Dense mineral data from the northwestern Himalayan foreland sedimentary rocks and recent river sediments: evaluation of the hinterland

Journal of Asian Earth Sciences 23 (2004) 25–35 www.elsevier.com/locate/jseaes

Dense mineral data from the northwestern Himalayan foreland sedimentary rocks and recent river sediments: evaluation of the hinterland B.P. Singh*, J.S. Pawar, S.K. Karlupia Postgraduate Department of Geology, University of Jammu, Jammu 180006, India Received 28 March 2002; revised 16 October 2002; accepted 11 March 2003

Abstract The World’s largest peripheral foreland basin, developed in front of the rising Himalaya, incorporates a sedimentary pile on the order of 104 m in thickness. Temporal variation in the heavy mineral record exists in the northwestern Himalayan Foreland succession due to a change in the composition of the hinterland. This study was conducted in order to correlate the heavy minerals occurring in sedimentary rocks with those of the present day small rivers/streams flowing exclusively either in the Higher Himalaya or in the Lesser Himalaya. The present study confirms some of the earlier views demonstrating temporal variation in the heavy minerals in the Cenozoic Himalayan Foreland sequences. In addition, their correlation with the heavy minerals of recent river-deposited sediments help in identifying exact sources which became positive areas due to tectonic rising of the Himalaya at different stages. The results suggest that the heavy mineral suites were mainly contributed from the low- to medium-grade metamorphic provenance at the initial stages and from the high-grade metamorphic provenance at the later stage of foreland sedimentation. This may be associated with the shifting of the channel pattern from axial to transverse as mountain chains grown in width over time. Also, Higher Himalayan Baspa river sediments contain staurolite and kyanite, in addition to tourmaline, epidote, garnet and other minor heavy minerals whereas Bhuzas stream sediments contain sillimanite in addition to staurolite, kyanite, tourmaline, epidote and garnet. Similarities in the heavy minerals exclusively derived from the Higher/Lesser Himalaya, and the Cenozoic heavy minerals of the Himalayan Foreland in the Jammu area suggest that staurolite is a contribution of the hinterland during the earlier stage and kyanite is a contribution of the Higher Himalaya during the later stage. Among the three mineral markers, the sillimanite-bearing suite was derived at a still later stage from the Lesser Himalaya and/or Higher Himalaya due to successive emplacement of the thrust sheets. q 2003 Elsevier Ltd. All rights reserved. Keywords: Heavy minerals; Provenance; Recent sediments; Cenozoic succession; Himalayan foreland

1. Introduction Heavy minerals occurring in sediments and sedimentary rocks are used as a guide for source-rock characterization, lithological variation, heavy minerals zonation and dispersal pattern. Heavy mineral suites provide a mineralogical basis by which the two source areas may be distinguished (Morton et al., 1992). Heavy minerals are additionally useful in evaluating pre-erosional weathering and tectonic history of the source terrain (e.g. Nechaev and Isohording, 1993). Some of the heavy minerals are lost during surface weathering and transportation, and the relative proportions * Corresponding author. E-mail address: [email protected] (B.P. Singh). 1367-9120/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S1367-9120(03)00097-X

of stable heavy minerals (ZTR) increase. Also, unstable heavy minerals disappear during intrastratal solution in the process of diagenesis and only stable heavy minerals remain in the rocks (Pettijohn, 1975). Sorkhabi and Arita (1997a) evaluated the effects of diagenesis in the heavy minerals of the Siwalik Group and interpreted that intrastratal solution is low in these sequences and these can be utilized for provenance determination. Short distance streams and rivers, which exclusively flow in specific terrains, and deposit denudation products of those terrains seems significant for correlation purposes. In this respect, heavy minerals data were collected from the Baspa river (Fig. 1) flowing for nearly 35 km (exclusively in the Higher Himalaya) and the Bhuzas stream extending for more than 50 km (exclusively in the Lesser Himalaya). The Himalayan Foreland succession shows temporal variation in

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Fig. 1. Outline map of northern India showing location of the areas under study.

