Physico-Chemical Conditions of Four Calc-Alkaline Granitoid Plutons of Chhotanagpur Gneissic Complex, Eastern India: Tectonic Implications

J. Earth Syst. Sci. (2018) 127:120 c Indian Academy of Sciences https://doi.org/10.1007/s12040-018-1022-4

Physico-chemical conditions of four calc-alkaline granitoid plutons of Chhotanagpur Gneissic Complex, eastern India: Tectonic implications

B Goswami*, P Roy, A Basak, S Das and C Bhattacharyya

Department of Geology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700 019, India. *Corresponding author. e-mail: [email protected]

MS received 28 February 2017; revised 3 March 2018; accepted 5 March 2018; published online 26 October 2018

Petrography and mineralogy of four calc-alkaline granitoid plutons Agarpur, Sindurpur, Raghunathpur and Sarpahari located from west to east of northern Purulia of Chhotanagpur Gneissic Complex, eastern India, are investigated. The plutons, as a whole, are composed of varying proportions of Qtz–Pl–Kfs–Bt–Hbl±Px–Ttn–Mag–Ap–Zrn±Ep. The composition of biotite is consistent with those of calc-alkaline granitoids. Hornblende–plagioclase thermometry, aluminium-in-hornblende barometry P T f and the assemblage sphene–magnetite–quartz were used to determine the , and O2 during the crystallisation of the parent magmas in different plutons. The plutons are crystallised under varying pressures (6.2–2.4 kbar) and a wide range of temperatures (896–718◦C) from highly oxidised magmas f − . − . (log O2 11 2to 15 4 bar). The water content of the magma of different plutons varied from 5.0 to 6.5 wt%, consistent with the calc-alkaline nature of the magma. Calc-alkaline nature, high oxygen fugacity andhighH2Omelt suggest that these plutons were emplaced in subduction zone environment. The depths of emplacement of these plutons seem to increase from west to east. Petrologic compositions of these granitoids continuously change from enderbite (opx-tonalite: Sarpahari) in the east to monzogranite (Raghunathpur) to syenogranite (Sindurpur) to alkali feldspar granite (Agarpur) in the west. The water contents of the parental magmas of different plutons also increase systematically from east to west. No substantial increase in the depth of emplacement is found in these plutons lying south and north of the major shear zone passing through the study area suggesting the strike-slip nature of the east–west shear zone. Keywords. Calc-alkaline granitoids; mineral chemistry; intensive parameters; Chhotanagpur Gneissic Complex; eastern India.

1. Introduction and temperature and oxygen fugacity of the magma. While total Al-in-hornblende is a function The mineral assemblages (quartz–alkali feldspar– of pressure (Hammarstrom and Zen 1986; Vyh- plagioclase–biotite–amphibole–sphe ne–magnetite nal et al. 1991; Schmidt 1992; Anderson 1996; and/or ilmenite) and evolving conditions of the Mutch et al. 2016), Ti-in-hornblende (Otten 1984) calc-alkaline magma during crystallisation are and the compositions of coexisting hornblende– closely related (Speer 1987; Vyhnal et al. 1991; plagioclase (Holland and Blundy 1994) are related Ague 1997). Particularly, the compositions of to the temperature of the magma. Further, com- hornblendes and biotites are related to pressure positions of biotite, sphene (titanite) and Fe–Ti 1 0123456789().,--: vol V 120 Page 2 of 33 J. Earth Syst. Sci. (2018) 127:120 oxides are important for the calculation of oxygen of granites, pegmatites, norites, anorthosites and fugacity (Wones 1989). Compositions of amphibole alkaline rocks (Mahadevan 2002). Ghose (1983) and biotite are also related to the water content and Banerji (1991) classified the CGC into several of the magma (Ridolfi and Renzulli 2012). On lithostratigraphic units, while Singh (1998) argued the other hand, the determination of pressure and that the formations within the CGC show grada- temperatures of the calc-alkaline plutons is impor- tional changes and do not, in general, ‘obey the tant for unravelling the evidence for the ascent (or law of superposition’ and hence suggested these as descent) of exposed crustal sections. ‘lithodemic’ group. Although in the Proterozoic Chhotanagpur A part of the study area (figure 1b) lying in Gneissic Complex (CGC) granitoids are the most the northern part of Purulia district, West Ben- important rock groups with a wide distribution of gal (eastern part of CGC) was described by Sen calc-alkaline granitoids, only few papers that dealt (1953, 1956, 1959), Mitra (1992), Goswami and with the mineralogical aspects of these granitoids Bhattacharyya (2008, 2014)andMaji et al. (2008). have so far been published (Ghose 1983, 1992). Two prominent lineaments: (i) the nearly E–W This contribution focuses on four calc-alkaline trending NPSZ and (ii) and ENE trending linea- granitoid plutons (Agarpur, Sindurpur, Raghu- ment (known as the northern megalineament) nathpur and Sarpahari) exposed in northeastern lying to the north of (i) pass through the area. Purulia, West Bengal. The occurrences of these The migmatitic/composite granitoid gneisses coun- plutons are restricted between the North Purulia try occupying the northern side of the north- Shear Zone (NPSZ) and the northen megalinea- ern megalineament and also the southern side ment (shear zone) and immediate south of the of the NPSZ contain enclaves of khondalites, NPSZ. The aims of this paper are to: (i) describe marbles, calc-silicate schists/gneisses, para- and the mineral–chemical evolution of the above four ortho-amphibolites belonging to amphibolite facies. plutons, (ii) decipher the physico-chemical condi- However, the leptynitic country in between the two tions (pressure and temperature of crystallisation lineaments contains minor patches of migmatites, and oxygen fugacity and water content) that pre- basic granulites, charnockitic rocks and calc-silicate vailed during the crystallisation of magmas, and rocks representing amphibolite and granulite facies. (iii) discuss the implications of the data on the Several intrusive bodies of granitoids intrude into geotectonic interpretation of the plutons of the the leptynitic country. These granitoid intrusions northern part of Purulia. have been traditionally viewed as Mesoproterozoic in age. The four representative plutons which are studied include the Agarpur, Sindurpur, Raghu- 2. Geologic setting nathpur and Sarpahari intrusions, of which, three are located between the E–W trending NPSZ Eastern Indian shield comprises the CGC and the northern megalineament while the Sin- (covering ∼100,000 km2 area) in the north, the durpur pluton is located south of NPSZ Singhbhum craton in the south and the east– (figure 1B). west (E–W) trending North Singhbhum Mobile Grey-coloured biotite granitoid gneiss, often Belt (NSMB) between these two (figure 1A). garnetiferous, is the major component of migmati- The southern boundary of the CGC with the tic granitoid gneisses country. Enclaves of migma- NSMB is tentatively marked by the South Purulia titic granitoid gneiss sometimes occur within the Shear Zone (Basu 1993). The northern and eastern intrusive granitoids. Numerous lensoidal meta- margins of the CGC are covered by the Ganga– sedimentary enclaves of garnet–sillimanite gneiss Brahmaputra alluvial deposits (figure 1A). In the (khondalite), calc granulites, amphibolite, mica west, the CGC is separated from the Central schist, etc., are noticed within the migmatitic gran- Indian Tectonic Zone by younger Gondwana itoid gneiss. The contact of the metasedimentary sediments. enclaves and the migmatitic granitoid gneiss is gra- The CGC is characterised by widespread dational. Long axes of the enclaves are aligned Palaeo- to Neo-Proterozoic predominant grani- parallel to the regional foliation. Pyroxene gran- toid gneisses and migmatites with older enclaves ulite, charnockitic rocks, nepheline syenite gneisses of metapelitic gneisses (khondalites), amphibo- and orthoamphibolites are also interpreted to have lites, calc-granulites, quartzites, charnockites, lep- igneous protolith (Goswami and Bhattacharyya tynites and mafic granulites, and younger intrusives 2008). J. Earth Syst. Sci. (2018) 127:120 Page 3 of 33 120

Figure 1. (A) Generalised geological map of the CGC showing the distribution of Archean–Proterozoic metasedimentary enclaves and granitic intrusives. Proterozoic Dalma lava in the Singhbhum mobile belt, the Cretaceous Rajmahal volcanics and Mesozoic Gondwana basins associated with the Damodar Graben are shown for reference. (B) Simpliﬁed geological map of the area of study in northern Purulia.

Major structural grains are represented by a The rocks of the area bear signatures of at least dominant foliation trending E–W to NE–SW with three phases of deformations (D1,D2 and D3). ◦ ◦ a northerly low-to-moderate dip (20 –40 ). The Nearly parallel S1 and S2 foliations are discernible ENE–WSW alignment of the intrusive granites is in quartzites and grey biotite granitoid gneisses. more or less parallel to the trend of the major shear S1 is the dominant foliation of the area. S1 is axial zones. planar to the tight, appressed intrafolial D1 folds 120 Page 4 of 33 J. Earth Syst. Sci. (2018) 127:120

(figure 2A). D2 folds are defined by form surface (figure 1B). These rocks often contain bands of of a set of gneissic banding (S1). In mesoscopic enclaves of amphibolites. The megacrysts of scale, D1 minor folds are highly plunging or nearly feldspar as well as enclaves are usually oriented reclined. D1 folds are rarely encountered in intraf- parallel to the gneissic trend of the country rock olial layers of biotite granitoid gneiss, quartzite and (figure 2I) but in some cases, the megacrysts locally calc-silicate rocks. D2 folds are tight to close, low show haphazard orientation indicating turbulent plunging and overturned (figure 2B). The shear flow in magma. The general trend of magmatic foli- ◦ movement represents the D3-deformation. Granite ation is ENE–WSW. The dip ranges from 70 to ◦ mylonites, augen gneisses and leptynites charac- 72 N. In places, the granitoid rocks show D2 folds terised by the formation of ribbon quartz occur (figure 2J). Hence, the pluton emplaced before the all along the NPSZ and northern megalineament. D2-deformation episode. The strong preferred ori- The strike-slip movement with a sinistral sense entation of the minerals reflects the shearing effect on the plan is the dominant nature of NPSZ during the D3-deformation (figure 2K). (figure 2C). The long axis of the Agarpur pluton is E–W The basic granulites show weak foliation (S1), (figure 1B). The rock shows impersistent E–W defined by the preferred orientation of orthopy- trending and steep dipping magmatic flow foliation roxene, which was subsequently folded by D2. (figure 2L). The southern boundary of the pluton is Similarly, the long dimension of rod-shaped silli- mylonitised by the D3-deformation. The magmatic manites in garnet–sillimanite gneisses got folded flow foliation and mylonitic foliation are parallel during D2. This suggests that the metamorphism to the gneissosity of the country rock gneisses. in the upper amphibolite to granulite grade was The flattened ribbon-shaped quartz grains paral- attained during D1-deformation. The country rock lel to E–W foliation defines a megascopic fabric attained granulite facies in the eastern part of indicative of ductile deformation. Joints develop the study area, i.e., around the Sarpahari pluton. parallel to this foliation and late mafic magma The grade of metamorphism gradually decreased invaded the rock along these joints (figure 2M towards the west and reached amphibolite facies and N). around the Agarpur pluton (Goswami and Bhat- tacharyya 2008). The intrusion/injection of enderbite (opx- tonalite) and/or charnockite (opx-granite), sensu Figure 2. (A) Intrafolial D1 folds in the granitised quartzite, stricto,alongtheS1 plane of the basic gran- north of Raghunathpur. (B) Overturned D2-antiform in the ulites (figures 2Band2D) and migmatitic gneisses basic granulites, north of Murlu. Note injection of ender- is commonly noticed. Primary banding of enderbite along the foliation plane of basic granulite. (C) Shear bite of the Sarpahari pluton was folded during fold related to D3-deformation in the migmatite east of Jaipur. Note the injection of pink granite along the foli- D2-deformation (figure 2E). The pluton emplaced ation of the host amphibolite. (D) Injection of enderbite before D2-deformation. magma in basic granulite at the foothill of Sarpahari. (E) The long axis of the Raghunathpur pluton is Antiformal D2 fold in enderbite. Note the older enclave of ENE–WSW. The porphyritic granitoids contain basic granulite is folded with the enderbite arising a false strongly aligned euhedral crystals of pinkish K- impression of hook-like geometry. (F) A preferred alignment of K-feldspar megacrysts in the porphyritic granite of Raghu- feldspar megacrysts (figure 2F) which is interpreted nathpur. Location: Bero Pahar. (G) Amphibolite xenolith to be due to magmatic flow (Goswami and Bhat- within porphyritic granite of Raghunathpur. Note: swerv- tacharyya 2014). The long dimension of feldspar ing of the K-feldspar megacrysts around the xenolith. (H) grains ranges from 3 to 10 cm. The flow foliation Augen-shaped megacrysts of K-feldspar at the northern mar- of porphyritic granitoids is deflected around the gin of the Raghunathpur granite, near Bero. (I) Parallel xenoliths of basic granulite (figure 2G). Along the alignment of older amphibolite enclave within the Sindur- pur pluton. Note the parallelism of the long dimension of northern and southern boundaries of the pluton, amphibolite and foliation of the host granite. (J)D2 folds microcline megacrysts are lensoid in shape and fer- within the porphyritic granite of Sindurpur. (K)Effectof romagnesian minerals tend to warp around them shearing on the megacrysts of the Sindurpur pluton. Note: giving rise to augen structures (figure 2H). This stretching of the megacryst. (L) Banding defined by the feature is interpreted to be due to shearing along alternate layers of ferromagnesian and quartzo-feldspathic minerals in the Agarpur pluton. (M) Injection of basic mate- the boundaries. rial along the joint planes of the Agarpur pluton. These joints The Sindurpur pluton occurs as a very are parallel to the shear planes. (N) A close view of the prominent E–W trending elongate batholithic body previous exposure (M). J. Earth Syst. Sci. (2018) 127:120 Page 5 of 33 120

