Geochemical studies of hybrid granite from Madugulapalli area,Eastern Dharwar Craton,Southern India: Implications for crustal mixing

Nagamma J · Ratnakar J · Ajay kumar A · Ashok Ch

Abstract Magma produced by melting of continental crust and mantle at the Archean-Proterozoic boundary are compositionally variable and chemical compositions provide evidence for the mixing of two sources.Understanding the composition of hybrid magma is essential for determining the comparative influence of crust and mantle sources during orogenesis.The hybrid granites are less documented in Indian cratons,especially less in Dharwar Craton.Here we present petrographic and whole-rock geochemical data of Madgulapalli granitic rocks situated in the NE part of the Eastern Dharwar Craton (EDC),to elucidate their petrogenesis and role in crust formation.The Madugulapalli granites (MPG) are composed chiefly of plagioclase,quartz,and alkali feldspar with associated biotite showing alteration and inter-granular textures.Geochemically,they are metaluminous to peraluminous in nature with calc-alkaline hybrid granite.The hybrid granites exhibit both negative and positive europium anomalies;the lower Rb/Sr,Rb,Sr,and higher Sr/Y,(Dy/Yb)N ratios suggest that the interaction of older rocks with residual garnet source melted at high pressures.We hypothesize that hybrid granites are formed by interaction (e.g.,metasomatism,mingling,or mixing) between parental magmas and pre-existing rocks with the influence of sanukitoid melts (heat source) in a subduction environment.The genesis of the hybrid granites demonstrates the mixing coupled with differentiation in the petrogeny’s residue system in a syn-collision setting followed by continental crust stability in EDC during the Neoarchean period.

Keywords Madugulapalli granite · Hybrid granite · Crustal mixing · Subduction

1 Introduction

The origin and secular history of the Archean continental crust in time and space impose significant constraints on the thermal and chemical evolution of the mantle and its involvement in the development of various geodynamic mechanisms via the cooling mantle and its differentiation (Laurent et al.2014;Jayananda et al.2018;Singh et al.2019).The mantle formation occurred due to the sluggish lid-to-plate tectonic process;some are retained in granitegreenstone Meso-Neoarchean terranes found in various cratons worldwide (Hawkesworth et al.2010;Cawood et al.2013).Granitic magmatism results from hydrous mantle melting and serves as a primary proof for subduction zone magmatism unique to the Earth (Martin et al.2005;López et al.2006;Moyen 2011).The formation of continental crust throughout the 3.4,3.0,2.7,1.7,and 1.0 Ga periods are present in cratons worldwide as described by Hawkesworth and Kemp (2006) and Roberts et al.(2015).Nevertheless,the majority of experts believe that 2.7-2.5 Ga represents a worldwide peak development in the continental crust as shown by the Dharwar Craton (Jayananda et al.2019).The corridor made of Archean crust was dominated by four lithotypes: (i) tonalite-trondhjemite-granodiorite (TTG),developed mainly during the early stages;(ii) volcano-sedimentary greenstone belt sequences;and (iii) late-stage high-K biotite granitic intrusions,and (iv) sanukitoids (Laurent et al.2014).The occurrence of hybridgranitoids has not been documented in every Late-Archean craton,and when they do exist,they may constitute either a negligible volume or a substantial portion of the crust.These hybrid granites formed due to the interaction (e.g.,metasomatism,mingling,and mixing) between magmas or sources of any of the previously described TTGs,biotite granites,and sanukitoids.They constitute a highly diverse family that cannot be classified only on geochemical criteria since their origins and petrogenetic processes vary considerably across locations.They are most frequently formed by interactions between sanukitoids and biotite-or two-mica granites,as seen in the Superior Province (Stevenson et al.1999;Whalen et al.2004) and the southern Indian Dharwar craton (Moyen et al.2001;Jayananda et al.2006).The term sanukitoid refers to a group of granitic rocks discovered in Canada’s Late Archaean Superior Province recommended by Shirey and Hanson (1984).These authors classified sanukitoids as diorites to granodiorites with a high Mg# (＞ 70) and high Ni and Cr contents.Late magmatism of granites in Archean time was widespread throughout the world’s cratons,where it has a critical role in the formation of crust,mineralization,tectonic assembly,as well as cratonic stabilization (Sylvester 1994;Moyen et al.2003;Dey 2013;Dey et al.2014,2017;Jayananda et al.2018).The Eastern Dharwar Craton (EDC) consists of Neoarchean greenstone and granite belts cover most of the craton,leaving a scant relic of 3.0 Ga TTG.The crust formation,its reworking,and tectono-magmatic processes of EDC are explained through the plume-arc accretion and cratonization (Smithies et al.2009;Manikyamba and Kerrich 2012;Barnes and Van Kranendonk 2014;Jayananda et al.2020).

