Study of Calc-Silicate Rocks of Hammer-Head Syncline from Southern Sandmata Complex, Northwestern India: Implications on Existence of an Archaean Protolith

0016-7622/2015-85-2-215/$ 1.00 © GEOL. SOC. INDIA

JOURNAL GEOLOGICAL SOCIETY OF INDIAVol.85, February 2015, pp.215-231

Study of Calc-Silicate Rocks of Hammer-Head Syncline fromSouthern Sandmata Complex, Northwestern India:Implications on Existence of an Archaean Protolith

RITESH PUROHIT1, DOMINIC PAPINEAU

2, PRAKSHAL MEHTA3, MARILYN FOGEL

4,and C.V. DHARMA RAO

5

1Department of Geology, Government College Sirohi, Rajasthan, India-3070012Deptt. of Earth and Env. Sciences, Boston College, Chestnut Hill, MA 02467, USA

3C/o 84 Shanti Nagar, Sirohi, Rajasthan - 307001, India4Department of Earth and Environmental Sciences, University of California, Merced, USA

5National Disaster Management Authority, A-1, Safdarjung Enclave, New Delhi, IndiaEmail: [email protected]

Abstract: Existence of an Archaean protolith is suggested in present study from an ensemble of rocks named as SandmataComplex from northwestern India which have a debatable stratigraphic status of Archaean vs. Proterozoic. Rocks of theSandmata Complex are represented by a highly metamorphosed volcano-sedimentary complex with multiple cycles ofdeformation. The manifold tectono-thermal events have obscured the pristine character of the protoliths. In this work wepresent geochemical features of calc-silicate protolith that show consistent Archaean affinity in the Hammer-Head Syncline(HHS) from southern part of the Sandmata Complex. Notable geochemical characteristics of calc-silicate metasedimentsin the HHS include high Th/U, high Cr concentrations, high La/Th, moderate La/Yb, and weak positive Eu anomaly.Carbon and oxygen stable isotope compositions of these carbonate metasediments vary between -3.0 and -0.3‰ (δ13Ccarb),-11.6 and -35.0 (δ13Corg) and -19.1 and -13.4‰, (δ18O) respectively. These geochemical observations are in conjunctionwith the recently published Neoarchaean ages from the HHS and the proximal Hooke syncline.

Keywords: Sandmata Complex, Archaean Protolith, Petrology, Geochemistry

The basement rocks are predominantly divided into twocontrasting metamorphic litho-facies terrains across theBanas Dislocation Zone (BDZ) passing through Nathadwara(Figs.1, 2). The basement rocks south of Nathadwara, namedas Mewar Gneiss (Roy et al., 1988), are metamorphosed toupper-greenschist facies. Rocks lying north of Nathadwaranamed as Sandmata Complex (Gupta et al., 1981) (Table 1)are metamorphosed to granulite facies. This difference inmetamorphic facies has created confusion in identificationof Archaean protolith in the basement rocks of the SandmataComplex.

The high grade metamorphism in the Sandmata Complexhas reset isochrons in the Archaean protoliths andconsequently most of the geochronological data gaveMesoproterozoic or younger ages. Besides this there areother features that raise doubt about the Archaean status ofthe Sandmata Complex. Such features include absence of‘well-marked unconformity’, conglomerates and palaeosolswhich mark the APB. Some earlier studies (Heron, 1953;

INTRODUCTION

Protolith identification in highly metamorphosedArchaean and Proterozoic terrains is a challenging task. TheArchaean-Proterozoic Boundary (APB) in such terrains maybe a useful marker horizon to delineate Archaean from theProterozoic but classical features associated with the APBare often overprinted and obscure by later crustal processes.A similar incomprehensible APB occurs in the northwesternIndian shield where the Proterozoic Aravalli and Delhiorogenic cycles have variably reconstituted the Archaeanbasement rocks in the Aravalli craton. The protracteddeformation and metamorphism of these basement rockshave caused tectonic mixing that resulted in difficulties torecognize protolith and correlation of the basement rocks.

Basement rocks of Archaean age in Aravalli craton werefirst described as the Banded Gneissic Complex (BGC)(Heron, 1953) (Table 1). The Archaean rocks were laterdifferentiated into overlying Proterozoic rocks of the AravalliSupergroup and the Delhi Supergroup (Roy et al., 1993).

JOUR.GEOL.SOC.INDIA, VOL.85, FEB. 2015

216 RITESH PUROHIT AND OTHERS

Ghosh and Naha, 1962) from the Hammer Head Syncline(HHS) suggested lesser degree of granulite metamorphicoverprinting in the Sandmata Complex (Figure 1, 2) andconsequently could have outcrops that represent theArchaean protoliths which might be occurring as relictremnants in the reconstituted basement. On the contrary laterstudy by Naha and Roy (1983) argued presence of truebasement in the HHS because of partial migmatization. Thepresent study aims at geochemical characterization of thecalc-silicate rocks that might have escaped from the impactof granulite facies metamorphism specifically targeted tothe rocks of HHS in the Sandmata Complex. In absence oftrue APB markers and convincing geochronological datawe attempt to target those geochemical features which couldbe pristine, identifiable and had Archaean affinity.

GEOLOGICAL SETTING

The Archaean basement rocks in the northwest India arecategorized into two domains on the basis of degree ofmetamorphism. Both the domains are separated by adistinct boundary known as Banas Dislocation Zone (BDZ)(Figs.1, 2).

Domain 1: The basement rocks south of the BDZ arecalled as the Mewar gneiss (Fig.1) with preserved pristineArchaean characters due to low-grade green-schist faciesmetamorphism. The rocks are further distinguished intoMavli sector with undisturbed isochron patterns and Berachgranite sector with insignificantly disturbed isochron

patterns due to signatures of low degree of reconstitution.The Berach granite sector also includes bodies of the Aharriver granite, the Sarara ‘inlier’ gneiss and the Berachgranite. Mewar gneiss exhibit Archaean age of 3.3 Ga to2.5 Ga. (Gopalan et al, 1990; Wiedenbeck et al, 1996 a, b;Roy and Kroner, 1996) (Table 2).

Domain 2: The basement rocks north of the BDZ arenamed as Sandmata Complex (Figure 1) with pronouncedimprints of Proterozoic granulite facies metamorphism. Thebasement rocks in the Nathadwara-Amet sector arereconstituted and cratonized along a thick basement-coverinterface zone while in the Sandmata-Bhinai sector the rocksare entirely reconstituted by tectono-thermal activities tohigh strain granulite facies. A single Archaean age of 2.89Ga is reported from composite gneiss of Masuda, in theSandmata-Bhinai sector in the entire Sandmata Complex(Tobisch et al., 1994).

