Central Pamir Research Articles

Studying the Process of Dissipation of Energy of Motion in Highly Fractured Glaciers using Remote-Sensing Techniques (Abstract)

New aspects of the physics of ice movement in glaciers are presented. An analysis of the equation for the energy of a moving ice mass shows that the energy which is dissipated into heat (internal friction in a glacier) occurs not only because of average ice-velocity profiles, as it is commonly considered when simulating glaciers by continuum laminar flow. It also turns out that a significant part of the internal friction is associated with the dissipation of motion energy on internal macroheterogeneities in a glacier: at places where fractures appear and, in the case of a block structure, at points of contact between individual blocks, on ice dams, ice bridges, etc. This mechanism seems to be dominant during rapid ice flow in highly fractured glaciers. The process was previously examined on the surging Medvezhiy Glacier in the central Pamir Mountains. On Medvezhiy Glacier the above phenomenon was particularly distinctive because of anomalously high ice-movement velocities during a calm period; that is, between consecutive surges (ice velocity amounted to 3–5 m d−1) and because of the block structure of the glacier against the background of its fracturing. Simple measurements of “instant” velocities of a large number of bench marks on the glacier surface, located across the middle flow course of the glacier, established that velocities at all points are of a fluctuating character, which outwardly resemble velocity fluctuations seen in turbulent liquid flow. It turns out that deviations of the “instant” velocity from the average velocity can amount to more than 50% of the latter. Using data obtained from periodic recordings of the “instant” velocity for fixed pairs of bench marks, which were located at different distances (so that it was possible to evaluate the difference in instant velocities), a structural function was constructed. This structural function meets the well-known, so-called Kholmogorov two-thirds law For local isotropic turbulence. This indicates that, as with turbulence, the energy of middle movement is transferred along a cascade of ice conglomerates of decreasing size down to the smallest, limited only by the dimensions of fundamental blocks. At the points of contact at dams and junctions, motion energy dissipates into heat. It is postulated that this phenomenon may have a much broader application; it may also be characteristic of the movement of any fractured mass of solid material. These findings may be used to formulate a theory which describes the mechanism of auto-oscillations in a surging glacier. According to this theory, the pseudoturbulent character of internal friction during a quiescent period (between surges) is one of the factors which prevents the appearance of a surge as long as possible, thus ensuring the growth of a new active glacier after each ice catastrophe. These studies also conclude research on the general concept of auto-oscillations of mountain glaciers — the so-called surging glaciers, originally formulated in the course of research on the cause of a surge on Medvezhiy Glacier in 1963. This concept was subsequently adopted and is now widely used in glaciology.

Seismotectonics and focal mechanisms of earthquakes from Pamir-Hindukush regions

The Hindukush, Pamir and Karakorum region lies to the north of the northern apex of the Indian subcontinent, approximately between latitude 34.5°–40°N and longitude 68°–80°E. From the point of view of seismicity, this region is one of the most active in the world, the seismicity being attributed to the collision of the northward-moving Indian plate with Eurasia. In this region lie the junctions of several major mountains such as the Himalayas, Karakorum, Pamirs, Hindukush and Kun-Lun. The northern part of this region is characterized by highly folded structures. Major faults in the region follow the trend of these structures. While a number of faults has a strike-slip nature, several are thrusts or overthrusts. The present paper discusses the seismicity of the Hindukush-Pamir region, its relationship to tectonics, the nature of focal mechanism solutions and their significance in terms of plate tectonics.Seismicity maps have been prepared for 0–50 km, 50–200 km depths. In the northwestern part of the area, the seismicity for shallow depths (0–50 km) follows a convex trend from the Hindukush mountains towards the north and northwest along the Kunduz foredeep, Kuliab foredeep, Pamir-Alai zone and the Pamir foredeep. The Badakshan massif is relatively less active, while the southern Kashmir zone in the southeast and Gardez-Chaman fault zones in the southwest are quite active. The seismicity is dispersed in the rest of the area.For intermediate depths (50–200 km), the seismicity has an east-west trend in the northern part of the Hindukush mountains and changes sharply to a NNE direction following the trend of the Badakshan massif and central Pamirs. A similar trend is observed in the Pamir-Alai zone. A number of seismic sections have been prepared through the Pamir-Alai fracture zone, the northern and central Pamirs, Badakshan massif, Kunduz foredeep and the Hindukush regions to show the nature of faults and of focal mechanisms occurring at different depths. In most cases it is found that the fault/fracture zones are steeply dipping and thrust as well as strike-slip faulting is taking place up to considerable depths. The present-day seismic activity appears to be a result of stresses generated by the northward collision of the Indian and Eurasian plates and Alpine orogenic movements which have possibly reactivated major faults of Caledonian and Hercynian age.

