International Journal of Geosciences, 2011, 2, 348-362
doi:10.4236/ijg.2011.23037 Published Online August 2011 (http://www.SciRP.org/journal/ijg)
Emplacement and Evolution History of Pegmatites and
Hydrothermal Deposits, Matale District, Sri Lanka
G. W. A. R. Fernando1, A. Pitawala2, T. H. N. G. Amaraweera3
1Department o f Phy si cs, The Open University of Sri Lanka, Nugegoda, Sri Lanka
2Department of Geology, University of Peradeniya, Peradeniya, Sri Lanka
3Department of Mineral Sciences, Uva-Wellassa University, Passara Road, Badulla, Sri Lanka
Received February 18, 2011; revised April 5, 2011; accepted June 11, 2011
Abstract
Excellent outcrops in Matale Sri Lanka provide unique insight into the emplacement and evolution history of
hydrothermal and pegmatitic rocks in the central highlands of Sri Lanka. Field, structural, petrological,
thermo-barometric studies in the metamorphic basement rocks in the central highlands and related hydro-
thermal deposits are presented in this study. Detailed petrographic and mineralogical data reveal peak meta-
morphic conditions for the crustal unit in the study area as 854 ± 44˚C at 10.83 ± 0.86 kbar. Hydrothermal
veins consisting of quartz and mica are closely related to cross-cutting pegmatites, which significantly
post-date the peak metamorphic conditions of the crustal unit. Field relations indicate that the veins origi-
nated as ductile-brittle fractures have subsequently sealed by pegmatites and hydrothermal crystallization.
Geological, textural and mineralogical data suggest that most enriched hydrothermal veins have evolved
from a fractionated granitic melt progressively enriched in H2O, F, etc. Quartz, K-feldspar, mica, tourmaline,
fluorite and topaz bear evidence of multistage crystallization that alternated with episodes of resorption. It
was suggested that the level of emplacement of pegmatites of the Matale District was middle crust, near the
crustal scale brittle-ductile transition zone at a temperature of about 600˚C. For this crustal level and tem-
perature range, it is considered very unlikely that intruding pegmatitic melts followed pre-existing cracks. As
such the emplacement temperatures of the pegmatites could be well below the peak metamorphic estimates
in the mafic granulites. The metamorphic P-T strategy and position of formation of hydrothermal deposits
and pegmatites is summarized in the modified P-T-t-D diagrams.
Keywords: Hydrothermal Veins, Pegmatites, Emplacement History, Brittle Deformation, Sri Lanka
1. Introduction
Pegmatite veins are supposed to form from hydraulic
fractures driven by the excess pressure of intruding hy-
drous melts (Brisbin [1]). For tensile cracks to form by
hydraulic fracturing, the fluid pressure must exceed the
magnitude of the least principle stress by the tensile
strength of the rock (Shaw [2]) or, in fracture mechanics
terminology, exceed the fracture roughness of the rock.
Upon cooling and crystallization, the portion of volatiles
in the pegmatitic melt that is not incorporated into min-
erals is liberated as a fluid phase (Burnham [3]). Trans-
port of this fluid phase away from the crystallizing
magma is governed by the porosity and permeability of
the host rock of the pegmatite vein.
Minerals of hydrothermal rocks have crystallized from
hot water or have been altered by such water passing
through them. Hydrothermal depo sits in ex tension -driven
subsidence basins from any geological period are found
worldwide (Kyser [4] references therein). Hydrothermal
systems are commonly related to the emplacement at
shallow levels of fractionated, hydrous magmas. In this
environment, crystallization of medium- to coarse-grained
granite, which is forcefully invaded by later, fine-grained
material, is common . Common precipitation mechanisms
are mixing of fluids (Baatartsogt et al. [5]), or changes in
fO2 or pH (Gleeson and Yardley [6]), whereas tempera-
ture and pressure decrease is thought to be less important
in most cases (Large et al. [7]). There is no satisfactory
answer to the question of the actual source of the fluids
and the reason for their ascent. Fluid circulation or fluid
migration in convection cells is often invoked to explain

G. W. A. R. FERNANDO ET AL.349
the ascent of fluids to the site of mineralization, but re-
quires a driving force (Oliver et al. [8]).
Matale district in Sri Lanka contains the highest num-
ber of pegmatites and hydrothermal deposits exposed in
the metamorphic basement, which is considered as an
important Gondwana fragment. Up to now, only a few
studies have been done on the mineralization and evalua-
tion of pegmatite and hydrothermal deposits in Sri Lanka
(Pitawala et al. [9]) because of lack of methods available
to ascertain the PT history of pegmatite and hydrother-
mal deposits although the metamorphic history of the
metamorphic basement is fairly known (Harley [10],
Newton and Perkins [11], Schumacher et al. [12], Voll et
al. [13], Raase, [14], Fernando [15], Sajeev and Osanai
[16,17], Osanai et al. [18]). This is attributed to the lack
of methods available to ascertain the PT history of peg-
matites and hydrothermal deposits, the fluid generation
and migration. Open questions still remain on the timing
of the mineralization, the emplacement history and gen-
eration of fluids to form pegmatite and hydrothermal
deposits in the Matale district and its relationship to the
metamorphi c b asement.
In this paper the authors: 1) describe the basic geomet-
ric properties of pegmatite and hydrothermal veins of
Matale District; 2) propose the P-T history of surround-
ing metamorphic rocks with garnet-orthopy roxene thermo-
barometry using the latest experimental data and; 3)
propose the timing and mineralization of the pegmatites
and hydrothermal rocks.
