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The occurrence of fluor-wagnerite in UHT granulites and its implications towards understanding fluid regimes in the evolution of deep crust: a case study from the Eastern Ghats Belt, India


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We report the occurrence of a rare phosphate mineral, fluor-wagnerite (Mg1.91–1.94Fe0.06–0.07Ca<0.01) (P0.99–1.00O4)(OH0.02–0.17F0.98–0.83) from the Eastern Ghats Belt of India, an orogenic belt evolved during Meso- to Neoproterozoic time. The host rock, i.e. high- to ultrahigh temperature (UHT) granulites (~1000 °C, 8–9 kbar) of the studied area was retrogressed after emplacement to mid-crustal level (800–850 °C, 6–6.5 kbar) as deduced from their pressure-temperature histories. Based on mineral chemical data and micro-Raman analyses, we document an unusual high Mg-F-rich chemistry of the F-wagnerite, which occur both in peak metamorphic porphyroblastic assemblages as well as in the retrograde matrix assemblage. Therefore, in absence of other common phosphates like apatite, fluor-wagnerite can act as an indicator for the presence of F-bearing fluids for rocks with high XMg and/or fO2. The occurrence of F-rich minerals as monitors for fluid compositions has important implications for the onset of biotite dehydration melting and hence melt production in the deep crust. We propose that fluor-wagnerite can occur as an accessory mineral associated with F-rich fluids in lower-mid crustal rocks, and F in coexisting minerals should be taken into consideration when reconciling the petrogenetic grid of biotite-dehydration melting.
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The occurrence of fluor-wagnerite in UHT granulites and its
implications towards understanding fluid regimes in the evolution
of deep crust: a case study from the Eastern Ghats Belt, India
Kaushik Das
&Naotaka Tomioka
&Sankar Bose
&Jun-ichi Ando
&Ichiro Ohnishi
Received: 1 May 2014 /Accepted: 18 September 2016 /Published online: 29 September 2016
#Springer-Verlag Wien 2016
Abstract We report the occurrence of a rare phosphate min-
eral, fluor-wagnerite (Mg
) from the Eastern Ghats Belt of
India, an orogenic belt evolved during Meso- to
Neoproterozoic time. The host rock, i.e. high- to ultrahigh
temperature (UHT) granulites (~1000 °C, 89 kbar) of the
studied area was retrogressed after emplacement to mid-
crustal level (800850 °C, 66.5 kbar) as deduced from their
pressure-temperature histories. Based on mineral chemical da-
ta and micro-Raman analyses, we document an unusual high
Mg-F-rich chemistry of the F-wagnerite, which occur both in
peak metamorphic porphyroblastic assemblages as well as in
the retrograde matrix assemblage. Therefore, in absence of
other common phosphates like apatite, fluor-wagnerite can
act as an indicator for the presence of F-bearing fluids for
rocks with high X
and/or fO
. The occurrence of F-rich
minerals as monitors for fluid compositions has important
implications for the onset of biotite dehydration melting and
hence melt production in the deep crust. We propose that
fluor-wagnerite can occur as an accessory mineral associated
with F-rich fluids in lower-mid crustal rocks, and F in
coexisting minerals should be taken into consideration when
reconciling the petrogenetic grid of biotite-dehydration
Keywords Fluor-wagnerite in Al-rich granulites .Biotite
dehydration melting .UHT granulites .Eastern Ghats
GranuliteBelt .India
Accessory mineral phases in deep-crustal granulites often pre-
serve a plethora of information regarding the pressure (P)-
temperature (T)-fluid-time (t) evolution of the deep continen-
tal crust undergoing orogenesis (e.g. Harlov and Foster 2007;
Harlov et al. 2011). Minerals like zircon and monazite are
widely used for retrieving the age information of
tectonothermal events that the deep crust undergo during their
orogenic evolution. They have shown to be of immense im-
portance to monitor the geological evolution of continental
blocks through time. At the same time, there are accessory
minerals, which are significant in properly assessing the PT
histories (Bingen et al. 1996; Bea and Montero 1999; Harlov
et al. 2006; Harley 2008; Harley and Nandakumar 2014).
Minor components present in the major and accessory phases
may play a crucial role in the topological relationships on
metamorphic petrogenetic grids (Bose et al. 2005). One such
minor component is fluorine (F), which is accommodated
within hydrous minerals like biotite in metapelitic granulites
of Bappropriate^bulk compositions (Motoyoshi and Hensen
2001;Boseetal.2005) and hornblende in high-grade
metabasites (Tsunogae et al. 2003). Experimental results
(Munoz and Ludington 1977; Hensen and Osanai 1994;
Icenhower and London 1997) and natural rock studies show
that F prefers incorporation in these minerals over melt over
the P-T range of anatexis. This stabilizes both minerals up to
Editorial handling: R. Milke
*Kaushik Das
Department of Earth and Planetary Systems Science, Hiroshima
University, Higashi Hiroshima, Japan
Institute for Study of the Earths Interior, Okayama University,
Okayama, Japan
Department of Geology, Presidency University, Kolkata, India
JEOL Ltd., Tokyo, Japan
Miner Petrol (2017) 111:417429
DOI 10.1007/s00710-016-0474-y
high temperature (HT) ultra-high temperature (UHT) condi-
tions (Tsunogae et al. 2003;Boseetal.2005). The stabilizing
effect of F necessitates the proper characterization of the meta-
morphic conditions of F-containing rock systems. If F is not
derived fromthe protolith, then thereis a further needto assess
the exact stage when F enters the system (e.g. via fluid) during
the metamorphic evolution. Such information becomes impor-
tant in assessing phase relations at different stages during the
evolutionary history of a granulite-facies metamorphic ter-
rane. Hence, the proper textural and chemical characterization
of major or accessory phases containing F is of immense
Though a common accessory mineral like apatite generally
serves as a sink for F, minerals such as wagnerite,
(F,OH)], can also serve as a F sink in
Ca-poor metapelitic granulites in differentgeotectonic settings
(Braitsch 1960; Irouschek-Zumthor and Armbruster 1985;
Leroux and Ercit 1992; Novák and Povondra 1984; Brunet
et al. 1998) and also in regional granulite terranes (Grew 1981;
Simmat and Rickers 2000). There have been reports that wag-
nerite occasionally forms during the retrograde stage in Mg-Al
granulites when the ambient fluid is hydrous and P is not
partitioned into apatite (Simmat and Rickers 2000; Ren et al.
2003). Here, we report occurrences of F-rich wagnerite from
two aluminous granulite samples located in the Eastern Ghats
Belt of eastern India.
Geological background
The Proterozoic Eastern Ghats Belt exposes deep crustal sec-
tion along the eastern part of India bearing crucial evidence for
India- East Antarctica correlation (Dasgupta et al. 2013 and
references therein). Although composed entirely of granulite-
facies rocks, this belt has a complex evolutionary history with
different crustal domains and provinces amalgamated in the
present configuration (Rickers et al. 2001a; Dobmeier and
Raith 2003; Dasgupta et al. 2013). The Eastern Ghats
Province (Dobmeier and Raith 2003) which is a combination
of isotopicdomains 2 and 3 (Rickers et al. 2001a) occupies the
major part of the belt wherein most of the petrological, struc-
tural and geochronological data are available. Aluminous
granulites from the Domain 2 are reported to preserve UHT
metamorphism (T>100Cat810 kbar) that ensued
through anticlockwise P-T trajectory (Sengupta et al. 1990;
Dasgupta et al. 1995;Korhonenetal.2013a) at a time frame
of ca. 1030990 Ma (Bose et al. 2011; Das et al. 2011). The
UHT metamorphosed lower crust was near-isobarically
cooled (T~ 800 °C at 6 kbar) before being reworked by a
second granulite grade event (T~ 850 °C at 78 kbar) at ca.
