Upper Jurassic radiolarians from the Naga Ophiolite, Nagaland, northeast India

Gondwana Research 20 (2011) 638–644

Contents lists available at ScienceDirect

Gondwana Research j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / g r

Upper Jurassic radiolarians from the Naga Ophiolite, Nagaland, northeast India Alan T. Baxter a, Jonathan C. Aitchison a,⁎, Sergey V. Zyabrev b, Jason R. Ali a a b

Tibet Research Group, Department of Earth Sciences, University of Hong Kong, Hong Kong SAR, China Institute for Tectonics and Geophysics, 65 Kim Yu Chen Street, Khabarovsk, 680000 Russia

a r t i c l e

i n f o

Article history: Received 27 August 2010 Received in revised form 2 February 2011 Accepted 2 February 2011 Available online 12 February 2011 Handling Editor: P. Eriksson

a b s t r a c t Radiolarians, extracted from cherts collected from an ophiolitic mélange near Salumi, Nagaland, NE India, have well-preserved tests and can be assigned to the Upper Jurassic (Kimmeridgian–lower Tithonian). These are the first well-preserved and clearly imaged radiolarians reported from the Naga Ophiolite. They are significantly older than fossils previously reported from this mélange, and their ages are similar to those determined radiometrically from associated igneous units. © 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Keywords: Radiolaria Ophiolite Jurassic Suture India

1. Introduction Naga Ophiolite is a highly dismembered and tectonised suite of ophiolitic rocks that crop out in the states of Nagaland and Manipur in north-east India. It lies at the northernmost extent of a larger belt of ophiolite-related material that runs for over 3000 km from NE India, through western Burma, to the Andaman Islands in the Andaman Ocean, that is referred to as the Naga–Andaman suture. This belt of ophiolitic rocks is suggested to be the eastern extension of the Yarlung Tsangpo suture zone (YTSZ) that extends across southern Tibet (Gansser, 1964, 1980) (Fig. 1). The suture zone marks the area where the Indian and Asian continents were once separated by a N4000 km wide Neotethyan Ocean. In southern Tibet, remnants of the Neotethyan Ocean are represented by elements of the Dazhuqu (Girardeau et al., 1985; Xia et al., 2003), Zedong (McDermid et al., 2002; Aitchison et al., 2007) and Bainang terranes (Ziabrev et al., 2004) at Xigaze (Nicolas et al., 1981), Luobusa (Zhou et al., 1996) Saga and Sangsang (Bédard et al., 2009). Further west, associated ophiolitic complexes crop out at Jungbwa (Miller et al., 2003; Chan, 2008), Nidar (Mahéo et al., 2004; Ahmad et al., 2008; Zyabrev et al., 2008) and Spongtang (Reuber et al., 1992; Corfield et al., 2001; Pedersen et al., 2001; Baxter et al., 2010). In Pakistan correlatives can be found in Waziristan, Bela and Muslim Bagh (Moores et al., 1980; Jan et al., 1985; Sarwar, 1992; Beck et al., 1995; Zaigham and Mallick, 2000) (Fig. 1).

⁎ Corresponding author at: Present address: School of Geosciences, The University of Sydney, Sydney, NSW 2006, Australia. Tel.: + 61 2 93513244; fax: + 61 2 93512442. E-mail address: [email protected] (J.C. Aitchison).

This paper describes the first assemblages of well-preserved and clearly imaged radiolarians from the Naga Ophiolite. The ages assigned to these assemblages reveal when deep marine conditions existed in this part of the Neotethyan Ocean. Further understanding of the nature of this ocean are crucial in any tectonic reconstructions related to the breakup of Gondwana and help to reveal the evolution of the Neotethyan Ocean.

