya / Natural Science 2 (2010) 402-408
404
planes with sub horizontal direction of maximum
stretching; hence these weak zones are shallow struc-
tures and cannot act as channelways for fluid ingress
from deeper levels. From the classical area of south In-
dia, Kabbaldurga, Bhattacharya and co-workers argued
that the charnockite patches are usually not emplaced
along the system of fractures, that are common in this
region; and 3) four varieties of Peninsular gneisses:
granite, trondhjemite, granodiorite and tonalite and three
varieties of charnockite: granite, trondhjemite and to-
nalite are recognized in the quarry and charnockite
patches occur within all varieties of peninsular gneisses;
hence chemical similarity between close-pairs, cited as
evidence of in- situ transformation by several workers,
could be fortuitous [17]. The reported abundance of
CO2-rich fluid inclusions in patchy charnockites has
been cited as evidence for the process of charnockitiza-
tion by fluid- streaming [42] But Sen and Bhattacharya
[16] argued that CO2-enriched fluid inclusions may be
due to preferential loss of H2O by crystal plastic defor-
mation and/or open system processes, as suggested by
Hollister [43] and Buick and Holland [44]. For the
patchy charnockites in the Eastern Ghats belt, CO2-rich
fluid streaming was also assumed by several workers
[45-47]. But the possibility of large-scale influx of
CO2-rich fluids in the Eastern Ghats was ruled out by
several workers [48,49]. Also deep mantle source of
CO2-rich fluid is not evident, while Bhowmik et al. [49]
presented isotopic evidence of local sedimentary source
(calc-granulites) in a granulite suite from the Eastern
Ghats belt.
Raith and Srikantappa [41] proposed an alternative
mechanism of this transformation. According to this
hypothesis, arrested charnockitization is internally
controlled; during near-isothermal uplift, the release of
carbonic fluids from decrepitating inclusions in the
host gneiss into developing fracture zones, resulting in
a change in fluid regime and development of an initial
fluid-pressure gradient, triggering the dehydration re-
action. What is common, however, between the two
hypotheses, is development of “arrested charnockite”
in structural weak zones. For the Kabbaldurga occur-
rence, Bhattacharya and Sen [17] pointed out that
“charnockite veins at Kabbal are usually not emplaced
along the system of fractures that are common in this
region.”
Time relations between charnockites and enclosing
gneisses, as also between patchy occurrence and massive
bodies, are important constraints, for validating or oth-
erwise of the hypothesis of in-situ transformation. Naha
et al. [24] pointed out that charnockites of Dharwar cra-
ton have formed in at least two distinct phases separated
in time and possibly by different mode of origin. And
Bhattacharya and Sen [17] pointed out that “patchy
charnockites seen in Kerala and in the Eastern Ghats are
mostly non-pegmatitic”; “the coarser-grained patches
could very well be modified versions of the smaller
patches”; and “… are basically earlier than the enclosing
gneisses”. It is imperative, therefore, to consider indi-
vidual cases of “patchy charnockite”, in terms of field
relations and if possible, in terms of isotopic age rela-
tions. For the Chilka Lake case in the Eastern Ghats belt,
Bhattacharya et al [50] reported older zircons in the
patchy charnockite to those of the host leptynite/granite
gneiss.
Another point of contention is the proposed link be-
tween patchy charnockite and massive charnockite, par-
ticularly in South India. Srikantappa et al [34] proposed
progressive charnockitisation, from some locales in the
Kerala Khondalite belt. But Sen and Bhattacharya [15]
argued that grain-size relation between smaller patches
and adjacent larger bands (supposedly final product)
does not support this hypothesis. Sen and Bhattacharya
[15] further argued on the evidence of field relation be-
tween them, that larger bands are actually older. On the
other hand, the proposed genetic link between the in-
cipient/arrested charnockite of the transition zone in
South India to regional scale granulites (massive char-
nockite), is strongly influenced by the CO2-influx hy-
pothesis [19,29,31-33,51]. According to this model as-
cent of the carbonic fluid front to higher crustal levels,
results in pervasive fluid flow and wholescale granuliti-
zation of the deeper crustal domains. However, Raith
and Srikantappa [41] argued on the evidence of field
relations, petrological, geochemical and isotopic data,
that development of arrested charnockites is a late-stage
phenomenon; and regional-scale granulites could have
been generated by dehydration melting processes.