953 Ma (Das et al. 2011).
Fluor-wagnerite is identified from two samples of Domain
2intheEasternGhatsBelt(Fig.1), where rocks have
reportedly undergone at least four phases of deformation and
at least three phases of metamorphism (Bhowmik 1997;Das
et al. 2011). The P-T conditions of the UHT peak metamor-
phism (M
) and subsequent reworking (M
) are mentioned
before. The third phase of metamorphism (M
) occurred at
500800 °C (Das et al. 2011). The first sample containing
fluor-wagnerite was collected from a locality near
Bondaguda (N 18°187.1, E 82°5759.2). Here, the major
rock unit is a quartz-plagioclase-garnet-K-feldspar gneiss (lo-
cally known as leptynitic gneiss), which shows magmatic fea-
tures (Fig. 2a). This leptynitic gneiss locally contains
foliation-parallel elongated enclaves of aluminous granulite
feldspar-quartz) and charnockite (quartz-K-feldspar-
orthopyroxene-plagioclase-garnet-ilmenite) (Fig. 2c). A peg-
matitic variety of quartzofeldspathic rock occurs as conform-
able layers along the gneissic foliation, but locally straddles
the regional foliated structure. From the textural and
compositional characteristics of the aluminous granulite, Das
et al. (2006) postulated the existence of an anomalously Al-
rich orthopyroxene at the peak of UHT metamorphism
(>1000 °C at 910 kbar; Das et al. 2006) which on breakdown
resulted in different intergrowth textures involving spinel, sap-
phirine and garnet, all enclosed within garnet porphyroblasts.
Using the sequence of mineral assemblages, this study docu-
mented UHT metamorphism at peak stage which was follow-
ed by near isobaric cooling and decompression in an overall
anticlockwise P-T path. The fO
evolution history of the entire
litho-assemblage was documented from intricate textural and
compositional characteristics of different Fe-Ti oxides along
with the fluid inclusion data (Bose et al. 2009; Das et al.
2013). Their results show that the cooling history occurred
at relatively high fO
conditions (34 log units higher than
FMQ buffer) when an oxygenated H
O fluid with a compo-
nent of possible F-rich brine was coexisting with the retro-
grade assemblage. Subsequently, a late low-fO
fluid (evident from fluid inclusion data in Bose et al. 2009)
with fluoride-bearing mixture infiltrated the litho-assemblage
from the outside, which broadly coincided with the final crys-
tallization of the pegmatite (Bose et al. 2009). Zircon U-Pb
SHRIMP analyses of the aluminous granulite sample yielded
an age population of ca. 950900 Ma, which possibly repre-
sents the timing for a pervasive metamorphic overprinting
(Bose et al. 2011). In the absence of more well-constrained
data (e.g. texturally constrained monazite and/or zircon), the
timing of the early UHT event could not be determined.
The second fluor-wagnerite occurs in Panirangini (N18°18
26, E82°5428), which is located approximately 10 km
north of Bondaguda. In the Panirangini, aluminous granulite
ite-K-feldspar-quartz) occurs as a small pod within the
leptynitic gneiss (quartz-K-feldspar-plagioclase-garnet-bio-
tite-ilmenite) (Fig. 2b and d). Other rocks include
418 Das K. et al.
sillimanite-garnet-K-feldspar-quartz gneisses (locally known
as khondalites), calc-silicate granulites (wollastonite-scapo-
lite-clinopyroxene-plagioclase-quartz-calcite), charnockites
and mafic granulites (orthopyroxene-clinopyroxene-plagio-
clase-garnet-ilmenite-hornblende). Based on textural,
microstructural and compositional criteria, Das et al. (2011)
documented polymetamorphic signatures with an early
counter-clockwise metamorphic evolution culminating in
UHT metamorphism (>1000 °C) at 6.58.5 kbar. Thermal
relaxation of the crust was later achieved by cooling down
to ~800 °C. Prominent granulite-facies reworking occurred
during a compressive event which accompanied folding, deep
crustal shearing and melt extraction. Based on texturally well-
constrained monazite, the early UHT metamorphism has been
dated at ca. 990 Ma (Das et al. 2011). Zircon SHRIMP U-Pb
data yielded a concordant age of 953 ± 6 Ma, which is
interpreted as the timing of granulite reworking as the cooled
lower crust underwent loading and heating by a prominent and
separate orogenic pulse (Das et al. 2011). Zircon age data
further yielded a younger group age of ca. 900 Ma which
possibly signifies the cooling event when zircon grains finally
crystallized from the extracted melt (Das et al. 2011). On the
contrary, Korhonen et al. (2013a) argued that the entire
Domain 2 witnessed prolonged thermal high and the proposed
counter-clockwise path resulted from one single cycle of oro-
genesis that was operative over 160 million years. This was
based on the monazite data (Korhonen et al. 2013b)showing
age spread from ca. 1130 Ma to ca. 970 Ma. Whether the
Domain 2 evolved in a single stage or two stages is thus
Fluor-wagnerite grains were identified by microscopic study
followed by back-scattered electron imaging (BSE) using a
JEOL JSM-6390 A scanning electron microscope equipped
with JED-2300 energy dispersive system at the Hiroshima
University, Hiroshima, Japan. Point chemical analyses of
fluor-wagnerite are carried out on a JEOL-JXA- 8900
EPMA (Electron Probe Micro-analyzer) at the University of
Kobe, Kobe, Japan. Other minerals were analyzed by EPMA
technique using the JEOL JXA 8200 Superprobe at the
Natural Science Center for Basic Research and Development
(N-BARD), Hiroshima University, Hiroshima Japan. The op-
erating conditions were 15 kV accelerating voltage, 12 nA
beam current, and 12μm beam diameter. JEOL standards
(JEOL Datum Ltd.) are used for analyses. Problems in the
proper analysis of F using EPMA have been discussed in
detail by several workers (e.g. Pitra et al. 2008; Fialin and
Chopin 2006; Stormer et al. 1993; Goldoff et al. 2012). The
choice of proper analytical conditions and Bappropriate^stan-
dards has a broad influence on the actual quantification of F by
EPMA. We used fluorite (CaF
lyzed for F in biotite, apatite and wagnerite using LDE1 crys-
tal. The time-dependent intensity of the FK
line for fluorite
shows differential changes using a 15 kV, 12 nA beam current
and0to50μmbeamdiameter(Fig.3). We chose a 15 kV,
12 nA and 10 μm beam as this represented the optimum con-
ditions with a very small change in intensity. Using this con-
dition, natural fluor-apatite (North Wales, UK, cf. page 665 of
Deer et al. 1992) yielded an F-content of 3.2 wt% (± 0.06). We
Fig. 1 Generalized map of
Eastern Ghats Belt (modified after
Ramakrishnan et al. 1998). Inset
shows the position of EGB in
present-day India. The present
study area (marked as star) be-
longs to the central migmatitic
zone according to Ramakrishnan
et al. (1998) and domain 2 of
Rickers et al. (2001a)
The occurrence of fluor-wagnerite in UHT granulites 419
Fig. 2 a Hand sketch of the Bondaguda quarry (modified after Das et al.
2006). bThe local geological map around Panirangini modified is after
Das et al. (2011). cOutcrop photograph of aluminous granulites and
associated rocks at Bondaguda. AG stands for aluminous granulite. The
pen cap is 4 cm long. (d) Outcrop photograph of Panirangini. The pen is
14.5 cm long. Darker patches are orthopyroxene-rich domains in the
aluminous granulite
Fig. 3 The time sequence analysis of fluorite using different probe
diameters to determine the best analytical conditions. During analysis of
standard F-apatite, and unknown wagnerite and apatite, a 15 kV
accelerating voltage, 12 nA beam current and 10 μm probe diameter
were used. The vertical bars represent the calculated errors in X-ray
counts (1 s.d.) for each data point
420 Das K. et al.
analyzed the same grain by the ISE (ion selective electrode)
method which also yielded an F-content of 3.1 wt%, though
the reported value of F in this fluor-apatite is 3.7 wt%. Pitra
et al. (2008) noted that measurement of F using an apatite
standard may underestimate the F-content in the unknown
sample compared to using other standards such as topaz.
There is a possibility that our estimation of the F-content is
also slightly on the lower side (i.e. 0.5 to 0.6 wt%). During
analysis of F in the CaF
standard, fluor-wagnerite, biotite and
fluor-apatite, peak and background values were measured for
40 s and 20 s, respectively. Other mineral phases were mea-
sured using a 15 kV of accelerating voltage, 20 nA beam
current and 12μmbeamdiameter.
Raman spectral analysis of fluor-wagnerite was done
in quasi-backscatter geometry using a home-built micro-
Raman spectrometer. An argon laser with wavelength of
488 nm (Ion Laser Technology Model 5500 A) was
focused with a 50× objective lense (NA 0.55) to a spot
size of 1 μm having a laser power of 10 mW on the
desired mineral grains in the polished thin section. The
system had been used in the confocal mode. Raman
signals from the samples were obtained using a
nitrogen-cooled CCD detector (Princeton Instruments
SPEC-10) with spectrograph (Acton SpectraPro-500i).