2. Outline of Geology of Sri Lanka
Sri Lanka was a part of East Gondwana, together with
fragments of Antarctica, Australia, India, Madagascar,
Mozambique and Tanzania (e.g. Powell et al. [19];
Kröner [20]; Yoshida et al. [21]; Jacobs et al. [22]). Sri
Lanka acted as a bridge through which Antarctica and
East Africa can be correlated. Thus Sri Lanka reveals
remarkable geological, geochronological and geotectonic
similarities to those of neighbouring Gondwana frag-
ments. The Proterozoic basement of Sri Lanka exposes
substantial parts of the lower continental crust. Four dif-
ferent units were distinguished on the basis of isotopic,
geochronological, geochemical and petrological con-
straints viz, the Vijayan Complex (VC) in the east, the
Highland Complex (HC) in the central Wanni Complex
(WC) in the west and the Kadugannawa Complex (KC)
(Kröner et al. [23]; Cooray, [24], Milisenda et al. [25])
(Fig.1). The VC consists mainly of amphibolite-facies
granitoid rocks, metadiorites, metagabbros and migma-
tites (e.g. Cooray [24]; Kröner et al. [23]; Kehelpannala
[26]), The HC is composed of intercalated meta-sedi-
mentary and meta-igneous rocks of pelitic, mafic such as
quartzo-feldspathic granulites, charnockites, marble and
quartzite. Most of HC rocks have attained granulite-facies
conditions whereas some contain ultra-high temperature
assemblages (Sajeev and Osanai [16,17] Osanai et al.
[18]). Rocks in the Wanni Complex are granitoid
gneisses, granitic migmatites, scattered metasediments
and charnockites, metamorphosed under upper amphibo-
lite to granulite facies conditions. Rocks of the KC are
seen in the cores of six doubly plunging synforms, which
were named as ‘Arenas’ by Vitanage [27]). The dominant
rocks of the KC are hornblende and biotite-hornblende
gneisses with interlayered granitoid gneisses in the core,
pink feldspar granitic gneisses at the inner rim and me-
tasediments at the outer rim of the arenas (Perera [28]).
Rocks of KC are metamorphosed under upper amphibo-
lite to granulite facies conditions. Some granulites are
exposed in the southern part of VC near Buttala and
Kataragama. Post-peak metamorphic magmatic and hy-
drothermal activities are responsible for the formation of
pegmatite, dolerite, carbonatite and granite bodies found
in Sri Lanka (Pitawala et al. [9,29]).
Numerous thermobarometers and different mineral
paragenesess have been used to estimate the peak P-T
conditions of crystalline rocks of Sri Lanka. Lowest
temperatures of 670 - 730˚C were estimated to represent
peak metamorphic conditions using garnet-clinopyro-
xene and garnet-orthopyroxene thermometry (Sandiford
et al. [30]). Maximum temperature of 900˚C for the HC
was obtained using two-pyroxene thermometry (Schenk
et al. [31]). Temperatures ranging from 760 - 820˚C were
also obtained for mafic granulites using garnet-orthopy-
roxene and garnet-clinopyroxene pairs (Schumacher et al.
[12]). Schumacher and Faulhaber [32] estimated the P-T
condition of the Eastern, North-Eastern and South-East-
ern parts of the HC at 760 - 830˚C (garnet-orthopyroxene
of Harley [10] and 9 - 10 kbar (garnet-clinopyro-
xene-plagioclase-quartz barometer of Newton and Per-
kins [11]). Peak temperatures of metamorphism at 850 -
900˚C were derived using two-feldspar thermometry
(Voll et al. [13], Raase [14]). Maximum temperatures of
875 ± 20˚C (orthopyroxene-clinopyroxene thermometer)
at the peak pressure of 9.0 ± 0.1 kbar (garnet-clinopyro-
xene-plagioclase-quartz) for the silicic granulite, peak
temperatures of 840 ± 70˚C (orthopyroxene-clinopyro-
xene thermometer) at 9 kbar for ultramafic rocks and 820
± 40˚C for coexisting spinel sapphirine the reaction zone
were calculated within the HC (Fernando [33]). Ther-
modynamic modeling in the CaO-Na2O-K2O-FeO-MgO-
Al2O3-SiO2 system for mafic granulites in Sri Lanka in-
dicates peak metamorphic conditions of 12.5 kbar at
925˚C (Sajeev et al. [18] ).
The sapphirine-bearing pelitic granulites of the HC
have been evidenced for ultrahigh-temperature (UHT)

G. W. A. R. FERNANDO ET AL. 350
3.1. Geological and Structural Setting metamorphic conditions at around 900 to 1150˚C (Faul-
haber and Raith [34], Hiroi et al. [35], Raase and Schenk
[36], Kriegsman and Schumacher [37], Sajeev and
Osanai [16,17], Osanai et al. [38]). However, many of
the previous studies on mafic granulites gave relatively
low temperatures even tho ugh the sample locations were
in the high–temperature-pressure zone (Faulhaber and
Raith [34]). This is probably due to the resetting of
co-existing minerals on slow rate of cooling (Chak-
raborty and Ganguly [39]).
Matale District is underlain by Precambrian crystalline
rocks of the HC (Figure 2). Major rock types in the area
are meta-sediments such as marble, garnet sillimanite
biotite gneiss, quartzite and calc gneiss. Orth ogneisses of
granitoid composition and charnockitic gneisses repre-
sent the meta-igneous affinity. Meta-sedimentary and
meta-igneous rocks are intercalated with each other in
the entire area. North south striking rock units are domi-
nant in the northern part of Matale whereas rocks from
southern part strikes towards the NNW direction.