SUMMARY:
Proposed hypothesis of charnockitisation, either by CO2
influx or drop in fluid pressure, could indeed be applica-
ble for individual cases; but each would require addi-
tional data pertaining to structural setting and field
structural data attesting to time relation. Additionally,
isotopic data would resolve the issue in favor or against
the hypothesis of progressive charnockitisation. It is
emphasized here that patchy occurrence itself should not
be taken as prototypes of incipient charnockite.
3.2. Magmatic Origin
Since Howie [2] proposed the hypothesis of plutonic
metamorphism, large-scale charnockitic rocks have been
described from many granulite terrenes [20-22,52-57].
Subba Rao and Divakara Rao [53] described char-
nockitic rocks of intrusive origin from Eastern Ghats
Belt, and identified two groups, namely basic granulite
and charnockite. From geochemical angle, these authors
proposed that protoliths of these charnockitic rocks are
the fractionated products of a melt, which was derived
from metasomatised mantle, and that these were affected

S. Bhattacharya / Natural Science 2 (2010) 402-408
405
by a depletion event probably coeval with granulite fa-
cies metamorphism. Although, two groups were said to
be identified “based upon field relations and chemistry”,
the actual field relation between basic granulite and
charnockite is not described in this publication. More-
over, as noted earlier by several workers, local structural
setting and sample locations are important criteria, and
without these information, the applicability of the mantle
melting model proposed by these authors can be ques-
tioned. In this context, it is important to note that from
detailed field mapping and structural analysis in the
Chilka Lake area of the Eastern Ghats belt, India, Bhat-
tacharya et al [57] argued that “certainly an igneous
protolith which has suffered granulite facies metamor-
phism (as evidenced by inter-layered basic granulites) is
a distinct possibility”. It is unfortunate that some work-
ers concluded that in the Eastern Ghats belt, age rela-
tions may be deduced from field relations, but neither do
they present any data, nor refer to published information;
hence their conclusion that “intruding magmas are either
mantle-derived (basic granulites, enderbites and char-
nockites with crustal contribution)…..” remains ques-
tionable [58]. Bhattacharya and co-workers described
two types of field relations between charnockitic rocks
and metapelitic rocks. First type is the interbanding of
the two lithologies; the time relation is uncertain, though
both may have undergone granulite facies metamor-
phism together [57,59]. The other type of field relation
between the two lithologies is all the more complex;
large-scale bodies of charnockitic rocks usually occur as
separate exposures, and no contact between the two
could be observed; no pelitic enclaves were observed in
charnockites. Only on the basis of the sequence of de-
formation structure, a tentative correlation has been
proposed: mafic granulite, occurring as folded enclaves
in charnockite, could be correlated to intrafolial folds in
pelitic granulites [57,60]. Dobmeier and Raith [13] also
observed that “since the enderbitic and metasedimentary
rocks have identical structural histories, the emplace-
ment (of enderbitic/tonalitic magma) happened prior to
the discernible deformation…” in the Chilka Lake area.
Magmatic origin of charnockite is also proposed by
several workers in the nineties. Kilpatrick and Ellis [7]
described Charnockite Magma Type, or C-type, from
different areas, with distinctive geochemical signatures.
This C-type magma was considered to be derived by
melting of a dry granulite source. It should be noted that
this C-type magma is not strictly charnockite sensu
stricto, but varies between charno-enderbite and char-
nockite (see K2O/Na2O ratios and SiO2 values in Table 1
of Reference [7]). Also the melting here is considered to
have been post-granulite facies metamorphism and a
crustal-melting event. Melting of dry granulite-facies
source rocks, for Antarctican charnockites, was also
proposed by some workers from geochemical and iso-
topic data [20,55,61]. On the other hand, Sheraton et al.
