Implications of pre-mesozoic orogeny in the geological evolution of the Himalaya and Indo-Gangetic Plains

Tectonophysics, 62 (1980) 67-86 @ Elsevier Scientific Publishing Company,

67 A~terdam

- Printed

in The Netherlands

~PLICATIONS OF PRE-MESOZOIC OROGENY IN THE GEOLOGICAL EVOLUTION OF THE HIMALAYA AND INDOGANGETIC PLAINS

A.K. JAIN *, R.K. GOEL and N.G.K. NAfR Deportment (Received

of Earth Sciences,.University

February

of Roorkee,

Roorkee-247672,

UP. (India)

23,197Q)

ABSTRACT Jain, A.K., Goel, R.K. and Nair, N.G.K., 1980. Implications of Pre-Mesozoic orogeny in the geological evolution of the Himalaya and Indo-Gangetic plains. In: J.M. Tater (Editor), The Alpine-Himalayan Region. Tectonophysics, 62: 67-86. An integrated geological analysis of the Himalaya and Indo-Gangetic Plains demonstrates that the Great Vindhyan Basin incorporating large parts of these morphotectonic units were uplifted into an uneven landmass due to the Pre-Mesozoic erogenic cycle. This uneven landmass was eroded off largely during a considerable part of the Devonian and Carboniferous thereby causing partial absence of sedimentary sequences of these periods except in parts of the Tethys Himalaya. The Late Paleozoic epeirogenic movements brought about renewed sedimentation in the Lesser and Tethys Himalayas in the Krol and Tethys Basins, respectively, which was terminated by the Himalayan Orogeny during Late Cretaceous-Early Eocene.

INTRODUCTION The Himalayan Am between the Indus and Brahmaputra Valleys encompassing Precambrian to Neogene sediments and affected by prominent unconformities during Paleozoic and Mesozoic, penecontemporaneous volcanism and plutonic activity, is separated from the Archean Indian Shield by vast Holocene alluvium of the Indo-Gangetic Plains (Fig. 1). In the present paper an integrated analysis of the various morphotectonic zones of the Himalaya, Indo-Gangetic Plains and northern parts of the Peninsular India incorporating stratigraphy, magmatism, deformation and metamorphism has been presented for better understanding of geological evolution of northern parts of the Indian Subcontinent during Late Precambrian-Paleozoic. ~ SUBSURFACE

STRATIGRAPHY

OF THE INDO-GANGETIC

PLAINS

Geophysical investigations and drilling in the Indo-Gangetic Plains have revealed an uneven northerly sloping configuration of this basin thereby indi* Present.address: many.

Geological

Institute,

University

of Karlsruhe,

Karlsruhe,

West Ger-

\

HIMALAYAN

&---1 .

\

‘La

-_B

.._cc:

PEN~N~ULAG

A RC

I

L

5

INDIA

Fig. 1. Generalized geological map of the Indian Subcontinent showing main physiographic and morphotectonic units of the Himalayan Arc (modified after Gansser, 1964). Himalayan Arc: 1 - Sub-Himalaya (Tertiary. sediments). 2 - Lesser Himalaya (Late Precambrian-Eocene sediments); A - Outer Sedimentary Belt, B - Inner Sedimentary Belt, C - Lesser Himalayan metamorphics. 3 - Central Himalaya. 4 - Tethys Himalaya. 5 - Indus Suture Line. Peninsular India: X - Pre-Aravalli metamorphic3 (Dharwar, Eastern Chats, Banded Gneissic Complex, Bundelkhand Gneiss including Precambrian and younger acidic intrusives). V-- Vindhyan Group, Bijawam Aravalli, Cuddapah and other Later Precambrian sediments. DT - Deccan Traps, P - Late Paleozoic Gondwana. M - Mesozoic.

eating the continuity of the Late Prec~b~an-Lower Paleozoic Vindhy~ and the Late Paleozoic-Mesozoic Gondwana succession of the Peninsular India into the Lesser Himalaya (Fig. 2a). Five distinct basins have been delineated by NW-SE, NE-SW and N-S trending basement ridges (Rao, 1973; Karunakaran and Ranga Rae, 1976). In the Indus Basin, the basement is overlain by the Mesozoic and Cainozoic sediments thinning towards the Rajasthan platform (Anon, 1959). The Panjab Basin reveals southerly overlapping Neogene sediments beneath the younger akvium (Fig. 2b) while Rao (1973) has even postulated that the Eocene and Pre-Cainozoic sediments are due to the presence of dolomitic limestone in the deep well at Bahl and the outcrops of Eocene sediments in the Panjab Sub-Himalaya. In the adjoining Ganga Basin, Archean basement is unconformably over-