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3. Analytical methods Intergrowth of quartz with microcline is not uncommon. Subidiomorphic to xenomorphic pla- Electron probe micro analyses (EPMA) of the gioclases (albite to oligoclase) mainly occur in representative minerals of these samples were per- the groundmass. Myrmekitic intergrowth is not formed using a CAMECA SX100 microprobe with uncommon. The actinolite (pleochroic from light wavelength dispersive spectrometers at the Cen- green to bluish green) and subordinate hornblende tral Petrology Division, Geological Survey of India, grains are coarse to medium grained, elongated, Kolkata. An accelerating voltage of 15 kV was irregular and ellipsoidal with subidiomorphic to maintained with a beam current of 12 nA and 1 µm xenomorphic grain boundary. Allanite (idiomor- beam diameter. phic to subidiomorphic) occurs as a cluster of laths The EPMA of the representative minerals of and patches in the ferromagnesian bands. Sphenes three samples of the Agarpur pluton was performed (pleochroic from light brown to dark brown; sub- in a CAMECA SXFive instrument at DST-SERB idiomorphic to xenomorphic) are fine to medium National Facility, Department of Geology (Centre grained, elongated parallel to the fabric. Mag- for Advanced Study), Institute of Science, Banaras netites are idiomorphic, squarish and equant and Hindu University. An accelerating voltage of 15 kV occur as the inclusion within biotite and amphibole was maintained with a beam current of 10 nA and grains. Apatite (idiomorphic to subidiomorphic, 1 µm beam diameter. Natural and synthetic stan- hexagonal to rounded, ellipsoidal to prismatic) dards supplied by CAMECA-AMETEK were used occurs as a discrete phase within groundmass and for precision and correction. also as inclusions within both felsic and mafic The EPMA of the representative minerals from minerals. two samples of porphyritic granitoids of the Raghu- In the mylonitised zones, impersistent, extremely nathpur pluton was performed using a JEOL thin ribbons or elongate streaks of quartz run JXA-8600M microprobe with wavelength disper- through the flesh-coloured feldspar parallel to the sive spectrometer at the IIC (Institute Instru- direction of mylonitic foliation (figure 3A). Phe- mentation Centre), Indian Institute of Technology, nocrysts of microcline and quartz survived as ellip- Roorkee. An accelerating voltage of 15 kV was soidal or augen-shaped porphyroclast with elonga- maintained with a beam current of 50 nA. Beam tion parallel to the direction of mylonitic foliation. diameter was fixed at 3 µm. Natural standards supplied by SPI Suppliers, Structure Probe Inc., Canada, were used for precision and correction. 4.2 Sindurpur pluton The precision of data of major elements for all the three instruments is ±3%. The porphyritic granitoids of Sindurpur are composed mainly of K-feldspar, plagioclase, quartz, 4. Petrography biotite, hornblende and minor orthopyroxene, opaque, apatite, muscovite, sphene, garnet, allanite 4.1 Agarpur pluton and zircon and show distinct banding (figure 3C). A preferred alignment of ferromagnesian (biotite The pluton is medium to coarse grained, grey and hornblende) and platy feldspars define the to brownish colour in outcrop and shows well- magmatic foliation. Quartz occurs commonly as developed magmatic flow foliation. The pluton coarse, elongate, lenticular grains, deformed or is composed of pink-coloured granite and alkali warped around microcline megacrysts. It occurs feldspar granite. The major minerals present in the also as tiny (medium to fine grained) xenomorphs rock are microcline, quartz, plagioclase and amphi- intimately associated with feldspar and biotite- bole. The accessory phases are allanite, magnetite rich groundmass. K-feldspar (microcline) occurs and apatite. The magmatic flow foliation in the as megacrysts and coarse subhedra along with rock is defined by alternate layers of aggregates aggregates of smaller subhedral crystals, embedded of ferromagnesian minerals with thicker bands of in quartz–plagioclase–biotite-rich medium-grained quartzo-feldspathic mass. The felsic bands contain groundmass. Plagioclase (oligoclase) occurs as phenocrysts of microcline giving rise to porphyritic medium to coarse, tabular, subidiomorphic grains texture (figure 3B). The ferromagnesian bands forming aggregates with other groundmass min- are composed mainly of a cluster of aggregates erals, mainly quartz, biotite, and occasionally of prismatic and lensoidal grains of amphibole. hornblende. Alteration of plagioclase is common. J. Earth Syst. Sci. (2018) 127:120 Page 7 of 33 120

Figure 3. (A) Fine ribbon-shaped quartz within the pink granite. (B) Feldspar megacrysts in the felsic bands of pink granite. (C) Banding deﬁned by the preferred alignment of felsic minerals in the Sindurpur granite. (D) Deformation of plagioclase megacrysts and formation of a ﬁner groundmass in the porphyritic granite of Raghunathpur. (E) Strong dimensional orientation shown by the quartzo-feldspathic minerals and lenses of ferromagnesian minerals in enderbite of Sarpahari. (F) Relict megacryst of plagioclase within a granulated groundmass.

Medium-sized laths and ﬂakes of biotite form green) and clinopyroxene may be present as relict clusters in the groundmass and oriented subpar- patch within hornblende. Magnetite, limonite, apa- allel to foliation. It is intimately associated with tite and sphene occur as accessories. Allanite, hornblende and replaces the latter. Hornblende zircon, sphene and garnet, when present, occur in occurs as xenomorphic to subidiomorphic medium trace amounts as subidiomorphic to idiomorphic to coarse grains. Orthopyroxene (colourless to light grains. 120 Page 8 of 33 J. Earth Syst. Sci. (2018) 127:120

