Pan-African Magmatism, and Sedimentation in the NW Himalaya

Condwuna Reseurch. V 2, No. 2, pp. 263-270. 0 I999 Internntionrtl A.ssociutionfi)r Gondwana Research, Jupun. ISSN: 1342-937 X

GR

Gondwana Research

Pan-African Magmatism and Sedimentation in the NW Himalaya R. Islam', R. Upadhyay], T-Ahmad',V.C.Thakur'and A.K. Sinha2

'Wadia Institute of Himalayan Geology, Delzra Dun-248001, India 2Birbal Sahni Institute of Palaeobotany, Lucknow, India (Mctniiscri@received

Jiiiit'

15,f99R;accepted Decenzbev 26,1998)

Abstract Correlation of early Palaeozoic, Pan-African (500 k 50 Ma) granites that intruded the Chail, Salkhala, I-Iaimanta Formations in the Lesser Himalaya, Zaiiskar crystallines, and Lower Taglaiig La of Tso-Morari crystallines in the northwestern Himalaya, is based on the field relationship, tectonic setting, mineralogical and geochemical cliaracteristics, and isotope dating of the granites. These granite plutons exhibit identical petrographical and geochemical character. The mineralogical composition of the granites is quite similar, consisting of quartz, K-feldspar, plagioclase feldspar, biotite, muscovite, garnet, tourmaline, 2 cordierite, andalusite and sillimanite fibrolite. The granite which are massive and iiiequigranular i n the core of the plutons, show strongly foliated character indicating development of ductile shear zone at the margins. These are peraluminous S-type granites having high A/CNK value (> 1).Presence of normative corundum, rounded shape of zircon ,and high initial Sr ratio suggest crustal source of the granites. Mantle normalized spider-diagram exhibits similar characters for all these granitoids. The intrusion of the Pan-African granites mark an abrupt end of the sedimentation that continued virtually uninterrupted from Palaeoproterozoic. The sudden break in sedimentation towards the terminal phases of the Lower Cambrian has been observed in almost all parts in Lesser as well as the Tethys Himalaya. Occurrences of large number of plutons along different tectonic belts of northwestern Himalaya are indicative of widespread tectono-thermal event during early Palaeozoic (500 k 50 Ma). The bracketing of the two features like, the break in sedimentation during post-Late Cambrian and the intrusion of granites around 500 f 50 Ma, is considered to be the result of a strong diastrophic orogenic event correlatable to the late phases of the Pan-African Orogeny in Africa.

Keywords: Pan-African orogeny, Lesser Himalayan granites, S-type granitoids.

Introduction A remarkable aspect of the Precambrian succession in the Lesser Himalaya as well is the evidence of abrupt termination of sedimentation towards the end of Lower Cambrian. The event is marked by intrusion of a series of granitic masses which are dated between 600 and 450 Ma, in the different parts of the Himalaya. Valdiya (1973,1984) described this event of granitic intrusions as a part of intracontinental diastrophism corresponding to the 600 Ma Baikalian orogenic cycle. Fuchs (1968,1987)considered the break in sedimentation in the Lesser Himalaya as the result of Caledonian (Late Cambrian to Ordovician) orogeny. A contrary view was expressed by other workers like, Garzanti et al. (1986),Shah (1991),Bagati et aL(1991)and Bhargava et al. (1991),all of whom referred to the break in sedimentation as a result of the last pulses of the Pan-African Orogeny in the Himalayan domain of the Indian shield. Valdiya

(1993,1995) seems to be the first to assert involvement of strong Late Cambrian diastrophic movement in the Himalayan domain of the northern Indian shield, which involved explosive and eruptive types volcanicity, and intrusion of synkinematic granites. The event is thought to be contemporaneous with the Pan-African Orogeny of Africa and Europe (cf.Dupret et al., 1990). In this paper, we propose to deal with the geochemical characters of the 500 5 50 Ma granite magmatism along with a brief description of sedimentation history, and the records of stratigraphic break in the sedimentary succession that developed in the northwestern Himalaya. Presumably, the study will help not only in the understanding of the Pan-African tectono-thermal record in the Himalaya, but also would provide a useful basis of tectonic/ palaeogeographic reconstruction of the post- Neoproterozoic crust of the Indian shield in the northwest Himalaya.

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Available geoclironological data indicate emplacement of granites in the Lesser and Tethys Himalaya was during 600 and 450 Ma (Thakur, 1992).However, barring one (the Rohtang granite gneiss) which is 600 Ma old, all other granites fall in the 500 i 50 Ma age range. In the text, therefore, these granites will be referred to as 500 i50 Ma granites as also as the Pan-African granites.