2. Naga Ophiolite Outcrop of the Naga Ophiolite trends over 200 km NNW–SSE and is up to 15 km in width (Brunnschweiler, 1966) (Fig. 2). All of the components of an ophiolite pseudostratigraphy, including gabbros, ultramafic rocks, sheeted dikes, pillow basalts and pelagic ocean sediments have been reported (Brunnschweiler, 1966; Ghosh et al., 1984; Venkatramana et al., 1986; Vidyadharan et al., 1986a, b; Sengupta et al., 1989; Acharyya et al., 1991; Acharyya, 2007). Eclogites and blueschists have also been reported from the mélange (Vidyadharan et al., 1986a; Chatterjee and Ghose, 2010). Serpentinite accounts for a major proportion of the ultramafic material in the Naga Ophiolite. Peridotites, including garnet-bearing lherzolite, are reported from horizons associated with serpentinite (Vidyadharan et al., 1986b). Within the central part of the ophiolite belt, dunites, pyroxenites, harzburgites and gabbros are reported and a magnetite horizon near Phokphur is associated with the cumulate rocks (Vidyadharan et al., 1986b). The upper portions of an ophiolite pseudostratigraphy are well represented. Pillow basalts have been observed 1 km north of Salumi. Red cherts are found throughout the Naga Hills and are intercalated with basic to intermediate volcanics or associated with iron-rich sediments.

1342-937X/$ – see front matter © 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.gr.2011.02.001

A.T. Baxter et al. / Gondwana Research 20 (2011) 638–644

639

Fig. 1. Map of the Himalayan region showing the location of Indus, Yarlung–Tsangpo and Naga–Andaman sutures zones. Also highlighted are nine regions from which Tethyan radiolarians have been reported. 1 = Kahi mélange (Beck et al., 1995); 2 = Shergol mélange (Kojima et al., 2001); 3 = Spongtang ophiolite (Baxter et al., 2010); 4 = Nidar ophiolite (Kojima et al., 2001; Zyabrev et al., 2008); 5 = Sangdanlin (Ding et al., 2005); 6 = Xigaze ophiolite (Ziabrev et al., 2003); 7 = Bainang terrane (Ziabrev et al., 2004); 8 = Zedong terrane (Aitchison et al., 2007); 9 = Naga ophiolite (this study). IS = Indus suture, YTSZ = Yarlung Tsangpo suture zone, BNS = Bangong–Nujiang suture, JS = Jinsha suture, STDS = South Tibet detachment surface, MCT = Main Central thrust, MBT = Main Boundary thrust.

On a regional scale, the Naga Ophiolite is bounded to the east by a west-directed thrust that places the mid-Cretaceous limestone of the Nimi Formation together with the Naga Metamorphics over the ophiolite. The Naga Metamorphics (Brunnschweiler, 1966) are an assemblage that includes pelites, psammites, phyllitic schists, quartz– chlorite–mica–schists, marbles, granite gneisses and quartzose gneisses. The Naga Ophiolite itself is thrust westwards over the Disang Formation, a series of deep-marine deposits including cherts, carbonaceous mudstones and fine-grained sandstones. The Disang Formation is thrust over younger Paleogene flysch to the west. It has been assigned to the Upper Eocene using foraminifers extracted from the upper portions of the formation. Evans (1964) assigned a shale horizon from the Disang Formation to the Upper Eocene, based on the presence of Nummulities sp. Recently, this biostratigrpahic work was confirmed by Uddin et al. (2007). In other areas of Nagaland, the Disang Formation grades conformably into the Barail Formation, a series of arenaceous beds containing plant fragments that is assigned to the Oligocene (Johnson and Alam, 1991). The Barail Formation is interpreted as being deposited in shallow marine or deltaic conditions. Nonconformably overlying the Naga Ophiolite is the Phokphur Formation, a series of shallow marine tuffaceous greywackes, conglomerates and shales. Fossils, including leaf imprints and ophiolite-derived material have been reported from this formation. It is assigned to the mid-Eocene, based on the presence of the foraminifera Assilina sp., in the type section (Acharyya, 1986). Sarkar et al. (1996) reported a single radiometric age of 148 ± 4 Ma (whole rock K–Ar) from a basalt flow found juxtaposed with red and green cherts at a locality SE of Waziho village (25° 38′N, 094° 44′E). From further to the south in Burma, Mitchell (1981) reported a similar age (158 ± 20 Ma) for a pegmatite intruding serpentinite in the Chin Hills ophiolite. Based on these data, ocean crust generation and marine sedimentation began by the latest Jurassic with ophiolite emplacement during the Eocene. This is comparable to observations from correlative ophiolites in southern Tibet, NW India and Pakistan.

