Syn- and post-tectonic granite plutonism in the Sausar Fold Belt, central India: Age constraints and tectonic implications

Accepted Manuscript Syn- and post-tectonic granite plutonism in the Sausar Fold Belt, Central India: age constraints and tectonic implications Anupam Chattopadhyay, Kaushik Das, Yasutaka Hayasaka, Arindam Sarkar PII: DOI: Reference:

S1367-9120(15)00203-5 http://dx.doi.org/10.1016/j.jseaes.2015.04.006 JAES 2333

To appear in:

Journal of Asian Earth Sciences

Received Date: Revised Date: Accepted Date:

19 September 2014 28 March 2015 2 April 2015

Please cite this article as: Chattopadhyay, A., Das, K., Hayasaka, Y., Sarkar, A., Syn- and post-tectonic granite plutonism in the Sausar Fold Belt, Central India: age constraints and tectonic implications, Journal of Asian Earth Sciences (2015), doi: http://dx.doi.org/10.1016/j.jseaes.2015.04.006

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

2

Syn- and post-tectonic granite plutonism in the Sausar Fold Belt, Central India: age constraints and tectonic implications

3

Anupam Chattopadhyay1*, Kaushik Das2, Yasutaka Hayasaka2, Arindam Sarkar1

1

1

4 5

2

Department of Geology, University of Delhi, India

Department of Earth and Planetary Systems Science, Hiroshima University, Japan

6

*Corresponding Author; Email: [email protected]

7 8

Abstract:

9

Sausar Fold Belt (SFB) in central India forms the southern part of the central Indian Tectonic

10

Zone (CITZ) – a crustal scale Proterozoic mobile belt dissecting the Indian craton, whose

11

tectonothermal history and age is important for understanding the Proterozoic crustal history of

12

the Indian craton. SFB comprises a gneissic basement (TBG: Tirodi Biotite Gneiss) overlain by a

13

supracrustal sequence of quartzite-pelite-carbonate (SSG: Sausar Group). SSG and TBG are

14

deformed and metamorphosed in greenschist to amphibolite facies. Two phases of granite

15

intrusion are observed in the SSG – a syntectonic foliated granite and a post-tectonic massive

16

granite, with clear structural relationship with the host rocks. Monazite chemical dating (U-Th-

17

total Pb) of the foliated and massive granites yield Neoproterozoic (ca. 945-928 Ma) ages that

18

contradict many earlier geochronological interpretations. Foliated granites and the immediately

19

adjacent TBG show monazite grains with ca. 945 Ma mean age, interpreted as the timing of D2

20

deformation and amphibolite facies metamorphism of SSG. The post tectonic granites intruded

21

these rocks around 928 Ma, and were largely undeformed. A terminal thermal overprint is found

22

in some monazite grain rims at ca. 785 Ma age. The younger Sausar tectonothermal events have

23

overprinted the adjacent high-grade granulites of Ramakona-Katangi Granulite (RKG) belt, and

24

should not be considered as parts of the same tectonothermal event representing different depth

25

sections only. 1

26 27 28

Keywords: Sausar Fold belt, Deformation and Metamorphism, Intrusive granites, Monazite dating, Central Indian Tectonic Zone.

29

2

30

1. Introduction:

31

The Central Indian Tectonic Zone (CITZ) is an E-W trending crustal scale Proterozoic

32

mobile belt that dissects the Indian peninsular block and is supposedly continuous through the

33

Chhotanagpur Gneissic complex up to the southern fringe of the Shillong plateau (Radhakrishna

34

and Naqvi 1986, Acharyya 2001, Roy and Prasad 2003) (Fig. 1: inset). It has recently been

35

proposed that two major cratonic blocks of the Indian landmass, i.e. the North Indian Block

36

comprising the Bundelkhand nucleus and the South Indian Block comprising a combined Bastar-

37

Singhbhum-Dharwar nucleus, were stitched together along the CITZ during Neoproterozoic

38

(~1.0 Ga), more or less coinciding with the building of supercontinent Rodinia through a global

39

Grenvillian orogenic event (Bhowmik et al. 2012 and references therein). Alternatively, Mohanty

40

(2010) argued that the major tectonic activity along the CITZ predates the Grenvillian orogeny

41

and should be correlated with the Paleoproterozoic (~1.8 Ga) Capricorn orogeny of Western

42

Australia. Geologically, CITZ comprises a vast country of unclassified Precambrian gneisses

43

within which three major supracrustal belts viz. the Mahakoshal, Betul and Sausar belts occur

44

from north to south (Fig. 1). CITZ is also marked by a number of E-W trending tectonic

45

lineaments e.g. Son-Narmada North Fault (SNNF), Son-Narmada South Fault (SNSF),

46

Gavilgarh-Tan Shear Zone (GTSZ) and Central Indian Shear (CIS) that delimit these

47

supracrustal belts (Fig. 1). Most of these lineaments are major terrain-bounding shear zones of

48

Precambrian ancestry but have since been reactivated repeatedly as brittle faults, and have

49

caused many earthquakes in this relatively stable continental region (Acharyya and Roy 2000,

50

Roy and Devarajan 2003, Chattopadhyay et al. 2008).

51

The Sausar Fold Belt (SFB) is a large (approximately 300 km long and 70 km wide)

52

supracrustal belt near the southern margin of the Central Indian Tectonic Zone (CITZ). SFB 3

53

comprises two major litho-tectonic ensembles viz. the Tirodi Biotite Gneiss (TBG) and the meta-

54

sedimentary Sausar Group (SSG) (Fig. 2). SSG is a typical platformal assemblage of quartzite,

55

pelite and carbonates with Mn-oxide ore horizons, metamorphosed from greenschist to upper

56

amphibolite facies (Bhowmik et al. 1999). TBG, on the other hand, is an ensemble of different

57

types of gneissic and plutonic igneous rocks (e.g. biotite-plagioclase gneiss, tonalite-

58

granodiorite-granite gneiss) with enclaves of meta-dolerite and mafic/felsic granulites (Bhowmik

59

et al. 1999, Chattopadhyay et al. 2001). The mafic granulites and high-grade felsic gneisses

60

occur along the northern margin of SFB, and constitute the Ramakona-Katangi Granulite (RKG)

61

belt. The RKG belt effectively marks the northern limit of SFB, which is separated from the

62

Betul supracrustal belt lying farther north, by the Gavilgarh-Tan shear zone (GTSZ) (Fig. 1),

63

marked as a zone of transpression and oblique collision (Chattopadhyay and Khasdeo 2011). The

64

southern margin of SFB exposes high-temperature meta-igneous granulites of the Balaghat-

65

Bhandara Granulite (BBG) belt which is separated from the adjacent Sakoli Fold Belt by the

66

Central Indian Shear (CIS) zone that also marks the southern boundary of CITZ (Roy and Prasad

67

2003, Bhandari et al. 2011) (Fig. 1). The central part of SFB is dominated by the metamorphosed

68

sedimentary rocks of Sausar Group (SSG), mainly represented by calc-silicate gneisses, calcitic

69

and dolomitic marble, garnet-staurolite-muscovite-(±fibrolite)-quartz schist and quartzite with

70

Mn-ore bearing gondite horizons (Fig. 3). SSG records evidences of polyphase deformation and

71

metamorphism during Sausar orogeny (Chattopadhyay et al. 2003 a, b). Within the SSG, two

72

phases of felsic plutonism – one early (syntectonic with Sausar deformation) and another post-

73

tectonic phase, have been identified (Pal and Bhowmik 1998, Chattopadhyay et al. 2003b). Time

74

of emplacement of these granites is important as these rocks have clear structural relationship

4

75

with the different deformation phases of SSG and therefore can bracket the timing of tectonic

76

deformation of the Sausar Group of rocks.

77

In the present contribution we describe the spatial distribution of these granitic rocks

78

within the deformed Sausar Group, their structural relationship and tectonic setting. We have

79

attempted to determine the ages of these granites through monazite chemical dating to constrain

80

the timing of the deformation of the Sausar Group, which is not clearly known so far. The

81

tectonic implications of the results and their significance in the context of presently available

82

geochronological data of the Sausar belt are discussed.

