Petrology and geochemistry of paleoproterozoic A-type granite at Kanigiri in the Nellore–Khammam schist belt, Andhra Pradesh, India

Journal of Asian Earth Sciences 30 (2007) 1–19 www.elsevier.com/locate/jaes

Petrology and geochemistry of paleoproterozoic A-type granite at Kanigiri in the Nellore–Khammam schist belt, Andhra Pradesh, India C.V. Dharma Rao b

a,*

, U.V.B. Reddy

b

a 16, S.B.I.Colony, Baghamberpet, Hyderabad 500013, India Department of Applied Geochemistry, Osmania University, Hyderabad, 500007, India

Received 28 September 2004; received in revised form 6 March 2006; accepted 31 March 2006

Abstract The Kanigiri Pluton (6.2 · 2.1 km2; 995 Ma) occurs close to a major fault and is intrusive into the meta-volcanics in the western margin of the Nellore–Khammam schist belt in Andhra Pradesh, India. The dominantly metaluminous pluton displays geochemical characteristics of A-type granites, including high abundances of Nb, Zr, Y, Ta, and REE (except Eu), and low concentrations of Sc, Ba, Sr, and Eu, displaying distinct variation trends with increasing silica content. It has less fractionated REE patterns and large negative Eu anomalies. The cluster analyses of major and trace elements indicate three main associations: (a) A primary magmatic association characterized by the presence of La, Ce, Fe, Ti, Mn, K, Ba, and Sr, (b) Ore related association consisting of Zr, Hf, Nb, Y, and (c) a volatile association with Rb, Ta, Li, and Cs. Systematic variation in Sr, Rb/Sr, Rb/Ba ratios along with and low K/Rb ratios, reflects fractionation of feldspars. Variations in Sc, and Ta result from fractionation of ferromagnesian silicates. Removal of zircon and allanite affected the Hf/Ta and Ce/Yb ratios. Limited variation in source-sensitive Y/Nb and Yb/Ta ratios is consistent with the results of melting experiments and indicates that metaluminous granitoids of this pluton were probably derived through melting of lower crustal sources. Geochemical, field and petrological data for the Kanigiri granite suggest that the granite is a partial melting product of mafic rocks like gabbros that are also present in the study region.  2007 Elsevier Ltd. All rights reserved. Keywords: Kanigiri; A-type granite; Trace elements; Proterozoic; Crustal melting

1. Introduction Proterozoic A-type granite magmatism in stable continents is currently at the focus of worldwide research. These granites, which presumably represent the most voluminous intraplate silicic magmatism, are often aligned in a linear or semi-linear manner across Precambrian cratons and are known from all continents (e.g., Anderson, 1983; Anderson and Morrison, 1992; Ra¨mo¨ and Haapala, 1995; Subba Rao et al., 1998; Rajesh, 2000). Contrasting hypotheses have been proposed for their origin, ranging from an entirely crustal origin to almost exclusive mantle derivation. (e.g., Anderson, 1983; Emslie, 1991; Anderson and Morrison,

*

Corresponding author. Tel.: +91 840 2742 3353. E-mail address: [email protected] (C.V. Dharma Rao).

1367-9120/$ - see front matter  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2006.03.014

1992; Dall’Agnol et al., 1994; King et al., 1997; Rajesh, 2000; Frost et al., 2001; Tollo et al., 2004). The A-type granitic suites vary in composition from quartz syenties to peralkaline granites and their volcanic equivalents. These suites are emplaced into non-orogenic settings – both within plate and along plate margins. The A-type granites are characterized by their relatively high alkali contents and low CaO contents (at SiO2 = 70%: Na2O + K2O = 7–11%, CaO < 1.8%), high FeOT/ MgO = 8–80, and often elevated halogen, particularly F, contents (F = 0.05–1.7%) [Reviewed by Eby (1990)]. The petrogenesis of the Proterozoic A-type granites, one of the key issues in the evolution and internal fractionation of Precambrian terranes, has been ascribed to a range of petrologic processes that include: (1) crystal–liquid fractionation, (2) incomplete separation of melts and source materials, (3) reaction between melts and surrounding wall

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rocks, and (4) mixing or mingling of coexisting magmas. Of these processes, crystal–liquid fractionation is significant in A-type granite magmas (e.g., Clemens et al., 1986; Tatsumi et al., 1986; Collins et al., 1982; Stolz et al., 1996; Dall’Agnol et al., 1999; Dostal et al., 2004; Dostal and Chaterjee, 2000). A fractionated, peraluminous, F-rich A-type granitic intrusion in the enigmatic Nellore–Khammam schist belt, India, provides an ideal opportunity to address the petrogenesis of this type of granite. The purpose of the present contribution is to constrain the petrogensesis, magmatic evolution and discuss the possible petrological model/s for its origin. We provide comprehensive geochemical coverage of the granitic pluton, which is a rare-metal bearing granitic pluton in India. Based on the extensive data set, we demonstrate the co-variation of the major and trace ele-

ment chemistry, and constrain the petrogenesis of the granite. 2. Geological setting The Proterozoic Kanigiri granite is located within the Nellore–Khammam schist belt (NSB) at the junction between low-grade Dharwar greenstone formations along the eastern margin of the Cuddapah basin and the highgrade Eastern Ghats granulite belt towards the east (Fig. 1). The Kanigiri area forms an important segment in the Nellore–Khammam schist belt. The area is mostly represented by metavolcanic sequences of the NSB that are intruded by granites and gabbros. West and north of Kanigiri, the western margin of the schist belt is in contact with the thrusted margin of the Cuddapah basin (see Fig. 1).

Fig. 1. Location map of Kanigiri granite and other intrusives along the Eastern margin of Cuddapah basin.The bold dashed lines indicate presence of thrust faults computed from DSS data superimposed on the geology of the area (modified after Kaila and Tewari, 1985). Thin solid lines indicate the boundary of the Nellore Schist belt.

C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

2.1. The Nellore–Khammam schist belt (NSB) The low-grade Nellore-Schist belt consists of a greenschist facies volcano-sedimentary sequence of pelites, psammites and conglomerates with local intercalations of cherts, limestones and felsic volcanics (Ramam and Murthy, 1997). Basic volcanic rocks are ubiquitous in the northern part of NSB which also consists of metasedimentary schists, gneisses and migmatites, and locally abundant felsic metavolcanic rocks. Marbles and calc silicate gneisses occur together with intermediate and felsic metavolcanic rocks, banded barite-magnetite layers, and kyanite-bearing schists to the west of Vinjamuru (Ramam and Murthy, 1997). The southern part of NSB hosts several economically important muscovite pegmatites (Babu, 1998). Coarse cumulate gabbros with rare interlayered ultramafic rocks, metamorphosed pillow basalts, and mafic (sheeted?) dykes constitute the Kandra Igneous Complex near the southwestern margin of the NSB. Leelanadam (1990) interpreted this assemblage as a remnant ophiolite sequence. An ophiolitic melange of chaotically intermingled blocks of ultramafic rocks, metamorphosed pillow basalts, and sedimentary rocks including finely laminated cherts, embedded in a serpentinized matrix is reported from an exposure near Kanigiri (Reddy et al., 1994). The NSB developed as a rifted volcanic margin, probably during the Meso-Proterozoic period, as evidenced by 1600 Ma granitic activity at the eastern margin of the Cuddapah basin (Ramakarishna, 2003). A Rb–Sr whole rock Proterozoic age of

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1534 ± 14 Ma is interpreted to reflect incomplete homogenization of the Sr isotopic system probably during the metamorphic overprint (Dobmeier and Raith, 2003 and references therein). 2.2. The Kanigiri pluton The Kanigiri area under investigation lies between latitudes 1524 0 3000 to 1524 0 3500 N and longitudes 7930 0 0000 to 7930 0 0600 E. and is about 86 km WSW of the Ongole, Prakasam district, Andhra Pradesh, India (Fig. 2).The Kanigiri granite (6.2 · 2.1 km2; 995 Ma, Gupta et al., 1984) is intrusive into the Dharwar schists of the NSB and is bounded on the west by sub- vertically dipping ridges of quartz–chlorite schists and quartzites. The granite body has a discordant relationship with the quartz–chlorite schists, quartzites and gneisses. On the eastern side, calcsilicate rocks and dolerite dykes are exposed. At its southeastern border, an oval shaped gabbroic intrusion is exposed (Fig. 2). The oldest rocks in the study area are TTG (tonalite–trondhjemite–granodiorite) gneisses that are equivalents to the Peninsular gniess of the adjacent Dharwar craton and have been folded and faulted locally.The general trend of these formations is NE-SW. The granite has an elliptical form covering an area of 6.2 · 2.1 km2 and is tilted towards the north with the longer axis running in a NE-SW direction. Although contact exposures are limited, the planar foliation of the granite and the geology of nearby open wells demarcate the

Fig. 2. A simpilified geological map of Kanigiri granite, Prakasam district, Andhra Pradesh with location of analyzed samples.