the heavy minerals record in the Jammu area (Fig. 1) and was used for correlation with the recent sediments. Based on a major study on heavy minerals of the Cenozoic succession of the northwestern Himalaya, Raju and Dehadrai (1962) and Raju (1967) concluded that staurolite, kyanite, hornblende, sillimanite, andalusite and sphene have a restricted vertical distribution and serve as positive mineral markers for different horizons. They found that the Lower Siwalik contains staurolite and epidote besides garnet, tourmaline and zircon. The Middle Siwalik is represented by kyanite whereas the Upper Siwalik sediments are characterized by sillimanite and hornblende. Sinha and Khan (1965) and Sinha (1970) studied the heavy minerals of the Siwalik Group in parts of Himachal Pradesh and Uttar Pradesh for provenance determination, and suggested a metamorphic provenance from the Himalaya for them. Chaudhri (1972, 1975) also studied heavy minerals of the Tertiary sedimentary rocks and suggested a northerly provenance. Tandon (1972) investigated heavy minerals of the Siwalik sequences for part of the Kumaun area and confirmed the earlier workers view that the Lower Siwalik contains staurolite as a marker and the Middle Siwalik contains kyanite as a marker. Chaudhri and Gill (1982) indicated, from the study of heavy mineral suites of recent sediments in Sukhna Lake in the vicinity of the Siwalik sequence at Chandigarh, that the mineral assemblage of lacustrine sediments is the same as that of the local Siwalik Group rocks. Chaudhri and Grewal (1984) studied heavy minerals from fluvio-glacial and fluvial sediments of

Kashmir and suggested that heavy minerals show more directional arrangement because of higher density. Singh et al. (1990), on the basis of the occurrence of garnet, epidote, chlorite, biotite and staurolite in the Murree Group, suggested a low to medium grade-metamorphic source. Singh and Tiwari (1996) studied heavy minerals of Ganga river sediments near Varanasi, and suggested their recycling and derivation from the Himalaya. Sorkhabi and Arita (1997a) gave a detail account of the works done by previous workers on the Cenozoic heavy minerals of the Himalayan Foreland and successfully correlated the heavy mineral zonation with the inverted metamorphism of the source terrain. Also, Sorkhabi and Arita (1997b) proposed a new method for approximate calculation of denudation rates of the Higher Himalaya based on metamorphic heavy minerals in the Siwalik molasses. In order to ascertain the temporal variation of heavy minerals in the Himalayan Foreland sedimentary successions and evaluate the sedimentological evidence regarding differences in the sources, the present study was carried out in the Jammu area. Also, the Himalayan Foreland heavy minerals are compared with the heavy mineral assemblages of the Higher Himalayan Baspa river (H.P.) and Lesser Himalayan Bhuzas stream (J and K) for the hinterland evaluation.

2. Geological setting The Himalayan Foreland developed due to continental collision. This collision resulted in crustal shortening accompanied by thrusting and folding, and uplift of the Higher Himalayan Crystallines over the Lesser Himalaya along the Main Central Thrust. A brief geological setting of the Himalaya is discussed below and the relationship of the tectonic units is shown in Fig. 2(A) and (B). The Tethys Himalaya consists of a sedimentary succession ranging in age from Late Proterozoic to Eocene and the contact is tectonic (e.g. Herren, 1987) with the Higher Himalayan Crystallines. The Tethyan sequence represents typical shelf sediments deposited on the Tethyan margin of India (Fuchs, 1982; Gaetani et al., 1985; Gaetani and Garzanti, 1991). The Higher Himalaya represents the high mountain chain and constitute a 10 –15 km thick slab consisting principally of metamorphic rocks (gneisses and schists) with granitic intrusions. The Higher Himalaya in Zanskar displays a domal arrangement with the highest-grade rocks in the core and the lowest-grade ones along the margin (Staubli, 1989; Vance and Harris, 1999). The Lesser Himalaya is bounded by the Main Central Thrust in the north and the Main Boundary Thrust (The Murree Thrust) in the south (Fig. 2). It consists of a number of more or less parallel belts of metasediments becoming

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Fig. 2. (A) Map of the Himalaya exhibiting major lithotectonic zones (modified after S.K. Acharyya, 2000); Also shown are the locations of the studied sections in different tectonic zones; (B) Cross-section along line A –B shown in the geological map.

