Geochemical systematics of the Mauranipur-Babina greenstone belt, Bundelkhand Craton, Central India: Insights on Neoarchean mantle plume-arc accretion and crustal evolution Academic research paper on "Earth and related environmental sciences"

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Geochemical systematics of the Mauranipur- Babina greenstone belt, Bundelkhand Craton, Central India: Insights on Neoarchean mantle plume-arc accretion and crustal evolution

S.P. Singh, K.S.V. Subramanyam, C. Manikyamba, M. Santosh, M. Rajanikanta Singh, B. Chandan Kumar

PII: S1674-9871(17)30156-1

DOI: 10.1016/j.gsf.2017.08.008

Reference: GSF 601

To appear in: Geoscience Frontiers

Received Date: 1 February 2017 Revised Date: 8 August 2017 Accepted Date: 29 August 2017

Please cite this article as: Singh, S.P., Subramanyam, K.S.V., Manikyamba, C., Santosh, M., Rajanikanta Singh, M., Chandan Kumar, B., Geochemical systematics of the Mauranipur- Babina greenstone belt, Bundelkhand Craton, Central India: Insights on Neoarchean mantle plume-arc accretion and crustal evolution, Geoscience Frontiers (2017), doi: 10.1016/j.gsf.2017.08.008.

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Metavolcanics

(252Ga) Na-Granite _Grey granite (2.82 Ga)

From right to left:

Basement rocks (TTG-Tonalite-Trondhjemite-Granodiorite); Meta volcanics (Koti Formation-Basalt-Andesite-Rhyolite-Dacite);

MS: Meta sedimentarles (Jhankari Formatoion);BIF: Banded Iron Formation(Raspahari Formation-Type II Basalt);

BF:Baragaon Formation (Pillow lavas-Type I basalts) KB-Komatiitic basalt; BnGC-Bundelkhand Gneissic Complex (Basement rocks)

Komatiitic Basalts

Type I Basalts

LITHOPHERIC

OCEANIC V? CRUST I .f

3iC MANTLE | f

Back Arc Basalts (Type II basalts)

Type III Basalts » I R DABI ♦ if &

ASTHENOSPHERE

MANTLE PLUME

ASTHENOSPHERE

1 Geochemical systematics of the Mauranipur- Babina greenstone

2 belt, Bundelkhand Craton, Central India: Insights on Neoarchean

3 mantle plume-arc accretion and crustal evolution

4 S.P. Singha, K.S.V. Subramanyamb, C. Manikyambab*, M. Santoshc, M.

5 Rajanikanta Singhb, B. Chandan Kumard

7 aDepartment of Geology, Institute of Earth Sciences, Bundelkhand University, Jhansi-284128, India

8 bCSIR-National Geophysical Research Institute, Uppal Road, Hyderabad-500007, India

9 cDepartment of Earth Sciences, University of Adelaide, Australia

10 cSchool of Earth Science & Resources, China University of Geosciences, Beijing, China

11 dDepartment of Geology, Central University of Kerala, Kasaragod, Kerala-671316, India

12 Corresponding author. Geochemistry Division, CSIR-National Geophysical Research Institute,

13 Uppal Road,Hyderabad,Telangana, India,500007,Telephone +9140-27012625, E-mail:

14 cmaningri@gmail.com (C.Manikyamba)

20 21 22

Abstract

The Neoarchean Bundelkhand greenstone sequences at Mauranipur and Babina areas within the Bundelkhand Gneissic Complex preserve a variety of magmatic rocks such as komatiitic basalts, basalts, felsic volcanic rocks and high-Mg andesites belonging to the Baragaon, Raspahari and Koti Formations. The intrusive and extrusive komatiitic basalts are characterized by low SiO2 (39-53 wt.%),high MgO (18-25 wt.%), moderately high Fe2O3 (7.1-11.6 wt.%), M2O3 (4.5-12.0 wt.%), and TiO2 (0.4-1.23 wt.%) with super to subchondritic (Gd/Yb)N ratios indicating garnet control on the melts. The intrusive komatiitic suite of Ti-enriched and Al-depleted type possesses predominant negative Eu and positive Nb, Ti and Y anomalies. The chemical composition of basalts classifies them into three types with varying SiO2,TiO2, MgO, Fe2O3, Al2O3 and CaO. At similar SiO2 content of type I and III basalts, the type II basalts show slightly high Al2O3 and Fe2O3 contents. Significant negative anomalies of Nb, Zr, Hf and Ti, slightly enriched LREE with relatively flat HREE and low £REE contents are observed in type I and II basalts. Type III basalts show high Zr/Nb ratios (9.8-10.4), TiO2 (1.97-2.04 wt.%), but possess strikingly flat Zr, Hf, Y and Yb and are uncontaminated. Andesites from Agar and Koti have high SiO2 (55-64 wt.%), moderate TiO2 (0.4-0.7 wt.%), slightly low A№ (7-11.9 wt.%), medium to high MgO (3-8 wt.%) and CaO contents (10-17 wt.%). Anomalously high Cr, Co and Ni contents are observed in the Koti rhyolites. Tholeiitic to calc alkaline affinity of mafic-felsic volcanic rocks and basalt-andesite-dacite-rhyolite differentiation indicate a mature arc and thickened crust during the advanced stage of the evolution of Neoarchean Bundelkhand greenstone belt in a convergent tectonic setting where the melts were derived from partial melting of thick basaltic crust metamorphosed to amphibolite-eclogite facies.The trace element systematics

58 suggest the presence of arc-back arc association with varying magnitudes of crust-

59 mantle interaction. La/Sm, La/Ta, Nb/Th, high MgO contents (>20 wt.%), CaO/Al2O3

60 and (Gd/Yb)N>1 along with the positive Nb anomalies of the komatiite basalts reflect

61 a mantle plume source for their origin contaminated by subduction-metasomatized

62 mantle lithosphere. The overall geochemical signatures of the ultramafic-mafic and

63 felsic volcanic rocks endorse the Neoarchean plume-arc accretion tectonics in the

64 Bundelkhand greenstone belt.

65 Key Words: Bundelkhand craton; Greenstone belts; Mantle dynamics; Plume-arc

66 accretion; Neoarchean crustal evolution

68 1. Introduction

69 Archean greenstone belts present in different cratons comprising wide

70 variety of volcano-sedimentary rocks recording various tectonic imprints and

71 evolutionary history, intrusive and extrusive magmatic episodes, metamorphism,

72 metasomatism and mineralization (Weaver and Tarney, 1981; Pearce, 2014).

73 Based on geological, geophysical, geochemical and geochronological

74 investigations, several studies have suggested that Phanerozoic type plate

75 tectonics were operative in the Archean era and correlated these with the modern-

76 style convergent margin processes (Condie, 2000; Benn et al., 2006; Furnes et al.,

77 2014; Santosh et al., 2016; Yang et al., 2016; Yang and Santosh, 2017). A peak in

78 continental crustal growth at 2.7 Ga, existence of hotter Archean mantle, eruption

79 of komatiites, occurrence of tonalite-trondhjemite-granodiorite (TTG)and adakites

80 that are geochemically analogous to their Phanerozoic counterparts lend support

81 to the operation of plate tectonics during Archean including both mantle plume and

82 island arc processes (Isley and Abott, 1999; Kerrich and Polat, 2006; Polat and

83 Kerrich, 2006and references there in).Convergent margins act as magma

84 producing centres through partial melting in the mantle wedge and subducted

85 oceanic slab representing important sites of crustal growth in both Precambrian

86 and Phanerozoic Eras (Taylor and McLennan, 1985; Rudnick, 1995;Tatsumi,

87 2005; Stern and Johnson, 2010; Xiao and Santosh, 2014; Santosh et al., 2015,

88 2017). Intraoceanic arc lithologies such as boninites, low-Ti tholeiites, picrites, high

89 magnesian andesites, and Nb-enriched basalts from greenstone belts of different

90 Archean cratons and their Phanerozoic counterparts provide clue to understand

91 convergent margin tectonics and crustal growth (Manikyamba et al., 2004, 2005, ,

92 2009, 2012, 2015; Manikyamba and Khanna, 2007; Manikyamba and Kerrich,

93 2012; Baitsch-Ghirardelloet al., 2014). The lithological assemblages of the

94 Neoarchean greenstone belts from different cratons of the world preserve distinct

95 geological and geochemical signatures of subduction processes (Smithies et al.,

96 2005; Hollings and Kerrich, 2000; Polat and Kerrich, 2006; Zhai and Santosh,

97 2011; Shchipansky et al., 2012; De Joux et al., 2014; Furnes et al.,2014; Santosh

98 et al., 2016).

99 The Bundelkhand Craton is one of the prominent Archean nuclei in the

100 northern part of the Indian shield across the north of Son-Narmada lineament

101 (Fig.1).Paleoarchean TTGs, Mesoarchean gneisses of 3551-3270 Ma (Mondal et

102 al., 1998, 2002; Kaur et al., 2014) and Neoarchean granitoids of 2583-2516 Ma

103 (Mondal et al., 2002; Kumar et al., 2010; Pandey et al., 2011; Joshi et al., 2013;

104 Sahaet al., 2015; Kaur et al., 2016) are extensively exposed covering an area >

105 30,000 km2 (Fig. 1 ).