Wavenumber calibration was done using plasma dis-
charge lines of the Ar laser; the resulting wavenumber
accuracy was 0.1 cm
. Peak fitting was done after ap-
propriate background correction, assuming Voigt-shaped
band profiles. The details of the method is described in
Kanzaki et al. (2012).
Mineral assemblages and petrographic textures in aluminous
granulites wherein fluor-wagnerite was observed are quite
similar for both samples. Mineral assemblages in aluminous
granulite include porphyroblastic garnet, cordierite,
orthopyroxene (± sapphirine, spinel), and quartz with minor
zircon and monazite representing the possible pre- to near-
peak conditions of metamorphism. The foliation- (i.e., trans-
posed S
foliation during D
) forming assemblage con-
sists of elongated quartz ribbons, perthitic K-feldspar, biotite,
garnet, orthopyroxene, sillimanite and cordierite (Fig. 4a).
Spinel is often associated with magnetite and presumed to
be exsolved from a spinel solid solution (Bose et al. 2009).
In the Panirangini sample, hemo-ilmenite is additionally pres-
ent as an opaque phase. Fine grained matrix minerals in a
mylonitic fabric (S
) formed by skeletal intergrowth of
orthopyroxene + sillimanite + quartz which represents the
breakdown products of cordierite porphyroblasts (Fig. 4b).
Biotite is late, replacing all the ferromagnesian minerals
along their grain boundaries and fractures irrespective of their
textural associations. Such biotite grains are more euhedral in
shape and have sharp boundaries compared to the ferromag-
nesian minerals with which they occur. While late patchy bi-
otite tends to be associated with fluor-wagnerite, there is an
early variety of biotite (chemically and texturally distinctive)
in this rock. This early variety occurs inside the garnet,
orthopyroxene and cordierite porphyroblasts (away from frac-
tures in these grains), and has rounded grain boundaries.
Formation of ribbon quartz and flattened garnet
grains are conspicuous in this rock. Centimeter-scale,
massive domains of aluminous granulite also occur, pos-
sibly as low-strain zones. The fluor-wagnerite grains oc-
cur in close association with the garnet porphyroblasts;
while in the foliated high-strained zones augen of fluor-
wagnerite occur in the fine grained matrix (Fig. 4ce).
Fluor-wagnerite is characteristically absent in the
porphyroblastic orthopyroxene-rich microdomains. In
the foliation (transposed S
) perpendicular section,
grains of fluor-wagnerite are elongated parallel to the
foliation and exhibit boudinage to pinch- and swell mi-
crostructures (Fig. 4f). Apatite grains occur in fractures
in the fluor-wagnerite, in the neck zones of the boudins,
and as rims around recrystallized grains of fluor-
wagnerite (Fig. 4f). The estimated modal percentages
of different minerals within the garnet-bearing microdo-
mainsinboththesamplesare23.325.8 % garnet,
19.424.1 % biotite, 12.923.3 % quartz, 14.217.3 %
cordierite, 4.15.6 % sillimanite, 3.24.5 % feldspars,
2.24.1 % spinel-magnetite-hemoilmenite, 0.50.8 %
monazite, 0.10.3%zirconand0.10.2 % wagnerite.
Based on these observations, two types of fluor-wagnerite
grains can be defined. Type I occurs in close association with
garnet. Type Ia occurs as inclusions within garnet and is not
associated with fluor apatite (Fig. 4c). Type Ib occurs along
grain boundaries or along fractures in garnet and is partly
overgrown by apatite (Fig. 4e). Type II fluor-wagnerite occurs
as elongated grains in the matrix assemblage parallel to the
foliation associated with fluor-apatite and carbonates (Fig. 4f).
Raman spectroscopy
Type I and II fluor-wagnerite grains were analyzed using
micro-Raman spectroscopy and compared with available
spectra from the RRUFF database of the University of
Arizona (Downs 2006). All the analyzed grains have similar
spectra with prominent bands at ~460, 985, 1005, 1056, and
1100 cm
and broader and smaller bands around 625, 812
and 1140 cm
(Fig. 5a). Type I and type II fluor-wagnerite
grains show slight differences with respect to bands
>1000 cm
. Type Ib fluor-wagnerite is characterized by the
reduction or non-appearance of the ~1056 and 1140 cm
The occurrence of fluor-wagnerite in UHT granulites 421
bands. While comparing these data with those available at
RRUFF database, we observed that most of the band spectra
are strikingly similar to that of wagnerite (R050519).
Particularly, the band occurring at 1005 cm
for types I and
II is similar to that of R050519 wagnerite (University of
Arizona Mineral Museum). This band is characteristically ab-
sent in other wagnerite samples from the RRUFF database
(Fig. 5b). Some of the differences in the positions of the
Raman bands among type I, type II, and the R050519 wag-
nerite could be caused by different F and Fe contents. The
calculated crystal structure for R050519 wagnerite from the
RRUFF database is that of a triploidite group wagnerite
polytype (Ma2bc) with space group of P2
/cor P2
et al. 1967; Tadini 1981). We consider that the fluor-wagnerite
in this study has a crystal structure similar to the Ma2bc
polytype, unlike the structure reported for wagnerite which
contains less Mg and F from a granulite-facies terrane like
Larsemann Hills, Prydz Bay, East Antarctica, which has a
different polytype Ma5bc (Ren et al. 2003). This is also sup-
ported by R060456 wagnerite with the Ma5bc polytype,
which does not show a strong Raman band at ~1005 cm
compared to R050519 wagnertite and the fluor-wagnerite in
these samples.Moreover, the spectral data of type Ia shows no
discernible O-H stretching vibration band at ~3580 cm
ported from Larsemann Hills sample (Ren et al. 2003).
Mineral chemistry
Wagnerite chemical compositions are F-rich (9.6 to 11.2 wt%).
The three petrographic types (types Ia, Ib and II) have subtle
chemical differences (Table 1). All types are very similar in
terms of magnesian content as X
ranges between 0.96 and
0.97 (type Ia being slightly lower than the other two types).
However, type Ia and II wagnerite grains are the most F-rich
= F/(F + OH) ~ 0.91 to 0.98], while those which occur
along the fractures of garnet grains (type Ib) are less F-rich
~ 0.83 to 0.85) (Fig. 6). The measured Ca, Mn and Ti
contents are low. The overall chemical compositions are close
to end-member stoichiometry. As mentioned above, type Ib
and type II wagnerite grains are replaced by fluor-apatite along
their fractures. In places, there is late replacement of fluor-
apatite (not affecting other minerals including adjacent fluor-
Fig. 4 Back-scattered electron
photomicrographs of rock
textures and different type
occurrences of fluor-wagnerite. a
Mylonitic fabric shown by
deformed porphyroclasts of
spinel, orthopyroxene, among
others in the Panirangini sample.
bSkeletal intergrowth of
orthopyroxene + sillimanite +
quartz surrounding
porphyroblastic cordierite. The
intergrowth phases are aligned
along the mylonitic foliation
shown by matrix quartz grains. c
Rounded grains occurring inside
garnet porphyroblasts (type 1a,
note that late fractures affect both
garnet and fluor-wagnerite). d
Fluor-wagnerite occurring along
the fractures of garnet
porphyroblasts (type Ib) and eal-
so along the grain boundaries. f
pinch-and-swell structured fluor-
wagnerite grains in the mylonitic
matrix of the aluminous granulite.
Note that apatite (white phase
with black arrow) develops on
fluor-wagnerite in (eand f). In (f),
a replacing phase (carbonate-
fluorapatite??) develops (slightly
grey, marked with white arrow)
on apatite
422 Das K. et al.
wagnerite) which results in a patchy phase with low oxide wt%
totals. Since the F and CaO contents are comparable with that
of fluor-apatite, the P
content is reduced, possibly partially
replaced by carbonate component during very low temperature
alteration of apatite (Shemesh 1990;Miyakeetal.1990).