Mesozoic ophiolites, sutures, and arge-scale tectonic movements in Afghanistan

The tectonic history of Afghanistan appears to be the result of successive accretion of fragments of Gondwana to the active margin of Laurasia since the end of the Paleozoic. The margin, in Afghanistan, lies along the present Herat and Panjshir faults, south of Hindu Kush, swings around the central Pamirs and can presumably be traced along the present western Altyn Tagh and Kunlun faults in Tibet. North of this boundary, Paleozoic rocks have been deformed in the Upper Paleozoic, whereas south of it, there is no trace of the Hercynian orogeny. The first collision of Gondwanian fragments with Laurasia probably occurred in the early Mesozoic along the Hindu Kush and Kunlun. To the south, ophiolites along the Panjao and Pangong-Nu Chiang sutures (respectively in central Afghanistan and central Tibet) testify for another suturing event in the Upper Jurassic or Lower Cretaceous. The Indus-Tsangpo suture between India and Tibet corresponds, in eastern Afghanistan, to two ophiolite subbelts, near Kabul and Khost. Both ophiolite complexes have been emplaced between Maestrichtian and Lower Eocene by choking of two northward-dipping subduction zones. After complete contact between the Indian and Asian continents was achieved, presumably in the end of Eocene, the penetration of India into Asia caused large-scale intra-continental shortening. A large part of the shortening was accommodated by strike-slip faulting along Mesozoic and more ancient sutures. Central Afghanistan, in particular, was extruded to the west along the Herat suture by the protrusion of the Pamir wedge. It subsequently collided with the Lut block.

Regional framework and geodynamic evolution of the Indus-Tsangpo suture zone in the Ladakh Himalayas

ABSTRACTThe Indus-Tsangpo suture and its adjoining tectonic zones are well displayed in the Ladakh Himalayas where four tectonic zones have been distinguished, viz. the Zanskar, Indus suture, Shyok suture and Karakoram zones. The Zanskar zone is made up of Precambrian basement of the Zanskar crystalline complex and overlying Phanerozic sediments including Upper Palaeozoic volcanic rocks of the Zanskar Supergroup; they form the northern margin of the Indian plate. The Indus suture zone consists of a remnant of tectonised oceanic lithosphere represented by the Shergol melange and the Nidar complex with a former volcanic arc indicated by the volcanogenic Dras and Khardung formations and the Ladakh plutonic complex. The Shyok suture zone does not represent a tectonic repetition of the Indus suture; it is interpreted as a relic of a back-arc basin. The Karakoram plutonic complex appears to be genetically related to the Ladakh plutonic complex; both were generated from the subducting Indian oceanic plate. It is proposed that the boundary between the Indian and Eurasian plates does not lie along the Indus and Shyok sutures, but is located further N at the junction of Central Pamir (Alpine-Himalayan) and North Pamir (Hercynian).

The Sarezsk series of the eastern part of the Central Pamir (Carboniferous-Upper Devonian)

The Sarezsk series of the eastern part of the Central Pamir (Carboniferous-Upper Devonian)

Problem of horizontal movements in Central Pamir region

Problem of horizontal movements in Central Pamir region

Metallogeny of southeastern and central Pamirs

Metallogeny of southeastern and central Pamirs

TECTONICS OF THE JUNCTION ZONE BETWEEN THE CENTRAL PAMIRS TROUGH AND NORTH PAMIRS UPLIFT

The Central Pamirs trough, trending E - W, lies between the North Pamir uplift and the Pamir- Hindukush uplift. The North Pamir uplift Was a positive Area during the Mesozoic, while continuous deposition took place in the trough. Within the trough the structures are Alpine. The North Pamir uplift is divisible into three zones. Adjacent to the trough and separated from it by a major northdipping thrust is a zone of highly contorted Ordovician strata. To the north, the central zone, also bounded by thrusts, has gently folded Paleozoic strata in the west, passing eastward into complex structures where the zone is narrowest. The Paleozoics of the northernmost zone lie in broad open folds, thrust southward over the central zone and northward over Permian volcanics and sediments. The northern part of the Central Pamirs trough is an area of broad open folds in Mesozoic and Paleozoic sediments, bounded on the north by a belt of generally north-dipping thrust slices of Paleozoic rocks, paralleling the fold trends....

ON THE GEOLOGY OF THE SOUTHEASTERN PAMIRS

The Southeastern Pamirs is considered as the Murgab-Aksuy zone, separate from the Central Pamirs. The Permo-Triassic of this zone is differentiated into three subzones stratigraphically: central or Istyk, intermediate, and marginal. Its isolation took place in the second half of the early Permian, following a deposition of thick elastic deposits. This isolation may have been associated with the major Pshart rift which served as a vent for Cretaceous granitic magma. Thick reef limestones were deposited in the central subzone in early Late Triassic, followed by Norian and Rhaetian sandstones and shales. A rapid emergence occurred at the Liassic boundary, to be followed by a new and differential subsidence. Another uplift and folding took place in the early Callovian, to be immediately followed by a slow subsidence. The Karakoram folding phase (end of Jurassic or beginning of Cretaceous) marked the end of sedimentation in the Murgab-Aksuy zone and introduced a new stage of development. An editorial emendation of the article provides for only three structural phases: two geosynclinal and one post-inversional instead of the five structural phases separated by four unconformities as stipulated in the article. This and other additions render the situation somewhat confusing. --Scripta Technica, Inc.