Structural, Geochronological and Tectonic Evolution of the Central Eastern Ghats Province, India: Araku-Anantagiri-Visakhapatnam

Structural, geochronological and tectonic evolution of the central Eastern Ghats Province, India: Araku-Anantagiri-Visakhapatnam

Billy Reid

Centre for Tectonics, Resources and Exploration

School of Earth and Environmental Sciences

The University of Adelaide, South Australia

[email protected] Table of Contents Abstract ...... 3 1 Introduction ...... 4 2 Geological and Tectonic Setting ...... 6 2.1 Geodynamic Context ...... 6 2.2 Geological Setting ...... 7 3 Methodology ...... 10 3.1 LA-ICP-MS U-Pb Zircon Geochronology ...... 10 3.2 LA-MC-ICP-MS Hf Isotope Analysis of Zircon ...... 12 3.3 Field Work ...... 13 4 Results ...... 13 4.1 Sample Descriptions and Petrography ...... 13 4.1.1 Sample B-EG008 ...... 13 4.1.2 Sample B-EG010 ...... 14 4.1.3 Sample B-EG014 ...... 14 4.1.4 Sample B-EG016 ...... 15 4.1.5 Sample B-EG020 ...... 15 4.1.6 Sample B-EG028 ...... 15 4.1.7 Sample B-EG032 ...... 16 4.2 U-Pb Zircon Geochronology ...... 16 4.2.1 Sample B-EG008 ...... 17 4.2.2 Sample B-EG010 ...... 18 4.2.3 Sample B-EG014 ...... 18 4.2.4 Sample B-EG016 ...... 19 4.2.5 Sample B-EG020 ...... 20 4.2.6 Sample B-EG028 ...... 21 4.2.7 Sample B-EG032 ...... 21 4.3 Hf Isotope Data ...... 22 4.4 Structural Setting and Field Relationships ...... 23 5 Interpretation ...... 25 5.1 U-Pb Zircon Geochronology ...... 25 5.2 Hf Isotope Analyses ...... 26 6 Discussion ...... 27 6.1 Age and Nature of Protolith Sources ...... 27 6.2 Age(s) of Metamorphism ...... 29 6.3 Tectonic Evolution ...... 30 7 Conclusions ...... 32 8 Acknowledgements ...... 32 9 References ...... 34 10 Figure Captions ...... 37 11 List of Tables ...... 41 12 Figures ...... 42 13 Tables ...... 61

Structural, geochronological and tectonic evolution of the central Eastern Ghats Province, India: Araku-Anantagiri-Visakhapatnam

Billy Reid

Centre for Tectonics, Resources and Exploration

School of Earth and Environmental Sciences

The University of Adelaide, South Australia

[email protected]

Abstract

The central Eastern Ghats Province is part of a series of terranes that collectively form the Eastern Ghats in India. The Eastern Ghats is a Mesoproterozoic to early Neoproterozoic orogen associated with the formation of the supercontinent Rodinia, c. 1.1 to 0.95 Ga. The central Eastern Ghats Province consists of metaquartzites and metapelites (khondalites) that are intruded by granitoids. The location of proto-India within Rodinia is disputed because of recently presented palaeomagnetic data. This has generated confusion about whether the protoliths to the Eastern Ghats Province metasedimentary rocks were deposited adjacent to proto-India or as an exotic terrane later accreted to India. U-Pb geochronology, in conjunction with Hf isotopes of zircons, constrain the maximum depositional age, determine provenance and identify the location of deposition. A maximum depositional age of 1.14 Ga on the protoliths to the khondalites has been determined from U-Pb zircon geochronology. The short period of time between deposition and the orogenesis related thermal event indicates that the sediments were deposited adjacent to the Bastar Craton. Provenance work identifies a number of sources within India and east Antarctica lending support to the theory that these continents were contiguous prior to the Eastern Ghats Orogeny. Structural transects and mapping reveals that shortening associated with the collision of east Antarctica and proto-India occurred along a NE-SW trending axis.

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1 Introduction

The central Eastern Ghats Province in south-eastern India is part of a late

Mesoproterozoic to early Neoproterozoic mountain belt that extends for ~1000 km along India’s east coast. It is bordered by the Bay of Bengal to the east, the Singhbhum

Craton to the north, the Bastar/Bhandara Craton to the west and the Godavari Rift to the south. The latter Godavari Rift records late movement c. 790 Ma (Chaudhuri & Deb

2004) and separates the Eastern Ghats Province from the Dharwar Craton, Cuddapah

Basin and Ongole Domain to the south (Fig. 1).

The term Eastern Ghats Province comes from a regional classification by Dobmeier and

Raith (2003) that is a revised version of that by Ramakrishnan et al. (1998). The Eastern

Ghats Belt is composed of separate crustal units called the Jeypore Province, Rengali

Province, Krishna Province and Eastern Ghats Province with differing tectonothermal histories (Fig. 2). The Jeypore Province is separated from the Eastern Ghats Province because it is dominantly composed of meta-igneous rocks that formed in a rift environment during the Archaean (Dobmeier & Raith 2003). The Rengali Province also records Archaean to early Palaeoproterozoic deformation and is separated from the

Eastern Ghats Province because it does not record granulite facies metamorphism or similar structural features. The Krishna Province is a combination of two areas recording granulite facies metamorphism at ~1.6 Ga but do not record the ~1.0 Ga deformation of the Eastern Ghats Province (Dobmeier & Raith 2003) (Fig. 2).

Orogenesis in the Eastern Ghats Province is dated at ~1.0 Ga (Shaw et al. 1997). The timing of this orogenesis has been linked to the amalgamation of Rodinia although the continents that collided to form the Eastern Ghats are a subject of controversy, e.g.

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

Torsvik et al. (2001a); Torsvik et al. (2001b); Dobmeier et al. (2006). The rocks within the Eastern Ghats Province include voluminous metasedimentary rocks. The age of deposition of the protoliths of these are not well understood. In addition, the tectonic location of their deposition is also unknown. Two aims of this study are to provide maximum depositional ages for the metasedimentary protoliths in the Eastern Ghats

Province and to elucidate whether the protoliths to these metasedimentary rocks were: a) deposited as a passive margin to the Bastar Craton; b) as an island arc, or; c) as a part of an exotic continent that later collided with the Bastar Craton. This will assist in understanding the arrangement of Rodinia during the Neoproterozoic and the locations of proto-India and east Antarctica. These aims will be achieved by analysing the U-Pb isotopes of zircons, identifying the age distribution of the source regions of the protoliths. A maximum depositional age will also be produced by the age of the youngest detrital zircon. Metamorphic events can be identified through dating metamorphic rims of zircons and zircons that have recrystallised. Hf isotopic data is presented constraining whether the detrital zircons crystallised from melted mantle material or whether they formed through melting of pre-existing continental rocks. This assists in constraining the nature and location of the source for these sediments.

Another aspect of this study is to produce a structural framework for the Eastern Ghats

Province incorporating structural transects and a map. This area has been chosen for its significance because it is the only area in the central Eastern Ghats Province where the entire orogen can be studied. Previous structural studies of the central Eastern Ghats

Province have been regional in scale and heavily interpreted from aerial imagery and not well related to a geochronological framework, e.g. Ramakrishnan et al. (1998);

Chetty (2001).

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2 Geological and Tectonic Setting

2.1 Geodynamic Context

The Eastern Ghats Province has been proposed to correspond to the suture zone between proto-India and east Antarctica in Rodinia reconstructions (Mezger & Cosca

1999; Kelly et al. 2002; Li et al. 2008). Deformational features and associated metamorphism are seen throughout the Eastern Ghats Province and comparable lithologies and thermal histories can be seen in east Antarctica. Orogenesis-related deformation and granulite facies metamorphism have been dated at 1.1 to 0.95 Ga by

Mezger & Cosca (1999) and Simmat & Raith (2008).

Correlations between the Eastern Ghats Province and east Antarctica are made by Kelly et al. (2002). Support for this relationship can be found by the timing of the Rayner

Structural Episode tectonically reworking the Rayner Complex in east Antarctica at the same time the Grenvillian Orogenic Event was affecting the Eastern Ghats Province.

The onset of the Rayner Structural Episode is recorded by granulite facies metamorphism and felsic magmatism c. 1.0-0.98 Ga. Charnockite intrusions have been dated at 982 ± 33 Ma in east Antarctica and are chronologically contiguous with plutonic activity in the Eastern Ghats. Further supporting evidence comes from the similarities between deformation and thermal impacts of the Pan-African event (Kelly et al. 2002; Halpin et al. 2005). This suggests that the Eastern Ghats Province and Rayner

Complex were contiguous until the Mesozoic when Gondwana fragmented.

Questions have been raised about the whereabouts of India within Rodinia. Li et al.

(2008) assume that India became a part of Rodinia by 900 Ma through collision along the c. 980-900 Ma Eastern Ghats Belt and the corresponding Rayner Province in east

Antarctica. However, palaeomagnetic data presented in Torsvik et al. (2001a; 2001b)

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

suggest that while the Eastern Ghats Province and east Antarctica formed part of

Rodinia, proto-India may not have been. This argument is supported by geochronology data implying that the central Eastern Ghats Province was not contiguous with the

Krishna Province until the Palaeozoic when the amalgamation of Gondwana sutured the

Eastern Ghats and east Antarctica to proto-India (Dobmeier et al. 2006).