The present research examines the geochemical properties of granites that represent hybrid characteristics from Eastern-Dharwar Craton to better understand their origin and involvement in crustal development processes.This study deciphers late phase intrusion of granites in EDC,contributing to a significant role in the emergence of geodynamic context and Neoarchean crustal accretion.We assess the involvement of older crust in the formation of investigated granites from Madugulapalli using geochemical indicators,which provide insight into tectono-magmatic processes and their implications on Neoarchean-Paleoproterozoic crustal formation in the EDC.

2 Regional geology

The Dharwar Craton (DC) is amongst the oldest cratons in southern India,with an age range of 3.4 to 2.5 Ga (Chadwick et al.2000;Jayananda et al.2018).DC preserved Paleoarchean to Neoarchean magmatism associated with crust formation and reworking,which contributed signifi-cantly to the continental crust evolution (Chadwick et al.2000;Jayananda et al.2018;Bhaskar Rao et al.2020).The enormous sequences of greenstone belts,younger granites and grey gneisses that make up the DC are well known.Based on the type and degree of metamorphism and melting of greenstone belts,the thickness of crust,and evolutionary history from tectonic to magmatic scenarios,the Dharwar craton (Fig.1 a) has been divided into ‘western Dharwar craton (WDC)’ and ‘eastern Dharwar craton (EDC)’ (Jayananda et al.2003;Moyen et al.2003).

Fig.1 (a) Generalized geological map of Dharwar Craton,southern India (Geological Survey of India 1996).(b) Geological map of a part of Nalgonda District showing the Madugulapalli area (GSI source).

The Neoarchean greenstone belts of EDC were associated with the 2.7 Ga granite gneisses,the transitional gneisses (TTG),high magnesium granitoids,and younger 2.5 Ga potassic anatectic granites showing the sporadic occurrence of older peninsular gneisses (Chadwick et al.2000;Moyen et al.2003;Dey et al.2014,2017;Nandy et al.2019) gave an account of the origin and sequence of emplacement of the granitoids in the NW part of the EDC,and the U-Pb zircon dates were taken on them.The formation of gneissic granodiorites with a composition intermediate between TTG magmatism and sanukitoid started about 2.68 Ga granitoid magmatism in the northern part of the Eastern Dharwar Craton (EDC).The transitional TTGs (large lithophile element enriched) were intruded at 2.58 Ga afterward.The cratonization of 2.53-2.52 Ga is marked by sanukitoid to Closepet type magmatism with the intrusion of K-rich leucogranite.According to Dey et al.(2017),microplates may have been the source of older crustal signs,and their accretion is a critical phase of Neoarchean crustal development worldwide.Researchers identified various sources in an evolving subduction zone,including the crust and enriched mantle,utilizing whole-rock geochemical data on the Neoarchean Tsundupalle greenstone belt (Nandy et al.2019).The geochemical attributes of the northern region of EDC imply magma mixing mechanisms during the genesis of the host granite and variations in the degree of diffusion of mafic magma and diffusional fractionation mechanisms in a subduction zone setting (Jayananda et al.2014;Shukla and Mohan 2019;Ashok et al.2022).