4.3 Raghunathpur pluton and accessory opaque, zircon and apatite. The foliation is defined by alternate thicker layers of The porphyritic granitoids are composed mainly quartzofeldspathic aggregates with thin impersis- of K-feldspar, plagioclase, quartz, biotite, horn- tant stringers and layers of ferromagnesian min- blende and accessory opaque, apatite, chlorite, erals through the quartzofeldspathic groundmass. epidote, allanite, muscovite, sphene, carbonate, Both quartz and feldspar show strong dimensional garnet, scapolite and zircon in variable propor- orientation and the impersistant layers and lenses tions. Although most of the porphyritic granitoids of ferromagnesian minerals are oriented parallel to lie in the granite and quartz monzonite fields of the foliation (figure 3E). Coarse plagioclase and QAP (Quartz–Alkali feldspar–Plagioclase) diagram quartz grains show protoclastic granulation formed (after Streckeisen 1976), few samples lie in the by shearing. Such a medium- to fine-sized gran- tonalite, granodiorite and alkali feldspar granite ulated mass occurs in the interspaces of coarser fields. quartz and feldspar. Plagioclase occurs as coarse, Quartz occurs commonly as coarse, elongate, equant to elongated, xenomorphic to subidiomor- lenticular grains, deformed or warped around phic grains as well as aggregates of fine-sized microcline megacrysts. Abundant tabular or subidiomorphic equant grains. Coarser plagioclase (rarely) ellipsoidal megacrysts (1–10 cm long) of generally shows the deformation effect in the form K-feldspar occur in quartz–plagioclase–biotite-rich of bending of twin lamellae and also shadowy medium-grained groundmass, often bordered by a extinction (figure 3F). Quartz occurs as coarse, narrow rim of very-fine-grained anhedral quartz, equant to elongated, xenomorphic to subidiomor- microcline, sericitised and turbid plagioclase and phic grains as well as aggregates of fine-sized subid- lobate myrmekite. Ellipsoid megacrysts have ‘tails’ iomorphic equant grains. Some of the quartz grains of millimetre-sized anhedral quartz, plagioclase are lenticular and such lenticles are more strongly and microcline which pinch out into more mafic oriented parallel to foliation. Biotite (pleochroic matrix several millimetres from both ends of the from straw yellow to reddish brown) occurs com- megacryst. Medium to coarse, tabular, subidiomor- monly as medium-sized laths. Biotites may replace phic plagioclase (An25−40) forms aggregate with orthopyroxene. Orthopyroxenes (pleochroic from other groundmass minerals. Plagioclase pheno- pale pinkish to pale greenish) and clinopyroxenes crysts may show bending of twin lamellae (fig- occur as aggregates of ragged grains running along ure 3D). Biotite occurs as medium-sized laths and the foliation. Coarser ragged grains are occasion- flakes forming clusters in the groundmass and ally marginally crushed. The fine- to medium-sized oriented subparallel to foliation. It may replace granules occupy the interspaces of the adjacent fel- hornblende. Hornblende occurs as xenomorphic sic grains. Hornblendes occur as an aggregate of to subidiomorphic medium to coarse grains. In subidiomorphic to xenomorphic elongated grains some samples, hornblende appears to be replaced and are closely associated with orthopyroxene. by scapolite (Ma72 Me28) xenomorphs. Metam- At places, orthopyroxenes are altered to horn- ict prisms of allanite are often rimmed by epi- blende. Sometimes hornblendes form corona struc- dote. Muscovite, when present, occurs both as ture around opaque minerals. Opaque minerals subidiomorphic tiny laths and xenomorphic ragged occur as both equant and elongated grains inti- grains secondary after biotite and plagioclase. Zir- mately associated ferromagnesian minerals. Fine con and garnet, when present, occur in trace zircon (elongated pyramidal grains) and apatite amount as subidiomorphic to idiomorphic grains. (equant, subidiomorphic grains) occur as inclusion in feldspar as well as the interspaces. 4.4 Sarpahari pluton 5. Nature of fabric in granitoid plutons The main rock type of the Sarpahari pluton is enderbite (opx-tonalite) and charnoenderbite (opx- Emplacement of granitic bodies can be considered granodiorite). However, thin bands of enderbite are either linked to orogenic processes (syn-tectonic) seen injected along the S1-foliation of the garnetif- or may be rift-related anorogenic (Pitcher 1997). erous gneisses and basic granulite country rock A granitoid pluton involved in regional deforma- (figure 2D). Enderbite in the area is a coarse- tion develops a flow fabric in response to tectonic grained foliated rock, composed of plagioclase, forces. If the granitoid pluton has been emplaced in quartz, biotite, hornblende, minor orthopyroxene the absence of tectonic forces, the magmatic fabric J. Earth Syst. Sci. (2018) 127:120 Page 9 of 33 120 reflects the dynamics of emplacement (Hutton deformation of feldspar. In the deformed zones of 1988; Brown and Solar 1998; Paterson et al. 1998; the Agarpur pluton, myrmekite is quite common Rosenberg 2004). The mineral fabric of granite and occurs in both, weakly deformed granites as records the strain field of the magma during the well as in granite mylonites. Completely recrys- final stages of emplacement (Paterson et al. 1998). tallised quartz ribbons and myrmekite suggest fab- The fabric defined by the alignment of subhedral to ric development under intermediate temperature euhedral zoned plagioclase or mafic minerals such (∼500–400◦C). as hornblende and biotite is considered as melt The broadly E–W elongation of these plutons present flowage (magmatic flow or submagmatic concurs with the trend of NPSZ which suggests flow with <20% melt; Hutton 1988; Paterson et al. control of this shear zone in framing the orientation 1989). of these plutons. The preferred E–W orientation of All the four plutons were primarily emplaced as the feldspar megacrysts and ferromagnesian miner- magmas in the country rocks under amphibolite als with the exception in some places is considered facies (Raghunathpur, Agarpur plutons) and gran- by us to suggest magmatic flowage differentia- ulite facies environment (Sarpahari and Sindurpur tion. The prolongation of the shearing movement plutons) (Goswami and Bhattacharyya 2008). after solidification of the granitoid magmas accen- The intensity of deformation in the interior of tuated the preferred orientation and granulation of all the granitoid bodies of the present study is minerals. In such a situation, the textural equilibra- different from their margin. The central part of tion is favoured in magmatic rocks if temperatures the granitoid bodies is massive with the hap- remain high in the system (Maaløe 1985; Hunter hazard orientation of megacrysts and show weak 1987). In the case of the four granitoid plutons imprints of solid-state deformation in the form of the present study, the chemical compositions of local shearing. The border zones of all these of the magmatic minerals have not been altered granitoid bodies show the development of augen and hence the physico-chemical parameters derived gneisses and mylonites. A detailed study on the ori- from the mineral chemistry reveal the original gin of the fabric of porphyritic granitoid batholith magmatic crystallisation. of Raghunathpur had been published earlier by Goswami and Bhattacharyya (2014). Typical igneous textures in these granitoids 6. Mineral chemistry include a porphyritic texture (e.g., Ridley 1992), characterised by idiomorphic to subidiomorphic 6.1 Feldspar K-feldspar and plagioclase (e.g., Shelley 1993; Frost et al. 2000), which show preferred orientation. Representative analyses of K-feldspar and However, anhedral feldspar is present in these plagioclase in the studied plutons are shown in granitoids due to impingement (Vernon 2004). Pla- tables 1 and 2. gioclase shows lamellar twinning typical of igneous In the Ab–Or–An ternary diagram (figure 4, rocks (Shelley 1993). Intergrowth of quartz within after Deer et al. 1992), plagioclase compositions microcline is a clear evidence of magmatic crys- in the Agarpur pluton range from oligoclase to tallisation of the Agarpur pluton. Biotitisation of albite (An26.9 and An9.3). The compositional vari- orthopyroxene in enderbite can be taken as an ation of plagioclase in the Sindurpur and Raghu- evidence for the presence of a melt phase where nathpur plutons ranges from andesine to albite. biotite–quartz were formed according to the reac- For Sindurpur pluton, the compositional variation Opx + melt = Bt + Qtz (Kramers and Ridley tion ranges from An43.2 to An3.9 and for Raghu- 1989; Bohlender et al. 1992; Ridley 1992). Elon- nathpur pluton, it ranges from An47 to An0.4. gated, bipyramidal, euhedral zircons in enderbite Such a large variation in Na-content is possi- suggest their igneous origin. bly related to alterations and the albite could Sheared parts of all of these granioid plutons are be secondary as seen in petrographic observa- marked by porphyroclasts of plagioclase (albite– tion. The composition of plagioclase in the Sarpa- oligoclase) and microcline in a matrix of undulose hari pluton varies from andesine to oligoclase quartz and granulated quartz–feldspar. Formation (An35.6−15.8). of ribbons of quartz is commonly found in the Alkali feldspar in the Agarpur pluton shear zones. Occasional bending of twin lamel- corresponds to orthoclase with Or content between lae in plagioclase indicates the limited plastic 85% and 100% (figure 4). These alkali feldspars 120 Page 10 of 33 J. Earth Syst. Sci. (2018) 127:120 Pink-coloured biotite 65.390.0818.38 64.80 0.12 18.51 65.30 64.82 0.06 18.36 66.35 18.37 0.00 64.92 17.81 0.06 62.63 18.360 0.00 62.29 18.30 62.89 0.04 18.65 18.46 0.06 0 64.17 0.04 18.09 64.19 0.01 0.00 18.32 63.57 0 18.34 0.00 62.91 0 18.48 0.00 0.01 0.008 0.00 0.006 0.024 0 0 0 0 Electron probe microanalysis of K-feldspar and cationic calculation on the basis of eight oxygen. 3 2 O 0.00 0.00 0.55 0.23 0.47 0.45 0.82 1.50 0.87 0.31 0.20 0.40 0.52 2 O 2 O 14.56 14.84 14.69 13.80 14.38 14.33 14.59 13.27 14.32 15.23 15.10 15.26 15.24 2 2 2 K TotalSiAl 98.42TiFe 98.26 12.117 4.011 0.011 99.05 12.059 97.22 4.055 0.016 99.07 12.062 12.12 98.19 3.993 96.44 0.008 12.206 4.045 95.83 12.065 0 3.859 11.931 96.74 4.019 11.887 0.008 11.928 4.107 97.83 0 4.191 97.80 12.053 4.124 0.005 12.041 97.56 0.008 4.002 11.988 0.006 97.16 11.931 4.046 0 4.073 4.128 0 0 0 Table 1. SamplePlutonAnalysis P18Location Agarpur 63/1MineralKFKFKFKFKFKFKFKFKFKFKFKFKF CoreSiO 64/1 Core 171/1 Core 172/1 Rim 179/1 180/1 Core 189/1 Rim 190/1 Core 191/1 P19 Mid 30/1 Rim 31/1 Core 35/1 Rim 36/1 Core Rim P20B TiO Al FeOMnOMgOCaO 0.00 0.00Na 0 0.00 0 0.00 0.00 0.00 0.00 0.00 0.06 0.04Mn 0.00 0.00Mg 0.00 0 0.00Ca0 0.00 0.00 0000000Na 0.00 0.00 0K 0.00 0.0050 0 0.06 0.001Cations 0.06 0 0.00Ab 0 0.00 0.05 0An0 19.582 0.00 0.00 0000000 0Or 0 3.442 0.00 0.04 0.03 0.10 0.00 0 19.652 0.00 0.15 0.00 3.522 0 0.00 100 0 0.00 0.006 19.775 0.00 19.54 0 0 3.461 0.00 0 0.00 19.631 100 0.197 3.293 0.00 19.735 0 0.082 0.00 0.03 3.374 19.958 0 0.00 5.4 94.6 0.168 19.906 3.399 0.00 0.01 19.917 0.00 0.00 0.162 97.6 2.4 3.547 0.00 0 0 0.00 0.304 95.3 3.232 4.7 0.00 0.00 19.82 0.554 0.00 3.466 95.5 0 0.00 4.5 0.004 0.321 92.1 19.773 0.00 0 0 7.9 3.649 85.4 19.878 0.111 91.5 14.6 3.612 19.938 0 0.074 8.5 0 3.671 96.9 0.146 3.688 0 0 2.9 98 0.191 2 0 96.2 0 95.1 3.8 0 0 4.9 0 Rock type amphibole granite Pink-coloured amphibole granite Grey-coloured biotite amphibole granite J. Earth Syst. Sci. (2018) 127:120 Page 11 of 33 120 Sarpahari tonalite Charnoenderbite Mylonitic biotite granite Granite Mylonitic amphibole Biotite amphibole 63.500.0018.04 62.96 0.00 18.28 63.30 0.00 18.18 64.43 18.20 0.05 64.480 18.01 0.00 63.39 18.12 0.005 0.00 63.14 0.008 18.06 63.23 0.09 0.005 18.07 62.46 0.03 0.005 18.50 64.22 0.00 0.003 18.86 0.00 0 0 0 0 (Continued.) 3 2 O 1.28 0.95 1.01 1.31 0.67 0.77 1.01 0.74 0.81 0.26 2 O 2 O 14.85 15.23 14.79 15.08 15.97 15.74 16.23 16.26 15.56 16.65 2 2 2 K i000700.0130.00400 TotalSiAlTi0000.00700 97.75Fe 97.47 11.974 4.006 11.927 97.36 4.078 11.97 99.10 4.048 99.17 11.985 3.987 12.018 98.04 3.953 11.959 98.53 4.026 11.907 98.35 4.011 11.932 97.34 11.872 4.016 100.04 11.899 4.141 4.115 Table 1. SamplePluton AD36a Sindurpur PR3E PR9 BA11A BA4A BG24 AnalysisLocationMineralKFKFKFKFKFKFKFKFKFPF SiO 15/1 Core 7/1 Core 8/1 Core 85/1 Core Core 86/1 Core 97/1 Core 38/1 Core 41/1 Core 15/1 Core 9/1 TiO Al FeOMnOMgOCaONa 0.00 0.02 0.00 0.06 0.03 0.00 0.00 0.02Mn 0.05 0.02Mg 0.01Ca 0.00Na 0.03K 0.00 0.003Cations 0.00 0Ab 0.00 0.012An 0.03 0.00 0 0.468Or 20.036 0.01 3.573 0.00 0.004 0 11.5 0.02 0.349 20.044 0.00 0.3 0.003 3.681 0.00 88.2 0 0.00 19.97 8.7 0.37 0.003 0.00 0.1 0.00 0 3.568 91.2 0.00 20.035 0.00 0.472 0 9.4 0 0.00 3.579 0.00 0 90.6 20.018 0 0.02 0.242 0.00 11.7 3.797 0.00 0 0.003 20.058 0.01 88.3 0.00 0 0.282 0 0.00 6 3.788 0 0.00 20.205 94 0.03 0 0.00 0.369 0 20.143 0.02 3.905 6.9 0 93.1 0 0.271 20.087 0 3.914 0 8.6 91.4 0.299 0 20.052 3.773 0.006 0 93.5 6.5 0.093 0 0 3.936 0.002 92.7 0 7.3 0 0.005 0 97.6 2.3 0.004 0 0.1 Rock type Charnockite granite 120 Page 12 of 33 J. Earth Syst. Sci. (2018) 127:120 Biotite amphibole Mylonitic biotite Pink-coloured biotite Grey-coloured biotite 67.820.0021.02 62.99 0.00 23.62 66.46 0.00 21.48 65.270 22.33 0.00 56.73 25.56 0.00 56.70 25.55 0.02 56.02 0 25.83 65.61 0.00 21.49 0 64.08 0.08 21.71 63.62 0 0.09 21.88 67.16 19.96 0.014 0.07 0.00 0.009 0.014 0.041 0.01 0.003 0 Electron probe microanalysis of plagioclase feldspar and cationic calculation on the basis of eight oxygen. 3 2 O 10.78 8.98 10.42 9.61 6.30 6.21 6.04 9.93 9.62 9.13 10.83 2 O 2 O 0.02 0.11 0.03 0.07 0.18 0.10 0.18 0.11 0.23 0.28 0.08 2 2 2 K TotalSiAl 101.65TiFe 11.704 4.273 0 100.39 100.85 11.102 101.16 4.903 11.58 97.43 0 4.408 11.38 97.03 4.585 10.425 0 96.63 5.531 10.444 100.17 0 5.542 10.372 99.03 11.527 98.17 5.632 0 98.84 4.446 11.412 11.407 0.003 4.553 11.871 0 4.62 4.155 0.011 0.012 0.009 0 Table 2. SamplePlutonAnalysis P18LocationSiO Agarpur 67/1 Rim P20B 29/1 Core 39/1 Rim 40/1 Core 17/1 Inclusion AD36a Sindurpur Inclusion 18/1 Core 23/1 Rim 89/1 PR3E Core 100/1 Core 103/1 Rim PR9 104/1 TiO Al FeOMnOMgOCaO 0.00Na 0.00 0.00 2.01Mn 0.00 0.00Mg 0.00Ca 4.70Na 0.00 0.00K 0 0.00Cations 0 2.46 0.00Ab 0.371 0.00An 3.606 0.00 19.958Or 0.004 3.88 0.09 0.00 90.6 0.00 9.3 8.57 0.1 0.06 0 0.05 0.887 0 0.01 3.067 19.984 8.33 0.025 0.09 0.458 0 0.00 19.972 3.52 77.1 0 0.01 0.006 0.28 0.725 8.46 22.3 19.954 0.00 0.6 3.249 88.4 0.01 0 0.015 19.944 1.687 2.66 0 11.5 0.07 2.245 81.4 0.2 0.01 0.042 19.894 0.01 18.2 1.644 0 0.02 3.21 0 56.5 2.218 0.01 0.4 19.91 0.023 0.00 42.5 1.678 0.00 3.16 0.00 19.937 2.168 0.008 57.1 1.1 0.02 0.501 0.043 0.003 42.3 0.79 3.383 19.979 0.025 0 55.7 0.003 0.6 0.613 43.1 19.886 3.322 86.5 0.003 0.607 0.052 0 19.911 12.8 3.174 1.1 0.15 0.064 83.3 0.003 3.712 0.6 15.4 0.018 0.002 82.5 0 15.8 0.002 95.7 1.3 3.9 0.005 0 1.7 0.5 Rock type amphibole granite amphibole granite Charnockite granite amphibole granite J. Earth Syst. Sci. (2018) 127:120 Page 13 of 33 120 Sarpahari tonalite Porphyritic biotite granite Mylonitic 60.860.0024.00 59.96 0.00 24.11 61.63 0.00 23.74 58.40 25.52 0.00 58.24 25.36 58.30 0.000000000 25.19 58.67 000.00100 0.02 25.75 0.00 59.39 25.61 59.73 0.00 25.24 59.37 0.01 25.78 59.07 0.00 25.57 59.79 25.97 0.00 0.00 (Continued.) 3 2 O 8.23 8.05 8.40 6.92 7.16 7.20 7.64 7.60 7.76 7.57 7.48 7.48 2 O 2 O 0.07 0.16 0.11 0.28 0.18 0.21 0.16 0.12 0.19 0.19 0.30 0.32 2 2 2 K TiO Al FeOMnOMgOCaONa 0.00 0.02 0.00 0.00 6.07 0.06 0.01 0.00 6.17 0.00Mn 0.00Mg 0.00 5.71Ca 0.00Na 0.00K 0.00 7.82 0.003 0.00Cations 0 0.00Ab 1.165 0.009An 0.00 7.95 2.858 0.01 20.001Or 0.01 0.016 1.194 0.003 0 0.00 7.65 2.82 20.024 70.8 7.61 28.8 0.037 1.09 0.00 0 19.983 0.4 7.61 2.903 69.6 0 0.025 29.5 19.976 1.513 0.00 0.00 2.423 0.9 0 72.2 20.032 0.065 0.01 27.1 1.541 0 0.00 6.46 2.511 0.00 60.6 20.022 0.6 0.042 0.01 37.8 1.486 0 2.531 0.01 6.65 20.518 0.002 61.3 0.00 0.049 1.6 1.41 37.6 0.03 2.563 0.00 7.04 0.003 1.115 62.2 0.035 0.02 19.972 36.5 1 0.02 0 0.00 7.05 63.9 1.241 20.016 0.02 2.643 35.2 0 0.00 0.027 1.2 20.023 7.15 1.275 2.692 0.043 67.6 20.031 0.003 1.346 0 0.9 31.7 2.618 20.011 0.043 67.1 0.003 1.355 31.8 2.602 0 0.069 65.3 0.008 1.357 0.7 33.6 2.569 0.072 64.6 0.005 0.003 1.1 33.7 0 64.3 0.003 33.9 1.1 1.7 1.8 TotalSiAl 99.25TiFe 98.52 10.898 5.061 99.59 0 10.832 5.129 98.94 10.983 0 4.982 98.89 10.547 98.59 5.428 10.535 0 107.44 10.57 5.403 10.149 5.378 0 99.19 5.246 99.59 10.65 0 99.99 10.685 5.408 99.51 0.003 10.591 5.317 100.73 0 10.596 5.416 10.592 5.401 0 5.418 0.001 0 0 0 AnalysisLocationSiO 35/1 Core 36/1 Core 37/1 Core 21/1 Core 22/1 Core 23/1 Core 18/1 Rim 10/1 Rim 11/1 Core 29/1 Rim 30/1 Mid 31/1 Core Table 2. SampleRock typePluton Sindurpur BA11A Granite BA13A Enderbite BA4A PR28E 120 Page 14 of 33 J. Earth Syst. Sci. (2018) 127:120 60.660.0624.71 60.43 0.01 25.15 59.260.016 0.00 25.65 59.23 0 25.80 0.02 60.14 24.82 0.00 0 60.30 25.38 0.00 0 59.99 25.05 0.01 0 0 0 (Continued.) 3 2 O 8.16 7.81 7.04 7.16 7.32 7.42 7.29 2 O 2 O 0.33 0.23 0.45 0.49 0.37 0.38 0.33 2 2 2 K TotalSiAlTiFe 100.12 10.794 5.178 0.008 99.80 10.762 5.275 99.68 0.001 10.607 5.407 100.27 0 10.562 5.418 99.01 0.003 10.792 100.30 5.245 0 10.707 99.56 5.307 10.726 0 5.275 0.001 Table 2. SampleRock typePluton AnalysisLocationSiO 73/1 PR30B Enderbite Core 74/1 Rim 28/1 Enderbite Core BG36 33/1 Core 8/1 Core Charnoenderbite BG24 10/1 Core 13/1 Core TiO Al FeOMnOMgOCaONa 0.11 0.07 0.00 6.02MnMgCa 0.00Na 0.00K 0.02Cations 6.15AbAn 0.011Or 0.00 0 0.08 1.148 0.01 2.816 20.046 7.19 0.075 69.7 0 28.4 0.00 0.09 1.9 1.173 0.005 0.01 2.697 19.965 7.47 0.052 68.8 29.9 0.012 0.00 1.379 0.03 0.003 19.954 1.3 2.443 0.03 6.30 0.103 62.2 0.014 35.1 0.00 1.427 20.012 0.003 0.05 2.474 2.6 0.02 0.111 6.75 61.7 0.005 35.6 19.893 1.211 0.00 0.008 0.00 2.547 2.8 0.05 0.085 6.84 66.3 0.008 19.952 31.5 1.284 0.005 2.555 0.086 2.2 65.1 19.927 0 32.7 1.31 0.013 2.527 0.075 2.2 64.6 33.5 1.9 J. Earth Syst. Sci. (2018) 127:120 Page 15 of 33 120