increasingly older towards the north. These exhibit reverse metamorphism with the high-grade rocks lying at higher levels over the low-grade ones (Jangpangi et al., 1978; Thakur et al., 1990). The Sub-Himalaya forms a more or less continuous belt traceable from the Potwar Plateau in Pakistan to Arunachal Pradesh in India. It is bounded by the Main Boundary Thrust in the north and by the Main Frontal Thrust in the south. The Lower Tertiary sequences in the Jammu area comprises the Murree Group underlain by the Late Palaeocene-Eocene Subathu Formation and disconformably overlain by the Siwalik Group (Fig. 3(A)). The Murree succession contains mud – pebble conglomerate, sandstone, siltstone, mudstone and calcrete. The Siwalik Group is the most extensively developed siliciclastic succession in the Himalayan Foreland basin. Medlicott (1879) divided this Group into mudstone, sandstone-dominated Lower Siwalik, sandstone, mudstone, conglomerate-dominated Middle Siwalik and conglomerate-dominated Upper Siwalik. 2.1. Baspa catchment The Baspa river flows exclusively in the Higher Himalaya before joining the Satluj river at Karcham in the Kinnaur district of Himachal Pradesh. This river forms a V-shaped valley up to the Sangla and a deep george beyond its confluence with the Satluj river. The river deposited braid bars occur along the entire channel course. The bars contain gravels in the base followed by coarse sand on top. The Baspa river normally flows with laminar flow except for

summers when the flow becomes turbulent. In the Baspa catchment, the rock types are quartzite, carbonaceous phyllite, crystalline limestone and schist in the up-stream part followed by porphyroblastic gneiss that shows alternating bands of quartz-feldspar and biotite in the mid-stream part. Psammitic gneiss with quartzite, garnetiferous mica schist, porphyroblastic gneiss and greyish-brown gneiss intercalated with kyanite bands occur associated with tourmaline-bearing granite and biotite granite in the down-stream part of the river (Fig. 3(B)). For details of the geology and tectonic setting, see Tewari et al. (1978) and Singh and Jain (1993). 2.2. Bhuzas catchment The Bhuzas valley is a broad V-shaped valley in the Lesser Himalaya formed by the Bhuzas stream (Bhuzas þ Bhut Nalas) that ultimately joins the Chenab river at Atholi (Fig. 3(C)). The high discharge during summers under turbulent flow condition is responsible for deposition of gravel and sand bars along the stream course. The Lesser Himalayan tectonic unit mainly comprised of metamorphic rocks with granite intrusives is exposed along the Bhuzas stream. Rock Formation around Bhuzas valley represents high-grade metasediments of sillimanite-almandine-orthoclase subfacies revealing regional metamorphism of Barrovian-almandine-amphibole facies and NNW-SSE trending thrust separates high-grades metamorphic rocks from the low-grade metamorphic rocks (Jangpangi et al., 1978; Thakur et al., 1990). The metamorphic rocks are composed

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Fig. 3. (A) Geological map of the Cenozoic belt of the Jammu area; (B) Geological map showing disposition of various rock types in the Baspa river valley (modified after Tewari et al., 1978); (C) Geological map exhibiting different rock units in the Bhuzas valley (modified after Thakur et al., 1990).

of garnetiferous-biotite gneisses associated with sillimanite and kyanite schists, marble and lenticular calc-silicate gneisses. These metasediments are intruded by acid and basic intrusives of amphibolites, granites, pegmatites and quartz veins at some places (Fig. 3(C)).

3. Methodology Forty-four representative sand and sandstone samples from the Baspa river bed, Bhuzas stream bed and the Cenozoic succession of the Jammu area were selected for

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investigation. The bulk samples were reduced to an appropriate weight by coning and quartering and 50 gm of the sample was taken for heavy mineral separation. In every case, clay content was removed by repeated decantation and sediment samples were dried at room temperature. The Cenozoic sandstone samples were gently crushed and treated with acetic acid to remove the carbonate coating. The samples having ferruginous coating were treated with stannous chloride. The cleaned samples were washed with distilled water and dried in an oven at 110 8C. Heavy mineral separation was carried out in separating funnels using bromoform as the heavy liquid. Permanent mounts were prepared for all samples studied under a petrological microscope and total counts were made for every mineral slide.

