Precambrian Research paper

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Precambrian Research 252 (2014) 1–21

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Precambrian Research

jo ur nal homep ag e: www.elsev ier .com/ locate /precamres

eoarchaean felsic volcanic rocks from the Shimoga greenstone belt,harwar Craton, India: Geochemical fingerprints of crustal growth atn active continental margin

. Manikyambaa,∗, Abhishek Sahaa, M. Santoshb, Sohini Gangulyc, M. Rajanikanta Singha,.V. Subba Raoa, M. Lingadevarud

CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad 500 606, IndiaSchool of Earth Science and Resources, China University of Geosciences, Beijing, ChinaDepartment of Geology, University of Calcutta, 35, B. C. Road, Kolkata 700 019, IndiaCentral University of Karnataka, Kadaganchi Campus, Gulburga, Karnataka 585 311, India

r t i c l e i n f o

rticle history:eceived 11 April 2014eceived in revised form 18 June 2014ccepted 20 June 2014vailable online 30 June 2014

eywords:hyoliteshimoga greenstone beltharwar Cratonctive continental marginrustal growth

a b s t r a c t

The felsic volcanic rocks of Neoarchaean Shimoga greenstone terrane of western Dharwar Craton in Indiaare dominantly represented by rhyolites occurring at stratigraphically upper horizons. The Shimoga rhyo-lites are associated with conglomerates, quartzites, argillites, limestones, cherts, basalts and intermediatevolcanic rocks clearly suggesting an accretionary package. The rhyolites of Daginkatte and Shikaripuraareas are potassic, with porphyritic alkali feldspar and quartz as essential minerals and chlorite, biotiteand opaques as accessory phases. Geochemically, the rocks show enrichment in LILE and depletion inHFSE relative to primitive mantle values, with negative Nb-Ta, Zr-Hf anomalies and positive Th anomalies.These features of the Shimoga rhyolites compare well with the geochemical characteristics of magmasgenerated in subduction-related tectonic settings. Their alkaline compositions, intermediate to low HFSEabundances, moderate to high Zr/Y values (1.5–8.3), with La/Ybn (2–28), pronounced negative Eu anoma-lies, and variable LREE/HREE fractionation trends resemble the FI and FII rhyolites of Wabigoon and Uchibelts of Superior Province, Canada. The Shimoga rhyolites are interpreted to be products of melting ofthick basaltic crust metamorphosed to amphibolite/eclogite grade, with garnet- and amphibole-bearingmantle residue. The rhyolites show prominent negative Eu and Ti anomalies, moderate to strong LREE
fractionation, flat to mildly fractionated HREE patterns and are geochemically analogous to Type 1 andType 3 rhyolites of Superior Province, Canada suggesting their derivation from intracrustal melting andfractional crystallization of basaltic liquids with prominent contribution from mantle wedge and slabcomponents. Our data suggest the contribution of Neoarchaean active continental margin processes forthe growth and evolution of continental crust in the western Dharwar Craton.
© 2014 Elsevier B.V. All rights reserved.

. Introduction

The Neoarchaean greenstone belts of the Dharwar Craton ineninsular India and in many other Archaean cratons over theorld such as the Superior Province (Wabigoon, Abitibi, Birch-chi, Wawa greenstone belts) of Canada, Baltic Shield (Karelian,umozero-Kenozero and Vedlozero-Segozero greenstone belts),
ilbara (Whundo greenstone belt) of western Australia, GreenlandIsua and Ivisaartoq greenstone belts), China (Wutaishan and Zun-ua greenstone belts) and the North China Craton are composed
∗ Corresponding author. Tel.: +91 9490705999.E-mail address: [email protected] (C. Manikyamba).

ttp://dx.doi.org/10.1016/j.precamres.2014.06.014301-9268/© 2014 Elsevier B.V. All rights reserved.

of distinct lithological assemblages which preserve geological andgeochemical signatures of magmatism associated with ancientplate-convergence processes (Kerrich et al., 1998; Polat et al.,1998; Hollings and Kerrich, 2000; Polat and Kerrich, 2001, 2006;Manikyamba et al., 2009; Zhai and Santosh, 2011; Dostal andMueller, 2013; Furnes et al., 2013). Tholeiite-komatiite mag-mas derived from plume magmatism and bimodal tholeiitic tocalc-alkaline assemblage of basalt-andesite-dacite-rhyolite (BADR)generated in island arc setting are the two dominant volcanicrock associations characterizing Neoarchaean greenstone terranes
(Kerrich et al., 2000; Wyman et al., 2002; Wang et al., 2008;Manikyamba et al., 2004a,b, 2005). The compositional diversity ofsubduction-derived volcanic rocks is manifested in terms of arc-picrites, boninites, Mg-andesites, adakites and Nb-enriched basalts
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hich represent a variety of magmatic processes in a wide spec-rum of geodynamic environment ranging from intra-oceanic arc

agmatism during ocean–ocean convergence to plume–arc inter-ction, arc-back arc magmatism and active continental marginagmatism in ocean–continent subduction (Wang et al., 2008;anikyamba and Kerrich, 2011, 2012; Manikyamba et al., 2007,

009, 2012). Convergent plate margins are principal sites of terraneccretion and crustal growth, while mixing of subduction-derivedafic magma and crust-derived felsic magma at active continen-

al margin setting accounts for one of the principal mechanismsf crust generation (Foley et al., 2002; Rudnick and Gao, 2003;anikyamba and Khanna, 2007). Rhyolites constitute an integral

omponent of the tholeiitic to calc-alkaline BADR association ofonvergent margin setting. The active continental margins arehe most important sites of generation of rhyolitic magmas inhe ancient and modern subduction systems (Manikyamba et al.,007; Khalifa et al., 2011; Eyuboglu et al., 2013; Praveen et al.,013). A combination of magmatic processes such as influx of slab-ehydrated fluids and melts into mantle wedge, wedge melting,ssimilation of crustal materials by arc magma and magma mixinglay a very important role in the petrogenetic evolution of tholei-

tic to calc-alkaline mafic to felsic magmas in these areas (Gao et al.,012; Guan et al., 2012; Qi et al., 2012; Santosh et al., 2013; Samuelt al., 2014).

In this paper, we report new high precision geochemical datan forty-six samples of felsic volcanic rocks from Daginkatte andhikaripura areas of the Neoarchaean Shimoga greenstone belt, inestern Dharwar Craton, India. The main objectives of this study

re to: (1) understand the type of felsic magmatism, (2) evaluateheir petrogenesis and (3) document the crustal growth processn the western Dharwar Craton which coincides with the globalrustal growth models during the Neoarchean.

. Geological setting

The Meso- to Neoarchean Dharwar Craton of south-rn Peninsular India preserves excellent exposures ofneiss–granite–greenstone associations and intrusive granit-ids which have been divided into the western (WDC) and easternEDC) sectors by the Closepet granite dated at 2518 Ma (Fig. 1A;aqvi, 2005; Ramakrishnan and Vaidyanadhan, 2008; Jayanandat al., 2013a,b and references there in). The volcano-sedimentaryssociations present in the greenstone terranes of the WDC andDC display distinct geodynamic settings, as endorsed by recenteochemical studies (Manikyamba and Kerrich, 2011; Jayanandat al., 2013a,b; Ram Mohan et al., 2013; Peucat et al., 2013;anikyamba et al., 2004a,b, 2005, 2008, 2009, 2012, 2013). Based

n U-Pb zircon ages and Nd isotope data, the Dharwar Cratons a whole has been divided into western (3.4–3.2 Ga), central3.4–3.2 Ga and 2.56–2.52 Ga), and eastern (2.7–2.52 Ga) provincesPeucat et al., 2013; Jayananda et al., 2013a). However, the westernnd eastern greenstone terranes record different geological, geo-hysical and structural characteristics (Manikyamba et al., 2014).ecent seismological studies documented variable thickness ofafic cumulate beneath the WDC (16–30 km) compared to that

f EDC (<5 km). A remarkably thick mafic-intermediate crust>50 km) has been interpreted to exist beneath the WDC relativeo much thinner intermediate-felsic crust (∼38 km) for the EDCith an almost flat Moho (Borah et al., 2014). One of the most

mportant aspects of the eastern Dharwar Craton is the presence ofold bearing greenstone terranes and a large number of kimberlite
ipes. Re-Os isotopic studies on Mesoproterozoic kimberlites and
amproites from the eastern Dharwar Craton suggest a coupling ofontinental crust and subcontinental lithospheric mantle during.5–1.1 Ga. Os isotopic signatures of Raichur and Narayanpet

n Research 252 (2014) 1–21

kimberlites are consistent with multiple sources involving plume,subduction and metasomatized lithosphere. The Re-Os isotopiccompositions of the lamproites indicate their derivation from asubduction modified source (Chalapathi Rao et al., 2013a). Thegeochemical studies on the greenstone belt lithologies have alsoinferred plume–arc interaction and terrane accretion processes inthe Dharwar Craton (Manikyamba and Naqvi, 2002; Manikyambaet al., 2004a, 2005, 2008, 2009, 2012, 2013; Manikyamba andKerrich, 2012). Recent U-Pb ages of groundmass perovskite andSr-Nd isotopic compositions of kimberlites from EDC invoke avariably enriched metasomatized subcontinental lithosphericmantle overprinted by an asthenospheric signature (C halapathiRao et al., 2013b). Geochemical signatures of the Siddanpallikimberlites of EDC have also indicated the interaction betweensubducted lithospheric slabs and plume-related asthenosphericmantle in kimberlite genesis (Khanna et al., 2009). Accordingto Dey (2013), the main crust building period in the westernDharwar Craton is between 3.35 and 3.0 Ga, while in the easternDharwar Craton it is 2.7 and 2.5 Ga. Lithologies of the westernDharwar Craton comprise two generations of greenstone beltsviz. older Sargur Group and younger Dharwar Supergroup, latecalc-alkaline to potassic plutons and TTG-type peninsular gneisses(Naqvi, 2005; Naqvi and Rogers, 1987; Manikyamba et al., 2012,2013; Jayananda et al., 2013a). Sm-Nd whole rock isochron age ofkomatiites of Sargur Group yields 3352 ± 110 Ma whereas SHRIMPU-Pb dating of zircons from felsic volcanic rocks yielded an ageof 3298 ± 7 Ma (Peucat et al., 1995; Jayananda et al., 2013a). TheSargur Group consists of the lower Bababudan Group and upperChitradurga Group. Sm-Nd whole rock isochron of mafic volcanicrocks of Bababudan Group yielded 2.9–2.8 Ga age (Kumar et al.,1996) and zircons from the upper felsic volcanic tuffs are datedas 2.2 Ga (Trendall et al., 1997a,b). The upper Chitradurga Groupcomprising of polymictic conglomerate, greywackes, argillites andlimestones with intercalations of mafic to felsic volcanic rock andBIFs (Chadwick et al., 1991).