69

PENINSULAR

q EASIERN

GANGA

a4.w @BENGAL

BASIN

mh

Fig. 2. Tectonic map and geological cross-sections through the Indo-Gangetic Plains (after Rao, 197 3). Basement Ridges: 1 - Delhi-Lahore-Sargodha Ridge, 2 - Delhi-Muzaffarnagar Ridge, 3 - Faizabad Ridge, 4 - Monghyr-Saharsa Ridge. Location of wells: Z - Zira, ZZ- Adampur, ZZZ- Hoshiarpur, IV - Janauri, V - Jwalamukhi, VI - Kasganj, VZZUjhani, VZZZ- Tilbar, IX - Raxaul, X - Purnea. 1 - Archean basement, 2 - Vindhyan Group, 3 - Gondwana, 4 - Mesozoic, 5 - Rajmabal Trap, 6 - Paleogene, 7 - Paleocene, 8 - Neogene-Holocene,

lain by a Late Precambrian-Lower Paleozoic orthoquartzite-carbonate blanket-type stable-shelf association of the Vindhyan Group attaining considerable thickness towards the Himalayan foothills (Fig. 2c; Sastri et al., 1971; Rao, 1973; Karunakaran and Ranga Rao, 1976). Undeformed Neogene Siwahk molasse unconformably overlies the deformed Vindhyan Group except in the Raxaul deep well where a nearly 70-m thick strata of unknown affinity intervenes. However, Lower and Upper Gondwanas in the Raxaul deep well in the eastern Ganga Basin clearly demonstrate the northerly extension of the main Rajmahal Gondwana basin in the Indo-Gangetic Plains and involvement in the Eastern Himalayan tectonics (Fig. 2d; Metre, 1968; Rao, 1973). The eastern parts of the Indo-Gangetic Plains incorporate the ENE-WSW trending basement ridge of the Satpura-Shillong Belt sloping towards the Eastern Himalaya as well as the Bay of Bengal and the Naga Hills. The Jurassic Rajmahal Traps and Miocene sediments have been discovered in the

(Gael

Fig.

w. SPITE (pI~;p$yIo)

3. C~~~ek&km of Zate Precambriail-Patedzoic and Nair, 1~‘i?);~~~waI-~~naon (Shah

PRECAMBRIAN

CAMBRIAN

OROOVfClAh

SILURIAN

DE VONlAN

ARBONIFEROUS

PERMIAN

lRIA,SSIC

KA5HMlk

and

Sinha,

1974);

stratigraphy

GARHWAL

Nepal

(Fuchs,

of the Tethys

1975);

Sikkim

Himahya.

KUMAON

(Wager,

Kashmir

NEPAL

1939).

(Kri&nan,

N

1960);

SIKKIM

Western

+iti

Fig. 4. Correlation of Precambrian-Paleozoic stratigraphy of the Lesser Himalaya with Salt Range, Kashmir, Indo-Gangetic Plains and Peninsular India. Salt Range, Kashmir, Chamba (G.S.I., 1976); Simla Hills (Bhargave, 1972); Garhwal-Kumaon (Auden, 1934; Jain et al., 1971); Darjeeling (Sinha Roy, 1973); Arunachal Pradesh (Jain et al., 1974); Indo-Gangetic Plains (Sastri et al., 1971); and Peninsular India.

72

Bengal Basin over a very shallow basement (Rao, 1973) with the MesozoicCainozoic sedimental cover (Fig. 2e; Sengupta, 1966). Although the northern banks of the Br~maputra valley have not been drilled deeply enough to penetrate the Neogene cover, Mathur and Evans (1964) and Karunakaran and Ranga Rao (1976) have postulated Gondwana rocks beneath the Neogene sediments; Rao (1973) even suggests the Precambrian-Lower Paleozoic, Mesozoic and Paleogene successions beneath the alluvium (Fig. 2f). PRE-MESOZOIC

STRATIGRAPHY

OF THE HIMALAYA

Well-defined dorrelatable biostratigraphy of the Tethys Himalaya from Kashmir to Bhutan contrast against unfossiliferous Lesser Himalayan units (Figs. 3 and 4) with different lithostratigraphic correlation schemes. The following salient features are therefore impo~~t in the Pre-Mesozoic stratigraphy of the Himalaya: (1) Enormously thick Late Precambrian meta-argillite and gneiss of the Central Himalaya passing upwards in the Tethys Himalaya Cambrian sediments in most of the sections.