106 Previous studies have reported supracrustal rocks of greenstone and

107 associated magmatic suites in the Bundelkhand Craton (Malviya et al., 2006;

108 Singh et al., 2007; Singh, 2012; Singh and Slabunov, 2015, 2016; Kaur et al.,

109 2016; Saha et al., 2016). However, detailed petrological and geochemical studies

110 on the mafic-ultramafic-felsic sequences documenting their tectonic setting along

111 with the style and nature of magmatism are very limited on Mauranipur-Babina

112 greenstone belt. In this paper, we document systematic geological, petrological

113 and geochemical studies on different lithologies of various Formations occurring at

114 Mauranipur, Babina-Dhaura and Umari sections of the central part of Bundelkhand

115 Craton to evaluate their geodynamic setting.

118 2. Geological Setting

119 The Bundelkhand Craton is bound by the NE-SW trending Great Boundary

120 Fault (GBF) in the west, ENE-WSW trending Son Narmada Faults (SSNF, NSNF)

121 in the south and NW-SE trending Yamuna Fault from Indo-Gangetic alluvium in

122 the north (Bhattacharya and Singh 2013; Fig.1).consisting of Mesoarchaean to

123 Paleoproterozoic lithologies (Mondal et al., 2002; Kumar et al., 2011 ; Mohan et al.,

124 2012 and references there in).The craton is semi-circular in shape and occupies

125 an area of about 30,000 km2 in north-central part of the Indian shield (Basu, 1986).

126 It is overlain in the east, west and south by the Meso-Neoproterozoic sedimentary

127 rocks of Vindhyan Supergroup (Ray, 2006) and in the south-east and south by

128 Paleoproterozoic Bijawar Group (Pandey et al., 2011) comprising low grade

129 volcano-sedimentary rocks. The south-western fringe is demarcated by a small

outcrop of the Deccan basalt and the northern part is hidden under the Recent alluvium of Indo-Gangetic Plains (Sing et al., 2007;; Fig.1).The Bundelkhand massif is mainly composed of (1) Mesoarchean Bundelkhand Gneissic Complex (BnGC) with tonalite-trondhjemite-granodiorites (TTG); (2) Neoarchean greenstone sequences consisting a variety of volcano-sedimentary rocks; (3) subsequent granites intruded into the greenstone belt sequences marks a major geological event for the cratonization and (4) Proterozoic quartz reefs and mafic dykes emplaced subsequent to transformation into a stable craton that are related to crustal scale extension and shearing (Basu, 1986; Rao et al., 2005; Patiet al., 2007; Singh, 2012; Bhattacharya and Singh, 2013).

The Neoarchean Bundelkhand granitoids occur extensively over a large part of the Bundelkhand Craton (>70% of the area), intrude the greenstone sequences and high grade (amphibolite-granulite facies) metamorphic (Singh et al., 2007). The Neoarchean felsic magmatism (2532-2516 Ma; Mondal et al., 2002, Kumar et al., 2010; Saha et al, 2011; Joshi et al., 2013; Singh and Slabunov 2015) is considered to mark the final stabilization of the craton (Ray et al., 2015). This belt is about 120 km long and 6-7 km wide, and carries E-W trending disseminated linear bodies in the central part of the craton (Mohan et al., 2012; Singh et al., 2012; Ray et al., 2015; Singh and Slabunov, 2015; Fig. 1b). The E-W trending greenstone belt has extensive outcrops at Umari-Bhauti (near Mohar), Babina-Dhaurra and Baragaon-Mauranipur areas and is dismembered by younger granites and quartz reefs. The greenstone belt is easily distinguished from rocks of BnGC by their grade of metamorphism, lithological associations, texture, structures and presence of sheared angular relationship with Bundelkhand gneisses (Singh et al., 2007). The metamorphic P-T conditions as derived from the

garnet-sillimanite±biotite±cordierite-feldspar-quartz and garnet-biotite-amphibole-plagioclase-quartz assemblages of gneisses (BnGC), range from 4.9 to 6.4 kbar and 680 to 730oC, (Singh and Dwivedi, 2009), suggesting amphibolite to granulite facies (Singh and Dwivedi, 2015). The presence of mineral assemblages such as garnet-chlorite-biotite-K-feldspar-quartz in pelitic rocks and cummingtonite±grunerite-magnetite-chlorite±biotite-quartz in BIF and talc-chlorite-actinolite-tremolite±quartz in metabasalts, and their P-T estimates of 500±50oC temperature and 4-5 kbar pressure (Singh, 2012) suggest generally low grade metamorphic conditions in the greenstone belt.

2.1 Bundelkhand Greenstone Belt

The E-W trending greenstone belt in the central part of the craton (Sharma 2000; Malviya et al., 2006; Singh et al., 2007) has been divided in to four Formations based on lithological characters, structural and field relationships (Table 1; Fig. 2). The Baragaon Formation is the lowermost unit of this belt and the rocks of this Formation are mainly confined to east of Mauranipur town (Table 1; Fig. 2a). The E-W trending Bundelkhand greenstone belt show angular relationship with the BnGC. The gneissic rocks are rotated to E-W towards the contact (Singh et al., 2007). The pink granite shows intrusive relations and is undeformed. A NE-SW trending quartz reef shows sinistral displacement of the metamorphic units of the greenstone belt and the BnGC at Mankua locality. The Baragaon Formation is represented by a variety of ultramafic-mafic extrusive and intrusive rocks (Fig.3a) in the lower part and Mg enriched andesite (Fig. 3c), basalt and dacite in the upper part (Singh, 2012). Several peridotite and gabbro dykes intrude into the middle and upper parts. Several exotic blocks of mafic and

ultramafic rocks along with the metamorphic units have been recorded in this study from the upper part. The Raspahari Formation comprises mainly clastic and non-clastic volcanogenic sediments (Fig. 3b) and minor amount of basic volcanics at some places (Prasad et al., 1999; Singh et al., 2007).Unlike the Baragaon Fm., thinly bedded rocks of BIF (Fig. 3d) occur throughout the greenstone belt in the form of long linear ridges confining to small mounds. Thick intercalated bands of magnetite-quartzites (up to 30 cm in thickness of magnetite) were recorded from east of Baragaon village in the eastern part of greenstone belt where this Formation has acquired the maximum thickness and extension. Tuffs with metabasic lenses, lenticular bodies of magnetite, quartzite, cherts and basic flows are also noted from the thick sequences of banded iron formation (BMQ) at Babina and Mauranipur areas (Singh, 2012). The lower part of this Formation is characterized by 3 to 4 m thick basaltic flows with minor ultramafics (Fig.3c) followed by BIF and micaceous quartzites. The Umari-Jhankari Formation is represented by thick succession of arkose-argillite-carbonate sequence with very rare occurrence of volcanic flows in the western part of greenstone belt (Pandey et al., 2011). The graded bedding, ripple marks and current bedding structures have been recorded from the Bhauti area. The upper part of this sequence also occurs at Jhankhari and Swargashram temple in the north of Mauranipur located in the eastern portion of greenstone where this is dominated by metapelites, sandstone, micaceous quartzite, greywacke and fuchsite quartzite (Sharma, 2000; Singh, 2012). The mafic lavas are very rare in this Formation. These rocks are highly deformed and metamorphosed into greenschist facies and are intruded by coarse grained granite. The Koti Fm. is the upper most sequence of Bundelkhand greenstone sequence that represents the felsic volcanism consisting of rhyolite,

rhyodacite (Fig. 3e, f), granite breccias, agglomerates, felsic dykes and andesite (Prasad et al., 1999; Singh et al., 2007). The basaltic lava occurs occasionally in this Formation. The rocks of this formation are observed throughout the greenstone belt. The presence of felsic dykes and thick shear zones are also noted in the KotiFm. The greyish pink variety of felsic volcanics are dominant in the western part, whereas pinkish and chocolate coloured rhyolites and rhyodacites occur in the eastern part of the greenstone belt. The medium to coarse grained K-rich pink granite demarcates the end of the evolution of greenstone belt in the central part of craton (Singh et al., 2007; Singh, 2012).

Geochronological data on this greenstone belt associated with the Bundelkhand gneisses is very scanty. The pink granite and granodiorite which intrudes the greenstone sequence have been dated as 2581 to 2516 Ma (Mondal et al., 2002; Kumar et al., 2011; Pandey et al., 2011; Joshi et al., 2013; Kaur et al., 2016). The Mesoarchean Bundelkhand gneiss is older than the associated greenstone belt (3551-3270 Ma; Sarkar et al., 1996; Mondal et al., 2002; Kaur et al., 2014; Saha et al., 2015). The felsic volcanic rocks of Koti Fm. from Babina and Bhauti areas are dated at 2542 and 2622_Ma (U-Pb and Pb-Pb whole rock; Pandey et al., 2011, Singh and Slabunov, 2015, 2016). The only available date for the crystallization age of the basaltic rock of Baragaon Formation shows 2780 Ma (Slabunov et al., 2013). On the basis of the available geochronological data it is suggested that the Bundelkhand greenstone belt comprising Baragaon, Raspahari, Umari-Jhankhri and Koti Formations (Table 1; Fig. 2) which were initiated ~ 2780 Ma with ultramafic-mafic magmatism and culminated around 2542 Ma with extensive felsic volcanism. The present study deals with extrusive and intrusive rocks of ultramafic, mafic and felsic volcanic rocks in which the basalts

have been classified as type I (pillow lavas associated with ultramafic rocks), II (massive and associated with BIF) and III (massive and associated with felsic rocks) based on their field and geochemical characteristics.

