Anorogenic Acid Volcanic rocks in the Kundal area of the Malani Igneous Suite, Northwestern India: geochemical and petrogenetic studies

Journal of Asian Earth Sciences 27 (2006) 544–557 www.elsevier.com/locate/jaes

Anorogenic Acid Volcanic rocks in the Kundal area of the Malani Igneous Suite, Northwestern India: geochemical and petrogenetic studies A. Krishnakanta Singha,*, R. K. Bikramaditya Singhb, G. Vallinayagamc a

Wadia Institute of Himalayan Geology, Northeast Unit, Itanagar 791113, India b Wadia Institute of Himalayan Geology, Dehradun 248001, India c Department of Earth Sciences, Kurukshetra University, Kurukshetra 136119, India Received 8 October 2003; revised 25 May 2005; accepted 25 May 2005

Abstract Acid volcanic rocks from the Kundal area of the Neoproterozoic (725G7 Ma) Malani Igneous Suite (MIS) are predominantly represented by rhyolite (porphyritic and non-porphyritic) with minor amounts of trachyte, welded tuff and volcanic ash beds. The nonporphyritic rhyolite is peralkaline (acmite normative;O1 AI and A/CNK ratio !1) whereas porphyritic rhyolite is peraluminous and metaluminous (corundum and anorthite normative; !1 AI). Acid volcanic rocks are characterized by low CaO, MgO, Fe2O3(t), Cr, Ba, Sr and Eu and high SiO2, NaOCK2O, Fe/Mg, Zr, Nb, Y and REEs (except Eu), indicating their A-type affinity. Negative anomalies of Ti, P, Sr and Ba in the multi-element spider diagrams indicate retention of plagioclase and accessory minerals in the source rock during partial melting. Rhyolite was probably derived from relatively low degrees of partial melting as they are enriched in LREE and incompatible elements compared to trachyte. Underplating of basaltic magmas at the base of the crust may have provided the heat source for extensive crustal melting. Petrogenetic modeling suggest that these acid volcanic rocks may have been derived from a melasyenite source by partial melting (5–20%) at w8 kbar pressure and w1000 8C temperature. An anorogenic setting for these acid volcanic rocks are also suggested which supports a rift-related tectonic environment for MIS in the Trans-Aravalli blocks of the Indian Shield. q 2005 Elsevier Ltd. All rights reserved. Keywords: Geochemistry; Petrogenesis; Anorogenic acid volcanics; Malani Igneous Suite; Western India

1. Introduction Malani magmatism (w 55,000 sq. km.) was a Neoproterozoic tectonomagmatic event in northwestern Peninsular India (Fig. 1A). This magmatism is characterized by volcano-plutonic ring structures indicative of an extensional tectonic environment. Blanford (1877) introduced the term ‘Malani beds’ for a volcanic series of porphyritic lavas and ash beds. La Touche (1902) documented the physical and petrographic features along with the nature of the eruption. * Corresponding author. Tel.:C91 0360 2215375. E-mail address: [email protected] (A.K. Singh).

1367-9120/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2005.05.008

Murthy et al. (1961) described the rhyolites and associated granites as the Malani Igneous Suite (MIS). The emplacement of Malani acid volcanics and granites was coeval, yielding a Rb/Sr age of 725G7 Ma (Dhar et al., 1996) which was contemporaneous with a major Pan-African event of widespread intraplate, anorogenic magmatism represented by acid volcanics. The rhyolites and alkali granites of Central Iran (Forster, 1987), Nubian-Arabian Shield (Kroner et al., 1989), Somalia (Kroner et al., 1990), Madagascar (Yoshida et al., 1999), Seychelles (Hoshino, 1986) and the Trans-Aravalli block of the Indian Shield are coeval with the Malani alkali granite and acid volcanic rocks (Bhushan, 2000; Kochhar, 2001). Torsvik et al. (2001)

A.K. Singh et al. / Journal of Asian Earth Sciences 27 (2006) 544–557

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Fig. 1. (A) Generalized geological map of the Neoproterozoic Malani Igneous Suite (MIS), Northwestern Peninsular India (modified after Pareek, 1981; Bhushan, 1985). (B) Simplified lithological map of the Kundal area, Malani Igneous Suite.

reported U–Pb ages for Malani rhyolite from 771 Ma to 751 Ma. Vallinayagam (2004) reported that peralkaline rhyolites of MIS show higher zircon saturation temperatures (1096 –1421 8C) compared to peraluminous rhyolites (1112 –1382 8C). The Malani magmatism is controlled by NE–SW trending lineaments and is associated with hot-spot magmatism and related tectonics (Kochhar, 1996; Bhushan and Chittora, 1999). The preponderance of acid volcanic rocks relative to intermediate and basic rocks is a distinctive feature of MIS. The steep northern migration of the Indian subcontinent during eruption of Malani rhyolite due to

plume activity may have contributed to Precambrian glaciation (Kochhar, 2001). Acid volcanic rocks in MIS have been studied beginning with La Touche (1902). Pareek (1981); Kochhar (1984); Bhushan (1985); Srivastava et al. (1989); Eby and Kochhar (1990); Maheshwari et al. (1996); Dhar et al. (1996); Vallinayagam and Kochhar (1998); Bhushan and Chittora (1999); Bhushan (2000); Kochhar (2000); Singh and Vallinayagam (2003); Vallinayagam (2004) discussed the geochemical characteristics and petrogenesis of Malani acid volcanic rocks.

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The present study area of Kundal is part of MIS and is located w4 km south of the Siwana ring complex (Fig. 1A). The area is characterized by bimodal A-type granite with a carapace of cogenetic acid volcanics (rhyolite, trachyte, welded tuff) and minor amounts of basic rocks (basalt, gabbro, dolerite) (Singh and Vallinayagam, 2002). To date, no detailed petrological and geochemical modeling of acid volcanic rocks in the area have been carried out. This paper presents a comprehensive geochemical study of Kundal acid volcanic rocks of MIS and discusses their petrogenesis and tectonic setting.

2. Field Relationship Systematic geological mapping of the Kundal area reveals that the rock units can broadly be grouped as Extrusive phase: basalt, trachyte, rhyolite (porphyritic rhyolite, non-porphyritic rhyolite) with minor amounts of welded tuff; Intrusive phase: gabbro, granite; Dyke phase: dolerite (younger) (Fig. 1B). A close association of acid volcanics (rhyolite, trachyte) with the granite and basic volcanic rocks (basalt) and gabbros, indicate an interrelationship between volcanism and plutonism. The trachyte occurs as flows associated with rhyolite and tuffaceous rhyolite. It is coarse grained, dark gray colored and porphyritic with phenocrysts of alkali feldspar. The contact between trachyte and rhyolite is sharp without any morphological change. Basic rocks (basalt, gabbro) occur in close proximity with the rhyolite. The area is predominantly occupied (w90%) by rhyolitic rocks. The non-porphyritic variety is medium grained with various shades viz. brick red, dark red whereas porphyritic rhyolite is variable in colour viz. light pink, dark pink, dark gray, light gray, greenish brown and consists of pink alkali feldspar and quartz as phenocrysts in the fine grained quartzofeldspathic groundmass. Volcanic tubes (1.5–2.5 m diameter and 1.0– 3.0 m depth) and vertical jointing are observed occasionally with porphyritic rhyolite. Minor amounts of fine grained, greenish brown and light pink colored welded tuff associated with rhyolite are also observed. The acid volcanic rocks are younger than the basalt flows as evidenced by the presence of basalt xenoliths within the trachyte and rhyolite flows. They are invariably cut by numerous NE–SW, NW–SE trending dolerite dykes.