3. The Study Area Basement rocks trending NNE-SSW and N-S direc-
tions occur as an intensely stretched. Isoclinally folded
series of antiforms and synforms (Figure 3) which may
have formed during the D3 deformation (Berger and
Jayasinghe [40]) and large-scale folds (in the western
part) formed due to refolding of earlier folds (Kehelpan-
nala [26]) are the other ductile structures of the area.
The study area (Matale District) is located in the central
part of the Highland Complex, which has been consid-
ered as the oldest metamorphic unit in Sri Lankan crust
(Figure 1). Pegmatites and hydrothermal deposits are
best exposed in Matale district, wh ich ideally suit for the
study of the emplacement and evolution history of the
metamorphic basement of Sri Lanka. Brittle structures characteristic of the study area are
Figure 1. Simplified geological map of Sri Lanka (after Kröner et al. [23];Cooray [24]).

G. W. A. R. FERNANDO ET AL.351
Figure 2. Detailed geological map of the Matale District.
lineaments, joints and fractures, as inferred by aerial
photo interpretation and field observations. Two sets of
fracture/fault zones are widespread in the area. Northern
part is characterized by a NW-SE trending pattern whereas
nearly E-W trending brittle fractures are predominant in
the southern part around Naula, Nalanda and Kaudu-
pelella (Figure 3). Fracture intensity is remarkably high
in the middle part around Owala, Kavudu pelella towards
Nalanda where the pegmatites and hydrothermal deposits
are abundant (Figure 3). The orientation of the veins is
irregular and short vein segmen ts with variable thickness
appear. In places the veins for irregular array with net
like appearance. These field relations suggest nearly
contemporaneous events within a single geological epi-
sode.
3.2. Occurrence of Pegmatites and
Hydrothermal Deposits
The rock types in the inv e stigated area are characterized

G. W. A. R. FERNANDO ET AL. 352
Figure 3. Major structural features of the study area. Note that most of pegmatites and hydrothermal deposits are closely
associated with the deformation of basement.
by high-grade metamorphic rocks. They are frequently
cut by discordant conspicuous light bands, as shown in
Figures 4 and 5. The middle of the light bands are inva-
riably constituted by a pegmatitic or aplite vein with a
thickness ranging from a few mm to several metres.
Pegmatites in the Matale district can be categorized
into two groups. The f irst group occurs as narrow (1 me-
tre wide) concordant or discordant bodies as dykes,
lenses, pods and veins in high-grade metamorphic rocks
(Figure 4). The composition of these varies widely from
felsic to mafic composition and contacts with th e country
rock are irregular and often gradational. These structural
features are interpreted as products of partial melting of
high grade roc ks.
The second category includes large pegmatitic plu-
tions which are made up of mega crystals of feldspars,
quartz and mica (Figure 5). Fluorite and topaz are also
found in some pegmatites. Mica-, hornblende o r tourma-
line-rich selvedges are rarely present at the contacts of
the pegmatites with HC lithologies. The area contains
over 50 individual pegmatite bod ies, some of which have
been investigated (Pitawala et al. [9]). Lateral contacts
with country rocks are generally sharp and steep to ver-
tical and some of the larger pegmatites contain deformed
country rock.
Field observations imply that these larger pegmatites
have been emplaced after the ductile deformation. Based
on macroscopic field parameters the pegmatite bodies
have been grouped into strongly zoned pegmatites in
contrast to the first group of pegmatites. The size of the
pegmatites is highly variable upto several hundred square
metres in outcrops. They occur as circular, lenticular or
rarely oval bodies up to several tens of meters in width
and extending up to several hundred meters in strike
length. Their modes of occurrence and petrography
clearly suggest that they have a magmatic origin.
Hydrothermal processes may have associated with the
mineralization of mica and vein quartz deposits. Vein-

G. W. A. R. FERNANDO ET AL.353
Figure 4. Pegmatite associated with metamorphic basement
as concordant body near Dambulla.
Figure 5. Formation of feldspar occurring as a hydrother-
mal deposit with quartz, fluorite and topaz at Kaikawala,
Sri Lanka.
type mineral deposits are regionally clustered in a zone
of large areas of highly fractured ro cks ar ound mig mati te
diapirs. The individual occurrences of them are located at
pockets or small areas of highly fractured rocks with
prominent development of cross fracture (Silva [41],
Dinalankara [42]). Mica deposits are mainly found as
fillings of brittle fractures within the high-grade rocks in
the vicinity of pegmatite bodies (Figure 3). Fairly large
veins of quartz extending to several hundred meters are
found in many parts of the Matale District including
Rattota, Kavudupelella and Kaikawala (Figure 3). Sharp
contact zones with the host rocks and their size (surface
area of each body covers greater than 200 m2) clearly
indicate their hydrothermal origin (Pitawala et al. [9]).
Further, field setting of hydrothermal and pegmatite
bodies clearly suggest that both formations are syngene-
tic and associated with brittle structures.
A topaz (Al2 (SiO4)(OH,F)2 and fluorite (CaF2) miner-
alization zone is located at the Kaikawela and Polwatta
Colony at the north of Matale town (Kumarapeli [43]).