2.2. Structure

The greenstone belt represents a syncline and trends NW-SE, traversed by Neoproterozoic granitoids at Mauranipur. The pink granite intrudes into the metavolcanics and gneisses (Fig. 1C) where the rocks occurring to the north of Mauranipur (Jhankhari and Raspahari Formations) display southward dip and those to the south of Mauranipur at Baragaon, north of Saprar and Baragaon Formation at Agar village, are inclined towards north (Fig.2a). Bedding as a planar structure observed in banded magnetite-quartzite (BMQ), fuchsite quartzite and greywacke are marked by compositional layering and colour bands (Fig. 3b). The thickness of BIF varies from few millimetres to centimetres. These rocks trend ENE to WSW direction with 60-70° northerly dips. Th e low- grade metamorphosed BIF of Saprar section (south of Mauranipur) exhibit crenulation cleavages (Fig. 3d). The fold axes trend NW to NE with 30-40° plung e. A series of ENE-WSW trending open folds, and sometimes overturned isoclinals folds, have been recorded form BIF (Singh et al., 2007). The E-W trending vertical crustal-scale shears are prominent in these two areas (Fig. 3f). The metavolcanic rocks of Koti Formation at Babina are characterized by E-W trending vertical shears where coarse grained granite cut across the vertical shear planes (Fig. 3f). These shears are ductile to brittle-ductile in nature, and are more or less parallel to the strike of the greenstone belt (Singh and Bhattacharya, 2010). The entire E-W trending greenstone belt is subsequently truncated by the NE-SW trending quartz reefs

and crustal scale shears, and sometimes dislocated by local faults that passes through the greenstone belt (Fig. 1 b, c and d). As a result, the rocks of the greenstone belt are displaced about 1.0-1.5 km at few places (Basu, 1986; Bhattacharya and Singh, 2013). In addition to the E-W and NW-SW trending crustal scale shear zones, a series of N-S trending conjugate type crustal scale shears also passes through metavolcanics of the Koti Formation at Babina and Dhaura areas. Thus, the NW-SE, NE-SW and N-S trending crustal scale shears (Singh and Bhattacharya, 2017) indicate the influence of post evolution structures in the greenstone belt (Table 1).

3. Petrographic Characteristics

The intrusive and extrusive ultramafic rocks show alteration including sassaurutization and uralitization effects. Altered minerals such as serpentine, chlorite, secondary amphiboles and opaques are present within the fine grained groundmass of plagioclase and clinopyroxene in pillow basalt of Mauranipur. The pseudomorph of olivine grains are occasionally observed with abundant talc and tremolite in komatite basalt. Similar texture was also reported by Malviya et al. 2006 from ultramafic of Baragaon. In the intrusive variety, the amphiboles are coarse grained. Disseminated granules of chromite are also present. The type-I basalt shows poorly developed foliation imparted by the actinolite and chlorite (Fig. 4a). The other mineral constituents include plagioclase (oligoclase), magnetite, quartz and epidote. Occasionally, relicts of olivine and pyroxene are also observed. Type-II basalts are more deformed and metamorphosed compared to type I and are characterized by fine to medium grained chlorite, tremolite and actinolite minerals aligned along the schistose plane (Fig. 4b). These rocks in

277 general exhibit schistose textures and rarely exhibit subophitic texture. Amphibole-

278 bearing pyroxenite occurs as thrust sheet at the base of BIF at Pura village

279 (Babina section), which is characterized by cumulate texture. The coarse grained

280 epidote, actinolite, flakes of chlorite are common as altered minerals. The

281 plagioclase and pyroxene are deformed and sometimes showing rotation texture

282 (Fig. 4c). The ultramafic rocks at Swargeswar Ashram (marked as "'Temple'' in

283 Fig. 1 c), are characterized by coarse grained pyroxene with relicts of plagioclase

284 and olivine. Malaviya et al. (2006) described them as komatiite basalts. The Mg-

285 andesites and dacites at Mauranipur are less deformed and metamorphosed than

286 pillow basalts.The and are characterized by frequent occurrences of secondary

287 epidote and actinolite (Fig. 4d). Phenocrysts of plagioclase and hornblende are

288 common in the Mg-andesite.

289 The meta-rhyolite and rhyodacites of Koti Formation show flow bands

290 imparted by oriented alignment of K-feldspar, quartz and rarely plagioclase (Fig.

291 4e). The accessory minerals include chlorite, magnetite and epidote (rare) which

292 are alteration products. Occasionally, phenocrysts of hornblende constitute part of

293 the flow banding. The rhyodacite is less deformed and metamorphosed compared

294 to the rhyolite and is characterized by fine to medium grained hornblende, chlorite

295 and actinolite (Fig. 4f). The phenocrysts of plagioclase and hornblende are

296 abundant in the rhyodacite compared to the rhyolite.

297 4. Analytical Methods

298 Sixty samples representing the major lithologies described in the previous

299 section were selected from Baragaon, Mauranipur, Koti, Saprar (Kuraichha),

300 Babina, Bhauti and Dhaura from east to west within the Bundelkhand greenstone

belt. Major and minor oxide determinations were carried out using XRF technique (Krishna et al., 2007) and whole rock trace, REE concentrations are estimated using HR-ICPMS at CSIR-NGRI, Hyderabad, following the standard methods of sample decomposition techniques and methods of analysis, instrument parameters and precision are referred to Subramanyam et al. (2013) and Manikyamba et al. (2015). The certified reference materials such as UB-N, BHOV-1, JB-2, JA-2 and JR-1 (United States Geological Survey and Geological Survey of Japan) have been used as matrix matching standards for trace and REE analysis. The precision, accuracy and Relative standard deviation (RSD) are given in Supplementary Table 1.

5. Results

5.1. Ultramafic Unit

(1) Komatiitic basalt (KB): The MgO enriched variety (>20 wt.%) has low-Cr contents with olivine adcumulates, whereas low MgO variety of KB (< 20 wt.%) is saturated in Cr contents and low content of orthocumulates of olivine. The Mg# varies between 81 and 86. Arndt and Lesher (2004); Arndt and Nesbit (1982) suggested that the term komatiitic basalt can be applied to volcanic rocks containing less than 18 wt.% MgO that can be linked, using petrological, textural or geochemical arguments, to komatiites. Further, they also argued that the MgO content varies from 18-50%, the limit between komatiitic basalt and komatiite, due to olivine fractionation or accumulation in low-viscosity ultrabasic liquids. Komatiite basalts have been reported from various stratigraphic sequences of greenstone belts (Arndt and Nesbit, 1982; Rollinson, 1999; Jayananda et al., 2013; Manikyamba et al., 2013;) and described as high- and low-Mg type komatiite

basalts (Sproule et al., 2002). In the present work, the ultramafic volcanics showing MgO contents are well above 18 wt.% (Supplementary Table 1). Hence, the term "komatiitic basalt'' is used in conjunction with other geochemical properties. In figure legends komatiite-1 and 2 are used to differentiate the intrusive komatiite basalt (amphibole bearing pyroxenite) and extrusive komatiite basalt respectively. The komatiite basalt flows (extrusive) and cumulates (intrusive) of present study area show very narrow range of MgO (22-25 wt.%) and a wide variation in Cr content (3,100 to 14,290 ppm in cumulates; 292-846 ppm in flows), indicating depleted to enriched mantle (heterogeneous mantle) conditions. The komatiite basalts of present study correspond to tholeiitic trend with Mg enrichment (Fig. 5a; Irvine and Baragar,1971).

On Nb/Y vs. Zr/TiO2x 0.0001 diagram (Fig. 5b), the studied samples plot in the field of sub-alkaline basalts with very low to moderate Zr/TiO2 ratios. The MgO relationship with different major elements and Ni shows that the analyzed samples plot below the olivine control line for SiO2, Fe2O3 and Ni and above olivine control line for Al2O3, TiO2 and P2O5. The komatiite basalts (MgO >20 wt.%; TiO2>0.5 wt.%) with low (Gd/Yb)N <1 and high (Gd/Yb)N >1 contents are related to cumulates and flows respectively (Rollinson, 1999; Manikyamba et al., 2013) and is related to presence of garnet in the melt source.