2.2 Geological Setting

Dobmeier & Raith (2003) provide a revised geological framework for the Eastern Ghats

Province based on earlier work by Ramakrishnan et al. (1998). Ramakrishnan et al.

(1998) used metamorphic grade amongst other criteria to group provinces of the Eastern

Ghats Belt. Later work by Rickers et al. (2001) and others, summarised in Dobmeier &

Raith (2003), redefined the Eastern Ghats Belt of Ramakrishnan et al. (1998) into the

Eastern Ghats Province, Rengali Province, Jeypore Province and Krishna Province based on their age (Fig. 2).

The new classification by Dobmeier & Raith (2003) places the area of this study in the

Visakhapatnam Domain of the Eastern Ghats Province (Fig. 2). The Visakhapatnam

Domain consists of intensely deformed and metamorphosed granulite facies rocks. They are metasedimentary, basic and enderbitic granulites interspersed with massif-type anorthosite and probably intrusive granite-charnockite suites (Gupta 2004).

Metasedimentary lithologies are dominantly khondalites and quartzofeldspathic gneisses. Both are interlayered with garnet and sillimanite-bearing quartzite and high- orthopyroxene garnetiferous gneisses (Dobmeier & Raith 2003). Lenses of high-Mg-Al granulites containing sapphirine and spinel recording ultrahigh-temperature metamorphism are dispersed throughout the Visakhapatnam Domain (Dobmeier &

Raith 2003; Gupta 2004; Mukhopadhyay & Basak 2009).

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A strong gneissic banding is found in the khondalites of the central Eastern Ghats

Province. This fabric is related to deformation during the amalgamation of Rodinia at c.

1.1-0.95 Ga. In places, an earlier fabric can be seen containing sapphirine-spinel bearing assemblages recording ultrahigh-temperature metamorphism dated at 1.1-1.2 Ga. This fabric only occurs as lenses within khondalites (Gupta 2004; Mukhopadhyay & Basak

2009; Upadhyay et al. 2009). The charnockites and megacrystic granitoids are largely void of any structural features. Megacrystic granitoids occasionally preserve a weak magmatic flow lineation but this is not consistent across different areas. Generally, topographically low areas are associated with intrusives and areas of raised topography are associated with khondalites.

Previous regional structural studies have identified a number of structural features defining the Eastern Ghats Province (Ramakrishnan et al. 1998; Chetty 2001). Recent research has revised subdivisions made in these papers on the basis of geochronological, geochemical and spatial evidence (Rickers et al. 2001; Dobmeier & Raith 2003;

Dobmeier et al. 2006). Dobmeier et al. (2006) concluded that the Eastern Ghats

Province north of the Godavari Rift is a separate crustal unit to the Eastern Ghats south of the rift due to their differing tectonothermal histories. These structural studies have identified important features like the southeast dipping foliation and major zones but due to the scope of their research, they have not been able to identify small features or relate their research to a geochronological framework.

The rocks forming the Eastern Ghats Province are enriched in radiogenic U, Th and K

(Gupta 1982; Kumar et al. 2007). Radiogenic isotopes of these elements release heat in their decay and may have contributed to the Eastern Ghats undergoing high and ultrahigh temperature metamorphism. The abundance of heat producing elements in the

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

Eastern Ghats may explain their recent tectonic uplift given that they are located away from tectonic boundaries. Stresses associated with the collision of India and Asia may be transferred to the Eastern Ghats, where the crust is hotter resulting in the raised topography. The Flinders Ranges, in South Australia, record Quaternary uplift even though they are far isolated from tectonic plate boundaries (Sandiford & Hand 1998;

Sandiford et al. 1998). Amongst other contributing factors, uplift has been linked to thermal weakening from heat producing elements below a thick sedimentary sequence.

Deformation is localised in the Flinders Ranges and Mount Lofty Ranges from stress transferred from collision of the Australian-Indian plate with Asia (Célérier et al. 2005).

The central Eastern Ghats Province is dominantly composed of two main rock types: khondalites and charnockites (Gupta 2004). Khondalites are garnet-biotite-sillimanite gneisses with small bodies of high-Mg-Al granulite, calc-silicate gneisses and quartzites

(Gupta 2004; Mukhopadhyay & Basak 2009). These are intruded by charnockites (high- orthopyroxene bearing granite) and megacrystic granitoids (Rickers et al. 2001;

Mukhopadhyay & Basak 2009). Rickers et al. (2001) produced a Nd model age between

2.1-2.5 Ga for the metasediments (khondalites). This shows that there is a significant

Archaean/Palaeoproterozoic component in the source of the protoliths to these rocks.

Emplacement of the massive K-feldspar megacrystic granitoids have been given an intrusion age of 965-935 Ma (Krause et al. 2001).

Previous regional structural studies have identified a number of terranes that collectively form the Eastern Ghats with differing tectonothermal histories

(Ramakrishnan et al. 1998). These have been reviewed and revised in later studies by

Chetty (2001), Rickers et al. (2001), Dobmeier & Raith (2003) and Gupta (2004).

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Revisions have been based on geochronological histories, isotope ratios, structural features and thermal histories.

3 Methodology

3.1 LA-ICP-MS U-Pb Zircon Geochronology

The main aim of geochronology in this study is to constrain the maximum depositional age of the protoliths to the khondalites, and further, confirm the location of their deposition relative to India. Seven samples were analysed using U-Pb zircon geochronology ranging from quartzites to garnet rich metapelites (see Table 3). All samples were analysed with the Laser Ablation-Inductively Coupled Plasma-Mass

Spectrometer (LA-ICP-MS) at Adelaide Microscopy. Whole rock samples were crushed, milled to medium sand size then sieved. The 75-425 µm fraction was retained and grains larger than 425 µm were re-milled and re-sieved. The 75-425 µm fraction was washed with water and detergent to remove any dust contained within the sample to ensure clarity of water when separating. This was then panned to isolate heavy minerals.

Sample B-EG008 was passed through methylene iodide heavy liquid to separate minerals with density greater than 3.3 g.cm-3. The heavy minerals were then washed with acetone. No other samples required the use of heavy liquids in mineral separation.

Magnetic minerals were separated using a conventional magnet then the sample was further separated using a Nd-magnet to remove weakly magnetic minerals. Zircons were handpicked from the remaining fraction and mounted in epoxy resin. The mounts were then polished to expose the core of the zircons then further polished with a cloth lapidary. These were then cleaned in a hydro sonic bath before being carbon coated.

Polished zircon mounts were imaged using a Philips XL-20 Scanning Electron

Microscope with a Gatan Cathodoluminesence (CL) detector to identify zonation within

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

zircon grains. An operating voltage of 15 kV and a spot size of 5 were used to obtain backscatter maps and 12 kV and spot size 7 was used to obtain CL images.

U-Pb analysis of zircon was conducted using an Agilent 7500cs ICP-MS coupled with a

New Wave 213 nm Nd-YAG laser. Ablation was performed in a helium atmosphere with a beam diameter of 30 µm, repetition rate of 5 Hz and laser intensity of 70 percent.

Total acquisition time for each analysis was 100 seconds, which included 30 seconds of background measurement, 10 seconds for beam stabilisation and 60 seconds of sample ablation. U-Pb drift was corrected for using the GEMOC GJ-1 (weighted average 602.1

± 1.3 Ma, MSWD = 0.96) standard (Jackson et al. 2004), and data reduction was completed using GLITTER software following procedures outlined in Griffin et al.

(2008). Accuracy was also monitored by repeat uses of the Sri-Lankan internal standard

BJWP-1 (weighted average 722.5 ± 4.5 Ma, MSWD = 2.5; 727 Ma TIMS (Payne et al.

2006)) and the Czech Republic internal standard Plešovice (Sláma et al. 2008)

(weighted average 344.0 ± 1.7 Ma, MSWD = 2.0).

All spots were analysed for common lead. Negligible common lead (<0.5 percent 206Pb) was detected for all samples. Therefore uncorrected isotope ratios are used in age calculations for these samples with conventional concordia, probability density and weighted average plots generated using Isoplot ver. 4.00.08.09.16. All errors shown on concordia diagrams and quoted in results tables are 1σ. For ages younger than 1000 Ma, the 206Pb/238U ages are used and for ages greater than 1000 Ma, the 207Pb/206Pb ages are used in weighted average plots. This practice is used due to the imprecise nature of

207Pb/206Pb ages for zircons less than 1000 Ma (after Collins et al., (2007)).

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3.2 LA-MC-ICP-MS Hf Isotope Analysis of Zircon

The Hf isotope data was acquired with a New Wave UP-193 Excimer laser (193 nm).