The range of molar Fe2+/(Fe2+ + Mg) of the biotite composition for these plutons is high. The highest variation of biotite composition is encountered in the Sindurpur pluton (0.42–0.95). Biotites of the Agarpur pluton are low in AlVI (∼p.f.u.). The Sindurpur pluton shows a bimodal distribution in the composition of biotite. Some biotites are clustered around Fe/(Fe+Mg) values 0.5 and other biotites show Fe/(Fe+Mg) ratio ∼0.95. Fe/(Fe+Mg) ratio in the Raghunathpur pluton shows clustering around 0.55. The Sarpahari pluton shows bimodal distribution in respect of Fe/(Fe+Mg) ratio. Biotites of enderbite samples of this pluton show Fe/(Fe+Mg) ratio around 0.5, but biotites from granite samples are richer in Fe and show Fe/(Fe+Mg) values around 0.75. Nachit et al. (2005) proposed TiO2–(FeO+ MnO)–MgO ternary diagram as a quantitative objective tool for distinguishing between primary magmatic biotites and those that are more or less reequilibrated, or neoformed, by or within a hydrothermal ﬂuid. The magmatic origin of biotites of the present study is supported by their chemical composition (ﬁgure 6).

6.3 Amphiboles

Amphibole is the predominant mafic phase in all Figure 4. Nomenclature of feldspar of granitoids according these granitoids. Ferrous and ferric iron in the to Deer et al. (1992) classification scheme. The data source amphibole formula was calculated using the charge of the Raghunathpur pluton: Goswami and Bhattacharyya balance method. Structural formulae of amphiboles (2014). were calculated on an anhydrous basis assuming 23 O atoms per half unit cell, with the general form A − B C T O (OH) representing 1 for- are totally devoid of anorthite content. Orthoclase 0 1 2 5 8 22 2 mula unit. According to the IMA classification component of alkali feldspars of the Sindurpur and Fe3+ calculation proposed by Leake et al. pluton ranges between Or and Or . .Asmall 94 88 2 (1997), all the amphiboles are classified as calcic amount of An component (up to 0.5 mol%) may amphiboles [ (Ca + Na) on M4 ≥ 1.00 with be present in the alkali feldspars of the Sindur- Na < 0.5 and Ca ≥ 1.5 on M4]. In the classification pur pluton. In the perthitic alkali feldspar of the scheme, the calcic amphiboles are further classified Raghunathpur pluton, the compositions of alkali into four groups: feldspar vary from Or54.1Ab45.3 to Or93.5Ab6.5, A while albite of composition Ab95.5Or0.9 exsolved (a) (Na + K) ≥ 0)50 and Ti < 0)50; from the alkali feldspar. (b) (Na + K)A ≥ 0 : 50 and Ti ≥ 0)50; Compositional variations of feldspar megacrysts (c) (Na + K)A < 0)50 and CaA < 0)50; from core to rim also attest to their igneous origin (d) (Na + K)A < 0.50 and CaA ≥ 0.50. (tables 1 and 2). Representative compositions of amphiboles from 6.2 Biotite different plutons are given in table 4. Amphiboles of the Agarpur pluton can be Representative analyses of biotite of all the four classified into two groups; however, both of these plutons are given in table 3 and their plots are given groups may occur in the same rock. Group (a) in figure 5. amphiboles, characterised by (Na + K)A < 0.5and 120 Page 16 of 33 J. Earth Syst. Sci. (2018) 127:120 tonalite Mylonitic Mylonitic biotite amphibole granite Granite Enderbite granite Biotite amphibole amphibole granite Charnockite Grey-coloured biotite 38.132.6813.770.00 38.36 2.24 13.89 36.85 0.08 5.76 13.55 35.66 31.93 0.00 13.00 5.30 12.88 3.15 0.01 32.67 0.04 12.95 33.362.628 3.13 13.21 0.00 33.33 2.394 3.44 14.81 0.03 34.50 2.672 35.30 2.67 14.34 35.37 2.774 14.20 0.12 35.65 4.64 5.286 14.18 34.07 5.66 13.59 0.03 5.315 16.83 4.49 0.00 5.72 0.00 4.939 3.19 0.00 0.04 4.836 2.291 2.472 2.722 2.606 2.71 Electron probe microanalysis of biotite and cationic calculation on the basis of 22 oxygen. 3 3 2 O 0.10 0.19 0.10 0.13 0.21 0.07 0.17 0.20 0.13 0.00 0.07 0.10 0.16 2 O O 2 O 9.09 8.04 9.08 9.59 8.50 8.86 7.41 7.48 7.76 9.56 10.03 9.27 9.28 2 2 2 2 K TotalSiAlIVAlVI 93.74TiFe 2.038 5.962 90.74 0.498 95.88 0.315 1.919 6.081 0.674 93.98 93.29 2.136 5.864 0.268 0.403 2.16 5.84 95.15 0.689 0.347 2.273 5.727 0.447 92.16 0.653 0.425 2.248 5.752 0.437 92.99 0.415 2.082 5.918 90.19 0.678 94.32 93.96 0.459 94.28 2.163 5.837 0.892 93.68 2.266 5.734 0.352 0.541 2.292 5.708 0.412 0.58 2.207 5.793 0.528 2.221 5.779 0.688 0.374 2.429 5.571 0.553 0.812 0.698 0.392 Table 3. SampleRock type PlutonAnalysisLocationSiO P20B Agarpur 41/1 Core 54/1 Core AD36a Sindurpur 10/1 Core 9/1 Core 84/1 Core PR3E 95/1 Core 102/1 Core PR9 110/1 Core 48/1 Core 49/1 BA11A Core 31/1 Core 32/1 Core BA13A 17/1 Core BA4A r .1 .0006 0.0040.0170.0040000.005 TiO Al Cr FeOMnOMgOCaONa 20.10 0.07 9.81 0.0010.0060 0.00 18.06 0.17 9.41 20.08 0.32 0.02Cr0 20.25 10.31Mn 0.010 35.24 0.13Mg 0.00Ca 10.04Na 0.39 0.90 0.00K 36.10Cations 0.01 0.05Fe/(Fe+Mg) 2.287 0.41 33.29 0.96Mg/(Fe+Mg) 0.53 0 0.47 0.03 15.581 0.022 0.00 2.224 1.813 0.25 33.02 0.84 0.52 0.48 0.003 15.331 0.059 0.054 0.16 2.446 16.48 1.626 0.35 18.28 0.52 0 0.85 16.109 0.48 2.451 0.031 0.022 19.87 1.843 0.16 16.271 0.241 0.53 0.22 19.22 11.95 0.059 0.47 16.492 0.041 0 0.96 10.90 19.82 0.33 2.004 0.04 0.073 0.14 9.83 0.252 1.945 0.01 16.494 0.01 0.061 0.09 10.45 0.95 0.11 0.024 0.05 0.11 0.222 16.105 10.14 0.038 1.99 0.05 0 0.17 0.96 0.058 0.04 16.14 0.222 0.10 1.677 0.052 16.12 2.961 0.96 0.03 0.068 0.031 0.04 16.233 2.628 1.671 0.045 16.341 0.44 0.042 2.4 16.197 0.56 0.001 0 0.03 1.645 0.48 16.403 0.52 0.015 2.526 1.972 0.53 0.007 2.472 0.47 0.025 2.096 0.022 0.51 0.016 0.49 1.917 0.031 0.52 0.019 1.936 0.051 0.48 0.03 0.018 J. Earth Syst. Sci. (2018) 127:120 Page 17 of 33 120 33.974.5015.630.03 33.89 4.81 15.98 0.11 33.96 4.68 15.71 0.17 34.573.612 15.62 4.58 0.07 33.77 3.738 15.62 4.53 0.03 36.97 3.707 13.62 5.42 36.17 0.17 3.592 13.32 5.18 36.48 0.08 3.804 13.16 4.95 2.648 0.16 2.742 2.584 (Continued.) 3 3 2 O 0.20 0.13 0.14 0.15 0.10 0.02 0.07 0.07 2 O O 2 O 8.80 8.87 9.04 9.36 9.12 10.01 10.00 10.00 2 2 2 2 K TotalSiAlIVAlVITiFe 95.04 2.365 5.635 0.688 96.64 0.561 2.442 5.558 0.645 96.21 0.593 2.405 5.595 0.643 96.46 0.58 2.342 5.658 95.73 0.669 0.564 2.39 5.61 97.26 0.666 0.566 96.57 2.169 5.831 0.361 0.643 95.90 2.227 5.773 0.277 0.622 2.172 5.828 0.304 0.595 Table 3. SampleRock typePlutonAnalysisLocationSiO Sarpahari 1/1 Rim 12/1 Rim Porphyritic biotite granite PR28E 13/1 Core 17/1 Core 18/1 Rim 50/1 Core Enderbite 55/1 Core PR30B 66/1 Core TiO Al Cr FeOMnOMgOCaONa 26.04 0.04 5.75 0.08Cr 27.25Mn 0.12Mg 5.44Ca 0.04NaK 26.91Cations 0.11Fe/(Fe+Mg) 5.46Mg/(Fe+Mg) 0.004 0.03 0.006 26.24 1.422 0.72 0.014 0.03 0.28 0.064 5.84 16.233 0.014 0.00 1.862 0.017 27.38 1.33 0.007 0.74 0.13 0.26 0.041 16.241 5.01 0.022 1.856 0.015 0.04 20.08 1.341 0.005 0.73 16.258 0.15 0.27 0.045 0.009 10.82 1.9 0.004 20.54 0.00 1.425 0 16.265 0.72 0.048 0.28 0.00 0.004 11.16 0.018 1.954 19.34 0.05 1.241 16.271 0.75 0.032 0.25 0.007 0.021 0.02 11.70 0.02 1.933 2.544 16.257 0.02 0.51 0.006 0 0.49 0.01 0 2.014 16.374 2.656 0.022 0.51 0.49 0.02 0.009 2.036 16.356 2.787 0.003 0.022 0.48 0.52 0.003 2.038 120 Page 18 of 33 J. Earth Syst. Sci. (2018) 127:120