Heron (1953) and Ghosh and Naha (1962) suggestedthe possibility of the Archaean remnant rocks in theNathadwara-Amet sector of the Sandmata Complex whichmight have partially escaped the reconstitution. Two majoroutcrops of such rocks in the block are named as “Hammer-Head Syncline” (HHS) and “Hooke Syncline” (Fig.2). Thename Hammer Head Syncline (HHS) was proposed by Nahaand Halyburton (1974 a, b), to set of rocks forming a regionalsyncline with an outcrop pattern like a head of a hammerwith pointed end towards south-west. These workersassumed that the BGC is ‘migmatized equivalent of theAravalli rocks’ in the HHS region. This was hypothesized

Table 1. Stratigraphic succession of the Precambrian rocks of North-western Indian Shield

Heron (1953) Gupta et. al. (1997) Roy and Jakhar (2002)Delhi system Delhi Supergroup Delhi Supergroup(2000-700m.y.)

Lakhwali Formation Jharol Formation“Raialo series” Jharol Dovda Nathdwara Upper Kabita dolomiteAravalli system Group Group Group Debari Formation(Archaean)

Barilake Group Kankroli Group

Tidi FormationUdaipur Group Middle Bowa Formation = Machla mangra Formation

Mochia Formation = Zawar FormationDebari Group Udaipur Formation(Babarmal Formation)

Jhamarkotra FormationLower Delwara Formation

Banded GneissComplex Bhilwara Supergroup Mewar Gneiss(>2500 m. y.)

AR

AV

ALL

I S

UP

ER

GR

OU

P

AR

AV

ALL

I S

UP

ER

GR

OU

P

https://www.researchgate.net/publication/226747705_Seawater-like_trace_element_signatures_REE_Y_of_Eoarchaean_chemical_sedimentary_rocks_from_southern_West_Greenland_and_their_corruption_during_high-grade_metamorphism?el=1_x_8&enrichId=rgreq-e75da931-21d0-4887-b1d5-dbcee0330ee2&enrichSource=Y292ZXJQYWdlOzI3MTY4NzYyODtBUzoxOTQ5NTQ4MzI5NDUxNTNAMTQyMzQ5MjI2MjExNQ==

https://www.researchgate.net/publication/248450172_Sm-Nd_evidence_for_33_Ga_old_rocks_in_Rajasthan_northwestern_India?el=1_x_8&enrichId=rgreq-e75da931-21d0-4887-b1d5-dbcee0330ee2&enrichSource=Y292ZXJQYWdlOzI3MTY4NzYyODtBUzoxOTQ5NTQ4MzI5NDUxNTNAMTQyMzQ5MjI2MjExNQ==


STUDY OF CALC-SILICATE ROCKS OF HAMMER-HEAD SYNCLINE FROM SOUTHERN SANDMATA COMPLEX 217

on the basis of two features- First was “a strict structuralcontinuity” of the BGC and the Aravalli rocks, emphasizingthe fact that they are structurally and stratigraphicallyindistinguishable and second was reinterpretation of the“Morchana conglomerate” between the BGC and Aravallirocks, which Heron (1953) had described as sign of“pronounced unconformity”. However Naha and Mazumdar(1971) proposed that Morchana conglomerate was a“tectonic mélange” formed due to stretching of competentquartzite band embedded in incompetent mica-schists. This

preposition of these workers evoked that the Aravalli rocksand BGC were coeval and Proterozoic in age. This was lateropposed by many workers through various evidences thatthe BGC was Archaean and the Aravalli Supergroup rocksare Palaeoproterozoic (Roy et al., 1993; Gupta et al., 1981;1995; 1997)

Controversy further prevailed on the stratigraphic statusof HHS rocks. Gupta et al. (1995 a, b; 1997) proposed aPalaeoproterozoic status for the HHS rocks and named theseas the Dovda Group of the Aravalli Supergroup (Table 1).

Fig.1. Generalized geological map of the Precambrian from the northwestern Indian shield (after Roy and Jakhar, 2002)

Alwar

DausaJaipur

Bhinai Agucha

Jahazpur

Bundi

Chittorgarh

Sandmata

Hill

Pali

Jodhpur

Sikar

Jhunjhunu

Delhi

Mt Abu

Sirohi

Udaipur

Dungarpur

Banswara

Bhilwara

Delhi

Ajmer

Nathdwara Marwar Supergroup

Decan Trap

Sand/Soil Cover

Malani Group

Post-Delhi Granites

Sirohi Group

Vindhyan Supergroup

Delhi Supergroup

Aravalli Supergroup

Sandmata Complex

Gneisses& granitoids

(Archaean basement)

26

76

28

26

24

74

24 U

N

M

A

P

P

E

D

0 100

500 Km

80

Ara

valli

Mounta

ins

SCALE

km

20

Study

Area

https://www.researchgate.net/publication/285884705_In_Cassyap_SM_Valdiya_KS_Eds_Lithostratigraphy_and_Tectonic_Evolution_of_Aravalli_Supergroup-A_Protogeosynclinal_Sequence?el=1_x_8&enrichId=rgreq-e75da931-21d0-4887-b1d5-dbcee0330ee2&enrichSource=Y292ZXJQYWdlOzI3MTY4NzYyODtBUzoxOTQ5NTQ4MzI5NDUxNTNAMTQyMzQ5MjI2MjExNQ==



The Dovda Group, which includes the Depti and Devatahriformations, represented shelf type sedimentation. Theserocks are underlained by the Archaean Bhilwara Supergroupbasement rocks and unconformably overlain by the rocksof Mesoproterozoic Delhi Supergroup (Gupta et al., 1997).On the contrary, Roy et al. (2005 a, b) on the basis ofstructural coherence proposed that the HHS (along withentire Sandmata Complex) and Mewar gneiss were coevaland Archaean. The rocks had undergone similarreconstitution which was estimated at 1.84 Ga (Choudharyet al., 1984) and correlated with the culmination of theAravalli orogeny. Roy et al., (2005a) suggested that granulitefacies metamorphism occurred later to Aravalli in SandmataComplex between 1.675 and 1.621 Ga which was correlatedwith the onset of Delhi orogeny. More U-Pb zircon agespoint to granulite facies metamorphism at 1.725–1.72 Gain several areas of the Sandmata Complex (Biju-Sekhar etal., 2003; Buick et al., 2006; Bhowmik et al., 2009; Saha etal., 2008; Sarkar et al., 1989). Disagreeing with thispreposition other workers stated that the granulite faciesmetamorphism occurred later and synchronous with theNeoproterozoic magmatism at ~940-950 Ma (Buick et al.,2006; 2010; Bhowmik et al., 2010; Bhowmik and Dasgupta,2012). The geochronological controversy related to granulitefacies mostly centred around Mesoproterozoic vs

Neoproterozoic, whilst the protolith which escapedmetamorphism remained unidentified.