The Bababudan and Shimoga greenstone belts form a supert-errane and are separated by the peninsular gneiss in the westernDharwar Craton. Harinadha Babu et al. (1981) divided the Shi-moga greenstone terrane (6000 km2) into Jhandimatti, Joldhal,Medur and Ranibennur Formations (Fig. 1B; Table 1). The Jhandi-matti Formation starts with basement gneiss complex followedby basal polymictic conglomerate, arenites, chlorite-quartz-schist,and quartzite with minor volcanic and pyroclastic rocks. The Jold-hal Formation is made up of chemogenic sedimentary rocks such aslimestone–dolomite (±stromatolites), manganiferous and ferrug-inous cherts, phyllites, carbonaceous phyllites and cherts whichare interlayered with volcanic rocks (Naqvi and Rana Prathap,2007). The Medur Formation predominantly consists of basicto intermediate volcanic rocks with subordinate chemical anddetrital sediments. The volcanic rocks include both porphyriticand pillowed varieties of basalt-andesites-dacite-rhyolite sequenceand volcanic tuffs. Ranibennur Formation consists dominantly ofgreywacke-argillite, chert and felsic volcanic rocks. Naqvi and RanaPrathap (2007) identified adakites within the Ranibennur Forma-tion of Shimoga greenstone belt. Chadwick et al. (1991) dividedthe Dharwar Supergroup occurring adjacent to the Honnali domeinto three stratigraphic units such as the Bababudan Group, andthe lower and upper Chitradurga Groups. The Bababudan Groupconsists of a sequence of metabasalt-orthoquartzite that has beensubdivided into Kudrekonda and Kalva Rangan Durga Formationsnear Honnali dome. The Bababudan Group is overlain by the lowerChitradurga Group which is composed of a lithological association
of polymictic conglomerate and limestone interlayered with maficto felsic volcanic rocks. The lower Chitradurga Group has been sub-divided into Musinhal, Adrihalli, Aleshpur, Medur and DaginkatteFormations, which are followed by the upper Chitradurga Group

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Table 1Stratigraphic succession of Shimoga greenstone belt (modified after Swanminath and Ramakrishnan, 1981; Harinadha Babu et al., 1981).

Basic and ult rabasic intrusives

Granit e, pegmatit e and quartz vein

Ranibennur Fm. Turbidites (graded bedding) like greywacke-argillites and chert-volcanic rock,

interlayered wit h ac id volca nics including adakit es

Medur Fm. Basic, intermediate and ac id volca nics rocks li ke quartz po rphyries, rhyolites,

andesit es, tuff s, pyroclasti c and pillowed andesite and basalt s of BAD R

(basalt -andesit e-dacit e-rhyolit e); subo rdinate chemica l and detrit al sediments,

(2.6 Ga; T rendall et al., 1997 )

Joldhal Fm. Chemogenic sedimentary unit s consist of li mestone-do lomit e (± stromatolit es),

mang aniferous and ferrug inous chert-phyllit e, ca rboniferous, phyllites and cherts,

volca nic rocks

Jhandimatti Fm. Basal or nea r basal polymicti c cong lomerate (graded bedd ing ), arenit es, chlorit e-

quartz schist (meta shale), quartzit es, volca nics and pyroclasti c rocks Unconformity

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Peninsular Gneiss Gneiss ic complex, TT G and diapiric trondhemit es (3.6 Ga, Bhaskar Rao et al., 2005 )

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ig. 1. (A) Simplified geological map of southern Peninsular India showing the wesnd the distribution of greenstone terranes. (B) Geological map of Shimoga greenst

onsisting of Basavapatna and Ranibennur Formations. The fel-ic volcanic rocks of Shimoga greenstone belt occur in Daginkattend Shikaripura areas in the eastern and north-western parts ofhe Honnali dome of the Shimoga greenstone belt (Fig. 1B). Theaginkatte Formation consists of felsic volcanic rocks (Fig. 2And B) with a strike length of ∼45 km and a variable width of–2 km. Primary igneous flow structure is preserved at some placesFig. 2C). SHRIMP U-Pb dating of zircons from felsic volcanic rocks ofaginkatte Formation yields a precise concordant age of 2614± Ma

Trendall et al., 1997b). The Shimoga belt underwent two phasesf deformation and amphibolite facies metamorphism. Geochem-stry and platinum group element (PGE) compositions of Channagiri

afic–ultramafic complex of Shimoga greenstone belt have beentudied by Devaraju et al. (2007). However, geochemical charac-eristics and petrogenetic evolution of the felsic volcanic rocks ofhimoga greenstone belt have not been evaluated in detail till date.n this paper, we investigate the geochemical systematics of rhy-lites from Daginkatte and Shikaripura areas of the Shimoga belto address their geodynamic setting and their role in the crustalvolution of the western Dharwar Craton.

. Sampling and analytical techniques

Relatively fresh samples were collected for the present
tudy from the quarries located at Daginkatte (14◦11′46.4′′ N:5◦47′27′′ E) and Shikaripura (14◦13′12.6′′ N: 75◦16′2.3′′ E) areasFig. 1). After petrographic screening, 46 samples (twenty threerom each locality) were selected for major, trace including rare
d eastern sectors of Dharwar Craton with the intervening belt of Closepet granitesrrane (modified after Harinadha Babu et al., 1981).

earth element (REE) analysis. The rock samples were powdered inan agate mortar. Major elements were determined by X-ray fluores-cence spectrophotometer (XRF; Phillips MAGIX PRO Model 2440)with relative standard deviations within 5%, and totals were all100 ± 1 wt.%. Trace elements including REE were determined byInductively Coupled Plasma Mass Spectrometer (ICP-MS; PerkinElmer ELAN DRC II). The following dissolution method has beenemployed at the National Geophysical Research Institute (NGRI),Hyderabad. A mixture of doubly distilled acids (HF + HNO3 + HCl,5:3:2 ml) was added to ca. 50 mg rock powder in Savillex Vesselsand kept on a hot plate at 150 ◦C for three days. Following this, theentire mixture was evaporated to dryness. The decomposition pro-cedure was repeated by adding 5 ml of the above acid mixture fortwo days. When the sample was dry, 10 ml of 1:1 HNO3 was addedand heated at 150 ◦C for 10–15 min. Then 5 ml Rh (1 ppm concentra-tion) was added as an internal standard. After cooling, the volumeof the solution was made up to 250 ml. JA-1 and JR-1 are used as ref-erence materials and the precision and reproducibility obtained arecompiled in Table 2. Chondrite and primitive mantle values usedfor plotting and calculating trace element ratios (e.g., Ce/Ce* andEu/Eu*, Nb/Th, (La/Yb)n, (La/Sm)n, and (Gd/Yb)n are from Sun andMcDonough (1989). Ce/Ce* and Eu/Eu* ratios were calculated usingthe method given in Taylor and McLennan (1985).

4. Petrography

The rhyolites from both the localities are composed of alkalifeldspar and quartz as essential minerals and chlorite, biotite and

C. Manikyamba et al. / Precambrian Research 252 (2014) 1–21 5

Fig. 2. (A) and (B) Field photographs showing occurrence of felsic volcanic rocks of Daginkatte Formation of Shimoga greenstone terrane. (C) Field photograph showing well-p ing th(

oatpwstdhltft

reserved primary flow texture in Shimoga rhyolites. (D) Photomicrographs showF) primary flow texture in Shimoga rhyolite.

paques as accessory phases. Chlorite is present in minor amounts a secondary mineral after amphibole. Petrographic studies ofhe samples show that these rocks are porphyritic rhyolites com-osed of K-feldspar (Fig. 2D) and quartz (Fig. 2E) phenocrystsith subordinate biotite and chloritized amphibole embedded in a

iliceous, microcrystalline, felsic groundmass of quartz, K-feldspar,iny flakes of chlorite and opaques. K-feldspar phenocrysts are pre-ominant in Shikaripura rhyolites (Fig. 2D). Opaques are mostlyaematite and ilmenite. In most of the samples of Daginkatte rhyo-

ites primary igneous flow texture is retained (Fig. 2F). In contrast,he Shikaripura rhyolites show rotational porphyroblasts of K-eldspar implying the syntectonic rotation of the grains. Some ofhe feldspar grains are altered along the grain boundary.

e occurrence of K-feldspar phenocryst. (E) Quartz phenocryst in Shimoga rhyolite.