This paper deals with the rock types in northeastern part of EDC around Madugulapalli village in Thipparthi Mandal of Nalgonda District in Telangana State,southern India (Fig.1 b).The study area is located 100 km SE of Hyderabad and is an extension of the Hyderabad batholith.This area is dominated by different Neoarchean granitoids (Dey et al.2017).The southern edge defines the Proterozoic Cuddapah basin’s boundary.The Peddavura greenstone belt (2.55 Ga) is a thin,linear band with an NW-SE pattern that is mainly composed of amphibolites and it appears towards the southern border of the study area (Jayananda et al.2013).Very little information is known about the nature,petrogenesis,and source characters of Madugulapalli granites and this paper is aimed in this direction.

3 Field and petrography

The Madugulapalli area consists of granitic rocks which are frequently massive,occasionally foliated,and rarely gneissic.In the field,the Madugulapalli granite appears in two colors,grey and pink.The grey granite is predominant over the pink granite (Fig.1 b).The grey granite is associated with mafic segregations of a few millimeters to several meters long (Fig.2 a).Rarely pink granite has feldspar crystals (Fig.2 b).Frequently,granite-hosted mafic magmatic enclaves (MMEs) with felsic layers percolate within the mafic portion (Fig.2 c).Granite shows features of deformations occasionally and appears heterogeneous in the field,and few post-magmatic pegmatite injections are encountered at some locations in the study area (Fig.2 d).The MPG shows heterogeneous nature due to the associated of MMEs and pre to post-magmatic fluid injections.

Fig.2 Field photographs of Madugulapalli granitic suite: (a) mediumgrained grey granite with mafic layers,(b) medium to coarse-grained pink with potash feldspar crytals within the granite,(c) mafic magmatic enclaves observed frequently in the study area with a concentration of mafic minerals associated with felsic portion consisting of quartz and alkali feldspar and (d) the grey granite have quartz vein associated with large mafic layers.

Megascopically,the Madugulapalli granites (MPG) are grey to pink in color,coarse-grained,and porphyritic to equigranular in texture.The chief rock-forming minerals of the rocks are orthoclase perthite,quartz,plagioclase (oligoclase-andesine),biotite,and amphibole.Accessory minerals include apatite,magnetite,ilmenite,and corundum.Quartz and alkali feldspar are in major quantities.Under the microscope,the granites show fractured,twined plagioclase associated amphibole,which may influence brittle deformation (Fig.3 a).Plagioclase was strongly sericitized and exhibit albite polysynthetic twinning (Fig.3 b).Rarely,did the altered plagioclase poikilitically enclose alkali feldspar,biotite,and amphibole minerals (Fig.3 c).Quartz anhedral crystals have intergrowth textures associated with feldspar.Perthite texture is defined as intergrowth between alkali feldspar and plagioclase and associated with quartz (Fig.3 d).Undulose extinction of quartz (Fig.3 e),textures are observed extremely frequently,suggesting that deformation aided metasomatism occurred.Occasionally,the alkali feldspar crystals are composed Fe-Ti oxides,quartz,and opaque minerals (Fig.3 f),suggesting late magmatic fluid interactions.Sericitization indicates that alteration has progressed to low temperatures.Biotite is often found as distinct laths or aggregates and variously altered to chlorite and epidote.These are the major phases in rough modal proportions of plagioclase (26-35 % by volume),quartz (27.5-32.5 %),and orthoclase (23-32 %) (Table 1),biotite (2-5 %) and amphibole (2-5 %).In the quartz-alkali feldspar-plagioclase (QAP,modal compositions,volume %) diagram all the MPG samples fall in the monzogranite field (Fig .4a).

Fig.3 Photomicrographs (thin section photos) of rocks of Madugulapalli area: (a) Fractured and twined plagioclase observed in the grey granite with amphibole,(b) twinned plagioclase with dominantly altered and associated mafic inclusions,(c) the plagioclase partially altered and associated with biotite and amphibole,(d) intergrowth of alkali feldspar and plagioclase defining perthite texture and associated quartz,(e) undulose extinction of quartz indicating influence of deformation,(f) alkali feldspar phenocryst consist Fe-Ti oxides and opaque inclusions due to the post magmatic alteration (pl: plagioclase,af: alkali feldspar,bt: biotite,qz: quartz,amp: amphibole,sr: sericite,mr: myrmekite).