3. Radiolarian Assemblages Radiolarians are commonly used as key indicators of the timing of deep-marine sedimentation within suture zones and often prove critical to constraining the timing of important events. They have been widely used in investigations of the Neotethyan Ocean and can be found as part of the sedimentary cover of the ocean floor or intercalated with pillow basalts. However, detailed descriptions of radiolarian assemblages are lacking from the Naga Ophiolite as previous work has only reported poorly preserved specimens identifiable to genus level. Here we present the first assemblages of well-preserved radiolarians from the Naga Ophiolite and comment on their age within the tectonic framework of the Neotethyan Ocean. Radiolarian assemblages have been reported from elsewhere along the length of the Neotethyan suture zone and are summarised briefly below.

3.1. NW India Radiolarian-bearing cherts occur in the Karamba Formation, a series of deep-marine shales, radiolarites, sandstones and carbonates. This sequence is part of the Zanskar passive margin sediments (Danelian and Robertson, 1997). Lower and Upper Jurassic, midAlbian to Cenomanian and Santonian radiolarian assemblages are reported (Fig. 3).

3.2. Spongtang Ophiolite Two newly identified assemblages of radiolarians have been reported from chert samples collected from the Spong Arc (Baxter et al., 2010). They are assigned to the mid-Valanginian–mid-Aptian. The fossil ages lie between published radiometric dates for the Spongtang Ophiolite (177 ± 1 Ma) and Spong Arc (88 ± 5 Ma) (Pedersen et al., 2001).

640

A.T. Baxter et al. / Gondwana Research 20 (2011) 638–644

100 km 90º

95º

Namche Barwa

YTSZ

30º

N

Himalaya

NO

20º Burma plate

mountain

n-Nicoba

ophiolite volcano

Andaman Trench

Andama

15º

Previous radiolarian biostratigraphic studies from the Nagaland Ophiolite are summarised in Acharyya (1986). Ghosh et al. (1984) reported Cretaceous foraminiferal, calcareous nannofossil and radiolarian assemblages from six locations in Nagaland. Unfortunately, the photomicrographs of the radiolarians are of poor quality and most fossils are identified only to genera-level, from thin sections (Ghosh et al., 1984). They suggest that the lower age limit for the formation of the Naga Ophiolite to be Late Cretaceous (Maastrictian),

Asian plate

r Is.

Bay of Bengal

Saigang Fault

NAS

25º Trough Shylet Indian Plate Oceanic plate

The discovery of well-preserved radiolarians, extracted from siliceous mudstones in the mélange (Liu and Aitchison, 2002) yielded a Paleocene/Eocene boundary (RP6) fossil assemblage, indicating that the development of the mélange occurred around, or shortly after, this time. 3.7. Nagaland Ophiolite

Shillong Plateau

CHO

MBT Shillong Plateau

3.6. Yamdrok Mélange

Spreading centre

Fig. 2. Outline of the ophiolites and magmatism related to the Naga–Andaman suture (NAS). CHO = Chin Hills ophiolite; NO = Naga ophiolite; MBT = Main Boundary thrust; NAS = Naga–Andaman suture. Modified from Chatterjee and Ghose, 2010.

3.3. Nidar Ophiolite Radiolarian assemblages reported from the Nidar Ophiolite have an upper Barremian to upper Aptian range (Zyabrev et al., 2008). This compares well with the radiometric age reported for a sample of ophiolitic gabbro 124 ± 1 Ma (Mahéo et al., 2004).

3.4. Dazhuqu Terrane Assemblages of radiolarians from the ribbon-bedded cherts at the top of the ophiolite sequence indicate its formation occurred during the late Barremian to early Aptian (Ziabrev et al., 2003; Aitchison and Davis, 2004).

3.5. Bainang Terrane A comprehensive study of radiolarian biostratigraphy in the Bainang terrane revealed a series of tectonic slices with repeated successions of basalts, red ribbon cherts and siliceous mudstones, capped by a fine-grained clastic sequence (Ziabrev et al., 2004). Deepmarine sedimentation occurred from the late Triassic to midCretaceous (Aptian). Further to the west, near Xialu, Matsuoka et al. (2002) also sampled cherts from the Bainang terrane. They reported Middle Jurassic (Aalenian)–Lower Cretaceous (Aptian) assemblages extracted from cherts and siliceous mudstones.