83 84

2. Previous geochronological study in the Sausar Fold Belt:

85 86

The Sausar Group (SSG) is known to contain only metasedimentary rocks without any syn-

87

depositional volcanic component (Narayanaswami et al. 1963, Pal and Bhowmik 1998,

88

Chattopadhyay et al. 2001), and has never been dated directly, possibly due the lack of suitable

89

material for geochronological study. Sarkar et al. (1986) reported an Rb-Sr whole rock age of

90

1525 ± 70 Ma and a biotite mineral-whole rock isochron age of ca. 860 Ma from Tirodi Biotite

91

Gneiss. The former age was interpreted by the authors as the timing of main amphibolite facies

92

metamorphism of SSG leading to the partial melting of basal psammo-pelitic units that generated

93

TBG. The latter age was attributed to a terminal thermal overprint on the Sausar rocks. Lippolt

94

and Hautmann (1994) reported an

95

manganese mines, and interpreted it as the age of cooling through the cryptomelane closure

96

temperature following the Satpura (≡ Sausar) orogeny. Recently, SHRIMP U-Pb zircon dating of

97

Tirodi biotite Gneiss from northern part of the RKG belt has assigned an age of 1618±8 Ma to

40

Ar/39Ar age of 950 Ma from cryptomelane in Sitapar

5

98

the time of magmatic crystallization of TBG protolith derived from a Paleoproterozoic source of

99

dominantly juvenile material with minor crustal components (Bhowmik et al. 2011). In this

100

northern domain, tourmaline-bearing granites intruding the TBG recorded an Rb-Sr whole rock

101

isochron age of 1147±16 Ma (Pandey et al. 1998). Roy et al. (2006) conducted Rb-Sr and Sm-Nd

102

dating of different tectonothermal events of Sausar Belt and proposed that the northern domain

103

(i.e. RKG belt) experienced peak granulite metamorphism prior to 1100 Ma, followed by

104

decompression and cooling at ca. 1100 Ma as reflected in the Sm-Nd age of coronal garnets in

105

metadolerites of this belt. Mafic granulites of the BBG belt, on the other hand, experienced peak

106

metamorphism at ca. 2672 Ma (Sm-Nd WR and mineral separate isochron in Charnockite), and a

107

subsequent cooling around 1400 Ma (mafic granulite and its mineral separate isochron). This

108

indicated a much older age of the BBG belt, which was possibly later juxtaposed with Sausar

109

belt around 1100 Ma. Both the RKG and BBG rocks, however, showed a consistent 800-900 Ma

110

Rb-Sr age which was interpreted as the effect of amphibolite facies Sausar orogenic event over

111

the pre-existing granulites that re-set the Rb-Sr isotopic clock. Mohanty (2010), however, re-

112

interpreted all the geological and geochronological data of the earlier workers to suggest that: (i)

113

the earliest deformation and metamorphism of Sausar Group occurred at 1900-1800 Ma, (ii) the

114

second major tectonothermal event, leading to the present E-W ‘Satpura trend’ in this belt,

115

occurred at 1500- 1400 Ma, and (iii) the 1000-900 Ma ‘Grenvillian’ event reported by some

116

earlier workers were only minor thermal overprints on the Sausar rocks. He thus concluded that

117

tectonic activity of the Sausar (or Satpura) mobile belt can be correlated with Paleoproterozoic

118

Capricorn orogeny of Western Australia, and not with the ~1000 Ma Grenvillian orogeny as

119

suggested by Bhowmik et al. (1999) and Roy et al. (2006). Recently, Bhowmik et al. (2012) have

120

dated different rocks from Northern (RKG) and central (SSG) domains using monazite. In

6

121

garnet-cordierite migmatite of the RKG domain, monazite grain cores have yielded weighted

122

mean ages of 1043±18 Ma while the rims show 955±11 Ma, which was interpreted as age of

123

peak granulite metamorphism and subsequent decompression respectively. Charnockite

124

emplaced during post-peak decompression recorded SHRIMP U-Pb mean age of 938±3 Ma.

125

Garnet-staurolite-kyanite schist and garnet-biotite-muscovite-quartz schist from eastern part of

126

the central domain showed mean monazite ages of 1062±13 and 993±19 Ma, tentatively

127

correlated with peak and retrograde metamorphism of Sausar Group rocks. On the basis of this,

128

Bhowmik et al. (2012) concluded that the amphibolite facies metamorphism of Sausar Group

129

occurred almost concurrently with peak granulite metamorphism of the RKG belt, representing

130

different crustal sections. This tectonic model doesn’t account for the earlier field observation

131

that a strong amphibolite facies ‘Sausar fabric’ was overprinted on the major granulitic fabric in

132

the RKG domain (Bhowmik et al. 1999). It also fails to explain a consistent 800-900 Ma Rb-Sr

133

reset age from all the rocks of RKG belt interpreted as the ‘Sausar imprint’ by Roy et al. (2006).

134

From petrologic evidences, Bhowmik and Roy (2003) suggested that after the peak granulite

135

metamorphism in RKG belt, the hydrous Sausar Group sediments were underthrusted below the

136

hot granulites which led to metamorphism of the Sausar Group and widespread retrogression of

137

the granulites. The nearly coincident monazite ages of peak metamorphism of SSG and RKG

138

reported by Bhowmik et al. (2012) contradicts this model.

139

In light of the above discussion on existing geochronological data of SFB, the timing of the

140

syn- and post-tectonic granites intrusive into Sausar Group sediments become very significant as

141

they can directly and tightly bracket the age of Sausar deformation events which have mostly

142

been judged indirectly from the age of the granulite metamorphism of RKG belt.

143

7

144

3. Structural character of the Sausar Group rocks and the granites:

145 146

Metasedimentary rocks of the Sausar Group and the underlying basement rocks (TBG)

147

show evidences of polyphase deformation. The first deformation manifested in large-scale

148

thrusting and associated recumbent/reclined folding (F1) along the northern margin of the SFB

149

(Fig. 4a). This involved southward transport of allochthonous basement slices over the SSG

150

rocks and their subsequent folding, leading to a large nappe-like structure, best demonstrated in

151

the Deolapar-Manegaon area (Deolapar Nappe: West 1936, Chattopadhyay et al. 2003a) (Fig.

152

3).These thrust planes and the early reclined folds were refolded into E-W trending, upright to

153

steeply northerly inclined, large-scale folds (F2) that define the present map pattern of the SFB

154

(Chattopadhyay et al. 2001, 2003a). The basement rocks (TBG) were often co-deformed with the

155

SSG and show strong nearly co-axial F1/F2 folding near the basement-cover boundary (Fig. 4b).

156

A set of small scale F3 folds was identified in Ramtek area which distorts the F2 fold-axis and

157

associated stretching lineations. Finally outcrop-scale, N-S trending, open folds (F4) overprinted

158

the earlier structures (Chattopadhyay et al. 2003b). As mentioned earlier, Sausar Group rocks

159

underwent Barrovian-type metamorphism varying from lower greenschist in the south and

160

southeast to upper amphibolite facies in the north and northwest. A clockwise P-T trajectory was

161

suggested for the metamorphism of Sausar Group, with peak metamorphism occurring at ~7

162

Kbar and ~ 675°C, followed by rapid decompression and cooling. Overall, four metamorphic

163

events were identified from SSG rocks (Bhowmik et al. 1999). However, different deformation

164

and metamorphic events were not correlated precisely. Study of porphyroblast-matrix

165

relationship in garnet and staurolite bearing mica-schist of Ramtek-Mansar area identified two

166

stages of garnet porphyroblast growth: first post-D1 (but pre-D2), and then syn-D2, while

8

167

staurolite grew only syn-D2 (Chattopadhyay and Ghosh 2007). This led to the conclusion that

168

peak metamorphism (amphibolite facies) in these rocks coincided with the D2 deformation and

169

F2 folding. In the northern part of SFB, near Deolapar, the peak metamorphic assemblage of

170

clinopyroxene-plagioclase±scapolite in calc-silicate gneisses occur along the S2 cleavage axial

171

planar to F2 folds (Khan et al. 2002, Chattopadhyay et al. 2003a).