5. Geochemistry

Major oxide compositions (Table 3) of the Daginkatte andShikaripura felsic volcanic rocks are marked by higher SiO2 ran-ging from 68 to 76 wt.%, moderate Al2O3 varying between 12.1and 15.8 wt.%, low Fe2O3 (0.18–2.24 wt.%) and extremely high totalalkali (Na2O + K2O) content spanning from 8.6 to 11.46 wt.%. TiO2shows a lower concentration from 0.12 to 0.26 wt.%. High SiO2,relatively lower CaO (0.07–1.74 wt.%) and MgO (0.25–3.1 wt.%)
contents imparts the felsic nature of these volcanic rocks. TheDaginkatte and Shikaripura samples have K2O (8.09–11.2 wt.%)content dominant over the Na2O (0.24–0.51 wt.%) showing a potas-sic character. Plots of major oxides with respect to SiO2 (Fig. 3)

6 C. Manikyamba et al. / Precambria

Table 2Major and trace concentrations of JR-1 and JA-1 obtained from XRF and ICP-MS.

wt.% JR-1 JA-1

A B %RSD A B %RSD

SiO2 75.40 75.41 0.01 64.05 64.06 0.60TiO2 0.11 0.10 0.05 0.88 0.87 1.26Al2O3 12.90 12.89 0.73 14.99 14.98 3.32Fe2O3

(T) 0.97 0.96 2.19 6.94 6.95 1.49MnO 0.10 0.10 4.16 0.15 0.15 5.44MgO 0.09 0.09 1.14 1.60 1.61 0.20CaO 0.62 0.63 0.17 5.69 5.68 2.83Na2O 4.11 4.10 0.16 3.85 3.86 0.00K2O 4.40 4.40 5.24 0.77 0.78 3.37P2O5 0.02 0.02 0.00 0.16 0.87 1.72

ppm

Sc 5.152 5.16 0.974 27.757 28.4 1.304V 0.994 1 1.338 101.028 105 2.007Cr 2.21 2.3 3.996 7.155 7.3 2.062Co 0.649 0.65 0.874 11.307 11.8 2.87Ni 0.653 0.66 0.614 1.742 1.8 0.859Cu 1.386 1.4 0.903 41.276 42.2 1.133Zn 29.73 30 1.278 89.399 90.6 0.703Ga 17.396 17.6 1.073 17.16 17.3 2.043Rb 254.604 257 1.095 11.677 11.8 0.77Sr 29.815 30 0.83 262.308 266 0.987Y 45.357 45.4 0.488 30.213 30.6 0.368Zr 100.511 101 0.563 88.236 88.3 0.376Nb 15.473 15.5 0.454 1.707 1.7 2.032Cs 20.002 20.2 1.206 0.636 0.64 1.679Ba 39.52 40 1.411 304.263 307 0.638Hf 4.57 4.67 1.563 2.326 2.41 6.084Ta 1.868 1.9 1.709 0.097 0.1 2.742Pb 18.888 19.1 1.351 5.741 5.8 2.757Th 26.44 26.5 0.62 0.818 0.82 0.346U 8.909 9 0.956 0.333 0.34 5.689La 19.622 19.7 0.638 5.121 5.1 1.019Ce 46.999 47.1 0.556 13.44 13.5 0.828Pr 5.597 5.62 0.951 1.985 1.98 1.594Nd 23.196 23.5 1.432 10.815 11 1.807Sm 5.968 6.07 1.724 3.458 3.52 1.247Eu 0.309 0.3 0.348 1.145 1.17 1.529Gd 5.214 5.24 0.551 4.349 4.36 1.579Tb 1.002 1.02 1.158 0.742 0.77 3.188Dy 5.656 5.78 1.356 4.31 4.53 2.75Ho 1.09 1.1 2.147 0.943 0.94 1.836Er 3.727 3.78 1.649 2.976 3.01 1.877Tm 0.657 0.67 1.969 0.472 0.48 1.374Yb 4.394 4.49 1.854 2.881 2.92 3.553Lu 0.705 0.71 1.947 0.45 0.47 4.078

Aa

sitra[gaistTwCtwtwm

: present study average of three values; B: reported values from Govindaraju (1994)nd GEOREM (georem.mpch-mainz.gwdg.de/).

how decreasing trends for Al2O3, MgO, Fe2O3 and TiO2 suggest-ng fractional crystallization during the evolution of the magma. Inerms of total alkali vs. silica (Fig. 4A) and immobile trace elementelationships (Fig. 4B), the analyzed rocks exhibit rhyolitic char-cteristics with distinct alkaline nature on SiO2 vs. alkalinity ratioA.R. = Al2O3 + CaO + (Na2O + K2O)/Al2O3 + CaO − (Na2O + K2O)] dia-ram (Fig. 4B; Wright, 1969). Incompatible trace elementbundances of these rocks suggest an overall enrichment in largeon lithophile elements (LILE) and relative depletion in high fieldtrength elements (HFSE; Table 3). Among transitional elements,he rocks display overall depletion in Ni and Cr concentrations.he Daginkatte rhyolites have 0.27–15 ppm Ni and 2.5–16 ppm Crhich are relatively lower than 0.20–65 ppm Ni and 1.9–207 ppmr contents of Shikaripura rhyolites (Table 3).

∑REE contents of

hese rhyolites exhibit a wide range from 37 to 1688 ppm (Table 3),
ith LREE dominant over HREE. Chondrite normalized REE pat-
erns (Fig. 5) show pronounced LREE/HREE fractionation trendsith negative Eu anomalies (Fig. 5; Eu/Eu* = 0.17–1.09). Primitiveantle normalized incompatible trace element patterns (Fig. 5)

n Research 252 (2014) 1–21

for Daginkatte and Shikaripura rhyolites show distinct negativeanomalies at Nb-Ta, Zr-Hf and Ti and positive anomalies at Th.

6. Discussion

6.1. Alteration and element mobility

Due to hydrothermal alteration, metamorphism and defor-mation, it is often difficult to identify the primary geochemicalsignatures of the Archaean volcanic rocks (Polat et al., 2002;Ordónez-Calderón et al., 2008, and references therein). How-ever, the least altered samples showing minimum deformationalimprints, preservation of primary igneous mineral phases and tex-tures, and the absence of carbonate or sulphides were selected forgeochemical analyses in this study. Due to the effects of seafloorhydrothermal alteration and greenschist to amphibolite faciesmetamorphism, the Archaean volcanic rocks have been tested toevaluate the mobility of different elements. In general, the majorelements Al, Ti, Fe, P, the HFSE (Th, Nb, Ta, Zr, Hf), REE (except-ing Ce and Eu), transition metals (Cr, Ni, Sc, V) and Y are relativelyimmobile and insensitive to alteration, whereas major elements,such as Na, K and Ca, and LILE (Cs, Rb, Ba, Sr) and Pb tend to bemobile during alteration and metamorphism (Kerrich and Fryer,1979; Dostal et al., 1980; Ludden et al., 1982; Murphy and Hynes,1986; MacLean and Kranidiotis, 1987; Lafleche et al., 1992; Arndt,1994; Manikyamba et al., 2009; Said et al., 2010). Polat et al. (2002)demonstrated that for Archaean metavolcanic rocks having Ce/Ce*ratios between 0.9 and 1.1 display limited LREE mobility, whereasthose with Ce/Ce* <0.9 and >1.1 are characterized by large LREEmobility. Out of forty-six analyzed samples of Shimoga rhyolites,thirty four samples have Ce/Ce* ratios between 0.9 and 1.1 therebyshowing limited LREE mobility (Table 3), whereas the remainingsamples show Ce/Ce* values <0.9 and >1.1 indicating LREE mobil-ity.

6.2. Types of rhyolites and their petrogenesis

Rhyolites commonly occur in intraoceanic arc, continentalarc and continental rift settings and their geochemical featuresare attributed to different petrogenetic processes (Ayalew andIshiwatari, 2011). Rhyolitic magmas in intraoceanic arc settings(e.g. Izu-Bonin arc) are inferred to be partial melts derived bydehydration melting of calc-alkaline andesites in upper to middleoceanic arc crust (Tamura and Tatsumi, 2002), whereas continen-tal arc rhyolites (e.g. Mt. Wasso rhyolites of Japan) are generated bypartial melting of metamorphosed basalts of thickened lower crustassociated with fractional crystallization and crustal assimilation(Deering et al., 2008). Continental rift zone rhyolites (e.g. rhyolitesfrom Ethiopia) are interpreted as products of fractional crystal-lization and crustal contamination of basaltic magma derived byintracrustal melting (Garland et al., 1997). The evolution of arc-type felsic magmas are controlled by fractionation of hydrous,oxidizing magmas carrying subduction-derived fluid influx andslab melts, whereas rift-type felsic magmas involve fractionationof anhydrous, reducing melts (Christiansen, 2005; Deering et al.,2008; Ayalew and Ishiwatari, 2011; Pankhurst et al., 2011). On thebasis of their geochemical signatures, rhyolites are classified as FI(calc-alkaline, low HFSE, moderate to high Zr/Y, La/Ybn: 5.8–34,strong subduction signatures), FII (calc-alkaline to transitional,intermediate HFSE, moderate Zr/Y, La/Ybn: 1.7–8.8; prominentsubduction signatures, FIIIa (tholeiitic, moderate HFSE, low Zr/Y,
La/Ybn: 1.5–3.5, weak subduction signatures) and FIIIb (tholeiitic,high HFSE and HREE, low Zr/Y, La/Ybn: 1.1–4.9, no subductionsignatures) types (Lesher et al., 1986). The geochemical charac-teristics of the Shimoga rhyolites marked by high-silica, potassic
http://georem.mpch-mainz.gwdg.de/


Table 3Major and trace element composition of rhyolite from Daginkatte (DAG) and Shikaripura (SKP) areas of Shimoga greenstone belt, WDC, India.