(2) Amphibole- bearing pyroxenite (Cumulate Ultramafic Intrusives): The SiO2, TiO2, MgO and Fe2O3 contents of intrusive ultramafic rocks are characterized by minor variations in their major elements with Mg# varying from 53 to 78 suggesting the depleted nature of the melts (Supplementary Table 1). These samples correspond to tholeiitic trend with Mg enrichment (Fig. 5a; Irvine and Baragar,

1971). On Nb/Y vs. Zr/TiO2x 0.0001 discrimination diagram (Fig. 5b), the studied samples plot in the field of sub-alkaline basalts. MgO relationship with different major elements and Ni, exhibit a cluster over a narrow range of MgO (except 2 samples) and plot below and above the olivine control line for SiO2, Fe2O3 and Ni and Al2O3, TiO2 and P2O5 respectively. These rocks are characterized by moderate Ni (197-463 ppm), Co (43-79 ppm) and Cr (292-847 ppm) contents. Except Nb (10.4-25.6 ppm) and Zr (8.75-24.54 ppm), the large ion lithophile elements (LILE) show relatively lower concentrations (Rb = 6-126 ppm; Sr = 5.49-14.27 ppm; Ba = 47-85 ppm) compared to high field strength elements (HFSE) such as Ta (0.010.06 ppm), Hf (0.38-0.98 ppm), Th (0.44-1.25 ppm) and U (0.02-0.14 ppm). The studied samples are characterized by enriched LREE [(La/Sm) N = 2.18-2.98], flat HREE patterns [(Gd/Yb) N = 0.40-0.45] and significant negative Eu anomalies (Fig. 6). Primitive mantle normalized multi-element diagram (Figs. 6 and 7) shows a progressive enrichment from Th to Yb, with positive Nb, Hf, Ti and Y anomalies.

5.2. Mafic Unit

The SiO2contentof the analyzed samples vary from 44.7 to 53.6 wt.% and plot in the field of sub-alkaline basalts and andesite/basalt in Nb/Y vs. Zr/TiO2 binary diagram (Fig. 5b; Winchester and Floyd, 1977) and exhibit sub-alkaline tholeiitic to transitional affinity (Ross and Bedard, 2009; Fig.4c; Supplementary Table 1). Their Mg# varying from 37 to 73. MgO relationship with selected major oxides depicts magmatic trends. Type-I basalts have £REE = 32.41-53.87 ppm and display flat chondrite normalized LREE patterns (Fig.6) with weak or no negative Eu anomalies, (La/Sm)N = 1.22-1.48, (Gd/Yb)N = 1.02-1.28 and (La/Yb)N = 1.13-1.66), whereas the type-II basalts have £REE = 10.9-90.44 ppm and

display flat chondrite normalized LREE patterns (Fig. 6) marked by weak positive and negative Eu anomalies, (La/Sm)N = 0.67-1.65, (Gd/Yb)N = 1.04-1.73; (La/Yb)N = 0.6-3.4 and Zr/Nb=6.5-16.8).

Primitive mantle-normalized multi-element patterns (Fig. 6) show significant negative anomalies of Nb, Zr, Hf and Ti for Type-II basalts, while Type-I basalts have insignificant Zr and Hf anomalies. The type III basalts are geochemically distinct with higher TiO2 contents (1.97-2.04 wt.%) compared to Type I and II varieties, lower £REE (88-90 ppm) compared to type I basalts and display slightly enriched LREE patterns [(La/Sm)N = 1.50-1.59; (Gd/Yb)N = 1.69-1.68; (La/Yb)N = 3.2-3.4] with flat HREE and without any Eu anomalies (Fig. 6). Primitive mantle-normalized multi-element patterns (Fig. 6) show distinct LILE and slight HFSE enrichment and exhibit near flat trend for Zr, Y and Yb. Thus, these three types of basalts of the Bundelkhand greenstone belt from different stratigraphic sequences are characterized by distinct geochemical characteristics showing Nb, Zr, Hf, Ti and Hf negative anomalies (Type-I and Type-II basalts) and a very smooth to near flat trend of Zr, Y and Yb (Type III).

5.3. Intermediate unit (andesite-dacite and Mg-andesite)

The intermediate unit from the upper part of Baragaon Formation shows SiO2 values ranging from 53.3 to 64.5 wt.% and classified as andesites (Fig. 4b) in which majority of the samples indicate calc-alkaline trend, while four of them plot in tholeiitic field (Fig. 4a; Irvine and Baragar, 1971; Supplementary Table 1). Their Mg# varies between 42 and 74, indicating their high Mg-contents. These samples possess similar HFSE and REE contents and inter-element ratios as Type-I basalts, however, there is slight enrichment in LREE compared to Type-I basalts

probably reflect their fractionation from the basaltic magma. The higher SiO2 of andesites relative to Type-I basalts is accompanied by greater Th, La and (La/Sm)N. These samples display LREE enriched chondrite normalized REE patterns (Fig.7) with weak negative Eu anomalies (La/Sm) N = 2.46-3.42, (Gd/Yb) n = 0.82-1.50 and (La/Yb) n = 3.14-6.55).

5.4. Felsic unit (Rhyolite-rhyodacite-dacite)

The felsic rocks associated with the type III basalts of the Koti Formation are characterized by high SiO2 (64.6-66.6 wt.%), low TiO2 (0.4-0.6 wt.%), MgO (1.9-3.1 wt.%), Cr (5-13 ppm) and Ni (1-2 ppm) contents (Supplementary Table 1). Their Mg# varies between 54 and 59. In terms of immobile trace element relationships (Fig.4b), the analyzed rocks exhibit rhyolitic characteristics with distinct alkaline nature (Fig. 4b; Irvine and Baragar, 1971). The REE and primitive mantle-normalized diagrams (Fig. 7) shows coherent LREE enriched patterns marked by weak negative Eu anomalies ((La/Sm)N= 1.61-5.57, (Gd/Yb)N = 1.11 — 1.97 and (La/Yb)N = 2.20-17.10)); pronounced negative Nb and positive Ti anomalies; variable negative to positive Zr anomalies, likely due to zircon fractionation or accumulation.

6. Discussion

6.1. Alteration and Crustal Contamination

Numerous studies on Archean volcanic rocks have shown that metamorphism and alteration are capable of mobilizing elements and resetting isotopic compositions (Lahaye and Arndt., 1996; Lesher et al., 1997; Polat et al., 2002; Ordônez-Calderônet al., 2008). High field strength elements (HFSE: Th, Nb,

420 Ta, HREE, Y, Zr and Hf) and transition elements (Cr, V, Sc, Ti, Mn, Fe, Mg, Co

421 and Ni) present within the igneous phases (olivine, pyroxene, chromite) or

422 accommodated in metamorphic minerals (amphibole and chlorite) retain their

423 original geochemical distribution of the rocks even they are subjected to alteration.

424 The large-ion lithophile elements (LILE: Cs, Rb, K, Na, Sr, Ba, Ca and Eu2+), are

425 not accommodated in metamorphic minerals, but are concentrated in the readily-

426 altered glass phase and are commonly mobile (Lahaye and Arndt, 1996; Lesher

427 and Stone. 1996; O'Hanley, 1997). Studies indicate that Ce anomalies occur in

428 response to oxidation of Ce3+ to Ce4+ from solution as CeO2 (Braun et al., 1993).

429 Ce/Ce* ratios between 0.9 and 1.1 display limited LREE mobility whereas those

430 with Ce/Ce* < 0.9 and > 1.1 are characterized by large LREE mobility (Polat et al.,

431 2002). With the exception of one sample, all the other samples have Ce/Ce* within

432 the range of 0.9 to 1.1 indicating limited LREE mobility. However, large scale

433 negative Eu anomaly observed in komatiites reflects mobilization of Eu by high

434 temperature hydrothermal fluids. Similar Eu anomalies observed in ultramafic

435 rocks from other cratons of the world are generally attributed to secondary

436 alteration processes (Sun and Nesbitt, 1978; Ludden et al., 1982; Arndt, 1994).

437 Except two samples, all the extrusive and intrusive ultramafic rocks have <3.6

438 wt.% loss on ignition (LOI). Except four samples in basalts and andesites, rest of

439 the samples are displaying <2 wt.% LOI. All the analysed samples of rhyolites

440 have <1.5 wt.% LOI. These LOI data of the analysed samples indicate least

441 altered nature of majority of the samples which are displaying smooth and

442 coherent REE patterns (Manikyamba et al., 2014a). However, moderate alteration

443 cannot be ruled out in few ultramafic and mafic rocks of the present study.

The Nb/Th ratio of primitive mantle is 8 whereas that of the Archean upper crustal value proxy by tonalites is 0.76, and hence, Nb/Th value of 8 is used as an indicator for crustally uncontaminated flows (Sun and McDonough, 1989; Rudnick and Gao, 2003; Condie, 2005). The Nb/Th ratios of majority of the analysed ultramafic rocks are greater than 8. Similar features are observed in the uncontaminated Neoarchean komatiites of the Abitibi terrane, where the ultramafics and associated tholeiitic basalts are interpreted as fragments of an oceanic plateau derived from a mantle plume erupting in an intra-oceanic setting (Xie et al., 1993). Manikyamba et al. (2008) accounted for the spectrum of Nb/Th from 8.1 to 21.2 and 3.2 to 7.2 observed in komatiites and associated tholeiitic basalts respectively in the Neoarchean Sandur greenstone terrane attest to a mantle plume erupted proximal to a rifted craton margin, wherein the values >8 represent eruption of komatiites in an oceanic domain while that of <8 were inherited from eruption through rifted continental crust.