-

Early Palaeozoic (Pan-African) Granite Magmatism A large number of granite plutons ranging in age from Palaeoproterozoic to late Tertiary occur in different parts of the Himalayan ranges. Isotope dates of these granitic activities, which span between 2000 Ma to 30 Ma, help in defining four major magmatic events showing the following age ranges (i) 2000-1800 Ma, (ii) 1400-1200 Ma, (iii)550-

*

450(500 50), (iv) 100-30 Ma. Of these, the 500 t- 50 Ma event seems to be the most widespread in different parts of the Himalaya. The majority of the early Palaeozoic granites are concentrated in the crystalline thrust sheets in the Lesser Himalaya, occurring as lenticular bodies and sheets along a linear belt subparallel to the regional Himalayan trends. These granites are termed as ’Lesser Himalayan Granitic belt’ (Le Fort et a1.,1983a). Several Pan-African granite plutons have also been reported from the crystallines of the Higher Himalaya. Scharer et al. (1986) also reported granites of similar age from southern Tibet. The granitoid belt in the Lesser Himalaya is made up of some fifteen independent plutons that occur along a short distance north of the MBT (Fig.l), constituting a part of the overthrusted slab of the MCT (LeFort et al., 1986) and are intrusive into the metasedimentaries. The gneissic character of the rocks is due to the strong development of foliation at

NW HIMALAYA

0

L

50 km

l

Fig. 1. Geological map of the NW Himalaya (after Thakur, 1992)Shaded dark area shows the location of the 500+ 25 Ma granites. >-

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Gorzdwcrn~iResecirch, 1/: 2, No. 2,I999

PAN-AFRICAN MACMATISM AND SEDIMENTATION IN THE NW HIMALAYA T&Ie 1. Average chemical composition of 500 k50 Ma granites of northwestern Himalaya. RG

JG

RGC

ZG

AG

DG

~~

SiO, TiO, A1203 Fe20; MnO MgO CaO Na,O K2O p20,

69.60 0.24 15.26 2.96 0.10 1.16 1.27 3.08 4.56 0.09

70.39 0.32 14.74 2.47 0.06 1.01 1.11 4.25 4.31 0.21

70.65 0.18 14.70 1.80 0.40 0.46 0.58 4.36 5.26 0.27

70.52 0.12 14.52 1.93 0.08 0.51 0.62 4.29 4.96 0.11

69.87 0.78 14.60 2.17 0.06 0.82 1.06 4.10 4.30 0.08

70.62 0.27 15.11 2.10 0.04 0.73 1.12 4.46 5.18 0.28

Rb Ba Th Nb La Ce Nd Zr Sm Y

291 594 29 13 30 53 27 123 4.44 36

280 573 24 14 31 60 28 134 4.88 41

341 524 15 18 26 50 26 168 5.32 36

252 412 25 18 41 87 37 213 8.00 27

230 526 21 11 36 73 28 157 17.76 23

359 566 16 12 16 36 16 78 3.10 36

Jispa Granite (JG), Ratilaman Granite (RG), Rohtang Gneissic Complex (RGC), Zanskar Granite (ZG), Akpa Granite (AG), Dalliousie Granite ( W .

their margins. The core regions of the granite bodies are massive without showing development of foliation. These plutons have been deformed and metamorphosed during the Tertiary Himalayan Orogeny. Several authors in recent

265

years attempted geochemical and geochronological studies of these granite bodies in order to constrain the petrogenetic model and age of the rocks (Sharma, 1983; Le Fort et al., 198313; Trivedi et al., 1984; Rao et al., 1990;Rao and Sharma, 1995; Chaudhuri, 1996; Hussain et al., 1994; Rashid and Zainuddin, 1995; Islam, 1995; Islam et al., 1995; Islam and Gururajan, 1997; Islam et al., 1997; Mukherjee et al., 1998). Average chemical composition of the Pan-African granites of the northwestern Himalaya is given in Table 1.The Table 2 shows Rb-Sr whole rock isotope dates of these granites. The 500 k 50 Ma Pan-African granite plutons are observed to intrude into the Chail, Salkhala, and Haimanta Formations of the Lesser and Tethys Himalaya, the Lower Taglang La Formation of Tso-Morari Crystallines, as also their equivalents in the Zanskar Crystallines (Thakur et al., 1990). The granites cut across the older schistosity of the Chail/Salkhala/Haimanta Formations, which are evidently a pre-Himalayan Precambrian fabric. The intrusion of PanAfrican granitoids in the Late Precambrian sediments caused contact metamorphism leading to the development of hornfelsic rock. Well developed hornfelses are reported from the Dalash in Satluj valleys (Gururajan and Virdi, 1984) and from the base of Mandi-Karsog granites (Islam and Gururajan, unpublished data). The pelitic hornfelses consist of quartz-biotite-muscovite- plagioclase feldspar, and quartz-biotite-muscovite-sillimani te-K-feldspar-plagioclase feldspar. A common feature of all the late Pan-African granite plutons is the broadly uniform petrological and geochemical

Table 2. Rb-Sr whole-rock isocliron dates from granites from the Chail, the Jutogh and the Haimanta Formations and the Tso-Morari Crystallines Locality