4. Heavy minerals Although heavy mineral assemblages contain a variety of mineral species, they rarely constitute more than 1% of the total volume of sediments. Species like zircon and rutile occur in small amounts due to their minor occurrences in the source rocks while abundant species in the source like amphibole and pyroxene are relatively unstable and are destroyed during weathering in the source area. In this study, the heavy mineral assemblages of the Baspa river and Bhuzas stream sediments and Cenozoic

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molasse sequence of the Himalayan Foreland were studied and modal counts were done in order to correlate, both qualitatively and quantitatively, between the heavy minerals of the source areas and sedimentary sequences. The Baspa River sediments contain tourmaline, staurolite (Fig. 4(A)), epidote, kyanite (Fig. 4(D)), garnet, zircon (Fig. 4(G)g), rutile, excluding the opaques (Table 1). Coarse sand sized heavy minerals show angular to subangular shape. Silt and very fine sand size minerals, however, have subrounded to rounded shapes. Tourmaline, staurolite, epidote and kyanite constitute a significant proportion of the heavy mineral assemblage, while zircon, garnet, zoisite and hornblende constitute , 30% of the bulk (Table 1). The heavy mineral assemblage from sediments of the Bhuzas stream beds consists of tourmaline, sillimanite (Fig. 4(I)), staurolite, kyanite, garnet, epidote, zircon, rutile and zoisite in addition to opaque minerals such as ilmenite, magnetite, hematite, limonite and pyrite. Tourmaline dominates the non-opaque heavies followed by sillimanite, staurolite and garnet (Table 1). The heavy mineral assemblage of the Murree Group consists of tourmaline, epidote, zircon (Fig. 4(F)), staurolite (Fig. 4(B)), garnet, zoisite and spinel. Opaque minerals form 11 – 18% of the heavy mineral assemblage. The proportion of heavy minerals present in the Murree sandstones of the Kalakot area are shown in Table 2. These heavy minerals

Fig. 4. Photomicrograph of heavy minerals; (A) Staurolite from Baspa river; (B) Staurolite from Murree sandstone; (C) Kyanite from Upper Siwalik; (D) Kyanite from Baspa river; (E) Sillimanite from Upper Siwalik; (F) Zircon from Murree Sandstone; (G) Zircon from Baspa river; (H) Hornblende from Upper Siwalik; (I) Sillimanite from Bhuzas stream.

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Table 1 Table-1 Heavy minerals in recent river sediments (in%) Heavy minerals

P1

P2

P4

NR

NR1

NR2

NR3

NR11

NR12

NR13

KR

ZR1

ZR3

BR

Tourmaline Staurolite Kyanite Sillimanite Garnet Zircon Epidote Zoisite Rutile Opaques n

28 32 10 – 6 6 6 2 – 10 250

32 28 10 – 7 4 10 – – 9 300

35 20 3 – 5 2 25 – – 7 300

32 30 7 – 5 5 8 2 – 11 250

25 31 5 – 8 3 16 – – 12 300

29 33 6 – 6 3 10 2 – 11 300

30 24 8 – 8 3 14 3 – 10 300

33 23 10 – 8 8 11 – – 7 300

34 24 6 – 8 9 5 2 – 12 250

30 21 10 – 9 5 9 2 – 14 250

29 15 7 19 10 7 5 – 2 6 300

34 16 6 20 9 7 2 – – 6 250

40 14 6 16 7 7 3 – – 7 250

21 18 7 18 13 10 6 – 2 5 300

P1 –P4, NR –NR13 ¼ Baspa river sediments; KR, ZR1, ZR3, BR ¼ Bhuzas stream sediments, n ¼ number of grains counted.

are subrounded to rounded in a medium sand-size range. In the Murree sandstones, subrounded, colorless or green and greenish red spinel occurs in some mineral slides. Bossart and Ottiger (1989) also reported spinel from the Murree sandstones of the Hazara area, Pakistan and indicated that to be of crome-spinel variety based on microprobe analysis. Similar to Palaeogene Murree heavy minerals, the Lower and Middle Siwalik heavy minerals are also rich in tourmaline and staurolite. However, the Upper Siwalik is rich in kyanite and sillimanite (Fig. 4(E)) in addition to tourmaline.

5. Discussion In light of the applicability of heavy minerals for source determination and correlation, the heavy minerals of the modern streams exclusively flowing out of the two metamorphic terrains (e.g. Higher Himalaya and Lesser Himalaya) and the heavy minerals of the Cenozoic rocks of the Jammu area will be discussed. The Higher Himalaya contains metamorphic rocks of gneissic character in addition to granites, phyllites and quartzites. The denudation of these rocks under monsoonal

Table 2 Heavy minerals in the Cenozoic (Murree and Siwalik) sandstones (in%) Heavy Minerals

Mk1

Mk2

Mk3

Ms1

Ms5

Ms16

Ms21

T1

T2

T3

T4

T5

T6

T7

T9

Tourmaline Staurolite Kyanite Garnet Zircon Epidote Zoisite Rutile Spinel Opaques n