DAG11 DAG15 DAG4 DAG14 DAG13 DAG2 DAG20 DAG7 DAG17

SiO2 70.43 70.29 71.28 74.72 72.11 72.53 70.07 75.40 67.66TiO2 0.21 0.18 0.17 0.13 0.15 0.17 0.19 0.14 0.21Al2O3 15.81 14.02 13.66 13.08 14.22 13.02 14.32 13.56 14.91Fe2O3 0.76 1.51 1.87 0.18 0.34 1.22 1.45 0.25 1.76MnO 0.01 0.03 0.02 0.02 0.01 0.02 0.02 0.01 0.03MgO 1.90 2.29 1.53 0.50 0.65 1.52 2.13 0.63 2.72CaO 0.10 0.67 0.46 0.96 0.28 0.77 0.62 0.28 0.99Na2O 0.35 0.43 0.49 0.41 0.44 0.51 0.41 0.42 0.39K2O 9.15 9.16 9.77 8.86 9.93 9.19 9.43 8.23 9.82P2O5 0.01 0.01 0.01 0.01 0.02 0.01 0.02 0.01 0.01LOI 1.00 1.00 1.00 2.00 1.00 1.00 1.00 1.00 2.00Total 99.73 99.59 100.26 100.87 99.15 99.96 99.66 99.93 100.50Na2O + K2O 9.5 9.59 10.26 9.27 10.37 9.7 9.84 8.65 10.21

Cr 3.6 3.1 4.0 3.3 15.7 3.2 3.0 3.3 3.3Co 0.6 0.6 0.6 0.5 54.7 1.3 0.6 0.4 0.8Ni 0.5 0.7 0.4 0.5 15.2 0.5 0.7 0.5 0.8

Rb 188 176 154 139 87 150 167 147 184Sr 15 18 18 19 139 23 19 16 19Cs 1.1 1.7 0.7 0.6 1.6 1.1 1.6 0.6 1.9Ba 385 334 348 296 166 344 326 303 342

Sc 4.1 3.9 3.5 3.3 20.8 3.3 4.1 3.5 5.4V 0.5 0.4 0.5 0.4 29.7 0.4 0.5 0.5 0.5Ta 3.0 2.1 2.2 2.1 0.2 1.8 2.3 2.4 2.7Nb 50.8 33.3 33.5 32.6 2.1 28.9 33.8 33.6 37.1Zr 286 242 229 215 54 209 252 230 285Hf 10.6 8.9 8.4 8.0 1.5 7.4 9.2 8.4 10.6Th 24 19 18 16 1 16 18 17 22U 4.3 3.4 3.0 2.8 0.2 2.9 3.2 3.2 4.8Y 100 71 65 61 16 81 75 51 178

La 113.12 53.74 233.98 61.51 4.68 137.39 202.85 149.11 59.81Ce 234.74 118.97 751.84 129.12 14.55 278.16 666.31 275.81 134.25Pr 24.11 12.37 46.31 13.64 1.27 29.03 41.85 27.83 14.92Nd 90.63 46.55 166.60 52.32 5.98 108.35 156.94 101.91 60.41Sm 19.24 10.67 24.54 10.72 1.71 21.02 29.00 16.92 18.31Eu 1.25 0.80 1.24 0.65 0.64 1.43 1.49 1.02 1.35Gd 16.53 9.58 19.32 9.13 1.82 17.57 23.43 13.23 17.51Tb 2.81 1.79 2.19 1.56 0.39 2.79 3.19 1.66 4.02Dy 13.59 9.51 7.98 7.43 2.19 12.59 12.34 6.56 23.39Ho 2.60 1.86 1.52 1.46 0.44 2.18 1.99 1.23 4.47Er 9.01 6.33 5.81 5.26 1.45 6.97 6.62 4.79 14.40Tm 1.50 1.07 0.97 0.93 0.23 1.04 1.06 0.83 2.31Yb 9.26 7.16 6.72 6.63 1.54 6.45 7.38 5.95 14.14Lu 1.35 1.13 1.04 1.05 0.23 0.94 1.15 0.95 1.99∑

REE 540 282 1270 301 37 626 1156 608 371Cu 1.8 1.3 1.6 2.1 3.4 1.7 1.5 1.7 1.3Pb 16 12 15 17 15 15 12 16 12Zn 21 36 17 16 51 31 19 20 39Ga 27 20 15 12 13 18 21 15 24La/Nb 2.22 1.61 6.98 1.89 2.28 4.75 6.01 4.44 1.61Nb/Ta 17.19 16.04 14.94 15.31 11.06 15.94 14.57 14.19 13.73Zr/Sm 14.87 22.65 9.35 20.10 31.60 9.95 8.67 13.60 15.56Th/Ce 0.10 0.16 0.02 0.12 0.06 0.06 0.03 0.06 0.16(La/Yb)n 8.76 5.38 24.96 6.66 2.18 15.27 19.71 17.96 3.03(La/Sm)n 3.67 3.15 5.95 3.58 1.71 4.08 4.37 5.50 2.04(Gd/Yb)n 1.44 1.08 2.33 1.12 0.95 2.20 2.57 1.80 1.00Eu/Eu* 0.21 0.24 0.17 0.19 1.09 0.22 0.17 0.20 0.23Ce/Ce* 1.10 1.13 1.77 1.09 1.46 1.08 1.77 1.05 1.10Cr/Ni 7.38 4.71 9.61 6.65 1.03 6.63 4.37 6.13 4.04Zr/Hf 27.03 27.12 27.33 26.89 35.02 28.29 27.46 27.48 26.92Zr/Y 2.85 3.38 3.55 3.51 3.33 2.59 3.37 4.52 1.60Ti/Sm 654.85 1012.18 415.70 727.61 5253.94 485.18 393.08 496.45 688.26


Table 3 (Continued)

DAG3 DAG6 DAG19 DAG22 DAG23 DAG24 DAG16 DAG5 DAG8


Cr 3.4 3.2 3.9 4.9 4.6 5.3 3.1 2.5 2.8Co 0.9 0.6 1.1 0.7 0.9 0.9 0.9 1.0 1.0Ni 0.5 0.6 0.5 0.4 0.4 0.5 0.5 0.4 0.5

Rb 153 154 188 144 155 178 206 190 189Sr 21 15 23 22 31 26 31 38 27Cs 1.4 1.4 1.5 0.8 1.1 1.2 1.8 1.7 1.5Ba 320 290 366 390 405 466 458 400 428

Sc 3.8 4.1 4.3 3.6 3.0 3.6 3.6 3.2 3.2V 0.5 0.4 0.5 0.5 0.5 0.5 0.4 0.5 0.5Ta 2.0 2.0 2.4 2.4 2.8 2.7 2.9 2.9 2.7Nb 32.1 28.9 36.2 38.3 32.9 36.0 42.5 40.1 35.9Zr 223 220 266 318 321 387 422 386 376Hf 7.8 8.0 9.8 10.2 10.1 12.1 13.4 12.3 12.1Th 16 16 20 18 19 21 23 21 20U 2.9 2.8 4.6 4.1 4.0 3.5 3.7 3.9 3.4Y 77 50 138 82 89 71 90 67 53


REE 489 304 528 370 1621 1668 1553 440 747Cu 1.7 1.5 1.8 0.8 0.8 0.7 0.8 0.8 0.8Pb 15 13 18 11 10 11 12 10 11Zn 34 29 23 19 32 29 27 47 28Ga 18 18 20 15 20 24 25 25 23La/Nb 3.45 2.19 2.95 2.00 8.61 8.36 6.39 2.34 4.92Nb/Ta 16.23 14.54 15.06 15.63 11.97 13.16 14.65 14.06 13.11Zr/Sm 13.85 20.86 15.23 25.89 10.56 11.06 11.40 24.62 17.42Th/Ce 0.08 0.12 0.09 0.12 0.02 0.02 0.03 0.11 0.06(La/Yb)n 10.76 7.65 6.09 6.47 23.74 28.98 19.40 8.40 17.70(La/Sm)n 4.30 3.76 3.82 3.89 5.82 5.37 4.57 3.73 5.10(Gd/Yb)n 1.52 1.19 1.00 1.09 2.45 3.16 2.50 1.36 2.05Eu/Eu* 0.23 0.23 0.23 0.23 0.18 0.17 0.18 0.21 0.18Ce/Ce* 1.03 1.11 1.13 1.05 1.82 1.78 1.79 1.05 1.04Cr/Ni 7.22 4.93 7.81 11.83 10.32 10.35 6.50 6.03 6.29Zr/Hf 28.46 27.56 27.05 31.14 31.91 31.94 31.45 31.46 31.20Zr/Y 2.89 4.43 1.93 3.87 3.59 5.46 4.70 5.79 7.09Ti/Sm 670.10 911.25 686.70 634.66 256.40 308.89 307.64 650.51 472.24


Table 3 (Continued)