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C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

contact between the granite and country rocks. The granite is partially separated into two blocks by a valley trending NE-SW. On either side of the valley the granite is exposed as hillocks. A radial joint pattern is observed in the southern side of the Kanigiri granite. Aplites cut across the granite as veins, stringers and irregular bodies. Displacement of aplitic veins is common in the southern side of the granite. The granite is intersected by a series of disoriented fractures that are filled mostly by fluorite and aplite; fluorite veins occur in large lenticular shaped fractures. Pegmatites occur as pods and vary in size from a few centimeters to several meters in dimension. The pegmatites mostly contain quartz and feldspars with some biotite. Large grains of fluorite and metamict chevkinite are observed in quarries at the southwestern side of the granite body. At places, quartz and feldspar are graphically intergrown. Clinopyroxene, locally overgrown by primary amphibole, occurs as a remnant high-temperature phase. Granitic gneisses are well exposed in the southeastern part of the granite. 3. Petrography of Kanigiri granite The Kanigiri granite is light gray, medium to coarsegrained rock, megacrysts of K-feldspar (microperthitic orthoclase) enclosed in a groundmass of K-feldspar, plagioclase, quartz, and minor amounts of biotite and muscovite. Individual minerals vary from a few mm to several centimeters. The Kanigiri granite has an average modal proportion of 38% quartz, 35% k-feldspar, 18% plagioclase, 4% biotite, 2% muscovite, and 2% hornblende. Hornblende occurs in nearly all granite samples in varying proportions. Relatively coarse grain size, subhedral shape, and intergrowths with primary feldspar and quartz indicate that the hornblende crystallized as a primary magmatic phase. Most of the orthoclase observed in thin sections is perthitic. Zircon, allanite, fluorite, titanite, and monazite are identified (identified in the XRD analyses) as common accessory minerals. Allanite is dark brown in color and optically metamict. Zircon crystals typically are euhedral and prismatic withoutcores or overgrowths. Purple to locally colorless fluorite is a characteristic accessory and occurs interstitially along with fine grained quartz and calcite with sharp boundaries. Flourite also occurs as fairly large crystals possibly of primary magmatic origin. Microscopic and X-ray studies indicate that the Kanigiri granite possesses several rare-metal bearing minerals, including titanite, monazite, columbite–tantalite, allanite, and chevkinite. Monazite grains are typically oval-shaped, with rather smooth and sub-rounded edges. Abundant sphene occurs mostly as lozenge-shaped crystals in some samples. Columbite–tantalite is the main ore mineral in the Kanigiri granite. Adjacent to the Kanigiri granite at its southeastern border is an oval shaped gabbroic intrusion. The gabbroic rocks show medium to heterogenous grain size and mainly granular texture. A few samples preserve cumulate

textures. They consist of albite, actinolite, clinopyroxene, clinozoisite, quartz, and minor quantities of chlorite, titanite, and calcite. Hornfelsic rocks are observed around the gabbro as scattered outcrops. Xenoliths and enclaves of older rock such as schist, fine-grained granite, and porphyritic granite and hornfels are seen within the Kanigiri granite, indicating a later emplacement. 4. Geochemistry 4.1. Analytical procedures Two hundred representative rock samples were collected during the fieldwork covering various rock types. Out of the 200 samples, 80 granitic samples (numbered as 1–80) were selected for major and trace element analyses.Their locations are shown in Fig. 2. The procedure proposed by Levinson (1974) and Rose et al. (1979) for preparation of the rocks for chemical analysis was adopted. Eighty samples were analyzed at the Geochemistry Department, Institute for Earth Sciences, State University of Utrecht, the Netherlands. A sequential wavelength-dispersive X-ray spectrometer, Philips PW 1400 was utilized for trace elements Nb, Y, Zr, and Sr and a PW1410 instrument was used for major elements. Five grams of sample were thoroughly mixed with 1.5 ml elvacite solution and pressed into pellets at a pressure of 20 T/cm2 in a hydraulic press for the determination of trace elements. For major elements determination 500 mg of sample powder was mixed with 5 g of lithium borate flux (LiBO2–Li2B4O7) and FUSED in a platinum crucible for 15 min at 1000 C. After cooling, the glassy bead was analysed. The absorption coeffieciant and the intensity of the scattered radiation (matrix effect) was used to correct for the influence of scattered radiation using correction factors with an in-house software programme. Using instrumental neutron activation analysis (INAA) at the Netherlands Nuclear and Energy Center, the Netherlands, 80 granite samples were analyzed for U, Th, Ta, Au, Sb, Mo, W, Hg, Sn, Ba, Rb, Ga, Li, Hf, Cs, As, Y, Sc, Zr, Zn, Co, La, Ce, Nd, Sm, Eu, Tb, Yb, and Lu using Fe as an internal standard and neutron-flux monitor. One hundred milligrams of powdered sample was placed in a quartz vial, heated, sealed and irradiated for a period of 2 h. High resolution Ge (Li) detectors were used for gamma ray spectrometry. A few samples were included in each series to check the reproduce ability of the analysis. The Ion selective electrode (ISE) method was used for determination of fluorine content. Approximately 0.25 g of rock sample was placed in a nickel crucible containing 3 gm of sodium carbonate, homogenized, and placed in a pre-heated furnace at a temperature of 500 C that was gradually increased to 700 C. The crucible was cooled and the glass melt was rinsed with 50 ml of water. A 100 ml of solution was made by adding distilled water. The solutions were brought to a pH 6, and the total ionic strength and adjusting buffer (TISAB) were added. All

C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

the dissolved samples were measured for flourine content using a specific ion meter (Orion research iono analyzer/ model 407 A) with an orion fluoride ion selective electrode. International standard USGS rock reference samples JB1, JB2, JB3, JG1, JG2, and JG3 were used. The analytical precision is: SiO2, Al2O3. 1–2.5%, Fe2O3 2–3%; MnO 10%, MgO 1–3%, CaO 2–5%, Na2O 2–3%; K2O 2–3%, TiO2 2–4 %, P2O5 5%. For trace elements and REE, the precision is better than 5%: for contents less than 30 ppm, the uncertanties are within 10% and for those elements with a concentration of less than 5 ppm, in the range of 10–50%. Table 1 gives major-oxide compositions of selected samples of Kanigiri granite and Table 2 presents trace element analyses. 4.2. Statiscal methods Table 3 presents the data range, mean, standard deviation, and coefficient of variation. As a possible aid to understanding the interrelationship of major and trace elements, a correlation matrix was calculated for 80 samples from Kanigiri (including 47 samples for major oxides) and a R-mode cluster dendrogram was constructed from the correlation coefficient matrix using the method of Davis (1973). From the correlation matrix, it is observed that TiO2 and Fe2O3 have a high correlation coefficient (r = 0.9) reflecting their sympathetic relationship. The most striking feature observed in the major element correlation matrix is an antipathetic relationship of SiO2 against Al2O3, TiO2, Fe2O3, CaO, K2O, and MnO suggesting an increase of SiO2 with a decreasing trend of other oxides. Among the trace elements, the most striking correlation exists between La and Ce with a coefficient value (r = 0.97). Rb, Li, and Cs have similar correlation coefficient values. Similarly, the correlation between U and Th (r = 0.75), Zr and Hf (r = 0.87), Nb and Y (r = 0.7) are high. Rb is sympathetic with Ta, Sn and Sb. Moderate correlation has been observed between Eu and LREE, but negligible or no correlation with HREE. The following five distinct cluster groupings are apparent from the dendrogram (Fig. 3) based on internal similarities. Cluster 1 is a ‘‘primary magmatic association’’ characterized by the presence La, Ce, Fe, Ti, Mn, K, Ba, and Sr. The association may be correlated to the primary crystal fractionation of the magma. The significant feature of this group is the relative depletion of Ba and Sr. Cluster 2 is the‘‘Ca–Mg–P association’’. These elements are concentrated in small amounts in the granite and have been distinguished from other clustered elements on the basis of their mutual correlation. Cluster 3 is ‘‘Uranium’’ based on the association of U, Th, and Mo. The presence of primary uranium and thorium minerals probably indicate that these minerals formed during the late stage of magmatic activity or early stages of post magmatic activity.

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Cluster 4 is the ‘‘Ore related association’’ consisting of Zr, Hf, Nb, Y, and Na because of their mutual correlation. The F in this cluster perhaps acted as a carrier of the ore elements for the formation of zircon and columbite. Cluster 5 is a ‘‘volatile group’’. The elements are Rb, Ta, Li, and Cs. Grouping of these elements is probably related to a known post-magmatic process like albitisation. 4.3. Major and trace element variations Arithematic mean, standard deviation, concentration ranges and coefficient of variation for major and trace elements are summarized in Table 3. Compositionally, the Kanigiri granite is similar to quartz monzonite with a K2O/ Na2O ratio>1 (Fig. 4a). In the CaO–Na2O–K2O diagram (Fig. 4b), the majority of samples plot in the field of quartzmonzonite. The molecular ratio Al2O3/(CaO + Na2O + K2O) (abbreviated A/CNK) shows a positive correlation with SiO2 (Fig. 4c). High silica groups fall in peraluminous field and most of the samples are characterized as metaluminous. The result can appropriately be termed as marginally peraluminous or weakly peraluminous. In the Harker variation diagrams, the Kanigiri granite shows a slight negative correlation between SiO2 and other major oxides (Fig. 5) suggesting a limited compositional variation in the Kanigiri granite. Overlapping data arrays indicate that the metaluminous pluton was significantly affected by feldspar fractionation. Systematic decrease in Fe2O3 with increasing silica content (Fig. 5) suggests that fractionation of primary ferromagnesian silicate minerals also was a factor in developing the compositional variation. Kanigiri granite compositions plotted on an Rb-BaSr ternary diagram shows marked enrichment in Rb and depletion in Ba and Sr (Fig. 6a). The plot of Sr vs Rb does not show any trend, (Fig. 6b) probably because of the wide variation in Sr contents. In the REE plot (normalized values of REE based on Hanson, 1978), the Kanigiri granite is characterized by a high content of total rare-earths (averP age REE = 516.5 ppm). As shown in Fig. 7, the chondrite-normalized pattern shows marked LREE enrichment (average LaN/SmN = 3.73) and relatively large negative europium anomaly. In the case of HREE a slight depletion has been observed. The overall pattern represents a concave-upward shape with mild depletion of rare earth elements in the granite. In the teconic discrimination diagram Zr + Nb + Ce + Y vs. K2O +Na2O/CaO of Pearce et al. (1984), the Kanigiri granite shows an A-type character (Fig. 8a). In the Rb–(Y + Nb) diagram(Fig. 8b), all the studied samples plot in the field of within- plate granites. In summary, the geochemical data arrays indicate that the Kanigiri granite is characterized by higher concentrations of large ion lithophile elements (LILE-Rb, U, and Th) and high field strength elements (Nb, Ta, and Y), including the rare-earth elements. The enrichment of certain rare-metals chiefly Nb, Ta, U, Th, Zr, and REE, along with elements and the depletion of Ba and Sr, indicate that the Kanigiri granite is unique.

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Table 1 Whole rock anlayses of Kanigiri granite S. No.