Topaz and fluorite have probably been formed along
with abundant quartz, feldspar and mica mineralization,
all of which are believed to form from as a granitic peg-
matite (Pitawala et al. [9]). Most of the granitic pegma-
tites in the Matale District, obstruct the general structure
of the study area suggesting these pegmatites are struc-
ture-controlled and p ost-date the regional granulite-facies
metamorphism.
4. Metamorphic Basement Rocks
Two localities that expose the mafic granulites, and
which are widespread within the metamorphic basement
of HC were identified as representative samples for this
study. All the samples from this locality are appeared as
unaltered and suit well for thermobarometric studies.
Sampling of metamorphic rocks was done in the entire
Matale district. Representative locations of the samples
used in this study are shown in the Figure 6. Approxi-
mately 20 thin sections from metamorphic rocks were
investigated by polarizing microscopy and electron mi-
croprobe.
4.1. Field Relationships
Mafic granulite exposures found at the Dambulu Oya
junction (location 1) consist predominantly of fine to
medium-grained matrix containing garnet prophyroblasts.
The host marble is a white coloured, coarse to medium-
grained rock composed of calcite and dolomite. A grada-
tional contact is observed between the host marble and
mafic granulite which has a composition of garnet, cli-
nopyroxene (Cpx) and orthopyroxene (Opx)-bearing
gneisses. Modal abundance of Cpx is rather high and
garnets (Grt) are coarse-grained.
Mafic granulite found at the 34th km post along the
Figure 6. Locations of sampling sites of metamorphic rocks.

G. W. A. R. FERNANDO ET AL. 354
Matale-Dambulla road (location 2) occurs as a boudinage
body with an average thickness of 1 - 10 m along the
strike direction within the marble and gneissic host
(Figure 7(a) and (b)). Garnet-biotite gneisses in a boudi-
nage contain high proportions of biotite usually around
garnets (Figure 7(a) and (b)). Pink coloured garnet bio-
tite gneiss comprising less biotite and k-feldpar as major
components surrounds the basic boudinage body. The
basic unit appears as an older unit, which found domi-
nantly in the area.
4.2. Mineral Assemblages
Mafic granulites are dark coloured, coarse-grained,
homogeneous mafic granu lites that consist mainly of Grt
(~30%), Opx (~40%), Cpx (~10%), plagioclase (Pl)
(~8%) with subordinate ilmenite (Ilm) (~1%) and biotite
(Bt) (~3%) (Table 1). The mafic granulite is character-
ized by th e Opx + Pl + Grt + Ilm ± Bt ( Figure 8(a)) and
Cpx + Opx + Pl + Grt + Ilm (Figure 8(b)). Garnet por-
phyroblasts are in equilibrium with orthopyroxene and
clinopyroxene in the matrix. Ilmenite is more commonly
found along the grain boundaries of garnet and pyroxene.
Biotite relics are embedded in garnet and are no t in equi-
librium with other mineral assemblages (Figure 8(c)).
Plagioclase distributed along the grain boundaries of
garnet and Cpx appears to have formed after garnet and
Cpx (Figure 8(b)).
K-Feldspar rich surrounding gneisses are mainly
composed of two feldspars (>90%), garnet (~5% and
biotite (~5%) as major constituents (Table 1). Newly
formed biotite is in good equilibrium with other mineral
phases (Figure 8(d)). Most of the K-feldspars appear as
undeformed augen shaped lenses at places (Figures 7(a)
and (b)). K-feldspar in perthite appears to be transformed
into microcline and sericitisation of plagioclase in to mica
is a common feature in these rocks.
Marbles in the area are medium to coarse grained
rocks that consist of 95 percent of carbonate minerals
and forsterite olivine (3 - 4 percent) as a common minor
constituent. Occasionally, coarse-grained tremolite, as-
sociated with ilmenite and spinel, is embedded in the
coarse-grained carbonate host (Table 1). Mafic granu-
lites are embedded in a marble host. Mineral assem-
blages show that there is no mass transfer between the
core of the mafic granulites and marble host.
4.3. Mineral Chemistry
Carbon-coated polished thin sections from granulites
were used for electron microprobe analyses. A CAM-
ECA SX 50 electron microprobe (EMP) equipped with 4
(a) (b)
(c) (d)
Figure 7. (a) (b) Boudinage with mafic granulite in a K-feldspar rich gneissic host. Note that development of augen gneisses at
places and coarse grained K-feldspar grains; (c) (d) Boudinage of mafic granulites in a marble host.

G. W. A. R. FERNANDO ET AL.355
(a) (b)
(c) (d)
Figure 8. Photomicrographs of studied rocks from the mafic granulites at Naula in Matale District. (a) Opx + Pl + Grt + Ilm
± Bt (CPL); (b) Cpx + Opx + Pl + Grt + Ilm (CPL); (c): Biotite Relics in mafic granulites (CPL); (d) Grt + Bt + Pl + Kflp
(PPL) in surrounding k-feldspar ric h gneisse s.
Table 1. Mineral assemblages from Mafic Granulites, K-Feldspar-rich gneisses and marble.