Tectonic Unit

Almora Ranikhe t Chaur

Almora (=Jutogli) Almora Jutogh Jutogli Cliail (Salkhala) Chi1 Chail Cliail/Jutogli

KLI~LI Mandi Mandi Dalhousie Manikaran (Sarang & Rangathacli Jispa Akpa (Rakcham) Rolit ang Nanga Parbat

Lower Haimanta Haimanta Central Crystallines Shengus gneiss

Kangan (Kashmir) Manselira Nimaling

Salkhala Tanols (Chail/Haimanta) Taglang La Fm. of Tso-Morari Crystallines Tso-Morari Crystallines Tso-Morari Crystallines

Polokong La Korzok

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Initial Sr Isotope ratio 506k20 485255 5302 40 51828 545~12 500+100 472~50 467~45

0.710+0.001 0 . 7 3 5 ~0.009 0.7326 0.719

512+16 477+29 601219 400-500 (U-Pb, Zircons) 470kll 516+16 46028

0.720 0.7201 0.711

0.719

Authors Trivedi et a1.,1984 Pandey et al., 1981 Kwatra, 1986 Melita, 1977 Melita, 1977 Jaeger et al., 1971 Bhanot et al., 1974 Bhanot et al., 1979 Frank et al., 1977 Kwatra, 1986 Mehta, 1977 Zeitler et al., 1989

0.7216+.0023 0.7189

Trivedi, et al., 1985 Le Fort et al., 1980 Stutz & Thony, 1987

487225

0.7154+.0067

Trivedi et al., 1986

487+4

0.7113+.0036

Trivedi et al., 1986

266

R. ISLAM ET AL.

Mantle Normalized Spider Diagram of Early Palaeozoic Granites of NW Himalaya 1000

c

t

-X-

RGC

+AG

100

-*-

DG

10

1

Rb

Ba

Th

K

Nb

La

Ce

Sr

Nd

P

%r

Sm

Ti

Y

Na

Pig. 2. Mantle normalized spider diagrams of the various granitoids of 5OOk 25 M,a age of the N W Hitrlillayii JC: (Jisl~ii gr>iiiih*),I<( (l
traits. The mineralogical composition of all the granite bodies arc quite similar in nature, consisting of quartz, Kfeldspar, plagioclase feldspar, biotite, muscovite, garnet , andalusitc, sillimanite fibrolite, (+) cordierite a n d tourmaline. The granites are inequigranular, medium to coarse grained rocks showing development of ductile shear zones at the contact of the host units. Numerous dark igneous and metasedimentary enclaves are present in the plutons, of which the latter appears to be more numerous in occurrences than the former. Some of the basic enclaves are of very large in size. Chemically the granitoids have a more or less similar composition (Table 1).Features like high A/CNK value (> 1), presence of normative corundum, absence of normative diopside characterise these granites as peraluminous Stype granitoids having crustal protoliths. The mantle normalized spider-diagram of the granite samples of the Jispa, Ratilaman or Batal, Rohtang gneissic complex, Akpa, Dalhousie and Zanskar plutons (Fig. 2 ) illustrates depletion of elements like Ba, Nb, Sr and Ti. The spider-diagram prepared for these granites show similarity to that of the average of the early Palaeozoic granites of the Lachlan fold belt of Australia (Wyborn et al., 1992).

Records of the Late Cambrian stratigraphic break There are records of a major stratigraphic gap in the Lesser and Tethys Himalaya sequences which can be related to the Pan- African tectonothermal event.

Evidence from Lesser Himalaya The prolonged and uninterrupted Proterozoic cycle of sedimentation shows abrupt termination in all part of Lesser Himalaya toward the end of the Lower Cambrian, and possibly a little earlier in all the Peninsular basins (Valdiya, 1993, 1995). Several examples of diamictites, horizons of black shale and slates ranging in age from late Proterozoic to Lower Cambrian have been reported from the Lesser Himalaya (Valdiya, 1980; Sinha, 1989). The Tal and Mandhali-Basantpur Formations are amongst those which represent the termination of the Proterozoic sedimentation. The Tal Formation of the outer Lesser Himalaya and the Mandhali-Basantpur of the inner Lesser Himalaya are lithologically very thick successions. The Tal Formation mainly comprises black shale, chert, siltstoiie, limestone, phosphatic shale, phosphorite, greywacke, arenite, orthoquartzite, algal limestone etc. Whereas, the dolomites Gonrlwonci Reseurch, I.!2, No. 2, 1999