3. Petrography Petrographically, rhyolite is more or less similar to trachyte except that quartz phenocrysts are invariably absent in the latter. Trachyte shows porphyritic and microcrystalline textures. It consists of alkali feldspar (sanidine, perthite), quartz, alkali amphibole (arfvedsonite, riebeckite) as essential minerals and zircon and opaque are accessories. Porphyritic rhyolite shows granophyric and flow textures

whereas non-porphyritic rhyolite displays microcrystalline and glomeroporphyritic textures. Porphyritic rhyolite consists of quartz, sanidine, perthite, hornblende and muscovite as essential minerals along with zircon and opaques as accessories. Non-porphyritic rhyolite contains quartz, sanidine, perthite, arfvedsonite, riebeckite and aegirine as essential minerals whereas zircon and opaques are accessories. Welded tuff shows a microcrystalline texture and consists of orthoclase, quartz, hornblende, muscovite and opaques. Quartz phenocrysts occur as bipyramidal crystals that are embayed or sutured. Embayment in quartz is due to magma resorption caused by changes in P–T conditions and may suggest a change in magma-composition around the embayed grains (Gupta, 1983; Gupta et al., 1994). However, it should be noted that embayed phenocrysts may represent highly localized resorption due to convection around gas bubbles, or may represent a growth phenomenon (Donaldson and Henderson, 1988). In non-porphyritic rhyolite, quartz crystals sometimes occur as veins that traverse the groundmass. Sanidine occurs as medium to large phenocrysts and shows carlsbad twinning. Perthite and orthoclase occur as subhedral crystals and show vein type perthitic textures and carlsbad twinning respectively. At places, perthite altered to sericite and kaolin whereas sanidine and orthoclase altered to kaolin. The small prismatic crystals of arfvedsonite (XZdark bluish green; YZbluish green; ZZyellowish green; extinction angle (ZoC) varies 128–158) and needles of riebeckite (XZdark blue; YZblue; ZZlight blue; ZoC varies 38–58) inclusions in alkali feldspar and groundmass are common. Hornblende in porphyritic rhyolite and welded tuff occurs as fine prismatic crystals and ZoC varies between 168 and 258. At places, it is dark green and almost isotropic which may be due to the high ferromagnesian content. Muscovite occurs in fine flaky forms and extinction angles are parallel to cleavage traces. Short, prismatic, fine crystals of zircon are encountered in the groundmass. All samples contain equate opaque grains scattered in the groundmass.

4. Geochemistry The major elements were analysed by using a digestion procedure modified after Shapiro and Brannock (1962). Samples were analysed using a UV–VIS Spectrometer-108 and Mediflame Photometer-127 at the Department of Earth Sciences, Kurukshetra University, India. Trace elements (including rare earth elements) were determined by using ICP-AES at the School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India, at USIC, University of Roorkee, India and at Wadia Institute of Himalayan Geology, Dehradun, India. Detailed analytical procedures, conditions and precision of analyses are given in Sohoo and Balakrishnan (1994); Giritharan and Rajamani (1998). The major element results together with CIPW

Table 1 Major element analyses and CIPW norms of the Kundal acid volcanic rocks, Malani Igneous Suite (MIS), Rajasthan, India Rock type

Porphyritic rhyolite

Sample No.

PKB01

PKB11

PKB12

PKB16

PKB22

PKB36

PKB42

PKB17

PVK20

Welded tuff WKN56

WKB25

Non-porphyritic rhyolite NKB14

NKB18

NKB26

NKB32

NVK34

NVK51

Trachyte TKB09

TKB10

TKB13

69.36 0.12 12.62 7.10 0.02 0.26 0.94 4.05 5.05 0.05 0.31 99.88 24.86 0.01 1.15 34.27 1.34 – 1.40 0.36 – – 7.10 0.04 0.24 – 0.12 88.98 0.95 9.10 0.80 0.91 1.04 0.03 6.76

72.02 0.13 12.69 6.29 0.03 0.29 0.82 3.01 5.27 0.08 0.26 100.89 32.38 0.74 31.15 25.47 3.55 – – – 0.72 – 6.29 0.06 – 0.10 0.19 89.00 0.83 8.28 0.57 1.04 1.19 0.12 10.43

71.98 0.09 12.51 5.84 0.06 0.22 0.86 3.89 4.46 0.05 0.31 99.37 29.45 0.01 26.31 32.91 3.50 – 0.28 – 0.42 – 5.84 0.13 0.05 – 0.12 88.72 0.87 8.35 0.87 0.97 1.11 0.07 6.94

69.21 0.11 12.00 6.84 0.04 0.25 0.72 5.21 4.31 0.07 0.25 99.06 22.82 – 25.47 37.73 – 5.59 1.39 0.49 – – 4.96 0.09 0.16 – 0.17 86.02 1.10 9.52 1.20 0.82 0.9 – 6.70

70.01 0.13 12.54 7.23 0.04 0.21 0.82 3.56 4.62 0.06 0.34 99.56 29.72 0.34 27.31 30.12 3.68 – – – 0.52 – 7.23 0.09 – 0.08 0.14 87.15 0.85 8.18 0.77 1.01 1.15 0.10 8.55

69.52 0.15 13.10 7.02 0.06 0.21 0.97 4.13 4.50 0.06 0.25 99.97 27.58 0.25 24.23 34.94 4.42 – – – 0.52 – 7.02 0.13 – 0.07 0.14 86.75 0.89 8.63 0.91 0.97 1.12 0.11 5.60

69.71 0.11 13.67 7.21 0.05 0.25 0.72 3.21 4.71 0.05 0.35 100.04 31.24 0.10 27.16 27.16 3.25 – – – 0.62 – 7.21 0.11 – 0.05 0.12 86.24 0.76 7.92 0.68 1.16 1.31 0.10 5.31

70.62 0.15 13.02 7.08 0.03 0.27 0.96 3.55 4.77 0.06 0.31 100.82 29.42 0.42 28.90 30.09 4.37 – – – 0.67 – 7.08 0.06 – 0.12 0.14 87.65 0.83 8.32 0.74 1.02 1.18 0.12 7.02

70.44 0.16 12.57 4.25 0.09 0.25 0.83 4.17 4.83 0.09 0.35 98.52 26.28 – 28.55 35.28 1.32 1.16 1.34 0.12 – – 4.25 0.19 0.14 – 0.21 90.11 1.03 9.00 0.86 0.92 1.03 0.03 10.43

72.17 0.13 11.82 6.1 0.07 0.18 0.77 3.24 4.87 0.05 0.22 99.53 32.99 – 28.78 27.41 3.33 – – – – – .01 0.15 0.12 – 0.12 89.18 0.88 8.11 0.66 0.98 1.11 0.10 5.60

70.21 0.15 12.52 5.22 0.04 0.19 0.82 3.65 5.10 0.03 0.27 98.20 27.75 – 30.14 30.88 0.61 – 0.61 – 0.14 – 5.22 0.09 0.26 – 0.17 88.17 0.91 8.78 0.71 0.96 1.08 0.08 6.72

74.19 0.10 11.19 3.61 0.04 0.13 0.72 3.68 5.28 0.05 0.31 99.30 32.36 – 31.21 28.16 – 2.62 0.70 0.90 – – 2.70 0.09 0.13 – 0.12 91.73 1.03 8.96 0.69 0.85 0.95 – 6.66

70.1 0.10 11.82 4.82 0.03 0.22 0.79 4.00 6.22 0.07 0.27 98.35 23.62 – 36.76 26.17 – 6.76 1.18 0.72 – – 2.48 0.06 0.16 – 0.17 87.55 1.12 10.22 0.64 0.80 0.88 – 8.29

72.07 0.07 11.44 5.28 0.02 0.26 1.17 4.92 4.01 0.03 0.29 99.06 29.61 – 23.70 36.52 – 0.77 1.40 1.52 – – 5.01 0.04 0.12 – 0.07 89.83 1.01 8.43 1.22 0.78 0.91 – 8.89