METHODOLOGY

Detailed lithological studies were conducted by mappingthe area on 1:10000 scale (Fig.3a) and the structural elementsof calc-silicates were analyzed in different outcrop sectors(Fig.3b, Table 3). For geochemical and petrological studiesrock samples of approximate 1kg were collected from twosections in HHS which form well-developed outcrops ofcalc-silicates at Gunjol (GJ series) and Devpuria (DP series)(Fig.3a). Samples were collected at an equal distance of 10mfor the study of stable isotope variations. Care was takenduring sampling and subsequent rock cutting to minimizeheterogeneities from intermixing of the surrounding rocks.Collected samples were chipped off with weathered surfaces,powdered using microdrill, sieved to -200 Mesh level, andanalyzed by Neutron Activation analysis (NAA) method atthe Analytical Chemistry Division of Bhabha AtomicResearch Centre (BARC) in Trombay, Mumbai, India. Theaccuracy levels were about 1-10% (RSD). Aliquots of

Fig.2. Regional geological map of the Nathadwara-Amet melt ofSandmata Complex (modified after Heron, 1953).

Table 2. Geochronological framework of the Archaean basement rocksof the Aravalli mountains (after Roy and Jakhar, 2002)

Age (Ma) Methods used Emplacement events

2450 ± 8 # Single zircon Berach Granite2505 ± 4 # Single zircon Vali River Granite (Jagat)2532 ± 5 # Single zircon Pink Granite Untala2562 ± 6 # Single zircon Ahar River Granite

Shearing and low temperature metamorphism

2620 ± 5 @ Single zircon Gingla Granite2658 ± 5 @ Single zircon Jagat Granite2666 ± 6 @ Single zircon Untala Tropndhjemite Gneiss

(enclave in pink granite)

Ductile deformation, repeated folding and metamorphism

2828 ± 46 * Sm/Nd isochron Mafic dykes/sills inage Rakhiawal greenstone belt

2887 ± 5 @ Single zircon Banded TTG gneiss at Jagat2890 Ma @1 Single zircon Gneiss at Masuda, Ajmer~2905 Ma @2 Single zircon Banded Gneiss, Darwal,

Rajsamandca. 3230 @ Single zircon Trondhjemite intrusion, folding3281 ± 3 $ Single zircon Age of igneous protolith of

& to banded gneisses of3307 ± 65 Sm/Nd isochron Jhamarkotra

age

# Single zircon ion-microprobe U-Pb age (Wiedenbeck et al., 1996)@ Single zircon (evaporation) age (Roy and Kröner, 1996)@1 Single zircon evaporation age (Tobisch et al., 1994)@2 Single zircon evaporation age (A.B. Roy, personal communication)* Sm/Nd whole rock isochron ages (Gopalan et al., 1990)$ Single zircon ion-microprobe U-Pb age (Wiedenbeck and Goswami,1994)


https://www.researchgate.net/publication/231902114_Single_zircon_evaporation_ages_constraining_the_growth_of_the_Archaean_Aravalli_Craton_northwestern_India_Shield?el=1_x_8&enrichId=rgreq-e75da931-21d0-4887-b1d5-dbcee0330ee2&enrichSource=Y292ZXJQYWdlOzI3MTY4NzYyODtBUzoxOTQ5NTQ4MzI5NDUxNTNAMTQyMzQ5MjI2MjExNQ==

https://www.researchgate.net/publication/248352905_Late_Paleoproterozoic_magmatism_in_Delhi_Fold_Belt_NW_India_and_its_implication_Evidence_from_EPMA_chemical_ages_of_zircons?el=1_x_8&enrichId=rgreq-e75da931-21d0-4887-b1d5-dbcee0330ee2&enrichSource=Y292ZXJQYWdlOzI3MTY4NzYyODtBUzoxOTQ5NTQ4MzI5NDUxNTNAMTQyMzQ5MjI2MjExNQ==




Fig.3a. Detail Geological map between the Gunjol and Pharara area in Hammer-Head Syncline of the Rajsamand District showingsample locations of GJ and DP series.

N

LEGENDS:-

DHANI

DEVPURIA (N)

DEVPURIA (S)

BARARARA

MAJA

PHARARA

Calc-Silicate

Granite &Amphibolite Gneiss

GUNJOL

F

F

F

F

F

F

F

F

F

F

FF Fault

GeochemicalSample

GJ - 01 to 12

DP- 01 to 19

F

F

F

F

0 100 200 300 400 500

F

F

73 82'

73 82'

24 95'

Rajsamand

0 1000 Km

52 50'

25 50'

Geopoltical Outline

Map of India



Table 3. S - pole interpretation of the Gunjol Region

S. Sub Location Nature of s pole diagram β (Beta) CommentsNo area

1 1a Dhani Several strong maxima widely spread on both sides of 41.2 = N 115.4 Open reclined foldthe girdle direction. One high population maxima is forming synclinespread along the girdle. Few low population maximaare present towards west side of the stereogram.

2 1b Dhani Three low population maxima spread on both sides of 36.8 = N 82.9 Open reclined foldthe girdle. One maxima which is present towardsNW side of the stereogram is elongated along the girdle.

3 2a Devpuria Two widely spread maxima are observed, both present 0.5 = N 42.5 Open horizontal normalalong the girdle but in different directions of the fold forming anticlinestereogram. First maxima is strong while second is weak.

4 2b Devpuria Three strong maxima narrowly spread on both sides of 7.2 = N 163.9 Open plunging Inclinedthe girdle. fold

5 3a Badarda One maxima is strongly spread along the girdle direction 24.2 = N 166.3 Isoclinal foldwhile several weak elongated sub-maxima spread alongthe girdle direction towards SE and SW side of stereogram

6 4a Khumanpura Several Strong maxima spread along the girdle, while 17.6= N 149.5 Open plunging inclinedsecond sub maxima of low population appears in NW side fold

7 4b Khumanpura Two maxima are observed. One is single maxima is 40.2 = N 166.9 Open plunging inclinedstrongly spread, elongated along the girdle direction whilefoldsecond is low population weak sub-maxima spread.

8 5a Banrinal Several strong maxima spread along the girdle while low 47.7= N 172.7 Open and recumbentpopulation sub-maxima appears on SW side fold

9 5b Banrinal Several maxima spread along the girdle, first maxima is 29.8 = N 152.1 Open recumbent fold,single and strong while second is low population sub- Plunging overturned fold,maxima appearing on WNW side. forming anticline

10 6a Gunjol One single strong maxima, second low population sub- 45.6 = N 126.5 Isoclinal fold andmaxima appears towards ESE side plunging Inclined fold

11 6b Gunjol Several maxima. One single strong maxima passes 41= N 39.5 Isoclinal fold andalong the girdle while other low population scattered plunging Inclined foldsub-maxima

12 7a Maja Strong single spread maxima passes along the girdle 34.6 = N 170.8 Open fold and plungingdirection while few sub maxima appears SW side Inclined fold

13 7b Maja Single maxima is strong spread along the girdle direction 31.2 = N 77.9 Isoclinal foldwhile few low population scattered sub-maxima

14 8a Madra Several strong maxima pass on both side of the girdle 31.7= N 97.5 Open and recumbentwhile some low population scattered sub maxima foldpresent on both side of the girdle

15 8b Madra Single strong maxima passes along the girdle while low 24.6 = N 165.7 Open fold, plungingpopulation sub maxima are present both N and S. inclined fold, anticline

16 9a Pharara Several maxima present. Two strong maxima pass 40.9 = N 104.6 Open fold, plungingalong the girdle while few low population sub-maxima inclined foldare present on S and N of the stereogram.