Fig. 5. Angular unconformity between the Muth Quartzite right bank of Pin Valley at Muth, Spiti valley, H.P.

and Carboniferous

Shale on

73

(2) Late Precambrian-Lower Paleozoic sediments being unconformably overlain by linearly disposed zoic rocks in the Krol Belt or thrust over the Permian (3) Pronounced Late Silurian-Early Devonian (Fig. 5) and disconformity during Late Carboniferous the Tethys Himalaya. LESSER

in the Lesser Himalaya Late Paleozoic-MesoGondwana Belt. angular unconformity or Early Permian in

HIMALAYA

The oldest Sundernagar Formation in the Inner Sedimentary Belt of the Himachal Lesser Himalaya, with orthoquartzite, slate and inter-stratified volcan&, is unconformably overlain by the Shah-Deoban carbonates which are unconformably overlain by the Simla and Jaunsar Groups of the Late Precambrian-Lower Paleozoic age as sequel to a Precambrian orogeny (the Shali Orogeny) (Srikantia, 1977). Elsewhere, the Late Precambrian-Lower Paleozoic unfossiliferous sequence is represented by impersistent intertonguing lithofacies (Gansser, 1964, 1974b; Valdiya, 1964a; Jain et al., 1971; Mehdi et al., 1972; Bhargava, 1972; Rupke, 1974; Fuchs, 1975; Le Fort, 1975). This can be broadly classified into the following facies which are characteristic of extensive platform conditions along the region, that subsequently became the Himalaya. Inner Lesser Himalaya (1) A lower orthoquartzite-slate sequence exposed only at those places where carbonate sequences intervene. The Saryu Valley Quartzite in Pithoragarh (Kumaon), Netala Quartzite in Bhargirathi valley and basal parts of the Shah Formation in Himachal Pradesh belong to this sequence. (2) Widespread argillo-calcareous inter-tonguing association with prolific Middle-Upper Riphean stromatolites. This incorporates the Shah Belt of Himachal Pradesh, Deoban Limestone in Garhwal, Uttarkashi Limestone along the Bhagirathi Valley, Chamoli Limestone along the Alaknanda Valley, Tejam Limestone, Kapkot Dolomite, Gangolihat Dolomite, Sor Slate and Pithoragarh Formation in Kumaon and the midland sedimentary succession of Nepal. (3) An upper orthoquartzitecarbonate stable shelf association of Gahrwal and Kumaon extending into the Lower Paleozoic and represented by Gamri Quartzite, Dichli Dolomite, Lameri Formation, Chamoli Quartzite and Berinag Quartzite having numerous interstratified spilitic volcanics. Outer Lesser Himalaya (1) Coeval Simla and Jaunsar Groups of the Late Precambrian-Lower Paleozoic with a quartziteshale-limestone sequence at the base (the Basantpur and Mandhali Formations); predominantly argillaceous succession

Fig. 6. Angular unconformity between the Nagthat Quartzite and Late Paleozoic Blaini Formation in Song Valley, Garhwal Lesser Himalaya. Nagthat Quartzite dips steeply towards NE and lies beneath the Lower Blaini Diamictite along undulatory eroded surface.

in the middle (the Kunihar-Chaossa-Chandpur Formations) and an upper arenaceous succession (the Sanjauli and Nagthat Formations). In parts of the Garhwal-Kumaon Himalaya, the Simla Group forms a major belt in the middle having undifferentiated Simla and Chandpur type sediments capped by the Nagthat Qua&rite. (2) The Blaini and Infra Krol-Krol-Tal sequence in the Krol Belt of the Late Paleozoic-Mesozoic was deposited over a strongly folded sedimentary basement with marked angular unconformity (Fig. 6). The Krol Belt sediments extend beneath the Siwalki Group of the Sub-Himalaya and were encountered in the Mohand deep well in U.P. and in the Janauri well in the Panjab (Karunakaran and Ranga Rao, 1976). (3) In the Himaehal Pradesh the Outer Sedimentary Belt is overlapped by the Inner Sedimentary Belt. In the Eastern Himalaya, the Haling Phyllite, Jaintia Quartzite and Buxa Dolomite of Sikkim and Bhutan, Miri Quartzite with dolomite-limestone bands and Abor Volcanics of Arunachal Pradesh of Late Precambrian-Lower Paleozoic age belong to Outer Sedimentary Belt. This is overlain unconformably by Permian “Gondwana” sediments in the Rangit window or thrust over the latter in southern parts of the Lesser Himalaya.