Fig. 3. Chronostratigraphic chart summarising the age constraints of deep-water sedimentation in the Neotethyan Ocean. Blocks with black outlines have wellconstrained ages. Blocks with no outline represent maximum ranges. References are given in the text.

A.T. Baxter et al. / Gondwana Research 20 (2011) 638–644

641

Fig. 4. Composite plate of biostratigraphically important radiolarians from the Naga ophiolite, from sample NG 5.1. (a, b) Thanarla sp. Pessagno; (c) Zhamoidellum ovum Dumitrica; (d) Transhuum maxwelli gr. (Pessagno); (e) Archaeodictyomitra ?apiarium (Rüst); (f) Transhuum brevicostatum gr. (Ozvoldova); (g) Cinguloturris sp. Dumitrica; (h, i) Parvicingula sp. Pessagno; (j) Xitus gifuensis Mizutani; (k) Wrangellium okamurai (Mizutani); (l) Zhamoidellum ventricosum Dumitrica; (m) ?Thanarla sp. Pessagno; (n) Hiscocapsa ?asseni (Tan); (o) Cryptamphorella clivosa (Aliev); (p) Gongylothorax favosus Dumitrica; (q) Williriedellum crystallinum Dumitrica; (r) Stichocapsa robusta Matsuoka; (s) Cinguloturris carpatica Dumitrica; (t) Podobursa tytthopora (Foreman). All scale bars are 100 μm.

but this is based primarily on the calcareous nannofossils record. Duarah et al. (1983) reported a Lower Cretaceous radiolarian assemblage, extracted from samples taken from the Disang Formation “in close association with the ultramafics”. Most radiolarians were only identified to genus-level and include Xitus sp., Parvicingula (?) sp., Holocryptocanium sp., Archaeodictyomitra sp., Acanthocircus dicranocanthos, Cecrops sp., indicative of the Lower Cretaceous. Acharyya et al. (1991) mis-cite this work and suggest that these radiolarians were assigned to the Late Jurassic to Cretaceous. On reexamination by the authors of radiolarian photomicrographs from Naga ophiolite samples, the level of preservation does not allow confirmation of previous identifications.

4. Samples Nine samples were collected, seven (NG1–NG4.4) of which were taken from a large block of coherent chert on the road to Salumi (25° 47.403′N, 094º 53.362′E). Two further samples were taken from a river outcrop of the mélange further to the north (NG5.1 and NG5.2). Samples NG5.1 and NG5.2 both yielded well-preserved radiolarian tests. Samples were processed in the HKU biostratigraphy lab and prepared using standard radiolarian extraction techniques (Pessagno and Newport, 1972). Each sample was broken into small (3 cm3) pieces, suspended in plastic netting and immersed in a 5% HF solution for 12–24 h. This was repeated, up to 10 times, for some samples, to capture as much

642

A.T. Baxter et al. / Gondwana Research 20 (2011) 638–644

Fig. 5. Composite plate of biostratigraphically important radiolarians from sample NG 5.2. (a, b) Williriedellum crystallinum Dumitrica; (c) Hiscocapsa sp. Verbeeki; (d) Holocryptocanium sp. Dumitrica; (e) Cryptamphorella clivosa (Aliev); (f) Xitus gifuensis Mizutani; (g) Archaeodictyomitra aparium (Rüst); (h) Parvicingula boesii (Parona); (i) Parvicingula sp. Pessagno; (j) Pseudodictyomitra primitiva Matsuoka & Yao; (k) Cinguloturris sp. Dumitrica; (l, m) Protunuma japonicus Matsuoka & Yao; (n) Syringocapsa sp. Neviani; All scale bars are 100 μm.