72.02 0.07 13.26 3.81 0.12 0.16 0.93 3.15 5.38 0.04 0.20 99.04 28.99 0.56 31.80 26.65 4.35 – – – 0.40 0.19 3.68 0.13 – – 0.09 87.44 0.82 8.53 0.58 1.04 1.2 0.14 7.68

69.22 0.09 13.11 5.07 0.07 0.28 1.12 3.92 6.52 0.09 0.41 99.99 20.34 – 38.54 31.14 – 1.79 1.50 1.44 – – 4.45 0.15 0.03 – 0.21 90.02 1.03 10.44 0.60 0.84 0.97 – 9.86

73.37 0.11 11.08 5.72 0.07 0.27 0.86 4.23 4.42 0.08 0.20 100.41 31.42 – 26.12 32.39 – 3.00 1.45 0.74 – – 4.68 0.15 0.08 – 0.19 89.19 1.06 8.65 0.65 0.83 0.94 – 8.55

67.02 0.35 14.52 3.13 0.08 0.32 1.92 4.11 6.72 0.24 0.42 98.83 14.91 – 39.72 34.77 1.33 – 1.72 1.47 – – 3.13 0.17 0.64 – 0.57 89.40 0.98 10.83 0.61 0.82 1.03 0.03 16.84

62.71 0.42 14.82 5.17 0.12 0.96 1.56 4.75 6.05 0.39 0.62 99.07 8.03 – 35.76 40.19 1.25 – 4.80 – 0.16 – 5.17 0.26 1.93 – 0.92 83.98 0.96 10.80 0.78 0.86 1.03 0.03 26.89

65.82 0.31 14.25 3.28 0.07 0.28 1.96 4.09 7.22 0.31 0.49 98.58 13.19 – 42.67 34.61 0.56 – 1.50 1.84 – – 3.28 0.15 0.57 – 0.73 89.47 0.96 11.31 0.56 0.78 0.97 0.01 14.46

Oxide

A.K. Singh et al. / Journal of Asian Earth Sciences 27 (2006) 544–557

SiO2 TiO2 Al2O3 Fe2O3(t) MnO MgO CaO Na2O K2O P2O5 H2O Total Quartz Corundum Orthoclase Albite Anorthite Acmite Diopsite Wollastonite Hypersthene Magnetite Hematite Ilmenite Sphene Rutite Apatite DI AI Na2OCK2O Na2O/K2O A/CNK A/NK An/AnCAb Mg#

547

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A.K. Singh et al. / Journal of Asian Earth Sciences 27 (2006) 544–557

Table 2 Trace elements data (in ppm) for Kundal acid volcanic rocks, Malani Igneous Suite, Rajasthan, India Rock type

Porphyritic Rhyolite

Non-porphyritic rhyolite

Trachyte

Sample No.

PKB01

PKB12

PKB36

PKB42

PVB20

NKB14

NKB26

NKB32

TKB09

TKB13

Cr Ni Ba Sr Rb Nb Zr Y Sc Th U Ratio Ba/Sr Sr/Y Zr/Y Zr/Rb Rb/Sr Nb /Y Zr/Nb

ND ND ND 69 126 32 ND 111 4 23 5

30 152 92 46 ND ND 2180 358 3 31 8

ND ND 192 41 142 24 ND 100 7 21 7

23 101 141 38 171 81 2091 289 7 34 7

70 266 147 40 187 87 2676 219 2 31 6

24 117 44 22 ND ND 2560 382 2 28 7

57 121 105 53 197 109 2405 326 2 30 6

36 137 67 35 201 96 2162 292 3 28 5

14 25 135 44 99 124 1416 392 2 21 6

15 30 151 42 ND ND 1309 411 ND ND ND

5.73 0.62 – – 1.82 0.28 –

2.00 0.13 6.08 – – – –

4.68 0.41 – – 3.46 0.24 –

3.71 0.13 7.23 55.02 4.5 0.28 25.81

3.67 0.18 12.28 14.15 4.72 0.39 30.75

2.00 0.05 6.70 – – – –

1.98 0.16 7.37 12.20 3.71 0.33 22.06

1.91 0.11 7.40 10.75 5.74 0.32 22.52

3.06 0.11 3.61 14.30 2.25 – 11.41

3.59 0.10 3.18 – – 0.31 –

NDZnot determined

norms are presented in Table 1. Trace elements and REE data are presented in Tables 2 and 3 respectively. The trachyte has a narrow range of SiO2 (62.71– 67.02 wt.%), K2OO Na2O and a strong variation in Na2O and CaO content with AI (Agpaitic Index Zmolecular proportion of Na2OCK2O/Al2O3) !1, indicating their peraluminous nature (Shand, 1927). Total alkali contents are high (10.80–11.31 wt.%), whereas CaO (1.92– 2.56 wt.%) and MgO contents (!1.0 wt.%) are low. The Differentiation Index (DI Zsum of normative QCOrC AbCNeCLc; Thornton and Tuttle, 1960) ranges from 83.98–89.47. Compared to trachyte, rhyolite (including welded tuff) shows higher concentration of SiO2 and lower

amounts of TiO2, Al2O3, MgO, CaO, K2O and P2O5. Trachyte and rhyolite show comparable concentrations of Fe2O3(t), MnO, Na2O. Non-porphyritic rhyolite show total alkali ranges between 8.43–10.44 wt.% whereas porphyritic rhyolite shows ranges of 7.92–9.52 wt.%. Non-porphyritic rhyolites show DI values of 87.44–91.73 with AIO1 and A/CNK (molecular Al2O3/Na2OCK2OCCaO; after Maniar and Piccoli, 1989) ratios !1 (except in sample no. NKB32), indicating a peralkaline nature (Giret et al., 1980). This is consistent with the presence of alkali amphibole/pyroxene under thin section and acmite in the norm (Table 1). The peraluminous and metaluminous porphyritic rhyolites show hornblende and muscovite under thin section,

Table 3 Rare earth elements data for Kundal acid volcanic rocks, Malani Igneous Suite, Rajasthan, India and REE data of the source rock Rock type

Porphyritic rhyolite

Non-porphyritic rhyolite

Trachyte

Sample No.

PKB01

PKB12

PVB20

PKB36

Ce Nd Sm Eu Gd Dy Er Yb REE(t) Ratio (Ce/Sm)N (Gd/Yb)N (Ce/Yb)N Eu/Eu*

210.12 106.23 19.03 1.74 14.93 18.00 9.24 11.60 390.89

244.18 111.90 20.12 1.06 15.30 19.18 9.85 12.21 433.80

226.12 115.01 28.49 2.16 24.61 20.97 15.18 12.70 445.24

2.60 1.03 4.63 0.31

2.86 1.00 5.11 0.18

1.87 1.55 4.55 0.25

Source rock (melasyenite)

PKB42

NKB26

NKB32

TKB09

TKB13

D125(i)

200.20 99.67 18.27 1.77 14.15 16.75 8.62 10.76 370.19

322.83 154.3 28.37 2.49 22.31 27.05 13.68 17.18 588.21

218.82 102.27 25.81 1.86 21.22 19.70 14.20 12.00 415.77

209.76 95.66 20.84 1.49 19.57 18.20 13.16 11.37 390.05

136.16 74.08 15.28 1.97 14.47 14.66 11.53 9.78 277.93

130.41 69.81 11.05 1.56 12.41 12.86 9.88 8.53 256.51

76.19 29.15 6.00 1.80 7.39 7.52 4.18 5.24 137.47

2.58 1.05 4.76 0.33

2.68 1.04 4.80 0.29

2.10 1.42 4.66 0.24

2.37 1.38 4.76 0.22

2.10 1.18 3.56 0.26

2.78 1.16 3.91 0.41

– – – –

A.K. Singh et al. / Journal of Asian Earth Sciences 27 (2006) 544–557

A

16

Porphyritic rhyolite Non-porphyritic rhyolite Trachyte Welded tuff

Phonolite

14 12

Tephritephonolite

Trachyte

Na 2 O+K 2 O (wt.%)