Komatiitic basalts of the present study plot in the fields of 1, 2 and 7 in Nb/Th vs. (La/Sm)N diagram (Fig. 8a) of Said et al., (2012) implying that they are crustally uncontaminated. Apart from crustal contamination, Nb/Th ratios of the komatiites and associated tholeiitic basalts of the Kalgoorlie terrane specifically, and the larger Eastern Goldfields superterrane in general, suggest that they were generated from subduction-metasomatized lithospheric mantle during the eruption of mantle plumes at the base of the lithosphere than crustal contamination (Said et al. 2012). The variation in the Nb/Th ratios <8 of the komatiitic basalt of the present study reflect on interaction of a mantle plume with metasomatized continental mantle lithosphere. Some of the extrusive ultramafic rocks of the present study exhibit negative Nb-Ta anomalies suggesting assimilation of

subduction-processed lithospheric mantle material by plume-derived magma (cf. Song et al., 2008), which is also manifested in the La/Sm versus La/Ta relationship (Fig. 8b), where the komatiitic basalts plot on the crustal contamination trend implying its role during the ascent of melts.

6.2. Mantle plume processes

Mantle plumes rise to impinge on either continental or oceanic lithospheric plates resulting in the eruption of great volumes of mafic-ultramafic melts. These eruptions form vast fields of lava flows and associated igneous complexes or oceanic islands. When the mantle plume impinges on sub-continental lithosphere, rifting may occur with subsequent eruption of continental flood basalts such as Karu, Siberian Traps and Deccan traps. Plumes when they impinge onto the mid oceanic ridge (MOR) forms large islands such as Iceland. When plumes interact with passive continental margins, thick piles of mafic rocks will be generated (ex. North Atlantic Volcanic margin) which have close links with south east coast of Greenland with Iceland. Plumes may impinge on active continental margins or island arcs resulting in the generation of back-arc basins. Such lava flows associated with large igneous provinces having long lived plume activity generate from core-mantle boundary caused by the heat of the outer core (Pirajno, 2000). In the head and tail structure of the plume, the head consists of the entrained asthenospehric material whereas the tail will be hotter and generates high Mg melts of picrites and komatiites (Cambell and Griffiths, 1992; Hill et al., 1992). Therefore, the presence of high Mg lavas in the greenstone belts indicate the features of plume magmatism. A compilation of least altered komatiites from the ca. 2.7 Ga Abitibi greenstone terrane, Sproule et al. (2002) identified three types of komatiites: Ti-depleted, Al-depleted-Ti-enriched and Al-undepleted. Al-undepleted

komatiites are derived from shallower or high-degree partial melting of a garnet peridotite source leaving a garnet-free residue; while Al-depleted komatiites are derived from either dynamic melting of a refractory source leaving a refractory harzburgite residue or high-degree melting of a garnet-rich source with a garnet peridotite residue and Ti-enriched komatiites are derived from partial melting of a garnet peridotite source leaving a garnet-bearing residue (Sproule et al., 2002). Based on the above criteria, two types of komatiitic basalts have been distinguished in the present study: (1) Ti-enriched-Al-depleted komatiitic basalts with low Al2O3/TiO2 ratios (8.2-8.5) and (2) Al-undepleted komatiitic basalts with near-chondritic Al2O3/TiO2 (13.0-18.91) ratios which are manifested in Fig. 9a.

The CaO/Al2O3 and Al2O3/TiO2 ratios (0.6-1.78 and 13-18.91 respectively) of Al-undepleted komatiitic basalts of the present study suggest garnet inclusion into the melt phase during partial melting of mantle. The low (La/Yb)N ratios (2.73.6) of the studied komatiitic basalts of Al-undepleted variety corroborate high degree (>30%) of mantle melting, while (Gd/Yb)N ratios varying between 1.20 and 1.49 with negative Zr, Hf and Ti anomalies on mantle normalized multi-element diagram suggest the derivation of parent magma by melting under anhydrous conditions at shallow mantle domain where garnet is precluded from the melt phase.

The Al-depleted variety of ultramafic cumulates are composed of amphibole, pyroxene and accessory plagioclase. These rocks occur beneath the Iron Formations in Babina-Dhaurra section at Pura village (Fig. 2). This ultramafic unit shows sheet like structure with a high angle dip (60-70°) to north. Amphibole-bearing pyroxenite shows high MgO (22-25 wt. %), Al2O3 (9-10 wt.%), Cr (292846 ppm), Ni (192-463 ppm), and are enriched in the Nb content (10.4-25.6 ppm).

These rocks have low Cao/Al2O3 (0.6 to 1.15), Al2O3/TiO2 (8.2--8.5), (La/Yb)N ratios (4.8-5.06), and (Gd/Yb)N ratios (0.39-0.44) displaying unfractionated REE patterns and exhibit negative Nb and Ta anomalies with respect to Th and positive Zr, Hf and Ti anomalies. These features reflect garnet inclusion into the melt phase during higher degrees of partial melting of mantle (>30%).The variation in the (Gd/Yb)N ratios (<1 and >1) for cumulates and flows suggest a garnet rich and garnet free sources from the spinel-peridotite and garnet-peridotite melting regimes are responsible for the genesis of cumulates and komatiite basalt flows respectively (Rollinson 1999; Manikyamba et al., 2013).Therefore, the amphibole bearing pyroxenite appears to be the geochemical equivalent of Al-depleted type komatiitic basalt like those of 2.7 Ga greenstone belts of Abitibi and are geochemically similar to the Munro-type komatiites which were generated by high degree (50%), shallow level partial melting of anhydrous mantle sources. The derivation of parent magma by high degree melting of mantle at shallow depth accounted for elimination of garnet from residue. Thus, we infer that these rocks may be a part of Archean thrusted oceanic wedge component that was involved in the collision and a representative of obducted oceanic unit.

6.3. Island arc processes

(1) Basalts

Fractionated LREE with HFSE/REE anomalies such as Nb, Ta, P and Ti, a characteristic feature of intraoceanic arc magmas which are resultant of slab dehydration-wedge melting processes wherein HFSE are retained in the slab whereas large ion lithophile (LILE), Th, U and LREE are contributed from slab derived fluids to the wedge (Perfit et al., 1980; Tatsumi et al., 1986; Hawkesworth

et al., 1993; Pearce and Peate, 1995; Keleman et al., 2004; Pearce, 2008). Consequently, HFSE contents and HFSE/HFSE (Nb/Zr, Nb/Ta) ratios have been used to address the melt enrichment-depletion characteristics of the mantle wedge (McCulloch and Gamble, 1991; Pearce and Parkinson, 1993; Woodhead et al., 1993; Pearce et al., 2000; Pearce, 2008). Type-I basalts of the present study show flat to slightly enriched LREE patterns and lower magnitude of negative anomalies at Nb, Zr, Hf and Ti (Fig. 6h), whereas Type-II basalts exhibit pronounced negative anomalies at Nb and Ti with insignificant negative Zr and Hf anomalies. Both Type-I and Type-II basalts display relative depletion of HFSE with respect to LILE and LREE manifested in terms of high LILE/HFSE, LREE/HFSE ratios and negative Nb, Ta, Zr, Hf and Ti anomalies which are diagnostic features of subduction zone magmatism in intra-oceanic arc environments (Pearce, 2008; Manikyamba and Kerrich, 2012). Intraoceanic subduction zone characteristics such as depletion of Nb, Ta, Zr, Hf and Ti may also arise in the active continental margin lavas. According to Pearce (1983), the magnitude of enrichment in Sr, K, Rb, Ba and Th will be relatively higher in case of active continental margin tholeiites when compared to the rocks of oceanic island arc. Besides, Ce, P and Sm also show variable degrees of enrichment and the elements such as Ta, Nb, Zr, Hf, Ti, Y and Yb form a flat trend in MORB normalized patterns in the magmas generated at active continental margin. The geochemical variation in the active continental margin lavas are dependent on variable contribution of (1) subduction zone components, (2) trace element enriched sub-continental mantle, (3) partial melting, (4) fractional crystalization and (5) crustal contamination. Zr/Y ratios are used as proxy to discriminate the oceanic and continental island arc magmas (Pearce and Norry, 1979). Zr/Y vs. Y plot clearly identify the oceanic and

continental magmatic processes in these rocks (Fig.11; Pearce, 1983). Higher abundances of Rb (0.7-44 ppm), Sr (34-655 ppm) and Zr (8-131 ppm) in Type-II basalts compared with Type-I basalts (Rb: 1-8 ppm; Sr: 68-150; Zr: 43-70 ppm) reflect contribution from subducted sediments. Mantle normalized trace element patterns of the basalts (Fig. 6) exhibit distinct peaks at U, Th and La relative to neighbouring REE. Though the magnitude of negative Nb, Ti and Hf anomalies vary from Type-I to II basalts, the original arc signatures are preserved in both the types. Zr/Hf and Zr/Sm ratios of Type-I basalts (33-40 and 18-26) and Type-II basalts (6-45 and 8-33) compared with primitive mantle values of 36 and 25 respectively reflect derivation of their parent magma from a depleted to enriched mantle source. The Nb depletion relative to Th is manifested in terms of Nb/Th (314 for Type-I and 4-18 for Type-II basalts) suggesting that source enrichment by hydrous metasomatism of the mantle wedge and varying degrees of influx of metasomatic fluids (Munker et al., 2004; Manikyamba et al., 2009). The Zr/Nb ratios of Type-I (4-18) and II basalts (7-22) are consistent with the primitive arcs suggesting variable enrichment of a depleted mantle wedge in an arc environment in contrast with that of average NMORB (Zr/Nb: 11-39; Sun and McDonough, 1989; Pearce and Peate, 1995). This interpretation in also displayed in figure 9 where most of the data plot within the MORB-OIB array and an enriched mantle source is interpreted for their generation. It is, therefore, inferred that the hydrous metasomatism of depleted mantle wedge by slab-dehydrated fluids and minor slab-derived subducted sediment input are the sources for the enrichment of LILE and LREE of the studied basalts. The higher TiO2 contents, lower £REE with slightly enriched LREE and absence of Eu anomalies of type III basalts compared to Type I and II varieties reflecting on the back arc nature of these basalts (Fig. 6).