17 9b Pharara Several strong maxima pass along the girdle while low 24.7 = N 162.0 Open fold, plungingpopulation sub-maxima are present on both side of girdle. inclined fold

18 10a Bhimela Two maxima are observed. One maxima is single and 39.6 = N 59.4 Open fold, plungingstrong while other low population maxima spread Inclined foldSW and ENE corner of the stereogram. Both themaxima are spread on both sides of the girdle.

19 10b Bhimela Several maxima. One strong maxima spread along the 28.0 = N 160.7 Isoclinal fold, plunginggirdle while second and three low population maxima inclined foldare spread on both sides of the girdle almost parallel.



Fig.3b. Detail structural patterns of different sectors of the calc-silicate outcrops.

38

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6851

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4560

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2040

3854

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6257

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406550

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3868

DHANI

PHARARA

DEVPURIA (N)

DEVPURIA (S)

BARARARA

MAJA

LEGENDS:-

Strike & dip of Foliation

35

85

38

44

57

45

53

59

N

52

52

65

MAP PREPARED BY:- Ritesh Purohit

(2007)

57

GUNJOL

5847

24 95 '

73 82 '

F

F

F

F

F

F

F

F

F

FFig. 10a

Fig. 1a

Fig. 2a

Fig. 2b

Fig. 3a

Fig. 4b

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Fig. 5a

Fig. 5b

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Fig. 6b

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Fig. 9b

Fig. 1b

Fig. 10b

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73 82 '

F

F

59

0 100 200 300 400 500

F

F

S - pole diagram with B

axis & Mean axial trace

Prakshal Mehta

Lineation

Fault

Joint

β

β

Beta

7.2

β24.2

β40.2

β

17.6

β47.7

β

29.8

β

45.6

β41

β3

1.2

β34.6

β3

1.7

β24.6

β4

0.9

β24.7

β28

β

39.6

β41.2

β3

6.8

β

0.5

41



powders were also analyzed for stable isotopes at theGeophysical Laboratory of the Carnegie Institution ofWashington in Washington D.C., USA. Carbon and oxygenisotopes of carbonates were measured with a Gas Benchlinked to a MAT 252 isotope ratio mass spectrometer, andgave a precision and accuracy better than 0.2 and 0.3‰,respectively. Carbon isotope compositions of organic matterin carbonate samples were measured on acidified powdersusing an elemental analyzer (EA; CE Instrument NA 2500series) linked to a Finnegan MAT DeltaplusXL isotope ratiomass spectrometer (IRMS) through a Conflo III interfaceand had reproducibility better than 0.2‰.

RESULTS

Lithology and petrography of calc-silicates: The calc-silicate sediments were metamorphosed to granulites faciesand hence referred in this study as calc-granulites. Calc-granulite protoliths outcrop as an eye-shaped body withdifferent structural patterns (Figs. 3a, b). Calc-granuliteoutcrops occur as non-discordant with “elephant skin”ornamented surfaces and unaltered bands which showcoloured and compositional banding (Fig.4a). Calc-granulites are predominantly composed of calcareousminerals intermixed with silicate minerals due to partialmigmatization and strong deformation. Calcareous bandsalso show intermittent association with mafic rocks resultingin amphibolitic gneisses representing partial transformationof the incompetent calc-silicate bands (Fig.4b). In fewoutcrops, calc-granulites graded into amphibolite gneiss,that show well-marked compositional banding.

The calc-granulites are characterized by presence ofcalcite, diopside, augite along with some hornblende (Fig.4c). The co-existence of clinopyroxene and amphiboledenotes that the two minerals locally reached retrogression.Irregular to rounded, semi-concordant layers ofmonomineralic orthopyroxene (Fig.4d) locally occur inclusters and are associated with smaller discordant diopsideveinlets. Massive clinopyroxene layer contains relicinclusions of calcite, quartz, ilmenite and, locally, biotite(Fig.4e). The main calc-silicate assemblage has beenpartially re-crystallized under amphibolite facies conditionsleading to the development of fine–grained bean shaped,pale brown hornblende (Fig.4f), plagioclase, scapolite,quartz and epidote. Calcite porphyroblast with exsolutionlamellae shows distinct grain contacts with plagioclase andmicrocline (Fig.4g). Such assemblages are characterized bycalcite, hornblende, tremolite-actinolite, sphene, plagioclase,scapolite, phlogopite and biotite. Development of calcic-garnet and scapolite with quartz inclusions is also seen in

the calc-granulites along with the presence of epidote. Theseassemblages are formed when Mg and Fe rich calcite reactedwith quartz. Alignment of biotite laths in few thin sectionsshow partial preservation of the original cleavage/schistosityplane. Elongated grains of biotite, calcite, quartz andhornblende often help to identify cleavage fabric thoughthe development of granulite fabric often obliterates thefoliations.

Major and minor element abundances in calc-granulites: The concentration of FeOt varies from 0.48 to2.64 %wt in both sample series (Table 4a) showing narrowrange variations. Average Na concentrations of the 30samples from both the series is around 0.033% (Table 4a).The GJ samples show 0.7 wt% average K2O, while the DPsamples show average values close to 0.3 wt%. In fewsamples the K2O values are zero while in some cases itnears to 3 wt% (Table 4a). Cr concentrations are lowaveraging around 14.7 ppm in DP samples and 18.3 ppm inGJ samples. These levels are similar to the metasedimentaryPalaeoarchaean rocks of Kalgoorlie sequence in Yilgarnblock (Nance and Taylor, 1977). Levels of Co are low in GJcalc-silicates (Average = 0.018 wt%, n=11) compared to DPcalc-silicates (Average= 0.041 wt% n=19) (Table 4b).Average U concentrations are around 0.32 ppm in GJsamples and 0.17 ppm in DP samples, but one sample fromeach section has relatively high U levels around 1.5 ppm.The average concentration of Th in the HHS calc-silicaterocks is around 0.63 ppm in DP samples and 0.32 ppm inGJ samples. Th/U (Table 4c) in the carbonate samples varybetween 4 and 0.8, with an average ratio of about 1.2 forthe DP samples and 1.8 for the GJ samples.

Rare Earth Element abundances in calc-granulites:The total REE content varied significantly in the studiedsamples, and higher average abundances generally occurredin GJ sample series compared to DJ sample series (Fig.5a).Rare Earth Element patterns for HHS calc-silicate rocksshow fluctuations in REE abundances and a flattened HREEpattern. Furthermore, the LREE/HREE was high and thereis a notable positive correlation between LREE and HREEvalues (Fig.5a). Comparisons of total REE abundances forour samples are presented with respect to average chondritecomposition (Taylor and McLennan, 1984) (Fig. 5b). Thestudied calcareous rocks do not show negative Eu anomaliesin the chondrite-normalized plot.

