AUGUST0 GANSSER Abstract. The 5000 krn long Peri-Indian Suture Zone has doubled in the western Himalaya and the northern branch forms the division hetween the Himalaya and the Karalmm. The northward directed Nanga Parbat-Haramosh crystalline spur controls structure and petrology of both the Suture Zones. It divides the over 2000 km long Transhimalayan batholith into the eastern Ladakh and the western Swat batholith. Geology and petrology of the Karakorurn north of the Northern Suture Zone strongly contrast with the Himalaya to the south of it. In order to shorten the description, many of the observed facts are presented in sketches drawn direct- The division between the Karakorum and the\ ly in the field (Fig. 2-17). Himalaya is marked by northern branch of the Peri-.' Indian Suture Zone (Gansser, 1980). For over 5000 km can we follow this major lineament from the Anda- man Island in the SE to Karachi in the SW. The iunc- .J tion between the Karakorurn in the north andc the In the Ladalch area two suture zones exist. They Himalaya in the south is, however, still somewhat are separated by the large Ladakh batholith, the west- * controversial. We have realized that from the eastern ern equivalent of the ZOO0 krn long Transhimalayan Ladakh region to the west, the suture zone has doub- batholith. While the southern suture zone along the led, one running along the Indus valley (southern Indus valley is well known - actually it is the best branch) the other along the Shyok and Nubra rivers known part of the total belt - the northern branch, in the north (Gansser, 1977). It is difficult to decide long suspected by earlier reports and the study of if this doubling is due to tectonic causes only, or if satellite pictures, has only recently been investigated two different belts existed originally with a different (Sharma and Gupta, 1978). Surprisingly thick (up to 8 composition and possibly in a different age (Stocklin, ltm reported) volcanics and volcano-clastics follow 1977). north of the Ladakh batholith. They were first men- tioned by Stoliclwa (3.874), who compared them to the Compared to the central and eastern Himalaya, Panjal traps. 'l'hey :?re well developed north of Khar- the western Himalaya within Palcistan is further corn- , dung and range from basalts to trachytes together with plicated by the remarkable north-northeast directed . rhyolites showing ignimbritic flow features. They basement spur of the Nanga Parbat-Haramosh, which ! seem to be different from the well Irnown Dras vol- is truncated in the north by the wide arch of the Kara- ' canics of the southern suture along the Indus. Further korum range, and which may be related to the western eastwards, north of Chang-La, which crosses the Lad- Himalayan syntaxis. Desio (1979) regards his "upper akh batholith, De Terra (1932) has observed "dia2- Indus Suture line" east of the Nanga Parbat-Hara- lagites" with amphibolites as well as porphyroids with mosh Spur and his "Kohistan line" (both correspond- diabases and well bedded tuffites. Along a sharp thrust ing to my southern suture zone) west of the massif (the Nubra-Shyolc thrust of Sharma and Gupta) gneisses as the main division, while I take the northern suture and granites of the Karakorum are thrust over the voE zone as the actual structural divide. Apparently the canics. Small sheared relics of serpentine suggest the geological and the geographical Karakorum do not actual trace of the northern suture zone. The thrust completely coincide. hades with about 40" to 50" to the north and is fol- lowed by a conspicuous row of hot springs. It contra- During summer 1977 and fall 1978, I visited the , sts with the steep south hade of the thrusts along the suture zone of the wesfern Himalaya (Pakistan) and southern suture zone. It is most significant that ultra- surrounding areas between the lower Shyok river in mafic rocks occur only as thin, highly sheared relics the east and the Chitral area in the west. In the fol- al-nq this northern suture zone, a fact well established lowing observations I present the preliminary results ' further to the west. of the reconnaissance, which is an extension of similsr investigations carried out in the Ladakh region (Frank Still unknown is the region between the Nubra et al., 1977). and the western Shyok on the Pakistan side. Possible Pm. Intern. Commit. Geodynamics, Grp. 6, Mtg. Pesh awar, Nov. 23-29, 1979: Spec. Issue, Gd.Bull. Univ. Peshawar, Vol. 13, 1980. 9 northern platform sediments (N Karakorum Babusar Pass S Pamir) Besham Baltit southern platform sediments (Zanskar, Chalt Kashrnir.) Chilas Dras Karakorum central batholith Gilgit Jijal Kargil south Karakorum schist, marble and gneiss Kalam zone (Dumordo or Baltit Group) Nomal Patan Sutur Zone: volcanics +pelagic sediments, Skardu ultrarnafics and melanges part, metamorphosed Yasin Transhimalayan Pluton : Ladakh and Swat batholith, included Large enclaves of "basement" and sediments Braldo Gilgit Basement type crystalline (Precambrian to Hushe Lower Paleozoic) Hunza I ndus Kandia Leucogranites, mostly Tertiary Nubra Shyok. Suru Za nskar Ladakh Molasse (Kailas Molasse) in E, Haramosh Jalipur "Molasse" in W Nanga Parbat Rakaposhi Tertiary to recent sediments (in Syntaxis belt, Chogo Lungma Kashrnir and Deosad basins) NSZ Northern Suture Zone Main Suture Lines along Sutur Zones SSZ Southern Suture Zone lineaments with fault zones Aghil Line Spongtang' Nappe Fig. 2. Khaplu-Machulu section (Shyok river) and lower Hushe valley. 