172

Two distinct types of granites have intruded the metasedimentary rocks (SSG) within the

173

type SFB: foliated and massive (non-foliated) types. Foliated granites are exposed at a number of

174

locations in SFB, e.g. north of Deolapar, east of Karwahi, south of Chorbaoli, near Mansar

175

(Kandri manganese mines) and in Satak mines (Fig. 3). In Mansar-Kandri mines area near

176

Waitola village, pink colored foliated granites intrude the mica-schist and gondite horizons and

177

show a moderate to strong subvertical foliation parallel to the S2 foliation in the host mica-schist

178

(Fig. 4c). Intrusion of granite along the S2 foliation in host rock, and their deformation producing

179

parallel fabrics in mica-schist and granite possibly indicates early syn-D2 granite intrusion into

180

SSG. Under microscope, the foliated granites show an assemblage of quartz, K-feldspar,

181

plagioclase and biotite, with minor muscovite and iron oxides. Quartz grains with undulose

182

extinction, cross-hatched twinning in K-feldspar (microcline), and perthitic intergrowths in alkali

183

feldspar are common. Quartz grains show well developed deformation bands indicating

184

significant strain, and grain boundary migration of less deformed grains into the more deformed

185

ones (Fig. 4d: near black arrow). These microstructures indicate high-temperature (≥ 450°C)

186

deformation of the granitic rocks (e.g. Stipp et al. 2002), possibly in the amphibolite grade

187

similar to the host rocks, as mentioned above. A crude foliation, defined by elongate, deformed

188

quartz grains is observed. Foliation is not as distinct in the thin section as in the field outcrop,

189

possibly because we consciously collected samples from relatively less foliated parts of the

9

190

granite exposure to minimize the effects of weathering and alteration along the foliation. The

191

massive granites typically occur in and around Maudi-Dahoda, around Tangla and near Alesur

192

(Fig. 3). These granites do not show any foliation or any deformation, despite being surrounded

193

on all sides by intensely deformed rocks (mainly calc-silicate gneiss and dolomitic marble) of

194

SSG. Moreover, they often contain xenoliths of biotite gneiss (TBG) (near Maudi) and angular

195

rafts of calc-silicate gneiss (near Tangla) (Fig. 4e), indicating their post-tectonic intrusive

196

character (Khan et al. 2002). Microstructurally, the massive granites represent an interlocking

197

texture comprising subhedral grains of quartz, K-feldspar, plagioclase and biotite, along with

198

small amount of chlorite and epidote (Fig. 4f). Foliation is not observed at either thin section

199

scale or in the outcrops.

200

4. Analytical methodology:

201

Geochemical analyses of the granite samples were carried out by X-ray fluorescence (XRF)

202

techniques using a Rigaku ZSX system at Hiroshima University, Japan. X-rays generated by an

203

Rh-W dual anode tube were radiated on fused bead samples. LOI are calculated after baking the

204

powdered sample successively at 120°C for 24 hours and 900°C for 6 hours. The analytical

205

precision (1σ) of major elements measured in XRF ranges between 0.001 and 0.14 wt%, while

206

that for minor elements ranges between 0.68 to 2.39 ppm. LA-ICPMS analysis (using 213 nm

207

Nd-YAG Laser (New Wave ResearchUP-213) coupled with Agilent 7500 ICP-MS at the

208

Department of Earth and Planetary Systems Science, Hiroshima University) was carried out on

209

glass of the same powdered samples for trace elements and rare-earth element concentrations.

210

NIST610 glass using same ratio of sample and flux was also measured as standard sample before

211

and after of each unknown analysis. Blank glass is also measured for REE-content (though very

212

low) correction. The error limits for REE range between 2 and 5%. 10

213

Monazite grains were selected through a detailed study of scanning electron microscope and

214

targeted grains were imaged in SEM-BSE mode with a JEOL JSM-6390A equipped with a JED-

215

2300 energy dispersive system at the Hiroshima University. The operating voltage was 15kV

216

with variable spot sizes. Monazite grains were analyzed for rare earth element concentrations and

217

U-Th-total Pb concentrations with the JEOL JXA 8200 Superprobe at the Natural Science Center

218

for Basic Research and Development (N-BARD), Hiroshima University. The operating

219

conditions were 15 kV accelerating voltage, 200 nA beam current, and 4 to 5 µm beam diameter.

220

The following 16 lines Al-Kα, Si-Kα, P-Kα, S-Kα, Ca-Kα, Y-Lα, La-Lα, Ce-Lα, Pr-Lβ, Nd-Lβ,

221

Sm-Mβ, Gd-Mβ, Dy-Mβ, Pb-Mβ, Th-Mα and U-Mβ were measured, and then recalculated as

222

oxide by ZAF correction. The measurements of Pb-Mβ were carried out with a high-sensitive

223

detector (R = 100 mm). The interferences of Th-Mγ on U-Mβ and U-Mζ on Pb-Mβ were

224

corrected. Correction for Nd-Lβ1 due to Ce-Lβ2 was also employed. Standard materials were

225

ThO2 compound silicate glass and natural thorianite for Th, U3O8 compound silicate glass and

226

natural uraninite for U and Pb–Te for Pb. The peak intensities of Th, U, and Pb were integrated

227

for 60, 120, and 440 s, respectively. The detection limit of Pb at the 2s confidence level is of the

228

order of 45 ppm, and the measurement errors of PbO are 55 ppm for 0.05wt% level, and 66 ppm

229

for 0.5 wt% level, respectively. Details of the followed procedures are described in Fujii et al.

230

(2008). The basic principle of age dating using the U-Th-total Pb CHIME technique was

231

developed by Suzuki and Adachi (1991). However, age calculation in the present study is carried

232

out by employing the improved method of Cocherie and Albarede (2001) and plotted with

233

Isoplot/Ex version 3.7 (Ludwig 2008). The consistency of age data was checked using a standard

234

monazite of 1033 Ma (Hokada and Motoyoshi 2006).

235 11

236

5. Geochemical character of the granites:

237

Four representative samples of granitic rocks of SFB were analyzed for bulk

238

geochemistry prior to the monazite dating work described in detail in the next section. These

239

included one sample of foliated granite (SFB1205) collected from Waitola, one sample of Tirodi

240

Biotite Gneiss (SFB 1204) collected in the north of Chorbaoli, and two samples of massive

241

granite (SFB 1207 and SFB 1209) collected near Maudi and from the west of Tangla,

242

respectively (Fig. 3). Detailed location and modal mineralogy of the samples are shown in Table

243

1. We have analyzed these four representative samples to ascertain their major element, trace

244

element and REE chemistry. The major element, trace element and REE data of the studied

245

samples are given in Table 2.

246

The chemical data of the granitic and gneissic rocks are plotted in different variation

247

diagrams to analyze their broad geochemical character. The modal quartz, alkali feldspar and

248

plagioclase volume percentage, measured from thin sections, when plotted on a QAP diagram of

249

IUGS classification, shows that TBG (SFB 1204) and one of the massive granites (SFB 1209)

250

fall in the granodiorite field, whereas the other massive granite (SFB 1207) comes under the

251

monzogranite field. The pinkish colored foliated granite (SFB 1205) shows lower modal quartz

252

and falls marginally in the quartz-monzonite field (Fig. 5a). Shand’s Index plot of

253

Al2O3/(Na2O+K2O) vs. Al2O3/(CaO+Na2O+K2O) (e.g. Maniar and Piccoli 1989) shows that all

254

the studied rocks (granites and TBG) have a peraluminous character (Fig. 5b). Primitive mantle-

255

normalized trace element spiderplot shows LILE-enriched patterns of all the samples with

256

characteristic enrichment of Rb and Th, and depletion of Ba and Ti (Fig. 5c). The foliated granite

257

with quartz monzonite character, i.e. SFB1205 stands out with its higher content of Nb, Ta, and

258

strong depletion of Sr, P and Eu, while one of the massive granites (SFB1207) shows variable

12

259

depletion of Ba, Sr, Zr and Ti. Mantle-normalized REE plot also shows a LREE-enriched pattern

260

(Fig. 5d) with differential Eu negative anomaly (Eu/Eu* ranges between 0.04 and 0.66).