4 Analytical techniques

Approximately 3 kg of samples were obtained from the field.Petrological research microscope was used to carry out petrographical studies of thin sections on Madugulapalli granite samples.A steel mortar and a jaw crusher were used for crushing the samples.Using a tungsten carbide ball mill,the samples were further reduced in size to less than 70 microns size.Nine powdered samples from Madugulapalli granites

were analyzed for XRF and ICP-MS analysis (Tables 2 and 3).Representative fresh in situ samples were analyzed for geochemical studies.Crushed and powdered samples were prepared with a pulverizer (200 mesh) and an agate mill.The concentrations of major elements in pressed pellets were measured with a 3% standard deviation using an X-Ray Fluorescence Spectrometer (XRF) (Phillips Magic-PRO 1400).XRF technique was used to measure the concentrations of major oxides such as SiO2,Al2O2,Fe2O2T,MgO,CaO,K2O,and Na2O and minor oxides: TiO2,MnO,and P2O5.The fine powders (～ 0.075 mm) of rock samples and matrix were prepared,along with corresponding International reference standards such as JG-2,and JG-1a for granites,from the Geological Survey of Japan,and other check standards were considered for the analysis.

Table 1 Modal compositions (volume percent of minerals) of Madugulapalli granites.

Table 2 Major oxide elemental and CIPW normative compositions of Madugulapalli granites.

Table 3 Trace elemental concentrations including REE (ppm) of Madugulapalli granites.

For trace element and REE analysis,Thermo XSeries II ICP-MS (Inductively Coupled Plasma Mass Spectrometer) was used with an analytical uncertainty of 1-2 %.The total dissolved solid level was 500 ppm which is well within the prescribed limit of 2000 ppm for trace elements,including REE analysis using ICP-MS.The sample introduction system consists of a standard nebulizer with a cyclonic spray chamber.ICP-MS was used to analyze fine rock powders and reference materials for roughly 34 trace elements (including REE,LILE,and HFSE).In 25 mL Savillex® Teflon pressure decomposition vessels,a test portion (0.05 g) of the sample was added.Each sample added 10 mL of an acid mixture comprising 7:3:2 HF-HNO3-HCl.Then,5 mL of Rh solution was added to each Savillex® vessel as an internal standard.Theaccuracyof the analysis was checked by using granite standards JG-2 and AGV-1.Theanalysis revealed that the analytical precision and accuracy were more than 5 % for major elements and 10 % for trace and rare earth elements.The XRF and ICP-MS instruments were used at CSIR-National Geophysical Research Institute (CSIR-NGRI),Hyderabad.

5 Results

5.1 Geochemistry

Madugulapalli rocks do not discriminate between syeno and monzogranite classified by IUGS-QAP diagram (Fig.4a;

Fig.4 (a) QAP (IUGS,Modal,volume%) classification diagram for Madugulapalli granites (Streckeisen 1976),Q.Quartz;A.Alkali feldspar;P.Plagioclase.(b) Normative classification diagram of Madugulapalli granites: Q’=100×[Qz/(Qz+Ab+Or+An)];ANOR=100×An/(An+Or) (Streckeisen and Le Maitre 1979).

Streckeisen 1976).However,Q-ANOR (CIPW normative,wt%) diagram for Madugulapalli rocks (Fig.4 b) represents these two types (Streckeisen and Le Maitre 1979).Hence,it is considered that the proportion of K-feldspar and plagioclase plays a significant role in the genesis of Madugulapalli rocks.The pink granites of the study area are syenogranite and grey granites are monzogranite.The rocks have a high proportion of silica (70.15-72.39 wt%),a moderate amount of CaO (1.23-2.52 wt%),and a little amount of MnO,MgO,and TiO2.The granites have a medium total alkali content (7.72-8.61wt.%) and an average to high aluminum concentration (12.96-14.15 wt%) (Table 2).