Foidite

10

Phonotephrite

Trachydacite

8 Tephrite basalite

Basaltic trachy andesite Trachy basalt

6 4

Rhyolite

Trachy andesite

Andesite

Basaltic andesite

Basalt

Dacite

2

Picro basalt

0

40

45

50

55

60

70

65

75

80

SiO2 (wt.%)

B

7 6

K-trachyte Banakite

K2 O (wt.%)

5 4

High K-dacite

3

High K-rhyolite

High K-andesite

2 1

Rhyolite (Calac-alkaline)

Dacite (Calc-alkaline)

Andesite (Calc-alkaline)

LowK-rhyolite

LowK-dacite

LowK-andesite

0 56

63

70

77

SiO2 (wt.%)

Fig. 2. (A) Total alkali-Silica (TAS) diagram (Le Bas et al., 1986) and (B) Plot of K2O vs SiO2 diagram (Peccerillo and Taylor, 1976) showing geochemical classification of the Kundal acid volcanics.

corundum and anorthite in the normative calculations, and AI!1. The peraluminous nature of porphyritic rhyolite is due to depletion in CaO and K2O. The acid volcanic rocks in the study area are characterized by high SiO2, Fe2O3(t)/MgO, K2O/Na2O, Zr, Nb, Y, REEs (except Eu) and low contents of MgO, CaO, Al2O3, Fe2O3 (t), Cr, Ni, Sr and Eu with a dominance of K2O over CaO. The Total alkali-silica (TAS) diagram (Fig. 2A) of Le Bas et al. (1986) for Kundal acid volcanic rocks confirm the classifications as rhyolites and trachytes. These acid volcanic rocks are potassic, with Na2O/K2O ratios!1. Based on the SiO2 vs K2O diagram of Peccerillo and Taylor (1976) and modified by Ewart (1979), the majority of rhyolite samples with!70 wt.% SiO2 plot in the high K-rhyolite field whereas trachyte samples fall in the K-trachyte field (Fig. 2B). In the K2O vs SiO2 plot (Le Maitre, 1989), these acid volcanic rocks also fall in the high-K series field. In the Harker variation diagram (Fig. 3), acid volcanics show a decrease in Al2O3, P2O5,

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TiO2, and Na2OCK2O with increasing SiO2, indicating fractionational crystallization of albite-oligoclase, K-feldspar and a small amount of accessory minerals (Li et al., 2002). Compared to trachyte, rhyolites are high in Cr, Ni, Sr, Rb and low in Nb and Y (Fig. 3). The high concentration of Zr in the melt, especially in peralkaline rhyolite, is common. Stoney (1981) documented cases where extended feldspar fractionation played a vital role in producing peralkaline rhyolite. The effect of feldspar fractionation on the evolution of the Kundal acid volcanic rocks are shown in the Sr vs Ba plot (Fig. 4A), Rb vs Sr plot (Fig. 4B) and Ba vs Eu/Eu* plot (Fig. 4C). The linear trends are largely controlled by alkali feldspar fractionation. A plot of SiO2 vs Eu/Eu* shows a negative trend and a similar negative correlation can be seen on the Zr vs Eu/Eu* plot. These correlations indicate feldspar fractionation in the more evolved compositions. The acid volcanic rocks are characterized by higher total REE contents (256–588 ppm), less fractionated patterns ((Ce/Yb)NZ3.56–5.11) and have a pronounced negative Eu-anomaly (Eu/Eu*Z0.18–0.41) with subparallel patterns (normalized value after Masuda et al., 1973) (Fig. 5A and B). The rhyolite and trachyte show similar REE contents and REE patterns, which confirm their comagmatic nature and are comparable with typical A-type acid magmatism (Cullers et al., 1981; Collins et al., 1982; Menuge et al., 2002). They show moderate LREE enrichment and flat HREE patterns, with the size of the Eu anomaly tending to be greater where the concentrations of the other REE are higher. Trachytes have less pronounced Eu negative anomalies and low ratios of (Ce/Yb)N (3.56–3.91) whereas rhyolites show strongly depleted Eu with higher ratios of (Ce/Yb)N (4.55–5.11) which indicate greater fractionation compared to rhyolite. However, both types of acid volcanic rocks show Eu/Eu* ratios !1, which may be due to feldspar fractionation or residual feldspar in the source region. Feldspar crystallization at high temperature (O600C) is also supported by the presence of bipyramidal quartz and sanidine as phenocrysts (Tuttle and Bowen, 1958). Feldspar fractionation plays an important role in the evolution of A-type magmatism (Stoney, 1981). The higher enrichment of HFS elements (Zr, Nb) is diagnostic of an alkaline magma (Salvi and Jones, 1990).

5. Petrogenesis Huang and Wyllie (1986); Montanini et al. (1994) explained the importance of crustal melting in the evolution of acid volcanic rocks. Partial melting of pre-existing crustal rocks produces A-type acidic magmas (Eby, 1992). The crustal origin for rhyolites by partial melting was suggested by Cullers et al. (1993); Black et al. (1997); Sengupta et al. (1998); Mingram et al. (2000). A similar mechanism for the evolution of acid volcanic rocks of MIS has been reported by Eby and Kochhar (1990); Maheshwari et al. (1996);

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500 400

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Zr (ppm)

TiO2 (wt.%)

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0.15

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0.10 0.05 2.2

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Rb (ppm)

80

1.6 1.4 1.2

2200 2000 1800

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0.6 11.5

1200

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Ni (ppm)

CaO (wt.%)

200

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Na 2O+K 2 O (wt.%)

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8.0 7.5

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SiO2 (w.t.%)

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SiO2 (w.t.%)

Fig. 3. Variation diagrams of some major and trace elements for Kundal acid volcanic rocks. Symbols are the same as in Fig. 2 (A).

Bhushan and Chittora (1999); Bhushan (2000) and Vallinayagam (2004). The Kundal acid volcanics are low in CaO and high in SiO2, Na2OCK2O, Fe/Mg, Zr, Nb, Y and REE (except Eu) indicating ‘A-type’, anorogenic magmatism (Collins et al., 1982; Pearce et al., 1984; Whalen et al., 1996). The

primodial mantle-normalized trace element spider diagram (normalized after Sun and McDonough, 1989) for the Kundal acid volcanic rocks are shown in Fig. 5C. The relative enrichment of Ce, Zr and Y is indicative of their compatibility with a crustal component in the melt. Negative Ti, P, Sr and Ba anomalies indicate retention

A.K. Singh et al. / Journal of Asian Earth Sciences 27 (2006) 544–557

Fig. 4. (A) Sr vs Ba plot (B) Rb vs Sr plot and (C) Ba vs Eu/Eu* plot for Kundal acid volcanic rocks. AF and PF are Rayleigh fractionation trends calculated for removal of alkali feldspar and plagioclase feldspar, respectively. Mineral fractionation vectors in (A) and (B) are according to Pearce and Norry (1979). Symbols are the same as in Fig. 2 (A).

of plagioclase and accessory minerals in the source during partial melting. A pronounced negative Ba anomaly is characteristic of rift-related rocks. The spidergram patterns for Kundal acid volcanic rocks compare well with A-type granites (Collins et al., 1982) and are also comparable with the Oslo anorogenic granite (Pearce et al., 1984) and A-type rhyolite (Menuge et al., 2002) (Fig. 5D). The acid volcanic