Sample Grt Ilm Pl Opx Cpx Bt Spl Ol Cal/Dol Tre Kf
Mafic
Granulites x x x x x x
Marble x x x x
K-feldspar
rich Gneisses x x x x
spectrometers (LiF-, PET-, TAP and PCO as detector
crystals) at the Ruhr-Universität Bochum, Germany was
used for the determination of quantitative mineral com-
positions. An additional EDX detector allowed the full
X-ray spectrum to be observed and the identification of
all elements with Z > 6 present in concentrations above
the limit of detection. Accelerating voltage was set to 15
kV with a beam current of 10 - 15 nA. Peak counting
time was fixed to 20 s for quantitative analysis. Sodium
bearing phases (e.g. plagioclase, micas) were measured
with a defocused beam of 5 μm diameter to minimise
signal drifts. Data reduction was performed using the
automated PAP correction procedure supplied by CAM-
ECA. Element distribution mapping was carried out us-
ing a CAMECA-CAMEBAX microprobe with three
wavelength-dispersive spectrometers. A Fortran pro-
gramme namely RCLC developed by Pattison et al. [44]
was used to refine the peak temperature and pressure.
Representative electron microprobe analyses of all
mineral assemblages are given in Table 2.
Garnet analysed is a solid solution of almandine-
grossular-pyrope (Alm53.9 - 54.8-Grs17.4 - 18.8-Pyr24.6 - 26.8)

G. W. A. R. FERNANDO ET AL. 356
Table 2. Representative Electron Microprobe Analyses of Garnet, Opx, Biotite and Plagioclase in Mafic Granulites.
Mineral Garnet Garnet Garnet Garnet Garnet Garnet Opx Opx Opx Opx
Sample 47 48 51 52 55 56 46 50 53 54
Position rim core rim core rim core core rim core rim
Al2O3 21.1 21.2 21 21.2 20.8 20.4 1.73 1.9 2.07 2.24
SiO2 37.9 38.2 37.9 38.2 37.7 37.5 50.7 50.5 50.3 50.2
CaO 6.74 6.5 6.79 6.41 6.28 6.43 0.65 0.58 0.62 0.61
FeO 28.1 27 28.1 27.3 28.4 28.1 27 26.3 27.9 27
MgO 5.16 6.04 5.34 6.1 5.43 5.73 19 19.2 18.2 18.3
MnO 0.59 0.52 0.55 0.56 0.62 0.55 0.2 0.17 0.17 0.2
Total 99.6 99.5 99.6 99.7 99.2 98.7 99.3 98.7 99.3 98.5
O = 12 O = 12 O = 12 O = 12 O = 12 O = 12 O = 6 O = 6 O = 6 O = 6
Al 1.96 1.96 1.95 1.96 1.95 1.92 0.08 0.09 0.09 0.1
Si 2.99 3 2.99 3 2.99 2.99 1.95 1.95 1.94 1.94
Ca 0.57 0.55 0.57 0.54 0.53 0.55 0.03 0.02 0.03 0.03
Fe 1.86 1.77 1.86 1.79 1.89 1.87 0.87 0.85 0.9 0.88
Mg 0.61 0.71 0.63 0.71 0.64 0.68 1.09 1.1 1.05 1.05
Mn 0.04 0.03 0.04 0.04 0.04 0.04 0.01 0.01 0.01 0.01
Sum-Cat 8.03 8.02 8.04 8.03 8.04 8.05 4.01 4.01 4.01 4.01
Sample Bt L7H 4-1 Bt L7H 4-2 Bt L7H-4-3Bt L7H-4- 4Plag L7D-1-1Plag L7D-1-2 Plag L7D-1-3 Plag L7D-1-4
Al2O3 14.2 14.4 14.3 14.1 26.7 27.7 24.7 24.9
SiO2 39.6 39.5 39.7 39.7 58.2 56.8 61 61
CaO 0 0 0.01 0 8.76 10.1 6.68 6.35
FeO 4.67 4.68 4.85 4.88 0.13 0.17 0.19 0.2
TiO2 3.94 4.27 4.11 3.95
MgO 22.7 22.9 23.3 23 0.01 0 0 0.01
MnO 0 0.01 0.01 0.01
BaO 0.64 0.8 0.73 0.73 0 0 0.03 0
Na2O 0.22 0.26 0.23 0.18 6.68 5.77 7.47 7.63
K2O 9.73 9.64 9.83 9.61 0.48 0.38 0.7 0.72
F 1.87 1.9 1.91 1.93 _ _ _ _
Cl 0.34 0.36 0.35 0.33 _ _ _ _
Total 97.9 98.7 99.3 98.4 101 101 101 101
O = 22 O = 2 2 O = 22 O = 22 O = 32 O = 32 O = 32 O = 32
Al 2.22 2.24 2.22 2.2 5.59 5.83 5.15 5.18
Si 5.27 5.22 5.22 5.26 10.4 10.1 10.8 10.8
Fe 0.52 0.52 0.53 0.54 0.02 0.03 0.03 0.03
Ti 0.39 0.42 0.41 0.39
Mg 4.5 4.51 4.56 4.54 0 0 0 0
Mn 0 0 0 0
Ca 0 0 0 0 1.67 1.92 1.27 1.21
Ba 0.03 0.04 0.04 0.04 0 0 0 0
Na 0.06 0.07 0.06 0.05 2.31 2 2.57 2.62
K 1.65 1.63 1.65 1.62 0.11 0.09 0.16 0.16
Sum-Cat 14.6 14.6 14.7 14.6 20 20 20 20
Ab 56.5 49.8 64.3 65.7
An 40.9 48 31.8 30.2
Or 2.7 2.2 4 4.1

G. W. A. R. FERNANDO ET AL. 357
mixture. Garnet associated with the othopyroxene is en-
riched in Mg and Ca.
Othopyrox ene has a formula of [Mg1.03 Fe 0.87 Al0.07
Ca0.03] Si1.9 Al0.01 O
6. It is noted that garnet coexisting
with orthopyroxene has altered its core composition due
to possible diffusion of trace elements during the cooling
stage (Fernando et al.[15]).