1

2

3

4

5

6

8

9

10

11

16

18

19

20

21

SiO2 Al2O3 TiO2 Fe2O3 MgO CaO Na2O K2O P2O5 MnO LOI

72.85 12.8 0.14 2.74 0.11 0.97 4.01 4.79 0 0.06 0.74

72.17 13 0.16 2.57 0.01 0.92 3.63 5.58 0.01 0.04 0.9

72.2 13.09 0.13 2.9 0.05 0.96 3.82 5.04 0 0.05 0.95

74.46 12.44 0.13 2.5 0 0.68 3.39 5.14 0 0.05 0.66

73.19 12.68 0.13 2.4 0 0.85 3.68 5.08 0 0.04 0.96

73.52 12.22 0.13 2.26 0.01 0.88 3.46 5.12 0 0.04 0.8

74.17 12.71 0.4 1.72 0 0.63 4.12 4.6 0.05 0.04 0.87

71.66 13.77 0.16 2.81 0.03 0.91 3.88 5.57 0 0.07 0.79

74.05 12.6 0.15 2.41 0 0.9 4.28 4.2 0 0.05 0.55

68.95 14.31 0.19 3.44 0.04 1.07 4.5 5.73 0.02 0.08 0.82

71.29 13.8 0.16 2.84 0.04 0.99 4.16 5.33 0.08 0.06 0.73

72.78 12.46 0.11 2.13 0 0.75 3.49 5.28 0.01 0.03 1.03

70.6 13.48 0.21 3.75 0.02 1.42 4.13 4.84 0.01 0.08 1.04

73.14 12.5 0.16 2.96 0.02 0.84 3.42 5.18 0 0.04 1.12

68.79 13.61 0.16 3.13 0 1.03 4.23 5.59 0.05 0.06 1.2

Total A/CNK A/NK A NK2C/Al*Si

99.21 0.95 1.09 0.92 1.01

98.98 0.96 1.12 0.9 1.24

99.22 0.97 1.1 0.91 1.22

99.45 0.95 1.07 0.93 1.18

99.2 0.97 1.1 0.97 1.22

98.43 0.95 1.09 0.92 1.22

98.95 0.99 1.08 0.92 1.28

99.65 0.98 1.11 0.9 1.19

99.19 0.95 1.09 0.9 1.19

99.15 0.92 1.05 0.95 1.1

99.48 0.96 1.09 0.91 1.23

98.07 0.91 1.05 0.96 1.07

99.67 0.98 1.11 0.9 1.3

98.89 1.03 1.06 0.94 1.31

97.68 0.91 1.05 0.96 1.09

S. No.

22

23

24

25

26

27

28

29

31

32

33

34

35

36

37

38

SiO2 Al2O3 TiO2 Fe2O3 MgO CaO Na2O K2O P2O5 MnO LOI

71.41 13.92 0.16 3.79 0 0.88 4.16 5.7 0.03 0.07 0.7

72.76 14.62 0.23 2.47 0 1.27 4.51 4.57 0.02 0.1 0.69

70.92 14.11 0.13 3.34 0 0.86 4.43 5.1 0 0.06 0.75

68.32 13.68 0.18 3.34 0 1.11 3.82 5.82 0 0.08 1.27

69.28 13.36 0.2 3.62 0.02 1.11 4.26 5.24 0 0.1 0.86

73.87 12.98 0.05 1.77 0.01 0.48 4.4 4.42 0 0.03 0.72

69.79 13.56 0.17 3.14 0.04 1.02 4.16 5.31 0 0.07 1.02

70.38 13.35 0.18 3.06 0.1 0.98 4.08 5.01 0.01 0.07 0.85

74.31 11.78 0.12 2.37 0 0.76 3.33 4.94 0.02 0.04 0.65

73.29 12.59 0.17 2.77 0 0.89 3.62 5 0.02 0.05 0.72

72.66 11.79 0.15 2.6 0.04 0.85 3.52 5.22 0.04 0.05 1.12

76 13.13 0.14 2.37 0 0.73 3.04 5.25 0.01 0.05 0.7

73.47 13.13 0.16 2.98 0 0.86 3.58 5.54 0 0.06 0.7

71.99 13.24 0.15 2.29 0.21 0.77 3.5 5.56 0.04 0.04 1.1

72.82 12.77 0.13 2.39 0 0.81 3.58 5.33 0.01 0.04 0.8

70.98 13.05 0.16 2.83 0.03 0.93 4.01 5.15 0.01 0.06 0.9

Total A/CNK A/NK A NK2C/Al*Si

100.16 0.94 1.09 0.92 1.18

102.56 1 0.18 0.85 1.29

98.83 1 1.18 0.85 0.82

97.62 0.98 1.1 0.91 1.22

98.05 0.92 1.12 0.89 1.18

98.73 0.91 1.05 0.95 1.1

98.28 0.94 1.08 0.93 1.2

98.88 0.95 1.08 0.92 1.17

98.32 0.97 1.09 0.92 1.35

0 0.97 1.11 0.9 1.22

98.84 0.97 1.11 0.9 1.25

100.08 0.92 1.05 0.95 1.12

100.48 1 1.13 0.88 1.3

98.89 1.01 1.13 0.88 1.3

98.66 0.97 1.1 0.91 1.26

98.11 0.94 1.07 0.93 1.18

S. No.

39

40

41

42

43

45

51

54

55

56

64

65

66

67

69

SiO2 Al2O3 TiO2 Fe2O3 MgO CaO Na2O K2O P2O5 MnO LOI

72.82 13.67 0.15 2.98 0 0.81 4.37 5.18 0.01 0.05 0.85

74.79 12.87 0.04 1.49 0 0.44 4.18 4.45 0.01 0.02 0.66

74.07 12.95 0.09 2.32 0.02 0.38 4.36 4.84 0.01 0.03 0.6

71.14 13.56 0.14 2.71 0.01 0.76 3.35 5.46 0.15 0.06 0.7

71.51 13.68 0.13 2.59 0.01 0.93 4.24 5.36 0 0.04 0.95

75.75 13.5 0.02 1.17 0 0.24 4.76 4.53 0 0.03 0.67

71.8 12.86 0.11 2.47 0 0.88 4.55 4.91 0 0.05 0.65

73.51 13.43 0.11 2.17 0.08 0.66 4.11 4.98 0 0.04 1

70 13.41 0.2 3.07 0.09 1.41 3.96 5.23 0.07 0.06 0.8

70.23 13.8 0.15 2.48 0.02 1.02 4.36 5.36 0 0.05 0.75

73.73 13.15 0.14 2.41 0 0.93 3.55 5.38 0 0.05 0.85

71.96 13.38 0.13 2.15 0.01 0.84 4.27 5.15 0 0.03 0.75

71.28 13.31 0.16 2.65 0.01 0.83 3.97 5.31 0 0.05 0.8

69.71 13.32 0.17 2.91 0.02 0.89 3.97 5.49 0.01 0.06 0.75

71.39 14.44 0.16 2.74 0.02 0.99 4.05 5.66 0.01 0.06 0.95

Total A/CNK A/NK A NK2C/Al*Si

100.88 0.96 1.07 0.94 1.25

98.94 1.03 1.1 0.91 2.38

99.66 0.99 1.04 0.96 1.23

99.04 1.06 1.19 0.84 1.32

99.44 0.95 1.07 0.93 1.19

100.67 1.01 1.11 0.9 1.24

98.28 0.95 1.08 0.92 0.86

100.09 1.01 1.08 0.93 1.28

98.3 1.1 1.23 0.81 1.45

98.22 0.93 1.06 0.94 1.17

100.31 0.98 1.13 0.89 1.33

98.67 0.95 1.06 0.94 1.2

98.37 1.08 1.23 0.81 1.34

97.29 1.12 1.31 0.76 1.387

100.46 0.99 1.13 0.89 1.23

5. Type of granite The A-type signature of the Kanigiri granite is the corroborated by occurrence of xenoliths of schistose rocks within the granite and perthitic texture. Relative to I- and S-type granitoids, A-type typically has compositions with high SiO2, high Ga/Al, F, Zr, Nb, Ta, Ga, Sn, Zn, Y, and REE contents, and low concentrations of CaO, Ba,

and Sr (Whalen et al., 1987 and Eby, 1990). The studied granites plot within the A-type granite field in the Zr– Nb–Ce + Y versus K2O + NA2O/CaO and K2O/Na2O versus CaO diagrams. (Whalen et al., 1987). Whalen et al. (1987) documented a correlation between agpaitic index (A.I., molar (Na + K)/Al) and Ga/Al ratio (expressed as 104 · Ga/Al) for a large population of A-type granites, indicating that 104 · Ga/Al values P4 were