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rocks are strongly enriched in highly incompatible trace elements. Strong depletions at Sr, P, Ti and Eu suggest that extensive fractional crystallization of plagioclase, apatite and Fe-Ti oxides occurred during evolution of the magma. The Ba and Sr depletions are a consequence of low plagioclase fractionation characteristic of A-type magmas (Pearce et al., 1984). Variations in most of these elements among the rhyolites are likely due mainly to crystal fractionation. The relative enrichment of Ce, Zr and Y is indicative of their compatibility with the crustal component in the melt. The negative anomalies of Ba and Sr along with the anomalous Zr enrichment are characteristic of riftrelated rocks. The enrichment of Rb also reflects alkali feldspar fractionation. The REE patterns of rhyolite and trachyte are enriched in LREE and also significantly enriched in incompatible elements. This suggests that the rhyolite and trachyte represent different degrees of partial melt from sources with similar characteristics. Rhyolite samples enriched in LREE and other incompatible elements represent lower degrees of partial melting. The Kundal acid volcanic rocks have low Mg #, MgO, Fe2O3(t), CaO and Sr and high SiO2, K2O, Na2O, Ba and Y that suggests a crustal origin. Trachyte and rhyolite have comparable concentrations of major, trace and REE which suggest that both types of acid volcanic rocks have common magmatic sources and petrogenetic processes. The restricted ranges of bulk chemical compositions, Larsen Index values [(1/3SiCK)-(CaCMg)] and A/CKN ratios [molar Al2O3/molar (CaOCNa2OCK2O)] suggest that the parental magmas evolved by partial melting and were not subjected to any noticeable magmatic differentiation. The low Sr is due to its compatibility with plagioclase and the high Zr is also due to the original alkalinity of the parent magma or source rock. The perceptible negative Eu anomaly is either due to partitioning into feldspar during fractionation, which is an important process in developing peralkalinity, or the presence of residual feldspar in the source. The enrichment of MREE with corresponding Eu depletion may be related to crystallization of earlier-formed perthite and late crystallizing alkali amphibole from the low temperature liquid enriched in volatiles (Bowden and Whitely, 1974). The flat HREE pattern suggests their incompatibility during later stages of crystal fractionation. The REE patterns are subparallel to one another indicating fractionation of REE in crustal proportions over a significant range of compositions. It is possible that the felsic volcanic rocks may have been derived by low partial melting of a felsic source. For smaller extents of partial melting, feldspar is the dominant mineral in the residue. Because of the high mineral-melt Kd for Eu and Sr (O1), the partial melts derived from a crustal source are often depleted in Eu and Sr relative to other REE. Basic rocks of the MIS have been considered to represent the parent magma. Using the batch melting equation of Schilling (1966) for petrogenetic modelling: CLZCO/D(1-F)CF (where CL and CO are the concentration of element in the melt and original source,

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B

1000 PVB20 NKB26 NKB32 TKB09 TKB13

100

1000 PKB01 PKB36 PKB42 PKB12

Sample/Chondrite

Sample/Chondrite

A

100

10 10

Ce

Nd

Sm

Eu

Gd

Dy

Er

Ce

Yb

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D

1000

100

10

1

NKB26 PVB20

Sm

Eu

Gd

Dy

Er

Yb

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Sample/Primitive mantle

C

Nd

1000

100

10

1 Kundal acid volcanic A-type rhyolite Anorogenic granite

TKB09

0.1

0.1

Rb Ba K Nb Ce Sr Nd P Zr Sm Ti Y Y b

Elements

Sr K Rb Ba Nb Ce P Zr

Sm Ti Y Y b

Elements

Fig. 5. (A) and (B) Chondrite normalized (Masuda et al., 1973) rare earth element patterns for the Kundal acid volcanic rocks. (C) Primitive-mantle normalized (Sun and McDonough, 1989) trace element spider diagram for acid volcanics. (D) The Kundal acid volcanic is compared with the Oslo anorogenic granite (Pearce et al., 1984) and A-type rhyolite from Missouri (Menuge et al., 2002).

respectively, and F is the melt proportion and D is the bulk distribution coefficient of the element for the residue) and the residual mineralogy for the chosen pressure and temperature conditions, the REE concentration of the source was calculated. The REE abundances and pattern of the calculated melt do not match those of the Kundal acid volcanic rocks, thus ruling out the possibility of the origin of these acid volcanics by melting of basaltic rocks. The melasyenite rock (sample no. D125i) of the Prakasam Alkaline Province, India (Sharma and Rathnakar, 2000) has been considered as a potential source rock. The source is chiefly composed of alkali feldspar, plagioclase feldspar, amphibole, quartz and biotite. It shows a moderate LREE enrichment, a slightly concave upward middle REE pattern, and negative Eu anomaly. The REE pattern of a typical crustal-derived melt shows an enriched HREE pattern because feldspar has lower Kd’s for HREE. Fig. 6A shows the REE pattern of the melt derived from partial melting of a typical granodioritic crust (after Hanson, 1980). It shows an enriched LREE pattern and negative Eu anomaly. Using the batch melting equation at 8 kbar pressure and 10000C temperature, with orthoclase 77%, plagioclase 18%, opx 2.5%, cpx 2%, sphene 0.3% and garnet 0.2% as the residual mineralogy, the REE pattern for the source was

calculated at 5% and 20% melting. The bulk distribution coefficient is calculated based on the reported Kd’s for REE for different minerals in the basic melt from Hanson (1980); Green and Pearson (1985). The chondrite normalized pattern of the melasyenite source and calculated patterns for partial melts derived from the source are shown in Fig. 6B. M1 and M2 represent REE patterns of magmas derived by 5% and 20% partial melting of a melasyenite source, respectively. The similarity of REE patterns of the Kundal rhyolite samples to the calculated REE pattern for 5% partial melting suggests that sources for the rhyolite rocks had similar REE abundances to that of the melasyenite rock (sample no. D125i) from Prakasam Alkaline Province, India. On the other hand partial melting at 20% assuming similar residual mineralogy, yields a melt with REE patterns similar to the Kundal trachyte rocks. Hence, moderate LREE enriched melt similar to melasyenite or any preexisting intermediate to felsic crust is the most likely source for the Kundal acid volcanic rocks. Thus we infer that the Kundal rhyolite composition can be obtained at an even lower extent (5%) of melting whereas the Kundal trachyte composition was obtained at a higher degree (20%) of melting from the same parent source. Furthermore, if the magmatic activity was related to a mantle plume, then fluids moving upwards from this plume

A.K. Singh et al. / Journal of Asian Earth Sciences 27 (2006) 544–557

A Rock/Chondrite

100 Partialmelt

10

Parent

Ce

Nd

Sm Eu Gd

Er

Dy

Yb

Rare Earth Elements

B

1000 (B)

M15%

Rock/Chondrite

REEpattern of rhyolite

100

M220% REE patternof trachyte

10

Source

1 Ce

Nd

Sm Eu Gd

Dy

Er

Yb

Rare Earth Elements

Fig. 6. (A) Calculated REE pattern of the melt derived from partial melting of typical granodioritic crust (after Hanson, 1980). (B) Chondrite normalized plot for a Melasyenite source and calculated patterns for partial melts derived from the source. M1 and M2 represent REE patterns of magmas derived by 5% and 20% partial melting of the source, leaving a residue consisting of 77% orthoclase, 18% plagioclase, 2.5% opx, 2% cpx, 0.3% sphene and 0.2% garnet. Note that the 5% partial melt pattern broadly coincides with the REE patterns of rhyolite, whereas the 20% partial melt pattern broadly coincides with the REE patterns of trachyte.

could metasomatise lower crustal material, thus providing a chemically anomalous region of enriched HFS and LIL elements in which the melt is generated. It is possible that large volumes of basic material would not be erupted, but rather stored at the base of the crust or in lower crustal magma chambers. These magmas would then provide the heat source for extensive crustal melting of lower crustal material. A plausible heat source for melting of the lower underplated basaltic/komatiitic crust could be a mantle plume, which is capable of transmitting large amounts of heat to the overlying crust and thereby inducing crustal melting (Taylor et al., 1984). Vallinayagam and Kochhar (1998) related the Malani magmatism to hot-spot activity. The development of a hot-spot begins with updoming of the continental crust and helps in the propagation of continental rifts. The high heat flow is created by injection of mantle derived basic rocks into the crust, which results in partial melting and generation of silicic components. Basaltic magmas are continually fluxed into the crustal system and intersect the shallow, stalled silicic magma bodies, supplying heat and volatiles to remobilize them. When a fair amount of felsic magma is accumulated, it ascends into the upper crust and helps