75 CENTRAL HIMALAYA

The Central Himalaya encompasses extensive developments of metamorphosed, mainly Late Precambrian rocks, e.g., the Salkhala and Dogra Groups in Kashmir; the Vaikrita and Haimanta Groups in Himachal; the Central Crystalline Group in Kumaon; the Tibetan slab in Nepal; the Paro-Darjeeling Gneiss in Sikkim-Bhutan; and the Bomdila-Sela Group in Arunachal Pradesh. Con~n~ing evidence for their Late Precambrian age is ava~able from the demonstrable gradual passage upwards into fossiliferous Cambro-Ordovician sediments in the Tethys Himalaya in Kashmir, Lahaul-Spiti Kumaon, Nepal, Sikkim and Bhutan (Stoliczka, 1866; Lydekker, 1883; Griesbach, 1891; Hayden, 1904; Heim and Gansser, 1939; Wager, 1939; Gansser, 1964; Fuchs, 1975). Isolated occurrences of folded unmetamorphosed Paleozoic fossiliferous sediments over the met~orphics much to the south of Tethys Himalaya at Phulchauki in Nepal and Tangchu in Bhutan (Gansser, 1964; Singh, 1973) again confirm a Late Precambrian age for these crystallines. Recent discoveries of scleractinian corals and cephalopod mollusks in calcschist within the Central Himalayan gneissic terrain of Lahaul provide evidence for the age of some parts of the Central Himalayan sediments to be Jurassic with their deformation and met~o~hism being Tertiary (Powell and Conaghan, 1973a; Picket et al., 1975). The Central Himalayan metamorphics separating the Kashmir-Chamba structural basin from the LahaulSpiti succession in the north seem to represent metamorphosed sediments affected by high geothermal gradient and deformation in this part of the axial zone. ~temativeiy, these Mesozoic sediments may be viewed as no more than a thin veneer over the Precambrian basement and that this was subsequently synclinally infolded into the underlying basement during the Himalayan Orogeny (Jhingran et al., 1976). Available evidence indicates that Precambrian basement of the Central Himalayan region of Kumaon includes rocks as old as 1800 f 100 m.y. (Bhanot et al., 1977); these were variously and extensively reconstitu~d by later metamorph~m. TETHYS HIMALAYA

*

Fig. 3 schematically presents the Paleozoic stratigraphy and correlation of the Tethys Himalayan sediments. (1)The Late Prec~b~~~arnb~~ contact in invariably gradational along most of the sections where the Central Himalayan crystallines pass un* The continued usage of the term “Tethys Himalaya” (=Tibetan Himalaya) by some authors is somewhat unfortunate as the authors are aware how many workers wince every time this term is used in the geographic sense. However, a substitute to it is not proposed since this term has attained considerable popularity in the literature to mean the fossiliferous sequence occurring north of Central crystalline axis. Resides, a substitute like “Inner Himalaya”, for instance, also is not without confusion.

interruptedly into the fossiliferous Cambrian. In Kashmir, the Salkhala Group merges without any break into the Dogra slate which is overlain by trilobite-bearing Cambrian sediments. To the southeast in Spiti, the argillaceous Haimanta Group grades upward into poorly fossiliferous ferruginous slate, micaceous quartzite and limestone of Middle to Upper Cambrian age. In the Kumaon Himalaya, the Late Precambrian-Lower Cambrian Martoli Formation is unconformably overlain by the Ralam Conglomerate (Heim and Gansser, 1939). (2) Although the Lower Paleozoic of Kashmir may perhaps be devoid of any marked stratigraphic breaks, Cambrian-Ordovician unconformity is well marked in Spiti, where the basal Ordovician conglomerate is transgressive over the gently folded Cambrian sequence (Hayden, 1904). (3) The Muth Quartzite is conspicuous throughout the Tethys Himalaya and marks a change from predominantly argillocalcareous Lower Paleozoic succession to arenaceous Silurian-Devonian from Kashmir to Nepal. Controversy regarding its age still persists and an evaluation of the Muth Formation is significant in the type section of the Pin Valley of Spiti rather than of its numerous outcrops where black Carboniferous shale overlies the formation with distinct angular unconformity (Fig. 5). Goel and Nair (1977) located two lithostratigraphic units at Muth: the lower quartzite making up about two-thirds of the succession being demonstrably part of the same sedimentary cycle as the underlying Llandovery (and perhaps Wenlock) Thanam Formation; this unit, making up the major part of the succession, should be classified as the Muth Quartzite, sensu stricto. The uppermost one-third of quartzite succession is obviously better bedded than the Muth, sensu stricto, and is separated from it by discontinuous rusty dolomite with evidence of minor disconformity. No fossils have been recorded from either quartzitic unit at Muth, and dolomite failed to yield a microfauna on prolonged acid leaching. Nevertheless, it is suggested that this part of the section at Muth may be part of the Lipak Formation (Lipak “Series” of Hayden, 1904, p. 44) in which case it would indeed be of Devonian age. Unequivocal Devonian (probably Givetian or Frasnian) faunas occur in the quartzite-shale-limestone succession of the Lipak Formation in the Lipak and Yulang valleys (Reed, 1911) southeast of Muth. Even if the upper part of the quartzite succession at Muth does not belong to the Lipak Formation (and knowledge of the Muth and Lipak formations is especially scrappy and unsatisfactory for the entire Spiti and Bashahr regions) it must be emphasized that there are two Silurian-Devonian sedimentary cycles in Spiti and adjacent regions. The older to which the Muth quartzite S.S. belongs, is the last phase of a marine regression of age somewhere in the Early or Middle Silurian (Llandovery/Wenlock). The other sedimentary cycle (the Lipak Formation) is a transgressive and regressive set of events that ocurred at some time in the late Middle Devonian to early Late Devonian. The same two sedimentary cycles are clearly in evidence in Kashmir and recognition of this may help clarify the confusion which surrounds the