Thus, these three types of basalts though spatially present at different stratigraphic sequences are characterized by arc-back arc association in the Bundelkhand greenstone belt complex.

(2) Andesites and Mg-andesites

Andesitic flows display composite geochemical characteristics of adakites and normal arc andesites. Adakites are generally interpreted as slab melts that hybridized with the mantle wedge in transit from the slab to the oceanic arc, acquiring enhanced Mg, Cr and Ni (Drummond et al., 1996; Martin et al., 2005). The andesites of the present study possess higher Na, Cr, Ni and Yb contents, Nb/Ta ratios and possess elevated K contents relative to normal arc andesites of the basalt-andesite-dacite-rhyolite (BADR) association (Ewart, 1979; Richards et al., 2006). In terms of SiO2 and MgO, four of the andesitic samples qualify as magnesian andesites, also known as high-magnesian andesites (HMA). HMA are primitive, intermediate to calc-alkaline volcanic rocks having Mg# > 50 with enhanced Co, Cr and Ni contents relative to normal andesites. Though, all the samples possess higher Cr contents, their Mg# and Ni contents are variable between HMA and normal andesites. They are characterized by enriched and fractionated REE ((La/Sm)N = 2.46-3.42, (La/Yb)N = 3.14-6.55, (Gd/Yb)N = 0.821.50; Fig. 7) and negative anomalies at Nb, Ta (except four samples) and Ti (Fig. 7), a characteristic feature of volcanic arc magmas at convergent margin (Perfit et al., 1980; Hawkesworth et al., 1993; Pearce and Peate, 1995). The studied samples plot close to the spinel-garnet Iherzolite (50:50) line, in between garnet-Iherzolite and spinel-garnet Iherzolite field, with 1-10% partial melting. In addition, the higher Nb contents (5-7 ppm) and Zr/Nb ratios (11-21) higher than those of

NMORB (2.3 ppm and 11-39; Sun and McDonough, 1989), suggesting that their mantle source was heterogeneous and enriched relative to NMORB.

(3) Rhyolite-rhyodacite

Hollings et al., (1999) identified two types of felsic volcanic rocks (Type 1 and Type 2) associated with komatiite-tholeiite sequence from the greenstone belts of northern Superior Province. Type 1 rhyolites have relatively aluminous compositions with strongly fractionated REE patterns which are comparable with Cenozoic adakites and Archean high-Al TTG suites. Both Type 1 and Type 2 rhyolites show LREE enriched patterns and negative Nb and Ti anomalies, but Type 1 rhyolites has strongly fractionated HREE patterns compared to flat HREE with elevated Ni and Cr contents of Type 2 rhyolites. Type 1 rhyolites are comparable to southern Superior Province felsic volcanic rocks associated with oceanic arc sequences and inferred to be the products of oceanic slab melting. The geochemical signatures of Type 2 rhyolites are explained to be the products of mixing of Type 1 rhyolites with tholeiitic magmas, or a contribution from mantle wedge sources located above the garnet stability field. Hollings and Kerrich (2000) reported Type 3 rhyolites from the arc basalt-Nb-enriched basalt-adakite association of 2.7 Ga Birch-Uchi greenstone belt. Type 3 rhyolites, characterized by moderate LREE fractionation, flat HREE, pronounced negative Eu and Ti anomalies, are interpreted to be the products of intra-crustal fractional crystallization of basaltic liquids. The geochemical characteristics of studied rhyolitic samples, marked by aluminous composition with low and fractionated HREE patterns and minor negative Eu anomalies, are in conformity with Type-I rhyolites. Th, Yb and Zr variations (Fig. 7) show low order negative anomalies in the studied rhyolites. On the basis of their geochemical signatures, rhyolites are

further classified as FI (calc-alkaline, low HFSE, moderate to high Zr/Y, (La/Yb)N = 5.8-34, strong subduction signatures), FII (calc-alkaline to transitional, intermediate HFSE, moderate Zr/Y, La/YbN = 1.7-8.8; prominent subduction signatures, FIIIa (tholeiitic, moderate HFSE, low Zr/Y, (La/Yb)N= 1.5-3.5, weak subduction signatures) and FIIIb (tholeiitic, high HFSE and HREE, low Zr/Y, (La/Yb)N = 1.1-4.9, no subduction signatures) types (Lesher et al., 1986). The geochemical characteristics of the analysed rhyolites are marked by high silica, calc-alkaline nature, Th and La enrichment, variably fractionated LREE/HREE patterns, low HFSE and moderate to high Zr/Y and (La/Yb)N (9-12 and 20.2-17.1, respectively) indicate their similarity with F1 type rhyolites from Archean greenstone belts of different cratons (Lesher et al., 1986). The Archaean FI rhyolites are interpreted to be generated by partial melting of thick basaltic crust metamorphosed to amphibolite/eclogite at ~40 km. The rhyolites of F1 type are suggested to have formed at depths of >30 km with a garnet bearing mantle residue whereas FII rhyolites from depths ranging from 10 to 30 km with amphibole-plagioclase residue and FIII type corresponds at <15 km in depth with plagioclase dominant garnet-amphibole free residue (Hart et al., 2004). The rhyolites of the present study are, thus, interpreted to be the products of partial melting of thick basaltic crust metamorphosed to amphibolite/eclogite facies at depths ranging from as high as 30 to 10 km with garnet and amphibole-plagioclase-bearing mantle residue. Few basaltic flows (Type-III) of present studies are associated with these rhyolites exhibit moderate MgO (7-8 wt.%); high TiO2(~2 wt.%), Na2O (~2 wt.%), Zr (~128 ppm), Nb (~13) and Zr/Y (8-13 ppm); low LREE/HFSE ratio (La/Yb)N = 3.2-3.4); HFSE/HFSE ratio (Zr/Hf = 37-39 ppm). The high zirconium and niobium contents of these basalts also testify their

derivation from a similar magma source as rhyolites. The REE and multi element distribution patterns (Figs. 6 and 7) of basalts indicate the metasomatic signature at the source. Thus, collectively these characteristics indicate that the associated basaltic flows are less fractionated and bear a similar magma source of studied rhyolites.

6.4. Geodynamic implications

Typical island arc lavas are enriched in LILE and LREE, but depleted in HFSE, particularly in Nb, Ta, and Ti on normalized trace element diagrams (Saunders et al., 1991; Hawkesworth et al., 1993; Hawkins, 2003; Pearce, 2003; Murphy, 2007). On Zr/Yb vs. Nb/Yb diagram of MacDonald et al., (2000) (Fig. 9b) komatiites plot near OIB on the MORB-OIB array, whereas basalts scatter in between NMORB and EMORB and plot close to the upper boundary of the MORB-OIB array. MORB-OIB array stems from shallow melting of depleted upper mantle asthenosphere for MORB, but deeper melting of a relatively enriched source for OIB, likely from a plume originating in the deeper mantle (Pearce, 2008). The CaO/Al2O3 ratio more than unity with very high MgO contents (>20 wt.%), (Gd/Yb)N in the range of 1.18-1.80 and positive Nb anomalies of the studied komatiitic basalts are indicative of mantle plume source for their origin (Xie et al., 1993; Kerrich and Xie, 2002; Pearce, 2008). Type-I, II and III basalts of the present study occupy the fields of arc and back arc on Ti/Zr, Ti/Sc and Ti/V vs. Zr plots (Fig. 10; Gribble et al., 1996), strongly suggests an intraoceanic tectonic setting for the generation of these rock types. However, type-III basalts are characterized by LREE enrichment relative to HREE and a feeble negative Eu anomaly (Fig. 6j). Enrichment of HFSE over HREE, with a concave downward pattern in primitive mantle normalized multielement plot (Fig. 6i), suggests that the

type-III basalts were generated by melting of a relatively enriched source at greater depth. Further, they plot closer to OIB on the MORB-OIB array in the Zr/Yb vs. Nb/Yb diagram of MacDonald et al., (2000) (Fig. 9b) reflecting oceanic island setting for their generation.

The enrichment of LILE (e.g. Cs, Rb Ba, Th, K and U) and depletion of HFSE (e.g. Zr, Hf, Nb, Ta, Y, Ti) relative to typical primitive mantle values, negative Nb-Ta, Zr-Hf anomalies, and positive Th anomalies (Fig. 7) for the studied andesites and rhyolites are in compliance with the geochemical characteristics of magmas generated in subduction-related tectonic settings. Ta, Yb, Th and Hf are used to discriminate felsic-intermediate compositions (54-77 wt.% SiO2) that are erupted from oceanic arcs, active continental margins, and within-plate volcanic zones (Schandl and Gortol, 2002; Wang et al., 2008). The Yb, Ta and Th variations in the studied samples indicate active continental margin setting (Fig. 7). The Th enrichment in the studied samples may reflect the influence of the subduction derived fluids.