Laser repetition rates of 5 Hz, four nanosecond pulse length and 50 µm spot size were used. Laser fluence was maintained at ~10 J.cm-2. Samples were ablated in a helium atmosphere mixed with argon sample gas upstream of the ablation cell. The laser was coupled to a Thermo-Scientific Neptune Multi-Collector ICP-MS. The multi-collector measured 171Yb, 173Yb, 175Lu, 176Hf, 177Hf, 178Hf and 180Hf on Faraday detectors with

1012Ω amplifiers.

A major uncertainty in accurate measurement of Hf isotope ratios in zircon by laser ablation is the interference of 176Lu and 176Yb on 176Hf. This study follows the interference correction protocols described in Woodhead et al. (2004). Hf mass bias was corrected using exponential law fractionation correction with a stable Hf isotope ratio of

178Yb/177Hf = ~0.5. Lu isobaric interference on 176Hf was corrected using a 176Lu/175Lu ratio of 0.02655 (Vertvoort et al. 2004), assuming that the mass bias behaviour of Lu is analogous to that of Yb.

For Yb signals below 10 mV interference corrections were made using an empirically derived 176Yb/173Yb ratio and the Hf mass bias factor similar to the method described by

Griffin et al. (2000). This was done as the potential errors involved in the method are outweighed by the significantly greater uncertainty caused by the small Yb beam. In this case an empirically derived ratio of 0.739689 was used. This was derived by analysis of a series of Yb and Hf doped glass beads.

Set up of the system prior to ablation sessions was conducted using analysis of JMC475

Hf solution and an AMES Hf solution. Confirmation of accuracy of the technique for

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

zircon analysis was monitored using a combination of the Plešovice, Mudtank and

QGNG standards. The average 176Hf/177Hf ratio for Plešovice was 0.282496 (2σ =

0.000022; n = 27) compared to the published value 0.282482 ± 0.000013 (2σ) in Sláma et al. (2008).

3.3 Field Work

Field work was conducted from 5th to 26th January 2010. During this time all sampling and structural mapping was completed and two structural transects from west of Araku to Visakhapatnam were compiled.

4 Results

4.1 Sample Descriptions and Petrography

4.1.1 Sample B-EG008

Sample B-EG008 is a quartzite from a quarry 23 km NNW of Visakhapatnam, roughly

1 km east off the Visakhapatnam to Araku road (17°56’03.6”N, 83°10’39.3”E; Fig. 3).

This quarry is characterised by the lack of variation in its mineralogy. Dark banding within quartzite was targeted to maximise the possibility of including heavy minerals

(e.g. zircon). The sample has glossy, flaked graphite crystals on its outer surface. The mineral assemblage is dominated by quartz (90 percent) which forms the groundmass.

Titanite grains are typically ≤2 mm with aspect ratios of 10:1. Partial to total replacement of titanate with sillimanite is common. Sillimanite orientation is random and does not follow the fabric defined by titanite. Minor graphite (<1 mm) is common and follows the fabric defined by titanite but has a lower aspect ratio of approximately

2:1. Platy biotite grains (0.5-1.0 mm) are rare and follow fabric defined by titanite.

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4.1.2 Sample B-EG010

Sample B-EG010 is from a quarry 40 km NNW of Visakhapatnam and 2.5 km west of

Visakhapatnam to Araku road (18°03’20.9”N, 83°07’21.5”E; Fig. 3). This quarry has a strong gneissic foliation and is intruded by a late pegmatite vein. This sample has been partially re-melted and consists of roughly 75 percent normal metapelite and 25 percent partially melted material. A fabric is defined by biotite grains (0.5-3.0 mm) but becomes less well defined closer to zones of partially melted material. Garnet grains occur in direct contact with biotite and are anhedral. They are replaced by biotite and cordierite and contain inclusions of quartz, biotite, zircon and magnetite. A sharp boundary exists between the garnet-biotite-cordierite zone and the quartz-plagioclase dominated area.

Quartz grains are typically 0.1-0.5 mm in diameter and occur inside plagioclase grains.

Plagioclase grades from well twinned in places to poorly twinned. Rare bladed quartz grains are ~4.0-5.0 mm in length. K-feldspar has weakly formed crosshatch twinning that is difficult to see due to grain size. Symplectite intergrowths can be seen with quartz and plagioclase. Magnetite is present in long lines and is included in garnet and biotite.

4.1.3 Sample B-EG014

Sample B-EG014 is from a quartzite outcropping near the Visakhapatnam-Araku railway line, 12 km SE of Anantagiri along the Visakhapatnam to Araku road

(18°12’55.4”N, 83°02’32.6”E; Fig. 3). The mineral assemblage is dominantly quartz, plagioclase, minor biotite and titanite. This sample was chosen because of the presence of dark mineral banding to maximise the chance of sampling heavy minerals (e.g. zircon).

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4.1.4 Sample B-EG016

Sample B-EG016 is a from a khondalite cropping out adjacent to the Visakhapatnam-

Araku railway line, 12 km SE of Anantagiri along the Visakhapatnam to Araku road

(18°12’55.4”N, 83°02’32.6”E; Fig. 3). The assemblage is dominantly quartz, biotite, garnet and plagioclase. Garnet is anhedral and ranges from 1.0-3.0 mm. Garnets contain inclusions of quartz, magnetite and biotite. Fine grain sillimanite is present, it is included within and along grain boundaries of biotite. Fine grained titanite is common as inclusions within quartz. No apparent fabric is present, see Fig. 4a; b.

4.1.5 Sample B-EG020

Sample B-EG020 is from a NE-SW striking ridge 8 km SE of Anantagiri along

Visakhapatnam to Araku then a further 2 km SW along a minor road servicing villages

(18°12’47.5”N, 83°01’22.4”E; Fig. 3). The assemblage is dominated by quartz (90 percent). Tabular grains of ~5 mm quartz form a fabric with polygonal aggregates of quartz forming the groundmass. Garnet forms less than 5 percent of the rock and is euhedral or subhedral. Plagioclase occurs in the groundmass and is typically ≤1 mm in diameter. Some sillimanite is present.

4.1.6 Sample B-EG028

Sample B-EG028 is from an outcrop of garnet-cordierite-sillimanite gneiss 4.5 km north of Araku Valley (18°21’43.3”N, 82°52’31.2”E; Fig. 3). The assemblage is dominantly garnet with quartz, plagioclase and biotite forming the groundmass. Sillimanite is common and is replacing orthopyroxene and as inclusions within quartz. Ultrafine grain quartz has salt and pepper texture in CPL along grain boundaries of garnet, orthopyroxene and cordierite. Plagioclase twinning grades from well formed to poor.

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Magnetite present usually as inclusions in garnet. Titanite and spinel present as inclusions in garnet and in close proximity to garnet, see Fig. 4c; d.

4.1.7 Sample B-EG032

Sample B-EG032 is from a khondalite cropping out 4 km north of Araku Valley

(18°21’31.1”N, 82°52’47.0”E; Fig. 3). It is composed of garnet, quartz, plagioclase, orthopyroxene and sillimanite. Garnet grains are heavily fractured and anhedral and contain quartz, sillimanite, titanite, biotite and spinel. Orthopyroxene has partially replaced garnet and in places occurs as a pseudomorph of garnet, see Fig. 4e; f.

Sillimanite rims orthopyroxene and is replacing it, and has a preferred crystal orientation parallel to the long axis of the orthopyroxene crystals. Ultrafine grained quartz is presence along garnet grain boundaries and is probably due to high grade metamorphism partially melting the rock. Titanite is found in direct contact with garnet and orthopyroxene. Orthopyroxene occasionally occurs as a rim around spinel inclusions within garnet.

4.2 U-Pb Zircon Geochronology

206Pb/238U ages are plotted on probability density diagrams for zircons <1000 Ma r, whereas 207Pb/206Pb ages are plotted for zircons >1000 Ma, due to the diminishing precision of the 207Pb/206Pb age as the planet ages. All data are summarised in Table 1.

Grains were targeted based on their cathodoluminescence signatures. Those with remnant oscillatory zoning were preferentially targeted to give the highest likelihood of extracting their magmatic crystallisation age.

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4.2.1 Sample B-EG008

The zircons are dominantly anhedral and display thick, dark metamorphic rims, usually

5-20 µm, in the CL images. Cores range in size from 20-200 µm and occasionally preserve oscillatory zoning but usually are sector zoned. Smaller cores are dominantly euhedral and larger cores are generally fragments of zircon grains. CL responses range from weak to very strong in metamict cores. They are dominantly cracked and occasionally contain inclusions of iron oxide (Fig. 5a).

Of the 60 spots analysed on 60 zircons, 17 record 90 to 110 percent concordance (see

Fig. 6a, inset.). Of the grains within 10 percent of concordance, peaks in age occur at

1175 ± 25 Ma (n = 6), 1272 ± 41 (n = 2), 1572 ± 37 (n = 2), 2423 ± 19 Ma (n = 4) and

2661 ± 26 Ma (n = 2) (see Fig. 6b). The youngest 90-110 percent concordance analysis

(Spot 32) gave a 207Pb/206Pb age of 1149 ± 27 Ma (100 percent concordant). In addition, many of the discordant grains lie along a broad discordia array with Neoarchaean to

Palaeoproterozoic upper intercepts and a lower intercept at ~650 Ma. A best fit line to this array gives an upper intercept of 2514 ± 40 Ma and a lower intercept of 665 ± 51

Ma with a large MSWD of 28. Model ages calculated from this line are shown in Table

1. The large MSWD is to be expected as these analyses are interpreted as detrital zircons of different original ages that have lost lead in the late Neoproterozoic (Fig. 6a).