The major associated minerals include garnet and bi-
otite (Table 2). Garnet is mainly a solid solution of
almandine and pyrope with a low grossular and spessar-
tine content (~Alm
). Biotite grains oc-
cur texturally as two types. These form inclusions in
garnet porphyroblasts (namely, early biotite) and those
occurring along the fracture, grain boundaries and in the
matrix (namely, late biotite). The former contains higher
Mg (X
~0.880.85) and F contents (F ~ 34wt%),
while the latter contains less Mg (X
~0.680.71) and
a lower F content (F ~ 2 wt%). This variation thus
follows the Fe-F avoidance trend (Nash 1993). At the
same time, the role of earlier biotite and fluor-wagnerite
in locking F from the effective bulk rock composition
can also be important. Both types of biotite are rich in
tematic. Associated cordierite is Mg-rich (X
0.86), while in the matrix orthopyroxene (X
0.62) intergrowth with sillimanite and quartz developed
on cordierite is quite aluminous (Al
=6.36.9 wt%)
(cf. Das et al. 2006,2011;andBoseetal.2006).
Among the Fe-Ti oxide minerals, green spinel contains
12 mol% gahnite and 34 mol% magnetite components
while magnetite is almost pure. Ilmenite contains 10
15 mol% hematite and 47 mol% geikielite component
while exsolved hematite contains ~16 mol% ilmenite
The Mg and F-rich wagnerite (Mg
) from the
Eastern Ghats Belt chemically and structurally differs
from an earlier reported, hydroxyl-rich variant of wag-
nerite (Simmat and Rickers 2000) from the nearby
Anakapalle region of the same terrane. This phase also
differs in composition and microstructurally from other
occurrences associated with high-grade assemblages
(e.g. Pitra et al. 2008), and from the Antarctic occur-
rence (e.g. Ren et al. 2003,2005;Grewetal.2007). In
the latter occurrence, wagnerite shows F/OH ratio of
1.56 compared to the present case (494.88) although
the Mg/Fe ratio is similar. For the Armorican occur-
rence (Pitra et al. 2008), the F/OH ratio varies widely
within the range 4.560.78 (with an exceptional value
of infinity; Analysis no. 301, sample VY11). The Mg/Fe
ratio for this wagnerite is much lower compared to the
present one.
Despite the known occurrence of F in the structure of
biotite and other accessory minerals, no direct evidence of
the source of F can be identified. It may either be in the
original protolith of the aluminous granulites or in the
coexisting halide-rich fluids present during the evolution
of these granulites (Higashino et al. 2013;Boseetal.
2005,2009; Pitra et al. 2008). Nevertheless, the mode of
occurrence and the characteristic mineral associations have
important implications for the petrogenesis of these fluor-
wagnerite-bearing rock suites. Both aluminous granulite
samples (Bondaguda and Panirangini) are characterized by
garnet porphyroblast microdomains and aluminous
orthopyroxene porphyroblast microdomains. Interestingly,
fluor-wagnerite occurs only within the garnet porphyroblast
domains, where rounded to prismatic grains of type Ia
fluor-wagnerite associated with F-rich biotite (34wt%F)
grains occur as mineral inclusions. These wagnerite grains
Fig. 5 a Representative micro-Raman spectra of fluor-wagnerite grains.
Spectra of different textural types are shown with vertical offset. Note the
two strong bands around 1000 cm
.bRaman band spectra for three
samples from the RRUFF database (; Downs 2006).
Note the similarity of the band spectra for R050519 with the natural
The occurrence of fluor-wagnerite in UHT granulites 423
are the most F-rich [X
=0.960.98] and possibly consti-
tute part of the prograde-to-peak metamorphic assemblage
in this rock. Larger fluor-wagnerite grains also occur as
boudinaged to pinch-and-swell grains (type II) in the matrix
of the Panirangini sample associated with the last metamor-
phic mylonitic fabric (i.e. S
). This implies at least pre-D
crystallization of this variety of fluor-wagnerite (D
stage identified as peak to early retrograde metamorphic
stage by Das et al. 2011, their Table 1). Type Ib fluor-
wagnerite (X
=0.830.85), on the other hand, occurs as
prismatic grains along fractures and at grain-boundaries of
garnet porphyroblasts partially replaced by apatite. All the
wagnerite grains are F-rich, but there are differences in F
contents among different textural types. As the type Ia and
type II wagnerite grains are more F-rich, we need to con-
ceive a process that can explain the preferential partitioning
of F over H
O in these wagnerites. Brunet et al. (1998)
experimentally showed that the synthetic hydroxyl equiva-
lent (β-Mg
OH) is stable above 10 kbar and argued
that for F-bearing system, wagnerite would be stable at
lower pressure (<10 kbar) conditions. Therefore, F-
enrichment in wagnerite could imply a decrease in pressure.
Tabl e 1 Representative electron microprobe point analyses data of different textural types of wagnerite
Type I wagnerite Type II wagnerite
type Ia (grains inside grt) Ib (along fracture and boundary of grt) matrix grains
Sample No. 4Q_1 4Q_2 Average s.d. (n= 10) 4Q_13 4Q_15 Average s.d. (n= 7) Pan10A_32 Pan10A_33 Average s.d.(n = 8)
43.09 42.77 42.84 0.17 42.87 42.87 42.92 0.14 43.08 42.53 42.73 0.19
0.16 0.19 0.18 0.02 0.23 0.23 0.21 0.01 0.34 0.23 0.28 0.04
0.01 0.01 0.01 0.01 0.02 0.01 0.01 0.01 0.01 0.02 0.01 0.01
FeO 3.68 3.35 3.10 0.27 2.84 2.97 3.04 0.16 2.70 2.54 2.98 0.24
MgO 46.80 46.83 47.25 0.43 47.38 47.82 47.43 0.21 47.67 47.37 47.27 0.20
MnO 0.11 0.08 0.08 0.02 0.03 0.10 0.08 0.02 0.05 0.05 0.07 0.02
CaO 0.26 0.25 0.25 0.02 0.28 0.31 0.26 0.02 0.21 0.15 0.19 0.03
F 11.25 10.55 10.99 0.26 9.62 9.87 9.56 0.17 10.52 11.23 10.67 0.32
Total 100.63 99.58 100.09 0.34 99.21 100.03 99.49 0.43 100.14 99.37 99.70 0.42
P 1.00 1.00 1.00 0.00 1.00 1.00 1.00 0.00 1.00 1.00 1.00 0.00
Ti 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.00
Al 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Fe 0.08 0.08 0.07 0.01 0.07 0.07 0.07 0.00 0.06 0.06 0.07 0.01
Mg 1.91 1.93 1.94 0.02 1.95 1.96 1.95 0.01 1.95 1.96 1.95 0.01
Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ca 0.01 0.01 0.01 0.00 0.10 0.01 0.01 0.00 0.01 0.00 0.01 0.00
F 0.97 0.92 0.96 0.02 0.84 0.86 0.83 0.01 0.91 0.99 0.93 0.03
OH 0.03 0.08 0.05 0.02 0.17 0.15 0.18 0.01 0.10 0.02 0.07 0.03
F/OH 34.39 11.01 4.94 5.73 9.10 49.50
0.96 0.96 –– 0.97 0.97 –– 0.97 0.97 ––
0.97 0.92 –– 0.83 0.85 –– 0.91 0.98 ––
= [Mg/(Mg + Fe
OH is calculated on charge balance criteria
Fig. 6 Compositional variation for different types of fluor-wagnerite.
The square symbol is for type Ia fluor-wagnerite, while triangles
represent type Ib fluor-wagnerite, and solid diamonds represent type II
424 Das K. et al.
None of the presently studied samples shows any evidence
for decompression to substantiate this model. Based on
textural, chemical and stable isotopic data, Pitra et al.
(2008) presented an alternative model of shear zone en-
hanced metasomatism which can explain F-enrichment in
wagnerite due to long-term multistage fluid-rock interaction
occurring both going up- and down-temperature. Such
widespread fluid-rock interaction is interpreted as the most
viable mechanism for F-wagnerite formed by non-
magmatic process (Pitra et al. 2008). The first mechanism
involving P-dependent incorporation of OH can be applied
to explain the occurrence of OH-wagnerite from Dora
Maira Massif (Chopin et al. 1993). Similarly the OH-
wagnerite reported from the nearby area of the Eastern
Ghats Belt (Simmat and Rickers 2000) also follows this
trend as petrological data from the aluminous granulite of
Anakapalle also imply early high-pressure (>10 kbar) con-
ditions during the metamorphic peak (Dasgupta et al. 1994;
Rickers et al. 2001b). Contrary to the two mentioned mech-
anisms, occurrence of wagnerite in anatectic rocks like the
present samples can be explained by melt-solid interaction
during migmatization, or by later-stage interaction of rocks
Tabl e 2 Representative EPMA analysis data of phases associated to wagnerite
Phase Grt Grt Opx Opx Sil Bt Bt Bt Crd Crd Ap Ap
Texture Por Por fine grain fine grain fine grain matrix matrix included in grt matrix matrix on wagnerite
39.56 39.39 48.66 47.94 36.46 39.67 39.29 38.90 48.70 49.23 CaO 55.21 55.63
0.01 n.d. 0.05 0.05 0.01 2.60 2.66 5.07 n.d. n.d. Na
O n.d. n.d.