Table 2 Trace element analyses of Kanigiri granite S. No. 1

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

3200 3840 3200 2560 3000 3800 2200 3400 2720 2960 4200 4460 4600 4800 5200 3000 2600 3000 4400 2720 350 290 330 220 225 220 280 130 325 275 445 425 450 535 530 370 270 220 330 245 145 230 190 190 150 180 125 195 150 150 240 260 280 320 425 150 135 160 205 170 8.85 6.58 8.31 9.24 7.4 8.27 7.71 22.9 8.11 7.95 11.4 12.7 10.09 12.7 10.9 9.51 8.37 9.39 9.07 6.4 1 1 1 1 1 1 1 9 1 1 1 1 2 2 1 1 1 1 2 1 17.8 22.3 23.6 17.9 13.5 22.6 16.9 20.7 17.8 12.9 15.2 17.6 21.2 25.1 28.9 17.1 12.7 16.9 34.1 16.4 56.5 89.4 80.5 62.2 60.2 81.7 51.5 61.2 49.5 55 48.4 52.4 56.9 59.7 69.8 59.9 53 64.9 166 91.3 165 236 63 83 186 141 169 51 238 127 112 157 101 122 73 182 194 111 211 220 19 15 13 12 17 13 20 2 16 14 20 15 19 12 8 20 20 15 13 14 254 262 283 280 275 330 278 501 255 187 284 282 287 316 293 301 284 300 344 286 36 34 45 36 48 41 24 54 31 22 40 32 46 49 41 38 34 32 62 37 13.3 11.5 12.6 10.1 9.68 11.1 10.9 10.4 12.4 9.75 20.2 16.9 18.8 18.8 21.2 14 11.4 9.97 11.4 10.3 2.76 1.45 2.14 2.01 1.81 3.38 1.43 2.74 0.51 1.02 2.54 1.14 3.57 2.76 3.98 2.1 2.69 1.89 3.34 2.35 14.7 13.1 13.1 11.9 11.8 12 12.4 12.6 12.9 12.5 13.8 13.5 13.2 13.1 14.1 14.1 13.2 11.4 12.5 11.3 0.85 0.75 0.76 0.69 0.69 0.71 0.74 0.75 0.77 0.76 0.83 0.83 0.81 0.81 0.87 0.88 0.83 0.72 0.79 0.72 0.26 0.23 0.23 0.21 0.21 0.21 0.22 0.22 0.23 0.22 0.24 0.24 0.23 0.23 0.25 0.25 0.23 0.2 0.22 0.3 4.62 1.28 1.31 1.9 1.2 1.49 4.21 1.33 3.36 2.12 2.01 4.04 1.4 2.82 1.51 3.9 4.16 2.11 1.3 1.09 1.15 15.6 14.5 10.6 11.1 15.2 7.89 0.97 1.01 0.98 1.09 11.4 17.7 1.07 25 1.12 8.47 3.67 15.3 11.9 14.3 55 52 37 52.7 11.9 53.8 12.1 12.5 51.8 13.4 26.5 13 38.7 30.6 13.5 12.8 76.6 99.1 22.2 1.46 0.43 1.43 1.18 1.21 1.14 1.11 0.81 1.87 1.91 1.86 1.09 1.62 1.05 0.51 1.84 1.87 1.24 1.19 1.38 – 80 – – 18 19 18 111 21 20 – 20 22 257 178 22 22 18 185 18 3.02 1.88 0.52 0.77 0.59 1.64 0.49 0.67 0.49 2.92 1.22 1.58 0.63 1.46 0.68 2.13 0.52 2.07 1.47 2.5 140 160 155 135 135 145 115 190 120 125 145 155 165 180 225 150 130 150 155 145 134 125 119 82 107 100 76 31 104 120 207 161 166 161 222 152 104 92 75 104 287 316 297 221 248 274 178 119 235 299 447 352 392 377 479 329 243 212 199 253 73.8 85.9 75.8 62.3 67.8 80.9 54.5 45.9 66.7 77.4 105 98.2 96.8 95.3 118 84.1 71.6 64.5 109 59 18.5 19.8 20.5 15.6 15.8 17.9 13.5 12.7 15.6 17.7 24.3 20.3 23.5 22 34 20.6 15.6 15.4 16 16 0.95 0.22 0.21 0.16 0.19 0.23 0.18 0.12 0.21 0.21 0.7 0.22 0.65 0.22 0.26 0.25 0.21 0.17 0.39 0.21 2.06 2.17 2.38 1.89 2.19 2.42 1.58 1.85 1.78 2.13 2.41 2.13 2.9 3.19 4.18 1.81 1.8 2.01 1.91 1.92 11.2 12.6 12.9 10.4 10.6 12.4 8.26 14.1 9.72 10.4 11.6 12.6 13.2 14.2 21.4 12.2 9.53 11.1 12.8 12.1 1.98 2.21 2.16 1.84 1.7 2.19 1.65 2.66 1.77 1.78 2.17 2.13 2.38 2.69 3.77 2.07 1.78 2.02 2.23 1.98 21

F Zr Nb Ta Sn U Th Ba Sr Rb Li Hf Cs Au As

3

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

7

2600 2950 3040 4600 5760 4080 3280 4400 2720 4160 2720 4160 2720 2880 3760 3440 3600 4200 6000 4000 430 395 530 350 660 545 185 430 355 150 255 305 270 160 310 240 210 235 355 130 270 295 175 200 810 280 235 275 185 235 175 200 165 190 210 120 217 375 235 180 7.24 14.3 9.42 12.7 33.4 18.9 24.8 10.7 11.11 23.9 8.45 8.32 7.64 8.43 10.2 8.45 11.1 11.6 18.7 20.7 1 4 1 1 1 1 2 1 1 9 1 1 1 1 1 1 1 1 1 1 14.7 18.3 18.4 16.5 51.7 17.7 12.8 19.9 14.8 14.3 19.4 21.5 19.1 15.1 21.1 16 25.9 19.9 19.9 15.7 49.9 54.4 62 47.8 137 61 39.2 58 57.9 42.7 65.9 79.1 65.2 67.3 91.5 46.5 96 64.6 54.9 40.5 106 63 228 132 80 84 57 81 281 52 43 65 69 73 149 413 107 260 68 55 16 9 35 20 2 14 8 17 40 20 11 15 20 10 10 20 10 30 16 11 286 328 233 430 340 352 509 309 346 616 266 338 279 262 333 311 345 326 479 479 25 25 24 68 41 28 90 24 38 94 150 28 24 38 32 38 47 41 42 100 17.9 17.1 17.2 14.1 33.2 20.9 13 19.8 14.5 11.4 11 13.7 12 6.99 13 10.6 10.1 14.3 15.7 9.73 1.23 3.36 2 4.25 2.78 3.97 3.5 2.42 1.42 4.25 1.56 2.83 2.21 1.6 4.01 2.19 3.29 2.3 3.17 2.49 13.2 12.4 13.1 13.7 14 13.6 12.5 7.78 7.18 5.78 5.91 6.79 5.56 6.91 6.81 7.79 6.13 6.32 6.52 5.97 0.85 0.8 0.85 0.89 0.92 0.9 0.82 0.91 0.85 0.7 0.71 0.83 0.81 0.86 0.85 0.77 0.78 0.82 0.86 0.78 (continued on next page)

C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

F Zr Nb Ta Sn U Th Ba Sr Rb Li Hf Cs Au As Sb W Ho Mo Sc Zn Co Y La Ce Nd Sm Eu Tb Yb Lu

2

8

Table 2 (continued)