77

“Muth problem” in that region. A large collection from Early and Middle Paleozoic sections at Kashmir have yielded abundant Silurian brachiopods from the basal quartzite of what many workers (e.g. Middlemiss, 1910) have regarded as Muth Quartzite in the Naubug valley; no unequivocally Late Silurian or Early Devonian faunas could be obtained (J.A. Talent, pers. comm., 1977). Evidence of a Devonian transgression more or less corresponding in time to the Lipak Formation has been brought forward by Gupta (1967). Conodont faunas indicative of horizons close to the Middle Devonian-Late Devonian boundary are now known from several localities in Kumaon, Kishtwar, near the boundary of Spiti and Ladakh and central Nepal (Gupta, 1975a, b). All of these are associated with sequences including quartz& which are assumed to be developments of the Muth Quartzite, but an alternative explanation is that some or all of these quartzites may not in fact correlate with the Muth Quartzite, but rather be correlatives of the Lipak sedimentary cycle. The desirability of detailed investigation of the stratigraphy and faunas of the Muth and Lipak Formations bed by bed is manifest. (4) In eastern Spiti, Devonian and Carboniferous are well developed while elsewhere Late Carboniferous strata disconformably overlie the Paleozoic. This break is most conspicuous in the Salt Range from about Middle Cambrian to about the beginning of the Permian while in the east it covers parts of Devonian-Carboniferous. PRE-MESOZOIC

MAGMATISM

The tectonomagmatic history of the Himalaya during Late PrecambrianLower Paleozoic correlates a prolonged, antedating and unrelated magmatism to the Cainozoic event; typical of which are spilitic volcanism penecontemporaneous with elastic sedimentation under distinctly stable shelf platform conditions and acidic plutons. According to Wakhaloo and Shah (1968), the Baifliaz Volcanics containing spilitic lava flows and pyroclastic rocks are associated with basal Cambrian sediments in western Pir Panjal. In the Shah Structural Belt of Himachal Pradesh, Late Precambrian spilitic submarine volcanism is manifested as the Dalhousie Traps, the Dharamsala Traps Darang and the Mandi Traps which are typically confined close to the base of the Shah Formations (Srikantia, 1973; Patwardhan and Bhandari, 1974). Further eastward, numerous bodies of dolerite, basalt, spilitic lave flows, metatuff and pyroclastics in the Lower Paleozoic Chandpur-Nagthat Formations of the Outer Lesser Gahrwal and Kumaon Himalayas (Auden, 1934) are also extensively associated with arenaceous sediments of the Inner Lesser Himalayan Belt, e.g., Karnprayag Volcanics, etc. (Gansser, 1964; Kumar and Agrawal, 1975). Rao et al. (1974) noted the spilitic character of the Bhowali Volcanics intruding the Nagthat Quartzite at the geosynclinal stage. In Arunachal Himalaya the Abor Volcanics of the Late Precambrian-Lower Paleozoic age containing penecontemporaneous lava flows, sills, dykes, volcanic breccia and metatuffs are associated with various lithounits of the Siang

diorite

Mylonitized

Quartz

granitoid

Barkot, Yamuna Valley, Garhwal

Darlaghat, H.P. Tatapani, H.P. Kuwa, Yamuna Valley, Garh wal

diabase

Amygdaloidal Greenstone Diorite basite

Gneiss

Kulu, H.P. Kulu, H.P.