28 18 – 8 13 14 2 2 1 14 300

25 18 – 12 12 19 1 2 – 11 300

28 20 – 10 11 15 – 1 – 15 250

26 16 – 10 8 18 4 – – 18 300

31 21 – 9 8 12 – 3 – 16 300

27 17 – 10 7 13 2 5 1 18 250

24 18 – 10 8 15 4 2 2 17 300

28 20 – 8 – 14 – – – 30 300

31 15 – 11 5 16 – – 2 20 300

24 22 – 13 8 12 – 3 – 18 300

29 14 – 10 – 15 – – – 32 300

21 25 – 7 5 10 6 – 1 25 250

29 18 – 12 10 13 – 1 – 17 300

30 16 – 5 8 5 – – – 36 300

33 20 – 8 4 8 5 – – 22 300

Heavy Minerals

S3

S9

S10

K1

K3

K6

K7

K8

Tm1

Tm2

Tm3

Tm4

Tm5

Tm6

Tm7

Tourmaline Staurolite Kyanite Sillimanite Hornblende Garnet Zircon Epidote Zoisite Rutile Spinel Opaques n

25 28 5 – – 7 – 15 – – – 20 300

32 20 6 – – 8 5 7 – 2 2 18 250

26 24 5 – – 5 – 5 – 1 – 34 300

33 15 5 – – – 5 15 5 – – 22 300

19 27 8 – – 12 – 8 – – 1 25 300

26 30 5 – – 8 5 8 – 1 – 17 250

24 12 8 – – 15 8 10 7 – – 16 300

31 18 7 – – 13 – 5 5 – – 21 300

20 10 10 12 – 20 2 – – – – 26 300

21 8 21 10 – 10 – 5 – – – 25 300

26 8 22 12 – 9 3 5 – – – 15 300

20 7 23 12 – 12 2 6 – – – 18 300

30 6 15 8 5 10 – 6 – – – 20 300

19 7 15 15 – 7 – 8 – – – 29 300

26 5 18 12 4 10 – 7 – – – 18 300

Mk1– Mk3, Ms1–Ms21 ¼ Murree sandstones; T1–T9 ¼ Lower Siwalik sandstones; S3 –S10 and K1–K8 ¼ Middle Siwalik sandstones; Tm1– Tm7 ¼ Upper Siwalik Sandstones; n ¼ Total number of grains counted.

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climatic conditions contributes sediments to the glaciofluvial Baspa river which have a total stretch of nearly 35 km before joining the Satluj. This river exclusively flows in the Higher Himalaya containing low to medium grade metamorphic rocks in its catchment. Heavy minerals present in the Baspa river sand include tourmaline, zircon, epidote, garnet, staurolite and kyanite. Tourmaline constitutes the major proportion and is mostly brown colored and has a euhedral shape characteristic of a low-grade metamorphic provenance. Zircon is contributed from the granitic bodies that occur in association with gneisses. The kyanite is contributed from the kyanite-grade metamorphic rocks in the catchment. Epidote and garnet further comes from the metamorphic rocks containing these minerals in the terrain. Heavy minerals present in the Bhuzas stream sediments and exclusively derived from metamorphic rocks of the Bhuzas valley are tourmaline, zircon, epidote, garnet staurolite, kyanite and sillimanite. In this case, tourmaline is mostly pale yellow and brown colored suggesting a lowgrade metamorphic source (e.g. Pettijohn, 1975). Since the Bhuzas valley is characterized by almandine-sillimanite grade metamorphism, sillimanite is present in the Bhuzas river sediments. The two river catchments can be differentiated on the basis of kyanite and sillimanite where both minerals show characteristic properties indicative of a short distance of transportation. 5.1. Heavy mineral zones Heavy mineral suites have been identified and used to distinguish different zones in the Cenozoic sequences of the Jammu area. These zones are similar to what have already been established by Raju and Dehadrai (1962). They reported that pre-Siwalik Tertiary sediments mostly contain tourmaline and zircon. However, garnet, epidote and staurolite may also be present. Also, Lower Siwalik sequences contain staurolite as a marker heavy mineral, Middle Siwalik is marked by the first appearance of kyanite and Upper Siwalik is marked by the first appearance of hornblende and sillimanite. The present study also demonstrates temporal variation of the heavy minerals in the Cenozoic rocks of the Jammu area. Heavy mineral associations reflect the reverse lithological sequence of the adjacent source area, as a function of the interaction between uplift and erosion along the boundary fault (Dill, 1995). This statement holds true in the case of Himalayan Foreland sediments and the present study also suggests that staurolite-grade metamorphic rocks present in the upper part were eroded and deposited in the basin first, followed by kyanite-grade metamorphic rocks. Metamorphic rocks of sillimanite-grade forming the root zone were exposed to further erosion in the source terrain and this resulted in a sillimanite-bearing suite that persists in the Upper Siwalik (Fig. 5). Raiverman et al. (1983) and Mukherjea et al. (1988), while applying the concept of energy sequence in the