Sb W Hg Mo Sc Zn Co Y La Ce Nd Sm Eu Tb Yb Lu

0.23 1.48 6.06 20.7 1.03 20 1.04 135 115 264 62.7 14.4 0.27 1.53 10.1 1.85

S. No. 41 F Zr Nb Ta Sn U Th Ba Sr Rb Li Hf Cs Au As Sb W Ho Mo Sc Zn Co

22 0.22 1.35 1.02 12.3 0.94 164 1.74 170 141 339 78.7 21.8 0.21 2.79 15 2.5 42

23 0.23 1.49 12 21 1.66 21 0.51 135 140 315 80.9 19.8 0.41 2.46 11.2 2.02 43

24 0.24 5.58 1.05 13.2 1.37 96 0.46 145 118 264 57.1 14.5 0.2 1.34 10.3 1.75 44

25 0.25 1.8 21.7 99.5 0.45 24 1.68 265 236 623 118 32 0.25 4.58 28.8 5.02 45

26 0.24 1.55 1.12 12.6 1.15 17 1.28 165 172 380 90.8 23.3 0.57 2.02 12.2 2.1 46

27 0.22 4.31 1.7 18.6 0.45 18 1.09 170 86 207 40.6 9.85 0.19 1.03 9.81 2.06 47

28 0.14 3.76 12.5 23.8 1.26 26 0.72 175 169 418 120 23 0.3 2.37 13.8 2.54 48

29 0.13 1.63 6.53 3.96 2.01 26 0.64 135 133 300 86.5 16.2 0.3 1.55 9.92 1.82 49

30 0.1 3.28 1.36 3.22 0.6 21 0.97 169 43 119 38 7.25 0.16 0.31 9.64 1.94 50

31 0.1 2.21 10.4 29.4 1.22 20 0.54 125 88 219 64.5 15.6 0.2 1.78 9.83 1.7 51

32 0.12 5.19 13 34.8 2.13 32 0.61 185 144 363 89.9 23.3 0.24 2.93 15.5 3.86 52

33 0.11 3.4 13.5 26.8 1.63 23 3.37 165 120 291 86.9 20.7 0.27 2.67 12.4 2.33 53

34 0.12 1.64 13.9 28.4 0.85 22 0.63 150 135 394 87.4 21.6 0.35 2.57 11.8 2 54

35 0.12 4.29 13.3 32.1 1.5 24 1.58 175 109 265 98.3 30.4 0.6 2.6 10.7 2.54 55

36 0.11 3.88 12.2 23.8 2.92 24 2.41 145 87 215 61.5 15 0.18 2.38 10.3 1.93 56

37 0.11 3.4 11.3 37.9 0.67 26 4.54 170 88 235 64.4 17.6 0.15 2.12 14.5 2.51 57

38 0.11 1.6 8.1 23.5 1.33 159 2.73 155 108 289 65.2 15.8 0.21 2.28 13.1 2.41 58

39 0.12 5.9 9.27 13.9 1.24 24 0.56 165 107 274 89.9 15.9 0.15 1.3 10.8 1.96 59

40 0.11 5.37 1.53 20.2 0.58 20 0.46 140 40 112 28.7 6.72 0.15 0.49 8.21 1.6 60

4200 4400 7200 3520 3280 2600 2720 3920 4200 4000 5600 5400 5100 3960 4800 5000 4800 4200 6000 6200 315 380 340 145 100 180 165 345 290 290 485 460 390 255 530 325 395 305 330 340 280 320 250 245 225 265 195 310 285 280 265 275 300 200 430 200 205 225 255 415 20.7 1470 13.2 28.8 32.4 40.6 33.8 19.7 25.9 20 22.5 18.8 11.4 16.5 23.3 14.4 17.9 29.5 11.5 12.1 6 6 8 20 25 10 18 12 9 10 11 15 3 6 7 3 5 6 5 9 20.9 20.7 31.7 12.9 12.7 18.5 16 20.9 19 20.5 16.1 19.6 19.1 8.94 18 12.1 15.7 14.4 14.3 21.8 66.9 56.5 55 27.7 23.53 37.7 26.9 65.5 53.3 59.6 57.6 56.3 65.3 49.6 77.5 60.4 56.2 53.3 62.8 69.1 106 63 228 132 80 84 57 81 281 52 43 65 68 73 149 413 107 260 68 55 16 9 35 20 2 14 8 17 40 20 11 15 20 10 10 20 10 30 18 11 286 328 233 430 340 352 509 309 346 616 266 338 279 262 333 311 345 326 479 479 25 26 24 68 41 28 90 24 38 94 150 28 24 38 32 38 47 41 42 100 17.9 17.1 17.2 14.1 33.2 20.9 1300 19.8 14.5 11.4 11 13.7 12 6.99 13 1.06 10.1 14.3 15.7 9.73 1.23 3.36 2 4.25 2.78 3.97 3.5 2.42 1.42 4.25 1.56 2.83 2.21 1.6 4.01 2.19 3.29 2.3 3.17 2.49 13.2 12.4 13.1 13.7 14 13.6 12.5 7.78 7.19 5.78 5.91 6.79 5.56 6.91 6.81 7.79 6.13 6.32 6.52 5.97 0.85 0.8 0.85 0.89 0.92 0.9 0.82 0.91 0.85 0.7 0.71 0.83 0.81 0.86 0.85 0.77 0.78 0.82 0.86 0.78 0.23 0.22 0.23 0.24 0.25 0.24 0.22 0.14 0.13 0.1 0.1 0.12 0.11 0.12 0.12 0.11 0.11 0.11 0.12 0.11 1.48 1.35 1.49 5.58 1.6 1.55 4.31 3.76 1.63 3.28 2.21 5.19 3.4 1.64 4.29 3.88 3.4 1.6 5.9 5.37 6.06 1.02 12 1.05 21.7 1.12 1.7 12.5 6.53 1.36 10.4 13 13.4 13.9 13.3 – 11.3 8.1 9.27 1.53 20.7 12.3 21 13.2 99.5 12.6 18.6 23.8 3.96 3.22 29.4 34.8 26.6 28.4 32.1 23.8 37.9 23.5 13.9 20.2 1.03 0.94 1.66 1.37 0.46 1.15 0.45 1.26 2.01 0.6 1.22 2.13 1.63 0.85 1.5 2.92 0.67 1.33 1.24 0.58 20 164 21 96 24 – 18 26 26 21 20 21 23 22 24 24 – 159 24 20 1.04 1.74 0.51 0.46 1.68 1.28 1.09 0.72 0.64 0.97 0.54 0.61 3.37 0.63 1.58 2.41 4.54 2.73 0.56 0.46

C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

S. No. 21

Y La Ce Nd Sm Eu Tb Yb Lu

135 115 264 62.7 14.4 0.27 1.53 10.1 1.85

170 141 339 78.7 21.8 0.21 2.79 15 2.5

135 140 315 80.9 19.8 0.41 2.46 11.2 2.02

145 118 264 57.1 14.5 0.2 1.34 10.3 1.75

265 236 623 118 32 0.25 4.58 28.8 5.02

165 172 380 90.8 23.3 0.57 2.02 12.2 2.1

170 86 207 48.6 9.85 0.19 1.03 9.81 2.06

175 169 418 120 23 0.3 2.37 13.8 2.54

135 133 300 86.5 16.2 0.3 1.55 9.92 1.82

170 43 119 38 7.25 0.16 0.31 9.64 1.94

125 88 219 64.4 15.6 0.2 1.78 9.83 1.7

185 144 353 89.9 23.3 0.32 2.93 15.5 2.65

165 120 291 86.9 20.7 0.24 2.67 12.4 2.33

150 155 394 87.4 21.6 0.27 2.63 11.8 2

175 109 265 98.3 30.4 0.25 2.65 13.7 2.46

145 87 215 61.5 15 0.6 2.38 10.3 1.93

170 88 235 63.4 17.6 0.18 2.12 14.5 2.51

155 108 289 65.2 15.8 0.15 2.28 13.1 2.41

165 107 274 89.9 15.9 0.21 1.3 10.8 1.96

140 40 112 28.7 6.72 0.15 0.49 8.21 1.6 C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

S. No. 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 F 11,400 5800 3440 2720 5400 2720 3400 4000 4400 3600 4400 6200 4000 6200 4400 2400 4960 3400 3400 3400 Zr 745 355 205 260 290 325 325 335 365 380 490 375 375 470 380 315 280 235 260 420 Nb 330 240 200 165 255 116 165 180 155 165 250 235 145 400 350 160 135 170 190 155 Ta 13.8 11.8 8.37 7.59 14.6 9.83 9.55 12 10.3 9.84 11.9 10.4 8.24 12.5 16.7 10.7 6.83 7.84 8.62 9.67 Sn 4 5 1 1 2 2 1 2 3 1 3 2 3 2 2 2 1 1 1 2 U 30.4 13.4 23.5 7.33 14.6 10.2 12.6 19.4 17.9 16.1 22.1 12.2 14.7 27.6 14.9 14.1 12.3 19.3 22.7 15.76 Th 95.5 49.8 82.5 52 46.7 54.7 58.7 70.1 61.1 58.1 75.1 48.5 55.4 69.6 50.6 61.1 46 84.3 89.1 58 Ba 93 112 60 76 55 232 217 195 113 63 111 173 157 102 62 200 321 82 151 249 Sr 14 23 17 24 21 36 27 27 25 28 28 23 30 14 16 26 35 18 21 33 Rb 312 344 279 262 369 284 333 364 363 302 265 335 257 280 365 297 242 285 319 308 Li 29 40 32 34 29 20 19 34 30 29 26 25 23 30 39 25 23 29 32 23 Hf 32.3 15.1 10 10.8 13.9 12.7 13.7 12.8 13.6 13.9 17.8 15.2 13.6 18.4 17.9 11.7 10.7 9.6 11 14.8 Cs 3.21 3.79 0.47 2.2 3.11 2.34 0.52 0.8 2.84 1.77 2.04 2.28 2.45 3.06 2.16 3.07 1.98 1.82 2.68 2.26 Au 17.2 13.4 11.5 11 11.5 12.8 12.3 12 12.1 11.7 57.2 13.2 26.1 13.2 12.2 11 11.2 10.4 11 11 As 1.05 1.2 0.72 0.69 0.72 0.8 0.78 0.77 0.78 0.75 0.89 0.86 0.76 0.88 0.8 0,75 0.76 0.71 0.76 0.76 Sb 0.3 0.24 0.2 0.29 0.2 0.22 0.22 0.21 0.21 0.21 0.24 0.23 0.2 0.23 0.21 0.2 0.2 0.18 0.19 0.19 W 1.75 1.44 2.68 2.52 1.27 1.4 2.16 1.33 2.37 1.32 5.86 1.51 1.32 1.53 2.77 2.14 1.34 1.25 1.35 1.34 Hg 41.3 1.07 11.8 10.4 7.6 8.99 8.69 0.95 14.9 0.92 15 1.02 14.5 1.13 12.9 9.09 12.3 12.2 16.9 11.3 Mo 17.3 13.1 18.7 23 19.8 12.4 44.5 23.8 36 11.4 26.4 12.8 12.5 18.1 11.9 11 12.3 34.3 68.1 11.1 Sc 48 0.88 0.89 1.83 0.93 2.19 1.99 1.42 1.7 1.96 1.8 0.99 1.74 0.53 0.92 1.38 2.59 0.63 0.85 1.95 Zn 276 22 34 20 18 23 21 20 20 – 25 21 108 138 21 186 78 67 84 20 Co 0.82 0.57 2.36 1.72 0.44 0.56 0.5 0.5 0.5 48 1.1 0.53 0.5 0.57 0.49 0.45 1.72 1.02 0.44 0.45 Y 210 145 150 135 130 135 130 165 140 130 185 140 135 215 175 140 130 140 155 135 La 479 139 88 99 86 114 116 111 141 120 198 122 148 197 132 112 121 94 110 129 Ce 1030 331 248 260 218 288 201 278 347 291 479 300 341 430 320 296 289 253 277 300 Nd 221 79.7 73.8 70 58.2 76.2 72.7 71.9 80.3 67.9 115 63.8 79.3 104 74.3 73.8 70.7 68.7 101 84 Sm 47.2 19.1 17.6 16.7 12.8 16.4 15.1 15.6 18 16.6 25 13.6 18.5 25.8 19.1 16 17.7 14.6 18.4 18.6 Eu 0.39 0.47 0.31 0.19 0.21 0.24 0.22 0.21 0.22 0.99 1.11 0.21 0.58 0.81 0.2 0.34 0.17 0.18 0.2 0.61 Tb 4.35 1.81 2.39 2.04 1.28 2.29 1.7 1.94 1.88 1.75 2.89 1.5 1.91 3.49 2.47 2 2.21 1.94 2.18 2.3 Yb 17 10.9 12.2 9.27 9.83 9.77 9.79 12.1 10.5 9.11 15.4 19.85 13.8 17.1 13.3 10.5 9.53 9.94 12 10.6 Lu 3.17 2.01 2.35 1.77 1.85 1.9 1.93 2.26 1.89 1.87 2.85 1.88 1.85 3.07 2.52 2.06 1.78 1.95 2.18 2.04

9

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C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

Table 3 The data range, mean, standard deviation and coefficient of variance of major and trace elements of Kanigiri granite Oxide (wt%) SiO2 Al2 O03 TiO2 Fe2O3 MgO CaO Na2O K2O P2O5 MnO Element (ppm) Hf Cs Au As Sb W Hg Mo Sc Zn Co Y La Ce Nd Sm Eu Tb Yb Lu

Lower limit 68.28 11.78 0.02 1.17 0 0.24 3.04 4.2 0 0.02 6.99 0.469 0 0.686 0.102 1.09 0 2.79 0.181 0 0.257 115 31 79 18 3.69 116 0.16 6.77 1.37

Upper limit 77.49 14.98 0.23 3.79 0.21 1.42 4.76 6.01 0.15 0.1 33.2 4.9 57.2 1.2 99.7 5.86 41,30 99.5 48.1 276 3,37 275 379 1030 221 49.2 1.11 4.58 28.8 5.02