DAG9 DAG10 DAG12 DAG21 DAG18

SiO2 71.57 72.15 71.87 69.27 72.75TiO2 0.17 0.17 0.20 0.26 0.15Al2O3 14.35 14.07 15.61 13.60 13.99Fe2O3 1.18 1.21 0.41 1.88 1.04MnO 0.02 0.02 0.01 0.05 0.02MgO 1.74 1.88 1.01 3.10 1.77CaO 0.35 0.60 0.31 1.28 0.41Na2O 0.41 0.39 0.43 0.38 0.36K2O 8.53 8.98 10.02 9.55 8.37P2O5 0.01 0.01 0.01 0.02 0.02LOI 1.00 1.00 1.00 2.00 1.00Total 99.33 100.48 100.88 101.39 99.88Na2O + K2O 8.94 9.37 10.45 9.93 8.73

Cr 3.5 3.2 2.6 2.6 5.6Co 0.9 0.9 0.6 0.4 0.8Ni 0.4 0.5 0.4 0.3 0.4

Rb 194 137 203 21 170Sr 26 24 27 7 23Cs 1.4 1.0 0.8 0.3 1.2Ba 437 324 475 90 396

Sc 3.7 3.0 3.2 1.6 3.2V 0.4 0.5 0.5 0.2 0.5Ta 3.5 2.2 3.6 0.3 2.3Nb 45.7 29.6 51.4 3.6 30.8Zr 410 306 445 41 330Hf 13.1 9.6 14.3 1.2 10.3Th 23 15 27 4 19U 4.5 3.2 4.6 0.5 2.8Y 109 69 127 27 40

La 84.81 51.59 96.59 26.48 101.18Ce 182.94 111.89 193.19 53.99 189.53Pr 19.84 11.98 21.46 5.53 19.93Nd 75.83 45.17 85.79 21.07 72.21Sm 17.33 10.11 20.11 4.16 12.19Eu 1.25 0.76 1.33 0.28 0.87Gd 15.39 8.96 18.07 3.68 10.49Tb 2.88 1.60 3.24 0.68 1.38Dy 15.72 9.12 17.15 3.88 5.96Ho 3.03 1.81 3.29 0.74 1.06Er 9.95 6.34 11.33 2.44 3.95Tm 1.66 1.10 1.93 0.41 0.71Yb 10.81 7.36 12.61 2.50 5.31Lu 1.61 1.16 1.90 0.36 0.89∑

REE 443 269 488 126 426Cu 0.7 0.9 0.8 0.2 0.8Pb 10 12 10 3 11Zn 30 46 26 14 38Ga 23 17 22 2 20La/Nb 1.85 1.75 1.88 7.37 3.29Nb/Ta 13.19 13.27 14.10 12.69 13.37Zr/Sm 23.64 30.21 22.13 9.76 27.08Th/Ce 0.12 0.14 0.14 0.07 0.10(La/Yb)n 5.63 5.03 5.49 7.59 13.67(La/Sm)n 3.06 3.19 3.00 3.97 5.18(Gd/Yb)n 1.15 0.99 1.16 1.19 1.60Eu/Eu* 0.23 0.24 0.21 0.21 0.23Ce/Ce* 1.09 1.10 1.04 1.09 1.03Cr/Ni 8.94 6.21 6.21 9.68 14.07Zr/Hf 31.36 31.94 31.16 33.12 32.04Zr/Y 3.76 4.45 3.52 1.48 8.26Ti/Sm 588.54 1008.50 596.60 3748.20 738.37


Table 3 (Continued)

SKP3 SKP6 SKP8 SKP10 SKP13 SKP21 SKP23 SKP26 SKP4


Cr 6.8 1.9 1.9 2.4 7.3 2.0 2.0 1.9 52.3Co 0.7 0.3 0.3 0.4 0.7 0.8 0.3 0.4 0.4Ni 0.4 0.2 0.2 0.3 0.3 0.3 0.2 0.2 4.6

Rb 184 195 192 187 169 201 215 180 239Sr 24 24 17 17 17 19 18 13 30Cs 0.6 0.7 0.7 0.8 0.6 0.9 0.6 0.7 0.8Ba 232 239 245 243 236 302 254 196 382

Sc 3.6 3.1 3.4 3.4 3.2 3.3 3.2 3.2 6.4V 0.7 0.4 0.3 0.4 0.7 0.4 0.3 0.4 3.4Ta 2.8 2.7 2.5 2.3 1.1 2.7 2.9 2.2 2.7Nb 39.6 39.4 30.5 35.3 40.7 38.3 37.9 34.1 52.9Zr 408.0 381.8 334.7 400.7 358.6 409.8 416.8 368.7 522.3Hf 12.8 12.2 11.0 12.6 11.3 13.1 13.4 11.7 16.0Th 16.9 15.9 14.3 15.4 15.3 16.7 16.4 14.9 20.0U 3.9 2.8 2.9 3.1 3.5 3.8 2.4 2.1 3.3Y 118.1 97.8 84.9 85.1 102.6 108.9 79.0 92.9 132.3


REE 478.5 512.5 266.9 337.5 524.9 486.0 381.5 584.4 529.9Cu 0.7 0.6 0.7 0.7 1.0 1.3 0.7 0.7 8.2Pb 14 12 10 14 15 14 14 16 13Zn 49 34 20 29 31 51 25 69 73Ga 21 18 15 18 15 24 17 21 28La/Nb 2.31 2.54 1.81 2.04 2.52 2.37 2.21 3.90 1.94Nb/Ta 13.92 14.66 12.43 15.61 35.57 14.11 13.20 15.58 19.54Zr/Sm 21.84 18.30 31.37 25.03 15.54 22.44 24.04 12.34 24.16Th/Ce 0.09 0.07 0.15 0.14 0.07 0.08 0.13 0.08 0.10(La/Yb)n 5.77 8.31 4.19 5.51 7.71 5.82 7.04 11.24 7.24(La/Sm)n 3.06 3.00 3.23 2.81 2.78 3.10 3.01 2.78 2.96(Gd/Yb)n 1.15 1.61 0.77 1.14 1.66 1.18 1.27 2.27 1.68Eu/Eu* 0.21 0.21 0.25 0.22 0.22 0.23 0.23 0.22 0.20Ce/Ce* 1.07 1.06 0.85 0.73 1.00 1.15 0.76 0.70 0.91Cr/Ni 18.95 8.10 8.42 7.20 21.61 8.15 8.50 9.49 11.47Zr/Hf 31.92 31.26 30.45 31.91 31.78 31.31 31.12 31.49 32.67Zr/Y 3.46 3.91 3.94 4.71 3.49 3.76 5.28 3.97 3.95Ti/Sm 449.53 373.96 731.16 524.77 364.06 460.05 484.62 281.22 416.40


Table 3 (Continued)

SKP9 SKP11 SKP25 SKP24 SKP27 SKP20 SKP28 SKP18 SKP22


Cr 115.8 56.0 46.0 41.8 48.6 137.7 207.9 78.3 92.8Co 0.6 0.5 0.4 0.4 0.5 0.7 1.0 0.6 0.6Ni 6.7 5.6 4.1 4.6 8.6 9.0 10.3 8.1 8.3Rb 187 199 196 190 187 169 189 233 222Sr 25 26 29 30 32 13 10 19 17Cs 1.1 1.2 1.0 0.8 0.8 0.6 0.9 1.1 0.9Ba 311 296 299 300 308 202 191 269 302

Sc 5.4 5.5 5.7 5.6 5.8 2.5 2.8 3.4 3.0V 4.2 3.5 3.2 3.1 3.2 4.7 7.6 3.8 4.0Ta 2.1 2.1 2.2 2.1 0.2 3.0 3.6 3.3 3.6Nb 40.7 39.5 45.1 40.5 24.2 28.6 30.0 27.6 37.5Zr 370.6 374.2 380.2 386.4 369.2 344.5 424.0 381.0 465.2Hf 12.1 11.5 12.1 11.9 12.0 11.1 12.9 12.2 14.5Th 15.5 14.9 16.1 15.4 14.9 12.8 14.2 17.2 18.4U 3.6 3.4 3.4 3.6 3.8 2.4 2.3 2.4 3.0Y 127.6 97.5 125.9 119.5 106.6 54.5 74.9 72.9 108.0


REE 468.6 456.4 564.4 437.0 437.6 339.1 351.7 342.1 450.9Cu 11.8 9.0 8.4 9.2 13.6 23.6 27.3 26.1 25.5Pb 19 20 16 17 20 15 8 13 12Zn 82 143 90 97 72 107 99 127 96Ga 20 19 16 20 16 15 20 20 15La/Nb 2.17 2.31 2.50 2.07 3.49 2.40 2.36 2.51 2.40Nb/Ta 19.38 19.00 20.10 19.48 124.19 9.57 8.29 8.49 10.54Zr/Sm 18.38 22.01 18.43 22.23 21.04 26.95 30.75 30.83 26.73Th/Ce 0.09 0.08 0.07 0.09 0.09 0.09 0.10 0.12 0.10(La/Yb)n 6.36 7.71 6.86 5.92 6.48 13.13 11.66 9.03 8.97(La/Sm)n 2.74 3.35 3.40 3.01 3.01 3.36 3.20 3.50 3.23(Gd/Yb)n 1.56 1.56 1.37 1.38 1.47 2.75 2.61 1.79 2.02Eu/Eu* 0.20 0.21 0.18 0.21 0.20 0.19 0.19 0.21 0.20Ce/Ce* 0.92 0.92 0.92 0.91 0.91 1.07 1.05 1.07 1.05Cr/Ni 17.25 10.06 11.10 9.07 5.68 15.33 20.13 9.65 11.21Zr/Hf 30.66 32.45 31.36 32.49 30.82 31.10 32.98 31.33 32.02Zr/Y 2.90 3.84 3.02 3.23 3.46 6.32 5.66 5.23 4.31Ti/Sm 386.73 494.06 378.00 448.77 444.62 563.16 565.63 679.72 551.66