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distribution of heavy minerals in the Cenozoic succession of the Himachal Pradesh, suggested that groups of heavy minerals are of better stratigraphic value than individual heavy minerals in demarcating three different zones here. Sorkhabi and Arita (1997a) suggested erosion of the roof, subsequent erosion of the middle part and the root, and its deposition in the Himalayan Foreland in a sequencial manner as a reason for the inverted metamorphism in the Himalaya. They suggested that biotite-garnet grade to staurolite to partially staurolite grade of metamorphism and kyanite grade of metamorphism is indicative of middle almandine amphibolite facies. This corresponds to the main metamorphic event (M2 at 23 Ma) of the Lesser/Higher Himalaya. The relative abundance of heavy minerals seems to be indirectly related to the age of strata but directly related to the depth of burial and length of time below sea level (Gazzi, 1965; Morton, 1979). The possible cause for the dearth of unstable heavy minerals in pre-Cenozoic sediments can be attributed primarily to intrastratal solution (Pettijohn, 1975). Although the Early Cenozoic sequences have a higher proportion of stable heavy minerals, Late Cenozoic sequences possibly have not undergone a greater depth of burial and this may be one reason for the presence of unstable varieties. In the heavy mineral suites described from the two streams and Cenozoic sediments of the Himalaya, the mineral species are similar. However, the contrast is mainly in the presence or absence of a particular heavy mineral species. Krynine (1942) believes that provenance changes are far more important in causing changes in the heavy mineral compositions. Our study supports this contention where heavy minerals originating from the Higher Himalaya contain staurolite- and kyanite-bearing suites whereas those originating from the Lesser Himalaya contains a sillimanite-bearing suite depending upon the local geology of the catchment. 5.2. Provenance and tectonic setting It is already mentioned that provenance determination is one of the important attributes of heavy minerals study (e.g. Basu, 1976; Morton et al., 1992; Nechaev and Isohording, 1993). In the Cenozoic sequences of Jammu Himalaya, tourmaline, zircon, epidote, garnet, staurolite, kyanite, sillimanite and hornblende are common. In the Palaeogene Murree Group, blue and bluish green tourmaline, zircon, epidote, garnet and staurolite are present. Blue tourmaline typically suggest a pegmatitic source and zircon originates from an acid igneous rock (Pettijohn, 1975). Both minerals suggest a source that seems similar to the Higher Himalayan gneisses and granite. These may be recycled from the metasediments as interpreted by DeCelles et al. (2000) from Nepal. Epidote and garnet are an indicator of a metamorphic provenance, whereas staurolite suggests a source where the degree of metamorphism is of low grade at lower depth.

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Fig. 5. Heavy mineral zonation of the Cenozoic succession in the Jammu area.

Staurolite persists up to the Lower Siwalik Subgroup, the sequences of which appear very similar to the Upper Murree Formation. A comparison of the heavy minerals present in the Murree Group and the Lower Siwalik Subgroup with that of the recent Baspa river sediments shows similarities. The only difference is in the grain size, grain shape and color of tourmaline. The Baspa river heavy minerals are angular to sub-angular and occur in the coarse sand-size range while heavy minerals in the Murree Group and the Lower Siwalik Subgroup are subrounded and within the medium sand-size range (Fig. 4). This suggests that Murree and Lower Siwalik sediments were transported for comparatively longer distances than the Baspa river sediments. Furthermore, brown tourmaline in the Baspa river sediments was derived from a low-grade metamorphic rock and blue/green tourmaline of the Murree Group was derived from pegmatites/coarse granites or may have been recycled from metasediments. The Middle Siwalik heavy mineral suite in the Jammu area contains kyanite in addition to the above-mentioned