[54] argued that more mafic varieties may be largely
mantle-derived. It is important to note that these reports
on Antarctican charnockites show a range of composi-
tion from quartz monzodiorite through granodiorite to
adamelite. Hence, discrimination between charnockite
and enderbite magma, in massif-type or intrusive char-
nockite, was considered inappropriate by these authors.
This model proposes high-temperature melting of pre-
viously dehydrated and dry granulite source rocks. But
tectonic perturbation subsequent to granulite facies meta-
morphism that might have been responsible for such
high-temperatures is not well constrained in this model.
A partial melting interpretation for vein type char-
nockite was advocated by Hansen and Stuk [62], and
these authors reported orthopyroxene-bearing leu-
cosomes, of tonalitic to granodioritic composition,
within mafic bodies of granulite facies rocks from Cali-
fornia.
Finally, melting experiments, particularly dehydra-
tion-melting experiments of mafic to intermediate rocks
in the nineties have added a new dimension to the prob-
lem of charnockite genesis [63-66]. These experiments
demonstrate a) significant melting at 8 to 10 kbar and
temperatures in excess of 850oC; these values are com-
monly recorded from many granulite terrains; b) the re-
sidual assemblage of two-pyroxene-plagioclase-quartz ±
garnet, clearly resemble mafic granulite, that are fre-
quently found associated with massif-type charnockite; c)
melt compositions in hornblende-dehydration melting
range from tonalite-granodiorite-trondjhemite, while
hornblende-biotite combined melting produced granitic
melts.
From the classic area, Kabbaldurga, in South India,
Bhattacharya and Sen [17] presented a new interpreta-
tion of vein type charnockite. These authors proposed
hornblende and biotite dehydration melting in two types
of mafic granulites observed in the area, producing two
types of charnockitic vein, of tonalitic and granitic
compositions respectively. Besides the field features,
such as orthopyroxene-bearing leucosomes within mafic
granulite enclaves in the peninsular gneiss; these authors
presented comparative mineral compositions in the
charnockite veins and mafic granulite enclaves and bulk
compositions of the charnockite veins, and these are
compatible with the results of experimental melting,
referred to above.
For the massif-type charnockite in the Eastern Ghats
belt, India, Kar et al. [56] proposed a hornblende- dehy-
dration melting in mafic rocks, now occurring as cognate
xenoliths, under granulite facies conditions. Additionally
these authors reported two types of mafic granulites,
namely prograde hornblende-bearing mafic granulite,
interpreted as restitic granulite and two-pyroxene mafic
granulite, interpreted as peritectic segregations.

S. Bhattacharya / Natural Science 2 (2010) 402-408
406
And unlike Subba Rao and Divakara Rao’s [53] man-
tle-melting model for the Eastern Ghats charnockite,
these authors described a crustal melting phenomenon,
coeval with granulite facies metamorphism. From pres-
sure-temperature estimates and P-T path constraints,
these authors further argued that melting could have oc-
curred in thickened continental crust undergoing de-
compression. Bhattacharya et al. [67] established the
link between partial melting and granulite facies meta-
morphism with isotopic data. Kar et al. [56] further
pointed out that trace element partitioning in dehydration
melting is likely to be complex, because incongruent
melting reactions result in two sets of solid mineral
phases, residual and peritectic [68]. Hence quantitative
modeling is inappropriate when the process involves
reactions producing a variety of solid peritectic phases.
Trace element partitioning then could be considered as a
two stage process; to some extent correlated with differ-
ent degrees of partial melting. At low degree of melting
the main process is melt-restite separation, whereas at
higher degrees of melting peritectic-melt separation be-
comes more important [69-71].
SUMMARY:
Although magmatic origin of charnockites, particularly
for the large scale bodies, are evident in many cases, the
question relating to either mantle-melting or crustal
melting and in case of crustal melting, the actual melting
process and conditions remain debatable in many cases.
Dehydration-melting in mafic to intermediate rocks un-
der granulite facies conditions could be the most poten-
tial hypothesis for the massif-type charnockite, provided
prograde hornblende/biotite bearing mafic granulite en-
claves are observed. Thus the concept of plutonic meta-
morphism may return with new vigor.
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