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propagate the extensional stress field. A relatively large volume of A-type felsic magmas are therefore generated due to partial melting of crustal rocks at elevated temperature under the affected area. Leat et al. (1986) considered subalkaline and peralkaline rhyolites to have evolved in the same magma chamber through fractional crystallization of basaltic magma and crustal melting. Fractional crystallization of a basaltic magma, if considered as the mechanism and source for generation of felsic derivatives, will require a huge volume of basic rocks nearby, since the felsic differentiate would only account for a small fraction of the original basic reservoir (Hyndman, 1985). Bevins et al. (1991) also states that, irrespective of tectonic setting, the generation of felsic magma in such associations is debatable since the volume of silicic magma generally exceeds that expected to be produced by differentiation of a basaltic source. However, the aerial distribution of basic and acid rocks in the Kundal area yields a ratio of approximately 1:85. As the amount of acid magma dominates over basic magma, it is difficult to explain their generation from a basic parental magma source. An absence of any large volume of basaltic melt therefore rules out fractional crystallization of basic magma as a process for the formation of peraluminous and peralkaline rhyolites in the present study area. Furthermore, the difference in Zr/Y and Zr/Nb values do not support the derivation of an acidic melt from basic magmas by fractional crystallization.

6. Tectonic implications Bickford and Anderson (1993) have proposed two contrasting tectonic environments for the Neoproterozoic granite-rhyolite provinces, an anorogenic, rift-related environment and an active continental margin (Lidaiak, 1996; Rivers and Corrigen, 2000; Karlstrom et al., 2001). An anorogenic, rift-related environment is more compatible with the apparent lack of compressive deformation or moderate to high-grade metamorphism throughout the granite-rhyolite provinces (Van Schmus and Bickford, 1981). The acid volcanic rocks surrounded by basalt and gabbro in adjoining areas of Siwana and Jalor, also further substantiate the pattern of an aborted rift at about 750 Ma. The high apparent magmatic temperatures calculated are typical of A-type felsic magmas worldwide (Menuge et al., 2002). On the tectonic discrimination diagrams of SiO2 vs- Rb and SiO2 vs Nb (Fig. 7A) YCNb vs Rb plot (Fig. 7B), Y vs Nb plot (Fig. 7C) and R1-R2 (Fig. 7D) show that the Kundal acid volcanics plot as within plate or A-type rocks. These features suggest an anorogenic setting for their emplacement and indicate of Malani magmatism as riftrelated (Eby, 1990). The A-type chemistry and within-plate environment of Malani magmatism, as characterized by a

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Fig. 7. Trace element discrimination diagrams showing the anorogenic nature of Kundal acid volcanic rocks. (A) SiO2 vs Rb and SiO2 vs Nb, (B) Rb vs YCNb and (C) Nb vs Y diagrams (after Pearce et al., 1984) (D) R1-R2 diagram (after Batchelor and Bowden, 1985). Symbols are the same as in Fig. 2 (A).

volcanic-plutonic ring complex, was possibly related to hot spot activity. This plume activity may have been associated with Aravalli-Delhi mobile belts about 950–750 Ma ago and coeval with the rhyolites of central Iran, NubianArabian shield, Somalia and Seychelles (Vallinayagam and Kochhar, 1998; Kochhar, 2000; Kochhar, 2004).

7. Conclusions The Malani Igneous Suite (MIS) is characterized by a bimodal suite of A-type granite with a cogenetic carapace of acid volcanics (rhyolite, welded tuff, trachyte, explosion breccia and perlite). These volcanic rocks display distinctive ring structures and radial dykes with minor amounts of basalt, gabbro and dolerite dykes, suggesting an interrelationship between volcanic activity and plutonism. The preponderance of acid volcanic rocks over intermediate

and basic rocks is a distinctive feature of MIS. The occurrence of xenoliths of basic rocks within the acid volcanics indicates a younger age for the latter. An isochron age for Malani acid rocks of 725G7 Ma marks a major PanAfrican tectono-magmatic event. Acid volcanic rocks of the Kundal area are high in SiO2, Na2O, K2O, Zr, Nb, Y and REEs (except Eu) but low in MgO, Fe2O3 (t), CaO, Cr, Ni, Sr, and Eu, indicating that they are A-type and anorogenic. These features support a tensional tectonic environment for generation of MIS. The rhyolite occurs in close association with trachyte, which strongly suggests a genetic relationship between these rock types. The geochemistry shows their mutual comparability which further strengthens the argument for a genetic relationship between them. Feldspar fractionation played a vital role in the evolution of these magmas. The present contribution also suggests that partial melting of a melasyenite source generated the acid magmas of the Kundal area. It is suggested that the rhyolite and

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trachyte represent different degrees of partial melt at 5% and 20% respectively, from sources with similar characteristics. The high heat flow or hot-spot was responsible for partial melting and generation of felsic magma. Thus, the acid volcanic rocks of the present study area are valuable indicators of the composition and evolution of crustal source rock in the Neoproterozoic Malani Igneous Suite of western Peninsular India. Work by Torsvik et al. (2001); Ashwal et al. (2002) on the Malani rocks and related rocks in the Sychelles and Madagascar shows that these rocks represent part of an Andean arc. However, their observation is not incompatible with our present interpretation of the Kundal rocks as rift related because the kind of rift in which the Kundal rocks occur is likely to have been an arc-crestal rift of the kind familiar in the Andes of Peru and Ecuador today (Dalmayrac and Molnar, 1981). Sylvester (1989) proposed that the volcanic-arc sources can persist beneath the old craton long after subduction had ceased and possibly be reactivated during post-orogenic magmatism. This reactivation was caused by a deep crustal fault (Martin et al., 1994).

Acknowledgements The authors are grateful to Dr. B.R. Arora, Director, Wadia Institute of Himalayan Geology (WIHG), Dehradun for permission and encouragement to publish present paper. We are also thankful to Prof. V. Rajamani, SES, Jawaharlal Nehru University, New Delhi for providing laboratory facility for chemical analysis and fruitful discussion and Prof. N. Kochhar, Department of Geology, Punjab University, Chandigarh for valuable suggestions. Dr. P.P. Khanna, WIHG, Dehradun has been duly acknowledged for analyses of trace elements. Comments and useful suggestions made by an anonymous referee have greatly helped in improving the quality of the paper. We appreciate the critical reviews and suggestions of Prof. Kevin Burke (University of Houston).

References Ashwal, L.D., Demaiffe, D., Torsvik, T.H., 2002. Petrogenesis of Neoproterozoic granitoids and related rocks from the Seychelles: the case for an Andeatype arc origin. Journal of Petrology 43, 45–83. Batchelor, R.A., Bowden, P., 1985. Petrogenetic interpretation of granitoid rocks series. Chemical Geology 48, 43–55. Bevins, R.E., Lees, G.J., Roach, R.A., 1991. Ordovician bimodal volcanism in SW Wales: geochemical evidence for petrogenesis of silicic rocks. Journal of Geological Society of London 148 (4), 719–730. Bhushan, S.K., 1985. Malani volcanism in western Rajasthan, India. Journal of Earth Science 12, 58–71. Bhushan, S.K., 2000. Malani rhyolites: a review. Gondwana Research 3 (1), 65–77. Bhushan, S.K., Chittora, V.K., 1999. Late Proterozoic bimodal volcanic assemblage of Siwana subsidence structure, Western Rajasthan, India. Journal of Geological Society of India 53, 433–452.