Table 3 (Continued)

SKP15 SKP12 SKP16 SKP14 SKP2

SiO2 72.68 71.45 72.21 72.44 67.56TiO2 0.14 0.13 0.13 0.13 0.21Al2O3 13.30 13.08 13.05 13.83 15.31Fe2O3 2.14 1.93 1.68 1.07 4.04MnO 0.03 0.04 0.03 0.04 0.03MgO 0.92 0.95 0.95 0.56 2.14CaO 0.51 1.16 0.58 1.11 0.24Na2O 0.37 0.34 0.36 0.45 0.36K2O 8.59 9.06 9.84 9.81 8.77P2O5 0.01 0.01 0.01 0.01 0.01LOI 0.66 1.13 1.21 0.91 1.21Total 99.35 99.28 100.05 100.36 99.88Na2O + K2O 8.96 9.4 10.2 10.26 9.13

Cr 80.6 63.0 83.2 120.5 65.5Co 0.6 0.5 0.6 42.7 0.7Ni 8.4 8.2 7.9 65.7 8.6

Rb 217 205 189 1 215Sr 21 23 15 133 11Cs 1.4 0.7 0.7 0.0 1.2Ba 255 252 212 12 239

Sc 3.0 3.1 2.5 25.3 3.2V 3.6 3.4 3.6 390.3 3.3Ta 3.1 1.6 2.7 0.5 4.9Nb 30.8 28.6 28.0 3.6 59.6Zr 406.0 373.2 364.8 99.3 622.6Hf 12.7 11.7 11.2 2.5 20.1Th 16.9 16.0 14.0 0.8 22.6U 2.8 2.8 2.5 0.2 3.8Y 104.0 82.5 59.2 15.7 128.6La 80.21 74.81 67.43 6.55 93.52Ce 158.31 148.40 145.89 16.24 186.99Pr 16.96 15.70 13.71 2.11 20.97Nd 74.63 68.87 59.59 12.06 92.54Sm 15.17 13.85 11.36 3.24 19.53Eu 0.97 0.98 0.78 1.05 1.25Gd 15.63 13.68 11.69 3.27 20.09Tb 2.17 1.86 1.55 0.46 2.98Dy 14.67 12.68 9.93 2.85 20.91Ho 2.96 2.48 1.93 0.53 4.31Er 8.40 6.94 5.19 1.43 12.68Tm 0.94 0.77 0.58 0.16 1.45Yb 6.12 5.10 3.53 1.15 9.09Lu 1.37 1.13 0.79 0.27 1.97∑

REE 398.5 367.2 333.9 51.4 488.3Cu 27.0 27.9 25.2 136.0 23.7Pb 16 14 11 14 31Zn 102 112 92 145 191Ga 21 18 18 16 18La/Nb 2.61 2.62 2.41 1.83 1.57Nb/Ta 9.82 18.33 10.45 7.32 12.28Zr/Sm 26.76 26.95 32.12 30.62 31.89Th/Ce 0.11 0.11 0.10 0.05 0.12(La/Yb)n 9.40 10.51 13.68 4.08 7.38(La/Sm)n 3.30 3.37 3.71 1.26 2.99(Gd/Yb)n 2.07 2.17 2.68 2.30 1.79Eu/Eu* 0.19 0.21 0.20 0.97 0.19Ce/Ce* 1.05 1.06 1.18 1.07 1.04Cr/Ni 9.63 7.66 10.54 1.83 7.58

cfaotm2bbp

Zr/Hf 31.96 31.80

Zr/Y 3.90 4.52

Ti/Sm 553.58 563.14

haracter, Th, La, Zr enrichment, higher Yb contents, variablyractionated LREE/HREE patterns and pronounced negative Eunomalies suggest them to be comparable with FI type rhyolitesf other Archaean greenstone belts (Lesher et al., 1986). Further,heir alkaline composition, intermediate to low HFSE abundance,

oderate to high Zr/Y values (1.5–8.3), La/Ybn ranging from 2 to
8 and pronounced negative Eu anomalies are comparable withoth FI and FII type rhyolites from other Archaean greenstoneelts (Lesher et al., 1986). The Archaean FI rhyolites are inter-reted to be generated by partial melting of thick basaltic crust
32.49 39.45 30.996.17 6.31 4.84

686.74 2405.18 645.26

metamorphosed to amphibolite/eclogite at ∼40 km. In a greenstoneterrane with the transition from arc basalts, boninites to adakites,Nb-enriched basalts and rhyolites suggest a gradual change fromslab dehydration-wedge melting in an intra-oceanic arc settingto slab melting-wedge hybridization processes triggered by slowsubduction, flattening of the subducted slab with gradual migra-
tion of intra-oceanic arc towards active continental margin markedby ocean–continent convergence, crustal melting, and the interac-tion between subduction-derived arc components and continentalcrust.


11

12

13

14

15

16

67 68 69 70 71 72 73 74 75 76 77

lA2O

3

0

1.5

3

4.5

67 68 69 70 71 72 73 74 75 76 77

eF2O

3

1

1.5

2

OaC 2

3

4

OgM

0

0.5

67 68 69 70 71 72 73 74 75 76 77

0

1

67 68 69 70 71 72 73 74 75 76 77

OgM

Sikaripura rhyolite

respe

tmmgFgtCiFpbgt

ie1aCefl2Tsii1ta

SiO2

Fig. 3. Variation plots of selected major element oxides with

The geochemical signatures of rhyolites have been linked withhe depths of partial melting (Hart et al., 2004). FI rhyolitic mag-

as are generated at depths of >30 km with a garnet bearingantle residue, whereas FII types are produced at depths ran-

ing from 10 to 30 km with amphibole-plagioclase residue. TheIII rhyolites originate from <15 depth with plagioclase dominant,arnet-amphibole free residue. Gaboury and Pearson (2008) iden-ified FI, FII, FIIIa and FIIIb rhyolites from Abitibi greenstone belt,anada and explained their distinct geochemical characteristics

n terms of variable degrees and depths of melting. The FI andII rhyolites of Shimoga are thus interpreted to be products ofartial melting of thick basaltic crust metamorphosed to amphi-olite/eclogite facies at depths ranging from >30 km to 10 km witharnet and amphibole-plagioclase-bearing mantle residue respec-ively.

Two types of felsic volcanic rocks (Type 1 and Type 2) occurn association with komatiite-tholeiite sequence from the north-rn Superior Province greenstone belts (Hollings et al., 1999). Type

rhyolites are characterized by relatively aluminous compositionnd strongly fractionated REE patterns which are comparable withenozoic adakites and Archaean high-Al TTG suites. These rhyolitesxhibit strongly fractionated HREE patterns, whereas Type 2 hasat HREE with elevated Ni and Cr contents. Both Type 1 and Type

show LREE enriched patterns and negative Nb and Ti anomalies.ype 1 rhyolites are comparable to southern Superior Province fel-ic volcanic rocks associated with oceanic arc sequences and arenferred to be the products of oceanic slab melting. The geochem-
cal signatures of Type 2 rhyolites may result from mixing of Type
rhyolites with tholeiitic magmas, or a contribution from man-le wedge sources located above the garnet stability field. Hollingsnd Kerrich (2000) reported another type of rhyolites from the arc

SiO2

ct to SiO2 for Shimoga rhyolites of western Dharwar Craton.

basalt-Nb-enriched basalt-adakite association of 2.7 Ga Birch–Uchigreenstone belt and designated them as Type 3 rhyolites. Theseare characterized by moderate LREE fractionation, flat HREE pat-terns, pronounced negative Eu and Ti anomalies, interpreted asthe products of intracrustal fractional crystallization of basaltic liq-uids. The Shimoga rhyolites of the western Dharwar Craton showprominent negative Eu, Ti anomalies, moderate to strong LREEfractionation and flat to low HREE patterns. LREE/HREE (La/Ybn:2–28), LREE/MREE (La/Smn: 1.16–5.95) and MREE/HREE (Gd/Ybn:0.95–3.16) fractionation trends suggest them to be geochemicallyanalogous to Type 1 and Type 3 rhyolites.

6.3. Subduction processes and rhyolite magmatism

Rhyolites are products of petrogenetic processes involving par-tial melting, fractional crystallization and assimilation (Hart et al.,2004; Gaboury and Pearson, 2008). The variation trends of majorelements in these rocks are marked by decreasing Al2O3, Fe2O3,MgO, TiO2 with rising SiO2 (Fig. 3) suggesting fractional crystal-lization of the magma. Lower concentrations of Ni (0.2–65 ppm)and Cr (1.9–207 ppm) and relative enrichment of Rb (21–239 ppm)reflect an evolved nature of these rocks marked by fractional crys-tallization and crustal contamination processes. High K2O contents,negative Ti and P anomalies (Fig. 5) of the studied samples indi-cate contamination by continental crust during the evolution ofthe magma. Negative Eu, P and Ti anomalies imply fractionationof plagioclase, apatite and titanite respectively. These geochem-
ical features are consistent with petrographic evidence markedby abundance of K-feldspar and quartz phenocrysts along withminor plagioclase, absence of apatite and titanite. The primitivemantle-normalized trace element distribution patterns (Fig. 5)

14 C. Manikyamba et al. / Precambria

SiO2

35 40 45 50 55 60 65 70 75 800

2

4

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16

rhyolite

daciteetisedna

citlasabetisednabasaltorcip

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phrit

eba

sinite

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phono-tephrite

tephri-phonolite

basal�ctrachy-andesite

trac hy-andesite

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phonolite

foidite

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Oa

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70

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Calc-alkalineAlkali ne

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1000.0 *OiT /rZ

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1 10

Peral kali ne+strongly al kali ne

A.R.