radiolarian tests as possible. They were concentrated on a 63 μm sieve and the residue was collected. The sieves were thoroughly cleaned of all materials between each sample. Radiolarians were picked and mounted onto an aluminium stub covered with sticky carbon tape then coated with Ti–Au alloy-coated and photographed using a scanning electron microscope. These images were compared with type specimens in the literature and an age range was compiled. 5. Age Assignment A well-established Jurassic to Cretaceous radiolarian zonation (Baumgartner et al., 1995) was used to ascertain the biostratigraphic position of the fossiliferous sediments with Unitary Association (UA) zones correlated to the Geological Time Scale of Gradstein et al. (2004). Overlapping age ranges of abundant, well-preserved taxa

within samples NG 5.1 (Fig. 4) and NG 5.2 (Fig. 5) suggest a Kimmeridgian to mid-Tithonian (UA Zones 10–11) age range (Fig. 6). 6. Discussion The discovery of well-preserved, Kimmeridgian to mid-Tithonian (UA Zones 10–11) assemblages, extracted from two chert blocks, collected from the Naga Ophiolite provides the first robust age constraints on deep-marine sedimentation in this portion of the Naga–Andaman suture zone. It significantly extends the age range of the oldest known deep-marine sediments in this region, from the Cretaceous (Acharyya, 1986) to the Middle Jurassic. Their age correlates well with the radiometric date reported for the Naga Ophiolite 148 Ma (Sarkar et al., 1996) and for the Chin Hills Ophiolite in western Burma (158 ± 20 Ma) (Mitchell, 1981). Furthermore, the

A.T. Baxter et al. / Gondwana Research 20 (2011) 638–644

643

Sample: NG 5.1 Zhamoidellum ovum Dumitrica Transhuum maxwelli (Pessagno) Archaeodictyomitra ?apiarium (Rust) Transhuum brevicostatum gr. (Ozovoldova) Cinguloturris sp. Dumitrica Parvicingula sp. Pessagno Xitus gifuensis Mizutani Wrangellium okamurai (Mizutani) Zhamoidellum ventricosum Dumitrica Podobursa tytthopora (Foreman) Cinguloturris carpatica Dumitrica Williridellium crystallinum (Dumitrica) Gongylothorax favosus Dumitrica 180 Lower Toarcian

175

170

160 165 Jurassic

150

155

Middle Upper Aalen. Baj. Bath. Call. Oxford. Kimm. 1

2

3

4 5 6

7

8

9

10

11

140

145

Tith. 12

Berr. 13

14

Val. 15 16

125 130 Cretaceous Lower Haut. Barr.

135

19

20

21

120

Aptian

115

Age Period Epoch Stage UAZ95

Archaeodyctomitra aparium (Rust) Parvicingula boesii (Parona) Parvicingula sp. Pessagno Williridellium crystallinum Dumitrica Pseudodictyomitra primitiva Matsuoka & Yao Cinguloturris sp. Dumitrica Xitus gifuensis Mizutani Syringocapsa sp. Neviani Protumuna japonicus Matsuoka Sample: NG 5.2 Fig. 6. Chart of stratigraphic ranges of radiolarians present in samples NG5.1 and NG5.2. Age assignments for Middle Jurassic to Middle Cretaceous radiolarian assemblages are based on recent taxonomic studies and biostratigraphic zonations of Tethyan radiolarians (Baumgartner et al., 1995).

temporal constraints of deep-marine sedimentation are consistant with those reported from ophiolites in Tibet (e.g. Nidar, Xigaze, and Zedong) and reinforces the hypothesis that the Naga and YTSZ ophiolites were once part of the same Neotethyan ocean floor.

Acknowledgements The authors would like to thank Oken Taying, Jimmy and all those at Abor Country Travels who assisted us on our trip to Nagaland. Miss Lily Chiu and Holly Wong are thanked for their technical help. This research was supported by a General Research Fund grant from the Research Grant Council of Hong Kong Special Administrative Region (project HKU7001/07) awarded to JCA. We thank an anonymous reviewer and Associate Editor Dr P. Eriksson for comments and suggestions that helped to improve the manuscript.