Ti < 0.5. Magnesian hastingsite is the most common amphibole of this pluton, followed by magnesian hastingsitic hornblende. Amphiboles of the Sindurpur pluton belong to all four groups. While amphiboles of the granite and charnockite of the Sindurpur pluton are classified as hastingsite and magnesian hastingsite, amphiboles of enderbites belong to edenite species. Group (c) amphiboles occur more rarely and are defined by (Na + K)A < 0.5withTSi < 6.5apfu, and are classified as tschermakite. Tschermakite rarely occurs in charnockite. Amphiboles of Sarpahari enderbites belong to two groups. Group (a) amphiboles are common and are defined by (Na + K)A > 0.5withlow TSi < 6.5 apfu and are classified as magnesian hastingsite and magnesian hastingsitic hornblende or pargasitic hornblende. Compositions of amphiboles are plotted in the Si vs. Ca+Na+K diagram of Leake (1971)inwhich most of the analyses plot well within the field of igneous amphibole while a few analyses from pink granite of Agarpur cross the boundary of the igneous field and enters into the metamorphic field (figure 7). Figure 5. Classification of biotite of granitoids according to Deer et al. (1992). The data source of the Raghunathpur pluton: Goswami and Bhattacharyya (2014). 6.4 Pyroxene Electron microprobe analyses of representative clino- and orthopyroxenes are shown in tables 5 and 6, respectively. All of the pyroxenes in this area are Na-poor and their composition falls in the quadrilateral pyroxene field according to the Mori- moto’s (1988) nomenclature (figure 8). Both clino- and orthopyroxenes are present in the Sindurpur pluton. While clinopyroxene is diopside (En34.21 Fs19.2Wo44.5 to En34.3Fs16.2Wo47.2), the orthopyroxene of the Sindurpur pluton is hypersthene (En52.5Fs48.8–En50.1Fs46.2) (figure 8). Both clino- and orthopyroxenes are present in the Sarpahari pluton. Clinopyroxene of the Sarpahari pluton is . . . . . Figure 6. The composition of biotites in the 10 TiO2– diopsidic (En34Fs17 5Wo45 7 to En30 7Fs20 8Wo46 2) FeO*–MgO ternary diagram (Nachit et al. 2005). FeO∗ = and orthopyroxene composition in this pluton [FeO + (0.89981 * Fe2O3)]. Symbols are same as those of varies from En60.2Fs49Wo1.2 to En48.7Fs39.0Wo0.0 figures 3 and 4. The data source of the Raghunathpur pluton: (figure 8). Goswami and Bhattacharyya (2014).

< . Ti 0 5 apfu (atoms per formula unit) are 7. Physico-chemical parameters of magmas dominant among the pink granite and magnesiohornblende is the dominant species of the 7.1 Pressure estimates granite with subordinate actinolitic hornblende. All the amphiboles of the Raghunathpur pluton Al-in-hornblende barometry has been widely used belong to Group (a) with (Na + K)A > 0.5, to calculate pressures of magmatic crystallisation J. Earth Syst. Sci. (2018) 127:120 Page 19 of 33 120 amphibole granite Pink-coloured amphibole granite Grey-coloured biotite amphibole granite Pink-coloured biotite 47.120.006.92 49.980.00 0.00 45.37 5.17 0.00 0.00 7.98 43.76 0.00 0.26 47.70 9.05 0.00 47.56 0.45 6.29000 00000 0.00 44.33 00000 0.28 7.02 48.02 0.000.319 0.13 8.51 42.56 0.46 0.00 0.111.908 6.71 48.09 0.319 0.00 1.517 0.57 43.13 9.61 2.014 0.00 0.502 44.34 0.00 4.46 0.1 0.00 2.017 42.60 0.56 9.62 1.972 0.00 0.426 0.30 9.06 1.792 0.569 0.00 0.96 10.02 1.948 0.386 0.00 1.908 0.606 2.075 0.166 2.139 0.49 2.172 0.52 2.088 0.472 2.25 Electron probe microanalysis of amphibole and cationic calculation on the basis of 23 oxygen. 3 cat 15.316 15.121 15.34 15.507 15.348 15.093 15.425 15.316 15.518 15.246 15.61 15.458 15.578 3 2 3 3 2 O 1.01 0.75 1.00 1.33 1.02 0.92 1.29 1.06 1.39 0.68 1.72 1.43 1.65 2 O O 2 O 0.61 0.34 0.57 1.07 0.64 0.48 0.92 0.69 1.17 0.44 1.30 1.08 1.37 2 2 2 K TiO Al Cr FeOMnOMgOCaO 17.64Na 00000 0.07 00000 10.74 16.10 00000 00000 11.77 0.19 12.63 18.13 11.73 0.18 9.66TTi000 11.71CAl 19.68 00000CCr000 00000 0.62CFe 8.94 16.41 11.60CTi 00000 0.345CMg 00000 0.46 17.48 11.10CFe 11.92CMn 0.233 19.65 0CCa000 9.83 0.43 10.64 2.419BCa 0.429BNa 18.52 0.009 11.35 9.03 0.64 2.766ACa000 0ANa 0.33 20.80 1.904 0.024AK 11.84 2.215 10.59 0.58 0.096Sum 17.89 1.846 0.024 0 0.321 11.34 0.2 8.37 0.154 2.04 0.17 0.117 20.82 1.93 0.471 11.84 0.081 0.07 10.56 0.058 2.498 0.36 0.063 20.48 0.03 0.324 11.27 0.059 1.903 8.44 0.229 2.224 0.111 21.18 0.17 0.097 0.282 11.20 0.051 0.056 1.928 8.59 2.062 0.072 0.297 0.25 11.05 0.032 0.307 0.21 0.082 1.73 2.339 7.78 0.27 0.226 0.015 0.221 0.18 0.073 0.122 1.862 1.923 0 0.138 0.012 0.329 0.094 0.022 1.879 2.427 0.121 0.376 0.066 0.181 0.047 0.245 1.873 1.924 0.361 0.127 0 0.131 0.022 0.185 1.949 1.955 0.045 0.033 0.231 0.288 1.782 1.847 0.064 0.153 0.023 0.086 0.16 1.827 0.034 0.173 0.254 1.82 0.111 0.356 0.18 0.21 0.248 0.268 0.31 TotalTSiTAl 95.87TFe 96.89 7.115 0.885 94.60 7.34 0.66 96.31 6.982 1.018 95.97 6.698 94.64 1.302 7.202 95.85 0.798 98.13 7.216 0.784 95.97 6.789 1.211 94.32 7.112 0.888 97.02 6.562 1.438 96.71 7.412 96.77 0.588 6.596 1.404 6.752 1.248 6.548 1.452 Table 4. SampleRock type PlutonAnalysisLocationSiO Agarpur 65/1 P18 Rim 66/1 Core 72/1 Core 160/1 Rim 161/1 Rim 165/1 Core 166/1 P19 194/1 Rim 13/1 Core 15/1 Core 17/1 Core 20/1 Rim 38/1 Core Rim P20B 120 Page 20 of 33 J. Earth Syst. Sci. (2018) 127:120 Sarpahari Biotite amphibole Mylonitic biotite Charno- 39.432.3311.71 39.930.21 2.08 0 11.64 37.91 00000000 0 0.12 1.36 10.30 37.41 0.00 10.20 1.87 36.83 0.01 37.27 10.01 1.250 0.360 37.41 10.13 0.00 1.91 42.70 10.180.564 0.05 1.79 42.85 10.30 0.02 1.706 1.861.93 40.99 10.09 0.00 41.29 11.03 0.928 1.68 0.19 40.48 11.15 0.00 2.02 0.837 3.514 11.76 0.16 1.51 41.76 0.872 3.621 0.13 11.45 1.92 0.95 0.00 3.604 0.97 1.70 3.495 0 0.00 3.499 2.013 0 1.956 0.588 1.858 0.609 1.832 0 2.296 1.605 0.806 (Continued.) 3 3 2 3 3 2 O 1.13 1.31 1.82 1.86 1.56 1.61 1.54 1.38 1.19 1.56 1.39 1.39 1.21 2 O O 2 O 2.04 2.15 1.69 1.81 1.73 1.81 1.77 1.44 1.40 1.71 1.83 1.78 1.78 2 2 2 K TotalTSiTAl 95.87TFe 6.116 104.51 1.884 96.81 5.688 1.953 97.27 6.185 1.815 94.02 6.111 95.82 1.889 96.22 6.194 1.806 95.43 6.138 1.862 94.45 6.138 97.20 1.862 6.58 96.94 1.42 93.81 6.64 1.36 6.244 97.94 1.756 6.294 1.706 6.417 1.583 6.25 1.75 Table 4. SamplePluton AD36a Sindurpur PR3E PR9 BA13A PR30B BG24 BG36 AnalysisLocationSiO 12/1 Core 24/1 Core 83/1 Core 88/1 Rim 101/1 Core 105/1 Core 106/1 Core 24/1 Core 26/1 Core 45/1 Core 64/1 Core 8/1 Core 32/1 Core TiO Al Cr FeOMnOMgOCaO 19.23Na 0.12 8.38 18.94 11.29 8.61 8.61 32.55 11.12 0.80TTi 0.48CAl 32.63 9.90CCr 0.81CFe 0 31.82 0.52CTi 10.15 0.255CMg 0 0.026 0 32.27CFe 0.43 0CMn 9.88 0.51 00000000 0 0.272 32.57 0CCa 0 1.938 0.013 0.44BCa 9.73 0.60 15.62BNa 0.016 0.223 0 0.50ACa0 0.164 1.828 0 0 15.09 9.90 0.54ANa 1.876 0.167AK 1.039 0.32 0.124 0.117 19.20Sum 0.073 11.88 9.93 0.001 1.697 0.111 0.216 0.22 19.15 0.23 0 0 11.81 0.303 0.127 10.12 0.404 0.177 15.62 17.32 1.731 0.30 0 11.24 0.112 0.059 8.99 0.269 0.103 0.158 0.128 0 0.391 11.24 0 0.29 15.45 1.776 19.27 0.306 0.106 0.237 8.96 0.007 0.147 0.061 0.224 0.352 11.15 0.29 15.658 0.449 0.221 0.003 0.061 0.132 7.72 0 1.78 0.365 0 0.22 0.482 0.216 0.377 11.23 0 0.069 2.281 15.743 1.717 0.00 0.289 9.54 0.223 0 0.283 0.196 0.042 2.338 15.66 1.74 0.371 0 0.231 0 0.296 0.26 0.231 2.042 0.029 15.611 0.38 0 1.961 0.23 0.612 0.173 0.039 2.036 0.039 15.601 0 0.019 0.371 1.961 0.374 0.229 15.657 0.037 1.824 0.039 0 0.268 0.016 1.835 0.283 15.6 0 0.318 0.165 0.039 0.191 0 1.836 2.129 0.277 0.295 15.628 0 0.164 0.332 0 0 1.894 15.603 0.247 0.106 15.681 0.356 0 0 0.321 1.801 0 0.36 0.199 15.492 0 0.152 0 0.34 0 0 0 0 Rock type Charnockite granite amphibole granite Enderbite Enderbite enderbite Enderbite J. Earth Syst. Sci. (2018) 127:120 Page 21 of 33 120