These data are interpreted as representing detrital zircon sourced from a terrane with ages of ~2.5 Ga, ~1.5 Ga, 1.27 Ga and ~1.175 Ga. These have then lost lead in the late

Neoproterozoic, probably during a metamorphic event.

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4.2.2 Sample B-EG010

Most zircons are tabular and display bright CL responses. Many contain dark inclusions and display evidence of partial recrystallisation such as irregular concentric zoning locally overprinted by zones of recrystallisation or new growth. The grains only preserve very thin rims, if any are preserved at all. All zircons appear to form one shape population and have aspect ratios of 2:1 to 3:1 (Fig. 5b).

Of the 39 zircons analysed, 23 are between 90 and 110 percent concordant (Fig. 7a, inset). The main age populations occur at 945 ± 8.6 Ma (n = 7) with smaller peaks at

858 ± 9 Ma (n = 5) and 1094 ± 30 Ma (n = 3). However, when analyses between 95 and

105 percent concordance are compiled, the peak at 943 ± 9 Ma (n = 6) peak is dominant. Only displaying zircons between 95 and 105 percent concordance reveals a peak at 894 ± 16 Ma (n = 2) and a broad peak spreading from 819 to 870 Ma (Fig 7b).

The youngest concordant grain occurs at 526 ± 7 Ma (Spot 19, 101 percent concordance) and the oldest at 1145 ± 33 Ma (Spot 21, 104 percent concordance). When the most discordant data are removed, the remaining data can be fitted to a broad discordia line with an upper intercept at 1036 ± 35 Ma and a lower intercept at 539 ± 56

Ma (Fig. 7a) (appreciably with a large MSWD of 6.6).

4.2.3 Sample B-EG014

The zircons in this sample are dominantly tabular and record dark CL response. They are mostly cracked and have thin metamorphic rims, if any are preserved (Fig. 5c).

Of the 18 zircons analysed, 8 spots on 10 zircons plot between 90 and 110 percent concordance (Fig. 8a, inset). These record a main peak at 1030 ± 45 Ma (n = 3) and smaller peaks at 1187 ± 29 (n = 2), 1298 ± 31 Ma (n = 2) and individual grains at 861 ±

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

12 Ma (Spot 13, 94 percent concordant), 1416 ± 20 Ma and 1550 ± 21 Ma (Fig. 8b).

The oldest zircon (Spot 05, 88 percent concordant) records a 207Pb/206Pb age of 1604 ±

19 Ma. Unfortunately, very little can be interpreted from these data with any confidence; except the occurrence of pre-1 Ga zircons.

4.2.4 Sample B-EG016

The zircons in this sample are tabular and range in size from 100 µm to 400 µm. They have bright CL responses. However, zones of uniform CL response rarely extend around entire zircons and often extend the entire length of the grain. Iron oxide staining is rare but inclusions of an opaque mineral, possibly magnetite, are common. Metamict cores are rare (Fig. 5g).

Of the 49 zircons analysed, 38 recorded concordance between 90 and 110 percent (Fig.

9a; 9a, inset). The main population of zircons occurs at 938 ± 8 Ma (n = 10) with smaller peaks at 1016 ± 16 (n = 9), 899 ± 9.5 Ma (n = 6) and 808 ± 13 Ma (n = 3) (Fig.

9b). When zircons within 1 percent of concordia are examined, two main populations of

207Pb/206Pb ages occur, one that has a weighted mean of 1013 ± 18 Ma (n = 7, MSWD =

0.2), the second with a weighted mean of 948 ± 13 Ma (n = 14, MSWD = 0.44). The

207Pb/206Pb ages give more precise result than the 206Pb/238U ages in this case, and this is interpreted to be because of small degrees of lead loss in the Ediacaran-Cambrian.

Concordant spots range in age from 581 ± 8 Ma (Spot 37, 96 percent concordant) to

1234 ± 16 Ma (Spot 48, 102 percent concordant) (Fig. 9b).

These data are interpreted to indicate that the youngest detrital zircon occurs at ~1.2 Ga.

The ~1013 Ma population of concordant zircons may also mean that deposition continued down to this age. However, the possibility that these are metamorphic zircons

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cannot be discounted. The 948 ± 13 Ma age is interpreted to date the main period of metamorphic zircon growth in these rocks with a second minor phase at ~800 Ma. The

Ediacaran grain is interpreted to indicate metamorphic rim growth or near-complete Pb loss at this time due to Ediacaran-Cambrian metamorphism.

4.2.5 Sample B-EG020

The zircons from this sample are dominantly rounded and have strong oscillatory zoning despite recording young crystallisation ages. They are relatively transparent and have a shiny lustre and range in size from 100 µm to >400 µm. They often contain inclusions of a dark mineral and display complex overgrowth histories. Cores of cracked zircons are often metamict and when a point in one of these areas (Spot 11) was analysed, the grain gave a 23 percent concordance value (Fig. 5f).

The main population has an age peak of 900 ± 10 Ma (n = 7) with smaller peaks at 951

± 10 Ma (n = 6) and 1358 ± 54 Ma (n = 2) (Fig. 11b). When grains between 90 and 110 percent concordance are analysed, the main peak has two peaks at 892 ± 13 Ma (n = 3) and 941 ± 14 Ma (n = 3). All concordant zircons plot between 851 ± 11 Ma and 976 ±

12 Ma (Fig. 10a). A discordia trend occurs in all the analyses less than 11 percent discordant (Fig. 10a). This discordia has an upper intercept of 991 ± 47 Ma and a lower intercept of 553 ± 270 Ma (MSWD = 1.4).

These analyses are interpreted to indicate growth of zircon at 991 ± 47 Ma that then subsequently lost lead at ~550 Ma during the Ediacaran-Cambrian metamorphic event

(Mezger & Cosca, (1999); Meert, (2003). The zircons are interpreted to represent growth from a partial melt during a Tonian thermotectonic event.

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4.2.6 Sample B-EG028

Sample B-EG028 has two populations of zircons. The first are euhedral and sub- rounded with thin metamorphic rims and range in size from 100 µm to 150 µm. They record bright CL images and have high CL responses associated with cracks. The second population are rounded and ~150 µm in diameter. They have strong oscillatory zoning in their cores and dark CL responses in their rims (Fig. 5d). All zircons display evidence of recrystallisation such as irregular zoning and complex overgrowth patterns.

Of the 29 zircons analysed, only 4 zircons fell within the desired 90-110 percent concordance range (Fig. 11a). Two strong peaks in ages occur at 1388 ± 14 (n = 10) and

1569 ± 16 (n = 7) with smaller peaks at 1140 ± 23 (n = 4) and 1670 ± 27 Ma (n = 3)

(Fig. 10b). The youngest zircon is 1138 ± 23 Ma (Spot 18, 93 percent concordant) and the oldest is 1669 ± 21 Ma (Spot 19, 90 percent concordant). These data are interpreted as indicating detrital zircon populations at ~1670 Ma, ~1570 Ma, ~1390 Ma and ~1140

Ma.

4.2.7 Sample B-EG032

The zircons in Sample B-EG032 are typically 50-200 µm in size and display dark CL signatures. They typically contain inherited cores and display thick metamorphic rims with low CL response. Often they are well rounded. Tabular shape zircons display complex histories and often consist of two inherited cores joined together (Fig. 5e).

Of the 19 zircons analysed, 13 were between 90 percent and 110 percent concordant

(Fig. 12a, inset). Ages are not strongly clustered so the largest peaks in ages occur at

1335 ± 32 Ma (n = 4) and 1119 ± 21 Ma (n = 4). Smaller peaks occur at 1552 ± 32 Ma

(n = 2) and 940 ± 13 Ma (n = 2). When only spots within 10 percent of concordia are

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analysed, the main population occurs at 951 ±12 Ma (n = 4) with smaller peaks at 1007

± 29 Ma (n = 2), 1099 ± 30 Ma (n = 2). Individual concordant grains plot at 1238 ± 21

Ma, 1319 ± 21 Ma and 1779 ± 21 Ma (Fig. 12b). Concordant zircons range in age from

900 ± 11 Ma (Spot 13, 93 percent concordant) to 1779 ± 21 Ma (Spot 05, 101 percent concordant). Single zircons yielded ages 1567 ± 26 Ma and 1542 ± 21 Ma. These data are interpreted to indicate the presence of Mesoproterozoic detritus in the protolith to this sample with subsequent metamorphic zircon growth at ~950 Ma.

4.3 Hf Isotope Data

From the four samples analysed for Hf isotopes, 42 analyses were conducted on 42 zircons. All data is summarised in Table 2. A bulk earth 176Hf/177Hf ratio of 0.015 was used in Fig. 13b. The 176Hf/177Hf in zircons from sample B-EG008 is highly variable

(0.280685-0.282145) representing the difference in unaltered cores to metamict cores.