heavy minerals. This suggests that when the Middle Siwalik basin came into existence, the sediments were being derived from a provenance that was metamorphic in character and may have attained a higher degree of metamorphism. Kyanite grade of metamorphism has occurred in the Higher Himalaya. In addition, Baspa river sediments also contain kyanite and point to the Higher Himalaya as the source for the Middle Siwalik sediments. However, the presence of both staurolite and kyanite in the present day Higher Himalayan derived sediments indicate that tectonics and thrust stacking played a major role in the hinterland during derivation of these sediments. The sillimanite and hornblende-bearing suite in the Upper Siwalik is correlable with the Lesser Himalayan metamorphic rocks present in the Bhuzas valley and elsewhere. The Bhuzas stream heavy mineral suite definitely contains sillimanite in addition to other heavy minerals. Thus, a correlation exists in heavy minerals of the Bhuzas stream sediments and heavy minerals of the Upper Siwalik sediments. However, sillimanite-grade

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metamorphic rocks present in the core of the Higher Himalaya reported by Staubli (1989) and Vance and Harris (1999) must have also contributed sediments when those areas were uplifted and exposed to denudation. Raju (1967) interpreted the appearance of each diagnostic mineral species in the Tertiary sediments as the result of a corresponding tectonic episode in the source area. Also, Sinha (1970), on the basis of the behavior of epidote and similarity in the structural trends and mode of variation in average percentages of minerals, inferred gradual uplift and unroofing of rocks in order to explain Siwalik heavy minerals in parts of Uttar Pradesh. Tandon (1972) recovered tourmaline, zircon, epidote, garnet, rutile, staurolite, kyanite and magnetite – ilmenite in lateral continuity from the Siwalik sequences of Uttar Pradesh. Chaudhri (1972, 1975) reported tourmaline, zircon, epidote, garnet and staurolite from the Lower Tertiary sequences of Shimla Hills and additionally kyanite, sillimanite, hornblende from the Upper Tertiary Siwalik sequences in that area and suggested a rising Himalayan provenance for them. Chaudhri and Gill (1981) reported that opaque heavy minerals predominate over nonopaques in the Siwalik sequences of Nepal and honrnblende is conspicuously absent in the Upper Siwalik sedimentary units there. The presence of hornblende in the western part of the Upper Siwalik succession and its absence in the eastern part is either due to its local absence in the provenance or its destruction during weathering and transportation. Staurolite, kyanite and sillimanite in Lower, Middle and Upper Siwalik successions of Nepal suggest unroofing of the lowto high-grade metamorphic rocks from the Himalaya which contributed sediments to the Siwalik basin (Chaudhri and Gill, 1981). DeCelles et al. (1998, 2000) found zircon of three different ages in the foreland sequences and river sediments that suggest derivation from Proterozoic metasediments and also from granites of Cambrian age. Although earlier workers suggested a metamorphic provenance for the Cenozoic sedimentary sequences of the Himalaya, the present correlation clearly demonstrates that the Palaeogene sediments were contributed by denudation of the peripheral parts of the Higher Himalaya and the Neogene sediments were derived through unroofing of both the Higher and the Lesser Himalayan ranges. Nechaev and Isohording (1993) have categorized heavy minerals into three groups such as the GM, MT and MF. The GM suite is characterized by zircon, tourmaline, staurolite and less commonly sillimanite, andalusite, monazite and kyanite forming an association derived from the weathering of continental igneous and metamorphic rocks (the earth’s sialic crust). The MT suite is rich in basic metamorphic minerals such as pale-colored and blue-green amphiboles, epidote and garnet. MF indicates mafic minerals like olivine, iddinsite, pyroxene and green –brown hornblende. The heavy mineral suites both in recent sediments and Cenozoic sedimentary rocks belong mainly to the GM and MT categories except for the Upper Siwalik Subgroup

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where hornblende is present in small proportion. The Himalayan Foreland basin sediments belong to a recycled orogen considering the sandstone petrography (e.g. Critelli and Garzanti, 1994; Singh, 1996) and the heavy minerals occupy the passive continental margin field of Nechaev and Isohording (1993). Therefore, we suggest that peripheral foreland heavy minerals are similar to passive margin heavy minerals (Fig. 6). We cannot rule out the lack of precision in the Nechaev and Isohording (1993) diagram. The Higher Himalaya uplifted along the Main Central Thrust and the Lesser Himalaya came up late along the Main Boundary Thrust (Le Fort, 1996). The Himalayan Foreland formed as a result of India-Asia collision and its forebulge progressively shifted towards the south with progressive filling of the basin. Paleocurrents from Late Palaeogene sequences in different sub-basins indicate rivers entering the foreland from the north, northwest and northeast (Raiverman et al., 1983; Srivastava and Casshyap, 1983; Singh and Singh, 1995). Similar to the Murree sandstones (Singh et al., 1990; Critelli and Garzanti, 1994; Singh, 1996), the lithic particles and heavy minerals of the late Palaeogene sandstones in Himachal Pradesh, India (Chaudhri, 1975) indicate derivation from a northerly provenance. A common presence of detrital illite, chlorite, and sepiolite in the Lower Tertiary mudrocks of the Jammu area, India, suggests derivation either from the Trans-Himalayan schists, phyllites and,