The recycling of Archean crust into the subduction zones generating more diversified mafic and felsic volcanic rocks (BADR) of tholeiitic to calc-alkaline affinity which has been witnessed worldwide in many Archean greenstone belts such as south western Greenland, Pilbara craton; Belingwe greenstone belt, Zimbabwe; Dharwar and Singhbhum Cratons of India (Nisbetet al., 1987; Eriksson et al., 1994; Smithies et al., 2005; Manikyamba and Kerrich, 2012; Polat, 2013; Manikyamba et al., 2014b; Rajanikanta Singh et al., 2017). Presence of different types of basalts and BADR type of differentiation at Baragaon and Babina-Koti areas in the east and west of the greenstone belt respectively demarcate a distinct genetic origin and involvement of mantle processes in the genesis of ultramafic-

717 mafic-felsic magmatism (Fig. 12a, b). Further, their close temporal association

718 observed in various locations Baragaon, Babina, Koti and Dhaura may also reflect

719 on fractional crystallization in a sub-arc environment. Such calc-alkaline series

720 have been reported from Salina, Aeolian arc, Italy (Gertisser and Keller, 2000).

721 The Nb-enriched ultramafic flows of Baragaon (11.2-25.6 ppm) may represent an

722 OIB like remnant of ocean crust which was obducted at the late stages of

723 convergence. Ce (27-56 ppm) in ultramafic cumulates, (1.89-3.5 ppm) in flows,

724 (2.81-29.89 ppm) of basalts, (17.0-30.9 ppm) of Mg-andesites and very low Yb

725 (0.1-4.0) contents of all the above attests to intraoceanic Island arcs such as

726 Tonga-Kermadec and South Sandwich that have very low Ce contents, whereas

727 Marianas, Aleutians, New Britain and Andes SVZ are indicated by moderate Ce

728 contents up to 40 ppm (Hawkesworth et al., 1993). Komatiite basalts occur at the

729 bottom-most horizon in the stratigraphy of the greenstone sequence conformably

730 in contact with crystalline basement which is a characteristic lithological unit of

731 Bundelkhand greenstone belt (Fig. 12b). Such stratigraphy clearly indicates the

732 obduction of remnant oceanic crust during complete convergence at a much faster

733 rate (e.g. Isua greenstone belt, Komiya et al., 1999). The plume generated

734 ultramafic rocks are associated with island arc volcano-sedimentary sequences of

735 Baragaon (komatiite-basalt-dacite-rhyolite and BIF). These litho units are

736 continued into Babina (andesites-rhyolites; cherts and BIFs), which are in turn

737 continued into Umri where the ultramafic-mafic rocks directly resting on BIFs (at

738 Pura village). The rocks of this Formation again appear towards north at

739 Sugeswarashram (shown as Temple in Fig. 1c) with ultramafic cumulates

740 overlayned by metasediments (fuchsite quartzite, greywackes). These geological

relationships and geochemical characteristics reflect on the plume -arc accretion in this part of Bundelkhand craton.

Similar type of ultramafics, pillow basalts, basalt-andesite-dacite and rhyolite and BIF associations trending in N-S to NNE-SSE greenstone belts from EDC (Sandur, Hutti, Penakacherla and Gadwal, Kadiri, Veligallu) have been reported from the southern part of Indian shield at nearly same geological time (Polat et al., 2011; Manikyamba and Kerrich, 2012; Kerrich and Manikyamba, 2012; Jayananda et al., 2013) where convergent margin tectonic setting with plume interaction have been proposed.

Studies in the southern Indian shield have revealed evidence for extensive crustal growth through arc magmatism during the Meso- and Neoarchean times (Santosh et al., 2015). The 3.3-2.5 Ga volcano-sedimentary greenstone sequences of Dharwar Craton are characterized by either komatiite-tholeiite association that has been interpreted to be the product of plume magmatism and plume-lithosphere interaction or tholeiitic to calc-alkaline basalt-andesite-dacite-rhyolite (BADR) volcanic sequences along with boninites, Nb-enriched basalts, adakites, Mg-andesites, shoshonites, leucitites and arc basalts considered to be the products of subduction-accretion processes (Anantha Iyer et al.,1980; Rajamani et al., 1985; Balakrishnan et al., 1990; Giritharan and Rajamani, 1998; Manikyamba et al., 2012, 2014, 2015).

The geochemical plots of rocks of E-W trending greenstone belt of Bundelkhand discriminate intraoceanic island arc to back arc to active continental margin setting and their accretion with the plume generated mafic-ultramafic magmas (Fig. 12) in the north of Son Narmada lineament for the Bundelkhand greenstone belt.

7. Conclusions

On the basis of field, petrographic and geochemical data of the major rock

formations from the greenstone belt in the Bundelkhand craton, we arrive at the

following conclusions.

(1) Four lithostratigraphic Formations and stratigraphic columns are identified in the Bundelkhand greenstone belt. These are the Baragaon (predominantly high Mg pillow basalts and Mg andesite), Raspahari (dominated by BIF, basaltic, cherts and other chemogenic sediments), Umari/Jhankri (with arkosic, argillaceous and arenaceous types of supracrustal sediments) and Koti Formations (dominated by rhyolites, andesite, rhyodacite, granite breccias, tuffs with rare basic flows) and are characterized by distinct mafic and felsic flows are identified.

(2) The ultramafic units of komatiitic basalts at Baragaon and amphibole bearing pyroxenite cumulate at Pura village from Baragaon Formation are stratigraphically and compositionally distinct and represent probable remnants of oceanic crust.

(3) Type I, II and III basalts have been identified which are associated with various lithologies and exhibit overlapping to variable geochemical characteristics reflecting on arc-back-arc association in the Bundelkhand greenstone terrain.

(4) The associated intermediate to felsic volcanic rocks were derived from partial melting of thick basalt crust metamorphosed to amphibolite to eclogite facies at a depth of around 30-40 km.

(5) The eastern part, where basalts of Baragaon Formation are associated with chemogenic sediments of BIF of Raspahari Formation, has least contaminated

mafic and ultramafic flows followed by andesite-Mg andesite, whereas the central part of greenstone belt at Dhaurra (Koti Formation) Raspahari Formations are dominated by felsic volcanics, basalts, tuffs and breccia of rhyodacites. The rocks in the extreme western part Umari-Jhakhari of the greenstone belt, developed around Mohar are dominated by supracrustal of felsic volcanics and tuffs, similar to those Koti Formation and are characterized by high abundances of crustal components.

(6) Our study suggests plume-arc accretionary tectonics for the greenstone belt sequences at Mauranipur, Babina-Pura and Umari-Jhakhari areas of Bundelkhand Craton.

Acknowledgements

The authors are grateful to Dr. V.M. Tiwari, Director, CSIR-NGRI for his kind encouragement and support to publish this work. Drs. C.M and K.S.V.S acknowledges the funds from Council of Scientific and Industrial Research (CSIR) to National Geophysical Research Institute MLP 6201-28 (CM). The authors thank the two anonymous reviewers for their critical and constructive comments. We thank Dr. Sohini Ganguly for efficient editorial handling. Dr. M. Satyanarayanan, S.S. Sawant, and A. Kehsav Krishna are acknowledged for help in the analytical work.

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1310 Figure Captions:

1311 Figure 1. (A) Inset map showing the major cratons of India (after Sharma, 2009),

1312 (B) Regional geological map of Bundelkhand craton showing Bundelkhand

1313 Gneissic Complex (BnGC) and E-W trending greenstone belt in the central

1314 part of the craton (modified after Singh et al., 2007; U-Umari; B-Babina; P-

1315 Prithipur; M-Mauranipur; A-Ajnar and K-Kabarai). (C) Geological map

1316 shows various lithounits of greenstone belt at Mauranipur and (D)

1317 represents the geological map of Babina-Dhaurrasection where the

1318 greenstone belt is truncated by different faults and shears.

Figure 2. Field relationship and correlations of different lithounits of various Formations of greenstone belt of Bundelkhand which are exposed at Umri in west, Babina-Dhaurra central part and Mauranipur in the east located in the Bundelkhand Craton representedby the locations 1, 2 and 3 in Fig. 1B. The legend and symbols are similar as shown as Fig. 1.

Figure 3. Field photographs showing different structures in the Bundelkhand greenstone belt (a) pillow structures (type I Basalt) showing deformation and alteration from Baragaon Fm., (b) oxide and sulphide faciesbanded magnetite -quartzite (BMQ) from Raspahari Fm., of Mauranipur (c) massive type II basalt from Kuraicha village (d) andesite from the upper part of Baragaon Fm., (e) massive rhyodacite from Koti Fm. of Babinaand (f) vertical shearing in the felsic volcanic rocks of Koti Fm. at Babina.

Figure 4. Photomicrographs of (a) Type - I basalt showing mild foliation defined by the presence of chlorite and elongated epidote, (b) development of chlorite and actinolite in type - I where coarse grained magnetite and relics of augite is present, (c) coarse grained cumulates of amphibole and pyroxene from ultramafic intrusive at Babina, (d) alteration and deformation texture in Mg -andesite showing needle shaped amphiboles and epidotes from the upper part of Baragaon Fm., (e) Rhyodacite showing banded structure represented by amphiboles and plagioclase from Babina and (f) bands and flow texture in metarhyolilte of Koti Fm. at Babina.