Himalayan

of

Nepal Manali-Jaspa, H.P. Nepal Mandi, H.P. Mandi, H.P. Mandi, H.P. Mandi, H.P. Mandi, H.P. Mandi, H.P. Dalhousie Kumaon Kumaon West Nepal Prospect Hill Simla Rohtang Pass Manali, H.P.

Location samples

AGES OF CERTAIN

Migrnatite gneiss Amphibolite and biotite

Central

Migmatized garnetiferous mica schist Crystallines Mandi Granite Mandi Granite Leueocratic Mandi Granite Metabasic xenoliths in granite Muscovite (Mandi Granite) Muscovite (Mandi Granite) Pegmatite K-feldspar in Almora Granite K-feldspar in Almora augen gneiss Granite pebble in Eocene conglomerate Amphibolite

-

Rock/minerals

LATE PRECAMBRIAN-PALEOZOIC

TABLE I

410-t 338rt 710 414 325

K/Ar K/Ar

2 2 2

10 10

500 Lf: 8 316 to 366

9

581 zt

Rb/Sr whole rock isochron K/Ar

ages

540 to 1194 730 -+ 20 693 500 rf: 100 545 + 12 311 rt 6 640 + 20 368 + 8.5 322+ 10 350+ 12 363 + 5 315t 5 354 343 _+ 17

Absolute in m.y.

K/Ar K/Ar K/Ar RblSr whole rock isochron Rb/Sr Rb/Sr Rb/Sr KlAr K/Ar K/Ar K/Ar

Method of analysis

ROCKS

K/Ar K/Ar K/Ar

-

5 -

5

-

-

3 3 3 1 1 -

1 -

-

Number of samples

HIMALAYAN

--

and Miller (197 2)

Sinha and Bagdasarian (1976)

..___

Mehta (1977) Mehta and Rex (in Mehta, 1977) Sinha (1977) Ashgirie et al. (1977)

Saxena

(1971)

et al. (1974) Krummenechter

Bhanot

Mehta (1977)

Khan and Tater (1970) Pande and Kumar (1974) Bordet et al. (1971) JEger et al. (1971)

Author

2

79

and Miri Groups (Jam and Thakur, 1978). A prePermian age of this volcanism is evident from the truncation of the NNW-SSE structural trends of the Abor Volcanics and Siang-Miri Groups by the Permian Gondwana Belt and by the presence of rock fragments of Siang-Miri rocks and Abor Volcanits in the Gondwana sediments. The peak of the Abor Volcanism seems to have been reached probably during the Lower Paleozoic under stable shelf platform conditions of sedimentation. Late Paleozoic volcanic activity nevertheless occurred in the Gondwana Belt of the Arunachal Himalaya (Acharyya et al., 1975) parallelling the Panjal Volcanics of the NW Himalaya. Poor stratigraphic control over the plutonic igneous activity, dearth of radiometric dates and their proper evaluation hampers visualization of the detailed tectonomagmatic cycles in the early geological history of the Himalaya. Nevertheless, a few absolute ages of the Himalayan granitoids indicate the possibility of Late Precambrian-Lower Paleozoic plutonic magmatic activity which was subsequently overprinted by strong Cainozoic deformation in different tectonic zones of the Himalaya (Table I). METAMORPHISM

AND DEFORMATION

Age determinations of minerals and structural analyses of the Central and Lesser Himalayan crystallines indicate strong Cainozoic metamorphism and deformation (Gansser, 1964; Krummenacher, 1971; Ray and Naha, 1971; Powell and Conaghan, 1973a; Frank et al., 1973; Le Fort, 1975) but many isolated regions in the Himalaya have evinced much older ages suggesting Late Precambrian-Lower Paleozoic metamorphism and deformation. That an older metamorphic episode in the Himalaya was subsequently overprinted by the Cainozoic Himalayan metamorphism is also evident from a few mineral ages (Table I). The following evidence also supports Pre-Cainozoic metamorphism and deformation probably during Late Precambrian-Lower Paleozoic: (1) Markedly unconformable Eocene Subathu Formation over folded and deformed stratigraphic units of the Lesser Himalaya including the epigrade metamorphic basement of the Simla Group in parts of Himachal and GarhWd.