Mean

Standard deviation

71.95 13.26 0.14 2.62 0.02 0.89 4 5.21 0.01 0.05

2.02 0.65 0.01 0.51 0.04 0.21 0.36 0.37 0.03 0.017

14.634 2.521 11.753 0.807 6.227 2.468 7.871 23.183 1.76 63.51 1.02 161.25 119.99 287.59 75.01 17.42 0.2967 2.058 11.96 2017

4.633 0.9492 6.535 0.088 23.523 1.345 7.056 19.592 0.6032 73.36 0.73 33.64 57.07 123.3 26.53 6.01 0.2032 0.775 33.192 0.527

Coefficient of variance 2.81 4.9 7.14 19.47 200 23.6 9 7.1 300 40 31.66 37.65 55.6 10.91 377.76 54.48 89.65 84.51 51.6 115.51 71.57 20.9 45.56 42,87 35.37 34,50 67.49 37.66 26.6 24.29

characteristic of A-type granites (A.I. P 1.0) rocks. A similar relationship was determined for the Kanigiri granite where the majority of rocks have 104 · Ga/Al values P4 (Thirupathi et al., 1996). The Kanigiri granite geochemical data plotted in Fig. 8a and b corresponds to the ‘‘within-plate granite’’ field on the tectonic discrimination diagrams of Pearce et al. (1984) attesting to derivation from sources consistent with an extensional encratonic environment. Landenberger and Collins (1996) and Fo¨rster et al. (1997) demonstrated that the trace-element discrimination diagrams of Pearce et al. (1984) more accurately reflect source characteristics than identify tectonic environments.

330 ppm. The depleted Zr contents in some samples suggests that the temperature estimates of the granite may closely resemble the initial temperature of the melt. This assumes there is no xenocrystic zircon, which is consistent with the lack of relict cores or overgrowths on the zircons in the granite. Consequently, it is concluded that the initial temperature(>800) of the granite melt is best represented by the zircon saturation model. These temperatures are consistent with Millers’s (1999) ‘‘cold granites’’.

6. Physical conditions

Variations of trace elements in granitic plutons are generally associated with mineralogically and texturally distinct facies of rocks within the pluton. Geostastical analyses of whole-rock geochemical data of the Kanigiri granitoid demonstrate the characteristic geochemical associations occurring within the pluton. The geochemical associations observed in the Kanigiri granite mainly include (a) A primary magmatic association characterized by the presence of La, Ce, Fe, Ti, Mn, K, Ba, and Sr, (b) Ore related association consisting of Zr, Hf, Nb, Y, and (c) A volatile association with elements Rb, Ta, Li, and Cs. Current models invoked to explain such variations include:

Estimates of magmatic temperatures can be obtained from the solubility of zircon in the melt to approximate temperatures of saturation (Harrison and Watson, 1983). Zircon saturation thermometry provides a simple and robust means of estimating magma temperatures. (Miller et al., 2003). The estimated temperatures using the zircon saturation model (Harrison and Watson, 1983) gives temperatures between 800 and 860 C, with only a few samples plotting along the 930 C line (Fig. 9). The Kanigiri granite has Zr contents in the range 100–745 ppm with a mean of

7. Petrogenesis 7.1. spatial variations

C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

11

Fig. 3. Dendogram of selected variables clustered according to their correlation coefficients.

(a) The variations due to two different intrusions (e.g., Kistler et al., 1986; Eichelberger et al., 2000; Schmitt et al., 2001), (b) The variation reflecting roof-ward assimilation of crust in the magma chamber before crystallization (e.g., Jhonson, 1989; Tegtmeyer and Farmer, 1989), and (c) Closed-system fractional crystallization (convective fractionation; DeSilva, 1991). Regarding (a), there are no field evidences for two intrusions, and the almost continuous gradients within the pluton indicate a single chemical gradient within the granite pluton. Regarding (b), relating to progressive contamination, studies of earlier workers (Banerjee et al., 1983; Gupta et al., 1984) indicate that contamination was not a significant process in the evolution of the Kanigiri pluton. However, model (c) relating to extensive fractional crystallization accompanied by late stage fluid involvement seems to best account for the observed elemental variations.

7.2. Fractionation indicators The Kanigiri granite ranges from metaluminous to mildly peraluminous in composition (Fig. 10). Most granite samples (over 75% of the analyzed samples) have SiO2 contents >70 wt%, indicating the highly evolved nature of the pluton. Rocks with relatively low-silica contents (<70 wt%) represent compositionally less evolved portions of the pluton. Geologically meaningful interpretation of such data arrays should address possible contributions from a range of petrologic processes that include: (1) magmatic, crystal fractionation (2) ortho magmatic, crystal–liquid fractionation, and (3) hydrothermal crystal fluid fractionation. Of the processes listed above, crystal–liquid fractionation is typically significant in A-type granitic systems because of the high proportion of melt that characterize such magmas during emplacement (Clemens et al., 1986; Collins et al.,

12

C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

Fig. 4. (a) Plot of Na2O and K2O contents of Kanigiri granite. (b) The CaO–Na2O–K2O diagram of Kanigiri granite.Note that the majority of samples plot in the field of quartz monzonite. Other fields include gneissic complexes (fine stippled towards the left), tonalite diapirs (checked pattern), tonalites (dark grey), sheet-like batholiths (light grey), and average compositions of Archaen granitic rocks from greenstone–granite terranes (after Condie, 1981). (c) Plot of SiO2 (wt%) and molecular proportion of Al2O3/CaO + K2O + Na2O abbreviated as (A/CNK).

1982; Dall’Agnol et al., 1999; Dostal et al., 2004 and Tollo et al., 2004). For the Kanigiri granite, physical evidence of crystal–liquid fractionation is present in feldspar-dominated cumulate gabbroic rocks of the study area. Restite was not observed in the pluton that was mapped in detail, an observation that is in agreement with experimental results of Clemens et al. (1986) and Dall’Agnol et al. (1999). Similarly, no field evidence of magmatic co-mingling or mixing was identified in this nor earlier studies. Field mapping indicates that some parts of the pluton incorporated xenoliths and screens of country rocks; however, field, petrographic, and geochemical studies did not find evidence for extensive reaction and/or assimilation. Indeed, as is characteristic of granitic plutons emplaced at shallow crustal levels (Clarke, 1992), most contacts

between granite and lithological inclusions are sharp and do not display mineralogical reaction assemblages. Mineralogical and compositional evidence of late stage fluid involvement is present in the Kanigiri pluton. Such alteration is always accompanied by changes in mineralogical assemblages, including extensive development of sericite, breakdown of primary ferromagnesian silicates, and precipitation of fluorite. Moreover, the effects of alteration on whole-rock compositions, which are typically most significant for alkalis and specific trace elements, are generally recognizable. The Kanigiri granite exhibits elemental trends that are similar to those of petrologically comparable rocks from other locations (Eby et al., 1992; McLelland and Whitney, 1990 and Smith et al., 1999; Tollo et al., 2004). In discussing trace elements or trace elements ratios

C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

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Fig. 5. Harker variation diagrams of selected trace elements versus SiO2.

in terms of crystal /or fluid fractionation of granite, we divide those elements that occur in rock-forming feldspars (K, Rb, Sr, and Ba) from those elements controlled by accessory minerals zircon and allanite (Zr, Ta, and Nb) and those related to fluids (F, Li). Experimental studies of A-type granitic melts indicate that plagioclase is stable at near liquids conditions and the alkali feldspar crystallizes at temperatures about 70–80 C lower than the onset of plagioclase (Clemens et al., 1986 and Dall’Agnol et al., 1999). As a result, fractionation processes in A-type magmas typically involves, and are locally dominated by, feldspar separation (Eby, 1990; Eby et al., 1992 and Turner et al., 1992). Like many A-type suites (Eby et al., 1992; Landenberger and Collins,

1996 and Smith et al., 1999), Kanigiri granite exhibits considerable variation in Sr concentrations (Fig. 6b). Further evidence is provided by co-variation in Rb/Sr (average = 27.70) and Ba/Rb ratios (0.40), both of which increase with progressive fractionation. Increasing Rb/Ba ratios are also indicative of fractionation involving alkali feldspar because of strong partitioning of Ba into that phase (Henderson, 1982). Large variations in Rb/Ba ratios in the pluton suggest that alkali feldspar fractionation was an important process in highly evolved magma systems throughout the region, consistent with the largely hypersolvus nature of most high-silica plutons. Fine-grained granitic enclaves provide further evidence of in situ fractionation. A decrease in Fe2O3 with increasing silica

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Fig. 6. (a) Rb–Ba–Sr-ternary diagrams of Kanigiri granite samples. (b) Variation diagram showing the field of variation in Rb and Sr.

content (Fig. 5a) suggests that fractionation of primary ferromagnesian silicate minerals also was a factor in developing intraplutonic compositional variation. The Kanigiri metaluminous pluton typically contains primary biotite ± hornblende. Experiments involving metaluminous bulk compositions by Clemens et al. (1986) and Dall’Agnol et al. (1999) indicate that pyroxenes are early crystallizing phases in A-type melts. Correspondingly, clinopyroxene, locally overgrown by primary amphibole, occurs as a remnant high-temperature phase. The amphibole stability requires relatively high fO2 in the melt and, to maintain stability at near-solidus temperatures, relatively high fO2 conditions. The common occurrence of biotite ± hornblende ± (rare) clinopyroxene in the Kanigiri granitoid suggests that the parageneses of metaluminous plutons involved a crystallization sequence similar to that described by Dall’Agnol et al. (1999), but without orthopyroxene. The occurrence of hornblende as a late precipitating phase in many Kanigiri samples suggests crystallization may have occurred under relatively reducing, hydrous conditions. The influence of fractionating primary minerals in the Kanigiri granite is illustrated by variations in trace elements that are unaffected by alteration, notably Sc which is compatible in all observed ferromagnesian minerals and Ta which is incompatible in feldspars (Henderson, 1982 and Mahood and Hildreth, 1983). Overlapping intrapluton trends of decreasing Sc with increasing Ta likely resulted from fractionation of primary phases (Fig. 11).

