Search

The Pamir plateau forms a prominent tectonic salient that marks the western end of the Himalayan orogen containing several terranes that were accreted to Eurasia from the Late Paleozoic to Cenozoic. A detailed knowledge of the tectonic evolution of the Pamir salient during the Cenozoic is important for our understanding of the intracontinental deformation in the western Himalaya. Although the tectonic evolution of the Pamir salient has long been studied, the timing of collision between the Indian Plate and the Kohistan-Ladakh arc is still a matter of debate. We present new U-Pb ages and Hf isotopes of detrital zircons, magnetic fabrics, and stable isotopes from the foreland basin on the northeastern margin of the Pamir that indicate a change in sediment provenance started at about 47 Ma. Sediments in the southwest Tarim Basin were partially derived from the uplifted and eroded Karakoram and Kohistan terranes created by the collision between the Indian Plate and the Kohistan-Ladakh arc at circa 47 Ma, as a result of northward thrusting and propagation of the Indian Plate under Eurasia.

The Turfan Basin extends approximately 550 km east-west by 100 km north-south within northwest China and is located between branches of the intracontinental Tien Shan orogenic belt. At present it is an intermontane foreland basin loaded by southward transported thrust sheets at its northern margin. This deformation is a long-distance manifestation of the India-Asia collision, but the orientation and location of Cenozoic structures is strongly influenced by the pre-Cenozoic history of the region. The exposed basement marginal to the Turfan Basin consists of volcanics, granitoids, volcaniclastics, and deepwater sedimentary rocks associated with the North Tien Shan island arc and subduction-accretion complexes north of the North Tien Shan fault. This arc had accreted to the Central Tien Shan by late Carboniferous to early Permian times. The North Tien Shan fault represents a major boundary between Paleozoic arcs and accretionary complexes to the north and Proterozoic basement of the Central Tien Shan and Tarim Block to the south. Postcollisional thrusting appears to have provided a tectonic load for Lower Permian subsidence and sedimentation. Early postcollisional strata are turbidites, but there was a shoaling of facies until the deposition of Permo-Triassic conglomerates. No marine sediments have been deposited in the region since the Paleozoic. At least two Mesozoic episodes of compressional deformation are recorded at the northern margin of the basin, which was an intermontane foreland basin during this era. Lower Jurassic fluvial and lacustrine clastic rocks lie above a regional unconformity. An Oligocene unconformity marks the onset of coarse clastic sedimentation in the Cenozoic and probably indicates the start of major compressional deformation related to the India-Asia collision. Sedimentation rates have increased through the Cenozoic. The neotectonics of the Turfan Basin are dominated by a southward directed thrust system, emergent within the basin at the Fire Mountains range. Southward directed thrusting appears to have been a feature of Mesozoic age tectonics, and possibly the late Paleozoic tectonics of the basin; the most important neotectonic structures in the Turfan Basin follow older structural trends.

[1] The Solonker suture records the termination of the central Asian Orogenic Belt (CAOB). However, tectonic development of the Solonker suture is poorly understood. We report new field data for the Ondor Sum melange in the Ulan valley, and present a new evaluation of the orogenic belt extending from the southern Mongolia cratonic boundary to the north China craton within the context of a new geological framework and tectonic model, which incorporates relevant data from the literature. The southern accretionary zone between the north China craton and the Solonker suture is characterized by the Mid-Ordovician-Early Silurian Ulan island arc-Ondor Sum subduction-accretion complex and the Bainaimiao arc. This zone was consolidated by the Carboniferous-Permian when it evolved into an Andean-type magmatic margin above a south dipping subduction zone. The northern accretionary zone north of the Solonker suture extends southward from a Devonian to Carboniferous active continental margin, through the Hegenshan ophiolite-arc accretionary complex to the Late Carboniferous Baolidao arc associated with some accreted Precambrian blocks. This northern zone had consolidated by the Permian when it developed into an Andean-type magmatic margin above a north dipping subduction zone. Final subduction of the central Asian ocean caused the two opposing active continental margins to collide, leading to formation of the Solonker suture in the end-Permian. Predominant northward subduction during final formation of the suture gave rise in the upper northern plate to a large-scale, postcollisional, south directed thrust and fold belt in the Triassic-Jurassic. In summary, the CAOB underwent three final stages of tectonic development: early Japanese-type accretion, Andean-type magmatism, and Himalayan-type collision.

Mica and hornblende K-Ar and Ar-Ar data are presented from each of the three crustal components of the Himalayan collision zone in North Pakistan: the Asian plate, the Kohistan Island Arc, and the Indian plate. Together with U-Pb and Rb-Sr data published elsewhere these new data (1) date the age of suturing along the Northern Suture, which separates Kohistan from Asia, at 102–85 Ma; (2) establish that the basic magmatism in Kohistan, which postdates collision along the Northern Suture, predates 60 Ma, and that the later granite magmatism spanned a range of 60–25 Ma; (3) show that uplift amounts within Kohistan are greater toward the Nanga Parbat syntaxis than away from it and that rate of uplift near the syntaxis increased over the last 20 Ma to a current figure of about 5.5 mm a year; (4) show that much of southern Kohistan had cooled to below 500°C by 80 Ma and that the major deformation which imbricated Kohistan probably predated 80 Ma and certainly predated 60 Ma and was related to the Kohistan-Asia collision rather than the Kohistan-India one; (5) imply that uplift along the Hunza Shear in the Asian plate together with imbrication of the metamorphics in its hanging wall took place at about 10 Ma and was associated with breakback thrusting in the hanging wall of the Main Mantle Thrust; (6) suggest that the Indian plate has a lengthy pre-Himalayan history with an early metamorphism at about 1900 Ma, major magmatism at 500–550 Ma and early Jurassic lithospheric extension or inversion; and (7) show that the Indian plate rocks were metamorphosed shortly after the collision within Kohistan, which occurred at circa 50 Ma, and subsequently cooled back through 500°C at circa 38 Ma and 300°C at 30–35 Ma with ages of cooling through 200° and 100°C (as determined by fission track data) locally controlled by Nanga Parbat related uplift tectonics.