261

However, the foliated granite (SFB 1205) also shows a characteristic profile than others with

262

strongest Eu-anomaly (Eu/Eu* = 0.04) and overall HREE enrichment than other samples.

263 264

6. Monazite chemical dating of granites:

265

Three samples namely, SFB1202 (foliated granite, same as SFB 1205 described in the

266

above section), SFB1204 (Tirodi biotite gneiss) and SFB1207 (massive post-tectonic granite)

267

were selected for monazite U-Th-total Pb analysis to calculate their ages and chemical

268

characteristics, as described below.

269

In the foliated variety, i.e. SFB1202, monazite grains are of different size and shape.

270

Majority of the grains are subhedral and equant shaped with complex internal zoning (Fig. 6a).

271

The size ranges between 10 and 40 µm. A few grains are elongate tabular shaped and euhedral in

272

nature. Such grains are 5-7 µm wide but 30-40 µm long. Some grains are having numerous

273

inclusions at their interior as well as at the rim. Selected points (31 in total) from 11 grains are

274

analyzed for REE and U-Th-total Pb. Careful selection is made based on SEM-BSE images

275

covering all the zoned parts, and also both core and rim parts. Strong zoning though are present

276

in terms of Th-content in some grains (ThO2 ranging between 4.6 wt% to 12.3 wt% in same

277

grain). The chondrite-normalized LREE-MREE pattern shows strong enrichment of LREE with

278

respect to the MREE (Fig. 6b). Irrespective of such chemical variability, all the analyzed points

279

in all the grains except one grain (grain 2) yield strong age probability peak at ~950 Ma (Fig. 6c).

280

The point age data ranges from 914 ± 29 Ma to 982 ± 41 Ma (errors in 2σ). The weighted mean

281

age of this pool of data yields an age value of 944 ± 5 Ma (95% confidence, MSWD = 1.4) (Fig.

13

282

6d). It is noteworthy that this strong probability peak seems to be a doublet, and unmixing this

283

peak yields two closely spaced peaks at 935 ± 9 Ma and 949 ± 6 Ma. On the other hand, Grain 2

284

yields quite older age, as two points on this grain estimate age values of 1338 ±28 Ma (near-rim)

285

and 1609 ±32 Ma (near core).

286

Tirodi biotite gneiss (sample SFB 1204) has sizable monazite grains in quartzo-

287

feldspathic part as well as in close association with biotite-rich zones. The grains are anhedral to

288

subhedral in shape, and their size ranges between 30 µm and 100 µm. The larger grains have

289

complex internal zoning in SEM-BSI (Fig. 7a). The chondrite-normalized LREE-MREE patterns

290

show very similar LREE-enrichment with slightly more depletion of MREE than SFB1202 (Fig.

291

7b). Eight analyzed grains (44 points in total), yield a single strong peak at ~950 Ma (Fig. 7c).

292

The data range between 897 ±38 Ma and 978 ±33 Ma (errors in 2σ). The weighted average for

293

all the data is estimated to be 948 ±4 Ma (95% of confidence, MSWD = 1.11) (Fig 7d).

294

Statistically though all the data are plotted as showing one broad peak, the probability curve

295

shows a broad shoulder on the younger age side due to the fact that some of the larger grains

296

have younger age data at the rim (ranging between 897 ±38 Ma and 931 ±34 Ma).

297

On the other hand, the massive post-tectonic granite (sample SFB1207, garnet

298

porphyroblast/megacryst-bearing) contains monazite grains of different size and shape. Grain

299

shape varies from subhedral to anhedral, while grain sizes vary from few µm to nearly 100 µm.

300

Some of the larger grains have complex internal zoning in SEM-BSI (Fig. 8a) and also core-rim

301

structure (Fig. 8a). 36 data points from 7 monazite grains of different size, shape and

302

mineralogical associations are analyzed, where points are selected covering all the visible zones,

303

core and rim of the grains. The REE content of the analyzed data plots again show a LREE-

304

enriched pattern but more variation on MREE spectra (Fig. 8b). It is noteworthy that this is the

14

305

only sample that contains garnet porphyroblasts and a potential sink for MREE to HREE. The

306

calculated age data are plotted on probability density diagram, which yields a major peak at ~930

307

Ma and a minor peak at ~ 780 Ma (Fig. 8c). All the data forming the major peak is calculated for

308

weighted average age, which yields a mean age of 928 ±4 Ma (2σ, 95% confidence) after 2 data

309

rejections (Fig. 8d). However, the pool of data forming this major peak can possibly be a mixture

310

of two peaks, i.e. at 936 ±5 Ma and 917 ±7 Ma. Some of the grains have thin rims (sometimes

311

along resorbed grain boundaries). One such grain yields younger age of 785 ±15 Ma of spot age

312

on the rim.

313 314

7. Tectonic interpretation of age data:

315

Looking at the monazite data and the field observations, the following tectonic interpretation

316

of the age data is presented. The foliated granite (SFB 1202) possibly intruded the Sausar Group

317

sediments along the F2 foliations (early syn-D2 intrusion?), and was deformed during the regional

318

D2 deformation of SSG at ca. 945 Ma. The TBG (SFB 1204), which formed the basement to the

319

SSG, also underwent D2 deformation and metamorphism at ca. 945 Ma along with the foliated

320

granites and the Sausar Group, considering that the mean age found from the foliated granite and

321

TBG samples are almost same within error limits. It also indicates that any older age of the

322

basement TBG is not reflected in the monazite grains as all monazite grains grew with the S2

323

foliation in the granite. Optical microscopy also shows that majority of the monazite grains are in

324

close association with the foliation-forming biotite grains (Fig. 9). In some cases the grains are

325

slightly elongated and direction of elongation is crudely parallel to the foliation. From Ramtek

326

area, very close to the present sample sites, Chattopadhyay and Ghosh (2007) interpreted that

327

Sausar D2 fabric records the peak metamorphism (in garnet-staurolite-muscovite schist). It has

15

328

also been observed from many parts of Sausar Belt that the TBG has been co-deformed with

329

SSG during D1 and D2 deformation (Khan et al. 2002). The foliated granite also shows the

330

strongest foliation parallel to S2 in SSG in the sampling area. All these indicate that ~945 Ma is

331

the possible age of D2 deformation and peak metamorphism (≡ M2 of Pal and Bhowmik 1998) of

332

the Sausar Group. The single older (ca. 1300-1600 Ma) grain found in SFB 1202 might be

333

inherited from its protolith. It is noteworthy here that inheritance of monazite in a granitic melt

334

depends on the LREE content of the protolith and the degree of heating suffered by it (Kelsey et

335

al. 2008) while producing granitic melt, as discussed in the next section.

336

The D2 deformation and metamorphism of Sausar Group was followed by another (ca.

337

928±4Ma) event of granite magmatism represented by the massive granites (SFB 1207) with

338

weak thermal effect on pre-existing rocks (e.g. the younger rim ages of monazite: ca. 897 ±38

339

Ma and 931 ±34 Ma, in SFB 1204 and SFB1202 as mentioned above). The massive granites

340

(SFB 1207 and 1209) post-date Sausar orogenic deformation, and do not record any foliation-

341

forming event, although at a very few places, a weak foliation has been observed in the

342

peripheral parts of the massive granite bodies, indicating terminal tectonic effect (Khan et al.

343

2002). The 785±15 Ma age from monazite rims and resorbed grain boundaries of some monazite

344

grains of the massive granite (SFB 1207) possibly represents a late thermal overprint on these

345

rocks. Presently it doesn’t coincide with any known tectonothermal event in this area.