The ɛHF of cores varies from 2.0 to -12.8 corresponding to depleted mantle Hf model ages of 3.17 to 1.61 Ga. For zircon grains within 10 percent of concordance in sample

B-EG008, there are three main populations of zircons. The oldest source corresponds with a TDM of 3.4 Ga. Zircons clustering at ~1.2 and ~2.4 Ga have TDM model ages of

2.05 and 2.8 Ga respectively, see Fig. 13b.

The 176Hf/177Hf in zircons from sample B-EG014 ranges from 0.281662 to 0.281780 for

207 206 three zircon cores. The ɛHf of the zircon range vary from -7.7 to -8.5. Their Pb/ Pb ages all fall between 1289 to 1416 Ma and their corresponding TDM model ages range from 2.27 to 2.15 Ga. The 176Hf/177Hf in zircon cores from sample B-EG028 are

relatively clustered between 0.281662 and 0.281792. ɛHf varies from -0.2 to -6.2 and the

TDM is ~2.5 Ga.

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

Of the six zircons sampled for Hf isotopes in Sample B-EG032, the 176Hf/177Hf ratios are relatively clustered around 0.281641 to 0.281767. The ɛHf values range from 4.2 to -

12.2 in the oldest and youngest grains respectively (see Fig. 14a). Their TDM model ages range from 2.23 to 2.04. Spot 10 from sample B-EG032 records a U-Pb age of 1779 Ma and an ɛHf of 4.2 indicating the zircon is derived from a relatively juvenile source.

The Hf isotopic data indicates that no zircons are sourced from juvenile melt fractionated from the mantle as no data points plot on the depleted mantle curve. Thus, all zircons are formed from reworked crustal material although some are more juvenile than others.

4.4 Structural Setting and Field Relationships

The khondalites of the central Eastern Ghats Province have been extensively reworked by deep and shallow crustal deformation associated with the assembly of Rodinia and

Gondwana (Shaw et al. 1997; Gupta 2004). Deformation ranges from relatively undeformed in megacrystic granitoids to intensely deformed in the folded gneisses near

Visakhapatnam. Deformation is best seen from a regional scale with the entire Eastern

Ghats Province having undergone extensive deformation and metamorphism. The foliation predominantly dips to the southeast except for where it has been folded close to Visakhapatnam and west of Araku, where it is flat to shallowly dipping. There are two sets of lineations. One plunges subhorizontally NE-SW and the other plunges at

~30 degrees towards ESE (see Fig. 15). Foliation is only present in metasedimentary rocks and consistently dips to the SE (see Fig. 16; Fig. 17).

A weak magmatic flow vector is occasionally apparent in the megacrystic granitoids.

Structure abruptly changes close to Araku (Fig. 17), where zones of partial melt

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crosscut the foliation (Fig. 14e). In the town it is subhorizontal and further west it is dips southward before returning to southeast near a major shear zone. (Fig. 17).

Localised folding has affected the hills close to Visakhapatnam and foliation dips to the

NNE or SSW (Fig. 14b; c; Fig. 17). Two folding events are evident near Visakhapatnam with one producing axial traces plunging to the east and west and a second with north- south trending axial traces. Fold interference patterns are present at loc. 52

(17°47’12.5”N, 83°21’31.9”E) and loc. 55 (17°50’33.4”N, 83°15’13.5”E) (Fig. 14a; f;

Fig. 16).

Kinematic indicators are rare in the central Eastern Ghats Province because the rocks have undergone high grade metamorphism and complex deformation. A large ~100 m wide shear zone in Orissa (loc. 134; 18°21’47.8”N, 82°44’09.5”E; Fig. 16) contains K- feldspar kinematic indicators in a fine grained matrix, which consistently record top to the west movement (Fig. 14c). Several other shear zones are inferred along transect A-B

(Fig. 17). These are interpreted from Google Earth imagery and offer an explanation for the abrupt change in foliation trend north of Araku (Fig. 17).

A large felsic melt vein crosscuts the charnockite at location 13 (18°13’08.9”N,

83°02’21.3”E; Fig. 16) and dips steeply to the east and may be related to Gondwana amalgamation c. 550 Ma (Fig. 14d). A conjugate set was found with similar mineralogy dipping steeply to the west at loc. 61.

The foliation and mineral lineation appear to be related to the peak mineral assemblage.

The south-westerly dipping foliation and eastward dipping mineral lineation are related to compression along a NE-SW axis. The pegmatitic-felsic melt record deformation resulting from an E-W trending stress field as a conjugate set was found. These melt

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

veins overprint the peak mineral assemblage indicating that they are younger than the charnockites that intruded the khondalites. The presence of the pegmatitic melt veins indicates a second deformation event post-cooling of the charnockites.

5 Interpretation

5.1 U-Pb Zircon Geochronology

The large spread in data in most samples suggests a prolonged period of deformation and metamorphism and multiple sediment sources. Multiple age populations suggest multiple phases of zircon growth. For the cluster of zircons at c. 1180 Ma in sample B-

EG008, the 232Th/238U ratios imply that zircons formed at this time are magmatic.

232Th/238U ratios range from 0.33 (Spot 51, 1185 Ma) to 1.12 (Spot 1, 1155 Ma) implying that magmatic zircon crystallisation occurred at this time and thus, the sediments were deposited after this time. This is also evident in sample B-EG010, where Spot 21 records an age of 1145 ± 33 Ma and a 232Th/238U ratio of 0.66. This feature is not preserved in sample B-EG014. Zircons recording a similar age have

232Th/238U ratios of 0.01-0.02. Spot 48 in sample B-EG016 is dated at 1209 ± 33 Ma and has a 232Th/238U ratio of 0.49. The most consistent feature between samples is the age cluster at 930-980 Ma.

The age peak of 945 ± 9 Ma recorded in sample B-EG010 is generated by metamorphic zircon recrystallisation. All zircons analysed (Spot 7, 9, 10, 15, 28, 31, 36) contain textures indicative of granulite facies metamorphism, such as irregular zoning, overgrowths and parallel CL response. The zircons that form a peak at 858 ± 9 Ma

(Spot 2, 3, 17, 30, and 35) are from a population of zircons that are well rounded. They all display complex internal structures consistent with undergoing high grade

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metamorphism. The peak at 1094 ± 30 Ma also appears to be from metamorphically altered zircons. The zircon at 527 ± 7 Ma record lead loss from a late thermal event.

Consistent age populations between sample B-EG008, B-EG014, B-EG028 and B-

EG032 occur at 1559 ± 19 Ma. While this uncertainty is large, all ages are within 1σ and the MSWD for this population is 0.32 (n = 5) implying a strong relationship. A source of detrital zircons to sample B-EG014 and B-EG032 may be 1305 ± 25 Ma. The

MSWD is good at 0.49 (n = 3). A possible sediment source for samples B-EG008 and

B-EG032 is at 1796 ± 35 Ma. The uncertainty is large because only two zircons were used and the MSWD is acceptable at 2.1. Two older sedimentary sources are present in sample B-EG008 that are not present in other samples. Age peaks occur at 2423 ± 19

Ma (MSWD = 1.6; n = 4) and 2661 ± 26 Ma (MSWD = 1.9; n = 2).

5.2 Hf Isotope Analyses

The large spread in data within samples B-EG008 and B-EG032 indicates multiple sediment sources and reworking of multiple reservoirs. At least three sediment sources occur in sample B-EG008 when only grains between 90 and 110 percent concordance are analysed. Zircons in the cluster at ~2400-2700 Ma are likely to be sourced from the

Dharwar Craton. Their ɛHf values range from -11.2 to -1.2 resulting from mixing juvenile and pre-existing crustal material and correspond to a TDM = 3.4 Ga. The ɛHf of zircon grains that record ages between ~1.15 and 1.35 Ga are -9.2 and 2.0 suggesting mixing between juvenile and older melts. The TDM of this population is 2.16 Ga.

Clustering of ɛHf values in sample B-EG014 indicates a single source for those grains (n

= 3) of reworked crustal material as they record negative ɛHf values. Zircon grains in sample B-EG032 record similar ɛHf values to samples B-EG014 and B-EG008 for the cluster at ~1.15 to 1.35 Ga. Given the inherent uncertainty in U-Pb age dating in

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

zircons, these zircon grains are within 1σ error of each other and, can therefore, be assumed to be from the same source as shown in Fig. 13b, corresponding to a TDM c. 2.3

Ga. This source is possibly the Dharwar and Bastar Craton as it corresponds to ages recorded from the Bastar Craton (Meert et al. 2010).

A second common source for sediments between samples B-EG028 and B-EG032 can be seen in Fig. 13a at ~1.55 to 1.7 Ga. This source has a more juvenile ɛHf signature than the source c. 1.2 Ga meaning it is unlikely that they are simply the same terrain reworked.