The concentration of K2O in the granites is between 4.34 and 5.94 wt%,whereas the Na2O concentration is between 2.39 and 3.38 wt%.The Na2O/K2O ratio and CaO contents are rich in grey granite compared to pink granite,consistent with the dominance of K-feldspars in the pink granites.A ternary relationship among the variables Ab-Or-An effectively categorizes granitoids based on the mineral compositions of series with solid solutions in which the investigated samples mostly occupy granite field (Fig.5 a) (Barker 1979).These granites have a higher MALI index indicating a calcic-alkali to an alkali-calcic character which corresponds to typical arc nature (Fig.5 b).These granites are metaluminous to peraluminous (Fig.5 c) and moderate ASI of 0.88-1.11,suggesting that the granites of Madugulapalli are I-type (Frost et al.2001).The granites have a low Fe# value of 0.49-0.69 which indicates that the MPG samples are of a magnesian nature (Frost et al.2001).The TTGs,sanukitoids,biotite granite,and hybrid granites may be classified according to their major and trace chemical elements.Based on the Na2O/K2O-2 A/CNK-2FMSB relationship,the samples under investigation were analyzed with a plot of a hybrid granite field (Fig.5 d) which is consistent with the mixed potassic and sodic character of the granitic melts (Laurent et al.2014).

Fig.5 (a) Normative Ab-An-Or diagram for Madugulapalli granites.All samples fall in the granite field (Barker 1979).(b) Modified alkali lime index (MALI=Na2 O+K2 O-CaO) (wt%) versus SiO2 (wt%) diagram showing calc-alkalic to alkali-calcic nature of the Madugulapalli granites (Frost et al.,2001).(c) Aluminum saturation index [molar Al/(Ca+Na+K)] versus alkalinity index [molar Al/(Na+K)] diagram showing the metaluminous to peraluminous nature of the Madugulapalli granites (Frost et al.,2001).(d) (Na2 O/K2 O) -2×A/CNK [molar Al2 O3/ (CaO+Na2 O+K2 O)] -FMSB [2×(FeOt+MgO wt%)×(Sr+Ba wt%)] diagram for the granites of Madugulapalli showing their hybrid nature (Laurent et al.2014).

In MPG rocks,a perceptible negative correlation exists between Na2O,CaO,MgO,P2O5,and Fe2O3,while a positive trend exists between K2O and SiO2(Fig.6).Ba,Rb,Nb,Sr,Zr,La,and Cr were all trace elements that have not displayed any trend but Y shows a good negative trend with SiO2(Fig.7),which is likely due to the mobilization.The investigated granite samples have a greater proportion of large ion lithophile elements (LILE) like Ba,Rb,and Sr than high field strength elements(HFSE) with a higher Sr/Y ratio (Table 3).Furthermore,these granites are rich in thorium (50-112 ppm) and uranium (26-38 ppm).Chondrite-normalized REE patterns (Nakamura 1974)show high to moderate fractionation of LREE/HREE [(La/Yb) N=34.42/173.33] and moderate fractionation of LREE/MREE [(La/Sm)N=4.09/10.56] and MREE/HREE (Fig.8 a) (Table 4).The chemical behavior of Eu has been noted to be influenced by the fractionation of minerals.These granites show a significant positive and negative Eu anomaly (Eu/Eu*=0.63 to 2.68) due to plagioclase fractionation during the magma evolution (Macpherson et al.2006;Davidson et al.2007).The granites show significant LILE enrichment (Ce,La,U,Rb) and substantial negative P,Nb,and Ti anomalies (Fig.8 b) on the normalized primitive mantle diagram (Sun and McDonough 1989).

Table 4 Representative chondrite normalization factors of Madugulapalli granites.

Fig.6 Harker’s diagrams for the granites of Madugulapalli showing variations of major oxides with SiO2 (wt%).