PAN-AFRICAN MAGMATISM A N D SEDIMENTATION IN T H E NW HIMALAYA

of the Mandliali-Basantpur Formations show development of late Proterozoic stromatolites (Valdiya, 1969, 1980). Similarly, the calc zone rocks of Tejam Group have also been described as a late Precambrian to Cambrian Formation (Valdiya, 1980; Sinha, 1989). The Precambrian Ramsu flysch of the Kashmir region which is capped by chert, shale and limestone of the Lower Cambrian age (Valdiya, 1993) is lithostratigraphically similar to the Lesser Himalayan rocks. This Lower Cambrian sequence is unconformably overlain by the Panjal Volcanics of the Lower Permian age. The sedimentary successions of the yarautochthonous zone (Wadia, 1934)of Pir Panjal is dominated by the slates, arenites and dolomitic limestones with diamictites and pockets of gypsum. These sedimentary sequcnces,therefore, appear homotaxial with tlie late Proterozoic Mandhali Formation (Valdiya, 1993, 1995). Presently, there exists no evidence of sedimentation beyond Lower Cambrian in the Lesser Himalayan region. Evidences ,therefore, confirm the existence of a break in sedimentation d u r i n g Lower Cambrian both in the Peninsular India and the Lesser Himalaya.

Eviderzcesfuonr Tetlrys Hziizalaya Tlie post- Lower Cambrian stratigraphic break in the Lesser Hiinalayan succession is also recorded in the Tethyan basins of the Himalaya. There is apparently no physical break in the Precambrian to Silurian sedimentary succession in the Kaslimir sub-basin (Valdiya, 1993),although a faunal break has been recorded in the Upper Cambrian and Lower Ordovician sediments (Shah, 1991). Similarly, in the Zanskar-Lahaul region of Hiinachal Pradesh a thick lithological sequence of bioturbated pelite and greywacke of Middle and (possibly) Late Cambrian age is seen to tectonically overlie the Vaikrita crystallines. Further north in the Tethys basin, these litliological sequences are unconformably overlain by conglomerate and red sandstone of the late Ordovician to early Silurian age (cf. Valdiya, 1993, 1995, and references cited therein). By contrast in the southern Lahaul, the late Precambrian Batal flysch is succeeded directly by the Permian sequence that go upto Jurassic (Srikantia and Bhargava, 1979). This implies the presence of a considerable hiatus in the depositional history, which is possibly caused by a tectonic activity (Valdiya, 1995).In the Spiti region also a hiatus is recorded in the stratigraphic succession. However, the break here is limited to the uppermost Cambrian and early Ordovician. The late Cambrian formation is unconformably overlain by the Middle Ordovician (Shah, 1991; Shah et al., 1988). A similar stratigraphic break is also recorded in the northern Kumaun (Valdiya, 1980,1993, 1995; Sinha, 1989) where the Ordovician Formation directly overlies the Lower Cambrian Formations. Goi?rhvtiiitrResrtir.c.li,

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TectoizostuatigraphicCouuelatzoii Tlie occurrence of 500 ? 50 Ma Pan-African granites in Chail, Salkhala, Haimanta, Sankoo (Zanskar) and Lower Taglang La in the NW Himalaya helps to correlate those formations. The other features which based on their lithostratigraphy, tectonic settings, mineralogy and geochemical characters. Wadia (1931) included both low grade rocks of greenschist facies and medium to high grade rocks of amphibolite facies in Salkhala. In the southern Kashmir the rocks comprising lowgrade green schist facies rocks of the Salkhala Formation are thrusted southward to lie over tlie Panjal imbricate zone along the Panjal Thrust. Whereas the Salkhala per se is overlain unconformably by the Palaeozoic Formations of Kashinir (Thakur,1992).The continuity of the Salkliala rocks is also traceable with the Phe (-Sankoo) Formation of the Zanskar Crystallines. When traced southeastward, the rocks of the Salkliala Formation are seen to underlie the Chamba Formation, forming a homotaxial sequence with the Chail Formation in the K u l and ~ Satluj valley (Thakur et al., 1990). The low grade Salkhala rocks which extend into Kashmir through Chamba, Beas and Satluj valleys show a number of intrusion of the Pan-African granites at Ramban, Kund Kapalas, Dalhousie, Mandi-Karsog and Dalash areas. The Ramban, Kangan and Kazinag granites of the Pan-African affinity are found to be intrusive into the Salkhala Formation but not into the Palaeozoic succession which overlie it, near the northwestern closure of the Kashmir basin. Along the southeastern closure of Kashmir syncline, the Salkhala occupying the base of Pal'ieozoic sequence extends northward through the Warwan valley and is continuous with Phe Formation, in Zanskar which contains Karpokhar granite of early Palaeozoic age (Thakur et a1.,1990).Hayden (1904)described a sequence in the LaliaulSpiti region which range in age from late Precambrian to Cambrian, and correlated with the Haimanta Formation. The Kunzum La Formation that occupy the upper part of the Haimanta Formation bears trilobites of Cambrian age. By contrast the Lower Haimanta (Batal Formation or Kade Unit of Pognante et al., 1990 and Lahaul Formation of Rawat and Thakur, 1988) shows intrusion of Pan-African granites at Jisya ,Ratilaman and Hanuinan Tibba (Islam and Gururajan, 1997; Islam et al., 1997). From the above description, it would appear that the low grade Salkhala and the Lower Haimanta have similar sedimentary facies character, undergone greenschist facies metamorphism and are intruded by the early Palaeozoic (500k 50 Ma) granites. Further, both the formations underlie the Palaeozoic-Mesozoicsequence. The Salkhala Formation occurring along the southern margin of the Chamba sequence extends northward encircling the southern closure of the Chainba syncline and are found to be physically