Stable isotope compositions in calc-granulites: δ13Ccarb

value for the GJ-series samples varies between -0.3 and-2.9 ‰ and between -0.9 and -3.0‰ for DP-samples.



� �

� �

� �

�

Fig.4. (a) Calc-silicate outcrop with, “elephant skin” ornamented surfaces. Unaltered bands show coloured and compositional banding(S0) with preferred orientations. (b) Calcareous bands show incompetent deformational behaviour. (c) Calc-silicate having veryhigh degree of intermixing of calcareous and silicate minerals (Bar = 0.28mm, +nicol). (d) Irregular to rounded, semi-concordantlayers of monomineralic orthopyroxene locally occur in clusters and are associated with smaller discordant diopside veinlets.(Bar = 0.28mm, -nicol). (e) Massive, metasomatic clinopyroxene layer contains relic inclusions of calcite, quartz, ilmenite and,locally, biotite. (Bar = 0.065mm, +nicol). (f) Recrystallized calc-silicate assemblage under amphibolite conditions leading to thedevelopment of fine–grained bean shaped, pale brown hornblende. (Bar = 0.28mm, +nicol). (g) Calcite porphyroblast withexsolution lamellae shows clear grain contacts with plagioclase and microcline (Bar = 0.065mm, +nicol)

a b

c d

e f

g



Organic matter in the HHS calc-silicate rocks often has heavyδ13C values up to -11.6‰. δ18Ocarb values has a narrow rangefor both GJ and DP samples between -13.8 & -18.0‰ and-13.8 and -19.1‰ respectively (Table 4d). Total organiccontents (TOC) in GJ-samples are between 0.17 and0.67 wt % and δ13Corg values between -11.6 and -32.7 ‰. Incomparison, the DP-samples have values between 0.11and 0.83 wt% organic carbon and δ13Corg values between-14.1 and -35.0‰. A cross-plot between δ13C and δ18Ovalues and δ13Corg vs TOC is drawn and shown asFigs. 6a, b.

DISCUSSION

The eye-shaped lithological outcrop pattern of the calc-

granulites in HHS (Fig.3a, b) suggests that the rocks mighthave escaped partially from the impact of tectono-thermalreconstitution. Calc-granulites show well-markedcompositional banding indicating preservation of possiblesedimentary features. Partially distorted calcic-garnet and

Table 4a. Major element values in calc-silicates of the study area in wt%

Sample no./ DP-1 DP-2 DP-3 DP-4 DP-5 DP-6 DP-7 DP-8 DP-9DP-10 DP-11 DP-12 DP-13 DP-14 DP-15Element

K2O 0 0 0.46 0 0.32 0.23 0.15 0.14 0.77 0.41 0.47 0.1 0.14 0.23 0.14

Na2O 0.82 0.36 0.51 0.25 0.61 0.04 0.14 0.05 0.27 0.56 1.01 0.04 0.05 0.05 0.15

Fe2O

3(T)2 2.56 1.84 1.45 2.64 0.78 0.65 0.74 1.12 0.92 1.13 0.49 0.59 0.72 0.58

Sample No. DP-16 DP-17 DP-18 DP-19GJ-1 GJ-2 GJ-3 GJ-4 GJ-5 GJ-6 GJ-7 GJ-8 GJ-9GJ-10 GJ-11Element

K2O 0.12 0.27 0 0.92 0.05 0.11 0.08 0.38 0.24 0.64 1 0.26 0.66 2.81 1.35

Na2O 0.07 0.12 0.22 0.32 0.02 0.05 0.04 0.21 0.16 0.37 0.420.1 0.44 1.34 0.85

Fe2O

3(T)0.47 0.61 1.17 1.36 0.48 0.72 0.64 1.22 0.74 1.16 2.08 0.75 0.75 2.621.3

Table 4b Minor element & REE values in calc-silicates of the study area in ppm

Sample No./ DP-1 DP-2 DP-3 DP-4 DP-5 DP-6 DP-7 DP-8 DP-9DP-10 DP-11 DP-12 DP-13 DP-14 DP-15Element

Co 10.3 10.1 6.41 5.24 7.18 2.02 1.94 2.73 4.71 3.854.11 3.06 1.7 2.02 1.92Cr 13.5 13.5 3.69 2.86 5.97 15.12 14.65 14.67 23.7 23.2 22.1 7.9 7.02 11.53 10.95Sc 6.79 4.97 5.98 2.69 6.32 1.87 1.85 2.16 3.06 3.19 2.74 0.67 1.37 1.72 2.18Th 1.32 0.67 0.66 0.59 1.97 0.42 0.95 0.52 0.49 0.490.5 0.3 0.2 0.2 0.4U 1.54 0 0 0 0 0 0 0 0 0.34 0.6 0.2 0 0 0La 4.62 6.42 3.89 4.36 7.84 2.01 2.21 2.45 2.13 1.45 1.74 0.68 1.79 1.86 2.31Ce 7.75 9.95 6.02 6.72 12.68 3.79 4.65 5.45 5.09 3.45 4.06 1.58 2.6 2.34 4.12Eu 0.47 0.44 0.41 0.45 0.67 0.17 0.17 0.22 0.190.2 0.56 0.13 0.4 0.44 0.58Sm 0.94 1.18 0.89 0.84 1.4 0.45 0.47 0.59 0.65 0.48 0.26 0.12 0.15 0.19 0.17Yb 0 0 0.82 0.59 1.11 0 0 0 0 0.37 0.35 0.09 0.29 0.27 0.53Lu 0.14 0.16 0.12 0.11 0.19 0.05 0.05 0.08 0.08 0.08 0.06 0.02 0.04 0.05 0.09Hf 1.1 0.48 0.36 0.38 0.58 0.32 0.3 0.3 0.29 0.31 0.85 0.17 - 0.25 0.32

Sample No./ DP-16 DP-17 DP-18 DP-19GJ-1 GJ-2 GJ-3 GJ-4 GJ-5 GJ-6 GJ-7 GJ-8 GJ-9GJ-10 GJ-11Element

Co 1.51 1.26 1.69 5.8 0.41 0.95 0.43 2.25 1.23 1.68 2.51 1.1 1.18 6.28 2.14Cr 10.27 17.64 27.39 32.84 6.01 11.86 4.67 17.3 10.87 13.53 33.9 16.7 11.2 49.4 26.4Sc 2.04 1.92 3.56 5.19 0.22 0.32 0.21 1.59 0.67 1.01 1.83 0.47 0.62 4.69 2.05Th 0.3 0.4 0.5 1.16 0.2 0.4 0.3 0.8 0.6 0.7 1.7 0.3 0.6 3.2 1.5U 0 0 0.6 0 0 0 0 0 0 0.5 1.1 0.2 0.5 0.8 0.5La 1.22 1.61 1.88 6.64 0 2.04 1.72 4.72 1.59 2.25 6.47 1.57 1.73 13.4 4.58Ce 2.32 3.36 3.42 8.71 1.88 2.74 2.69 6.85 2.73 3.5210.84 2.47 2.61 19.6 7.67Sm 0.37 0.43 0.55 1.36 0 0 0 0.85 0.44 0.53 1.12 0.26 0.34 2.15 0.84Eu 0.16 0.21 0.17 0.34 0.12 0.14 0.12 0.26 0.16 0.16 0.180.2 0.1 0.24 0.1Yb 0.36 0.32 0.48 0.68 0 0.16 0 0.35 0.18 0.16 0.41 0.1 0.13 0.75 0.35Lu 0.06 0.06 0.09 0.13 0.03 0.04 0.07 0.07 0.03 0.04 0.09 0.03 0.04 0.12 0.07Hf 0.22 0.24 0.33 0.57 0.13 0.22 0 0.33 0.26 0.36 0.43 0.23 0.26 0.97 0.64