6 Discussion

6.1 Age and Nature of Protolith Sources

The maximum depositional age for sample B-EG008 is certainly younger than the source dated at 1572 ± 31 Ma and is probably represented by the zircon at 1149 ± 27

Ma. The zircons forming the peak at 1175 Ma both have the internal appearance and

232Th/238U ratios of magmatic zircons. This trend is also consistent in sample B-EG008,

B-EG010, B-EG016 and B-EG028 with 232Th/238U implying magmatic zircon crystallisation c. 1140-1210 Ma, and hence, a short period of deposition before being metamorphosed. Zircons in sample B-EG032 have also crystallised during this period but do not possess the internal appearance of magmatic zircons and have low 232Th/238U ratios. The zircons recording the growth event at ~1.10-1.17 Ga from sample B-EG008 have 232Th/238U ratios greater than ~0.5 and oscillatory zoning and are interpreted to be detrital zircons. Similar zircons to these have been interpreted by Upadhyay et al.

(2009) as metamorphic zircons formed during the early UHT event dated at 1.2 Ga

(Dasgupta & Sengupta 2003). However, similar assemblages have dated UHT

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metamorphism at ~1.1 Ga (Jarick 1999; Mukhopadhyay & Basak 2009). The TDM for the zircons analysed for zircons c. 1.1 Ga from sample B-EG008 (1.61-2.01) suggest reworking of crustal material prior to the crystallisation of these zircons shortly before their deposition.

Detrital zircons that crystallised c. ~1.6 Ga may be sourced from the Rayner Complex in

Antarctica or the Ongole Domain south of the Eastern Ghats. These two regions may have been contiguous at this time as there is an abundance of ~1.6 Ga zircons in these areas (Upadhyay et al. 2009). The population of zircons at 1559 ± 19 Ma (1σ) is certainly within uncertainty of this age. The TDM model age of these zircons is ~2.8 Ga, which implies that the zircons are sourced from the Dharwar and Bastar Cratons. The source of the 1796 ± 35 Ma zircons is possibly the Phulbani Volcanics in the Vinjamuru

Domain of the East Dharwar Craton (Dobmeier & Raith 2003). Upadhyay & Raith

(2006) recorded zircon crystallisation c. 1.4-1.5 Ga related to crustal extension along the eastern margin adjacent to proto-India. This may be the source of the 1416 Ma population in sample B-EG014. This is consistent with research by Upadhyay (2008) proposing that the Eastern Ghats Province sediments were deposited in a rift related basin between proto-India and east Antarctica c. 1.4-1.2 Ga. Upadhyay et al. (2009) assumes all zircons that crystallised after 1.2 Ga are metamorphic based on low Th content. However, in sample B-EG010, spot 21 records a 207Pb/206Pb age of 1145 ± 32

Ma and a 232Th/238U ratio of 0.66. Therefore, as Hoskin and Schaltegger (2003) state that 232Th/238U ratios ≥0.5 correspond to magmatic zircon crystallisation, zircons from samples examined suggest the period of deposition could be extended to ~1.14 Ga.

The zircon populations at 2423 ± 19 Ma and 2661 ± 26 Ma are probably from the

Dharwar Craton or Bastar Craton. Nutman et al. (1996) dated possible sources from the

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

Dharwar Craton as the Sandur greenstone belt as 2658 ± 14 Ma and the Dharwar

Batholith emplacement as 2700-2500 Ma. The population at 2423 ± 19 Ma may also be sourced from the Napier Complex in east Antarctica (Upadhyay et al. 2009). Sources c.

2.2 to 2.5 Ga are dated in Meert et al. (2010).

6.2 Ages of Metamorphism

Multiple metamorphic events are recorded in zircon grains shown in Fig. 5.

Metamorphic zircon growth is not recorded across all samples. This may be due to a number of factors, including sample bias in targeting zircons with detrital appearance when picking and ablating, spatial separation and mineralogy not permitting zircon growth. The earliest metamorphic event (M1) recorded in sample B-EG010 occurs at

1094 ± 30 Ma and in sample B-EG032 at 1099 ± 30 Ma and correlates with UHT assemblage dated by Mukhopadhyay & Basak (2009) at 1099 ± 56 Ma. A similar assemblage has dated UHT metamorphism at 1139 ± 24 Ma (Jarick (1999); quoted in

Simmat & Raith (2008)). Internal recrystallisation in these zircons and overprinting of oscillatory zoning suggests these features formed in a high temperature thermal event.

A later thermal signature of M2 is recorded in sample B-EG014 at 1030 ± 45 Ma, 1014

± 25 Ma in sample B-EG016 and 1007 ± 29 Ma in sample B-EG032. This large spread may be caused by prolonged heating or the large errors associated with 207Pb/206Pb ages.

The irregular patterns in CL in these zircons suggest internal resetting at this time. The dominant peak in ages occurs at 945 ± 9 Ma in sample B-EG010, 937 ± 10 Ma in sample B-EG016, 941 ± 14 Ma in sample B-EG020 and 951 ± 12 Ma in sample B-

EG032 and has been dated by Mukhopadhyay & Basak (2009) ~950 to 1000 Ma representing Grenvillian age deformation. Zircons recording this event are shown in

Fig. 5b, Spot 36; f, Spot 10; g, Spot 22. The CL response showing sector zoning and

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overgrowth textures of these zircons indicates that they have undergone metamorphic recrystallisation, which may be related to plutonic intrusions dated at c. 950 Ma (Harvey

2010). A thermal signature in zircon grains is recorded at 894 ± 16 Ma in sample B-

EG010, 893 ± 11 Ma; sample B-EG016, 892 ± 13 Ma; sample B-EG020, 900 ± 11 Ma; sample B-EG032. This event may be a thermal pulse associated with a prolonged M2 event and the cessation of orogenesis in the Eastern Ghats that has been dated at 1.1-

0.95 Ga (Dobmeier & Raith 2003).

Samples B-EG010 and B-EG016 record a late thermal event at 818 ± 10 Ma and 797 ±

11 Ma, respectively. Pervasive deformation and metamorphism is noted in

Mukhopadhyay & Basak (2009) extending to c. 800 Ma and later (Shaw et al. 1997;

Crowe et al. 2001; Krause et al. 2001; Dobmeier & Raith 2003). This event may be an extension of M2 or a separate event (M3) and further work is needed to date metamorphic zircon crystallisation in the central Eastern Ghats Province. Sample B-

EG008 records a discordia line intercepting at 665 ± 51 Ma and 2514 ± 40 Ma. This event resulted in lead loss in zircons. Dobmeier & Raith (2003) report deformation in the Chilka Lake Domain (see Fig. 2) at 690-660 Ma resulting in reactivation of major shear zones. This event may be recorded by lead loss in zircons from sample B-EG008 as this sample is spatially isolated from others analysed. Several zircons in this sample also record ages c. 540 Ma. Similar ages are recorded in samples B-EG010 and B-

EG016. They are likely the result of lead loss due to heating during the Pan-African collision of proto-India and Antarctica dated at 500-550 Ma by Mezger & Cosca (1999).

6.3 Tectonic Evolution

The earliest visible feature in the metapelites is the strong gneissic mineral banding defining the foliation. Generally, the foliation dips towards the southwest suggesting

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

shortening along a northwest-southeast axis. The mineral lineation dipping to the ESE also indicates shortening along a NE-SW axis related to D1 c. 940 Ma. The southwest dipping foliation is absent in the megacrystic granitoids and charnockites indicating it formed before a major plutonic event c. 950 Ma (Harvey 2010). The earliest folding event F1 can be linked to shortening along a NE-SW axis and occurred coevally or later than peak metamorphism as all zones of partial melt east of Araku are folded with the foliation. Large open-scale folding recorded by Mezger & Cosca (1999) related to Pan-

African collision may be responsible for the apparent doubly plunging fold structure east of Anantagiri. The later folding event only apparent in the Visakhapatnam area may be the result of a late folding event reported to cause dome and basin fold interference patterns along an east-west trending fold axis, perpendicular to the pre-existing fold axis

(Bhowmik 1997; quoted in Gupta (2004)).

Deposition of the protoliths to the central Eastern Ghats Province quartzites and metapelites occurred until at least ~1140 Ma for samples B-EG008, B-EG010, and B-

EG028 and probably sample B-EG014. Due to the spatial distribution of these samples, it is assumed that deposition of the protoliths to other samples continued until this time.

The short period between deposition of sediments and M1 indicates that deposition probably occurred adjacent to the Bastar Craton. Therefore, the sediments were accreted to the Bastar Craton during the ~1.1 Ga collision between east Antarctica and proto-

India. Provenance work presented implies sediment sources are from east Antarctica and proto-India, inferring it is likely that these continents were contiguous prior to the

Eastern Ghats Orogeny.

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7 Conclusions

Deposition of the protoliths to the central Eastern Ghats Province metasedimentary rocks occurred until ~1140 Ma from U-Pb isotope analysis of detrital zircon. Deposition of the protoliths occurred adjacent to the Bastar Craton, possibly in a rift environment between proto-India and east Antarctica. Sources of sediment to the protoliths are the

Bastar Craton, Dharwar Craton, Krishna Province and, the Rayner Province and Napier

Complex in east Antarctica. Deformation in the central Eastern Ghats Province occurred in the Mesoproterozoic to early Neoproterozoic and was associated with the formation of Rodinia and high-temperature metamorphism. Deformation associated with the formation of Gondwana occurred c. 540 Ma.