Fig.7 Harker’s diagrams showing variations of trace elements with SiO2 (wt%) in the rocks of Madugulapalli.

6 Discussion

6.1 Petrogenesis

The Archean-Proterozoic boundary is represented in the Dharwar Craton by Neoarchean granitic activity,a critical event in the differentiation and crustal melting process (Jayananda et al.2000,2013).Generally,granites exhibit a broad range of geochemistry depending on their source,degree of melting,and crystallization history (DePaolo 1981;Ray et al.2011).The EDC granites explain the evidence that younger granites are produced by older crust melting (gneisses and TTG) followed by fractional crystallization (Sylvester 1994;Dey et al.2012;Mikkola et al.2012;Pahari et al.2020).The aluminum saturation index [ASI=molar Al/(Ca+Na+K)] of Madugulapalli rocks is suggestive of meta-aluminous to per-aluminous character compatible with melts produced by partial melting of continental crustal rocks which is further substantiated by Zr/Hf (21-26),Nb/Ta (2.5-6.8),and Th/U (1.1-3.3) ratios (Kaygusuz et al.2016).In a source discrimination diagram (Fig.9 a),the granite of MGP fall in the metasediments field (Laurent et al.2014) indicating that the granites are derived from older TTG gneisses plus metasediments of EDC.

The consistently high Sr/Y values and the calc-alkaline trends are caused by the initial fractionation of magnetite and amphibole (± garnet) and the restriction of plagioclase fractionation under high pH2O and fO2environments (Sisson and Grove 1993;Zimmer et al.2010).The latter circumstances seem to be favoured by high-pressure intracrustal magmatic growth,in which Y-bearing minerals (i.e.,amphibole ± garnet) are stable while Sr-bearing plagioclase is not (Lee et al.2014;Chiaradia 2015).Numerous investigations have indicated that garnet and amphibole as source residuals display substantial Sr/Y and La/Yb dissolution (Lieu and Stern 2019;Nandy et al.2019).With a partition coeffi-cient Kd larger than one for MREE,amphibole consolidates MREE more than HREE,while garnet consolidates HREE more than MREE (Davidson et al.2007).In melting,the garnet-rich residues would have a high Dy/Yb ratio,while the amphibole-rich residues would have a low Dy/Yb ratio (Macpherson et al.2006;Davidson et al.2007).The hybrid granites exhibit positive and negative europium anomalies with LREE enriched,and HREE depleted patterns coupledwith a higher ratio of Sr/Y (Fig.9 b) (Nandy et al.2019) and (Dy/Yb)N;all these factors suggest a higher melting pressure of TTG and metasediment source with garnet residue.In this research,granites having higher Sr/Y,Mg# and Ni,Eu,LREE,depleted HREE,and lower Rb/Sr concentration reflect mixed/heterogeneous crustal and mafic sources during their formation.It also implies relatively higher pressure and mesozonal melting of the crust.The granites investigated here geochemically resemble the Nidgundi monzogranites,which are developed from a heterogeneous source of TTG.The geochemical characteristics of MPG samples represent heterogeneous sources from hybrid granite samples.The hybrid granitoids are usually produced as a result of the interaction (e.g.,metasomatism,mingling,or mixing) between magmas or previous sources.Similarly,the later Archean granites were found in Australia’s Yalgran Craton (Champion and Sheraton 1997),Superior Provinces of Canada (Stevenson et al.1999;Whalen et al.2004).In light of the geochemical similarities to Nidgundi monzogranite of EDC,it is proposed that the Madugulapalli granites are developed by fusion/melting of the heterogeneous older crust.

Fig.9 (a) Source discrimination diagram [with parameters Al2 O3/(FeOt+MgO) -3*CaO -5*(K2 O/Na2 O)] (Laurent et al.2014) and (b) Sr versus Y plot for Madugulapalli granites (Nandy et al.2019).