Table 5. Electron probe microanalysis of clinopyroxene and cationic calculation on the basis of six oxygen. Sample BA13A BG24 Rock type Enderbite Charnoenderbite Pluton Sindurpur Sarpahari Analysis 28/1 29/1 2/1 3/1 Location Core Core Core Core SiO2 51.47 51.57 50.36 51.15 TiO2 0.12 0.10 0.08 0.12 Al2O3 1.25 1.26 1.17 1.55 FeO 11.61 9.77 12.31 13.75 Cr2O3 0.04 0.04 0.05 0.04 MnO 0.38 0.45 0.15 0.20 MgO 11.59 11.62 10.19 10.48 CaO 21.37 22.61 21.61 20.98 Figure 7. The plot of amphibole composition in the Si vs. Na2O 0.35 0.40 0.40 0.38 Ca+Na+K discriminating diagram separating the fields of igneous and metamorphic amohiboles (Leake 1971 in Deer K2O 0.00 0.00 0.04 0.00 et al. 1997). Note: most of the amphiboles of the present Total 98.18 97.82 96.36 98.65 study plot within the field of igneous amphibole. Symbols TSi 1.981 1.983 1.986 1.975 are the same as those of figures 3 and 4. The data source TAl 0.019 0.017 0.014 0.025 of the Raghunathpur pluton: Goswami and Bhattacharyya M1Al 0.037 0.040 0.040 0.045 (2014). M1Ti 0.003 0.003 0.002 0.003 M1Fe2 0.293 0.290 0.357 0.347 of calc-alkaline granitoids and to constrain the M1Cr 0.001 0.001 0.002 0.001 emplacement depths of batholiths. This barometry M1Mg 0.665 0.666 0.599 0.603 can be used only when the suitable mineral assem- M2Fe2 0.080 0.024 0.049 0.097 blages, i.e., quartz + plagioclase + alkali feldspar M2Mn 0.012 0.015 0.005 0.007 + biotite + hornblende + titanite + magnetite M2Ca 0.881 0.931 0.913 0.868 or ilmenite are present in the granitic rocks (e.g., M2Na 0.026 0.030 0.031 0.028 Vyhnal et al. 1991; Anderson and Smith 1995). In Sum 4.000 4.000 3.998 4.000 this paper, all the selected samples have the above Q 1.920 1.912 1.918 1.915 mineral assemblage. According to Anderson and J 0.052 0.060 0.061 0.057 Smith (1995), this barometry is applicable to horn- WO 45.605 48.354 47.478 45.165 blendes which have crystallised at approximately EN 34.415 34.577 31.150 31.391 the same temperature close to the isothermal FS 19.980 17.070 21.371 23.445 solidus and they recommended measurement of rim WEF 97.368 96.997 96.917 97.124 JD 2.632 3.003 3.083 2.876 composition for this study. Moreover, this barome- AE 0.000 0.000 0.000 0.000 try is applicable for those hornblendes only which occur in contact with quartz and K-feldspar (Stein and Dietl 2001). For each sample, rim composition hornblende remains low under high oxygen of co-existing hornblende and plagioclase was mea- fugacity. In low oxygen fugacity, on the contrary, sured. In all cases, hornblende is in contact with the introduction of Fe2+ is favoured in the horn- quartz and K-feldspar. blende lattice. Additionally, high Fe2+/Fe3+-ratio Oxygen fugacity plays an important role in prevailing during low oxygen fugacity condition the Al substitution in hornblende. Oxygen fugac- favours the substitution of Mg by Al during the ity controls the Mg # {=Mg/(Mg + Fe)} and tschermak substitution. So a low oxygen fugac- Fe3+/(Fe2+ +Fe3+) ratios in the magma. Ander- ity favours the preferential introduction of Al in son and Smith (1995) estimated that Mg # of hornblende lattice. Therefore, hornblendes with hornblende in the range from 0.4 to 1, 0.2 and Mg #> 0.35 and Fe3+/(Fe2+ +Fe3+)-ratio ≥ 0.25 0.4 and 0.4 to 0 indicates, respectively, the high, are recommended for geobarometric calculation medium and low oxygen fugacity. A high oxygen (Anderson and Smith 1995; Anderson 1997). fugacity favours incorporation of Fe3+ and sub- But the determination of Fe2+ and Fe3+ by stitutes Al in hornblende lattice. So Al-content of stoichiometric calculations may not reflect the real 120 Page 22 of 33 J. Earth Syst. Sci. (2018) 127:120

Table 6. Electron probe microanalysis of orthopyroxene and cationic calculation on the basis of six oxygen. Sample AD36a BG24 Rock type Charnockite Charnoenderbite Pluton Sindurpur Sarpahari Analysis 1/1 11/1 2/1 20/1 21/1 5/1 6/1 1/1 4/1 5/1 Location Core Core Rim Core Rim Core Rim Core Core Core SiO2 50.05 50.1 49.74 49.74 49.46 47.53 49.36 49.44 49.69 49.83 TiO2 0.09 0.15 0 0 0.07 0 0.06 0.06 0.04 0.04 Al2O3 1 0.85 0.87 1.05 0.95 0.82 0.77 0.56 0.43 0.55 FeO 30.72 31.35 30.33 31.03 30.69 30.82 30.81 35 35.43 35 Cr2O3 0 0.02 0.12 0 0 0.54 0.07 0 0.04 0 MnO 0.63 0.6 0.61 0.66 0.51 0.51 0.65 0.52 0.55 0.59 MgO 16.24 15.99 16.44 15.89 16.78 15.21 16.31 13.01 12.87 13.15 CaO 0.59 0.55 0.5 0.49 0.51 0.52 0.48 0.36 0.41 0.46 Na2O 0 0.05 0.02 0.02 0 0.02 0 0 0 0 K2O 000000.020000 Total 99.32 99.66 98.63 98.88 98.97 95.99 98.51 98.95 99.46 99.62

TSi 1.956 1.956 1.954 1.956 1.934 1.932 1.945 1.985 1.988 1.986 TAl 0.044 0.039 0.04 0.044 0.044 0.039 0.036 0.015 0.012 0.014 M1Al0.002000.0040000.0110.0080.012 M1Ti 0.003 0.004 0 0 0.002 0 0.002 0.002 0.001 0.001 M1Fe2 0.049 0.065 0.034 0.064 0.02 0.061 0.038 0.208 0.222 0.206 M1Cr 0 0.001 0.004 0 0 0.017 0.002 0 0.001 0 M1Mg 0.946 0.93 0.963 0.931 0.978 0.921 0.958 0.779 0.768 0.781 M2Fe2 0.954 0.959 0.963 0.956 0.984 0.986 0.977 0.967 0.964 0.96 M2Mn 0.021 0.02 0.02 0.022 0.017 0.018 0.022 0.018 0.019 0.02 M2Ca 0.025 0.023 0.021 0.021 0.021 0.023 0.02 0.015 0.018 0.02 M2Na 0 0.004 0.002 0.002 0 0.002 0 0 0 0 Sum 4.000 4.000 4.000 4.000 4.000 3.999 4.000 4.000 4.000 4.000 Q 1.975 1.977 1.98 1.972 2.003 1.992 1.994 1.969 1.971 1.967 J 0 0.008 0.003 0.003 0 0.003 0 0 0 0 WO 1.238 1.152 1.052 1.035 1.058 1.127 1.006 0.779 0.883 0.988 EN 47.409 46.6 48.126 46.702 48.423 45.864 47.54 39.188 38.587 39.312 FS 51.354 52.248 50.822 52.263 50.519 53.009 51.455 60.032 60.529 59.7 WEF 100 99.622 99.848 99.847 100 99.843 100 100 100 100 JD0000.153000000 AE 0 0.004 0.002 0 0 0.003 0 0 0 0

oxygen fugacity. High oxygen fugacity condition Bando et al. 2003); amphibole should coexist with may be retrieved from an assemblage of accessory quartz (Hammarstrom and Zen 1986) and/or K- minerals. Enami et al. (1993) suggested that occur- feldspar (Stein and Dietl 2001), because their rences of euhedral titanite and magnetite as early activity also inﬂuences the Al content of horn- crystallising phases indicate high oxygen fugacity blende; water saturation of the magmatic system condition. In our present study, the presence of (Anderson and Smith 1995); and plagioclase coex- euhedral titanite, magnetite and allanite suggests isting with hornblende should range between An25 high oxygen fugacity of the melt. and An35 (Stein and Dietl 2001). Other prerequisites for a correct application All the analyses of amphiboles chosen for ther- of the barometers are as follows: the Si-activity of mobarometric computations satisfy the criteria the melt must have been SiO2-saturated (Si≤7.5 described in the preceding paragraph. apfu), because the Al-content of hornblende is Calibrations of Johnson and Rutherford (1989) directly related to its Si content; hornblendes with and Schmidt (1992) have been more commonly Ca ≥ 1.6apfu(Hammarstrom and Zen 1986; used because of their experimental derivation. A J. Earth Syst. Sci. (2018) 127:120 Page 23 of 33 120