Biotite enri ched in Fe. XMg = [Mg/(Mg+ Fe)] of garnet
is 0.23 in cores and 0.22 in rims when in contact with
biotite. XMg of garnet is 0.26 - 0.28 in cores and 0.24 -
0.25 in rims when in contact with orthopyroxene. Garnet
core and rim compositions suggest its chemical zonation
after the equilibrium at the peak metamorphism. Relict
biotite in garnet are en riched in Mg with XMg = 0.89.
Feldspars belong to albite (Ab) – anorthite (An) series
and have a composition raining from Ab 65.70 - 49.8 and An
30.2 - 48.0.
5. Pressure Temperature Estimates of
Metamorphic Basement Rocks
The mineral assemblages of Opx + Pl + Grt + Ilm ± Bt in
the mafic granulites at Naula can be represented by the
CaO-FeO-MgO-Al2O3-TiO2-SiO2 system. Coexisting
garnet and Opx pairs were used for temperature estima-
tion. In order to estimate maximum equilibrium tem-
peratures, core-core compositions of Grt and Opx were
used at 9, 10, 11 and 12 kbars conditions using the solu-
tion model of Ganguly et al., 1996. Rim-rim composi-
tions were also used to determine the resetting tempera-
tures in the garnet-orthopyroxene pairs. Temperature
estimates from garnet-orthopyroxene thermometry are
summarized in Table 3. It was observed that the maxi-
mum equilibrated temperatures of 830 - 842˚C at 9 kbar
were obtained from the core compositio ns of co-existing
Table 3. Peak Metamorphic Temperatures Estimated using
Co-existing Garnet and Orthopyroxene Compositions after
the Method of Ganguly et al. [47].
Opx Grt Estimated Temperatures (˚C)
9
kbar 10 kbar 11 kbar 12 kbar
Core (46) Core
(48) 842.0 847.7 853.4 859.0
Core(53) Core(56) 830.1 835.7 841.3 847.0
Core(46) Rim (47) 752.0 757.2 762.4 767.6
Core (53) Rim (55) 796.6 802.1 807.5 813.0
Rim (50) Core
(52) 820.7 826.3 831.8 837.4
Rim (54) Core
(56) 814.3 819.8 825.3 830.9
Rim (50) Rim (51) 750.5 755.7 760.9 766.1
Rim (54) Rim (55) 781.7 787.1 792.5 797.9
Grt and Opx whereas temperatures of 750 - 766˚C at 9
kbar were obtained from the rim-rim compositions.
Co-existing Opx-rim and garnet-core were recorded as
814 - 820˚C, which is much higher than the temperature
estimates of the co-existing Opx core- and the garnet-rim
of 752 - 796˚C. It suggests that compositions of the or-
thopyroxene have re-equilibrated to a lesser degree al-
tered than the garnet compositions during the cooling
stages of the rocks.
This idea is further supported by the observation of
identical temperatures of core opx (46)-rim garnet (47)
and rim opx( 50)-rim garnet( 51) as shown in the Table 3.
It is not rather surprising that the diffusion coefficients of
orthopyroxene are much less than those of garnet by
several magnitudes (Chakraborty and Ganguly[39]).
The results of thermobarometry of current study com-
pare well with the P–T estimates of other areas of the
Highland Complex. Schumacher and Faulhaber[32] es-
timated the P–T conditions of the Eastern, North-eastern
and South-eastern part of the Highland Complex at 760 -
830˚C and 9 - 10 kbar. Sandif ord et al. [30] used Gt–Cpx
and Gt–Opx thermometry to illustrate the minimum
temperature of metamorphism to be 670 - 730˚C. They
noted that the actual peak metamorphism could easily be
much higher than these conditions. Kriegsman [45] ob-
tained peak equilibrium temperatures for sapphirine-
bearing granulites at 830˚C and 9 kbar using petrogenetic
grids. Schenk et al.[31] derived a maximum temperature
of 900˚C from two-pyroxene thermometry. Voll et al.[13]
estimated the peak temperatures of metamorphism be-
tween 850 - 900˚C using revised two-feldspar ther-
mometry. However, the general observation of the cur-
rent study is that a significant number of thermobarome-
try based temperature estimates of granulites determined
over past 30 years are too low and are therefore mislead-
ing. Many of these estimates are inconsistent with the
stability of the mineral assemblages of the rock.
6. Refining the Peak PT Conditions
Table 4 shows the pressure and temperature estimates
using co-existing garnet and orthopyroxene compositions
incorporating Fe-Mg exchange and Fe-Al exchange of
the Grt-Opx. Solution model of Berman [46] with the
TWQ software for mineral assemblages mentioned above
were used. Pressure-temperature estimates obtained from
this method too shows identical values with the prev ious
calculation made using Ganguly et al. [47]. However,
initial temperature estimates made from the Fe-Mg ex-
change of the garnet and orthopyroxene (Ganguly and
Tazzoli [48]) are significantly different from the tem-
perature estimate corresponding to Fe-Al composition of
orthopyroxene. It is not surprising that Al diffusion of

G. W. A. R. FERNANDO ET AL. 358
Table 4. Peak Metamorphic Temperatures Estimated using
Co-existing Garnet and Orthopyroxene Compositions Un-
corrected for Fe-Mg Exchange and Fe-Al Exchange after
the Method of Berman [46].
