The Nanga Parbat–Haramosh (NPHM) massif is a unique structural and topographic high in the northwestern corner of the Himalayan convergence zone. Previously, the NPHM was thought to be bounded by the Main Mantle Thrust (MMT), a fault along which the Kohistan-Ladakh island arc was obducted onto the northern margin of India. This study presents field evidence that the recently active dextral reverse Raikot fault truncates the MMT and forms the western boundary of the NPHM. The Raikot fault separates medium-grade, Mesozoic to middle Cenozoic mafic metasedimentary and intrusive rocks of the Kohistan island arc (Kohistan Sequence) from high-grade Proterozoic metasedimentary rocks (Nanga Parbat Group) and orthogneisses of the Indian craton. The Kohistan Sequence rocks have experienced one tight to isoclinal folding event, probably associated with obduction of the island arc, and a second folding event associated with movement on the Raikot fault. The Nanga Parbat Group rocks were transposed by an early (possibly Proterozoic) isoclinal folding event and have subsequently been folded around east-trending axes in the early Cenozoic by the obduction of Kohistan, then around north-trending axes in late Cenozoic time in association with the uplift of the NPHM and initiation of the Raikot fault. The Raikot fault consists of both mylonite zones and numerous major and minor faults. Slickensides and mylonitic lineations both indicate dextral reverse slip. The Raikot fault and associated folds appear to have accommodated as much as 15 to 25 km of uplift during late Cenozoic time. The localization of the uplift and the involvement of the Moho suggest that the Raikot fault follows a major crustal structure, possibly a pre-collision Indian plate boundary. If this is the case, rotational underthrusting of greater India along the MMT would require dextral slip along the Raikot fault. It is proposed that the Raikot fault is a terminal tear fault on the MCT.

Thick deposits preserved in deep valleys in the Indus, Gilgit, and Hunza River Basins, and a variety of dates, allow new definition of Quaternary events in the Karakoram and Nanga Parbat Himalaya. An unusually long record for an actively eroding high mountain area is recognized in three major episodes of glaciation during Pleistocene time. An early glaciation is represented by the indurated lower Jalipur tillites and heterogeneous upper Jalipur valley-fill sedimentary rock younger than 1 to 2 Ma, which are folded, overturned, or overridden by rapid movement on the dextral-reverse Raikot fault. This is associated with high overall uplift rates of the Nanga Parbat–Haramosh massif during late Cenozoic time. The middle glaciation is represented by two tills intercalated within variable sediments, including thick lacustrine units dipping as much as 43° along the fault. The Indus-Shatial till of the early middle glaciation records the farthest advance of Pleistocene glaciers down the Indus River valley. The last glaciation apparently occurred after about 140,000 yr ago and consists of three to four or more separate advances, as recorded by morainic topography. The most prominent of these is the Dianyor moraine near Gilgit, which was produced by a major longitudinal glacier. Near Haramosh and downstream at Nanga Parbat, Shatial, and elsewhere, transverse glaciers blocked the Indus River to produce lake deposits now dipping as much as 6° near the fault. Catastrophic floods from failure of the ice dams, and possibly landslide dams as well, emplaced some Punjab erratics and sediments that may have been reworked into loesses and other sediments at the mountain front.

Abstract The Main Mantle Thrust (MMT) represents the tectonic boundary between metamorphic shield and platform rock of the Indian plate hinterland, and dominantly mafic and ultramafic rock of the Kohistan-Ladakh arc complex in Pakistan. In some areas, this boundary is a sharp planar fault with development of mylonite; in other areas, it is a brittle-ductile imbricate zone; in still other areas, it contains large, discontinuous, slices of internally sheared and deformed ophiolitic mélange. The character of the MMT along its entire trace is discussed and it is concluded that there is no single continuous fault which marks the contact between the Indian plate and the Kohistan-Ladakh arc. On this basis, we propose a revised definition for the MMT that is consistent with both the original definition and with the usage of the term in literature. We suggest that the MMT fault contact be defined as the series of faults, of different age and tectonic history, that collectively define the northern margin of the Indian plate in Pakistan. On this basis, faults that define the MMT vary in age from Quaternary to possibly as old as Late Cretaceous. Discontinuous lenses of ophiolitic mélange that overlie the MMT fault contact, and which intervene between the Indian plate and the Kohistan-Ladakh arc, are considered to be part of an MMT zone that is equivalent with the Indus Suture Zone.