Table 4c. Ratios of different elements

Average Devpuria GunjolRatios Section Section

(N=19) (N=11)

K2O/Na

2O 1.73 1.99

Th/U 1.2 1.84Ce/La 1.72 1.71La/Yb 9.1 15.2La/Lu 33.4 60.7La/Th 3.7 5.1



scapolite in the calc-silicates suggests the presence ofremnant material. Reconstitution is also observed by thepresence of scapolite and epidote which point tohydrothermal alteration and/or replacement of plagioclase.The effect of potash metasomatism results in kaolinite and/or illite formation as an end-product (Fedo et al., 1997).Both these minerals have transformed under granulite faciesmetamorphism. A fair possibility of potash metasomatismis evident by the presence of kaolinites/illites/sericites inthe calc-silicates since they partially escaped metamorphism.However, the presence of these minerals in calc-silicatesalso leads to the possibility of post-depositional alterationwhich were likely responsible for some of the observedvariations in K concentrations.

Fe compositions represented more or less homogenouscomposition suggesting poor transformations. Graf (1960)showed that FeOt was a first-order controlling factor inArchaean limestone compositions with an averageconcentration of about 1%. DP and GJ sample seriescarbonates had FeOav of 1.09%, (average of 30 samples),consistent with the observations by Graf (1960). Na2O

concentrations had a bimodal distribution pattern and hencepoint to the influence of soda-metasomatism (McLennan etal., 1984). The large range of K2O abundance suggests eitherthe effect of potassic metasomatism or post-depositionalalteration. K2O and Na2O abundances suggest a generaldepletion from the normal marine carbonate values. K2O/Na2O was 1.73 (av. of 15 samples) in DP sample series whileit was close to 2 in GJ sample series (av. of 15 samples)indicating the possibility of local scale differences in palaeo-weathering conditions. Potassium was enriched in GJsamples compared to DP samples. Elevated K concentrationsare common in ancient sediments as compared to the modernsediments (Roscoe et al., 1992) and can indicate that theweathering profiles had a provenance enriched in K derivedfrom granitoids. In the present case, it may suggest that thecarbonates of the GJ series in the HHS had a proximalprovenance and/or may be authigenic carbonates. This isfurther established by comparing the Co concentrations inthe two sections. Levels of Co were low in GJ calc-silicatescompared to DP calc-silicates (Table 4b) that suggests feweradmixtures from the proximal rocks in the former ascompared to latter section. Ahrens (1953) stated that thecoherence of Co and MgO in the sedimentary cycle is poor.So comparing the Co variations in the two sections it ispossible that the GJ section samples were depositedauthigenic. Variations of Th/U in the studied carbonatesamples were on lower side compared to post-Archaeansedimentary rocks in which Th/U typically vary between4.5 to 5.5 (McLennan and Taylor, 1984). Minor element

Table 4d. 13C and 18O Stable isotope data of the carbonates from Devpuria(DP series) section and Gunjol section (GJ series)

Sample δ 13Ccarb

δ 18OPDB

δ 13Corg

TOC δ 13Ccarb–org

(%wt)

DP-01 -1.4 -17.2 -20.0 0.21 18.6DP-02 -2.2 -16.9 -35.0 0.83 32.8DP-03 -1.2 -15.7 -16.0 0.16 14.8DP-04 -1.5 -18.7 -17.9 0.16 16.4DP-05 -2.5 -18.3 -19.1 0.24 16.7DP-06 -1.1 -13.8 -19.7 0.14 18.6DP-07 -1.0 -14.3 -21.2 0.18 20.2DP-08 -1.8 -17.6 -15.8 0.15 14.0DP-09 -1.1 -14.5 -14.1 0.17 13.1DP-10 -1.1 -16.0 -15.7 0.11 14.6DP-11 -1.5 -15.4 -15.0 0.11 13.5DP-12 -0.9 -15.1 -23.9 0.22 23.0DP-14 -1.1 -13.4 -19.9 0.14 18.8DP-15 -1.1 -19.1 -18.2 0.16 17.2DP-16 -1.0 -14.7 -22.0 0.22 20.9DP-17 -1.1 -14.3 -23.7 0.29 22.6DP-18 -3.0 -15.5 -18.5 0.16 15.5DP-19 -2.0 -15.3 -18.9 0.15 16.9GJ-01 -0.7 -16.0 -16.0 0.20 15.3GJ-02 -0.7 -14.8 -20.1 0.25 19.4GJ-03 -0.5 -14.6 -11.6 0.20 11.1GJ-04 -0.5 -14.1 -23.6 0.32 23.1GJ-05 -1.6 -18.0 -21.5 0.67 19.9GJ-06 -0.6 -14.1 -15.8 0.26 15.2GJ-07 -2.4 -13.8 -20.2 0.29 17.9GJ-08 -2.8 -16.6 -32.7 0.55 29.9GJ-09 -0.4 -13.9 -20.3 0.42 19.9GJ-10 -0.3 -14.0 -19.1 0.23 18.7GJ-11 -2.9 -16.9 -17.9 0.17 14.9GJ-12 -1.8 -16.7 -17.3 0.16 15.5

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Fig.5. (a) REE distribution pattern showing a flattened HREEpattern. (b) Chondrite normalized REE values of carbonatescharacterized by positive Eu anomalies



concentrations in the calc-silicates suggest that the rocks ofHHS have signatures consistent with an Archaean affinity.

Studies have shown that the changes from Archaean topost-Archaean sedimentary REE patterns were possiblyrelated to the intrusion of K-rich granites near the end ofArchaean (Veizer and Jansen, 1979; Taylor and McLennan,1985). It has been postulated that there is no fractionationof the REE with increasing metamorphic grade up togranulite facies (cf. Herrman, 1970; McLennan, 1981;Taylor and McLennan, 1985). Friend et al. (2008) gave analternative view on this and suggested that the REEcompositions may be altered during high-grademetamorphism. The most significant observation in thiscomparison is that all the Archaean sedimentary carbonates,sandstones and mudstones are characterized by non-depletion of Eu in contrast to the post-Archaean sediments(McLennan, 1981). The studied calcareous rocks do notshow negative Eu anomalies in the chondrite-normalizedplot. This non-depletion of Eu in calc-silicate rocks fromthe HHS is consistent with an Archaean provenance of thesemetasediments (McLennan and Taylor, 1984). The calc-silicate rocks have an average Ce/La of 1.7, which is muchhigher than the modern marine range of 0.2-0.3 (Turkianand Wedepohl, 1961) and suggests that diagenetic changeswere insignificant. Ce has unique redox state transformationand variations in Ce anomaly have been used to trace palaeo-oceanic redox conditions (Holser, 1977). The positive Ceanomaly observed in the HHS calc-silicate rocks (Figure5a) is consistent with a relatively anoxic setting. The REEconcentrations of the calc-silicates from the HHS suggestthat they preserve Archaean components that may haveoriginated during sedimentation.