Fig. 4. Total alkali vs. silica diagram for the Shimoga rhyolites (after LeMaitre, 2002).SWr

eaNCLmdmc2

himoga rhyolites plotted on the immobile trace element discrimination figure ofinchester and Floyd (1977). Plots of silica vs. alkalinity ratio (A.R) for the Shimoga

hyolites (after Wright, 1969).

xhibit enrichment in large ion lithophile elements (LILE) rel-tive to high field strength elements (HFSE) and the negativeb-Ta, Zr-Hf and Ti anomalies attest to a subduction-related origin.hondrite-normalized rare earth element patterns (Fig. 5) exhibitREE enrichment with respect to HREE. The LILE and LREE enrich-ent and relative HFSE depletion may be accounted in terms of

ehydration of subducted oceanic lithosphere and influx of fluidobile elements into the mantle wedge through metasomatic pro-

esses (McCulloch and Gamble, 1991; Manikyamba et al., 2005,014). La/Ybn ranging from 2 to 28 shows a wide variation in

n Research 252 (2014) 1–21

LREE/HREE fractionation, while La/Smn: 1.16–5.95 and Gd/Ybn:0.95–3.16 values corroborate low to moderate LREE/MREE andMREE/HREE fractionation. The REE fractionation trends and a largevariation in Y contents (15.7–138 ppm) of these rhyolites mayreflect a heterogeneous source marked by subduction-derived arccomponents and input from continental crust. These geochemi-cal fingerprints point to their derivation in a subduction-processedcontinental arc related to an active continental margin.

Global correlation studies have suggested that the geochem-ical compositions of arc magmas are predominantly influencedby the geometry and age of the subducting lithospheric slab(Polat and Kerrich, 2001). During steep subduction of hot, youngoceanic lithosphere (<30 Ma), partial melting of basaltic crust ofthe subducting slab (eclogitic composition) with garnet in theresidual melt produces tonalities, trondhjemites, adakites, anddacites characterized by low Yb (<1.9 ppm) and Y (<18 ppm)contents. In contrast, higher Yb (>2 ppm) and Y (20–25 ppm)contents of basalt-andesite-dacite-rhyolite (BADR) magmas oftholeiitic to calc-alkaline association suggest shallow subductionof older oceanic lithosphere (>30 Ma). Their petrogenetic processesinvolve slab dehydration-wedge melting and wedge hybridizationby melting of metamorphosed basaltic crust (low-Mg amphiboliticcomposition) of subducted oceanic slab without residual garnet.The Shimoga rhyolites with Yb (2.5–14 ppm) and Y (15.7–138 ppm)are therefore interpreted to be part of a basalt-andesite-dacite-rhyolite association that was derived by shallow and flat subductionof an older oceanic lithosphere beneath an overriding continen-tal plate. Partial melting of low-Mg amphibolite of subducted andmetamorphosed basaltic crust resulting in low Nb/Ta and highZr/Sm ratios in the melts which has been considered as one of thecontrolling factors for the growth of Archaean continental crust(Foley et al., 2002).

The Shimoga rhyolites show wide variations in Zr/Sm(9–32) andNb/Ta (7–36, with one exception) ratios compared with primitivemantle values (Zr/Sm = 25 and Nb/Ta = 17) which suggest magmamixing in the source and contributions from amphibolitic/basalticcrust of subducted oceanic slab and in their origin. The Nb/Th (<8)ratios of the rhyolite samples with distinct Nb-Ta depletion withrespect to La suggest the role of continental crust in the contamina-tion of the melt. Geochemical characteristics of the studied sampleslike high Al2O3, K2O and Th enrichment, Nb/Th <8 demonstrate theeffects of crustal assimilation coupled with fractional crystalliza-tion (AFC). This observation corroborates the inference of partialmelting of metamorphosed basaltic crust and interction with man-tle wedge melts that incorporated slab-dehydrated fluid influx andslab-derived melts, which subsequently evolved by AFC processesin a continental margin arc regime.

6.4. Adakites and rhyolites in arc environment

Partial melting of metasomatized mantle wedge and subductingoceanic crust are the principal processes responsible for the gen-eration of arc magmas (Castillo, 2006; Straub and Zellmer, 2011;Sato et al., 2012). K-adakites, adakitic rhyolites, rhyolitic adakites,adakitic andesites, and adakitic rhyodacites have been suggestedas products of subduction processes controlled by significant con-tributions from subducting slab and intracrustal components ofoverriding plate (Macpherson et al., 2006; Falloon et al., 2008;Shuto et al., 2013). Experimental studies on melting of hydratedor dehydrated metabasalts, Archaean and modern amphiboliteshave supported the origin of adakitic magmas from slab melt-ing. Archaean tonalite–trondhjemite–granodiorite (TTG) suites are
products of direct partial melting of subducted oceanic crust(Martin, 1999; Tsuchiya et al., 2007), whereas adakites are inter-preted to be generated by slab melting and interaction of slabmelts with overlying mantle wedge (Smithies, 2000; Falloon et al.,


1

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La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Nb Ta La Ce Pr Nd Zr Hf Sm Eu Ti Gd Tb Dy Y Ho Er Tm Yb Lu

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eltna

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H

Fig. 5. (A), (C), (E), (G), (I), (K), (M) and (O) Chondrite normalized REE patterns for Shimoga rhyolites. Normalizing factors are from Sun and McDonough (1989). (B), (D), (F),(H), (J), (L), (N) and (P) Primitive mantle-normalized multi-element plots for Shimoga rhyolites. Normalizing factors are from Sun and McDonough (1989).


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La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Th Nb Ta La Ce Pr Nd Zr Hf Sm Eu Ti Gd Tb Dy Y Ho Er Tm Yb Lu

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e tirdnohC/

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Fig. 5. (Continued)

mbrian Research 252 (2014) 1–21 17

2tdm(Ohapeucscai2batf1Kcsiplsatmgonraas

6

rbAabacchdprvtgmp(achst

Fig. 6. Plots of (A) Th/Ta vs. Yb (after Pearce and Peate, 1995) and (B) Th vs. Ta (Pearceet al., 1984) discrimination figures for Shimoga rhyolites of western Dharwar Craton.


008; Sato et al., 2012; Eyuboglu et al., 2013). Alternative tohe slab-melting mechanism, fractional crystallization of mantle-erived basaltic magma or lower crust-derived andesitic-daciticagma accounts for the non-slab origin for adakitic magmas

Castillo, 2006; Macpherson et al., 2006; Sato et al., 2012). Lateligocene to Middle Miocene adakitic andesites associated withigh-magnesian andesites and basalts from SW and NE Japanrcs and Middle Miocene adakitic rhyodacites from NE Japan arcsrovide insights into adakitic magmatism in a cool subductionnvironment. The generation of adakitic magmas was induced bypwelling of hot asthenosphere into subcontinental lithosphereausing partial melting of overlying mantle wedge and the coldubducting Pacific plate (Sato et al., 2012; Shuto et al., 2013). Geo-hemical studies on komatiite–tholeiite, arc basalts and adakitessociation in the Sandur greenstone terrane suggest mantle plumempingement beneath continental lithosphere (Manikyamba et al.,008). Komatiite–basalt–rhyolite associations from greenstoneelts of Northern Superior Province suggest interaction of plumend subduction processes (Hollings et al., 1999). Plume–arc interac-ion and associated accretionary processes have been documentedrom the Holenarsipur schist belt of WDC (Kunugiza et al.,996). Petrogenetic modelling of volcanic rocks from Holenarsipur,udremukh and Bababudan suggest rift-controlled volcanism asso-iated with plume activity (Rajamani, 1990). The geochemicalignatures of uncontaminated and crustally contaminated komati-tes of Sigegudda greenstone terrane of western Dharwar recordslume magmatism with significant contributions from continental

ithosphere (Manikyamba et al., 2013). This observation is sub-tantiated by the arc picrite–potassic adakitic-shoshonitic volcanicssociation of Sigegudda that preserves geochemical signatures ofransition from mantle wedge melting to arc crust and lithospheric

antle melting (Manikyamba et al., 2012). The adakites of Shimogareenstone terrane have been interpreted to be derived by meltingf a hydrous basaltic slab at shallow subduction in an active conti-ental margin setting (Naqvi and Rana Prathap, 2007). The potassichyolites of Shimoga are considered to have formed in a continentalrc through intracrustal melting, assimilation of crustal materialsnd fractional crystallization with prominent contributions fromubduction components.