8 Acknowledgements

First and foremost, I thank my supervisors Guillaume Backé and Alan Collins for their guidance during fieldwork, in Adelaide and wherever else they happened to be during this project. For their help in explaining high-grade terranes and the Eastern Ghats I thank Martin Hand and Saibal Gupta. For keeping me entertained and making fieldwork a thoroughly enjoyable experience, I thank Sarah Marshall, Andrew Barker, Campbell

Harvey, Milo Mawby and Anando Modak. Thanks go to Justin Payne, or as he is commonly known, Pappa Payne, for driving us all over New Zealand and South

Australia and for his invaluable knowledge of the intricate details of U-Pb zircon geochronology and Hf isotope analysis. To Ben Wade and Angus Netting and all the staff at Adelaide Microscopy, thank you for your help in my analytical work and thank you for trusting me to operate a high-powered laser. For helping me make sense of Hf isotope data, thanks go to Katie Howard. Special thanks go to Cari Bertram and Julie

EVOLUTION OF THE CENTRAL EASTERN GHATS PROVINCE

Mackintosh for always being up for a conversation in the office and for accompanying me to hospital in the early hours of the morning in Canberra. To Brianna Telenko, thank you for ironing my shirts when I was otherwise incapable and to Jade Anderson for keeping me company in the waiting room. I would like to express my gratitude to

Caitlin Rowett for her discussions on structural geology and for always coming on my frequent coffee, lunch and ice cream breaks. To Steph Mclennan, thank you for putting your name on my acknowledgements list. You truly are an inspiration. To the honours group of Room 211, thank you for your patience and friendship this year. To Carissa

Digance, Andrew Lewan and Katherine Stoate, my honorary Honours friends, thank you for your visits that helped to break up the days. Thanks must go to the Honours class of 2010 and especially to the Friday night drinks group for making this a year to remember.

For making this project possible, my thanks go to the Australian Government for supporting this work through the Australia-India Strategic Research Fund, the

University of Adelaide and the Geological Society of Australia.

Last and by no means least, I thank my family. To my sister Jessica, thank you for your help proof reading this thesis, for always keeping me entertained with a constant stream of comedic emails and for supplying a second home for me. For their ever-reliable emotional and financial support and for making me laugh every day, special thanks go to my mum and dad.

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9 References

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KELLY N. M., CLARKE G. L. & FANNING C. M. 2002. A two-stage evolution of the Neoproterozoic Rayner Structural Episode: new U-Pb sensitive high resolution ion microprobe constraints from the Oygarden Group, Kemp Land, East Antarctica. Precambrian Research 116, 307-330. KRAUSE O., DOBMEIER C., RAITH M. M. & MEZGER K. 2001. Age of emplacement of massif- type anorthosites in the Eastern Ghats Belt, India: constraints from U-Pb zircon dating and structural studies. Precambrian Research 109, 25-38. KUMAR P. S., MENON R. & REDDY G. K. 2007. The role of radiogenic heat production in the thermal evolution of a Proterozoic granulite-facies orogenic belt: Eastern Ghats, Indian Shield. Earth and Planetary Science Letters 254, 39-54. LI Z. X., BOGDANOVA S. V., COLLINS A. S., DAVIDSON A., DE WAELE B., ERNST R. E., FITZSIMONS I. C. W., FUCK R. A., GLADKOCHUB D. P., JACOBS J., KARLSTROM K. E., LU S., NATAPOV L. M., PEASE V., PISAREVSKY S. A., THRANE K. & VERNIKOVSKY V. 2008. Assembly, configuration, and break-up history of Rodinia: A synthesis. Precambrian Research 160, 179-210. MEERT J. G. 2003. A synopsis of events related to the assembly of eastern Gondwana. Tectonophysics 362, 1-40. MEERT J. G., PANDIT M. K., PRADHAN V. R., BANKS J., SIRIANNI R., STROUD M., NEWSTEAD B. & GIFFORD J. 2010. Precambrian crustal evolution of Peninsular India: A 3.0 billion year odyssey. Journal of Asian Earth Sciences. MEZGER K. & COSCA M. A. 1999. The thermal history of the Eastern Ghats Belt (India) as revealed by U-Pb and 40Ar/39Ar dating of metamorphic and magmatic minerals: implications for the SWEAT correlation. Precambrian Research 94, 251-271. MUKHOPADHYAY D. & BASAK K. 2009. The Eastern Ghats Belt... A Polycyclic Granulite Terrain. Journal Geological Society of India 73, 489-518. NANDA J. K., AUGUSTINE P. F., PANDA P. K. & RAMALINGASWAMY G. 1998. Geological map of the Eastern Ghats Mobile Belt. NUTMAN A. P., CHADWICK B., B. K. R. & VASUDEV V. N. 1996. SHRIMP U/Pb zircon ages of acid volcanic rocks in the Chitradurga and Sandur groups, and granites adjacent to the Sandur Schist Belt, Karnataka. Geological Society of India 47, 153-164. PAYNE J. L., BAROVICH K. M. & HAND M. 2006. Provenance of metasedimentary rocks in the northern Gawler Craton, Australia: Implications for Palaeoproterozoic reconstructions. Precambrian Research 148, 275-291. RAMAKRISHNAN M., NANDA J. K. & AUGUSTINE P. F. 1998. Geological evolution of the Proterozoic Eastern Ghats Mobile Belt. Geological Survey of India Special Publications 44, 1-21. RICKERS K., MEZGER K. & RAITH M. M. 2001. Evolution of the Continental Crust in the Proterozoic Eastern Ghats Belt, India and new constraints for Rodinia reconstruction: implications from Sm-Nd, Rb-Sr and Pb-Pb isotopes. Precambrian Research 112, 183- 210. SANDIFORD M. & HAND M. 1998. Controls on the locus of intraplate deformation in central Australia. Earth and Planetary Science Letters 162, 97-110. SANDIFORD M., PAUL E. & FLOTTMANN T. 1998. Sedimentary thickness variations and deformation intensity during basin inversion in the Flinders Ranges, South Australia. Journal of Structural Geology 20, 1721-1731. SHAW R. K., ARIMA M., KAGAMI H., FANNING C. M., SHIRAISHI K. & MOTOYOSHI Y. 1997. Proterozoic events in the eastern Ghats granulite belt, India: Evidence from Rb-Sr, Sm- Nd Systematics, and SHRIMP Dating. Journal of Geology 105, 645. SIMMAT R. & RAITH M. M. 2008. U-Th-Pb monazite geochronometry of the Eastern Ghats Belt, India: Timing and spatial disposition of poly-metamorphism. Precambrian Research 162, 16-39. SLÁMA J., KOSLER J., CONDON D. J., CROWLEY J. L., GERDES A., HANCHAR J. M., HORSTWOOD M. S. A., MORRIS G. A., NASDALA L., NORBERG N., SCHALTEGGER U.,

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SCHOENE B., TUBRETT M. N. & WHITEHOUSE M. J. 2008. Plešovice zircon -- A new natural reference material for U-Pb and Hf isotopic microanalysis. Chemical Geology 249, 1-35. TORSVIK T. H., ASHWAL L. D., TUCKER R. D. & EIDE E. A. 2001a. Neoproterozoic geochronology and palaeogeography of the Seychelles microcontinent: the India link. Precambrian Research 110, 47-59. TORSVIK T. H., CARTER L. M., ASHWAL L. D., BHUSHAN S. K., PANDIT M. K. & JAMTVEIT B. 2001b. Rodinia refined or obscured: palaeomagnetism of the Malani igneous suite (NW India). Precambrian Research 108, 319-333. UPADHYAY D. 2008. Alkaline magmatism along the southeastern margin of the Indian shield: Implications for regional geodynamics and constraints on craton-Eastern Ghats Belt suturing. Precambrian Research 162, 59-69. UPADHYAY D., GERDES A. & RAITH M. M. 2009. Unraveling Sedimentary Provenance and Tectonothermal History of High-Temperature Metapelites, Using Zircon and Monazite Chemistry: A Case Study from the Eastern Ghats Belt, India. The Journal of Geology 117, 665-683. UPADHYAY D. & RAITH M. M. 2006. Petrogenesis of the Kunavaram alkaline complex and the tectonothermal evolution of the neighboring Eastern Ghats Belt granulites, SE India. Precambrian Research 150, 73-94. VERTVOORT J. D., PATCHETT P. J., SÖDERLUND U. & BAKER M. 2004. The isotopic composition of Yb and the precise aand accurate determination of Lu concentrations and Lu/Hf ratios by isotope dilution using MC-ICPMS. Geochemistry Geophysics Geosystems. WOODHEAD J., HERGT J., SHELLEY M., EGGINS S. & KEMP R. 2004. Zircon Hf-isotope analysis with an excimer laser, depth profiling, ablation of complex geometries, and concomitant age estimation. Chemical Geology 209, 121-135.