The stable isotope compositions of calc-silicate rocksare determined to trace post-depositional fractionation andfor possible inferences on the depositional setting.

Considering the Archaean affinity of the above geochemicalsignatures, the stable isotope compositions of the calc-silicates should be distinct from the nearby Palaeo-proterozoic carbonates. The Jhamarkotra Formationdolomitic carbonates from the lower Aravalli Group areknown to preserve δ13Ccarb excursions up to +11‰(Maheshwari et al., 1999; Sreenivas et al., 2001). The bestestimates of δ13Ccarb for the least altered Archaean carbonateswere near zero ‰ with values typically around +1.5 ± 1.5‰(Veizer et al., 1989 a, b). The δ13Ccarb values in the SandmataComplex calc-silicates were systematically depletedcompared to the least altered Neoarchaean carbonates, whichsuggests significant metamorphic overprint. Depletedδ13Ccarb values in such high grade rocks (-0.3 to -2.9 ‰ forthe GJ-series and -0.9 to -3.0‰ for DP-samples) suggestthat the pre-metamorphic values were higher and possiblycloser to zero permil. The studied carbonates aremetamorphosed to the granulite facies and under suchconditions, δ13Ccarb values became depleted in 13C (Valley,1986; DesMarais, 2001; Kaufman, 1996).

Estimates of δ18O for the least altered Archaeancarbonates were around -7‰ (Veizer et al., 1989 a&b). Therelatively depleted δ18O compositions in the studied calc-silicates were likely affected by fluid exchange duringmetamorphism up to the level of migmatization becauseoxygen isotope fractionation is sensitive to high temperatureexchanges (Valley, 1986). Veizer et al. (1989 a&b)categorized carbonates on the basis of heavy oxygen isotopefractionation patterns when metamorphosed regionally. Theplot between δ18Ocarb and δ13Ccarb values (Fig.6a) show thefield of delta values where the least altered values would lietowards heavier δ18Ocarb and near zero δ13Ccarb but thecorrelation between these isotopic compositions was notclear due to the relatively small range of values.

There was no systematic relationship between the TOC

Fig.6. (a) plot of δ13Ccarb vs. δ18Ocarb and (b) plot of TOC vs. δ13Corg.

-20.0

-15.0

-10.0

-4.0 -3.0 -2.0 -1.0 0.0

d1

8O

carb

d13Ccarb

-40.0

-35.0

-30.0

-25.0

-20.0

-15.0

-10.0

0.00 0.50 1.00

d1

3C

org

TOC (%)

DP-series

GJ-series

a) b)


https://www.researchgate.net/publication/222324923_Positive_delta13C_excursion_in_carbonate_and_organic_fractions_from_the_Paleoproterozoic_Aravalli_Supergroup_Northwestern_India_Precambrian_Res?el=1_x_8&enrichId=rgreq-e75da931-21d0-4887-b1d5-dbcee0330ee2&enrichSource=Y292ZXJQYWdlOzI3MTY4NzYyODtBUzoxOTQ5NTQ4MzI5NDUxNTNAMTQyMzQ5MjI2MjExNQ==



Ma (Roy and Kroner, 1996). Similarly recent study by Royet al., (2012) has shown a detrital zircon age of 2905 Mafrom Darwal granitic gneiss which is closely associatedwith the HHS calc-silicates (Fig.2). Another recent studyby Rao et al. (2011) from north of the Hooke syncline hasyielded detrital zircon ages of 2750 Ma and 2698 Ma from2 closely located samples. These ages from the HHS andHooke syncline suggest that the protolith which acted asprovenance for the gneisses was essentially Mesoarchaeanin age. The similar age brackets (2800-2900 Ma) for theMewar gneiss and the HHS gneiss indicate that they couldbe coeval but had significant difference in grade ofmetamorphism possibly due to separation by the BDZ.

We therefore conclude that the rocks from HHS displayevolutionary history in conjunction with the ArchaeanMewar gneiss. The older protolith in HHS is representedby calc-granulites which is exclusive and noteworthy. Thecalc-granulites indicate some geochemical features like highTh/U, Cr concentrations, and La/Th, as well as intermediateLa/Yb values, the absence of negative Eu anomaly whichsuggests Archaean affinity of these calcareousmetasediments. Stable isotope compositions of organiccarbon displayed a correlation between low TOC and highδ13Corg, which indicates a relatively strong metamorphicoverprint.

Lowe (1982) noted that Neoarchaean sedimentary rocksfrom the Canadian shield and Australia lack a terrigenouscomponent and argued for the lack of extensive sialicbasement. Alternate views exist on the existence and extentof sialic basement in the Neoarchaean (Condie, 1982; 1997;Kroner, 1984). Calc-granulites from the HHS had traceelements and REE abundances that suggest the influence ofgranite-gneiss debris indicative of a sialic basement in theSandmata Complex. This interpretation has also been echoedby Eriksson (1982 a & b) and Peucat et al., (1993) whilestudying similar metasediments from greenstone belts ofAustralia, Canadian Shield and Dharwar craton from southIndia respectively. The presence of amphibolites as well assynkinematically folded granitoid bodies suggest that theterrain was influenced by a bi-modal igneous suiteprovenance (cf. Roy et al., 2012).

Occurrences of calc-granulites outcrops as detachedlenses forming an en-echleon pattern in few cases (Figure3), is similar to Neoarchaean “Internal sediments” of theYilgarn craton. However, an important difference betweenthe two areas is of the associated rocks. The HHSmetasediments are associated with bi-modal igneous suites,whereas, the Yilgarn rocks are generally associated withmafic and ultramafic suites (Bavinton and Taylor, 1980).Taking into consideration the structural analyses and the

and δ13Corg values, but we note that the lowest andpresumably least altered δ13Corg values also had the highestTOC. This stands in contrast with samples that had highand presumably more altered δ13Corg values also had thelower TOC (Fig.6b). This trend further suggests significantmetamorphic alteration of isotopic compositions andtherefore, pre-metamorphic δ13Corg values were likely moredepleted in 13C than most measured values (GJ samplesδ13Corg values between -11.6 and -32.7 ‰; DP-samplesδ13Corg values between -14.1 and -35.0‰). According toValley (1986), (DesMarais, 2001) and Kaufman (1996)δ13Corg values will tend to become enriched in 13C whenthese were thermally altered. Hayes et al. (1983) stated thatthe thermal breakdown causes devolatilization of 12C andhence 13Corg values of residual organic carbon can beconsidered as maximum values of pre-metamorphic organicmatter. In zeolite and lower greenschist facies, C isotopefractionations are possibly less than 2–3‰ (Watanabeet al.,1997), whereas greenschist facies and higher grademetamorphism could impart fractionations of up to 4‰ oreven higher (Hayes et al., 1983). However, precise carbonisotope fractionations for such processes have not yet beendetermined experimentally. Alternatively it is possible thatorganic carbon in these calc-silicate rocks formed from thedecarbonation of carbonate minerals (McCollom, 2003)during high grade metamorphism.