346 347

8. Discussion:

348 349

The geochemical data of the studied rocks suggest that they are peraluminous

350

granodiorite to monzonite in nature. They all show LILE- and LREE enrichment with negative

16

351

Eu anomaly. Such fractionated character (with possible crustal contamination) is typical of

352

continental granites, and also matches with the suggested continental collision set-up for the

353

high-pressure granulites (RKG belt) along the northern margin of the Sausar Fold belt (e.g.

354

Bhowmik et al. 1999). However, the monazite age data presented here throws new light on the

355

possible ages of deformation and metamorphism of the Sausar Group, and opens up some

356

questions regarding the earlier proposed collisional tectonic model. Roy et al. (2006) reported a

357

number of Rb-Sr ages in the range of 800-900 Ma from different granulitic rocks of RKG and

358

BBG belt and interpreted this age range as the timing of Sausar metamorphism. Later work

359

(Bhowmik et al. 2012) argued against this interpretation and suggested that the Sausar Group

360

was metamorphosed between 1062 Ma and 940 Ma. They correlated the peak metamorphism of

361

Sausar Group with that of RKG granulites at ca. 1043 Ma. However, two samples of Sausar

362

Group meta-sediments from Tumsar and Balaghat yielded widely different monazite ages of

363

1062±13 Ma and 993±19 Ma (Bhowmik et al. 2012). These two samples yielded only single

364

monazite age, and the younger age was interpreted by the authors as the result of monazite

365

growing with a post-peak decompression event. Interestingly, the most well constrained core-rim

366

age of monazite from RKG belt (e.g. sample R23B) reported by Bhowmik et al. (2012) showed a

367

retrogression age of ca. 955 Ma. Our work correlates the deformation phases in syn-tectonic

368

granites and the host rocks (SSG) from the central part of Sausar Belt (near Mansar-Kandri) and

369

suggests that the peak metamorphism and deformation of Sausar Group (D2/M2) took place

370

around 945 Ma (i.e. during the retrogression of the RKG granulites). This interpretation assigns a

371

younger age for peak metamorphism and deformation of the Sausar Group than that of the RKG

372

granulites, and therefore does not agree with simultaneous deformation and metamorphism of

373

SSG-RKG rocks as was tentatively suggested by Bhowmik et al. (2012). On the other hand, the

17

374

present age data indirectly corroborates the earlier interpretation of Bhowmik and Roy (2003)

375

that metamorphism of Sausar Group rocks, placed in an underthrusted pile below the RKG rocks,

376

resulted in devolatilization of Sausar sediments and led to the decompression and retrograde

377

metamorphism of overlying RKG mafic granulites. This may also explain the imprint of a

378

younger amphibolite facies fabric over the granulite fabric in mafic granulites, earlier reported by

379

Bhowmik et al. (1999) and Roy et al. (2006) from the field. Bhowmik and Roy (2003) also

380

suggested a small post-peak heating of the mafic granulites, possibly because of the heat

381

received from syn-tectonic granitoids. The ca. 945 Ma age of the syn-tectonic foliated granite

382

presented here temporally broadly coincide with the retrogression of RKG granulites and

383

therefore supports this assumption. The age of post tectonic granites (ca. 928 Ma) is the first age

384

data of the massive granites from Sausar Belt, and indicates that all major tectonothermal events

385

of the SFB were over by this time.

386

It is now known that during cooling of a granitic melt different proportion of monazite

387

may form at different stages of cooling (Kelsey et al., 2008). Hence, age data spread in monazite

388

forming a broad probability peak should be a natural consequence of differential growth at

389

different stages of cooling. However, a new probability peak at ca. 928 Ma and absence of

390

deformation fabric help to separate this temporally close but a new granitic magmatism at ca.

391

928 Ma. Furthermore, resorbed grain boundaries of some of the monazite grains and much

392

younger age of 785±15 Ma found in such monazite rims seem to indicate an age of monazite

393

dissolution and re-precipitation during a later thermal pulse. It is noteworthy that this youngest

394

age is something new for the Sausar belt, as no major tectonothermal event of such young age

395

has been reported till date from this area. However several ca. 800-900 Ma age Rb-Sr ages have

396

been reported from Sausar belt by earlier workers (e.g. Sarkar et al. 1986, Roy et al. 2006), as

18

397

discussed in section 2 above. For example, garnetiferous metadolerites from the RKG belt were

398

reported to yield an Rb-Sr age of ca. 834±21 Ma (Roy et al. 2006). This ca. 800 Ma age was

399

interpreted as the age of Sausar metamorphism by the authors. However, in light of the present

400

age data, this must be reinterpreted as a later thermal overprint post-dating the Sausar

401

deformation and metamorphism. Broadly, the present age data shows that the tectonothermal

402

history of the Sausar Group and adjacent high-grade rocks temporally correspond to the global

403

Grenvillian orogenic event, and do not match the age of Capricorn Orogen as suggested by

404

Mohanty (2010). It is noteworthy here that the chemically distinct foliated granite has some

405

monazite grains of older age, and we consider them as inherited age from the protoliths of this

406

granite.

407

On a larger perspective, this new set of data of tectonothermal events and granite

408

magmatism in the Sausar Fold Belt between ca. 950 Ma to ca. 800 Ma needs some special

409

attention in terms of the reported ages of similar deep crustal events from other parts of India.

410

The ca. 950 Ma age is considered to be an age of superposed metamorphism and deformation on

411

ca. 1000 Ma UHT granulites in the central part of the Eastern Ghats Belt (EGB) (Das et al. 2011,

412

Bose et al. 2011), possibly due to the Rayner orogenic pulse that primarily affected neighboring

413

east Antarctica in the ‘Rodinia’ supercontinent (Kelly et al. 2002, Harley 2003, Halpin et al.

414

2005, 2007). The present data suggest that the peak metamorphism and deformation in the

415

Sausar Group (D2/M2) is coeval with the orogenic pulse affecting deep crust of EGB, India and

416

Rayner complex, Antarctica. Although the ca. 930 Ma age of post-tectonic massive granite from

417

the present study indicate the end of major tectonic pulses in this cratonic interior part of India,

418

the central EGB and Rayner complex were tectonically active till ca. 900 Ma (Das et al., 2011;

419

Dasgupta et al., 2013). Though the present database imply a minor peak at ca. 800 Ma possibly

19

420

representing an event of thermal perturbation, regionally this age is not that uncommon.

421

Intriguingly it represents different events at different parts. Chatterjee et al. (2010) defined an N-

422

S trending tectonic zone, namely East Indian Tectonic Zone (EITZ) on the eastern boundary of

423

Chhotanagpur gneissic complex and North Singhbhum Mobile Belt of comparable age. This

424

zone seems to have its southward extension beyond Indian craton to the submarine Kerguelen

425

Plateau (Chatterjee and Nicolaysen 2012). Though this inter-continental zone primarily

426

represents deep crustal deformation zone in India, the northern EGB represented by Chilka Lake

427

granulites record a major deep-crustal metamorphism around ca. 785 Ma (Bose et al. 2008).

428

Similarly, the marginal granulite belt in the southern part of West Dharwar Craton also had

429

suffered a deep crustal metamorphism at ca. 800 Ma (Das et al. 2013). Though the exact nature

430

of this ca. 800 Ma event is not yet clear but it seems to be increasingly clear that this represents a

431

major event of tectonic to tectono-metamorphic pulse at the margins of erstwhile Indian cratonic

432

blocks from south to central portion, and to the east.

433 434

9. Conclusions:

435 436

1) Monazite chemical dating of foliated and massive granites from Sausar Fold Belt, central

437

India, yield Neoproterozoic ages which can be interpreted as the timing of regional

438

metamorphism and deformation. The foliated granite and the Tirodi Biotite Gneiss show

439

monazite grains of ca. 945 Ma age which is interpreted as the timing of D2 deformation and

440

accompanying peak amphibolite facies metamorphism of SSG. The massive granites represent

441

post-tectonic intrusion at ca. 928 Ma.

20

442

2) A late thermal imprint is identified in the monazite rims at ca. 785 Ma. This might be the

443

same thermal event (ca. 800 Ma) that was earlier interpreted as the main Sausar metamorphic

444

event by Roy et al. (2006).