References Acharyya, S.K., 1986. Tectono-stratigraphic history of the Naga Hills ophiolites. In: Mitra, N.D., Acharyya, S.K., Datta, A.K., Ghosh, S., Nandy, D.R., Roy, D.K., Vidyadharan, K.T., Venkataramana, P., Srivastava, R.K., Bhattacharyya, S., Joshi, A., Jena, S.K., Goswami, H.K. (Eds.), Geology of Nagaland Ophiolite, D. B. Ghosh Memorial Volume Geological Survey of India Memoirs, 119, pp. 94–103. Acharyya, S.K., 2007. Collisional emplacement history of the Naga–Andaman ophiolites and the position of the eastern Indian suture. Journal of Asian Earth Sciences 29, 229–242. Acharyya, S.K., Ray, K.K., Sengupta, S., 1991. The Naga Hills and Andaman ophiolite belt, their setting, nature and collisional emplacement history. Physics and Chemistry of The Earth 18, 293–315. Ahmad, T., Tanaka, T., Sachan, H.K., Asahara, Y., Islam, R., Khanna, P.P., 2008. Geochemical and isotopic constraints on the age and origin of the Nidar Ophiolite Complex, Ladakh, India: Implications for the Neo-Tethyan subduction along the Indus suture Zone. Tectonophysics 451, 206–224. Aitchison, J.C., Davis, A.M., 2004. Evidence for the multiphase nature of the India–Asia collision from the Yarlung Tsangpo suture zone, Tibet. Geological Society, London, Special Publications 226, 217–233. Aitchison, J.C., Ali, J.R., Davis, A.M., 2007. When and where did India and Asia collide? Journal of Geophysical Research 112, 1–19.

Baumgartner, P.O., O'Dogherty, L., Gorican, S., Urquhart, E., Pillevuit, A., De Wever, P., 1995. Middle Jurassic to Lower Cretaceous radiolaria of Tethys : occurences, systematics, biochronology. Mémoires de Géologie, Universite de Lausanne. . 23, 1172 pp. Baxter, A.T., Aitchison, J.C., Ali, J.R., Zyabrev, S.V., 2010. Early Cretaceous radiolarians from the Spongtang massif, Ladakh, NW India: implications for Neo-Tethyan evolution. Journal of the Geological Society of London 167, 511–517. Beck, R.A., Burbank, D.W., Sercombe, W.J., Riley, G.W., Barndt, J.K., Berry, J.R., Afzal, J., Khan, A.M., Jurgen, H., Metje, J., Cheema, A., Shafique, N.A., Lawerence, R.D., Khan, M.A., 1995. Stratigraphic evidence for an early collision between Northwest India and Asia. Nature 373, 55–58. Bédard, E., Hébert, R., Guilmette, C., Lesage, G., Wang, C.S., Dostal, J., 2009. Petrology and geochemistry of the Saga and Sangsang ophiolitic massifs, Yarlung Zangbo Suture Zone, Southern Tibet: evidence for an arc-back-arc origin. Lithos 113, 48–67. Brunnschweiler, R.O., 1966. On the geology of the Indoburman ranges — Arakan Coast and Yoma, Chin Hills, Naga Hills. Journal of the Geological Society of Australia 13, 137–194. Chan, H.N., 2008. Petrogenesis and tectonic evolution of Yarlung Tsangpo ophiolites, south Tibet. University of Oxford, D. Phil thesis. 152 pp. Chatterjee, N., Ghose, N.C., 2010. Metamorphic evolution of the Naga Hills eclogite and blueschist, Northeast India: implications for early subduction of the Indian plate under the Burma microplate. Journal of Metamorphic Geology 28, 209–225. Corfield, R.I., Searle, M.P., Pedersen, R.B., 2001. Tectonic Setting, Origin, and Obduction History of the Spontang Ophiolite, Ladakh Himalaya, NW India. Journal of Geology 109, 715–736. Danelian, T., Robertson, A.H.F., 1997. Radiolarian evidence for the stratigraphy and palaeo-oceanography of the deep-water passive margin of the Indian Plate (Karamba Formation, Indus Suture Zone, Ladakh Himalaya). Marine Micropaleontology 30, 171–195. Ding, L., Kapp, P., Wan, X., 2005. Paleocene–Eocene record of ophiolite obduction and initial India-Asia collision, south central Tibet. Tectonics 24, TC3001. doi:3010.1029/ 2004TC001729. Duarah, R., Saikia, M.M., Bhattacharjee, C.C., 1983. Occurrence of the ophiolitic complexes along the Indoburman orogenic belt. Geological Magazine 120, 175–182. Evans, P., 1964. The tectonic framework of Assam. Journal of the Geological Society of India 5, 80–96. Gansser, A., 1964. Geology of the Himalayas. John Wiley, London. 289 pp. Gansser, A., 1980. The significance of the Himalayan suture zone. Tectonophysics 62, 37–52. Ghosh, S., Chattopadhyay, B., Roy, D.K., Venkataramana, P., 1984. On the Radiolaria-bearing rocks of Naga Hills ophiolite. Records of the Geological Survey of India 113, 89–97. Girardeau, J., Mercier, J.C.C., Yougong, Z., 1985. Origin of the Xigaze ophiolite, Yarlung Zangbo suture zone, southern Tibet. Tectonophysics 119, 407–433. Gradstein, F., Ogg, J., Smith, A., 2004. A Geologic Time Scale 2004. Cambridge University Press, Cambridge. 589 pp. Jan, M.Q., Windley, B.F., Khan, A., 1985. The Waziristan ophiolite, Pakistan: general geology and chemistry of chromite and associated phases. Economic Geology 80, 294–306.