22.12 21.97 7.16 7.13 62.09 13.75 14.40 14.20 32.96 33.25 MnO n.d. 0.07
n.d. 0.01 0.02 0.02 0.03 n.d. 0.06 0.06 n.d. 0.02 FeO 0.33 0.36
FeO 26.37 26.71 22.33 22.85 1.02 8.61 8.40 6.22 4.41 4.14 P
41.98 41.46
MnO 0.59 0.66 0.19 0.18 n.d. 0.00 0.00 0.00 0.05 0.07 Cl n.d. n.d.
MgO 11.39 10.90 20.08 20.43 n.d. 21.71 20.76 21.16 10.79 11.17 F 4.39 4.20
CaO 0.78 0.75 0.02 0.04 0.01 n.d. n.d. 0.17 n.d. n.d. O = F,Cl -1.85 -1.77
O n.d. n.d. 0.01 0.01 0.02 0.33 0.28 0.38 0.03 0.01 Total 100.06 99.95
O n.d. 0.01 n.d. 0.01 n.d. 9.89 10.70 10.16 0.02 n.d.
F n.d. n.d. n.d. n.d. n.d. 4.18 4.27 2.53 n.d. n.d.
F = O -1.76 -1.80 -1.06
Cl n.d. n.d. n.d. n.d. n.d. n.d. 0.08 0.07 n.d. n.d.
Cl = O n.d. -0.02 -0.02
Total 100.83 100.40 98.53 98.65 99.63 99.03 99.08 100.84 96.97 97.90
O basis 12 6 5 22 18 O basis 25 25
Si 2.99 3.00 1.84 1.82 0.99 5.68 5.64 5.54 4.99 4.99 Ca 9.53 9.65
Ti 0.00 0.00 0.00 0.00 0.00 0.28 0.29 0.54 0.00 0.00 Na 0.00 0.00
Al 1.97 1.97 0.32 0.32 1.99 2.32 2.44 2.39 3.98 3.97 Mn 0.00 0.01
Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.00 Fe 0.04 0.05
Fe 1.67 1.70 0.71 0.72 0.02 1.03 1.01 0.74 0.38 0.35 P 5.72 5.69
Mn 0.04 0.04 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.01 Cl 0.00 0.00
Mg 1.28 1.24 1.13 1.15 0.00 4.63 4.45 4.50 1.65 1.69 F 2.24 2.15
Ca 0.06 0.06 0.00 0.00 0.00 0.00 0.00 0.03 0.00 0.00
Na 0.00 0.00 0.00 0.00 0.00 0.09 0.08 0.11 0.01 0.00
K 0.00 0.00 0.00 0.00 0.00 1.81 1.96 1.85 0.00 0.00
F––– – – 1.89 1.94 1.14 ––
Cl ––– – – 0.00 0.02 0.02 ––
Total 8.02 8.01 4.00 4.02 3.01 17.73 17.82 16.85 11.02 11.02
(Fe total) 0.44 0.42 0.62 0.61 0.82 0.82 0.86 0.81 0.83
Oxide weight measured less than 0.005 % is represented as 0.00
Elements calculated less than 0.005 pfu are represented as
BPor^indicates porphyroblasts
The occurrence of fluor-wagnerite in UHT granulites 425
with P-rich melts (Ren et al. 2005;Grewetal.2007)or
even fluids (Webster et al. 1997;Thomasetal.2003). In
absence of experimental data on partition coefficients (D)
between wagnerite-biotite and wagnerite-melt, we cannot
quantify the mechanism any further. However, from the fact
that F/OH ratio in wagnerite is much higher than that of
biotite, an extreme partitioning of F between wagnerite and
melt can be inferred.
Except for type 1a grains, which are included in the
metamorphic peak garnet porphyroblasts, the other two
types i.e., type Ib and type II responded to later
physico-chemical changes. These two latter types are ex-
tensively fractured with development of late-stage fluor-
apatite along those fractures. Apatite is a very common
phosphate mineral in geological environment when com-
pared to wagnerite and relative stability of these two phos-
phate minerals often depends on the Ca/P ratios of the
host rock vis-à-vis apatite (Pitra et al. 2008). The shift
of wagnerite to apatite stability in a rock therefore implies
increase in Ca/P ratio. Pitra et al. (2008) envisaged Na-
metasomatism as a viable mechanism to explain the sta-
bility of wagnerite over apatite in cordierite-gedrite-bearing
rocks of Armorican Massif, France. These authors argued
that Na metasomatism enhanced stability of plagioclase at
a later stage which helped in sequestering Ca and reducing
the stability of apatite. Stability of apatite over wagnerite
thus requires increased availability of Ca, but there is no
evidence of Ca-metsomatism in the present samples. The
source of Ca during this replacement in an overall Ca-
poor bulk composition is not well-understood, although
the very low modal presence of plagioclase in these rocks
may possibly act as a source. The following model bal-
anced reaction involving wagnerite, apatite and plagioclase
can be formulated.
wagnerite anorthite apatite pyrope sillimanite quartz
Textural and chemical characteristics, therefore suggest
that fluor-wagnerite was present as a part of the pro-
grade assemblage (Type Ia being pre-D
), be-
came part of the subsequent D
assemblage (Type
II) and late post D
assemblage (Type Ib) along
with late-stage biotite. The Fe-Ti-oxide assemblages
from the two samples are represented by the spinel-
magnetite solid solution along with ilmenite. Studying
oxide mineral assemblages from various rocks of the
Bondaguda locality, Bose et al. (2009) suggested that
oxygenated fluid coexisted with the mineral assemblages
all throughout the metamorphic history. Such high fO
conditions presumably helped to change Fe
to Fe
and effectively increase the bulk X
, eventually stabi-
lizing high-Mg phases including wagnerite. High-F ac-
tivities during the peak and retrograde stages have two
implications, its effect on fluid activities (e.g. reduced
in local-scale) and its effect on the stability of
biotite-bearing assemblages in deep crustal levels.
Possible implication for wagnerite-Ti-F-biotite-bearing
assemblages in Ca-poor metapelites
Type Ia and type II fluor-wagnerite and coexisting Ti-F-
rich early biotite included in garnet porphyroblasts im-
ply that F-availability during prograde metamorphism
was quite high in these microdomains. This stabilizes
the prograde biotite-bearing assemblages to comparative-
ly higher temperature (Hensen and Osanai 1994)com-
pared to the F-free biotite-dehydration melting region
which has been experimentally deduced to be ~800
850 °C, in aluminous metapelites (Carrington and
Harley 1995; Das et al. 2003). The behavior of F in
aluminous melt is not well-known. However, theoretical
considerations (Bose et al. 2005) and experimental data
(Hensen and Osanai 1994; Tareen et al. 1998;Nairand
Chako 2002) indicate that biotite-dehydration melting
curves in an F-bearing system may shift as much as
100 °C towards higher temperatures at lower crustal
depths. In a simplified KFMASHTiF system where bio-
tite and partial melt are the only two potential F hosts,
the stability fields of F-biotite-bearing assemblages are
expanded towards higher temperatures. For a reaction
involving biotite, K-feldspar and orthopyroxene, the cal-
culated shift in temperature is 120150 °C assuming an
ideal phlogopite mixing model. This implies that our
earlier estimates of initial biotite-dehydration melting
of the rocks (Das et al. 2006,2011;Boseetal.2009)
needs to be increased up to 900 °C which is close to
UHT conditions (see discussion in Bose et al. 2005).
This shift has been schematically shown in Fig. 7with
an experimentally constrained KFMASH petrogenetic
grid at relatively high oxygen fugacity (Das et al.
