Northern Tectono stratigraphic Basin and Range Terrene:

The Indus Basin in its north is delimited by the Northern Sector of the Axial Belt (Fig. 1),

north of which the entire area, earlier known as “Northern Mountain Area”, is a very broad zone of complicated tectonic activities. It is here named, informally, as the Northern Tectonostratigraphic Basin and Range Terrene. The name implies that basins of different origin arc huddled together in the intermountanc region. The
Northern Basin and Range Terrene have a complicated diastrophic history, while many puzzles are
still to be worked out; the area represents the most critical segment of the Pakistan geology. A
tectonic sketch map exhibiting mega shears is shown in Fig.3.

It represents subduction overtaken by continent's collision, obduction and thrusting, where Indian lithosphere is under thrusting Eurasia. Part of the area comprising Kohistan Terrene has been interpreted as a fossil island arc. The Northern Basin and Range Terrene comprises dominantly of Precambrian, Palaeozoic and Mesozoic stratigraphic units and the plutonic product of collision during Tertiary period. Generally, the rock units of this area are thrust southwards. Allochthonus in numerousÿ numbers cap some of the autochthonus and then in some eases both of them arc thrust southwards. Examples can be seen especially in the northern most area of Pakistan. This area is a large tectonostratigraphic domain and no single criterion can be made for its further break-up or division, however, sedimentary, metamorphic and igneous complexes individually maintain their dominance in certain areas and help in delineating the zones of respective rock type. Nevertheless, a sharp boundary cannot be drawn, because predominantly sedimentary rocks, with few igneous bodies, may still be present in some areas. Similarly, a long belt exclusively formed of metamorphic
rocks may have some igneous complexes. Stated in another way, the area displaying a single
characteristic or similar characteristics and unified in someway is considered as a whole. Thus, for the sake of stratigraphic description, classification and correlation, the entire Northern Tectonostratigraphic Basins and Ranges Terrene can roughly be divided into different basins, belts and provinces so as to equate or compare the region (by parametric analogy) with Indus and Balochistan Basins.A brief description of its component parts is given below.
Himalayan Tectonostratigraphic Basin: This is a large intermontanc basin, extending from Punjal Thrust to Main Mantle Thrust (MMT). Thearea covered in this basin(Fig. 1) lies north ofAxial Belt, covering northern 1Iazara and Kashmir in the south-east and Peshawar Basin in the south-west, comprising mostly of sedimentary and meta sedimentary rocks, and the Malakand, Saidu and Kaghan-Naran in the north comprising mostly metamorphic and igneous complexes. The metamorphism gradually increases from south to north. The dominant rock throughout the metamorphic zone is greenstone in melange zone, and blue schist and large bodies of serpentine in adjacent areas. Chaudhri et al. (1994) divided this basin into Higher and Lesser Himalaya based on the position and partition made by Main Central Thrust (MCT). The position of MCT in Pakistan is controversial. It is however, tentatively being used here for a rough or approximate division of Higher and Lesser Himalayas.

Higher Himalaya: The range of the Higher Himalaya include areas between MMT and areas north of Batal and Naran in Kaghan Valley and north of Luat in Neelum Valley, the Bcsham Block and areas north of Girarai in Swat and Malakand Pass.The MCT passes close to the localities mentioned and constitutes the southern boundary of the Higher Himalaya(Zakaetal.,1997). The Higher Himalaya is composed of a lower basement and an upper cover. Detailed work in this region has been carried out by Greco (1989); Spencer ct. al (1990); Spencer (1993); Greco and Spencer (1993); Pognante and Spencer (1991) and Chaudhry et al. (1994, 1997). According to Chaudhry et al. (1997), the lower basement (known as Purbinar group east of Thakot fault and the Pacha formation to the west) is composed predominantly of granitoid, migmatites, pelites and psammites. Minor carbonates, calc-pelites and amphibolites are also present. The upper cover (Burawai group in upper Kaghan east of Thakot fault and the Alpurai group to the west in Lower Swat) is composed predominantly of marble sand calc-pelites with subordinate pelites,amphibolites and psammites. The whole block has undergone metamorphism in upper amphibolite facies, with minor relics of eclogitc facies within this predominant metamorphic grade.

Lesser Himalaya:Lesser Himalaya is delimited to the north by MCT and to the south by Punjal Thrust. It covers the areas of Kashmir, Kaghan, parts of northern Hazara and parts of Swat. The Precambrian and Palaeozoic sediments have, in general, suffered low-grade metamorphism and are overlain by younger sediments in various places in Peshawar, northern Itazara and Kashmir basins, (and by high grade Precambrian metasediments and gneisses occurring as nappes eastwards in Shimla and Gharwal of Indian Himalayas). The brittle deformation is characterized by tight to overturned folds and a schuppen structure or imbricate faulting (Chaudhry et al., 1994). In this review, the Lesser Himalaya broadly covers metamorphic zone from Punjal Thrust to MMT. Chaudhry and Ghazanfar (1993) divided the Lesser Himalaya into Northern Metamorphic Zone and the Southern Sedimentary Zone. The Southern Sedimentary Zone is considered as part of Axial Belt in this review.
kohistan isaland Arc:
The area of island arc extends northward from Main Mental Thrust (MMT) and ends at Main Karakoram Thrust (MKT). The Kohistan island arc is alien to the Gondwana element of Indian Plate as well as to the Asian Plate Enormous work on the island Arc is available in the literature. A list of contributors is given in the chapter of Kohistan island arc sequence. The predominant rock type in the Kohistan island arc is amphibolite. In fact, the amphibolite in this area is present in the form of belts, on southern and northern sides of the island arc. Briefly, the island arc is composed of basic rocks, metasedimentary formations, volcanic series, younger clastic sediments and intrusions of deep-seated igneous rocks. A comparable situation is found also with Chagai area in the Balochistan Basin: both having been formed because of crustal subduction and represent fossil island arcs. According to Treloar ct al. (1996), the rocksof the dominantly Cretaceous age extend across the northern part of the arc, where they are divided into three intrusive complexes, the Kamila Amphibolite belt, the Jijal and the Chilas complexes. The Kamila Amphibolite belt consists of amphibolite and subordinate homblcndite, dioritc and plagiogranitc. The Jijal complex is divided into a southern part composed of ultramafic rocks and a northern part dominated by garnet granulite (Jan,1979).

The core of the arc is marked by the Chilas complex, a massive body of locally layered, gabbronorites up to 50km wide and 300 km long. Extrusive volcanic activity spanned from the Mid Cretaceous to Eocene (Treloar et al., 1989). As to the origin of the Kohistan island arc, Treloar et al. (1989), added that it was initiated offshore of Asia during Midddlc Cretaceous and was sutured to Asia between 100 and 85 Ma. Subduction of Tethyan oceanic crust beneath the island arc continued until ca60Ma when finaly the subduction seized and the collision occured (Beck etal.,1995).