Fig. 7. Envelope of chondrite normalized REE patterns for Kanigiri granite.

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Fig. 10. Plot of agpaitic index (Na + K)/Al versus aluminum saturation index (Al2O3/CaO + Na2O + K2O) for the Kanigiri granite.

Fig. 8. (a) Zr + Nb + Ce + Y vs. K2O+Na2O/CaO diagram showing the A-type character for Kanigiri granite. (b) Plot of Kanigiri granite on Rb– (Y + Nb) tectonic discrimination diagram.

Fig. 9. Zircon saturation temperature estimates (Harrison and Watson, 1983).The estimated tempeartures are between 800 and 860 C with only a few samples plotting along the 930C line.

Crystallization of accessory minerals such as zircon could modify the relationships as illustrated in Fig. 9 (Sawka, 1988 and Mahood and Hildreth, 1983), and the effect of ubiquitous zircon is probably responsible for some of the observed scatter. Allanite and zircon occur in many samples and are responsible for some of the observed variation in petrologically sensitive REE and HFS elements. Hf/Ta

Fig. 11. Plot of Ta vs. Sc for the Kanigiri granite.

ratios vary considerably, throughout the pluton. The influence of nearly ubiquitous zircon and allanite is indicated by the co variation in Hf/Ta and Ce/Yb that generally decrease with increasing fractionation (Fig. 12). These ratios are especially sensitive indicators because of the strongly compatible nature of Hf in zircon KD = 1190; (Sawka, 1988) and Ce in allanite KD = 1279; (Sawka, 1988). These and other trace-element ratios illustrate several important aspects of the role played by accessory minerals in the petrogenetic evolution of the Kanigiri granite. The effect of allanite fractionation on granites is illustrated by large decreases in Ce/Yb at relatively restricted Hf/Ta ratios (Fig. 12); probable late-stage crystallization and fractionation of allanite in the latter is further indicated by marked depletion in Nb and decreases in Nb/Ta and Ce/ Yb (not shown). The fractional crystallization outlined above, however, cannot explain some of the characteristics of the Kanigiri pluton. The low values of K/Rb (average of 130; compared to the crustal average of 240; Shaw, 1968) and its rough correlation with F and Li imply the involvement of fluid phases (see Dostal et al., 2004). Involvement of a fluid phase is also supported by the presence of albite and fluorite which are typical phases in these type of granites

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Fig. 12. Plot of Ce/Yb vs./Ta for Kanigiri granite. Arrows shows relative effects of Rayleigh fractionation of Zircon (Zr. 0.05%) and allanite (0.5%) calculated using crystal-liquid fractionation of zircon (Mahood and Hildreth, 1983 and Sawka, 1988).

(Cunny et al., 1992). Pegmatitic pods, aplite formation and polymetallic mineralization (Nb-Ta, U, Th, Zr, and Mo) observed in the Kanigiri granite also clearly indicate fluid involvement in the late-magmatic stage. The predominance of fluorine bearing vein minerals also suggest that fluorine enriched aqueous fluids played an important role in the late stage evolution of the pluton. The calculated zircon saturation temperatures indicate low temperatures(<800 C). Such cold granites appear to form at temperatures too low for dehydration melting involving biotite or hornblende and require a fluid influx(Miller et al., 2003). Infiltration of the source region by a water-rich fluid phase appears to be the only mechanism for inducing melting at T < 800 C (Miller et al., 2003). In summary, the observed enrichment of volatile elements resulted from a combination of crystal-fluid fractionation processes. The initial stages of the Kanigiri parent magma was dominated by crystal fractionation. However, towards later stages of crystallization of the most evolved rocks, the fluid phase became significant as manifested by the dramatic increases in F, Li, and Sn. 8. Petrolgical models for A type granites Petrologic models for derivation of A-type granites include a range of processes including: (1) fractionation of alkali basalt, (2) partial melting or fractional crystallization of ferrodiorite formed through magmatic underplating (3) melting of lower crustal source rocks that experienced metasomatism, and (4) low degrees of partial melting of (a) relatively anhydrous, typically granulitic source rocks or (b) high-temperature melting of tonalitic to granodioritic crustal source rocks that did not experience a prior episode of melting. Detailed reviews of these models were presented by various authors (Collins et al., 1982; Clemens et al., 1986; Whalen et al., 1987; Eby et al., 1992 and Landenberger and Collins, 1996). Characteristics of the Kanigiri granite realted to these models to petrogenesis of Kanigiri granite and indicate its possible genetic model

include (a) location along a major fault represented by the Mekeru river; (b) spatial association with gabbroic and (quartz) syenitic rocks; (c) numerous fine-grained enclaves in the Kanigiri pluton preserve evidence of early-formed, chemically primitive magmatic predecessors. Trace-element characteristics indicate that the metaluminous granitoid was likely derived through melting of lower crustal sources. Systematic variation in Sr, Rb/Sr, and Rb/Ba ratios reflect fractionation of feldspars, whereas variations in Fe, Sc, and Ta resulted from fractionation of ferromagnesian silicates. The emplacement age of ca.985 ± 20 Ma with high (87Sr/86Sr) i of 0.735 ± 0.012 (Gupta et al., 1984) indicates a crustal origin. Taking into account these characteristics of the Kanigiri granite and the cited petrological models for the A-type granites indicated above, it appears that most of the observed features can best be explained by the model of low-degree partial melting of mafic rocks like gabbros present in the study region at lower-middle crustal depths. Relatively primitive granites and mafic enclaves are most likely to approximate the composition of parental magmas and reflect the geochemical characteristics of their source. The Kanigiri granite displays petrologic similarities to lower crustal rocks considered as A-type sources elsewhere, (Subba Rao et al., 1992). Subba Rao et al. (1992a,b) concluded that some of the Dharawar Craton biotite granites formed by anatexis of TTG-like sources (either old Peninsular Gneisses or the younger ‘‘Krishnagiri Type’’ TTG). The geochemical characteristics of these and Kanigiri rocks are in good agreement with such a conclusion (e.g: high A/CNK, K/Na, high Rb, and negative Eu anomalies). The (87Sr/86 Sr) i of 0.735 ± 0.012 supports a crustal origin, and the heat source necessary to induce melting of sialic crust is likely to be intruding mafic magma. Consequently, it is likely that the Kanigiri granite formed by melting of a mafic rock like gabbro present near the pluton. The range of P–T conditions for the origin of such a granitic melt, as indicated by Zr saturation temperatures (Miller et al., 2003) is about 800 C at about 11 kb. The maximum temperatures of about 800 C seems reasonable for the origin of the granitic melt from a lower crustal source, considering that the thickened, stabilized Proterozoic crust with a low geothermal gradient was thought to be responsible for the formation of post-tectonic alkali magmatism (Leelanandam, 1993) in the study region. The incompatible element enriched Kanigiri granite and the presence of rare metals like Nb, Ta, Zr, U Th, and Rb indicate that the degree of partial melting was low (ca. <5%). Furthermore, this granitic melt was also rich in volatiles as evidenced by cluster five elements in the correlation matrix, especially F. In this model the unusual enrichments in Zr, Nb, Y are explained by either higher temperature (>900 C) required for second partial melting and/or high F contents that promote the complexing of ions, thus increasing the HFSE contents in the melt (Collins et al., 1992). However, the calculated range of P–T conditions, as indicated by Zr saturation temperatures (about 800 C) are lower than <900 C,

C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19

even considering that they would be higher than that of the magma, due to the presence of zircon showing calculated age inheritance. Fluorite occurs locally and as veins in the Kanigiri granites. The experimental results of Dooley and Patin˜o Douce (1996) and Patin˜o Douce and Beard (1996) show that high F contents in the source favors Al enrichment in the melt, even if the source is not oversaturated in alumina. Fluorite in the Kanigiri granite occurs as rare interstitial, anhedral crystals with sharp boundaries believed to be of primary magmatic origin and as late-stage crystals occurring mostly as veins.The increase in F contents in the melt may be due to fractionation. We suggest the formation of F rich Kanigiri granite can be explained using a model invoking high F contents in the melt. It is suggested that much of magmatic fluorine was lost upon crystallization because low Ca, P and Al contents of the melt precluded fixation of F in crystalline phases. Our idea that fluorine was first concentrated in the magma, and afterwards removed during crystallization, can explain the columbite–tantalite mineralization of the Kanigiri granite. Keppler (1993) showed that addition of F to the haplogranite system strongly increases the solubility of Nb and Ta in the melt. Thus a build up of F in the residual melt would prevent crystallization of early formed columbite–tantalite. Final crystallization, perhaps following the loss of F, would then cause mineralization of columbite– tantalite. 9. Conclusions The biotite rich Kanigiri granite is undeformed and occurs as a discordant intrusion in the meta-sedimentary rocks. Fine-grained enclaves in the pluton preserve evidence of early-formed, chemically primitive magmatic predecessors. The pluton exhibits A-type geochemistry. Systematic variation in Sr, Rb/Sr, and Rb/Ba reflects fractionation of feldspars, whereas variations in Sc, and Ta result from fractionation of ferromagnesian silicates. Removal of zircon and allanite affected Hf/Ta and Ce/ Yb ratios. These compositional characteristics indicate the importance of crystal fractionation in the evolution of A-type granites. Incompatible trace-element correlations that suggest fluid accompanying fractional crystallization played a key role in developing chemical variation signatures. The overall geochemical data and the variation in important major and trace elements and their ratios suggest that the granite is of anorogenic type; formed from primary magma produced by partial melting of relatively anhydrous lower crustal rocks. Acknowledgements The authors are grateful to R.D. Schuiling, Department of Geochemistry, Utrecht University, the Netherlands, for providing facilities for carrying out the chemical analysis at Utrecht University. The valuable help and facilities extended by Das, Netherlands Energy center, for REE anal-