2003). Due to lack of experimental data, the exact
amount of shift is still unknown. Moreover, in more
complex natural pelitic systems with P-rich and Ca-
poor bulk compositions, wagnerite may act as another
competing solid for the incorporation of F. Although
this occurs as an accessory mineral in most of the alu-
minous granulites and amphibolites, the preferential
426 Das K. et al.
partitioning of F into wagnerite over coexisting biotite
can marginally enhance the production of melt at UHT
conditions (>900 °C). Obviously, the stability of other
common but accessory phosphate phases like monazite
at these P-T conditions is also important. Thus, depend-
ing on the relative stabilities of different phosphates and
F-bearing phases during biotite dehydration-melting P-T
space, and the relative contents of REE, P and F in the
bulk chemistry, fluor-wagnerite may act as a sink for F
and eventually help to stabilize HT/UHT assemblages
(e.g. sapphirine-quartz-Al-orthopyroxene ± spinel)
coexisting with partial melts in the deep continental
crust. However, the exact controlling factors cannot be
quantified without experimental data.
Textural and phase chemical data for F-wagnerite from two
samples of aluminous granulite of the Eastern Ghats Belt,
India indicate fluid/melt-rock interaction involving F-rich
agents during the evolution of lower crust. Stability of F-
wagnerite in the early stage of granulite metamorphism could
result either from an F-rich protolith, or by melt/fluid-solid
interaction during partial melting. F-rich conditions were
maintained during the early retrograde stage when F-biotite
was stabilized and this has direct bearing on the partial melt
productivity based on biotite dehydration melting in the deep
continental crust. Replacement of F-wagnerite by F-apatite
possibly indicates availability of Ca from plagioclase in local-
ized microdomains during the latter part of the evolutionary
history. Characterization of such unusual F-bearing accessory
minerals is important for proper assessment of the P-T-fluid
evolution of deep crustal granulites.
Acknowledgments We thank M. Kanzaki for his generous assistance
with the Raman spectroscopy at the Institute for Study of the Earths
Interior, Misasa, Japan. We thank Yasuhiro Shibata for assisting in
EPMA analysis. We thank Dirk Spengler, Tetsuo Kawakami and Silvio
Ferrero for their insightful comments on an earlier version of the manu-
script that certainly helped to improve the quality of the paper. Helpful
comments and suggestions from Peter Tropper, Simon Harley and one
anonymous reviewer significantly improved the manuscript quality.
Efficient editorial handing by Lutz Nasdala is greatly appreciated. This
work is partially supported by the Visiting Scientist program at ISEI,
Okayama University for KD. Partial funding for this research was pro-
vided by CSIR, Govt. of India, via grant 24(0333)/14-EMR II to SB.
Fig. 7 The experimentally constrained petrogenetic grid in the
KFMASH system (modified after Das et al. 2003) showing the possible
positions of invariant points and univariant lines. The low-temperature
sides of the thick univariant lines represent the stability of biotite-bearing
assemblages, which may shift towards the high temperature side along the
three univariant lines (thick dashed) towards the (Bt) absent invariant
points. The thin lines represent the reactions involving anhydrous solid
UHT assemblages. Note that the exact degree of shift for the biotite
dehydration melting reactions (the shift of dashed thick lines) in the F-
present system (Ca-poor) is not known, since other components like Ti, P
and REE would influence this shift in presence of different competing
accessory minerals such as wagnerite and monazite. The two P-T paths
represent the reported paths from the two study areas (dark shade is for
Bondaguda area, Bose et al. 2006; light shade is for Panirangini area, Das
et al. 2011)
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The occurrence of fluor-wagnerite in UHT granulites 429
... Natural silicates (jadeite for Na and Si, wollastonite for Ca), and synthetic oxide (Fe 2 O 3 for Fe, TiO 2 for Ti, Al 2 O 3 for Al, Cr 2 O 3 for Cr, MnO for Mn, KTiOPO 4 for K and MgO for Mg) standards were used for calibration. Fluorite is used to measure fluorine following the analytical modalities mentioned in Das et al. (2017). The raw data were corrected using the ZAF program. ...
... The Eastern Ghats Province has recorded the Meso-to Neoproterozoic evolutionary history of the deep continental crust that underwent accretionary orogenesis involving India and East Antarctica (Dasgupta et al., 2013). While the peak metamorphism reached UHT conditions along a counterclockwise P-T path, the post-peak evolution is (Bose et al., 2005;Das et al., 2017) well-within the granulite grade condition. A separate orogenic pulse is believed to have reworked the cooled crust, which also exhumed the cooled lower crust to a shallower level . ...
... This also validates the fact that the lower crustal fluid composition is dominated by the C-O-H system (COH fluid) with a possible saline component. Although the existence of a saline component in the lower crustal fluids of the Eastern Ghats Province could not be proved, circumstantial evidence from mineral chemical characteristics has led to this possibility (Bose et al., 2005;Das et al., 2017;Mondal and Bose, 2019). ...
A suite of high-grade granulite rocks occurring close to one of the earliest reported ultra-high temperature rocks (“Paderu” rocks) from the central part of the Eastern Ghats Belt, India has been studied. Here we present a detailed pressure-temperature-time-fluid history of the suite of aluminous granulite and associated gneisses from a single exposure, which were injected by granitic aplite veins at a high angle at a ductile depth of the host gneissic rocks. Detailed studies of the sapphirine-spinel-quartz-bearing aluminous granulite reveal a peak metamorphic condition of ~1000 °C at ~8 kbar. Porphyroblastic garnet and quartz in the peak assemblage have mono-phase, high-density, CO2-rich primary fluid inclusions (~1 g/cm3). Orthopyroxene-garnet-sillimanite forming corona textures in the aluminous granulite and the presence of cordierite-K-feldspar-quartz intergrowths imply post-peak cooling and subsequent decompression down to ~6 kbar. Secondary fluid inclusions in quartz grains of the aluminous granulite have the signature of bi-phase CO2-H2O fluids with a comparatively low estimated density (0.8 g/cm3). The CO2 isochore plots suggest a pressure drop from 7 to 8 kbar to 4–5 kbar (simultaneous or after the cooling from 1000 °C to 800 °C). Texture-constrained monazite dating using U-Th-total Pb EPMA technique reveals that there are strong peaks at ~940 Ma, ~900 Ma, and ~ 800 Ma with several smaller and younger peaks. On the other hand, the U-Pb SHRIMP dating of zircon from the same rock reveals discordant ages with upper and lower intercepts at ~1700 Ma and ~ 990 Ma. Late pegmatite dykes and aplite veins were emplaced cutting across the dominant structural fabric of this litho-assemblage at a high angle. The asymmetric dragging of the foliation of the host leptynite possibly implies a shear-induced intrusion. The fluid inclusion study of the aplite reveals that the quartz grains contain numerous primary and pseudosecondary fluid inclusions (CO2 monophase to biphase). The calculated density is in the range of 0.71–0.82 g/cm3, suggesting the entrapment of carbonic fluid at <3 kbar. Monazite dating yields a strong single peak at 497 ± 4 Ma, one of the rare dates from the orogenic interior of the Eastern Ghats Belt. The studied suite of deep crustal granulites with aplite veins preserves a history of at least two events of fluid-rock interactions during its residence at the extremely hot deep crustal level until its exhumation to shallower levels where a magmatic fluid is trapped, through a time corridor between the Grenvillian and Kuunga orogenies.
... It is well documented that FKa and ClKa X-ray counts may vary with grain composition and orientation as well as EPMA operating conditions and electron-beam exposure times (Stormer et al. 1993;Goldoff et al. 2012;Stock et al. 2015). Fluorine standards are problematic, as fluorite (Das et al. 2017) as well as fluorapatite (Stormer et al. 1993) display systematic variance under electron beam exposure. We chose the Durango fluorapatite to best match the expected variations of the apatite. ...
The compositions of resistant indicator minerals are diagnostic of their original host environment. They may be used to fingerprint different types of mineral deposit as well as vector towards them. We have characterised the composition of apatite and Fe-Ti oxides in variably-mineralised mafic-ultramafic rock units of the Montagnais Sill Complex in the Labrador Trough to assess their suitability for vectoring magmatic sulphide occurrences. Two broad types of apatite were identified: (i) fluoro- to hydroxy-apatite (Cl/[Cl+F] < 0.2); and (ii) chloro- to hydroxy apatite (Cl/[Cl+F] > 0.5). The former reflects variable degrees of degassing and Cl-loss during Rayleigh fractionation and is not indicative of Ni-Cu-mineralisation or host rock. The latter exists only in sulphidic olivine cumulate units and thus, may be used to vector similar rock types in the Labrador Trough. Ilmenite is the dominant oxide, except for the upper parts of differentiated gabbroic sills in which titanomagnetite is dominant. Magnetite occurs only as a secondary phase in serpentinised olivine cumulates and is not discriminative for magmatic sulphides. Ilmenite and titanomagnetite in the sulphidic olivine-bearing units have characteristically high Mg (~ 1,000-10,000 ppm), Cr (~ 100-1,000 ppm), Ni (~ 10-1,000 ppm), and Cu (~ 1-10,000 ppm) concentrations relative to those from other rock units. Their composition is consistent with Fe-Ti oxides derived from evolved sulphide melts in ultramafic-hosted Ni-Cu-(PGE) sulphide deposits and thus may be used to vector towards similar magmatic sulphide occurrences in the Labrador Trough.