(2) Pre-Permian E-W trends in the Rupshu region overprinted by the NW-SE Cainozoic trends (Berthelsen, 1953). Likewise, Srikantia et al. (1977) correlated the northeast-trending folds in the Haimanta Group being truncated by northwest-trending Himalayan folds to the Kurgiakh Orogeny (Caledonian) in the Zanskar valley Ladakh. (3) Marked angular unconformity between folded Simla and Jaunsar Groups and the Late Paleozoic Blaini Formation (Fig. 5) which was deposited over a epimetamorphosed and mildly deformed basement of Precambrian-Lower Paleozoic rocks (Bhargava, 1972; Jain and Varadaraj, 1978). (4) Early NNE-SSW trending compressed isoclinal reclined folds of the

80

Almora-Dudatoli crystallines of the Lesser Kumaon metamorphic belt being absent from the Garhwal Group and Blaini Krol-Tal sequence (Ghose, 1973). (5) Unconformity between the epigrade metamorphosed folded basement of Daling Phyllite/Buxa Dolomite and Permian Gondwanas in the Rangit window (Sinha Roy, 1973; Jain and Thakur, 1975). Sinha Roy (1973) recognized an older deformational phase in the Daling-Darjeeling group that resulted in flattened flexture-slip highly appressed to rootless folds associated with an axial plane cleavage. (6) Low grade metamorphic and deformed sedimentary cfasts in the Late Paleozoic diamicites of the Himalaya, e.g. Rangit Pebble Slate, the Blaini Formation and their equivalents in Kashmir and other parts of the Tethys Himalaya. These have clasts of slate, phyllite and schist having distinct foliation; phyllite exhibiting strain-slip cleavage deforming an earlier foliation within the clasts (Thakur and Pande, 1972). Other clasts include volcanics, muscovite gneiss, schistose quartzite and mylonitized quartzite and dolomitic limestone with silica veins along joints terminating against the clast boundaries. The Lesser Himalayan low grade metasediments and other rocks were thus subjected to extensive erosion after Lower Paleozoic (Balasubramanian, 1975; Jain and Varadaraj, 1978). (7) In the Siang district, ~nach~ Pradesh, Thakur and Jain (1974) delineated a large inverted domal “Siang Structure” which is deformed along NNW-SSE and ENE-WSW trends, the former sharply abut the ENE-WSW trending Gondwana and Siwalik Belts and seem to have originated prior to the Late Paleozoic Gondwana. PRE-MESOZOIC INDO-GANGETIC

OROGENY PLAINS

IN

GEOLOkCAL

HISTORY

OF

HIMALAYA

AND

Opinions regarding the earlier orogenies in the Himalaya vary considerably from Powell and Conaghan (1973b), Frank et al. (1973), Gansser (1974a) and Le Fort (1975) propounding mainly the Cainozoic Orogeny in its geological history. Many earlier erogenic and epeirogenic movements have been visualized by Berthelsen (1953), Valdiya (1964b), Fuchs (1968, 1975), Saxena (1971a, b), Rupke (1974) and Pande (1975). Wadia (1957), Krishnaswami and Swaminath (1965), Fuchs (1968) and Saxena (1971a, b) postulated that a Central Himalayan crystalline ridge separating the fossiliferous Tethyan marine sequence from unfossiliferous Lesser Him~ay~ rocks controlled sedimentation in both the realms since the Late Proterozoic or Paleozoic. Valdiya (1964b) visualized the geological history of the Himalaya as extending from Proterozoic times, with Precambrian, “Caledonian” “Hercynian” and Himalayan movements. Saxena (1971a) likewise has postulated five distinct epeirogenic and erogenic movements in the Himalaya, occurring in the period between the Late Proterozoic and the Cainozoic. Within the framework of plate tectonics, the Cainozoic Himalayan Arc has originated due to continent-to-continent collision by northward underthrust-

81

ing of the India Plate beneath the Asiatic Plate since the Late Mesozoic (Dewey and Bird, 1970; Powell and Conaghan, 1973b,l975; Le Fort, 1975). Powell and Conaghan (197313) have proposed a detailed Cainozoic geological history of Himalaya in relations to plate tectonics. Recent geological and geophysical investigations in the Indo-Gangetic Plains have clearly demonstrated that many stratigraphic elements of the Peninsular India extend beneath the thick Neogene cover (Sastri et al., 1971; The Precambrian-Lower Paleozoic Vindhyan Group 1973). Rao, encountered in many deep wells in the Indo-Gangetic Plains shows maximum thickness near the Himalayan foothills. Furthermore, Late Precambrian and presumably Lower Paleozoic sediments of the Lesser Himalaya, Central Himalaya and Tethys Himalaya have a common sedimentation history. In the Tethys Himalayan succession of Kumaon and Nepal, Banerjee (1974), Shah and Sinha (1974) and Colchen (1975) have indicated very shallow water platform conditions with northerly paleocurrents during Cambrian and Ordovician. As in the Lesser Himalaya, shallow platform conditions prevailed throughout its geological history, except during the Late Cretaceous. As has been visualized earlier by Krishnan and Swaminath (1959), Late Precambrian-Lower Paleozoic sediments extend beneath the Indo-Gangetic Plains into the Lesser Himalaya in the northerly sloping Great Vindhyan Basin with maximum depth along its northern margin. It seems obvious that this basin was connected to the Tethys Ocean in the Lower Paleozoic so that the Vindhyan Group was deposited over regions now occupied by the Indian Shield, the Indo-Gangetic Plains, and the Himalaya. In the Central Himalaya, intense Cainozoic metamorphism and deformation have largely obliterated the original character of the sediments, but monotonous argillaceous, calcareous and arenaceous lithologies are still found in Kumaon; these have been interpreted as having been deposited over a Proterozoic basement (Jhingran et al., 1976). Subsequent geological history involves the uplift of large parts of the Lesser and Central Himalaya. Two Late Paleozoic-Mesozoic basins were thus evolved over this basement: (a) the Krol Basin of the Lesser Himalaya extending southwards beneath the Sub-Himalaya and into the Indo-Gangetic Plains and comprising Gondwana-type diamictite sediments at the base, and (b) the Tethys Basin in the north. These basins were largely deriving detritus from this mildly deformed basement. The Himalayan cycle was initiated in the Late Paleozoic with the deposition of glaciomarine sediments in both basins along with penecontemporaneous volcanism. SUMMARY