.5. Petrogenesis of Shimoga rhyolites

The possible modes of origin for active continental marginhyolites have been interpreted in terms of (i) direct melting ofasalt producing extremely fractionated REE patterns and highl2O3; (ii) a single-stage melting of a sialic source resulting inn LREE-enriched liquid; and (iii) fractional crystallization of aasaltic magma giving rise to a low K2O rhyolitic melt (Edwardsnd Hodder, 1991). The Archaean (2.7 Ga old) Phinney-Dash Lakesomplex (PDLC) in western Wabigoon of Superior Province, Canadaonsists of felsic volcanic rocks viz. rhyodacite, rhyolite whichave been metamorphosed to lower greenschist facies. Inferencesrawn from the geochemical studies of rhyolites from PDLC sup-ort their generation by fractional crystallization of associatedhyodacite (Edwards and Hodder, 1991). The PDLC is a bimodalolcanic complex which lacks rocks of intermediate composi-ions, however, bimodal volcanic sequences from Abitibi and Uchireenstone belts preserve much diverse chemistry marked byafic-intermediate-felsic compositions that developed in com-

ositionally zoned magma chambers in thick continental crustThurston et al., 1985; Edwards and Hodder, 1991). The remark-bly higher K2O (8.09–11.2 wt.%), moderate Al2O3 (12.1–15.8 wt.%)
ontents, and variably fractionated LREE/HREE patterns of theigh-silica, alkaline rhyolites (metamorphosed to lower green-chist facies) of the Shimoga greenstone belt suggest that none ofhe above described processes were involved in their genesis. The
Field of Bijli rhyolites is after Sensarma et al. (2004) and Malani rhyolites is afterSingh and Valliniyagam (2013).

geochemical signature of the studied rhyolites invokes heteroge-neous sources of parent magma, probably derived by a combinationof two-stage melting process: (i) partial melting of mantle wedgeinfiltrated by slab melts and slab-dehydrated fluid influx; (ii) intra-crustal melting of thickened continental crust induced by ascentof wedge-derived melts and crust–mantle interactions followed by(iii) fractional crystallization with assimilation of upper continen-tal crustal materials. The melt subsequently evolved during ascentand acquired a continental signature through crustal assimilation-fractional crystallization (AFC). Therefore, the tectonic affiliationand petrogenetic characters of the high-silica, potasssic rhyolites ofShimoga greenstone belt of western Dharwar clearly point towardstheir generation and emplacement in a geodynamic setting involv-ing subduction of oceanic lithosphere at an active continentalmargin arc environment. The tectono-magmatic evolution of theultrapotassic rhyolites of the Lhasa terrane in South Tibet pro-vides an evidence for early Paleozoic Andean-type orogeny along
the northern margin of the Gondwana supercontinent (Ding et al.,2014). Petrogenetic studies have identified partial melting of midProterozoic lower crustal rocks for the generation of Cambrian


ga rhy

ut

6

ovlgr(batamM1nc

dItfv

afimflncarrpto

Fig. 7. Cartoon showing schematic model for the generation of Shimo

ltrapotassic rhyolites during an extensional episode of active con-inental arc magmatism.

.6. Tectonic setting of Shimoga rhyolites

The enrichment of LILE (e.g. Cs, Rb Ba, Th, K and U) and depletionf HFSE (e.g. Zr, Hf, Nb, Ta, Y, Ti) relative to typical primitive mantlealues, negative Nb-Ta, Zr-Hf anomalies, and positive Th anoma-ies (Fig. 5) for the Shimoga rhyolites are in compliance with theeochemical characteristics of magmas generated in subduction-elated tectonic settings. Furthermore, the high silica, potassicK2O > Na2O) composition of these metavolcanics suggest contri-ution of crustal components in the evolution of the parent magmand point to their eruption at active continental margin ratherhan intra-oceanic arc setting (Pearce et al., 1984). Negative Eunomalies for the Daginkatte and Shikaripura rhyolites of Shi-oga greenstone belt conform to the characteristic negative Eu ofesoarchaean crust of the Dharwar Craton (Gao and Wedepohl,

995; Naqvi, 2005) and provide evidence in support of contami-ation by older continental crust which in turn suggest an activeontinental margin setting for their eruption.

HFSE compositions have been used as geochemical proxies foriscriminating the tectonic environment of felsic volcanic rocks.

mmobile HFSE like Ta, Yb, Th and Hf are used to discriminate felsico intermediate compositions (54–77 wt.% SiO2) that are eruptedrom oceanic arcs, active continental margins, and within-plateolcanic zones (Schandl and Gortol, 2002; Wang et al., 2008).

The Yb, Ta and Th variations in the studied samples indicatective continental margin setting, with some samples falling in theeld of within-plate volcanic zone (Fig. 6A and B). The Th enrich-ent in the studied samples may reflect the influence of the Th-rich

uids in the subduction zone. The Shimoga rhyolites carry sig-atures of both subduction-derived and continental crust-derivedomponents suggesting an active continental margin setting with

distinct arc affinity. HFSE variations in the Paleoproterozoic Bijlihyolites of Dongargarh, Central India and Neoproterozoic Malani
hyolites of Rajasthan suggest active continental margin to withinlate tectonic setting (Fig. 6A). The Bijli rhyolites distinctly plot inhe active continental margin whereas the Malani rhyolites plotutside the fields due to higher abundance of Th and Ta (Fig. 6B).
olites at an active continental margin setting. See text for discussion.

6.7. Proposed tectonic model

Magmas generated at convergent plate margin are associatedwith bimodal mafic–felsic volcanism and intermediate varieties ofBADR (basalt-andesite-dacite-rhyolite) and have been central tomodels on continental crust generation. Felsic magmatism con-trolled by ocean–ocean or ocean–continent subduction processesconstitutes an integral part of the construction and growth of con-tinents. Felsic magmatism is predominantly a product of subcrustaland intracrustal melting associated with magmatic arcs at con-vergent plate margins (Sato et al., 2012; Shuto et al., 2013). Incontinental arc systems, the overriding plate (continental), thesubducted oceanic slab and the mantle wedge all contribute tothe generation of felsic magmas and crust formation. Vertical andlateral accretions are the two processes of addition of juvenilecrustal materials that control continental growth. Juvenile magmasderived by melting of mantle wedge fluxed with slab-dehydratedfluids and subducted slab result in vertical growth and thickeningof arc crust, whereas the accretion of oceanic and trench mate-rials onto the active continental margins cause lateral growth(Santosh, 2013). The geochemical trends in young arc volcanicrocks are attributed to contributions from slab components as wellas to melting, assimilation, storage and homogenization (MASH)processes in the arc crust (Stern, 1991; Goss et al., 2013). The geo-chemical and geodynamic similarities of Archaean greenstone beltswith the Recent island and continental arcs suggest a petrogeneticmodel involving melting of a sub-arc mantle wedge carrying inputsfrom slab dehydrated fluid influx, and melting of dehydrated, sub-ducted oceanic crust, where the subduction-derived melts ascendand cause partial melting of thickened continental crust (for conti-nental arc) resulting in felsic magmas. A schematic diagram (Fig. 7)illustrates the magma tectonics and evolution of the Shimoga rhyo-lites at an active continental margin arc setting. The parent magmafor the Shimoga rhyolites was generated by partial melting of a het-erogeneous source containing mantle wedge components markedby slab-dehydrated fluids and slab-derived melts from subductedbasaltic (low-Mg amphibolite) crust. This magma evolved through
assimilation and contamination by crustal materials and expe-rienced fractional crystallization during its passage through thecontinental crust before erupting as rhyolites. Therefore, the geo-chemical systematics and petrogenetic processes suggest that the

mbria

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•

•

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•

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rvmDRaRtanptuS

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ontinental-arc rhyolites of the Shimoga greenstone belt of westernharwar Craton were derived by partial melting of lower conti-ental crust with assimilation of upper crustal components. Therc signatures are inherited from slab dehydration-wedge melting,lab melting-wedge hybridization and continental characters arettributable to intra-crustal melting and assimilation of continentalrust.

. Conclusions

The Daginkatte and Shikaripura rhyolites of the Shimogagreenstone belt are high-silica, potassic type associated with con-glomerate, quartzite, limestone, greywacke, argillite, chert andmafic to intermediate volcanic rocks.These rocks are calc-alkaline with enrichment of LILE and deple-tion of HFSE relative to primitive mantle values having negativeNb-Ta, Zr-Hf anomalies, positive Th anomalies resembling withthe magmas generated in subduction zone tectonic setting.HFSE compositions such as Ta, Yb, Th and Hf indicate that theyerupted at active continental margins. The Th enrichment in thestudied samples may reflect the influence of the Th-rich fluids inthe subduction zone.The Shimoga rhyolites exhibit prominent negative Eu, moderateto strong LREE fractionation and flat to low HREE patterns andare analogous to Type 1 and Type 3 rhyolites suggesting theircontribution from mantle wedge and are products of intracrustalfractional crystallization of basaltic liquids.The geochemical characteristics of Shimoga rhyolites are consis-tent with Neoarchean active continental margin processes which,along with mantle plume activity, contributed to the growth andevolution of continental crust in the western Dharwar Craton.

cknowledgements

We gratefully acknowledge Prof. Guochun Zhao for his edito-ial handling and two anonymous journal reviewers for providingaluable suggestions that helped to improve the quality of theanuscript. The authors are grateful to Prof. Mrinal K. Sen, formerirector, NGRI for his kind patronage. We thank Dr. Y.J. Bhaskarao, Acting Director, NGRI for permitting to publish this work. CMcknowledges the funds from Council of Scientific and Industrialesearch (CSIR) to National Geophysical Research Institute throughhe projects of India Deep Earth Exploration Programme (INDEX)nd MLP 6201-28 (CM); and Department of Science and Tech-ology (SR/S4/ES-510/2010). AS acknowledge DST INSPIRE Facultyroject (DST/INSPIRE/04/2013/001169). This work also contributeso the Talent Award to M. Santosh from the Chinese Governmentnder the 1000 Talents Plan. We thank Drs. M. Satyanarayanan, S.awanth, and A. K. Krishna for providing the geochemical data.

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