... Ga (Mezger and Cosca, 1999;Upadhyay et al., 2009;Bose et al., 2011a;Das et al., 2011;Korhonen et al., 2013;Dasgupta et al., 2017;Bose and Dasgupta, 2018). Several studies from this belt reveal that the pressure-temperature-fluid history of the lower crust underwent multiple stages of metamorphism (Mohan et al., 2003;Sarkar et al., 2003;Gupta et al., 2005;Bose et al., 2009Bose et al., , 2016aDas et al., 2017;Ganguly et al., 2017). The Chilka Lake granulite complex occurs at the north-eastern corner of the Eastern Ghats Province (Fig. 1 inset) although it was assigned the status of a separate crustal domain. ...
Orthopyroxene-bearing felsic gneiss occurs as foliation-parallel layers and bands together with aluminous granulite, mafic granulite, and quartzofeldspathic granulite in the Chilka Lake migmatite complex of the Proterozoic Eastern Ghats Belt, India. The rock was classified previously as charnockite which underwent granulite-facies metamorphism. Field and textural features of this rock show evidence of the partial melting of a biotite-bearing greywacke protolith. Orthopyroxene with/without garnet and cordierite were produced with K-feldspar as peritectic phases of incongruent melting of presumed metaluminous sediments. Fluid-inclusion data suggest the presence of high-density CO 2 -rich fluids during peak metamorphism, which are similar to those found in associated aluminous granulite. Whole-rock major and trace element data show wide variability of the source materials whereas REE distributions show enriched LREE and flat HREE patterns. Zircon grains from representative samples show the presence of inherited cores having spot dates (SHRIMP) in the range c. 1790–3270 Ma. The overgrowth on zircon was formed predominantly during c. 780–730 Ma and sporadically during c. 550–520 Ma. Some neoblastic zircons with c. 780–730 Ma ages are also present. U-rich dark zones surrounding cores appear partially metamictised, but spot ages from this zone vary within c. 1000–900 Ma. The <1000 Ma ages represent metamorphism that mirrors the events in associated aluminous granulite. The sources of metaluminous sediments are speculative as the rock compositions are largely modified under granulite-facies metamorphism and partial melting. Considering the accretionary tectonic setting of the Eastern Ghats Belt during the c. 1000–900 Ma time frame, a greywacke-type protolith for the migmatite complex has been proposed.
... Fluid inclusion data from the EGB (Chilka Lake by Bose et al. (2016); Simliguda by Bose et al. (2009); G. Madugula by Mohan et al. (2003); Vizianagaram by Sarkar et al. (2003)) show evidence of CO 2 -H 2 O fluid species without any direct evidence for brine. Interestingly, the high F contents in fluor-biotite (>3 wt%; Bose et al. 2005;Ganguly et al. 2017) and fluor-wagnerite (>6 wt% F; Das et al. 2017) in mineral assemblages indicate the possible association of halogen-rich fluid species during peak and retrograde metamorphic stages. For the granitic rocks, the composition of brine is dominated by NaCl, whereas CaCl 2 dominates in mafic rocks (Möller et al. 1997;Stober and Bucher 2005). ...
Mafic granulites from key localities of the Eastern Ghats Province preserve Fe–Ti oxides, Cu–Fe sulphides and traces of sulphate minerals along with silicate phases. Two different varieties of mafic granulite exhibit slightly contrasting mineral assemblages. While the massive type of mafic granulite contains minerals assemblage orthopyroxene + clinopyroxene + plagioclase + magnetite + ilmenite + pyrite + pyrrhotite, the migmatitic variety contains garnet as an additional phase. Both oxide and sulphide minerals show contrasting textural characters. Textural analysis and construed mineral reactions imply that the variation of oxide–silicate, oxide–sulphide and sulphate relations is linked to variation of \(f\hbox {O}_{2}\) during the pre-peak, peak and post-peak stages of metamorphism. The calculated \(f\hbox {O}_{2}\) values range up to +4 log units relative to the QFM (quartz-fayalite-magnetite) buffer among the samples, except for one sample which shows lower values (−10 log units relative to the FMQ (fayalite-magnetite-quartz) buffer). The consistently high \(f\hbox {O}_{2}\) condition at the lower crust could result from several factors, but the role of the externally derived fluid appears to be plausible. Hot brine solution with \(\hbox {CaCl}_{{2}}\) species can explain the oxidation as well as local metasomatism of the mafic lower crust even though its presence is not verified from direct characterisation like fluid inclusion analysis.
... Natural silicate and oxide standards were used for calibration in both instruments and the raw data were corrected using the ZAF program. Fluorine contents in biotite were measured using natural fluorapatite as a standard [details have been given by Das et al. (2017)]. Representative mineral compositions in the aluminous granulite and associated rocks are given in Tables 2 and 3. ...
We present zircon U-Pb (SHRIMP) and monazite U-Th-total Pb (EPMA) ages from a suite of high-grade rocks of the Phulbani domain of the Eastern Ghats Belt, India. These ages are integrated with the metamorphic and magmatic histories of the Phulbani domain to put precise time constraints on the tectonothermal evolution of the northern part of the Eastern Ghats Belt. Zircon from the coarse-grained charnockite rock shows crystallization age of ca. 970 Ma. Aluminous granulite contains spinel and quartz-bearing mineral assemblage indicating ultrahigh temperature metamorphism (>900 °C at 8–10 kbar) which possibly occurred during ca. 987 Ma as revealed from monazite included in porphyroblastic garnet. Monazite in the aluminous granulite and the migmatitic felsic gneiss grew dominantly at 966 ± 4 Ma and 968 ± 4 Ma ages respectively, which are interpreted as the cooling ages subsequent to peak metamorphism. Oscillatory-zoned zircon grains of the felsic augen gneiss yield ca. 1173 Ma age which is interpreted as the crystallization age of the granitic protolith. This ca. 1173 Ma age granite possibly composed a part of the Proterozoic basement of the Eastern Ghats Province. A monazite age of 781 ± 15 Ma from the aluminous granulite may indicate the timing of a localized shear-induced thermal process in the Phulbani domain. The presently studied rock suite thus recorded three distinct events (ca. 1173 Ma, ca. 1000–900 Ma and ca. 781 Ma) of magmatism, metamorphism and deformation of Eastern Ghats Belt. Metamorphic and magmatic histories of the Phulbani domain are similar to those of the adjacent Visakhapatnam domain and the Rayner Province of East Antarctica during the time frame ca. 1000–900 Ma.
... Natural silicate and oxide standards were used for calibration in both instruments and the raw data were corrected using the ZAF program. Fluorine contents in biotite were measured using natural fluorapatite as a standard [details have been given by Das et al. (2017)]. Representative mineral compositions in the aluminous granulite and associated rocks are given in Tables 2 and 3. ...