R. ISLAM ET AL

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?hhlc 3. l.itliostmtigra,liic correlation of Kaslimir, LCili~~il, Zaiiskar, Tso-Morari, aiid Lesser Himalaya Kas Iimi I_ Sal kha Li

0

8 3:

5

Shte, black limestone, flaggy quartzite, phyllitr a n d schist along with foliated biotite grmite of 500 Ma age (Ramban, 1 lant, Kangiii)

Laliaul-Spi ti H,iimanta (- Kade) Biotite-chlorite schist, Phyllite, cpirtLitic phyllite, metagreywacke along with 500 Ma granites (Jispa, Ratilainaii Haiiumaii Tibba).

Zanskar Crystallines Plie (-Sankoo) Clilorite-biotite schist, tliiniily bedded limestone, quartzite, amphibolite, carbonaceous pliyllite and deformed biotite-muscovite granite body of 500 Ma age (Karpokhar)

continuous with the Haimanta in the Lahaul-Spiti region. The Lower 'Taglang La Formation of Tso-Morari Crystalline is flyshoid and is also intruded by the early Palaeozoic Polokong La and the Korzok granites of 487 k 25 and 487 f 14 Ma age respectively ( Trivedi et a1.,1986). The Lower Taglang La can be correlated with tlie Lower Haimanta Formation of Lah;i~tlon the basis of their similarity in lithostratigraphy, grade of greenschist metamorphism, and intrusion of early Palaeozoic granites. Therefore it is possible to correlate the Haimanta, the Phe, the low grade Salkhala, the Lower Taglang La a n d the Chail Formations as homotaxial successions. 'The lithostratigrapliic correlation of Salkha, Haimanta, Phe (-Sankoo), Lower Taglang La and Chail are suimnerised in Table 3.

leetonic Implications This discussion is aimed at relating tlie Pan-African (500 i 50 Ma) granites to a possible late Precambrian to early

Cantbrian orogeny in the northwestern Himalayan domain. Field relationship coupled with the studies on, petrography, geochemistry and the available geochronological data of the early Pan.-African granites, suggest that they are the products of crustal melting of older sedimentary source. The occurrence of large number of plutons of early Palaeozoic age in various sectors of the Himalaya with similar mineralogical, geochemical a n d geochronological characteristics indicate a widespread tectono thermal event. Various workers (Kumar et al., 1984;Bhargava, 1980; Jain et al., 1980; Baud et al., 1984; Garzanti et al., 1986; Baig et al., 1988) have discussed the possibility of a pre-Himalayan deformation based on stratigraphic evidences. It may be significant to note that Hayden as early as 1904 recognised the presence of Cambro-Ordovician angular unconformity in the Spiti region. The Iib/Sr whole rock ages of the granites of Lesser and Higher Himalaya are found to cluster around 500+50 Ma. The event is presumed to mark the culmination of an orogenic cycle of sedimentation, folding, regional metamorphism and granite intrusion (Mehta, 1978). The

Tso-Morari Crystallines Lower Taglang La Chlorite-biotite scliist, metamorphosed calcareous marly and argillaceous metasedimentaries together with ampliibolite, along with 500 Ma granites (Polokong La and Korzok )

Lesser Himalaya Chi1 Mica schist, pliyllite, quartzite with subordinate limestone and amphibolite bands (largely of tlie greenschist facies, along with 500 Ma granites (Dalliousie, Mandi, K~iiid-Kapiltis).