445

3) The peak tectonothermal event affecting SSG (ca. 950 Ma) are younger than that in the

446

RKG granulites (ca. 1043 Ma), and in fact temporally coincides with the decompression and

447

retrogression of these granulites (ca. 955 Ma). Therefore the Sausar S2 foliations overprint the

448

pre-Sausar granulite fabric in these rocks as observed in the field by many earlier workers.

449 450

Acknowledgement:

451

This work was partly funded by the University Grants Commission (UGC) (grant no.

452

F.42-66/2013(SR)-HRP) and by the University of Delhi R&D grant (grant no. Dean

453

(R)/R&D/2012/917) to AC. Department of Geology provided the necessary microscopic facility.

454

We are thankful to Prof. M. Santosh for his comments and editorial handling. Critical comments

455

and suggestions of two anonymous reviewers were extremely helpful for revising the manuscript.

456

21

457

References:

458

Acharyya, S.K., 2001. Geodynamic setting of the Central Indian Tectonic Zone in central,

459 460 461

eastern and northeastern India. Geol. Surv. India Spl. Pub. 64, 17–35. Acharyya, S.K., Roy, A., 2000. Tectonothermal history of the Central Indian Tectonic Zone and reactivation of major faults/shear zones. J. Geol. Soc. India 55, 239 –256.

462

Bhandari, A., Pant, N.C., Bhowmik, S.K., Goswami, S., 2011. 1.6 Ga ultrahigh-temperature

463

granulite metamorphism in the Central Indian Tectonic Zone: insights from metamorphic

464

reaction history, geothermobarometry and monazite chemical ages. Geol. J. 46, 198–216.

465

Bhowmik, S.K., Pal, T., Roy, A., Pant, N.C., 1999. Evidence for Pre-Grenvillian high-pressure

466

granulite metamorphism from the northern margin of the Sausar mobile belt in central India.

467

J. Geol. Soc. India 53, 385–399.

468

Bhowmik, S.K., Roy, A., 2003. Garnetiferous metabasites from the Sausar Mobile Belt:

469

petrology, P-T path and implications for the tectonothermal evolution of the Central Indian

470

Tectonic Zone. J. Petrol. 44, 387–420.

471

Bhowmik, S.K., Wilde S.A., Bhandari, A., 2011. Zircon U-Pb/Lu-Hf and monazite chemical

472

dating of the Tirodi biotite gneiss: implication for latest Palaeoproterozoic to Early

473

Mesoproterozoic orogenesis in the Central Indian Tectonic Zone. Geol. J. 46, 574–596.

474

Bhowmik, S.K., Wilde S.A., Bhandari, A., Pal T., Pant N.C., 2012. Growth of the Greater Indian

475

Landmass and its assembly in Rodinia: geochronological evidence from the Central Indian

476

Tectonic Zone. Gond. Res. 22, 54–72.

477

Bose, S., Dunkley, D.J., Arima, M., 2008. Zircon U–Pb SHRIMP ages from Eastern Ghats Belt,

478

India and their implication in the Indo-Antarctic correlation. In: AGU Fall Meeting, San

479

Francisco, USA, Abstract Vol. 2159. 22

480

Bose, S., Dunkley, D.J., Dasgupta, S., Das, K., Arima, M., 2011. India–Antarctica–Australia–

481

Laurentia connection in the Paleoproterozoic–Mesoproterozoic revisited: evidence from new

482

zircon U–Pb and monazite chemical age data from the Eastern Ghats Belt, India. Bull. Geol.

483

Soc. Am. 123, 2031–2049.

484

Boynton, W.V., 1984. Cosmochemistry of the rare earth elements; meteorite studies. In: Rare

485

earth element geochemistry. Henderson, P.(Eds), Elsevier Sci. Publ. Co., Amsterdam, 63-114.

486

Chatterjee, N., Banerjee, M., Bhattacharya, A., Maji, A.K., 2010. Monazite chronology,

487

metamorphism-anatexis and tectonic relevance of the mid-Neoproterozoic Eastern Indian

488

Tectonic Zone. Precam. Res. 179, 99-120.

489

Chatterjee, N., Nicolaysen, K., 2012. An intercontinental correlation of the mid-Neoproterozoic

490

Eastern Indian Tectonic Zone: evidence from the gneissic clasts in Elan Bank conglomerate,

491

Kerguelen Plateau. Contrib. Min. Pet. 163, 789-806.

492

Chattopadhyay, A., Bandyopadhyay, B.K., Khan, A.S., 2001. Geology and structure of the

493

Sausar Fold Belt: a retrospection and some new thoughts. Geol. Surv. India, Spl. Pub. 64,

494

251–263.

495

Chattopadhyay, A., Ghosh, N., 2007. Polyphase deformation and garnet growth in pelitic schists

496

of Sausar Group in Ramtek area, Maharashtra, India: a study of porphyroblast-matrix

497

relationship. J. Earth Syst. Sc. 116, 423-432.

498

Chattopadhyay, A., Huin, A. K., Khan, A. S., 2003a. Structural framework of Deolapar area,

499

central India and its implications for Proterozoic nappe tectonics. Gond. Res. 61, 107-117.

500

Chattopadhyay, A., Khan, A.S., Huin, A.K., Bandyopadhyay, B. K. 2003b. Reinterpretation of

501

stratigraphy and structure of Sausar Group in Ramtek-Mansar-Kandri area, Maharashtra,

502

central India. J. Geol. Soc. India 61, 75-89.

23

503

Chattopadhyay, A., Khasdeo, L., 2011. Structural evolution of Gavilgarh-Tan Shear Zone,

504

central India: A possible case of partitioned transpression during Mesoproterozoic oblique

505

collision within Central Indian Tectonic Zone. Precam. Res. 186, 70-88.

506

Chattopadhyay, A., Khasdeo, L., Holdsworth R. E., Smith S. A. F., 2008. Fault reactivation and

507

pseudotachylite generation in the semi-brittle and brittle regimes: examples from the

508

Gavilgarh–Tan Shear Zone, central India. Geol. Mag. 145, 766-777.

509 510

Cocherie, A., Albarede, F., 2001. An improved U–Th–Pb age calculation for electron microprobe dating of monazite. Geochim. Cosmochim. Acta. 65, 4509–22.

511

Das, K., Bose, S., Karmakar, S., Dunkley, D.J., Dasgupta, S., 2011. Multiple tectono-

512

metamorphic imprints in the lower crust: first evidence of ca. 950Ma (zircon U–Pb SHRIMP)

513

compressional reworking of UHT aluminous granulites from the Eastern Ghats Belt, India.

514

Geol. J. 46, 217–239.

515

Das, K., Kimura, K., Bose, S., Hayasaka, Y, Hidaka, H., 2013. Neoproterozoic reworking of

516

Archean deep continental crust in the Coorg Massif, India: SHRIMP zircon and EMP

517

monazite geochronology and implication on Dharwar craton margin orogenesis during the

518

assembly of Gondwana. Annual Meeting Abstract, Geol. Soc. Japan.

519 520

Dasgupta, S., Bose, S., Das, K., 2013. Tectonic evolution of the Eastern Ghats Belt. Precam. Res. 227, 247-258.

521

Fujii, M., Hayasaka, Y., Terada, K., 2008. SHRIMP zircon and EPMA monazite dating of

522

granitic rocks from the Maizuru terrane, southwest Japan: Correlation with East Asian

523

Paleozoic terranes and geological implications. Island Arc 17, 322-341.

24

524

Halpin, J.A., Gerakiteys, C.L., Clarke, G.L., Belousova, E.A., Griffin, W.L. 2005. In-situ U-Pb

525

geochronology and Hf isotope analyses of the Rayner Complex, east Antarctica. Contrib.

526

Min. Pet. 148, 689-706.

527

Halpin, J.A., White, R. W., Clarke G. L., Kelsey D. E., 2007. The Proterozoic P–T–t evolution of

528

the Kemp Land Coast, East Antarctica; constraints from Si-saturated and Si-undersaturated

529

metapelites. J. Petrol. 48, 1321-1349.