6.2 Tectonic setting

The MPG samples exhibit calc-alkaline nature,magnesian character,mixed potassium and sodium source,and other geochemical signatures suggesting that they originated in the late evolutionary phase of Archean time.Their metaluminous to peraluminous character and trace element geochemistry precludes them from evolving in an intraplate or within plate tectonic context but favors collisional environments (Debon and Lemmet 1999;Frost et al.2001;Bonin 2004;Clemens et al.2010).The primitive mantle normalized trace element distribution diagram displays negative Ba,Sr,Nb,and Ti anomalies representing the subduction setting (Fig.8 b).Additionally,these granites with HFSE systematics indicate that they are arc type and syn-collisional in the subduction setting (Fig.10) (Pearce et al.1984).As a result,it is hypothesized that the Madugulapalli granites originated through subduction accompanied by collisional orogeny in the EDC.Most of the researchers have recommended the general geodynamic two-stage growth model (Fig.11) for Neoarchean granites (Laurent et al.2014;Dey et al.2017;Mohan et al.2019;Jayananda et al.2020),which is also applicable to the research region.The first magmatic stage is controlled by subduction (of the hydrous basaltic oceanic crust);the fluids metasomatized the underlying mantle wedge,resulting in many pulses of juvenile TTG magmatism over a prolonged period (derived due to the melting of the basaltic source or terrigenous sediments).The first step results in a continental collision and the closing of an oceanic basin (Fig.11 a).Sanukitoids are produced during the continent-continent collision as a result of the interaction of TTG melts (from stage 1) with peridotite,while crustal thickening initiates partial melting,producing two mica and biotite granites (Fig.11 b).The interaction of sanukitoids and crustal melts results in the formation of compositionally variable hybrid granitoids.The studied granites exhibit moderate sodium and potassic contents,low Fe contents,and metaluminous to peraluminous character reflecting their origin via interaction (e.g.,metasomatism,mingling,or mixing) between magmas or previous sources during subduction succeeded by a collisional episode that marks the end of the Neoarchean cratonization event in the Eastern Dharwar Craton (Smithies and Champion 2000;Dey et al.2012,2014;Nandy et al.2019;Pahari et al.2020).

Fig.10 (a) Yb versus Ta,and (b) Nb+Y versus Rb tectonic discrimination diagrams for the Madugulapalli granites (Pearce et al.1984).

Fig.11 Tectonic model diagram showing the evolution of Madugulapalli granites in a subduction-collision sequence (modified after Laurent et al.2014).

7 Conclusions

● The Madugulapalli granites (MPG) are metaluminous to peraluminous having a calcic-alkali to alkali-calcic character and are composed chief ly of K-feldspar,plagioclase,quartz,biotite,and minor amphibole.

● These granites have higher silica,alumina,and moderate alkalis.They are calc-alkalic to alkali-calcic and hybrid granite type.

● Madugulapalli granites (MPG) exhibit a relative increase in LREE over HREE,rich (Dy/Yb) and Sr/Y ratios with negative Ti,Sr,Ti,and Nb anomalies suggesting the high pressure melting of source with garnet residue in a subduction environment.

● The present research shows that the Madugulapalli granites (MPG) are formed in a syn-collisional environment via interaction (e.g.,metasomatism,mingling,or mixing) between magmas and previous sources with an inf luence of sanukitoid melts (heat source) in a subduction zone environment.This process seems to have prevailed throughout the Neoarchean period resulting in granite formation indicating the end of the cratonization event of the Eastern Dharwar Craton of which the Madugulapalli area shares a part.

AcknowledgementsThe authors would like to thank the Head,Department of Geology,Osmania University (Hyderabad) and CSIRNational Geophysical Research Institute (Hyderabad) for Lab facilities.JN thanks the Director,State Mines and Geology Department,Nalgonda,Telangana,for constant encouragement.JN and ChA wish to thank the UGC (New Delhi) for awarding RGNF-Research Fellowships and,JR thank for a UGC-Emeritus Fellowship (# 201718-Emeritus-10196-1).

Declarations

Statements and declarations:The authors declare that they have no conflict of interest.