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ysis is gratefully acknowledged. The authors also thank J.B. De Smeth, M.G. Oosterm and J.B.H. Hensen for their assistance in the field and in the lab. Most of the work was carried out with the financial assistance of applied geochemistry project (collaborative programme between Osmania University and University of Utrecht, Netherlands.) This paper has benefitted from valued suggestions and constructive comments by M.K. Panigrahi, G. Grantham, and an anonymous reviwer. References Anderson, J.L., 1983. Proterozoic anorogenic granite plutonism of North America. Geological Society of America Memoir 161, 133–154. Anderson, J.L., Morrison, J., 1992. The role of anorogenic granites in the Proterozoic Crustal development of North America. In: Condie, K.C. (Eds.), Proterozoic Crustal Evolution. Developments in Precambrian Geology 10, pp. 263–299. Babu, V.R.R.M., 1998. The Nellore schist belt: an Archean Greenstone belt, Andhra Pradesh, India, Precambrian crustal processes in East Coast Granulite–Greenstone regions of India and Antartica within East Gondwana. Gondwana Research Group Memoir 4, 97–136. Banerjee, D.C., Maithani, P.B., Ranganath, N., Jayaram, K.M.B., 1983. Rare metal mineralization in granitic rocks of Kanigiri area in Prakasam district, Andhra Pradesh. Chemical Geology 39, 319–334. Clarke, D.B., 1992. Granitoid Rocks. Chapman and Hall, New York, p. 283. Clemens, Holloway, J.R., White, A.J.R., 1986. Origin of A-type granite: experimental constraints. American Mineralogist 7, 317–324. Collins, W.J., Beams, S.D., White, A.J.R., Chappell, B.W., 1982. Nature and origin of A-type granites with particular reference to Southeastern Australia. Contributions to Mineralogy and Petrology 80, 189. Condie, K.C., 1981. Geochemical and isotopic constraints on the origin and source of Archaen granites. In: Glover, J.E., Groves, D.I., (Eds). Archaen geology, International Sympoium, second, Perth: Geological Society of Australia, Special Publication 7, 469–479. Cunny, M., Marignac, C., Weisbrod, A., 1992. The Beauvoirtopaz– lepidolite–albite granite (Maasif central, France): the dessiminated magmatic Sn–Li–Ta–Be mineralization. Economic Geology 87, 1766–1794. Dall’Agnol, R., Lafon, J.M., Macambira, M.J.B., 1994. Proterozoic anorogenic magmatism in the Central Amazonian Province, Amazonian craton: Geochronological, Petrological and Geochemical aspects. In: Haapala, I., Ra¨mo¨, O.T. (Eds.) IGCP Project 315, Publication No. 12. Mineralogy and Petrology 50, pp. 113–138. Dall’Agnol, R., Scaillet, B., Pichavant, M., 1999. An experimental study of a lower Preoterozoic A-type granite from the eastern Amazonian craton, Brazil. Journal of Petrology 40, 1673–1698. Davis, J.C., 1973. Stastical and Data Analysis in Geology. Wiley, NewYork, NY, p. 550. DeSilva, S.L., 1991. Styles of zoning in central Andean ignimbrites: insights into magma chamber processes. In: Harmon, R.S., Rapela, C.W. (Ed). Andean Magmatism and its Tectonic Setting. Geolgical Society of America Spl. Paper 265, pp. 233–243. Dobmeier, C., Raith, M.M., 2003. Crustal architecture and evolution of the Eastern Ghats belt and adjacent regions of India. Proterozoic east Gondwana: Supercontinent assembly and break up. Geological Society, London, Special Publications 206, 145–168. Dooley, D.F., Patin˜o Douce, A.E., 1996. Fluid-absent melting of F-rich phlogopite + rutile + quartz. American Mineralogist 81, 202–212. Dostal, J., Chaterjee, A.K., 2000. Contrasting behaviour of Nb/Ta and Zr/Hf ratios in a peraluminous grantic pluton Nova Scotia, Canada. Chemical Geology 123, 67–88. Dostal, J., Chaterjee, A.K., Kontak, D.J., 2004. Chemical and isotopic (Pb,Sr)zonation in a peraluminous granite pluton:role of fluid fractionation. Contributions to Mineralogy and Petrology 147, 58–73.

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Rajesh, H.M., 2000. Characterization and origin of compositionally zoned aluminous A-type granite from South India. Geological Magazine 137, 291–318. Ramakarishna, M., 2003. Craton–mobile belt relations in Southern Granulite terrain. Memoir Geological Society of India 50, 1–24. Ramam, P.K., Murthy, V.N., 1997. Geology of Andhra Pradesh. Geological Society of India. Bangalore, p. 245. Ra¨mo¨, O.T., Haapala, I., 1995. One hundred years of Rapakivi Granite. Mineralogy and Petrology 52, 129–185. Reddy, U.V.B., Naryana, B.L., Shanti Kumar, C., 1994. Ophiolite me´lange from Nellore Schist belt: an evidence for Precambrian plate tectonics. Workshop on Eastern Ghats Mobile Belt, Vishakapatnam, pp. 21–22 (abs). Rose, A.W., Hawkes, H., Web, J.S., 1979. Geochemistry in Mineral Exploration, Second ed. Academic press, London. Sawka, W.N., 1988. REE and trace element variations in accessory minerals and hornblende from the strongly zoned McMurray Meadows Pluton, California. Transactions of Royal Society. Edinburgh: Earth Science 79, pp. 157–168. Schmitt, A.K., DeSilva, S.L., Trumball, R.B., Emmermann, R., 2001. Magma evolution in the Purico ignimbrite complex, nothern Chile:evidence for zoning of a dacitic magma by injection of rhyolitic melts following mafic recharge. Contributions to Mineralogy and Petrology 140, 680–700. Shaw, D.M., 1968. A review of K–Rb fractionation trends by covariance analysis. Geochimica et Cosmochim Acta 32, 176–573. Smith, D.R., Noblett, J., Wobus, R., Unruh, D., Douglass, J., Beane, R., Davis, C., Goldman, C.S., Kay, G., Gustavson, B., Saltoun, B., Stewart, 1999. Petrology and geochemistry of late-stage intrusions of the A-type, mid-Proterozoic Pikes Peak batholith (Central Colorado, USA): implications for petrogenetic models. Precambrian Research 98, 271–305. Stolz, A.J., Jochum, K.P., Spettel, B., Hofmann, A.W., 1996. Fluid and melt-related enrichment in the subarc mantle:evidence from Nb/Ta variations in island-arc basalts. Geology 24, 587–590. Subba Rao, M.V., Narayana, B.L., Diwakar Rao, V., Reddy, G.L.N., 1998. Petrogenesis of the protolith for the Tirodi gneiss by A-type granite magmatism: the geochemical evidence. Current Science 76, 1258–1262. Tatsumi, Y., Hamiliton, D.L., Nesbitt, R.W., 1986. Chemical characteristics of fluid phase released from a subducted lithosphere and origin of arc magams: evidence from high pressure experiments and natural rocks. Journal of Volcanology and Geothermal Research 29, 293–309. Tegtmeyer, P.B., Farmer, G.L., 1989. Isotopic evidence for the origin of late metaluminous and peralkaline rhyolites from the great Basin,western U.S. In: Abstracts, International Association of Volcanology and Chemical Earth Interiors. New Mexico. Bureau of Mines Miner Resources Bull 131. Thirupathi, P.V., Sudhakar, Ch., Krishna, K.V.G., Dhana Raju, R., 1996. Petrology and geochemistry of the proterozoic A-type granite of Kanigiri, Prakasam district, Andhra Pradesh: implications for rare metal mineralization. Exploration and Research for Atomic Minerals 9, 61–72. Tollo, R.P., Aleinikoff, J.N., Mervin, J., Bartholomew, M.J., Rankin, D.W., 2004. Neoproterozoic A-type granitoids of the central and southern Appalachians: intraplate magmatism associated with episodic rifting of the Rodinian supercontinent. Preacmbrian Reasearch 128, 3–38. Turner, S.P.J., Foden, D., Morrison, R.S., 1992. Derivation of some Atype magmas by fractionation of basaltic magma: an example from the Padthaway Ridge, South Australia. Lithos 28, 151–179. Whalen, J.B., Currie, K.L., Chappel, B.W., 1987. A-type granites: geochemical characterstics, discrimination and petrogenesis. Contributions to Mineralogy and Petrology 95, 407–419.

Further reading Chappel, B.W., White, A.J.R., 1992. I- and S-type granites in the Lachlan Fold belt. In: Brown, P.E., Chappel, B.W. (Eds.), The second Hutton

C.V. Dharma Rao, U.V.B. Reddy / Journal of Asian Earth Sciences 30 (2007) 1–19 Symposium on the Origin of Granites and Related Rocks. Geological Society of America Special Paper 272, pp. 1–26. Pitcher, W.S., 1982. Granite type and tectonic environment. In: Hsu, K.J. (Ed.), Mountain Building Processes. Academic Press, London, p. 263. Pitcher, W.S., 1993. The Nature and Origin of Granite. Blackie Academic and Professional Publishers, London, 321 p. Taylor, S.R., McLennan, S.M., 1985. The Continental Crust: Its Composition and Evolution. Blackwell Scientific Publications, Oxford, p. 311. Tollo, R.P., Lowe, T.K., 1994. Geologic map of the Robertson River Igneous Suite, Blue Ridge Province, Virginia. U.S. Geological Survey Miscellaneous Field Studies Map MF-2229, scale 1:100,000, p. 15.

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Tollo, R.P., Hackley, P.C., Aleinikoff, J.N., 2000. Petrologic evolution of Grenville-age basement, central Blue Ridge, Virginia. Geological Society American Abstract Programs 32, 79. Vriend, S.P., Oosterom, M.G., Bussink, R.W., Jensen, J.B.H., 1985. Trace element behaviour in the W–Sn granite of Regoufe, Portugal. Journal of Geochemical exploration 23, 13–25. Wolf, J.A., Worner, G., Blake, S., 1990. Gradients in physical parameters in zoned felsic magam bodies: implications for evolution and eruptive withdrawal. Journal of Volcanolgy and geothermal research 43, 37–55.