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Bickford, M.E, Anderson, J.L., 1993. Middle Proterozoic magmatism. In: Reed Jr., J.C., Bickford, .M.E., Houston, R.S., Link, P.K., Pankin, D.W., Sims, P.K., Van Schmus, W.R. (Eds.), Geology of North America, C-2. Conterminous US Geological Society of America, Precambrian, pp. 281–292. Black, S., Macdonald, R., Kelly, M.R., 1997. Crustal origin for peralkaline rhyolite from Kenya: evidence from U-series disequilibria and Thisotope. Journal of Petrology 38 (2), 277–297. Blanford, W.T., 1877. Geological notes on the great Indian desert between Sind and Rajasthan. Records of Geological Survey of India 10 (1), 10–21. Bowden, P., Whitely, J.E., 1974. Rare-earth patterns in peralkaline and associated granites. Lithos, 15–21. 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 (2), 189–200. Cullers, R.L., Koch, R.J., Bickford, M.E., 1981. Chemical evolution of magmas in the Proterozoic terrane of the St Francois Mountains, southeastern Missouri, 2: trace element data. Journal of Geophysical Research 86, 10388–10401. Cullers, R.L., Stone, J., Anderson, J.L., Sassarini, N., Bickford, M.E., 1993. Petrogenesis of Mesoproterozoic Oak Creek and West McCoy Gulch plutons, Colorado: an example of cumulate unmixing of a midcrustal, two-mica granite of anorogenic affinity. Precambrian Research 62, 139–169. Dalmayrac, B., Molnar, P., 1981. Parallel thrust and normal faulting in Peru and constraints on the state of stress. Earth and Planetary Sciences Letters 55, 473–481. Dhar, S., Frei, R., Kramers, J.D., Nagler, T.F., Kochhar Sr.., N., 1996. Sr, Pb and Nd isotope studies and their bearing on the petrogenesis of the Jalor and Siwana complexes. Journal of Geological Society of India 48 (2), 151–160. Donaldson, C.H., Henderson, C.M.B., 1988. A new interpretation of round embayments in quartz crystals. Mineral Magazine 52, 27–33. Eby, G.N., 1990. The A-type granitoids: a review of their occurrence and chemical characteristics and speculations on their petrogenesis. Lithos 26, 115–134. Eby, G.N., 1992. Chemical subdivision of the A-type granitoids: petrogenetic and tectonic implications. Geology 20, 641–644. Eby, G.N., Kochhar, N., 1990. Geochemistry and petrogenesis of the Malani Igneous Suite, North Peninsular India. Journal of Geological Society of India 36, 109–130. Ewart, A., 1979. A Review of the Mineralogy and Chemistry of Tertiary– Recent Dacitic, Latitic, Rhyolitic and Related Sialic Volcanic Rocks. Elsevier, Amsterdam, pp.13-121. Forster, H., 1987. Ignimbritic cauldrons, alkali granites and mineral deposits in fault block mountains. Geoloical Rundsches 76, 373–388. Giret, A., Bonin, B., Leger, J., 1980. Amphibole compositional trends in oversaturated and undersaturated alkaline plutonic ring complexes. Canadian Mineralogist 18, 481–495. Giritharan, T.S., Rajamani, V., 1998. Geochemistry of the metavolcanics of the Hutti–Maski schist belt, South Indian: implications to gold metallogeny in the Eastern Dharwar craton. Journal of Geological Society of India 51, 583–594. Green, T.H., Pearson, N.J., 1985. Rare earth partitioning between clinopyroxene and silicate liquid at moderate to high pressure. Contributions to Mineralogy and Petrology 91, 24–36. Gupta, R.K., 1983. Embayed quartz crystals in Shyok volcanics, Ladakh. Contemporary Geoscientific Researches in Himalaya 2, 65–68. Gupta, L.N., Ghildiyal, H., Chawla, H.S., 1994. Petrochemistry and tectonic environment of granites and porphyries of Amritpur–Ramgarh area, Lesser Himalaya, Uttra Pradesh. Journal of Himalayan Geology 5 (2), 103–116. Hanson, G.N., 1980. Rare earth elements in petrogenetic studies of igneous systems. Annual Review of Earth Planetary Science Letters 8, 371–406.

556

A.K. Singh et al. / Journal of Asian Earth Sciences 27 (2006) 544–557

Huang, W.L., Wyllie, P.J., 1986. Phase relationships of gabbro–tonalite– granite–water at 15 kb with applications to differentiation and anatexis. American Mineralogist 71, 301–306. Hyndman, D.W., 1985. Petrology of igneous and Metamorphic Rocks. McGraw–Hill Book, New York, p. 766. Karlstrom, K.E., Aahall, K.I., Harlan, S.S., Williams, M.L., McLelland, J., Creissman, J.W., 2001. Long-lived (1.8–1.0 Ga) convergent orogen in southern Lourentia, its extentions to Australia and Baltica, and implications for refining Rodina. Precambrian Research 111, 5–30. Kochhar, N., 1984. Malani igneous suite: hot-spot magmatism and cratonization of the northern part of the Indian shield. Journal Geological Society of India 25 (3), 155–161. Kochhar, N., 1996. A-type Malani magmatism. Northwestern peninsular India. In: Deb, M., Banerjee, D.M. (Eds.), Procedure in National Seminar on Mineralisation in the Western Indian Craton. University of Delhi, New Delhi, pp. 10–14. Kochhar, .N., 2000. Attributs and significance of the A-type malani magmatism, north western Peninsular India. In: Deb, M. (Ed.), Crustal Evolution and Metallogeny in the Northwestern Indian Shield. Norosa Publisher, New Delhi, pp. 158–188. Kochhar, N., 2001. Anorogenic magmatism, mantle plume and assembly of the late proterozoic malani supercontinent, NW Indian shield. International Symposium on the Assembly and breakup of Rodinia and Gondwana and Growth of Asia. Osaka City University, Osaka, Japan. Osaka City University, Osaka, Japan pp. 23–27. Kochhar, N., 2004. Geological evolution of the Trans-Aravalli (TAB) of the NW Indian shield: constraints from the malani igneous suite (MIS) and its seychelles connection during late proterozoic, Geological Survey of India, pp.247–264 [special publication No. 84]. Kroner, A., Reischmann, T., Todt, Y., Zimmer, M., Stern, R.J., Hussein, I., Mansour, M., Eyal, M., Eyal, Y., Sassi, P., 1989. Timing mechanism and qeochemical pattern of are accretion in the Arabian–Nubian shield and its extension into Israel and Somalia extended. Abstract of 28th IGC, Washington DC, USA, vol. 2, p. 2/231. Kroner, A., Eyal, M., Eyal, Y., 1990. Early Pan-African evolution of the basement around Elat, Irael and the Sinai peninsula revealed by single zircon evaporation dating and implications for crustal accretion rate. Geology 118, 545–548. La Touche, T.H.D., 1902. Geology of western Rajputana. Memoir of Geological Survey of India 35 (1), 1–116. Le Bas, M.J., Le Maitre, R.W., Streckeisen, A., Zanettin, B., 1986. A chemical classification of volcano rocks based on the total alkali–silica diagram. Journal of Petrology 27, 745–750. Le Maitre, R.W., 1989. A Classification of Igneous Rocks and Glossary of Terms. Blackwell, Oxford p. 193. Leat, P.T., Jackson, S.E., Thorpe, R.S., Stillman, C.J., 1986. Geochemistry of bimodal basalt-subalkaline/peralkaline-rhyolite provinces within the southern British Caledonides. Journal of Geological Society of London 143, 259–276. Li, X.H., Li, Z.X., Zhou, H., Liu, Y., Kinny, P.D., 2002. U–Pb zircon geochronology, geochemistry and Nd isotopic study of Neoproterozoic bimodal volcanic rocks in the Kangdian Rift of South China: implications for the initial rifting of Rodinia. Precambrian Research 113, 135–154. Lidaiak, E.G., 1996. Geochemistry of subsurface Proterozoic rocks in the eastern Midcontinent of the United States: further evidence for a within-plate tectonic setting. In: Van der Pluijm, B.A., Catacosinos, P.A. (Eds.), Basement and Basins of Easter North American Geological Society Special paper, vol. 308, pp. 45–66. Maheshwari, A., Coltori, M., Sial, A.N., Mariano, G., 1996. Crustal influences in the petrogenesis of the Malani rhyolites, south-western Rajasthan: combined trace element and oxygen isotope constraints. Journal Geological Society of India 47 (5), 611–619. Maniar, P.D., Piccoli, P.M., 1989. Tectonic discrimination of granitoids. Geological Society of American Bulletin 101, 635–643.