644

A.T. Baxter et al. / Gondwana Research 20 (2011) 638–644

Johnson, S.Y., Alam, A.M.N., 1991. Sedimentation and tectonics of the Sylhet trough, Bangladesh. Geological Society of America Bulletin 103, 1513–1527. Kojima, S., Ahmad, T., Tanaka, T., Bagati, T.N., Mishra, M., Kumar, R., Islam, R., Khanna, P., 2001. Early Cretaceous radiolarians from the Indus suture zone, Ladakh, northern India. News of Osaka Micropaleontologists, Special Volume 12, 257–270. Liu, J., Aitchison, J.C., 2002. Upper Paleocene radiolarians from the Yamdrok mélange, south Xizang (Tibet), China. Micropaleontology 48, 145–154. Mahéo, G., Bertrand, H., Guillot, S., Villa, I.M., Keller, F., Capiez, P., 2004. The South Ladakh ophiolites (NW Himalaya, India): an intra-oceanic tholeiitic arc origin with implication for the closure of the Neo-Tethys. Chemical Geology 203, 273–303. Matsuoka, A., Yang, Q., Kobayashi, K., Takei, M., Nagahashi, T., Zeng, Q., Wang, Y., 2002. Jurassic–Cretaceous radiolarian biostratigraphy and sedimentary environments of the Ceno–Tethys: records from the Xialu Chert in the Yarlung–Zangbo Suture Zone, southern Tibet. Journal of Asian Earth Sciences 20, 277–287. McDermid, I.R.C., Aitchison, J.C., Davis, A.M., Harrison, T.M., Grove, M., 2002. The Zedong terrane: a Late Jurassic intra-oceanic magmatic arc within the Yarlung–Tsangpo suture zone, southeastern Tibet. Chemical Geology 187, 267–277. Miller, C., Thöni, M., Frank, W., Schuster, R., Melcher, F., Meisel, T., Zanetti, A., 2003. Geochemistry and tectonomagmatic affinity of the Yungbwa ophiolite, SW Tibet. Lithos 66, 155–172. Mitchell, A.H.G., 1981. Phanerozoic plate boundaries in mainland SE Asia, the Himalayas and Tibet. Journal of the Geological Society of London 138, 109–122. Moores, E.M., Roeder, D.H., Abbas, S.G., Ahmed, Z., 1980. Geology and emplacement of the Muslim Bagh ophiolite complex. In: Panayiotou, A. (Ed.), Ophiolites Symposium. Nicosia, Geological Survey Department, pp. 424–429. Nicolas, A., Girardeau, J., Marcoux, J., Dupre, B., Xibin, W., Yougong, C., Haixiang, Z., Xuchang, X., 1981. The Xigaze ophiolite (Tibet): a peculiar oceanic lithosphere. Nature 294, 414–417. Pedersen, R.B., Searle, M.P., Corfield, R.I., 2001. U–Pb zircon ages from the Spontang Ophiolite, Ladakh Himalaya. Journal of the Geological Society of London 158, 513–520. Pessagno, E.A., Newport, R.L., 1972. A technique for extracting Radiolaria from radiolarian cherts. Micropaleontology 18, 231–234. Reuber, I., Colchen, M., Mevel, C., 1992. The Spongtang Ophiolite and ophiolitic mélanges of the Zanskar, NW Himalaya, tracing the evolution of the closing Tethys in the Upper Cretaceous to the Early Tertiary. In: Sinha, A.K. (Ed.), Himalayan Orogen and Global Tectonics. A.A. Balkema, Rotterdam, pp. 235–266. Sarkar, A., Datta, A.K., Poddar, B.C., Bhattacharyya, B.K., Kollapuri, V.K., Sanwal, R., 1996. Geochronological studies of Mesozoic igneous rocks from eastern India. Journal of Southeast Asian Earth Sciences 13, 77–81. Sarwar, G., 1992. Tectonic setting of the Bela Ophiolites, southern Pakistan. Tectonophysics 207, 359–381.