Uncorrected Fe-Al Uncorrected Fe-Mg
Mineral Pair Temp
(˚C) Pressure (Kbar) Temp (˚C) Pressure (Kbar)
Grt core (48) -
Opx core (46) 827 11.3 827 11.3
Grt core (56) -
Opx core(53) 851 10.7 807 9.8
Grt rim (47) -
Opx core(46) 805 11.3 724 9.8
Grt rim(5 5 ) -
Opx core(53) 863 11.0 786 9.7
Grt core(52) -
Opx rim(50) 803 9.7 786 9.5
Grt core(56) -
Opx rim(54) 863 11.0 786 9.7
Grt rim(5 1 ) -
Opx-rim(50) 791 9.9 712 8.6
Grt rim(5 5 ) -
Opx rim(54) 845 10.4 748 8.8
garnet and orthopyroxene is several magnitudes lower
than Fe-Mg diffusion and hence temperature estimates
done using the Fe-Al exchange is closer to the real peak
metamorphic estimates.
Temperature estimates from Grt-Opx of this study
suggests that both garnet and orthopyroxene composi-
tions were reset during the retrograde changes. It is also
possible that complete garnet compositions even in the
core of the garnet have reset (Fernando et al.[15]).
Therefore, the temperature estimates based on coexisting
core-core compositions of the Grt and Opx do not reflect
the peak metamorphic conditions of the area. A method
is required to refine the peak temperatures by consider-
ing the Fe-Mg exchange between Grt and Opx and the
Al- content of the Opx.
The method proposed by Pattison et al. [44] may be
most useful for thermobarometric calculations because it
adjust the Fe-Mg ratios of Grt and Opx accord ing to their
modal abundance by incorporating the intergranular and
intragranular exchange of Fe-Mg between two phases. In
rocks that contain Fe-Mg phases in addition to Grt and
Opx, (in this case Bt) are also incorporating their modal
abundance into the mass balance equation, and is simul-
taneously solved for Fe-Mg ratio of each phase, so that
each of the Grt-Opx and Grt-Bt are accounted (Table 5).
Modal abundances of Fe-Mg phases are used as men-
tioned under the petrography. RCLC is a Fortran pro-
gramme developed by Pattison et al.[44] to refine the
peak temperature and pressure accounting the in-
ter-granular and intra-granular diffusion of Fe-Mg during
Table 5. Peak Metamorphic Temperatures Estimated
using Co-existing Garnet and Orthopyroxene with due
Consideration of Fe-Mg Exchange with the other Phases
(Biotite) after the Method of Pattison et al. [44].
Corrected for Al in orthopyrox-
ene and Fe-Mg bearing minerals
Mineral Pair Temp (˚C) Pressure (kbar)
Grt core (48) - Opx core (46)825 11.3
Grt core (56) - Opx core(53)870 10.7
Grt rim (47) - Op x c ore(46) 847 11.5
Grt rim(55) - Opx core(53) 871 10.5
Grt rim(51) - Opx-rim(50) 830 10.0
Grt rim(55) - Opx rim(54) 888 10.6
retrograde conditions. Aluminium component of or-
thopyroxene was taken into consideration during the es-
timates as it is obvious that diffusion co efficient of Al in
orthopyroxene is less than diffusion coefficients of Fe
and Mg in orthopyroxene by several magnitudes (Patti-
son et al, 2003). A model assuming ideal Tschermak
exchange [(Fe,Mg)vi +Siiv =Alvi+Aliv] give rise to scheme
XAlOpx = (Al/2)/2 (for six-oxygen Opx formula unit )]
was used because it gives reasonable and less scattered
temperature estimates and less erroneous values than the
calculating XAlOpx by the site occupancy method as
XAlOpx = Al M1 = Altotal – (2-Si ) (Pattison et al.[44]).
Pressures and temperatures refined from the above
method reveal that the mafic granulites experienced
granulite facies metamorphism at conditions of 854 ±
44˚C at 10.83 ± 0.86 kbar. It is notewo rthy that tempera-
ture estimate from garnet-biotite pairs are much less than
(~400˚C) temperature estimate from other methods. This
suggests that garnet and biotite are not in equilibrium
(see also Figure 4(c)).
7. Geometry of Veins and Level of
Emplacement
Owing to incomplete reactions in the alteration zon e, the
level of vein emplacement can hardly be constrained by
thermo-barometry based on mineral phase equilibria.
Most of these veins cluster in the southern part of the
Matale district and around Rattota-Kaikawala (Figure 3),
but are spread over the whole district. The mineraliza-
tions are thought to have formed from H2O-F-dominated
cooling hydrothermal fluids (Baatartsogt et al. [5]). In
the view of K-feldspar in perthite transformed into mi-
crocline, sericitisation of plagioclase and newly formed
biotite, a broad range of temperatures between 500˚C and
600˚C appears feasible (Parson and Lee[49]). Tempera-
tures near 600˚C must have been reached for a short time
at the contact with the intruding pegmatitic melt, with a
temperature of at least 650˚C, and hot fluids liberated

G. W. A. R. FERNANDO ET AL.359
from the magma upon solidification.