orogenic event is generally referred to as the Caledonian (Frank et al., 1977; Srikantia, 1977; Fuchs, 1981) or PanAfrican orogenic cycle (Powell and Conaghan, 1978; Baud et al., 1984; Garzanti et al., 1986). The granites of the early Palaeozoic ages of the various part of the NW Himalaya show crude to well developed foliation and metamorphosed under greenschist facies conditions indicating the effect of Tertiary (Himalayan) deformation and metamorphism. The strong peraluminous characters and high initial strontium ratio indicate the melting of pelitic metasedimentary source. Le Fort et al. (1986) suggested that the presence of dark microgranular inclusions in the early Palaeozoic granites point towards the likely basic contribution to the magmas. They further suggested that the early Palaeozoic granite belt may thus be considered as a mega-zone of crustal extension and thinning along which the lower crust melted to a fair amount in rather dry conditions. Even though evidences based on stratigraphy in the Himalaya and possible early Palaeozoic deformation and metamorphism in Pakistan region (Baig et al., 1988) is proposed but clear cut evidence of Pre-Himalayan deformation and metamorphism is lacking. One of the reasons for their absence is the strong superimposition of Tertiary deformation and metamorphism. The enormous volume of early Palaeozoic peraluminous granites indicate widespread crustal melting. The magma produced intruded shallow crustal levels as suggested by Le Fort et al. (1986).If these granites are related to crustal extension and thinning, then this must have associated with regional scale lower pressure metamorphism. However the preservation (and identification) of low pressure metamorphism has not been so far recognised. Loosveld and Etheridge (1990) suggested crustal thickening/ convecture lithosphere thinning model in place of lithospheric extension for many of the Hercyno-type (Zwart, 1967) orogens, for example, the early Palaeozoic Lachlan Fold Belt of south-eastern Australia. The early history of this fold belt is characterised by a widespread Ordovician Gonclcvcinri Resecirch, 1! 2, No. 2, 1999

PAN-AFRICAN MAGMATISM AND SEDIMENTATION IN THE NW HIMALAYA

quartzose flysch facies that w a s deposited in relatively deep water, at least in part of their continental crust. In the Higher Himalaya, the late Precambrian to Cambrian sediments are dominantly continental shelf and slope clastics equivalent to t h e deltaic a n d s h a l l o w m a r i n e deposits of Lesser Himalaya a n d Indian shield (Garzanti et al., 1986). They gave definite sedimentological evidences from the late Proterozoic-early Palaeozoic sequence of the northern Himalaya, towards an orogenic event (Pan -African) close to the Cambrian Ordovician boundary.

Acknowledgement We thank Professor A.B. Roy, Deptt. of Geology, Mohanlal Sukhadia University, for his suggestion and encouragement to write this paper. Shri Shiv Singh Negi has ably typed this manuscript.

References Bagati, T.N., Kumar, R. and Ghosh, S.K. (1991) Regressivetransgressive sedimentation in the Ordovician sequence of t h e Spiti (Tethys) basin, Himachal Pradesh, India. Sed.Geol.,v. 73, pp. 171-184. Baig, M.S., Lawrence, R.D. and Snee, L.W. (1988) Evidence for Late Precambrian to Early Cambrian Orogeny in the northwest Himalaya, Pakistan. Geol. Mag.,v.125, pp.83-86. Baud, A., Gaetani, M., Garzanti, E., Fois, E., Nicorra, A. and Tintori, A. (1984) Geological observations in southwestern Zanskar and adjacent Lahul area (northwestern Himalaya). Eclogae. Geol. Helv.,v. 77, pp. 171-197. Bhargava, O.N. (1980) Pre-Tertiary Orogenesis in the Himalaya: a review of various evidences. Geol. Rundsch.,v. 69, pp. 811823. Bhargava, O.N., Srivastava, R.N. and Gadhoke, S.K. (1991)LateProterozoic-Palaeozoic Spiti basin. In : S.K. Tandon, Charu C.Pant and S.M.Cassyap (Eds.) Sedimentary Basins of 1ndia:Tectonic Context. Gyanodaya Prakashan, Nainital, pp.236-260. Chaudhuri, N. (1996) Geochemistry and petrogenesis of the Palampur Granitoids, Dhauladhar range, northwestern Himalaya, India. Chem. Erde.,v. 56, pp. 25-43. Dupret, L., Dissler, E., Dore, F., Gresselin, F. and Le Gall, J. (1990) Cadomian geodynamic evolution of the northeastern American massif (Normandy and Maine) In :R.S. D’Lemos, R.A. Strachan, C.G. Topley (Eds.) The Cadomian Orogeny. Geological Society of London, Spl.Publ., No.51, pp.115-131. Frank, W., Thoni, M. and Purtscheller, F. (1977) Geology and petrography of Kulu-Lahaul area. Colloq.Int. CNRS,v. 268’, pp.147-172. Fuchs, G. (1 968) The geological history o f the Himalaya. Report 22nd Intern. Geol. Congr. Prague, v. 3, pp. 161-174. Fuchs, G. (2981) Outline of the geology of the Himalaya. Mitt. Osterr. Geol. Ges., v.74, pp.101.-127. Fuchs, G. (1987) The geology of Southern Zanskar (Ladakh) evidence for the autochthony of the Tethys zone of the Himalaya. Jb. Geol., B-A ,v. 130, pp.465-491. Goiiclwciiici