Sengupta, S., Acharyya, S.K., Van Den Hul, H.J., Chattopadhyay, B., 1989. Geochemistry of volcanic rocks from the Naga Hills Ophiolites, northeast India and their inferred tectonic setting. Journal of the Geological Society of London 146, 491–498. Uddin, A., Kumar, P., Sarma, J.N., 2007. Early orogenic history of the eastern Himalayas: compositional studies of Paleogene sandstones from Assam, northeast India. International Geology Review 49, 798–810. Venkatramana, P., Datta, A.K., Acharyya, S.K., 1986. Petrography and petrochemistry of the ophiolite suite. In: Mitra, N.D., Acharyya, S.K., Datta, A.K., Ghosh, S., Nandy, D.R., Roy, D.K., Vidyadharan, K.T., Venkataramana, P., Srivastava, R.K., Bhattacharyya, S., Joshi, A., Jena, S.K., Goswami, H.K. (Eds.), Geology of Nagaland Ophiolite: Memoirs of the Geological Survey of India, Calcutta, pp. 33–45. Vidyadharan, K.T., Shukla, A.K., Bhattacharyya, S., 1986a. Blueschists, C-type eclogites and garnet-bearing mafic segregations from Naga Hills ophiolite belt. Geological Survey of India Records 114, 7–13. Vidyadharan, K.T., Srivastava, R.K., Bhattacharyya, S., Joshi, A., Jena, S.K., 1986b. Distribution and description of major rock types. In: Mitra, N.D., Acharyya, S.K., Datta, A.K., Ghosh, S., Nandy, D.R., Roy, D.K., Vidyadharan, K.T., Venkataramana, P., Srivastava, R.K., Bhattacharyya, S., Joshi, A., Jena, S.K., Goswami, H.K. (Eds.), Geology of Nagaland Ophiolite: Geological Survey of India Memoirs, 119, pp. 18–27. Xia, B., H.X., Y., Chen, G.W., Qi, L., Zhao, T.P., Zhou, M.F., 2003. Geochemistry and tectonic environment of the Dagzhuka ophiolite in the Yarlung–Zangbo suture zone, Tibet. Geochemical Journal 37, 311–324. Zaigham, N.A., Mallick, K.A., 2000. Bela ophiolite zone of southern Pakistan: tectonic setting and associated mineral deposits. Geological Society of America Bulletin 112, 478–489. Zhou, M.F., Robinson, P.T., Malpas, J., Li, Z.J., 1996. Podiform chromitites in the Luobusa Ophiolite (Southern Tibet): implications for melt-rock interaction and chromite segregation in the upper mantle. Journal of Petrology 37, 3–21. Ziabrev, S., Aitchison, J., Abrajevitch, A., Badengzhu, Davis, A., Luo, H., 2003. Precise radiolarian age constraints on the timing of ophiolite generation and sedimentation in the Dazhuqu terrane, Yarlung–Tsangpo suture zone, Tibet. Journal of the Geological Society of London 160, 591–599. Ziabrev, S.V., Aitchison, J.C., Abrajevitch, A.V., Davis, A.M., Lo, H., 2004. Bainang Terrane, Yarlung–Tsangpo suture, southern Tibet (Xizang, China): a record of intraNeotethyan subduction–accretion processes preserved on the roof of the world. Journal of the Geological Society of London 161, 523–539. Zyabrev, S.V., Kojima, S., Ahmad, T., 2008. Radiolarian biostratigraphic constraints on the generation of the Nidar ophiolite and the onset of Dras arc volcanism: tracing the evolution of the closing Tethys along the Indus–Yarlung–Tsangpo suture. Stratigraphy 5, 99–112.