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10 Figure Captions

Figure 1. Simplified geological map of cratonic India showing the position of the

Eastern Ghats Province relative to the Singhbum Craton, the Bastar Craton, Dharwar

Craton, Krishna Province and Cuddapah Basin. Modified after Dobmeier and Raith

(2003).

Figure 2. Map of subdivisions of the Eastern Ghats Province based on tectonothermal histories, Sm-Nd isotope model ages and deformation features: 1, Rengali; 2, Angul; 3,

Tikarpara; 4, Khariar; 5, Rampur; 6, Phulbani; 7, Chilka Lake; 8, Visakhapatnam; 9,

Jeypore; 10, Ongole; 11, Vinjamuru; 12, Udayagiri. Map resources are indicated in Fig.

3; box indicates Fig. 3. Modified after Dobmeier and Raith (2003) and Upadhyay et al.

(2009).

Figure 3. Geological map of the central Eastern Ghats Province showing sample locations, roads and railways. Modified after Nanda et al. (1998).

Figure 4. Thin section photomicrograph showing petrological mineralogy and relationships of sample. Mineral abbreviations are as follows: qtz = quartz; pl = plagioclase feldspar; bi = biotite; gt = garnet; opx = orthopyroxene; ti = titanite; mag = magnetite; sill = sillimanite; sp = spinel. (a) Plain-polarised light (PPL) image of sample

B-EG020 showing typical mineralogy of local quartzites; (b) Cross-polarised light

(CPL) image of sample B-EG020; (c) PPL image of sample B-EG028 showing typical mineralogy of local fresh metapelites; (d) CPL image of sample B-EG028; (e) PPL image of sample B-EG032 showing features associated with undergoing high grade metamorphism; (f) CPL image of sample B-EG032. Field of view is 3 mm.

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Figure 5. Cathodoluminesence images representative of zircon grains extracted from (a) sample B-EG008; (b) sample B-EG010; (c) sample B-EG014; (d) sample B-EG028; (e) sample B-EG032; (f) sample B-EG020; (g) sample B-EG016. Displayed spot ages are model ages, and spot size shown is 30 µm.

Figure 6. Sample B-EG008 LA-ICP-MS U-Pb geochronological data for detrital zircons; (a) Conventional U-Pb concordia plot for all zircons. Inset: Conventional U-Pb plot for zircons with 90 to 110 percent concordancy; (b) Probability density distribution, peaks are labelled with calculated weighted average ages with 1σ error

(calculations are summarised in Table. 3). All data shown in blue and zircons with 90 to

110 percent concordancy shown in orange.

Figure 7. Sample B-EG010 LA-ICP-MS U-Pb geochronological data for detrital zircons; (a) Conventional U-Pb concordia plot for all zircons; (b) Probability density distribution, peaks are labelled with calculated weighted average ages with 1σ error

(calculations are summarised in Table. 3).

Figure 8. Sample B-EG014 LA-ICP-MS U-Pb geochronological data for detrital zircons; (a) Conventional U-Pb concordia plot for all zircons. Inset: Conventional U-Pb plot for zircons with 90 to 110 percent concordancy; (b) Probability density distribution, peaks are labelled with calculated weighted average ages with 1σ error

(calculations are summarised in Table. 3). All data shown in blue and zircons with 90 to

110 percent concordancy shown in orange.

Figure 9. Sample B-EG016 LA-ICP-MS U-Pb geochronological data for detrital zircons; (a) Conventional U-Pb concordia plot for all zircons. Inset: Conventional U-Pb plot for main population of zircons; (b) Probability density distribution, peaks are

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labelled with calculated weighted average ages with 1σ error (calculations are summarised in Table. 3). All data shown in blue and zircons with 99 to 101 percent concordancy shown in orange.

Figure 10. Sample B-EG020 LA-ICP-MS U-Pb geochronological data for detrital zircons; (a) Conventional U-Pb concordia plot for all zircons. Inset: Conventional U-Pb plot for zircons with 90 to 110 percent concordancy; (b) Probability density distribution, peaks are labelled with calculated weighted average ages with 1σ error

(calculations are summarised in Table. 3). All data shown in blue and zircons with 90 to

110 percent concordancy shown in orange.

Figure 11. Sample B-EG028 LA-ICP-MS U-Pb geochronological data for detrital zircons; (a) Conventional U-Pb concordia plot for all zircons. Inset: Conventional U-Pb plot for zircons with 90 to 110 percent concordancy; (b) Probability density distribution, peaks are labelled with calculated weighted average ages with 1σ error

(calculations are summarised in Table 3).

Figure 12. Sample B-EG032 LA-ICP-MS U-Pb geochronological data for detrital zircons; (a) Conventional U-Pb concordia plot for all zircons. Inset: Conventional U-Pb plot for zircons with 90 to 110 percent concordancy; (b) Probability density distribution, peaks are labelled with calculated weighted average ages with 1σ error

(calculations are summarised in Table 3). All data shown in blue and zircons with 90 to

110 percent concordancy shown in orange.

Figure 13. Hf isotope data from samples B-EG008, B-EG014, B-EG028 and B-EG032;

(a) ƐHf values plotted against model ages for individual zircon grains from the central

Eastern Ghats Province khondalites and quartzites (b) Initial 177Hf/176Hf values plotted

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against model ages for individual zircon grains from the central Eastern Ghats Province khondalites and quartzites. 176Hf/177Hf = 0.015.

Figure 14. Outcrop photographs from various locations throughout the central Eastern

Ghats Province. (a) Folded khondalite from locality 55 along NE-SW axis; (b) Folded foliation in khondalite from locality 52 along E-W axis; (c) Sigma clast kinematic indicator showing topside to west from locality 134; (d) Pegmatite intrusion in charnockite dipping steeply to the east; (e) Zone of partial melt overprinting flat foliation from locality 86; (f) Folded foliation in khondalite.

Figure 15. Stereonet of foliation and mineral lineations measured in the central Eastern

Ghats Province. Poles to D1 foliation (red) form a profile plane suggesting D2 shortening along a NE-SW axis. Mineral elongation lineations (blue) plunge in two directions. One set plunges subhorizontally NE-SW from west of Araku. The other population from east of Araku plunges at ~30 degrees towards the ESE.

Figure 16. Structural map of central Eastern Ghats Province showing structural transects (Fig. 17), measured foliation, lineation and fold axes and structural features modified after Nanda et al. (1998).

Figure 17. Structural cross sections of the central Eastern Ghats Province showing the transport direction of mapped and inferred shear zones and inferred structural form surface. Lithological units correlate with descriptions in Fig. 3 and are based on Nanda et al. (1998).

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11 List of Tables

Table 1. U-Pb zircon LA-ICP-MS data for samples B-EG008, B-EG010, B-EG014, B-

EG016, B-EG020, B-EG028 and B-EG032.

Table 2. Hf isotope zircon LA-MC-ICP-MS data for samples B-EG008, B-EG014, B-

EG028 and B-EG032.

Table 3. Mineralogy and geochronological zircon growth summary table.

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12 Figures

Figure 1.

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Figure 2.

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Figure 3.

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Figure 4.

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Figure 5.

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Figure 6.

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Figure 7.

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Figure 8.

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Figure 9.

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Figure 10.

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Figure 11.

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Figure 12.

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Figure 13.

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Figure 14.

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Figure 15.

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Figure 16.

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Figure 17.

13 Tables Table 1.

Table 2.

Table 3.

Interpreted Maximum U-Pb Hf Source Age Metm. Sample Mineralogy Depositional geochronology Isotope Components Events Age (Ma) (Ma) 1175 ± 21 Quartz, titanite, 1272 ± 41 sillimanite, 1572 ± 37 Yes Yes 1149 ± 27 665 ± 51 B-EG008 graphite, biotite, 1832 ± 31 zircon 2473 ± 19 2661 ± 26

Quartz, biotite, garnet, zircon, 858 ± 9 B-EG010 Yes magnetite, 1145 ± 33 1145 ± 33 945 ± 9 plagioclase, K- 1094 ± 30 feldspar

Quartz, 1187 ± 29 plagioclase, K- 1298 ± 31 861 ± 12 B-EG014 Yes Yes 1187 ± 29 feldspar, magnetite 1416 ± 20 1030 ± 45 1550 ± 21

Quartz, biotite, 797 ± 11 garnet, plagioclase, 893 ± 11 B-EG016 Yes 1431 ± 25 ≤1431 ± 25 magnetite, biotite, 937 ± 10 sillimanite, titanite 1014 ± 25

Quartz, 892 ± 13 B-EG020 Yes plagioclase, Pre-1 Ga Pre-1 Ga 941 ± 14 sillimanite

Quartz, plagioclase, biotite, 1140 ± 23 sillimanite, 1388 ± 14 B-EG028 Yes Yes orthopyroxene, 1140 ± 23 1569 ± 16 cordierite, 1670 ± 27 magnetite, titanite, spinel

Quartz, plagioclase, 1238 ± 21 900 ± 10 orthopyroxene, 1329 ± 21 951 ± 12 B-EG032 Yes Yes ≤1238 ± 21 sillimanite, garnet, 1552 ± 32 1007 ± 29 titanite, biotite, 1779 ± 21 1099 ± 30 spinel