Figure 8. Nomenclature of pyroxenes of granitoids according to the IMA classification scheme (Morimoto 1988). Symbols: green open triangle – charnoenderbite, Sarpahari; green box: charnockite, Sindurpur; yellow box: enderbite, Sarpahari. new and revised Al-in-hornblende geobarometer for the final emplacement level and crystallisation is recently proposed by Mutch et al. (2016) who (table 7). However, following the same calibra- have made an experimental study of amphibole tion the average pressure estimate for the Agarpur stability in low-pressure granite magmas. Their pluton yields 3.2 ± 0.5 kbar indicating a shallow Al-in-hornblende geobarometer is applicable to depth of emplacement of the studied rocks. granitic rocks with the low-variance mineral assemblage: amphibole + plagioclase (An15−80)+biotite 7.2 Temperature estimates + quartz + alkali feldspar + ilmenite/titanite + magnetite + apatite. They have recommended Coexisting hornblende and plagioclase are that amphibole analyses should be taken from commonly used for thermometric calculations in the rims of grains, in contact with plagioclase calc-alkaline igneous rocks (Blundy and Holland and in apparent textural equilibrium with the 1990; Holland and Blundy 1994). According to rest of the mineral assemblage at temperatures Holland and Blundy (1994), the constrains for ± ◦ using this thermometer are: (i) temperature should close to the haplogranite solidus (725 75 C), as ◦ determined from amphibole–plagioclase thermo- be in the range of 400–900 C; (ii) amphiboles A > . VI< . metry. Mean amphibole rim compositions that should have Na 0 02 pfu, Al 1 8pfuand meet these criteria can then be used to calculate Si in the range of 6.0–7.7 pfu; and plagioclases < . P (in kbar) from Altot (in apfu) according to the should have XAn 0 90. These compositional con- expression: straints in the studied amphiboles satisfy the use of this geothermometer. The estimate of pressure required for computation of this geothermometer P . . × tot . × tot 2. (kbar) = 0 5+0331 (Al )+0995 (Al ) is taken from Schmidt’s (1992) pressure calculation. The hornblende–plagioclase geothermome- Since the Agarpur pluton is emplaced in relatively ter of Holland and Blundy (1994) is based on shallower level (see later), this new geobarometer is the edenite–richterite reaction and is applicable used for calculation. According to the calibration also to quartz-free igneous rocks. The average of Mutch et al. (2016), the average pressure esti- temperatures of equilibration calculated with the mates for Sarpahari, Raghunathpur and Sindurpur outer margin compositions of adjacent hornblende plutons are 5.4, 5.4 and 4.5±0.5 kbar, respectively, and plagioclase in the granitoid rocks of 120 Page 24 of 33 J. Earth Syst. Sci. (2018) 127:120 ) et al. 775 703 734 2005 ( Henry ) 2010 ( et al. Ridolfi ) 1984 ( Otten ) 1994 ( Holland and Blundy ) 1992 ( Schmidt ) 2016 Pressure Temperature et al. Al-in-hornblende Hbl-plag Ti-in-Hbl Hornblende chemistry Ti-in-biotite Depth (km) (using Mutch ) et al. 2016 ( Mutch Intrinsic parameters of granitoid rocks. Table 7. Sample RockAgarpur type pluton P18P19P20B Pink graniteSindurpur pluton Pink granitePR3E Grey granitePR9 GraniteBA4A Mylonitic granite Mylonitic 2.4 tonalite 3.5 4.3 5.1 5.1 7.9 11.6 14.2 16.8 16.8 2.6 2.6 4.7 6.4 6.4 896 885 724 747 545 650 589 788 776 808 661 665 677 BA13ABA11A EnderbiteAD36a Granite Raghunathpur pluton CharnockiteCB6CB38CB38c Porphyritic graniteH1 4.5BG14 5.6BG13c 5.2Sarpahari pluton BG24BG36 CharnoenderbitePR30B 14.9 EnderbitePR28E Enderbite 18.5 17.2 Porphyritic granite 4.9 6.0 5.7 5.3 5.4 5.6 6.2 5.2 5.1 7.2 6.5 16.2 19.8 18.8 718 17.5 17.8 20.5 17.2 793 16.8 763 6.2 7.0 7.1 801 838 6.7 6.3 787 7.2 6.6 6.5 779 780 766 886 719 796 735 775 909 749 808 810 738 634 829 764 734 776 789 760 775 904 907 760 744 731 754 767 729 J. Earth Syst. Sci. (2018) 127:120 Page 25 of 33 120 ) 1998 ( et al. O(wt%) 2 Moore (bar) H O 2 H f ) ). O 2 1981 H ( f 2014 ( rocks Wones Calc-alkaline ) 2010 ( et al. O(wt%) log 2 H chemistry Hornblende Ridolfi Goswami and Bhattacharyya ) 2010 ( 11.812.0 5.3 5.0 3.12 1310 4.9 12.1 5.2 3.26 1821 5.9 12.2 5.6 2.76 575 2.8 13.0 6.5 et al. − − − − − chemistry Hornblende Ridolfi ) 2 O 1989 f ( 13.6 13.8 14.6 14.8 3.06 1135 4.4 13.2 3.58 3799 6.4 15.4 2.83 672 3.1 14.0 3.32 2104 6.3 14.2 13.8 3.39 2459 6.7 13.3 3.57 3681 6.6 15.6 15.3 3.69 4886 4.4 14.6 3.62 4174 5.9 11.2 4.25 11.2 4.22 log − − − − − − − − − − − − − − − rocks Wones ) 1965 ( 15.5 13.1 15.5 14.8 15.5 15.0 14.2 14.3 12.5 13.5 13.5 13.5 17.8 17.5 14.0 − − − − − − − − − − − − − − − Wones and Eugster Biotite Biotite chemistry Calc-alkaline Mg/(Fe+Mg) (Continued.) PR28E 0.28 BG36 Sarpahari pluton BG24 PR30B 0.50 BG13c 0.41 BG14 0.41 H1 0.38 CB38c 0.42 Raghunathpur pluton CB6CB38 0.45 0.46 BA11AAD36a 0.54 0.48 BA4ABA13A 0.48 0.48 PR9 0.04 Sindurpur pluton PR3E 0.04 P20B 0.48 P19 Table 7. Sample Agarpur pluton P18 Dataset: Agarpur, Sindurpur and Sarpahari plutons: present study; Raghunathpur pluton: 120 Page 26 of 33 J. Earth Syst. Sci. (2018) 127:120

Figure 9. The P –T and T –log fO2 diagrams of the selected studied amphiboles. The NNO and NNO+2 curves in (B), (C) and (D) are taken from O’Neill and Pownceby (1993). ‘Arc magmas’ areas from Harald and Galliard (2006). (E)AT–H2O melt diagram (after Ridolﬁ et al. 2010). The data source of the Raghunathpur pluton, Goswami and Bhattacharyya (2014).

Sarpahari, Raghunathpur, Sindurpur and Agarpur temperature is co-relatable with compositional are 768◦C, 760◦C, 746◦C and 891 ± 40◦C, respec- variation of plutons from enderbite (Sarpahari) tively (table 7). to monzogranite (Raghunathpur) to syenogranite Ridolﬁ et al. (2010) proposed a geothermometer (Sindurpur) to alkali feldspar granite (Agarpur) based upon the composition of magnesian amphi- (ﬁgure 9A). This observation strongly supports bole. Only a few amphibole grains are magnesian that the crystallisation temperature of magma and crystallisation temperatures (808–909◦C) of depends on the composition of the magma, espe- these amphiboles are given in table 7. Tempera- cially silica content. In our study, silica content tures obtained using Ti-content of amphibole are is minimum in enderbite and maximum in alkali also given in table 7. A westward decrease in feldspar granite. J. Earth Syst. Sci. (2018) 127:120 Page 27 of 33 120

7.3 Oxygen fugacity estimates Equilibrium expression of Wones (1989)isused in the present study to estimate the prevailing The oxygen fugacity of magma can be calculated oxygen fugacity in the different plutons (table 7). using the distribution coefficient of Ti from coex- Temperatures and pressures estimated from isting magnetite and ilmenite. But this method hornblende–plagioclase thermometry (Holland and cannot be satisfactorily used in plutonic rocks Blundy 1994) and aluminium-in-hornblende bar- because during slow cooling, magnetite becomes ometry (Schmidt 1992) were used to calculate f Ti-free and ilmenite undergoes oxidation and exso- log O2 of the magma following Wones (1989) lution (Haggerty 1976). However, biotite is a expression (figure 9C). very good indicator of the oxidation state of the Ridolfi et al. (2010) proposed an empirical magma from which it is crystallised. The coexis- universal amphibole sensor to estimate tempera- f tence of biotite, alkali feldspar and iron-titanium ture and log O2 parameters. However, only a few oxide minerals in the granites provides the basis data of the present study admit the validity level. for tentatively estimating oxygen fugacity. The The present study depicts (figure 9d) the slightly Ti4+ and Fe3+ contents of biotite depend mostly increasing oxygen fugacity trend with decreasing on the temperature of crystallisation and oxygen temperature. Following the calibration of Ridolfi f VI fugacity ( O2 )andtheAl depends on the Al et al. (2010), the calculated range of values of 3+ t/ t f activity. The Fe content and Fe (Fe +Mg) log O2 for Sarpahari enderbite rocks are found ratio provide at least the relative information to be −11.8and−12.0 bar. In Raghunathpur, about the oxygen fugacity during crystallisation porphyritic granitoids and Sindurpur granites, the 3+ 2+ f − . − . (Wones and Eugster 1965). Since Fe and Fe log O2 are found to be 12 1and 12 2 bar, cannot be estimated by EPMA, a quantitative respectively, at about 900◦C. According to Ridolfi estimation of the oxygen fugacity or tempera- et al.’s (2010) calibration, the oxygen fugacity (log f − ture can be obtained using the experimental work O2 ) of the Agarpur pluton is about 13 bar at of Wones and Eugster (1965) modified by Sha- 808◦C temperature. bani et al. (2003) for biotites coexisting with magnetite and alkali feldspar. The crystallisa- 7.4 Hygrometric estimates tion temperatures of biotites of the present study have been obtained from the calibration of Henry The assemblage biotite–K-feldspar–magnetite acts et al. (2005), where Ti-content of biotite was used as a buffer of oxygen and water fugacities in the (table 7; figure 9B). magma (Wones and Eugster 1965; Czamanske and The rocks of the present study show oxygen Wones 1973): fugacity between NNO and NNO+2 buffers which KFe AlSi O (OH) +0.5O is consistent with the presence of sphene, allanite 3 3 10 2 2 and magnetite/ilmenite. In this diagram, the NNO = KAlSi3O8 +Fe3O4 +H2O. and NNO+2 curves were obtained from O’Neill and Pownceby (1993). The Sarpahari enderbites equi- Annite activity (aann) of biotite reflects the f librated at an oxygen fugacity (log O2 ) between fugacities of oxygen and water in magma. In a crys- − . − . a 13 4and 14 4 bar, for the temperatures of tallising magma, the H2O increases with decreas- crystallisation interval between 780◦ and 749◦C. ing T due to crystallisation of anhydrous phases. f In porphyritic monzogranites of the Raghunath- Concomitantly, when O2 of the magma is buffered, f pur, the oxygen fugacity (log O2 ) varies between annite in biotite increase through reaction of K- −13.1and−15.2 bar for crystallisation temper- feldspar with magnetite, with resulting growth ature range between 796◦ and 719◦C. The rocks of the Fe2+/(Fe2++Mg) ratio. At the constant f f of Sindurpur show more or less similar range of temperature and constant H2O, when O2 decrea- f − . − . oxygen fugacity (log O2 ) between 13 1and 15 4 ses, annite of biotite also increases either by ◦ 3+ bar for a temperature range between 793 and a decrease of Fe /Fetot or by an increase of ◦ 2+/ 2+ f 718 C. The oxygen fugacity is quite high for the Fe (Fe +Mg) ratios. If O2 of the magma Agarpur pluton and is about −11.2 bar at a and activities of magnetite and K-feldspar are temperature range between 885◦ and 896◦C. known, the activity of annite in biotite may be Wones (1989) suggests a quantitative used to derive the water fugacity through the estimation of oxygen fugacity of granitoid rocks reaction (Wones 1972; Czamanske and Wones with assemblage sphene + magnetite+ quartz. 1973): 120 Page 28 of 33 J. Earth Syst. Sci. (2018) 127:120 f /T . . f a log H2O = 7409 +425 + 0 5log O2 +log ann The water content of magma can also be obtained by the empirical calibration of Ridolfi −log a − log a . Kf mag et al. (2010) using magnesiohornblende compo- Later on, Wones (1981) revised it as sition. According to the amphibole hygrometer of Ridolfi et al. (2010), the water contents in f /T . . f a the Sarpahari pluton range from 5.0 to 5.3 wt% log H2O = 4819 +669 + 0 5log O2 +log ann (table 7). The water contents of Raghunathpur, − a − a − . P − /T, log Kf log mag 0 011( 1) Sindurpur and Agarpur plutons were about 5.2, 5.6 and 6.5 wt%, respectively. These values are in where T is in kelvin and activities are given as conformity with the typical values of calc-alkaline molar fractions. The activity of annite in biotite magma crystallisation in an arc-related environ- can be calculated by various ideal activity mod- ment (figure 9E; Ridolfi et al. 2010). els (Mueller 1972; Wones 1972; Czamanske and Like temperature, a slight increase in water Wones 1973; Bohlen et al. 1980; Holland and Powell content of magmas of different plutons from east 1990; Nash 1993;Patińo Douce 1993). The activ- to west, enderbite of Sarpahari in the east, mon- ity of K-feldspar is 0.6 for magmatic temperatures zogranite of Raghunathpur, syenogranite of Sin- (Czamanske and Wones 1973) and activity of most durpur and alkali feldspar granite of Agarpur to f re-equilibrated magnetites is close to 1. The H2O the west is noticed which is correlatable with the then can be calculated using the Wones’ (1981) change in magma composition. equation. The water activity of magma can be given by 8. Nature of magma a f /f 0 , H2O = H2O H2O In the present study, biotite compositions are used where f 0 is the standard state water fugacity. H2O as effective tools for fingerprinting the magma On the basis of water solubility models of Burn- type and potentially reflecting the nature of the ham (1979)andBurnham and Nekvasil (1986), it is magma and tectonic environment in which they a f X possible to convert the H2O, H2O to H2O,which are formed (e.g., Nachit et al. 1985; Abdel-Rahman can then be expressed in wt%. We use the empirical 1994). Biotites from different granites are alumi- model of Moore et al. (1998) for determining the nous (Al =3.01–3.54 apfu) and ferric (X = f total Mg H2O (wt%) from H2O (vapour) in magmas. This . ◦ ◦ 0 36–0.47), typical of biotites from subalkaline to model can be applied between 700 and 1200 C calc-alkaline to aluminopotassic granites (table 2; and 1–3000 bar and can be applied to any natu- figure 10A). Biotite compositions show a contin- ral silicate liquid in that range. For the conversion uous increase in Al and decrease in Mg from f total of H2O to H2O (wt%), the following regression eastern to western plutons, i.e., from Sarpahari equation is derived from the experimental data of to Agarpur granites. The progressive increase of Moore et al. (1998): the total Al contents and the Fe2+/(Fe2++Mg) ratios in biotite (figure 10A) are consistent with H O (wt%) = −7 × 107(f )2 +0.0042(f ) 2 H2O H2O a compositional trend of biotite in continental +0.5798. collision-related granites (Lalonde and Bernard 1993). It indicates the contribution of crustal f The H2O of the Sindurpur pluton is estimated to material (metasediments) during the petrogenesis be 575–4886 bar corresponding to 2.8–6.6 wt% of of the granitoid magmas, either by assimilation or water in the magma (table 7). The Raghunathpur anatexis (Shabani et al. 2003). f pluton gives a more consistent H2O values ranging Biotites of the Agarpur pluton show FeO/MgO between 672 and 3799 bar corresponding to 3.1 and ratios in the 1.92–2.05 range and plot well within 6.7 wt% of water. One sample of the Sarpahari plu- the calc-alkaline field of the MgO–FeO–Al2O3 f ton has requisite assemblage and gives H2O value discrimination diagram (figure 10B). at 1310 bar corresponding to 4.9 wt% of water in Although the FeO/MgO ratios of biotite f the magma. Very high log H2O values are obtained analysed from the Sindurpur pluton are moderately from the samples of the Agarpur pluton and these enriched in Mg, showing FeO/MgO ratios ranging values are out of range of experimental values of from 1.38 to 2.26, these plot within the calc-alkaline Moore et al. (1998). field in the MgO–FeO–Al2O3 diagram. However, J. Earth Syst. Sci. (2018) 127:120 Page 29 of 33 120