IMPLICATIONS

The debated status of the basement rocks from theSandmata Complex has recently received considerableattention (Roy et al., 2012; Bhowmik and Dasgupta, 2012;Rao et al., 2011; Bhowmik et al., 2010; 2009; Saha et al.,2008). Debate among these workers has mostly centred onthe evolutionary pattern and age. Calc-granulite rocks fromthe HHS are the most suitable candidates to test the Archaeanaffinity in Sandmata Complex. Multiple metamorphic anddeformational events have led to difficulties in determiningthe stratigraphic status of various assorted components inthe HHS. Due to this complexity we decided to trace theArchaean parentage in the rocks of HHS giving preferenceto compare with the well defined Archaean terrane of Mewargneiss which lies proximal to HHS and separated by BanasDislocation zone (BDZ).

Similar to the Mewar gneisses, metasediments of theSandmata Complex were also metamorphosed duringNeoarchaean (Sharma, 1988; Guha and Bhattacharya, 1995)and hence have Archaean sedimentary protoliths. Detritalprovenance is affirmed from detrital zircon in metasedimentsof Mewar gneiss where detrital zircon yield an age of 2887



relationship derived between the gneisses and the carbonatelitho-assemblages in the HHS and considering the age dataof 2.9 Ga (cf. Roy et al., 2012), we propose that thedepositional age for these carbonates could have been before2.9 Ga.

The carbonates display δ13Corg values down to -35.0‰suggesting that pre-metamorphic organic carbon could stillbe more depleted. The datasets indicate that relatively 13C-depleted organic matter occurred in India, similarly toorganic matter in Neoarchaean carbonates from elsewhere(Strauss and Moore, 1992; Shields and Veizer, 2002;Eigenbrode and Freeman, 2006). Highly depleted δ13Corg

values are thought to reflect methanotropy (Hayes, 1994;Hinches, 2002) but the possibility of an alternativemechanism that controls the burial fractions of organic matteras well as carbonate cannot be ruled out. The mechanismthat involves organic carbon burial either directly orindirectly reflects the oxygen contents of the atmosphere(Fischer et al., 2009). The oxygen contents of the atmosphereare also reflected by carbonate deposition. The depositionof carbonates in HHS prior to 2.9 Ga suggests that therewas a possible Neoarchaean rise in atmospheric O2 levelswhich is in corroboration to the observations made fromthe carbonates of the Witwatersrand basin in South Africa(Ono et al., 2006). The recent report of molecular fossilrecords from the Transvaal Group of South Africa alsoprovides evidence for oxygenic photosynthesis during theNeoarchaean (Waldbauer et al., 2009).

The Archaean affinity of the HHS carbonates is alsorevealed from the geochemical characters. Cr abundancesand Th/U were relatively high and comparable to otherArchaean metasediments from Canadian shield and Yilgarancraton of Australia. Average values of 3.7 and 4.1 for GJand DP sections respectively were similar to La/Th valuesof 3.6±0.4 for the Archaean sedimentary rocks and incontrast to the post-Archaean sediments with La/Th valuesof 2.7±0.2 (McLennan et al., 1980). These are eitherconsistent with a more mafic Archaean upper crust thatwould have contributed these geochemical signaturesthrough weathering processes (McLennan et al., 1983 a, b)and/or with fractionation processes during high-temperaturemetamorphism.

The calc-silicates show positive Eu anomalies in thechondrite-normalized plot which is very much unswervingto Archaean affinity of these metasediments (McLennan andTaylor, 1984). Positive anomalies are generally restrictedto plagioclase-rich samples (Nance and Taylor, 1977) orcan be ascribed to hydrothermal activity (Bavinton andTaylor, 1980). Eu has an average concentration of 0.16 ppm

in DP samples and 0.27 ppm in GJ samples (Table 4b), butthese concentrations could have been marginally altered bygranulite facies metamorphism (Friend et al., 2008). REEpatterns and the absence of negative Eu anomaly in the HHScalc-silicates are comparable to those of Neoarchaeanmetasediments in the Dharwar craton from south India(Peucat et al., 1993). HHS calc-silicates showed moderatelyhigh La/Yb values close to 11, similar to Archaeansupracrustal enclaves in southern block of BGC or Mewargneisses (cf. Ramakrishnan and Vaidyanathan, 2008),Yilgarn and Pilbara blocks of Western Australia (McLennanet al., 1983a), the Fig Tree and Moodies Group of SouthAfrica (McLennan et al., 1983b) and the Isua Supracrustalbelt of West Greenland (McLennan et al., 1984). The litho-petrological, geochemical and stable isotope studies on theHHS calc-silicate rocks of Sandmata Complex rocks maysuggest an Archaean status with the following characteristics:1. The HHS bear components of Archaean relicts in the

form of calc-silicate rocks.2. Geochemical features of calc-silicate rocks from the

HHS include high Th/U, La/Th, intermediate La/Ybvalues, absence of negative Eu anomaly. Thesegeochemical compositions suggest Archaean affinity,although post-depositional effects may have affectedthese compositions insignificantly.

3. The correlation between low TOC and high δ13Corg aswell as the systematically negative δ13Ccarb values indicatea relatively strong metamorphic overprint. However, pre-metamorphic values may have been closer to the mostdepleted δ13Corg value measured (-35‰) and isotopicallyheavier than -3‰ for δ13Ccarb, which may have possiblybeen acquired under shallow marine conditions.

Acknowledgements: We would like to thank M. Jacksonfor constructive suggestions that helped improved themanuscript. RP wishes to thanks Prof. A.B. Roy for thepersonal communications during manuscript preparation. RPalso wishes to thank UGC Selection and Award Bureau, NewDelhi, India for the “Research Award” to conduct the presentstudy. RP wishes to acknowledge the permissions grantedby The Commissioner College Education, Govt. ofRajasthan and The Principal Govt. College, Sirohi,Rajasthan, India to undertake the research work. DPgratefully acknowledges support from the GeophysicalLaboratory of the Carnegie Institution of Washington, theNASA Astrobiology Institute, the NASA Exobiology andEvolutionary Biology Program, and the Fond québécois dela recherche sur la nature et les technologies. We wouldalso like to thank to the anonymous reviewers who withthere suggestions made the manuscript more meaningful.


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(Received: 29 March 2013; Revised form accepted: 18 October 2013)








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