Abstract The Himalayan–Tibetan orogen provides one of the best natural laboratories in which to examine the nature and dynamics of landscape development within continent–continent collision zones. Many new tectonic–climatic–geomorphological theories and models have emerged and/or have been greatly influenced as a consequence of the study of the region and the quest to understand its geomorphological development. These include models of the interactions between tectonics, climate and surfice processes, notably, the influence of climate on surface uplift by denudational unloading; the limiting of topography by glaciation (the glacial buzz-saw model); localized uplift at syntaxes by enhanced fluvial and glacial erosion that, in turn, weaken the lithosphere, enhancing surface uplift and exhumation (the tectonic aneurysm model); climate-driven out-of-sequence thrusting and crustal channel flow; glacial damming leading to differential erosion and uplift; paraglaciation; and the influence of extreme events such as earthquakes, landslides, and floods as major formative processes. The development of new technologies, including satellite remote sensing and global positioning systems, and analytical methods such as numerical dating is now allowing these theories and models to be tested and will inevitably lead to new paradigms.

Abstract A ‘blank on the map’ only 60 years ago, the Karakoram Range has been explored and surveyed with greater difficulty than the Himalaya and Tibet due to its rugged terrain and extensive glaciation. In the past ten years we have succeeded in doubling the number of gravity stations. A substantial improvement in coverage and overall quality was obtained by concentrating on previously unsurveyed areas and by validating older data with more accurate measurements. Our data were merged with earlier data, converted to full Bouguer anomalies and gridded. The resulting Bouguer anomaly map defines very precisely the gravimetric low associated with the Nanga Parbat-Haramosh syntaxis, and the huge negative anomalies between the Karakoram Fault and the Main Karakoram Thrust. Large negative values are now visible also in the Ghujerab-Khunjerab areas. Correlation of the topography and Bouguer anomaly shows that a plate of flexural rigidity with D = 2 × 10 24 Nm fits the coherence data in the Karakoram at all but two distinct frequency ranges centred at wavelengths of 80 and 300 km. In a rheologically layered lithosphere developing a buckling instability under horizontal compression, the observed spectral features of the topography and Bouguer gravity anomalies constrain the depth of the competent layers to be in the range 13–20 km and 50–75 km respectively.

Abstract Regional metamorphic rocks in the Pakistan Himalaya include both UHP coesite eclogite-facies and MP/T kyanite–sillimanite-grade Barrovian metamorphic rocks. Age data show that peak metamorphism of both was c. 47 Ma. 40 Ar– 39 Ar hornblende cooling ages date post-peak metamorphic cooling of both through 500 °C by 40 Ma, some 20 Ma earlier than for metamorphic rocks in the central and eastern Himalaya. Typically these ages have been explained by obduction of the Kohistan arc onto the Indian plate at about 50 Ma and India–Asia collision. We suggest instead that the earlier metamorphic and cooling ages of the Pakistani Barrovian metamorphic sequence could be partially explained by Late Cretaceous to Early Paleocene crustal thickening linked to obduction of an ophiolite thrust sheet onto the leading edge of the Indian plate, similar to the Spontang Ophiolite in Ladakh. Heating following on from this Paleocene crustal thickening explains peak Barrovian metamorphism within 5–10 Ma of subsequent obduction of Kohistan. Remnants of the ophiolite sheet, and underlying Tethyan sediments, are preserved in NW India and in western Pakistan but not in northern Pakistan. Tectonic erosion removed all cover sequences (including the ophiolites) from the Indian plate basement.

Abstract The Kohistan–Ladakh terrane, northern Pakistan/India, offers a unique insight into whole-arc processes. This research review presents summaries of fundamental crustal genesis and evolution models. Earlier work focused on arc sequence definition. Later work focused on holistic petrogenesis. A new model emerges of an unusually thick ( c. 55 km) arc with a c. 30 km-thick batholith. Volatile-rich, hornblende ± garnet ± sediment assimilation-controlled magmatism is predominant. The thick batholith has a complementary mafic–ultramafic residue. Kohistan crustal SiO 2 contents are estimated at >56%. The new-Kohistan, silicic-crust model contrasts with previous lower SiO 2 estimates ( c. 51% SiO 2 crust) and modern arcs that imply <35 km crustal thicknesses and arc batholith thicknesses of c. 7 km. A synthetic overview of Kohistan–Ladakh volcanic rocks presents a model of an older, cleaved/deformed Cretaceous volcanic system at least 800 km across strike. The Jaglot–Chalt–Dras–Shyok volcanics exhibit predominant tholeiitic-calc-alkaline signatures, with a range of arc-related facies/tectonic settings. A younger, post-collisional, Tertiary silicic volcanic system (the Shamran–Dir–Dras-2–Khardung volcanics) lie unconformably upon Cretaceous basement, and erupted within an intra-continental tectonic setting. Kohistan–Ladakh tectonic model controversies remain. In essence, isotope-focused researchers prefer later (Tertiary) collisions, whilst structural field-geology-orientated researchers prefer an older (Cretaceous) age for the Northern/Shyok Suture.