AND CONCLUSIONS

An integrated analysis of Late Precambrian-Lower Paleozoic stratigraphy, magmatism, deformation and metamorphism along the northern parts of the Indian subcontinent clearly demonstrates that considerable parts of the Himalaya have evolved from the Great Vindhyan Basin; the Holocene sedimentation of the Indo-Gangetic Plains being the youngest in its evolution.

82

I -------

--

GREAT

VIN~~HYAN BASIN

f

7

’

-

~~ 1

/

Fig. 7. Schematic cross-section across morphotectonic units of the Indian subcontinent during Late Paleozoic-Mesozoic. 1 - Indian Archean Basement. 2, 3, 5 -Uplifted Pre2 - Central Himalayan metamorphics and cambrian-Lower Paleozoic basement. granitoids (Salkhala and Valkrita Groups, Central Crystalline Group). 3 - Southern CambroTethys Himalaya (A - Dogra Slate, Haimanta Group, Martoli Formation, Silurian argillites, B - Muth Quartzite). 5 - Vindhyan Ranges, Indo-Gangetic Plains and Southern Lesser Himalaya. A - Areno-Calcareous sediments: Vindhyan sandstone, Sundernagar Group, Shali-Deoban Groups, Garhwal Group, Buxa Pormation; B - Calcareous intercalations; C - Argillaceous rocks: Simla Group, Chandpur Group; I) - Volcanics: Mandi-Darla, Bhowali-K~nprayag, Abor. 4 - Late Paleozoic-Mesozoic Basins: A - marginal Krol Basin; B - Tethys Basin.

Prior to the advent of the Himalayan Orogeny in the Late Cretaceous, the Indian Plate had the following morphotectonic units along its northern margin on the continential crust (Fig. 7): (a) The Archaean shield of metamorphic and igneous rocks of Aravalli and Satpura Provinces with the Bundelkhand massif along the northern margin. The Archaean basement was covered by a thin veneer of Wndhyan sedimentary prism ~icken~g towards the north. (b) A marginal Krol Basin to the Indian shield evolved during Late Paleozoic-Mesozoic and received sediments from the southern as well as northern provenances. (c) Uplifted Lesser and Central Wimalayan terrain of Late ProterozoicLower Paleozoic sediments, episodic and medic-volc~ic rocks of the Paleozoic cycle forming the provenance of Late ~eo~ic-Mesozoic sediments. (d) Open epicontinental Tethys ocean to the north.

83 ACKNOWLEDGEMENTS

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and their

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Int. Geol. Congr., 11; 269-282. Wadia, D.N., 1967. Geology of India, 3rd ed. Macmillan, London, 536 pp. Wager, L.R., 1939. The Lachi Series of North Sikkim. Rec. Geol. Surv. India, 74: 171188. Wakhaloo, S.N. and Shah, S.K., 1968. A note on the Bafliaz Volcanics of Western Pir Panjal. Pub. Cent. Adv. Study Geol. Punjab Univ., 5: 53-64. Note added in proof An undoubtful Late Llandovery or Early Wenlockage of the Muth Quartzite is further indicated from the abundant Pentamerid brachiopod fauna collected by the two authors (Jain and Goel) in situ from a basal section of the Muth Quartzite exposed along SumnaLapthal track in Kiogad valley of the Thethys region of the Garhwal Himalaya during the 1978 expedition.