530

Harley, S.L., 2003. Archean-Cambrian crustal development of East Antarctica: metamorphic

531

characteristics and tectonic implications. In: Yoshida, M., Windley, B.F., Dasgupta, S.

532

(eds.) Proterozoic East Gondwana: supercontinent assembly and breakup. Geol. Soc. Lon.

533

Spl. Pub. 206, 203-230.

534

Hokada,T., Motoyoshi, Y., 2006. Electron microprobe technique for U-Th-Pb and REE

535

chemistry of monazite, and its implications for pre-, peak- and post- metamorphic events of

536

the Lutzow-Holm Complex and the Napier Complex, East Antarctica. Polar Geosc.19, 118-

537

151.

538

Kelly, N.M., Clarke, G.L., Fanning, C.M., 2002. A two-stage evolution of the Neoproterozoic

539

Rayner Structural Episode: new U–Pb sensitive high resolution ion microprobe constraints

540

from the Oygarden Group, Kemp Land, East Antarctica. Precam. Res. 116, 307-330.

541

Kelsey, D.E., Clarke, G.L., Hand, M., 2008. Thermobarometric modeling of zircon and

542

monazite growth in melt-bearing systems: examples using model metapelitic and

543

metapsammitic granulites. J. Met. Geol. 26, 199-212.

544

Khan, A.S., Huin, A.K., Chattopadhyay, A., 2002. Final report on Specialized Thematic

545

Mapping in the Sausar Fold Belt in Manegaon-Deolapar-Ramtek area, Nagpur and Bhandara

25

546

districts, Maharashtra, for elucidation of stratigraphy, structure, metamorphic history and

547

tectonics. Unpub. Rep. Geol. Surv. India, Nagpur. 72 p.

548 549 550 551 552 553

Lippolt, H.J., Hautman, S., 1994.

40

Ar/39Ar ages of Precambrian manganese ore minerals from

Sweden, India and Morocco. Mineral. Deposita 18, 195-215. Ludwig, K. R., 2008. User’s manual for Isoplot 3.6. Special Publication no. 4, Berkley, Berkeley Geochronology Center, 77p. Maniar, P. D., Piccoli, P. M., 1989. Tectonic discrimination of granitoids. Bull. Geol. Soc. Am. 101, 635-643.

554

McDonough, W.F., Sun, S.-S., 1995. Composition of the Earth. Chem. Geol. 120, 223-253.

555

Mohanty, S., 2010. Tectonic evolution of the Satpura mountain belt: a critical evaluation and

556

implication on supercontinent assembly. J. Asian Earth Scs. 39, 516-428.

557

Narayanaswamy, S., Chakravarthy, S.C., Vemban, N.A., Shukla, K.D., Subramaniam, M.R.,

558

Venkatesh, V., Rao, G.V., Anandalwar, M.A., Nagarajaiah, R.A., 1963. The geology and

559

manganese ore deposits of the manganese belt in Madhya Pradesh and adjoining parts of

560

Maharastra. Part I: general introduction. Bull. Geol. Surv. India, A-22 (I).

561 562

Pal, T., Bhowmik, S.K., 1998. Metamorphic history of Sausar group of rocks. Unpubl. Report Geol. Surv. India. 98p.

563

Pandey, B.K., Krishna, V., Chabria, T., 1998. An overview of Chotanagpur gneiss–granulite

564

complex and adjoining sedimentary sequences, eastern and central India, In: International

565

Seminar on Precambrian Crust in Eastern and Central India 1998. Abstract Volume

566

UNESCO-IUGSIGCP-368, 131–135.

567 568

Radhakrishna, B. P., Naqvi, S. M., 1986. Precambrian continental crust of India and its evolution. J. Geol. 92, 145-166.

26

569

Roy, A., Devarajan, M.K., 2003. Tectonics and Seismicity of Central India: A Review. In: Roy,

570

A., Mohabey, D.M. (eds.) Seismicity of Central India, Gond. Geol. Mag. Spl. vol. 5, 23-44.

571 572

Roy, A., Prasad M. H., 2003. Tectonothermal events in Central Indian Tectonic Zone (CITZ) and its implications in Rodinian crustal assembly. J. Asian Earth Scs. 22, 115-129.

573

Roy, A., Kagami, H., Yoshida, M., Roy, A., Bandyopadhyay, B.K., Chattopadhyay, A., Khan,

574

A.S., Huin, A.K., Pal, T., 2006. Rb–Sr and Sm–Nd dating of different metamorphic events

575

from the Sausar mobile belt, central India: implications for Proterozoic crustal evolution. J.

576

Asian Earth Scs. 26, 61–76.

577

Sarkar, S.N., Trivedi, J.R., Gopalan, K., 1986. Rb-Sr whole-rock and mineral isochron age of the

578

Tirodi Gneiss, Sausar Group, Bhandara district, Maharashtra. J. Geol. Soc. India 27, 30-37.

579

Stipp, M., Stunitz, H., Heilbronner, R., Schmid, S. M., 2002. The eastern Tonale fault zone: a

580

‘natural laboratory’ for crystal plastic deformation of quartz over a temperature range from

581

250 to 700°C. J. Struc. Geol. 24, 1861–84.

582

Suzuki, K., Adachi, M. 1991. Precambrian provenance and Silurian metamorphism of the

583

Tubonosawa paragneiss in the South Kitakamiterrane, Northeast Japan, revealed by the

584

chemical U–Th–total Pb isochron ages of monazite, zircon and xenotime. Geochem. J. 25,

585

357–376.

586 587

West, W.D., 1936. Nappe structure in the Archaean rocks of the Nagpur district. Trans. Nat. Inst. Sci. India 1, 93-102.

588

27

589

Figure captions:

590

Fig. 1: Simplified Geological Map of the Central Indian Tectonic Zone showing the position of

591

Sausar Belt and the bounding lineaments (modified after Chattopadhyay and Khasdeo

592

2011).

593

(modified after Radhakrishna and Naqvi 1986). Box in the inset shows the area of Fig. 1.

594 595

Inset: Map of India showing different Proterozoic cratons and mobile belts

Fig. 2: Simplified Geological Map of the Sausar Fold Belt (modified after Chattopadhyay et al. 2003a). The box shows the area of the present study, detailed in Fig. 3.

596

Fig. 3: Geological map of the central part of Sausar Fold Belt relevant to the present study,

597

showing the locations of granitic samples (sample numbers in white boxes). Map

598

modified after Khan et al. (2002).

599

Fig. 4: (a) Small-scale reclined F1 fold

in quartzite of Sausar Group. (b) Early

600

reclined/recumbent F1 fold superposed by steeply inclined F2 folds in TBG. (c) Field

601

outcrop of foliated granite near Waitola railway crossing. The yellow box is parallel to

602

the subvertical foliation in the granite. (d) Deformation bands and grain boundary

603

migration microstructure in quartz grains (near black arrows) in foliated granite. (e)

604

Angular xenolith of calc-silicate rock floating in the intrusive massive granite. Lens cap

605

for scale. The host rock (calc-silicate) is seen in the left side of the photo. (f)

606

Inequigranular granitic texture of the massive granite.

607

Fig.5: Geochemical data plots of the granites: (a) Modal percentage values of Quartz, Alkali

608

Feldspar and Plagioclase of the samples plotted in IUGS QAP diagram to indicate broad

609

geochemical classification of the samples. (b) Samples plotted on a Shand’s Index (molar

610

A/CNK ratios) plot indicate a general peraluminous character of the granites. (c) 28

611

Primitive mantle-normalized trace element spider plot indicates overall LILE enrichment.

612

Note particular enrichment of HFSE (Nb and Ta) in foliated granite. (d) Mantle-

613

normalized REE spider plot shows LREE-enriched patterns with variable Eu anomaly

614

strong depletion. REE data of primitive mantle is from McDonough and Sun (1995).

615

Sample SFB 1205 is same as sample SFB 1202 used for monazite dating, as explained in

616

Table 1. See text for more details.