Fig. 6. GM–MT– MF plot for the heavy minerals of the Cenozoic and Recent Himalayan Foreland sediments. Heavy minerals data of Kumaun Siwalik and Nepal Siwalik are taken from Tandon, 1972; Chaudhri and Gill, 1981, respectively. MT ¼ Total content of epidote and garnet. GM ¼ Total content of tourmaline, staurolite, zircon, kyanite, sillimanite and zoisite. MF ¼ Total content of hornblende, pyroxene and olivine.

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B.P. Singh et al. / Journal of Asian Earth Sciences 23 (2004) 25–35

granites or from the Higher Himalayan Crystallines and the Indus Suture zone (Singh et al., 2000). Furthermore, the detritus composition of early Himalayan Foreland basin sediments from Pakistan to Nepal and Bangladesh is consistent with progressively later closure of the Neotethys along the suture, from latest Palaeocene time in the west to Eocene time or even later in the east (Najman and Garzanti, 2000). This suggests that the general palaeoslope was southerly and southeasterly when the Palaeogene sediments accumulated in the Himalayan Foreland, and the sediments were mainly derived from the rising Himalaya to the north. During Neogene time, the palaeocurrent was again dominantly southerly with diversification in the flow directions in the Jammu area (Pandita and Bhat, 1996), in Himachal Pradesh (Kumar et al., 1999) and in Punjab (Kumar and Tandon, 1985). The overall southerly palaeocurrent suggests that the hinterland was still to the north and the source terrain shifted with the rising of the Lesser Himalayan sequences. The sillimanite-bearing heavy mineral suite in the present day stream flowing out of the Lesser Himalaya certainly reflects contribution from the Lesser Himalayan nappes in the Siwalik sequences, especially in the Upper part. DeCelles et al. (1998) suggested that the Tethyan Himalaya contributed much of the sediments for the pre-Siwalik basin, the higher Himalaya for the Lower and the Middle Siwalik and Lesser Himalaya for the conglomerate bearing Upper Siwalik in Nepal. Ghosh and Kumar (2000) also suggested reactivation of the Main Central Thrust and resulting contributions from the Higher Himalaya between 9 and 7 Ma on the basis of the presence of very high amounts of mica in some beds. This suggests that in addition to the Lesser Himalaya, the Higher Himalaya also contributed substantial amounts of sediment during accumulation of the Siwalik sequences.

6. Conclusions The Himalayan Foreland represents a succession that formed due to successive unroofing of the hinterland, and as such, the collisional tectonics played a major role in the shifting of the hinterland vis-a-vis shifting of the sediment depocentre. Based on our present study and several other studies, it is established that the Himalayan Foreland sequences may be classified into three different zones: a lower staurolite zone, middle kyanite zone and an upper sillimanite zone. The reverse zonation may be the result of successive emplacement of the older thrust sheets and/or successive unroofing of the hinterland. A qualitative correlation exists in the heavy minerals suite of the Higher Himalayan river sediments and the heavy minerals of the early Cenozoic (up to ,5 Ma) succession. Similarly, the heavy mineral suite of the Lesser Himalayan stream sediments is correlable with the later-deposited heavy minerals of the Upper Siwalik succession when the Lesser Himalaya contributed much of the sediments towards the Foreland.

Acknowledgements The authors are thankful to the Head, Postgraduate Department of Geology, University of Jammu, Jammu for providing working facilities. Dr R. Kumar of the Directorate of Geology and Mining is gratefully acknowledged for providing sediment samples of Bhuzas stream. We are thankful to Dr S.K. Ghosh for reading an earlier version of the manuscript and suggesting improvements. Prof. Abhijit Basu and Dr E. Garzanti are thanked for suggesting modifications that improved the manuscript substantially.

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