t Figure 10. (A)Altotal vs. Mg (p.f.u.) diagram (Nachit et al. 1985) for biotites of the present study. (B)Al2O3–FeO – MgO discrimination diagram for distinguishing the nature of the granitoids of northern Purulia (Abdel-Rahman 1994). t FeO =[FeO+(0.89981 * Fe2O3)]. The data source of the Raghunathpur pluton: Goswami and Bhattacharyya (2014). higher FeO/MgO values (38.85–42.22) are obtained are plotted on the boundary between calc-alkaline from biotites of Sindurpur and Tilaboni hillocks. and alkaline granitoid fields. Similarly, enderbites In the MgO–FeO–Al2O3 discrimination diagram of Sarpahari plutons are plotted in the field of calc- (Abdel-Rahman 1994), the most biotites from the alkaline granite (figure 10A). Biotite chemistry of Sindurour pluton fall within the calc-alkaline field four plutons of the present study suggests that they and some samples plot in the alkaline suite field were formed from subduction-related calc-alkaline (figure 10B). Biotites of the Raghunathpur pluton magma (Abdel-Rahman 1994). show the most consistent variation in FeO/MgO ratio (2.08–2.96) and all the analysed biotites are plotted on the boundary between calc-alkaline and 9.2 Implications of pressure estimate alkaline granitoid fields in the MgO–FeO–Al2O3 discrimination diagram of Abdel-Rahman (1994) In the present study, the Al-in-hornblende (figure 10B). barometer (Mutch et al. 2016) is used to under- An enderbite sample of the Sarpahari pluton stand the vertical crustal upliftment on a regional shows FeO/MgO ratios of biotites in the range scale, after complete solidification of the magma 1.65–1.86 which are consistent with the calc- because the calculated pressures probably represent alkaline nature of the magma. But porphyritic conditions during final emplacement (Stein and granitoids from the same pluton show relatively Dietl 2001). high FeO/MgO values (4.49–5.47), consistent Although different samples from the same pluton with the peraluminous nature of the magma may give different depths of emplacement, a sys- (figure 10B). tematic variation of general depth of emplacement is discernable from the eastern to western part of the study area. Moreover, calculations of intrin- 9. Tectonic implications sic parameters (table 7) enable us to realise the following conclusions: 9.1 Implications of biotite composition (i) The Raghunathpur pluton and Sindurpur Biotite compositions clearly define the nature of pluton are separated by E–W trending NPSZ magmas from which they have been crystallised. and these plutons are located north and south In the MgO–FeO–Al2O3 discrimination diagram of the shear zone (figure 1B). Slightly deeper of Abdel-Rahman (1994), biotites of the Agarpur emplacement of the Raghunathpur pluton pluton plot well within the calc-alkaline field (16.2–20.5 km) relative to the Sindurpur plu- (figure 10B). Most of the biotites from the Sin- ton (14.9–18.5 km) suggests that negligible durpur pluton also fall within the calc-alkaline vertical upliftment might have taken place field and some samples plot in the alkaline suite on the northern block relative to the south- field, while biotites of the Raghunathpur pluton ern block. This is consistent with the field 120 Page 30 of 33 J. Earth Syst. Sci. (2018) 127:120

observation that NPSZ is a sinistral strike-slip samples were collected, have not been altered due shear zone with minute dip-slip component. to shearing at the marginal parts. (ii) The Sarpahari pluton (16.8–19.8 km) which is The mineral compositions of these plutons were located about 60 km ENE from the Agarpur used to estimate the physico-chemical parameters pluton (7.9–14.2 km) must have been uplifted of the crystallisation conditions of the parent mag- 5–8 km relative to the latter pluton. This, in mas and also to establish the chemical nature of turn, suggests a weak ENE trend of increasing parent magma and the tectonic environment in depth of emplacement (figure 1B). which these plutons were emplaced. Biotite compositions of all the four plutons of the 9.3 Implication of oxygen fugacity present study suggest that these were crystallised from subduction-related calc-alkaline magma The oxygen fugacity of magma is related to its (Abdel-Rahman 1994). source material and tectonic settings. Sediment- The pressure of emplacement of these plutons derived S-type granitic magmas are usually redu- was estimated using Al-in-hornblende barometry ced, while I-type granites are relatively oxidised (Mutch et al. 2016;table7). Slight pressure dif- (Haggerty 1976). Highly oxidised magmas are com- ference of emplacement of Raghunathpur (4.9 and monly associated with convergent plate boundaries 6.2 kbar) and Sindurpur plutons (4.5–5.6 kbar) (Ewart 1979), while felsic magmas that are formed lying north and south of NPSZ, respectively, sug- by fractionation from mantle-derived magmas in gests that vertical upliftment along shear zone rift zones are reduced (Loiselle and Wones 1979). was negligible and the strike-slip movement was Hammarstrom and Zen (1986) suggest that calcic dominant in the shear zone. The Sarpahari plu- amphibole crystallised under fairly ‘oxidising’ con- ton (P =5.1–6.0 kbar) which is located about f ditions, with O2 probably buffered between NNO 60 km ENE from the Agarpur pluton (P =2.4– f and HM. The oxygen fugacity (log O2 ) values cal- 4.3 kbar) must have been uplifted 5–8 km relative culated from the calcic amphiboles by means of to the latter pluton. This, in turn, suggests a Ridolfi et al.’s (2010) formula varied between −11.8 weak ENE trend of increasing depth of emplace- and −13.0 bar (figure 9D), and all of the samples ment. are plotted in the arc magma field described by The average temperatures of equilibration Harald and Galliard (2006). These values show a calculated by the method of Holland and Blundy relatively high oxidation state (higher than NNO (1994) using compositions of adjacent hornblende buffer condition) during the late-stage crystalli- and plagioclase in the granitoid rocks of Sarpa- sation of biotite and show a trend for magma hari, Raghunathpur, Sindurpur and Agarpur are crystallisation in oxidising conditions (figure 9C). 768◦, 760◦, 746◦ and 891 ± 40◦C, respectively. The crystallisation temperatures of biotites of the 9.4 Implication of water activity present study have been obtained from the calibration of Henry et al. (2005), where Ti-content The concentration of H O in the studied 2 melt of biotite was used and showed a systematic vari- plutons ranges from 5.0 to 6.5% (as estimated fol- ◦ ◦ ation from Sarpahari (734 –767 C), Ragunathpur lowing Ridolfi et al. 2010) and from 2.8 to 7.01% ◦ ◦ ◦ ◦ (729 –760 C), Sindurpur (677 –775 C) to Agarpur (as estimated following Moore et al. 1998). These ◦ (661 C). values are in conformity with the typical values The four plutons of the present study have of calc-alkaline magma generated in an arc-related been equilibrated at the oxygen fugacities of cal- environment (Naney 1983). f − − cic amphiboles (log O2 ) between 11.8 and 13.0 bar (using calibration of Ridolfi et al. 2010). The 10. Conclusions assemblage K-feldspar–biotite–magnetite–quartz– sphene displays consistent oxygen fugacity values f − . − The fabric of the four granitoid plutons (Sarpahari, (log O2 = 11 2to 15.6 bar) (using calibration Raghunathpur, Sindurpur, and Agarpur) from nor- of Wones 1989) typical for the calc-alkaline magma thern Purulia is interpreted to be primarily of crystallisation. igneous origin. The marginal parts of these plu- The water content of the melt (H2Omelt) ranges tons were affected by regional shearing. However, from 5.0 to 6.5% for the four plutons. the chemical compositions of the magmatic miner- The high oxygen fugacity (higher than Ni–NiO als of the central parts of the plutons, from where buffer) and high water content of the parental J. Earth Syst. Sci. (2018) 127:120 Page 31 of 33 120 granitoid magma are consistent with their Bohlen S R, Essene E J and Boettcher A L 1980 emplacement in a subduction zone. 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