617

Fig. 6: (a) SEM-Back Scattered Electron image of representative monazite grain of foliated

618

granite (SFB1202). Grains show complex internal zoning. (b) Chondrite-normalized

619

LREE to MREE plot shows strong LREE enrichment. (c) Density probability diagram of

620

U-Th-total Pb age (n = 31). (d) Weighted average age is plotted for <1000 Ma age data

621

points yielding an age of 944 ± 5 Ma.

622

Fig. 7: (a) SEM-BSE image of representative monazite grain of Tirodi biotite gneiss (SFB1204)

623

with less pronounced internal zoning. (b) Chondrite-normalized LREE to MREE plot

624

shows strong LREE enrichment with more enriched and constrained values of MREE

625

than that of SFB1202. (c) Density probability diagram of U-Th-total Pb age (n = 44). (d)

626

Weighted average age is plotted for all age data points yielding an age of 948±4 Ma.

627

Fig. 8: (a) SEM-BSE image of representative monazite grains of massive post-tectonic granite

628

(SFB1207) with complex internal zoning (left) and core-rim structure (right). (b)

629

Chondrite-normalized LREE to MREE plot shows high LREE enrichment with large

630

variation of MREE than that of both SFB1202 and SFB1204. Note that monazite grains

631

close to garnet grains are highly MREE-depleted.(c) Density probability diagram of U-

632

Th-total Pb age (n = 36). The broad peak ~928 Ma is possibly a mixed one of two closely

29

633

spaced peaks, at 936 ±5 Ma and 917 ±7 Ma. Rare rim of monazite indicates a possible

634

younger thermal event~ 780 Ma.(d) Weighted average age is plotted for all age data

635

points yielding an age of 928 ± 4 Ma.

636

Fig. 9: Photomicrograph showing development of monazite, spatially closely associated with

637

biotite and muscovite grains oriented parallel to S2 schistosity, in the foliated granite

638

(SFB 1202).

639

.

640 641

30

642 643 644 645 646

Highlights: • • • •

Sausar Fold Belt in Central India shows polyphase deformation and metamorphism Intrusive granites are either foliated (syn-D2) or massive (post-tectonic) Monazite ages of granites constrain the timing of Sausar tectonothermal events The new ages cast some doubts on the earlier proposed tectonic models of CITZ

647

31

Figure 1 Click here to download high resolution image

Figure 2 Click here to download high resolution image

Figure 3 Click here to download high resolution image

Figure 4 Click here to download high resolution image

Figure 5 Click here to download high resolution image

Figure 6 Click here to download high resolution image

Figure 7 Click here to download high resolution image

Figure 8 Click here to download high resolution image

Figure 9 Click here to download high resolution image

Table 1

Table 1: Inventory of Granite samples from Sausar Fold belt, used in Monazite dating Sample No.

Location

Rock Type

Structure/ microstructure

Modal mineralogy

Remarks

SFB1202/12 05**

N21˚23'41.1'' E079˚17'07.9'' Near Railway crossing, Waitola village (GPS accuracy: 10 m)

Foliated pink Granite intrusive in to Sausar Group sediments (Mansar Fm)

Moderately to weakly foliated, locally strongly foliated. Foliation in granite is parallel to S2 of Sausar Group in adjacent schistose rocks

Quartz (41%)- K feldspar (39%)-Plagioclase (18%)biotite-muscovite- oxides(±Monazite±Zircon)*

Syn-D2 intrusion into Sausar Group: foliations in granite are parallel to S2 in SSG *Very small grains of monazite and zircon were identified by SEM in all samples ** SFB 1202 and 1205 are from same outcrop – one used for dating, another for geochemistry

SFB1204

N21˚27'38.0'' E079˚18'39.8'' South of Chobaoli, near mile stone No. 680 (on NH-31 to Jabalpur) (GPS accuracy 16 m)

Folded Tirodi Biotite Gneiss (TBG)

Perpendicular to shallow plunging fold axis (F2 of Sausar deformation) defined by gneissic foliation

Quartz (16%) -K-feldspar (38%) –Plagioclase (24%)Biotite (14%) – Muscovite (7%) (±Apatite ±Monazite ±Zircon)

Basement gneiss to Sausar Group and the granites Basement gneiss has been codeformed with Sausar Group during F1 and F2 of Sausar deformation.

SFB1207

N21˚31'25.8'' E079˚19'00.2'' West of Maudi village (GPS accuracy 09 m)

Unfoliated Granite intrusive into calcareous sediments (Lohangi Fm)

No foliation recognized either in the outcrop or in thin sections.

Quartz (29%)-K-feldspar (42%)-Plagioclase (25%) Biotite±Muscovite (~1%) ± Garnet (Pyr-Sps) ± Monazite

Post-tectonic undeformed granite intrusive into deformed Sausar Group rocks

SFB1209

N21˚35'08.5'' E079˚24'31.1'' near Umri-Junewani in Sagra Nala (GPS accuracy 10 m)

Un-foliated Granite (intrusive into Sausar Group))

No foliation

Quartz (19%) -K-feldspar (45%)-Plagioclase (35%) Biotite- Garnet (low modal) ±Monazite ±Zircon

-do-

Table 2

Table 2: Major, Trace and REE chemical data of granites and TBG from Sausar Fold Belt SFB1204 SFB1205/1202** 70.63 78.55

SFB1207 75.10

SFB1209 73.80

SiO2

wt%

TiO2

wt%

0.46

0.07

0.04

0.15

Al2O3

wt%

14.24

12.15

14.08

13.82

Fe2O3 MnO MgO CaO Na2O

wt% wt% wt% wt% wt%

4.79 0.06 1.75 1.31 2.63

1.48 0.04 0.38 0.53 4.30

0.98 0.03 0.09 0.84 3.71

1.89 0.02 0.28 1.02 2.94

K2O

wt%

3.35

3.00

4.39

5.44

P2O5

wt%

0.12

0.01

0.04

0.04

LOI (H2O+) Total

wt% wt%

1.26 100.60

0.52 101.03

0.69 99.99

0.60 100.01

Sc V Cr Co Ni Cu Zn Ga Rb Cs Ba Pb Sr Y Zr Nb La Ce Pr Nd Sm Eu

ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm ppm* ppm* ppm* ppm* ppm* ppm* ppm* ppm* ppm* ppm*

10.79 66.65 398.61 9.38 24.99 33.23 100.07 18.97 195.36 4.48 353.58 27.74 114.78 29.94 169.71 13.26 55.32 71.57 7.58 29.06 5.74 1.15

1.78 7.95 383.46 2.49 7.89 8.64 38.96 34.37 278.88 3.42 55.19 29.82 9.38 51.06 170.47 118.08 31.21 70.34 2.14 8.69 3.76 0.06

2.02 2.47 380.14 0.65 5.70 9.74 36.07 28.26 279.35 b.l. 188.29 69.44 46.55 18.62 58.32 16.63 45.38 47.17 4.10 17.37 4.15 0.49

2.92 9.45 413.00 2.16 9.11 6.33 40.51 20.36 191.49 10.07 866.27 69.53 156.02 6.88 126.05 7.65 90.52 122.00 11.76 43.34 7.28 1.13

Gd ppm* 4.97 6.10 Tb ppm* 0.79 1.33 Dy ppm* 4.65 9.81 Ho ppm* 1.06 2.22 Er ppm* 2.65 6.41 Tm ppm* 0.46 0.98 Yb ppm* 3.03 6.79 Lu ppm* 0.45 0.86 Hf ppm* 4.31 9.35 Ta ppm* 1.17 10.11 Th ppm* 18.28 56.02 U ppm 3.40 2.85 b.l. stands for below detection level. * data by LA-ICPMS.

3.79 0.67 3.62 0.65 1.45 0.24 1.52 0.20 3.23 2.14 24.64 5.76

4.27 0.46 1.96 0.31 0.73 0.11 0.40 0.06 3.62 0.50 42.90 3.37

** SFB 1202 and SFB 1205 are samples of foliated granite collected from the same outcrop near Waitola – one used for geochemistry (SFB 1205) and the other for monazite dating (SFB 1202)