1 tonalita with aplita pnd metadolerite dykes, the latter often intruding the aplitic dyke forming a bic mrc 2 gabbros cut by tonalites with same dykes as in 1 2a microgabbros to meta-dolerites and diabases 3 biotite schists and finegrainde gneisses with chlorite schists 4 epidote chlorite schists, partly prasinitic (mylonitid 5 phyllites, quartzites and schists 6 white marbles T biotite augengneisses 8 biotite granite, often with large alkalifeldspar phenocrysts traces are indicated on the sketch map (Fig. 1) partly based on satellite pictures. The Aghil fault zone run- ning through the Nubra Valley to the Agh1.1 pass may have displaced the suture zone as well as the continua- tion of the Ladakh batholith. I found the northern suture zone again in the lower Shyok river at the confluence with the Hushe river at Machulu (Fig. 2). The steep thrust hades here to the south with chlorite schists thrust northwards on mylonitic phyllites and thin marbles, which become more metamorphic towards the main Karakorum batholith [Baltit group of Stauff er (1968) or Dumordo group of Desio (1974) 1. The Karakorum rocks are well displayed along the Hushe valley and on the south face of Masherbrum (Fig. 3). South of the suture zone Fig. 3. The southflank of Masherbrum, seen from the UP the green schists pass through diabases and micro- Hushe valley. gabbros into the main gabbro body bdonging already to the western continuation of the Ladakh batholith. migmatized biotite granite gneiss Tonalite cut into the gabbro and are traversed by para- brown weathered calcschists (Paleozoic) llel dykes of aplitic granites and dolerites (Fig. 2). The white marble bands batholithic rocks are particularly well exposed along Baltoro type granites with basic dykes . P ion. ig. 4. %ion along the Shyok river near Pion steep belt of mylonitic chlorite epidote schists with prasinitic layers thrust southwestwsrds on gneisses (2). Could be part of the northern Suture Zone continuing into the Shyok/Nubra zone folded biotite gneisses and schists, rich in quartz veins, locally rnigrnatitic with some Cu mineralisation. Could represent older "basement" striking mostly northwards small bands and lenses of diorite within the gneisses white to slightly pinkish biotite granite representing youngest undefonned intrusions tonali te gabbros to norites cut by the tonalites irregular pyroxenite lenses in gabbro pegmatitic and aplitic veins and dykes doleritic dykes, mostly parallel and southwards handing locally intruded and brecciated by youngest aplite granite dykes the lower Shyok river as well as along the Indus. I . longing to an enclave of metamorphic rocks. This followed the Shyok river for about 70 km upstream section also exposes the complicated relations of the to beyond Pion and the Indus river for about various plutonic roclcr and the dyke intrusions (Fig. 4). 40 kth towards Khurmang. The outline of the plutonic rocks is much more complex in this western Westwards, the continuation of the northern suture extension of the Ladakh batholith; particularly by the zone can be traced from Hushe over the Thalle pass frequent enclaves of metamorphic, volcanic and sedi- into the Shigar valley (see Fig. 1). Ebblin (1976), who mentary rocks. The batholithic rocks composed of investigted this section on structural grounds distin- pyroxenites, norites, tonalites and younger granite in- guishes n volcanic and a sedimentary sequence, with trusions are cut by numerous dykes, with a predomi- some conglomerates in contact with ccgabbrudiorites" nance of meta-dolerites clearly cutting aplites and peg- of the main pluton in the south. The suture zone enters matite~, the Shigar valley just west of Shigar and disappears below the alluvial flats. Apart from chlorite schists and I observed the following enclaves: Intensely fold- f coarse prasinites, lenticular marbles, locally with an ed old biotite gneisses and schists, which are locally ) intense flow-folding, are of particular interest, together migmatized. They frequently st rile in a northerly with smaller fragments of serpentine, which outline direction. Sediments are well exposed near Tolti in ', the character of the suture zone. Along the western the Indus, where they form an impressive antiforrn ' end of the Shigar valley, near the confluence with with an a&al plunge ti the north. he sediments con- the Braldo river coming from the Baltoro region, thc sist of limestones and dolomites altered to marble and northern suture zone is again well displayed in the tremolite marble and black slates.