Figure 5. (a) AFM diagram of Irvine and Baragar (1971) showing calc-alkaline nature of andesites and rhyolites and komaatiic basalts and basalts in tholeiitic field (b) Nb/Y vs. Zr/TiO2 diagram (after Winchester and Floyd,

1343 1977) showing variation from sub-alkaline basalts to dacites (c) Zr vs. Y plot

1344 of Ross and Bedard (2009) indicating the tholeiitic nature of these rocks.

1345 Figure 6. Chondrite-normalized REE and primitive mantle-normalized multi-

1346 element diagrams of ultramafic flows (a, b), cumulates (c, d), Type I (e, f), II

1347 (g, h) and III (i, j) basalts (Normalizing value are from Sun and McDonough,

1348 1989)

1349 Figure 7. Chondrite-normalized REE and primitive mantle-normalized multi-

1350 element diagrams of andesite (a, b) and dacites (c, d) of Bundelkhand

1351 greenstone belt.

1352 Figure 8. (a) (La/Sm)N versus Nb/Th diagram after Said et al. (2012); (b) La/Sm vs

1353 La/Ta illustrating the different trends (arrows) for contamination of plume

1354 liquids by continental lithospheric mantle (CLM).

1355 Figure 9. (a) (Gd/Yb)N vs. Al2O3/TiO2 binary plot of Sproule et al., (2002) indicating

1356 ultramafics as Al-depleted and Al-undepleted varieties (b) Zr/Yb vs. Nb/Yb

1357 binary plot (modified from Macdonald et al., 2000) showing MORB-OIB

1358 affinity for three types of basalts.

1359 Figure 10. Tectonic discrimination diagrams of (a) Ti/Zr, (b) Ti/Sc and (c) Ti/V vs.

1360 Zr, after Gribble et al.(1996) showing arc-back arc affinities type I, II and III

1361 basalts, andesites and dacites.

1362 Figure 11. Zy/Y vs. Y plot (after Pearce, 1983) reflecting on the intraoceanic to

1363 continental island arc tectonic setting for the generation of the basalts-

1364 andesites-rhyolites.

1365 Figure 12: (a) Schematic model showing genesis of Type I, II basalts along the

1366 andesite-rhyolite-dacite sequence in an intra-oceanic island arc setting,

1367 Type III basalts are erupted in a back-arc-basin setting. The komatiitic

1368 basaltswere erupted through mantle plume in an ocean crust (Vertical and

1369 horizontal- Not to Scale) and (b) Schematic cross section representing

1370 presently exposed sequence of Bundelkhand Greenstone Belt

1371 atMauranipurarea (not to scale).

ACCEPTED MANUSCRIPT

Table 1. Tectonostratigraphic elements of the greenstone belts, Bundelkhand craton

Mauranipur Section (age in Ma) Babina -Dhaurra Section (age in Ma) Umari-Bhauti Section Major lithologies Minor lithologies Volcanic/ Sedimentary/ Metamorphic structures Intrusive Units Metamorphic grade/facies Tectonic structures Structural Trend

Bhauti Fm. (3b) Carbonates, siltstone quartzite, C-shale, phyllite andesite, chert, calc schists Stromatolite type structure, ripple marks, graded beds Basic dykes, granites Greenschist facies F1-F2;F3 S1-S2 E-W, NE-SW

Jhankari Formation (3a) (3a) Quartzite, Graywackes, phyllite and chlorite schist Micaceous quartzite, fuchsite quartzite, tuffacious greywacke Cross bedding, Graded bedding Mafic dykes, Granites Lower greenschist facies F1-F2; S1 NNW-SSE/ ENE-WSW

Koti Fm (2542±17 Ma) Umari Fm. (4a) Rhyodacite, andesite, dacite, rhyolites (4b) Agglomerates, rhyolites and tuffs agglomerate, massive basalts (rare), mylonites tuffacious cherts Felsic flows, tuffacious structures Vertical shears and mylonites Pink granite, Mafic dykes Mylonitised and lower greenschist facies F1-F2; S1-S2 E-W, NE-SW

Raspahari-Dhaurra Formation Dhaurra Fm (2a)Mafics and ultramafics (2b) Banded magnetite quartzite, basalt, cherts, quartzite tuffs, basic volcanics intercalated with BMQ, ultramafic dyke sheets Penecontemporaneous deformational structure in BMQ Pink granite and mafic dykes Greenschist to lower amphibolites facies F1;S1 F1-F2 S1-S2 Open folds E-W, NE-SW

Baragaon Formation (2750±8 Ma) Pura Fm (1a) Basalts (pillow & massive) (1b) komatiite basalt, peridotite (1c) Felsic volcanics, andesites & dacite (Id)grabboic dykes (1e)K2O enriched basalt and tuffs Mg-andesite, dacite, volcanogenic/chemogenic sediments quartzite, sepentinised peridotite, asbestos sheets chl schist, talc schist, mafic and ultramafic flows Pillows and amagdular basalts, flow structures in andesites Gabbroic dyke, quartz reefs Greenschist facies F1-F2 F3 S1-S2 Mostly open folds WNW-ESE, NE-SW

Bundelkhand gneissic complex (3200-3300 Ma) Gt -crd gneisses, Gt sill gneisses, gt -bt gneisses, granite gneisses migmatites and TTGs Quartzites, amphibolites, gt-amphibolites Gneissose and granulose structures TTGs invade the pelitic gneisses Upper amphibolite to granulite facies Hook folds sheeth fold, tight folds NW-SE , NE-SW and E-W

78° E

1 Metavolcanics (GB)

Mafic & BIF (GB) ] Bundelkhand Gneissic Complex

§Na-feldspar-enriched granite I I Gwalior & Bljawar Sediments K-feldspar enriched granite | Vlndhyan Sediments

Blotite-enriched granite

+ + + +/ + J.+ + ++N

+ Jr 2532 Ma

■ + + / + + + + + + + i

Quartz Reef Granite

Greenstone Belt Bundelkhand Gneissic Complex (BnGC)

Alluvium Shear zone Fault

Schistosity

• Type-I Basalt ■ Type-I I Basalt

• Type-Ill Basalt 0 Andesite

o Continental arc

Oceanic arc

J_I_I_L

Zr Fig,11

Metavolcanics ^^^^a)

(2 52 Ga) Na-Granite ____Grey granite (2.82 Ga)

From right to left:

Basement rocks (TTG-Tonalite-Trondhjemite-Granodiorite); Meta volcanics (Koti Formation-Basalt-Andesite-Rhyolite-Dacite);

MS: Meta sedimentarles (Jhankari Formatoion);BIF: Banded Iron Formation(Raspahari Formation-Type II Basalt);

BF:Baragaon Formation (Pillow lavas-Type I basalts) KB-Komatiitic basalt; BnGC-Bundelkhand Gneissic Complex (Basement rocks)

Komatiitic Basalts

Type I Basalts

Type III Basalts

LITHOPHERIC

OCEANIC Vf CRUST f ff -f

RIC MANTLE ^ f

MANTLE PLUME

ASTHENOSPHERE

--> i r dabl -> <-

Back Arc Basalts 3 Intra-oceanic Trench

(Type II basalts) ♦

ASTHENOSPHERE

Oceanic Crust

Fig.12

LITHOSTRATIGRAFHIC SEQUENCES OF GREENSTONE BELTS IN BUMDELKHAND CRATON

Umri Section Babina Dhaura Section Mauranipur Section

F¡g.3

F¡g.4

LEGEND

Kormatiite - I Komatiite - 2 Type-! Basalt Type-II Basalt Type-]iI Basalt Andesite Rhyolite

0 10 20 30 40 50 50 70 SO

4 (1(1

La Ce P» Kd 5« Eu fi Tl Dj Hd 6 Til n

Tn Mb Ta La Ce Pr He Zr Hf SmEu T1 Gd Tb Df ¥ Hu E( Tm Yb Lu

Fig. 7

Ef3 ji

E-HMT2

E-KB2 *

D-KB2 J_

A Komatiite -1

♦ Komatiite - 2 Type-! Basalt

■ Type-1 i Basalt

• Type-Ill Basalt

Komatiitic basaft

% i hJ

/ i i i b

— uc Cmstal Contamination —

F A A A

- A * * A A A -

■ S m a B

■ ; M

• Plume/CLM Mixing

i i i 1

Komatirte - I Komatiite - 2

Ti-depleted

Ai-undepleted

At-depleted - Ti-enriched

Steep Rock Belt

_ L 1 1 1 1 1 = b M| 1 1 1 MIL

~ Average N-MORB - - ■ ^ ' "" W • MORB-OIB Array _

♦ vV • ^ - •

- " •

- . i \ -

Average N-MORB _

..... .»1 1 ; Type-I Sasait — ■ Type-I! Basalt • Type-Ill Basalt ......

Nb/Yb Fig. 9

Research Highlights

❖ East-west trending (Mauaranipur-Babina-Dhaura) Bundelkhand Greenstone Belt

❖ Geochemistry of komatiitic basalts-island arc tholeiitic BADR association

❖ Crustal growth through Neoarchean plume -back arc- arc accretion in Bundelkhand Craton

❖ Southward subduction polarity