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A suite of high-grade rocks including felsic gneiss, aluminous granulite, charnockite and calc-silicate granulite is exposed at Phulbani, which belongs to a petrologically little understood crustal domain (Phulbani domain) of the Eastern Ghats Belt. The aluminous granulite is constituted of corundum + spinel + ilmenite + garnet + sillimanite + quartz ± K-feldspar ± plagioclase ± biotite. Textural analysis indicates that corundum, spinel, garnet and/or K-feldspar were formed as a result of biotite dehydration melting of a Si-poor protolith during prograde metamorphism. Although corundum and quartz coexist in micro-scale domains, phase diagram modelling suggests that garnet + corundum + spinel + ilmenite + sillimanite (up to 800°C at 8 kbar) and garnet + spinel + sillimanite + ilmenite + quartz (above 950°C at 8 kbar) assemblages were stabilized in two different temperature intervals while attaining the ultrahigh-temperature metamorphic peak. The transformation from corundum- to quartz-bearing assemblages was principally governed by chemical reactions. Quartz, formed at the peak stage, produced complex reaction textures involving spinel, corundum, garnet and sillimanite during near-isobaric cooling. Intersection of the same mineral reactions during the prograde and the retrograde paths implies the near-closed-system behaviour of the lower crust, at least at microdomain-scale, possibly achieved after large-scale melt loss along the prograde-to-peak stage of evolution. The pressure–temperature path remained near-isobaric during the prograde and the retrograde evolution of the assemblages. High-density (up to 1·03 g cm–3) CO2-rich fluid inclusions in aluminous granulite, coarse-grained charnockite and felsic gneiss indicate that peak metamorphism and subsequent evolution occurred under a CO2-dominated fluid regime. The pressure–temperature–fluid evolutionary history of the Phulbani domain shows similarity to that of the adjacent Visakhapatnam domain of the Eastern Ghats Belt and poses questions on the status of the boundary separating these two domains.
In this paper, a fast load shedding remedial action scheme (RAS) is developed considering generation pattern of local wind farms using wide area monitoring framework. In the proposed RAS, the shedding candidates are selected and prioritized based on load types and their impacts on the voltage profile and transient performance of the system. The dynamics of wind farms are also included in the shedding requirements and formulas by defining effectiveness indices which are calculated based on the contribution of each generator to the dynamic performance of the system. This allows secure operation of the system after major contingencies while impacted customers are minimized. The proposed methodology, shedding formulas, and corresponding requirements are verified for the BC Hydro system using the PSS/E dynamic simulation package.
Wagnerite was found in a pyrope-rich rock with the primary phase assemblage pyrope + phlogopite + wagnerite + orthopyroxene I. A secondary phase assemblage occurs as a symplectite, orthopyroxene II + cordierite + sapphirine. The chemical composition of wagnerite (MgO 46.08, FeO 3.32, MnO 0.04, P2O5 41.80, H2O⁺ 1.18, F2 8.80, H2O⁻ 0.20, insol. 2.92, less O = F 3.71 = 100.63) yields a crystallochemical formula Mg3.771Fe0.152Mn0.002(P1.945O7.780/F1.531OH0.436). An elevated content of H2O⁺ suggests the existence of a series between wagnerite and hydroxy-wagnerite (hypothetical). Unit-cell parameters a 11.925(6), b 12.647(6), c 9.635(4) A beta 108.21o; alpha 1.569(2), gamma 1.582(2), 2Vgamma 34o, Dcalc. 3.092 g/cm³. The atomic ratio M = 100 Mg/SIGMA oct. exhibits a negative correlation with the a and b parameters. There is a positive correlation between a and b cell parameters and mean radii of octahedrally coordinated cations, and a tight positive correlation between the parameter c and the fluorine content. Wagnerite apparently formed at T and P of the eclogite facies. Its formation requires a high activity of Mg²⁺ and a low activity of Ca²⁺ (the rock contains 23 wt.% MgO and 0.58 wt.% CaO). The presence of rutile, rather than sphene, confirms the low availability of Ca²⁺ in the rock. (Authors' abstract)-E.v.P.
The ion exchange characteristics of B-type carbonate apatites (CAP) containing 6 or 16 wt.% CO32- ions, for Zn2+, Cd2+, Hg2+, and Pb2+ in aqueous solution at 25 °C are investigated at 25 °C and compared with those of CO32--free hydroxyapatite.
The unit cell parameters of magniotriplite (Mg, Fe)₂ (PO₄)(F, OH), from Albères (Pyrénées, France), are : a = 12.035(5), b = 6.432(4), c = 9.799(2) Å, β = 108.12°(2) ; Z = 8. The crystal structure can be derived from that of the members of triplite-triploidite group : magniotriplite and triplite are isotypic. The least-squares refinement, carried out in both space-groups I2/a and Ia, reduced the conventional R factor to 0.033 for centric and 0.034 for acentric space group. (F, OH) atoms have a disordered distribution on the sites of the space group I2/a and ordered arrangement in the sites of the space group Ia.
Wagnerite (Mg,Fe,Ca,Mn)2[PO4(F,OH)] was found in high-MgAl granulite near Anakapalle, ca. 40 km W of Vishakhapatnam, East-India. This is the first reported occurrence of this mineral in the granulite-facies Eastern Ghats Belt (EGB). The high-MgAl granulite occurs as xenoliths of several meters in diameter within basic granulite. The rocks experienced Grenvillian ultra-high-temperature (UHT) metamorphism (8 kbar; T > 900°C). Still at high-grade conditions, the rock assemblage was intruded by large volumes of felsic melt (charnockite). Hence, the MgAl granulite became partially metasomatised, resulting in microdomains with variable Ca/(Ca+Mg) - ratios and different assemblages. Three principal wagnerite-bearing petrographic domains are distinguished. Within domains 1 and 2 (Ca/(Ca+Mg) ~ 0.02) wagnerite occurs as a stable phase of the UHT-assemblage and is the major phosphorus-bearing phase, while apatite is absent. In domain 3 (Ca/(Ca+Mg) ~ 0.25), wagnerite reacted with the intruding felsic melt and is now rimmed by apatite. Isokite, CaMg[PO4F], was not observed and seems not to be stable at UHT-conditions. Wagnerite from Anakapalle is characterised by unusually high OH content (F/(F+OH) = 0.47-0.60) and low Ca content (0-0.5 wt% CaO). The Fe content in domain 3 is slightly higher (3-3.5 wt% FeO) compared to domains 1 and 2 (1.5-2.5 wt%).
The geology is outlined and XRD, chemistry, and mineralogy are described for these minerals together with analyses for cordierite, rutile, and almandine-pyrope. -K.A.R.
Fluorine-rich phlogopite [F content up to ~8 wt%; F/(F + OH) ~0.9] in ultra-high-temperature metapelitic granulites from the Napier Complex, East Antarctica is associated with aluminous orthopyroxene, osumilite, sapphirine, garnet, and quartz. Textural relationships imply that some of the phlogopite is of primary origin and stable under ultra-high-temperature conditions. This is in accord with recent experimental evidence on the stability of F-rich phlogopite. Because the F-rich phlogopite also occurs as rounded inclusions in aluminous orthopyroxene (Al2O3 up to 12.8 wt%), sapphirine, osumilite, and garnet, it is inferred that the ultra-high-temperature mineral assemblages, which includes these minerals formed during prograde partial melting reactions at the expense of phlogopite, at a depth of less than 30 km. Thus the coarse-grained peak metamorphic assemblages formed below 9 kbar, and there is no evidence the rocks underwent any significant degree of decompression during or soon after peak metamorphic conditions. The phlogopite breakdown reactions we suggest on the basis of textural arguments differ from those postulated from experiments on F-free systems.
zircon, monazite, garnet and feldspar trace element microanalysis, zircon and monazite U-Pb isotopic ages and monazite Th-U-Pb chemical dating, determined in situ,from a leucogranitic vein in migmatitic gneiss at Kulappara in the Kerala Khondalite Belt (Trivandrum Block), India, demonstrate accessory mineral crystalization from an evolving melt-bearing system from c.545 to 535 Ma at temperatures of greater than 780 degrees C. Marked changes in zircon chemistry to tower Th/U and Yb-n/Gd-n occurred during its growth in the evolving melt, correlated with a dramatic change in microtexture from initial `hopper'-like feathered-core and outer planar sector domains to darker planar zones and elliptical to lobate infilling and replacement zircon. Initially high Th/U, high heavy rare earth element (HREE) zircon crystallized rapidly from melt from 544 9 Ala under open-system conditions in which the host-rock mineralogy had no chemical impact. This zircon precipitated prior to crystallization of significant garnet, trapping melt as inclusions that later crystallized to cryptogranite within zircon cores. Further zircon crystallization ensued under localized closed-system conditions leading to the establishment of zircon-garnet REE equilibrium at least on local (i.e. millimetre to centimetre) scales, consistent with melt entrapment, at 542 6 Ala. Monazite crystallized in this fractionated melt by 535 +/- 6 Ma. These results demonstrate that zircon can be a sensitive indicator of changing conditions and scales of. melt transfer and interaction in high-temperature migmatities, recording in this instance a transition from melt-dominated open-system behaviour to closed-system crystallization and mineral melt interaction at T>780 degrees C in the deep crust of a hot orogenic belt.