Martin, H., Bonin, B., Capdevila, R., Jahn, B.M., Lameyre, J., Wang, Y., 1994. The Kuiqi peralkaline granites complex (SE China): petrology and geochemistry. Journal of Petrology 35, 983–1015. Masuda, A., Nakamura, N., Tanaka, T., 1973. Fine structures of mutally normalized rare earth patterns of chondrites. Geochimicalet Cosmochimical Acta 37, 239–248. Menuge, J.F., Brewer, T.S., Seeger, C.M., 2002. Petrogenesis of metaluminous A-type rhyolites from the St Francois mountains, missouri and the mesoproterozoic evolution of the southern laurentian margin. Precambrian Research 113, 269–291. Mingram, B., Trumbull, R.B., Littman, S., Gerstenberger, H., 2000. A petrogenetic study of anorogenic felsic magmatism in the cretaceous paresis ring complex, Namibia: evidence for mixing crust and mantlederived components. Lithos 54, 1–22. Montanini, A., Babieri, M., Castorina, F., 1994. The role of fractional crystallization, crustal melting and magma mixing in the petrogenesis of rhyolite and mafic inclusion bearing dacites from the Monte Arci volcanic complex (Sardinia, Itlay). Journal of Volcanology and Geothermal Research 61, 95–120. Murthy, M.V.N., Siddqui, H.N., Venkataraman, P.K., 1961. Riebeckiteaegirine rhyolite and granites in the Malani Suite of igneous rocks, western Rajasthan. Indian Minerals 15 (4), 427–428. Pareek, H.S., 1981. Petrochemistry and petrogenesis of the Malani Igneous Suite, India. Geological Society of American Bulletin 92, 206–273. Pearce, J.A., Norry, M.J., 1979. Petrogenetic implications of Ti, Zr, Y and Nb variations in volcanic rocks. Contributions to Mineralogy and Petrology 69, 38–47. Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace elements discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology 25, 956–983. Peccerillo, A., Taylor, S.R., 1976. Geochemistry of some calc-alkaline volcanic rocks from the Kastamonu area, northern Turkey. Contributions to Mineralogy and Petrology 58, 63–81. Rivers, T., Corrigen, D., 2000. Convergent margin on southeastern Laurentia during the Mesoproterozoic: tectonic implications. Canadian Journal of Earth Sciences 37, 359–383. Salvi, S., Jones, A.E.W., 1990. The role of hydrothermal processes in granite hosted Zr, Y, REE deposit at strange Lake, Quebec, Labrador. Evidences from fluid inclusions. Geochimical et Cosmochimical Acta 54 (9), 2403–2418. Schilling, J.G., 1966. Rare earth fractionation in Hawaiian volcanic rocks. Unpublished PhD Thesis, Massachusetts Institute of Technology, Cambridge MA, USA. Sengupta, S., Ghosh, M., Gangopadhyay, P., Chattopadhyay, A., 1998. Petrology of post-Archaean magmatic rocks in the eastern Indian craton. Journal Geological Society of India 51, 31–42. Shand, S.J., 1927. The Eruptive rocks. Wiley, New York, p. 488. Shapiro, L., Brannock, W.W., 1962. Rapid chemical analysis of silicate, carbonate and phosphate rocks. US Geological Survey Bulletin 114A, 56. Sharma, V.N., Rathnakar, J., 2000. Petrology of the Gabbro–Diorite–Syenite– granite complex of Chanduluru, Prakasam alkaline province, Andra Pradesh, India. Journal of Geological Society of India 55, 553–572. Singh, A.K., Vallinayagam, G., 2002. Geochemistry and petrogenesis of granites in Kundal area, Malani Igneous Suite, Western Rajasthan. Journal of Geological Society of India 60, 183–192. Singh, A.K., Vallinayagam, G., 2003. Petrochemical characteristics of acid volcanics from Kundal area, barmer district, Western Rajasthan. Journal of Mineralogical Society of India 37 (1), 1–12. Sohoo, J., Balakrishnan, S., 1994. Geochemistry and petrogenesis of dolerite dykes in and around Kolar Schist Belt, South India. Journal of Geological Society of India 43, 511–528. Srivastava, R.K., Maheshwari, A., Rajani, U., 1989. Geochemistry of felsic volcanics from Gurupratap Singh and Diri, Pali districts, Rajasthan. Journal of Geological Society of India 34, 617–631. Stoney, M., 1981. Trachytic pyroclastic from Agua de Volcano, Sao Miquel Azores: evolution of a magma body over 4000 years. Contributions to Mineralogy and Petrology 12, 423–432.

A.K. Singh et al. / Journal of Asian Earth Sciences 27 (2006) 544–557 Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematic of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in the Ocean Basins; Geological Society Special Publication, vol. 42, pp. 313–345. Sylvester, P.J., 1989. Post collisonal alkali granites. Journal of Geology 97, 261–280. Taylor, R.P., Strong, D.F., Frayer, B.J., 1984. Volatile control of contrasting trace element distributions in peralkaline granite and volcanic rocks. Contributions to Mineralogy and Petrology 77, 267–271. Thornton, C.P., Tuttle, O.F., 1960. Chemistry of igneous rocks. Part. I. Differentiation Index. American Journal of Science 258, 664–684. Torsvik, T.H., Carter, L.M., Ashwal, L.D., Bhushan, S.K., Pandit, M.K., Jamtveit, B., 2001. Rodinia refined or obscured: palaeomagnetism of the Malani Igneous Suite (NW India). Precambrian Research 108, 319–333. Tuttle, O.F., Bowen, N.L., 1958. Origin of granite in the light of experimental studies in the system NaAl Si22O8–SiO2–H2O. Memoir Geological Society of America 74, 153.

557

Vallinayagam, G., 2004. Peralkaline–Peraluminous A-type rhyolites, Siwana ring complex, Northwestern India: petrogenetic modeling and tectonic implication. Journal of Geological Society of India 64, 336–344. Vallinayagam, G., Kochhar, N., 1998. Geochemical characterization and petrogenesis of A-type granites and the associated acid volcanics of the Siwana ring complex. Northern Peninsular, India. In: Paliwal, B.S. (Ed.), The Indian Precambrian. Scientific Publishers, Jodhpur, pp. 460–481. Van Schmus, W.R., Bickford, M.E., 1981. Proterozoic chronology and evolution of the Midcontinental region, North America. In: Kroner, A. (Ed.), Precambrian Plate Tectonics. Elsevier, New York, pp. 261–296. Whalen, J.B., Jenner, G.A., Long Staffe, F.J., Robert, E., Goriepy, C., 1996. Geochemical and isotopic (O, Nd, Pb and Sr), constraints on ‘A’ type granite petrogenesis based on the topsails igneous suite, New Land applachians. Journal of Petrology 37, 1463–1489. Yoshida, M., Rajesh, H.M., Santosh, M., 1999. Juxtaposition of India and Madagascar: a perspective. Gondwana Research 2, 449–467.