Abstract The dynamic mountains of the western Himalaya are the result of complex interactions involving tectonic, structural, lithological, climatic and surface processes. The multi-scale dynamics of surface processes in this region are largely unknown. This paper assesses the spatial complexities of the topography at Nanga Parbat, as we seek to understand erosion dynamics, differential denudation and the geodynamics of uplift and denudation. Spatial analysis of a high resolution digital elevation model and three-dimensional terrain simulations using satellite imagery indicate that the topographic complexity of Nanga Parbat is highly scale-dependent and exhibits a hierarchical order that is reflective of erosion dynamics. Observations and analyses reinforce prior understandings of rapid rates of uplift and high rates of surficial denudation. Results indicate that climate controls the topographic complexity of the massif, although a tectonic influence is present and is largely masked by the overprinting of surface processes with time. Consequently, Nanga Parbat is seen to owe its origin to erosionally induced tectonic uplift and rapid surficial denudation. Rapid uplift altered erosion dynamics and further accelerated erosion resulting in extreme relief. Nonetheless, the differential denudation resulting from erosion dynamics does not appear to be in spatial balance with the regional scale tectonic mass flux. Systematic integration of dynamic models that account for the scale-dependencies of subsurface and surface processes are required to study the nature of this complex system and explain topographic evolution.

Abstract The rapid erosional unroofing of the Nanga Parbat Himalaya in late Cenozoic time is thought to have been initiated when the Indus River, initially flowing somewhat north and well to the west of its present location, was captured and diverted south close to the massif of today by extensional structures and downfaulted topography across the Kohistan-Ladakh island arc terrane. It is hypothesized that the Nanga Parbat pop-up structure was initiated at c. 12–10 Ma, as a tectonic aneurysm caused by rapid incision by the Indus River and other surface processes. Because of this subsequent rapid unroofing of the region, however, the oldest sediments to record erosion in the immediate region of Nanga Parbat are < 200 ka old: most sediments and our cosmogenic and ISRL exposure dates are more than five times younger. Diverse field measurements of rates of local incision and areal denudation for mass movement, glacial, river and catastrophic floods for the past c. 55 ka are highly differential but internally replicative and externally consistent with research indicating long-term, severe denudation. Averaged rates of maximum incision at more than 15 points around the massif are 22 mm ± 11 mm a –1 . Late Pleistocene surface processes at Nanga Parbat were capable of erosional unroofing of the massif sufficiently vigorous to produce the pronounced relief of today.

Abstract New amphibole, muscovite and biotite Ar-Ar and K-Ar data and zircon and apatite fission track data are presented from the western margin of the Nanga Parbat syntaxis as well as from the Indus and Astor valley sections which cross the syntaxis. Amphibole data date a regional cooling through 500 °C at 25 ± 5 Ma and are inconsistent with earlier suggestions that the peak of regional metamorphism was Neogene in age, although there is no doubt that some rocks were still at upper amphibolite facies temperatures as recently as 5 Ma. The data can be used to constrain structural models for syntaxial uplift. After an initial phase of crustal-scale buckling, bodily uplift of the syntaxis was along subvertical shear zones developed along its margins, although with a significantly higher time-averaged strain rate for shears developed along the western margin than along the eastern margin. The latter may be antithetic to the former. These shears were operative from 10 to < 1 Ma. In the southwestern part of the syntaxis, this subvertical uplift was superseded, since 6 Ma, by uplift along moderately SE-dipping NW-vergent shears on the hanging wall of which are located Neogene-aged migmatites.

Abstract This paper describes the geology, tectonometamorphic history and geochronology of part of the northern flank of the Neelum valley in Azad Kashmir, NE Pakistan. Metamorphic crystalline rocks in this area belong to the Lesser and Higher Himalayan Crystalline complexes. Geological mapping of about 1500 km 2 confirms the presence of three main tectonic units characterized by similar lithostratigraphic sequences but with different tectonometamorphic histories. Whether these tectonic units belong to the Lesser or Higher Himalayan Crystallines depends on the, still controversial, position of the Main Central Thrust. A tectonic model, involving syn-convergent exhumation, is suggested that is consistent with new petrographic and geochronological data, and with a revised interpretation of the Main Central Thrust.