Information on the crustal level can also be achieved
from geometric features that reflect brittle failure of the
crust. The veins observed in Matale district are mostly
straight and approximately plane parallel boundaries, and
reveal a high degree of fitting be tween the oppo site walls
(Figure 5), suggesting that veins formed along the brittle
tensile cracks. At a deep crustal level brittle failure re-
quires a high pore fluid pressure. Therefore it is con-
cluded that pegmatite veins formed along hydralulic
fractures driven by the pressure of the hydrous melts. In
places the veins occur as sets of different orientations
without uniform crosscutting relations, suggesting a nearly
contemporaneous timing of the different propagation
events. The shape of pegmatite bodies as a function of
crustal depth, regional stress field and rock anisotropy
has been discussed by Brisbin [1]. A tabular shape and
preferred orientations are proposed to indicate the em-
placement along dilatants fractures in the brittle upper
crust, while more irregular shapes may reflect emplace-
ment beneath the brittle-ductile transition zone.
The vast majority of pegmatites in the study area,
however, consist almost exclusively of quartz and feld-
spars and lack of exotic minerals, and hydrothermal al-
teration envelopes. Where there are minerals other than
quartz and feldspar (e.g. topaz, tourmaline and fluorite),
the commonly cited fluxing components in pegmatite
magmas are H2O, B, and F. As fluxes, they lower the
melting and crystallization temperatures (e.g., London,
1997 [50]), and they enhance miscibility among other-
wise less soluble constituents.
Based on these considerations, it is concluded that the
level of emplacement of pegmatites of the Matale Dis-
trict is middle crust, near the crustal scale brittle-ductile
transition zone at a temperature of about 600˚C and even
lower, whenever the H2O, B, and F rich fluxes are in-
corporated. For this crustal level and temperature range,
it is considered very unlikely that intruding pegmatitic
melts followed pre-existing cracks. Th is suggests that th e
emplacement temperatures of the pegmatites are well
below the peak metamorphic estimates of 854 ± 44˚C at
10.83 ± 0.86 kbars in the mafic granulites.
8. Revisiting the P-T-t Path of Sri Lankan
Crust
This study assesses temperatures of formation of mafic
granulites by combining experimental constraints on the
PT stability on the granulite facies mineral associations
with a garnet-orthopyroxene thermometry scheme based
on Al-solubility of orthopyroxene corrected for the late
Fe-Mg Exchange. Mass balance method along with mo-
dal abundance of Fe-Mg bearing minerals was used to
assess the Fe-Mg exchange among minerals present in
the rocks. It accounted for corrections not only for late
Fe-Mg exchange but also Al diffusion of orthopyroxene.
From the detailed petrographic and mineralogical data
of the mafic granulites in the Matale district, we inferred
peak metamorphic conditions of the crustal unit belong-
ing to Matale district as 854 ± 44˚C at 10.83 ± 0.86 kbar.
Hydrothermal veins consisting quartz and mica are
closely related to cross-cutting pegmatites, which sig-
nificantly post-date the peak metamorphic conditions of
the crustal unit. Development of brittle structures of the
pegmatites and other hydrothermal deposits appears to be
concurrent with the brittle deformation of the area.
The metamorphic P-T strategy and post-metamorphic
structural history inferred from this area is summarized
in the modified version after P-T-t-D diagrams after
Kriegsman [45] (Figure 9). The P-T strategy made here
is based on the combination of P-T conditions estimated
in this study and direct evidences obtained from struc-
tural settings of the Matale district.
9. Conclusions
The Earth’s crust thins during extensional tectonics,
leading to exhumation and decompression of deep- and
mid-crustal rocks. Due to the strong difference in com-
pressibility between rocks and fluid, pore fluid becomes
over-pressured during this decompression. If pressure
re-equilibration is achieved by draining of excess fluid,
significant volumes of fluid can be produced. We thus
present a new model to explain the derivation of hydro-
thermal fluids from the middle and upper crust of the
metamorphic basement of Sri Lanka.
Figure 9. P-T-t-D path for the granulites of the Highland
Complex in Sri Lanka (after Kreigsman, 1993). The pro-
grade path is characterized by crustal thickening (D1), and
subsequent heating, while the retrograde path shows early
isothermal decompression (D2), followed by isobaric cooling
and late cooling and thrusting (D3). P-T-t-D diagram after
Kreigsman [45] was modified after incorporated the new
PT data from this study. Mineralization of Matale district
may be depicted after all of major deformational events.

G. W. A. R. FERNANDO ET AL. 360
The unique outcrops of mafic granulites and associ-
ated pegmatites and hydrothermal mineralization of the
central highlands found in the Matale District, Sri Lanka
yield insight into a high temperature metamorphism fol-
lowed by magma driven mineralization. A detailed field,
structural and petrographical study reveals that the
crustal unit of the central highlands had metamorphosed
at 854 ± 44˚C at 10 .83 ± 0.86 kbar un der granulite facies
conditions. The pegmatitic veins are interpreted to rep-
resent hydraulic fractures driven by volatile-rich melt
with minimum temperature of 600˚C, emplaced in a
middle crust near the brittle-ductile transition zone. Hy-
drothermally derived pegmatite dikes are largely unde-
formed and reveal a coarse-grained matrix devoid of any
obvious preferred or ientation and compatible with condi-
tions in the mid crustal levels with low geologic strain
rates. Hydrothermal veins associated with pegmatites are
also emplaced at a shallower crustal level and within a
cooler country rock as a brittle event. Mineralization of
pegmatites in Matale District was attributed to occur in
the late event after the D3 deformations of Berger and
Jayasinghe [40].
10. Acknowledgments
Financial assistance by NSF a research grant from a Na-
tional Science Foundation (NSF, Sri Lanka) RG/2005/
EB/01 and editorial assistance given by Prof. K. Daha-
nayake is gratefully acknowledged.
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