Resenrclr, V 2,No. 2,1999

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Gass, I.G. (1981) Pan-African (Upper Proterozoic) plate tectonics of the Arabian Nubian Shield. In: Kroner, A. (Ed.), Precambrian Plate Tectonics, Elesevier, Amsterdam, pp. 387-405. Garzanti, E., Casnedi, R. and Jadoul, F. (1986) Sedimentary evidence of a Cambro-Ordovician Orogenic event in the NW Himalaya. Sed. Geol., v. 48, pp. 237- 265. Gururajan, N.S. and Virdi, N.S. (1984) Superimposition of early Palaeozoic contact metamorphism by Tertiary regional metamorphism, Dalash, District Kul u, Himachal Pradesh, India. Jour. Geol. Soc. India,v. 25, pp.522-527. Hayden, H.H. (1904) The geology o f Spiti with parts o f Bashar and Rupshu. Mem. Geol. Surv. India, v.36, pp.1-29. Hussain, S., Fareeduddin, Raju, S. and Dayal, B. (1994) Petrochemistry and tectonic setting of the Champawat granite suite of Lesser Himalaya, Pithoragarh district, lJttar Pradesh. Jour. Geol. Soc. India, v.44, pp.17-25. Islam, R. (1995) Geochemistry and petrogenesis of CambroOrdovician granitoids from Northwestern Himalaya. (Extended Abstract) Symp. O n Recent Advances in Geological Studies of Northwest Himalaya and the Foredeep. G.S.I. Lucknow, pp. 145-146. Islam, R., Rawat, B.S., Ahmad, T. and Thakur, V.C. (1995) Petrological and geochemical studies of granite plutons from Zanskar Crystallines. Symp. O n Tethys of the Himalaya and adjoining region, W.I.H.G., Dehra Dun, 1517 NOV.1995, pp.47-48. Islam, R. and Gururajan, N.S. (1997) Geochemistry and petrogenesis of Lower Palaeozoic meta-granites of LahaulSpiti region, Himachal Pradesh, India. Geochem. Jour., v.31, pp.1-16. Islam, R., Bist, K.S., Choudlluri, B.K., Rawat, B.S. and Purohit, K.K. (1997) Geochemistry and petrogenesis of Hanuman Tibba Granite of KuIlu Valley, Himachal Himalaya. Jour. Geol. Soc. India, v.49, pp.13-23. Jain, A.K., Goel, R.K. and Nair, N.G.K. (1980) Implication of Pre-Mesozoic Orogeny in the geological evolution of the Himalaya and Indo-Gangetic plains. Tectonophysics, v . 6 2 , ~67-86. ~. Kumar, G., Raina, B.K., Bhargava, O.N., Maithy, P.K. and Rabu, R. (1984)Precambrian-Cambrian boundary problem and its prospects, NW Himalaya, India. Geol. Mag.,v. 121, pp. 211-219. Le Fort, P., Debon,F. and Sonet, J. (1983a) The Lower Palaeozoic ”Lesser Himalayan” granitic belt: emphasis on the Simachar pluton of central Nepal. In: Shams, F.A. (Ed.) Granites of Himalayas, Karakoram and Hindukush, Punjab Univ., Lahore, pp.235-255. Le-Fort, P., Michard, A., Sonet, J. and Zimmerman, J.L. (198313) Petrology, geochemistry and geochronology of some samples from the Karakoram Axial Batholith (Northern Pakistan). In : Shams, F.A. (Ed.), Granites of Himalayas, Karakoram and Hindukush, Punjab Univ., Idahore, pp. 377-388. Le-Fort, P.,Debon, F., Pecher, A., Sonet, J. and Vidal, Ph. (1986) The 500 Ma magmatic event in Alpine southern Asia, a thermal episode at Gondwana Scale. Sci. De La tere, Memorie, v.47, pp.191-209. Loosveld, R.J.H. and Etheridge, M.A. (1990) A model for low pressure facies metamorphism during crustal thickening. Jour. Meta. Geol., v.8, pp.257-267.

270

R. ISLAM ET AL

Mehta, I’K (1978) Rb/Sr Geoclironology o f tlie KUILI Mandi belt, its implication for the I-Iimalaym tectonogenesis a reply Geol Rundsch , v68, pp 383-392 Mukherjee, P K , Puiohit, K K , Kathi, M S,Khanna, P P , Saini, N K aiid lslain, R (1998) Geochemistry and petrogenesis o f Supracrustal granite from D a h u s i e , Himachal Himalaya, India Jour Geol Soc India,v52, pp.163-180. Pogiiante, U , Castelli, D , Benna, P, Genovese, G I Oberali, F, Meier, M and Tonarini, S.(1990) The crystalline units of t h e I l i g h Himalayas i n t h e Lahaul-Zanskar region (noi tliwest India) metamorphic-tectonic history aiid geochionology of tlie collided and imbiicated Indian plate Geol M a g , v.127, pp 101-116 Powell, C., Mc, A a n d Conaghan, P J (1978) Rb/Sr Geocliionology o f the K u l u Mandi belt, its implication for the Himalayan tectogenesis (Discussion) Geol Rundsch , v 68, pp 380-383. Rao, D R , Sharma, K K , Sivaraman, ‘r V , Gopalan, K and Trivedi, J I7 (1990) Rb/Sr dating and petrochemistry of I-Iant granite (Baramulla area), Kashmir Himalaya Jour Him Geol , v 1, pp 57-63 Rao, D.R and Sharma, K K.(1995)T’etrological and geochemical constraints on the petrogenesis of the Jaspa granitic pluton, Lalia~di egion, NW Himalaya Jour. Geol Soc Tndia,v45, p p 629-642 Rashid, S A aiid Zainuddin, S M (1995) The Lower Paleozoic granitic magmatisin near Ranikhet, Kumaun Himalaya M a p and trace element geochemistry and tectonic setting. Joui Geol Soc Tndia,v46, pp 15-25 Rawat, B S and Thakur, VC (1988) Lithostratigraphy and stiuctuie of the Central Crystallines and the Phanerozoic metasedimentaries of the Laha~dand Bharmour regions of Himaclial in Noith western Himalaya Pub1 Cent Adv Study in Gcol , v3(NS),pp 87-111 Scliarei, U , Xu, R H a n d Allegre, C J (1986) U-(Tli)-Pb systematic5 and age of Himalayan leucogranites, south Tibet Eai th Planet Sci. Lett, v 77, pp 35-48 Sh‘ih, S K (1991) Stratigraphic setting of the Phanerozoic rocks along the northern boundary of the Indian Plate. In .K K Sharma (Ed.), Geology and Geodynamic Evolution o f the Himalayan Collision Zone Pergamon, Oxford, pp 317-328 Shah, S K , Shaima, VP, IZainci, B K and Razdan, M L (1988) Field Excursion Guide to parts of Kashmir Valley Deptt of Geol Univ of Jammu, 10 p Sharma, K K (1983) Granitoid Belts o f tlie Himalayas In Shams, F A (Fd ), Granites of 1-Iimalayas, Karakoram a n d Hindukush, Punjab IJniv, Lahore, pp 11-37 Smha, A K (1989) Geology of Higher Central 1-limalayai. John Wiley and Son%,Chichester, 219 p

Srikantia, S.V. (1977) Sedimentary cycle in the Himalaya and their significance on the orogenic evolution of the mountain belt. Colloq. Ind. CNRS,v. 268, pp.395-407. Srikantia, S.V. and Bhargava, O.N. (1979) The Tandi Group o f Lahaul-its geology and relationship with the Central Himalayan gneisses. Jour. Geol. Soc. India, v.20, pp. 531-539. Thakur, V.C. (1992) Geology of Western Himalaya, Pergamon, London, 362 p. Thakur, V.C., Rawat, B.S. a n d Islam, R. (1990) Zanskar Crystallines - Some observations on its lithostratigraphy, deformation, metamorphism and regional framework. Jour. Him. Ceol.,~.1, pp.ll-25. Trivedi, J.R., Gopalan, K. and Valdiya, K.S. (1984) Rb-Sr ages of granitic rocks within the Lesser FIimalayan nappes, Kumaun, India. Jour. Geol. Soc. India, v. 25, pp. 641-654. Trivedi, J.R., Sharina, K.K. and Gopalan, K. (1986)Widespread Caledonian magmatism in Himalaya and its significance. Terracognita, v. 6, p.144. Valdiya, K.S. (1969)The stromatolites of the Lesser Himalayan carbonate formations and Vindhyan. Jour. Geol. Soc. India, v.10, pp. 1-25. Valdiya, K.S. (1973)Tectonic framework of India : A review and interpretation of recent structural and tectonic studies. Bull. Geophy. Res.,v.ll,pp.79-114. Valdiya, K.S.(1980) Geology o f the Kumaun Lesser Himalaya. WTHG, Dehra Dun. 291p. Valdiya, K.S.(1984) Evolution of Himalaya. Tectonophysics. v . 1 0 5 , ~229-248. ~. Valdiya, K.S.(1993) Evidence for Pan-African-Cadomian tectonic upheavals in Himalayn. Jour. Palaeontol. Soc. India, v.38, pp.51-62. Valdiya, K.S. (1995)Proterozoic sedimentation and Pan-African geodynamic development in the Himalaya. Precamb. Res.,v. 74,pp. 35-55. Wadia, D.N. (1931) The syntaxis of the northwest Himalaya : Its rocks tectonics and orogeny. Rec. Geol. Surv. India,v. 65,pp. 189-220. Wadia, D.N. (3934) The Cambrian-Trias sequence of Northwestern Kashmir. Rec. Geol. Surv. Tndia,v. 78,pp. 121-176. Wyborn, L.A.I., Wyborn, D., Warren, R.G. and Drummond, B.J. (1992) Proterozoic granite types in Australia: implication for lower crust compositjon, structure and evolution. Trans. R. Soc. Edinburgh, Earth Sciences,v. 83, pp.201-209. Zwart, IHJ. (1967) The duality o f orogenic belts. Geologic en Mijnbouw. v.46, pp.383-309.

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